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Background Through improved understanding of the structure-activity relationship attributes of fluoroquinolones, molecule development has improved efficacy, safety, and tolerability of the class. Adverse events (AEs) associated with the fluoroquinolones are well defined and a prospective part of the development process. However, not all fluoroquinolones have the same AE profile with different substitutions on the core molecule resulting in differences in side effects and spectrum of activity. Unique structural attributes of delafloxacin (DLX) may differentiate its AE profile compared to other fluoroquinolones. This analysis compared the incidence of AEs between DLX and vancomycin/aztreonam across two phase 3 ABSSSI studies in order to provide a broader overview of DLX safety. Methods Safety events occurring in all subjects in the pivotal phase 3 trials were pooled to provide a broad overview of DLX safety. Results DLX was safe and well-tolerated in the pooled phase 3 ABSSSI trial population of 741 subjects. Treatment-emergent AEs (TEAEs) were seen in the DLX group versus the comparator group at 45.1% and 47.7%, respectively. Most were mild or moderate in severity. Treatment-related TEAEs were reported in the DLX group versus the comparator group at rates of 22.1% and 26.1%, respectively. Conclusions Available data show DLX is well tolerated in both intravenous and oral formulation for the treatment of ABSSSI and does not appear to be associated with increased risk of AEs associated with other fluoroquinolones. It remains important to monitor for potential AEs that have been observed with other fluoroquinolones.

Background Delafloxacin is an oral or intravenous (IV) antibiotic indicated for the treatment of acute bacterial skin and skin structure infections (ABSSSI), including both gram-positive (including methicillin-resistant Staphylococcus aureus [MRSA]) and gram-negative organisms. Chemically distinct from other quinolones, delafloxacin exhibits enhanced potency, particularly against gram-positive pathogens. The integration of efficacy data across the Phase III ABSSSI studies is presented here and allows for additional examination of results across subgroups. Methods Results of 2 multicenter, randomized, double-blind trials of 1510 adults with ABSSSI were pooled for this analysis. Subjects in the vancomycin arm received 15 mg/kg, plus 1–2 g of aztreonam every 12 hours. Delafloxacin was dosed at 300 mg IV every 12 hours in Study 302; dosing in Study 303 was 300 mg IV every 12 hours for 3 days, with a mandatory, blinded switch to delafloxacin at 450 mg orally every 12 hours. The primary endpoint was objective response (OR), defined as a ≥20% reduction of lesion spread of erythema area at the primary infection site at 48 to 72 hours (±2 hours), in the absence of clinical failure. Investigator-assessed response, based on the resolution of signs and symptoms at follow-up (FU; Day 14 ± 1) and late follow-up (LFU; Day 21– 28), were secondary endpoints. Results In the intent-to-treat analysis set, the OR was 81.3% in the delafloxacin arm and 80.7% in the comparator arm (mean treatment difference 0.8%, 95% confidence interval -3.2% to 4.7). Results for OR in the defined subgroups showed delafloxacin to be comparable to vancomycin/aztreonam. Investigator-assessed success was similar at FU (84.7% versus 84.1%) and LFU (82.0% versus 81.7%). Delafloxacin was comparable to vancomycin/aztreonam in the eradication of MRSA, at 98.1% versus 98.0%, respectively, at FU. The frequencies of treatment-emergent adverse events between the groups were similar. Conclusions Overall, IV/oral delafloxacin fixed-dose monotherapy was non-inferior to IV vancomycin/aztreonam combination therapy and was well tolerated in each Phase III study, as well as in the pooled analysis, regardless of endpoint or analysis population.

Background MBL-producing strains of Enterobacteriaceae are a major public health concern. We sought to define optimal combination regimens of ceftazidime/avibactam with aztreonam in a hollow-fibre infection model (HFIM) of MBL-producing strains of Escherichia coli and Klebsiella pneumoniae. Methods E. coli ARLG-1013 (blaNDM-1, blaCTX-M, blaCMY, blaTEM) and K. pneumoniae ARLG-1002 (blaNDM-1, blaCTXM-15, blaDHA, blaSHV, blaTEM) were studied in the HFIM using simulated human dosing regimens of ceftazidime/avibactam and aztreonam. Experiments were designed to evaluate the effect of staggered versus simultaneous administration, infusion duration and aztreonam daily dose (6 g/day versus 8 g/day) on bacterial killing and resistance suppression. Prospective validation experiments for the most active combination regimens were performed in triplicate to ensure reproducibility. Results Staggered administration of the combination (ceftazidime/avibactam followed by aztreonam) was found to be inferior to simultaneous administration. Longer infusion durations (2 h and continuous infusion) also resulted in enhanced bacterial killing relative to 30 min infusions. The rate of killing was more pronounced with 8 g/day versus 6 g/day aztreonam combination regimens for both tested strains. In the prospective validation experiments, ceftazidime/avibactam with aztreonam dosed every 8 and 6 h, respectively (ceftazidime/avibactam 2/0.5 g every 8 h + aztreonam 2 g every 6 h), or ceftazidime/avibactam with aztreonam as continuous infusions resulted in maximal bacterial killing and resistance suppression over 7 days. Conclusions Simultaneous administration of aztreonam 8 g/day given as a continuous or 2 h infusion with ceftazidime/avibactam resulted in complete bacterial eradication and resistance suppression. Further study of this combination is needed with additional MBL-producing Gram-negative pathogens. The safety of this double β-lactam strategy also warrants further study in Phase 1 clinical trials.

Background Ceftriaxone is the only consistently active antimicrobial agent recommended for the treatment of Neisseria gonorrhoeae. Although some new antimicrobials are in development, the necessity to expand treatment options in the near term may require using older drugs that have not been widely used to treat gonorrhoea. Methods We conducted a literature review of clinical trials and case series, published from 1983 to 2017, reporting treatment efficacy results following administration of 1 g aztreonam intramuscularly or IV for uncomplicated gonococcal infections. We summed trial data, stratified by anatomical site of infection, and calculated summary efficacy estimates and 95% CI for each site of infection. Results The 10 identified clinical trials enrolled 678, 38 and 16 individuals with urogenital, rectal and pharyngeal gonorrhoea, respectively. Aztreonam had an efficacy of 98.6% (95% CI: 97.5%–99.4%) for urogenital, 94.7% (95% CI: 82.3%–99.4%) for rectal and 81.3% (95% CI: 54.4%–96.0%) for pharyngeal gonococcal infections. Conclusions Although most clinical trials included in this meta-analysis were conducted >30 years ago, aztreonam appears to have excellent efficacy for urogenital gonorrhoea; its efficacy at extragenital sites remains uncertain.

Background Ceftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination that can inhibit class A, C and some class D β-lactamases. Resistance caused by these β-lactamases often results in multidrug-resistance (MDR). This study evaluated the in vitro activity of CAZ-AVI and comparators against MDR Enterobacterales and Pseudomonas aeruginosa isolates collected from patients in Latin America. Methods Non-duplicate clinical isolates were collected in 2017-2018 in 10 countries in Latin America. Susceptibility testing was performed using CLSI broth microdilution and interpreted using CLSI 2020 and FDA (tigecycline) breakpoints. MDR was defined as resistant (R) to ≥3 of 7 sentinel drugs: amikacin (AMK), aztreonam (ATM), cefepime (FEP), colistin (CST), levofloxacin (LVX), meropenem (MEM), and piperacillin-tazobactam (TZP). Results The activity of CAZ-AVI and comparators against all isolates and MDR subsets is shown in the table. MDR rates for the studied species ranged from 17.6% among E. cloacae to 31.0% among K. pneumoniae. CAZ-AVI was active against 99% of Enterobacterales isolates and maintained activity against 85-99% of MDR isolates of the examined species. Only tigecycline showed comparable or higher activity. Among P. aeruginosa, CAZ-AVI was active against 86% of all isolates and 45% of MDR isolates; no other studied drug was more active. The three most common MDR phenotypes among Enterobacterales were 1) R to ATM, FEP, and LVX (n=538, 50% of all MDR Enterobacterales; 100% susceptible (S) to CAZ-AVI), 2) R to all sentinel drugs except AMK and CST (n=112, 10% of all MDR isolates; 88% S to CAZ-AVI), and 3) R to ATM, FEP, LVX, and TZP (n=111, 10% of all MDR Enterobacterales; 100% S to CAZ-AVI). The three most common MDR phenotypes among P. aeruginosa were 1) R to all sentinel drugs except CST (n=70, 22% of all MDR isolates; 20% S to CAZ-AVI), 2) R to AMK, LVX, and MEM (n=33, 10% of all MDR isolates; 33% S to CAZ-AVI), and 3) R to all sentinel drugs except AMK and CST (n=30, 9% of all MDR isolates; 70% S to CAZ-AVI). Table Conclusion These in vitro data suggest that CAZ-AVI can be an effective treatment option for infections caused by MDR Enterobacterales and P. aeruginosa collected in Latin America. Disclosures Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Greg Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)

Objective Reported penicillin allergies result in alternative antimicrobial use and are associated with worse outcomes and increased costs. Penicillin skin testing (PST) has recently been shown to be safe and effective in immunocompromised cancer patients, yet its impact on antimicrobial costs and aztreonam utilization has not been evaluated in this population. Method From September 2017 to January 2018, we screened all admitted patients receiving aztreonam. Those with a self-reported history of possible immunoglobulin E (IgE)-mediated reaction to penicillin were eligible for PST with oral challenge. Results A total of 129 patients were screened, and 49 patients were included and underwent testing. Sixteen patients (33%) had hematologic malignancies and 33 patients (67%) had solid tumors. After PST with oral challenge, 46 patients (94%) tested negative, 1 patient tested positive on oral challenge, and 2 patients had indeterminate results. The median time from admission to testing was 2 days (interquartile range, 1–4). After testing negative, 33 patients (72%) were switched to beta-lactam therapy, which resulted in a total of 390 days of beta-lactam therapy. For identical therapy durations, the direct total antibiotic cost was $15 138.89 for beta-lactams versus $78 331.50 for aztreonam, resulting in $63 192.61 in projected savings. A significant reduction in median days of aztreonam therapy per 1000 patient days (10.0 vs 8.0; P = .005) was found during the intervention period. Conclusions Use of PST in immunocompromised cancer patients receiving aztreonam resulted in improved aztreonam stewardship and significant cost savings. Our study demonstrates that PST with oral challenge should be considered in all cancer patients with reported penicillin allergies., Among immunocompromised cancer patients with reported penicillin allergies, 94% tested negative on skin allergy testing with oral challenge; of these, 72% were transitioned to beta-lactam therapy, leading to significant cost savings and a reduction in institutional aztreonam use.

Background Reported β-lactam allergy (BLA) is very common, yet less than 10% of these patients exhibit true hypersensitivity. When faced with reported BLAs, physicians often choose alternative antibiotics which can be associated with C. difficile infection, drug-resistance development, poorer outcomes, & increased costs. Effective identification of these patients is necessary for subsequent, appropriate BLA “de-labeling.” Here, we conducted a single-center analysis of alternative antibiotic utilization amongst patients reporting BLA and compare the frequency of drug-resistant infections and C. difficile infection in allergic & non-allergic patients. Methods This is a retrospective review of adult patients hospitalized at The University of Texas Medical Branch from 1/1/2015 to 12/31/2019. Pooled electronic medical records were filtered by antibiotic orders and reported allergies to penicillins or cephalosporins. Patients with drug-resistant and/or C. difficile infection (CDI) were identified by ICD-10 codes. Microsoft Excel & MedCalc were used for statistical calculations. Results Data were available for 118,326 patients and 9.3% (11,982) reported a BLA, with the highest rates seen in those receiving aztreonam (85.9%, 530/617) & clindamycin (33.7%, 3949/11718). Amongst patients reporting BLA, high ratios-of-consumption (relative to all patients receiving antibiotics) were seen with aztreonam (7.0), clindamycin (2.7), cephalosporin/β-lactamase inhibitors (2.4), & daptomycin (2.1). Compared to the non-BLA population, BLA patients more frequently experienced MRSA infection (3.0% vs 1.5%, OR 1.99, 95% CI 1.79–2.23, p< 0.0001), β-lactam resistance (1.2% vs 0.6%, OR 2.07, 95% CI 1.72–2.49, p< 0.0001), and CDI (1.2% vs 0.7%, OR 1.85, 95% CI 1.54–2.23, p< 0.0001). Conclusion Our measured BLA rate matches approximate expectations near 10%. Moreover, these patients experienced significantly higher frequencies of drug-resistant bacterial infections and CDI. Targeted inpatient penicillin allergy testing stands to be particularly effective in those patients receiving disproportionately utilized alternative agents (e.g. aztreonam, clindamycin, daptomycin). β-lactam allergy “de-labeling” in these patients is likely a valuable antimicrobial stewardship target. Disclosures All Authors: No reported disclosures

Background Aztreonam (ATM) is a monobactam stable to hydrolysis by metallo-β-lactamases (MBL). Avibactam (AVI) is a non-β-lactam β-lactamase inhibitor that inhibits serine carbapenemases (CPEs), such as ESBLs, KPCs, AmpC, and some OXAs. ATM-AVI is under clinical development for treatment of serious infections caused by Gram-negative bacteria (GNB), including MBL-producers. Methods 2,582 GNB (1,630 Enterobacterales [ENT] and 952 nonfermentative-GNB) were consecutively collected (1/patient) from 56 medical centers located in Western Europe (W-EU; 22 centers in 10 nations), Eastern Europe (E-EU; 12 centers in 9 nations), Latin America (LATAM; 10 centers 6 nations), and the Asia-Pacific region (APAC; 12 centers in 8 nations) in 2019 and susceptibility (S) tested against ATM-AVI and comparators at a central laboratory by reference broth microdilution methods. Results Overall, 99.9% of ENT (MIC50/90, 0.06/0.25 mg/L), including 99.1% of carbapenem-resistant ENT (CRE; MIC50/90, 0.25/0.5 mg/L), were inhibited at an ATM-AVI MIC of ≤ 8 mg/L (Table). CRE rates were 1.4%, 23.7%, 6.3%, and 9.6% in W-EU, E-EU, LATAM, and APAC, respectively (6.9% overall). A CPE was identified in 95 of 113 CRE isolates (84.1%). These CPEs included NDM-like (31.0% of CRE), KPC-like (26.5%), OXA-48-like (24.8%), and VIM-like (7.1%). Six isolates produced 2 CPEs. The highest ATM-AVI MIC value among MBL-producers (n=43; MIC50/90, 0.12/0.5 mg/L) was 4 mg/L. Among P. aeruginosa, 75.1% were inhibited at ≤ 8 mg/L of ATM-AVI; S to meropenem (MEM), piperacillin-tazobactam, and ceftazidime were 69.4%, 72.5%, and 75.7%, respectively, and ranged from 64.3% in E-EU to 82.0% in W-EU. MEM non-S P. aeruginosa varied from 22.2% in W-EU to 54.8% in E-EU. ATM-AVI was highly active against S. maltophilia, inhibiting 95.0%, 100.0%, 100.0%, and 90.0% of isolates from W-EU, E-EU, LATAM, and APAC, respectively, at ≤8 mg/L. S. maltophilia S to cotrimoxazole were 90.0%, 97.7%, 85.7%, and 100.0% in W-EU, E-EU, LATAM, and APAC, respectively. ATM-AVI also was very active against Burkholderia spp. (highest MIC, 8 mg/L). Conclusion Our results support clinical development of ATM-AVI to treat pneumonia caused by ENT (including MBL-producers), P. aeruginosa, S. maltophilia, and Burkholderia spp. Table 1 Disclosures Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Cecilia G. Carvalhaes, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Pfizer (Research Grant or Support) Timothy B. Doyle, Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Rodrigo E. Mendes, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Pfizer (Research Grant or Support)

Background Acute pulmonary exacerbations (APE) are a frequent cause of hospitalization for patients with CF. PSA is among the most common pathogen implicated in CF APE. Due to repetitive antibiotic courses, multidrug resistance (MDR) must be considered leaving few available intravenous antibiotic options. CZA and C/T are newer anti-PSA antibiotics that have been used to treat CF APE, but little data are available to compare their in vitro activity. Methods Non-duplicate, contemporary, clinical PSA (n=105) isolates were acquired from 85 patients during CF APE from 3 US hospital systems. MICs were assessed in at least triplicate by reference broth microdilution for C/T, CZA, aztreonam (ATM), cefepime (FEP), ceftazidime (CAZ), ciprofloxacin (CIP), levofloxacin (LVX), meropenem (MEM), piperacillin/tazobactam (TZP), and tobramycin (TOB). Current CLSI breakpoints were used to define susceptibility. Activity was further assessed in MDR, CAZ and MEM non-susceptible (NS) phenotypes. Results The mean patient age at isolate retrieval was 31 years (IQR: 21-43), and 20% were under 18 years. Mucoid morphology was observed in 48 (46%) isolates, and MDR defined in 41 (39%). Rates of susceptibility (MIC50/MIC90/%S) were: C/T (1/4/92%), CZA (2/8/90%), CAZ (4/64/68%), TZP (8/256/67%), TOB (2/32/63%), MEM (1/32/58%), ATM (8/64/57%), FEP (8/≥128/50%), CIP (2/8/27%), and LVX (4/16/24%). A mucoid phenotype did not alter %S (non-mucoid vs. mucoid) for C/T (93 vs. 92%) or CZA (91 vs. 88%). Among the 41 MDR PSA, activity was 2/16/83% and 4/16/76% for C/T and CZA, respectively. C/T, CZA, and MEM %S was 77, 69, and 23% for the 35 CAZ-NS isolates. C/T, CZA, and CAZ %S was 84, 77, and 39% for MEM-NS isolates. Conclusion These contemporary PSA from patients with CF displayed low susceptibility rates to most β-lactams, fluoroquinolones, and tobramycin, and MDR was common. C/T and CZA retained similarly high susceptibility against these isolates, including MDR strains and CAZ-NS/MEM-NS phenotypes. These data justify that both CT and CZA may be considered for CF APE due to PSA non-susceptible to current standard of care treatment options. Disclosures David P. Nicolau, PharmD, Cepheid (Other Financial or Material Support, Consultant, speaker bureau member or has received research support.)Merck & Co., Inc. (Consultant, Grant/Research Support, Speaker’s Bureau)Wockhardt (Grant/Research Support) Joseph L. Kuti, PharmD, Allergan (Speaker’s Bureau)bioMérieux (Research Grant or Support, Other Financial or Material Support, Speaker Honorarium)Melinta (Research Grant or Support)Merck & Co., Inc. (Research Grant or Support)Paratek (Speaker’s Bureau)Summit (Other Financial or Material Support, Research funding (clinical trials))

Background Aztreonam is often given to patients with a documented β-lactam allergy in lieu of a first-line anti-pseudomonal β-lactam (APBL). However, aztreonam offers no gram positive coverage and data suggest that gram negative organisms have lower susceptibility rates to this antibiotic than to APBLs. Septic patients are especially vulnerable to poor outcomes since inappropriate initial antimicrobial therapy has been shown to be an independent predictor of increased mortality. The purpose of this study was to determine whether septic patients treated with aztreonam experience inferior outcomes compared to those treated with an APBL. Methods This was a retrospective, multicenter, cohort study of all adult patients in metro Charlotte Atrium Health facilities treated for sepsis or septic shock from January 2014 to October 2017. Patients receiving either aztreonam or an APBL were identified using the system-wide sepsis database and enrolled in a 1:2 ratio. Patients were excluded if there was no infection-related discharge ICD-9 or ICD-10 code, if they received both aztreonam and an APBL in the first 8 hours, or if they received fewer than 2 doses of the study antibiotic. The primary endpoint was in-hospital mortality. Results A total of 194 patients received aztreonam and 388 patients received an APBL. β-lactam allergies were more common in patients who received aztreonam compared to APBL (97% vs. 14.2%, p < 0.01). In-hospital mortality rates were greater in the patients who received aztreonam vs. APBL (22.7% vs. 12.9%, p = 0.0025). After adjusting for APACHE II score, initial aztreonam exposure remained independently associated with hospital mortality (OR = 1.74, 95% CI: 1.0 – 2.8, p = 0.02). Additionally, we identified an increase in combination therapy with the use of aminoglycosides (28.9% vs. 12.4%, p < 0.0001) and fluoroquinolones (50.5% vs. 25.8%, p < 0.0001) in patients receiving aztreonam. No difference was found in overall length of stay or ICU length of stay. Conclusion In septic patients, the use of aztreonam as the backbone of antimicrobial therapy may result in increased mortality. This highlights the importance of stewardship interventions that obtain an accurate allergy history and encourage the use of APBL antibiotics whenever feasible. Disclosures Kelly E. Pillinger, PharmD, BCIDP, Pharmacy Times (Other Financial or Material Support, Speaker)

Background Nacubactam (NAC) is a novel serine β-lactamase inhibitor in clinical development, and inhibits Ambler class A, class C, and some class D β-lactamases. In addition, it has penicillin-binding protein (PBP) 2-dependent antibacterial activity and an ‘enhancer’ effect when combined with β-lactams bound to PBP3. This study assessed the in vitro activity of NAC alone and in combination with β-lactams against IMP-type metallo-β-lactamase-producing and ESBL-producing Enterobacterales isolated in Japan. Methods The MICs for the clinical isolates in Japan were determined and time kill studies were performed. IMP and ESBL genes were detected by PCR. The MICs were determined by broth microdilution method following CLSI methodology. β-lactams and NAC were tested as a ratio of 1:1. Time kill profiles were also studied according to CLSI methodology. Results The MIC50/MIC90s of NAC alone against 112 IMP-producing Enterobacterales and 154 ESBL-producing Enterobacterales were 2/ >32 and 2/8 mg/L, respectively. Regarding the MICs of cefepime (FEP)/NAC and aztreonam (ATM)/NAC against IMP-producing isolates, the MIC90s were 2 and 1 mg/L and the MIC ranges were 0.06 - 32 and 0.06 - 4 mg/L, respectively. The MIC90s of FEP/NAC and ATM/NAC against ESBL-producing isolates were 0.5 and 1 mg/L. These MIC90s of β-lactam/NAC against IMP-producing and ESBL-producing isolates were significantly lower than those of β-lactam alone (>128 mg/L). The highest MIC of ATM/NAC against IMP-producing isolates was lower than that of FEP/NAC. In addition, bactericidal activities of β-lactam/NAC were observed at the lower concentration of β-lactam compared to that of β-lactam alone. Conclusion NAC in combination with β-lactams showed excellent in vitro activities against not only ESBL-producing Enterobacterales but also IMP-producing Enterobacterales isolated in Japan. ATM/NAC tended to show higher antimicrobial effect against IMP-producing isolates by the enzyme stability of ATM. These results support the complex activities of NAC which works as a β-lactamase inhibitor, an antibacterial agent and also an enhancer when combined with β-lactams. Furthermore, these will be useful for selecting a partner β-lactam for NAC. Disclosures Yu Nagira, MS, Meiji Seika Pharma Co., Ltd. (Employee) Keiko Yamada, BS, Meiji Seika Pharma Co., Ltd. (Employee) Hayato Okade, Ph.D, Meiji Seika Pharma Co., Ltd. (Employee) Nami Senju, BS, Meiji Seika Pharma Co., Ltd. (Employee) Yuko Tsutsumi, MS, Meiji Seika Pharma Co., Ltd. (Employee) Yuji Tabata, Ph.D, Meiji Seika Pharma Co., Ltd. (Employee)

Background Metallo-β-lactamases (MBLs) have been identified as emerging resistance determinants in Enterobacteriaceae, A. baumanii, and P. aeruginosa. Early identification of carbapenemase-producing organisms (CPOs) is essential to prevent dissemination within healthcare settings. We report a case of a patient who was blood culture positive for a multidrug-resistant E. cloacae which was subsequently found to be positive for the MBL blaIMP-13. Methods A 74-year-old female, with no significant past medical or travel history, developed sepsis 2 days after undergoing debulking surgery for stage IIIc ovarian carcinoma. Blood cultures were positive for Gram-negative bacilli and the organisms identified as Enterobacter spp. with blaIMP MBL (Verigene). Antimicrobial susceptibility testing demonstrated high-level resistance to all penicillins, ureidopenicillins, cephalosporins, and β-lactam/inhibitor antibiotics, and susceptibility to colistin, tigecycline, and monobactams. Results Further testing using micro-broth dilution, BD phoenix, and Etest, demonstrated susceptible MICs to meropenem and imipenem, with intermediate to resistant MICs to ertapenem. The patient was treated with a combination therapy of amikacin, aztreonam, and ceftazidime-avibactam and responded clinically. Per standard protocol, the organism was sent to WI Laboratory of Hygiene for further characterization. Phenotypic testing using the modified carbapenem inactivation test (mCIM) was positive, indicating the presence of a carbapenemase; however, results using Xpert CarbaR (Cepheid) were negative. Subsequent sequencing of the isolate confirmed the presence of blaIMP-13. Conclusion This was an important case for several reasons. First, blaIMP-13 is historically reported in Pseudomonas aeruginosa. Indeed, this was the first report of Enterobacteriaceae harboring blaIMP in WI. Second, it had unique susceptibility pattern to carbapenems and was not detected by the CarbaR. Third, these data demonstrate clinical success in treating an MBL CPO with a combination anti-microbial regimen, based on an understanding of resistance mechanisms involved. This report calls for more vigilant screening for CPO using both phenotypic and genotypic methods. Disclosures N. Ledeboer, Luminex: Consultant, Consulting fee.

Background Penicillin allergies are the most commonly reported drug allergies and are documented in up to 17% of patients. Incomplete reaction histories and exaggerated concerns regarding the risk of cross-reactivity often leads to unnecessary avoidance of β-lactams in patients with reported allergies. Utilization of alternative non-β-lactam therapy in patients with reported allergies has been associated with increased incidence of multidrug-resistant organisms, including C. difficile infection. Per the Infectious Diseases Society of America guidelines for implementing an antibiotic stewardship program (ASP), ASPs should promote allergy assessments and penicillin skin testing in patients with a history of a β-lactam allergy. Implementation of penicillin skin testing in the acute care setting is often limited by the education, skill, and time required in administering and interpreting the result. Investigators sought to assess the impact of a β-lactam allergy assessment on aztreonam utilization within a healthcare system. Methods This is a multicenter, retrospective study comparing aztreonam utilization in five hospitals within a healthcare system after implementation of a β-lactam allergy assessment. The program included education as well as development of criteria for utilization and a β-lactam allergy assessment algorithm. A β-lactam allergy assessment was performed on any patient with an order for aztreonam. The Mann–Whitney U test was used to assess the impact of the restriction program on aztreonam utilization and expenditure. Results The hospital system experienced roughly a 50% decrease in aztreonam days of therapy per 1,000 patient-days [P < 0.01] and 67% reduction in annual expenditure [P < 0.05]. Of the 204 patients with an order for aztreonam, 151 (74%) patients received at least one dose; however, 97 (48%) patients ultimately received and tolerated a β-lactam. Only 112 (55%) patients had a prior reported reaction with 68 (61%) of those having a history of a Type I reaction. Conclusion Implementation of a β-lactam allergy assessment for patients with reported allergies can enhance appropriate use of β-lactams and result in reduced aztreonam utilization and expenditure. Disclosures All authors: No reported disclosures.

Background Several studies have demonstrated that patients with reportedly β-lactam allergies (BLA) receive less efficacious and more toxic alternative antibiotics. A previous study at our institution utilizing aztreonam as a surrogate marker for BLA demonstrated nearly 50% of patients receiving aztreonam had previously tolerated an alternative β-lactam (BL). In response to those results, our Antimicrobial Stewardship Program (ASP) provided dedicated hospitalist, medical resident and pharmacist education on appropriate utilization of aztreonam and BLA. Additionally, members of the ASP team began receiving real-time clinical surveillance alerts for all aztreonam orders. Methods A retrospective chart review of inpatients >18 years old who received at least one dose of aztreonam between July 1, 2018 – December 31, 2018. Patients were excluded if they did not have a documented BLA or if they received aztreonam as de-escalation therapy. Cost of aztreonam therapy was compared with the cost of alternative BL agents based on prior and subsequently tolerated classes of BLs. Comparator agents included: piperacillin/tazobactam (penicillin), cefepime (cephalosporin) and meropenem (carbapenem). Comparisons of total number of aztreonam patients and doses, cost of aztreonam, and cost of alternative therapy were compared with the index population from 2017 Results Similar to our prior study, 43.7% (48.5% in 2017) had prior BL tolerance with an additional 31.3% (19.4% in 2017) demonstrated subsequent BL tolerance following aztreonam administration. Following the ASP interventions, orders, doses and cost of aztreonam was reduced. Forty-eight patients during the 6-month period received aztreonam, a 26.7% reduction. There was a 38.5% reduction in the number of aztreonam doses (P = 0.001), which yielded a cost savings of $14,067.67 (extrapolated to 1 year). Median aztreonam cost in 2017 $382.40 vs. $191.20 in 2018 (P = 0.004). In 2018, 41.7% of patient’s allergy profiles were appropriately updated compared with 3.3% in 2017. Conclusion Our study demonstrates that ASP interventions including increased education, allergy documentation and clinical surveillance alerts targeted at reducing aztreonam utilization can reduce pharmaceutical expenditures. Disclosures All authors: No reported disclosures.

Background Penicillin (PCN) allergy is a serious adverse reaction that prevents the use of first-line therapy. 10% of the population reports a PCN allergy; however, less than 1% is truly allergic. Elimination of false allergies significantly impacts patient’s lives and decreases antimicrobial resistance and cost. Inova Mount Vernon Hospital (IMVH) has reported lack of pharmacist’s interventions in allergy clarification and counseling thus leading to an increase in aztreonam usage. The primary objective of the study was to increase pharmacist’s interventions in patient allergy clarification and counseling. The secondary objective was to decrease aztreonam duration of therapy (DOT) by 10%. Methods This project was conducted and monitored M-F on the pharmacy true north board March-December 2018. The initial step was to create a standard work and educate pharmacists on individualized PCN allergy patients interviewing and counseling. Pharmacist’s interventions tracking were made using the electronic reporting system. To quantify aztreonam usage, duration of therapy (DOT/1000) was collected during the study period and compared with data from 2017. Results During the study implementation, a total of 551 interventions pertaining to PCN allergy were documented by pharmacists between March-November 2018, compared with only 72 interventions made in March-November 2017 (7x increase, P < 0.005). Pharmacists while intervening clarified the allergy added the severity of the reaction, documented whether patients recently tolerated any PCN-based antibiotics, and de-labeled patients when appropriate. Allergy assessments lead to a decrease in aztreonam DOT/1000 by 12% in 2018 compared with 2017 and the overall antimicrobial stewardship goal was achieved. Conclusion Pharmacists interventions in allergy clarification helped with antibiotic de-escalation, improved safety, and de-labeled patients when appropriate. This initiative also increased physician and nursing awareness of the importance of clarifying PCN allergies. After successfully hardwiring this practice the pharmacy is partnering with nursing to implement PCN skin testing service at IMVH. Disclosures All authors: No reported disclosures.

Background Drug resistance in Gram-negative bacteria is of particular concern in children. Relebactam, a novel diazabicyclooctane inhibitor, coupled with imipenem has broad-spectrum activity against β-lactamase producing organisms. Here, we compare the in vitro activity of imipenem-relebactam to 10 standard comparator drugs against resistant Gram-negative isolates from two US pediatric hospitals. Methods We tested 100 isolates (50 per site) from pediatric clinical specimens tested during 2015–2017. All isolates were extended-spectrum cephalosporin-resistant (ESC-R); more than half were multidrug resistant (67%). Selected ESC-R isolates included Escherichia coli (90), Klebsiella pneumoniae (8), Klebsiella oxytoca (1), and Enterobacter cloacae (1) that were resistant or intermediate to ≥1 cephalosporins and/or aztreonam. A 0.5 McFarland suspension was prepared from colonies grown on blood agar plates (Thermo Scientific) at 35 ± 1°C for 18–24 hours. A final inoculum of 5 × 105 CFU/mL was prepared in Mueller–Hinton broth. Sensititre plates (Thermo Fisher Scientific) containing graded concentrations of imipenem/relebactam and 10 comparator drugs were inoculated and incubated at 35 ± 1°C for 18–24 hours. The minimum inhibitory concentration (MIC) was determined using the Sensititre Vizion system (Thermo Fisher Scientific) and endpoints were interpreted using CLSI (2019) breakpoint criteria, with the exception of colistin (EUCAST 2019). Results Selected ESC-R isolates had high rates of resistance to cephalosporins (64%–97%), aztreonam (80%), and levofloxacin (61%). All isolates were susceptible to imipenem/relebactam, imipenem and meropenem (MIC, ≤1 μg/mL for all). The imipenem/relebactam MIC50 (0.06 μg/mL) and MIC90 (0.12 μg/mL) values for ESC-R isolates were within one dilution of MICs of imipenem alone (0.12 μg/mL and 0.25 μg/mL). Among the comparators, colistin, amikacin, and piperacillin/tazobactam demonstrated comparable activities with 100%, 99%, and 94% susceptibilities, respectively. Conclusion Meropenem, imipenem alone and in combination with relebactam exhibited 100% susceptibilities against ESC-R Enterobacteriaceae isolated from pediatric specimens, demonstrating the high potency of carbapenems. Disclosures All authors: No reported disclosures.

Background There are limited options available for the treatment of infections caused by Enterobacteriaceae that produce an NDM metallo-β-lactamase. The purpose of this study was to compare the in vitro activity of aztreonam in combination with three different β-lactam/β-lactamase inhibitors (ceftazidime–avibactam, amoxicillin-clavulanate, piperacillin–tazobactam) vs. NDM-positive Enterobacteriaceae clinical isolates. Methods Seven Escherichia coli and three Klebsiella pneumoniae clinical isolates (all NDM-positive by PCR) were included in this study. The in vitro activities of ceftazidime–avibactam, amoxicillin-clavulanate, piperacillin–tazobactam, and aztreonam were determined by disk diffusion as described by CLSI. For synergy testing, disks containing a β-lactamase inhibitor (ceftazidime–avibactam, amoxicillin-clavulanate, piperacillin tazobactam) were applied to Mueller–Hinton agar plates inoculated with the test organisms, and the plates were incubated for 1 hour. The disks were then removed and aztreonam disks were dropped on the previous disk sites. The plates were then incubated as per standard CLSI recommendations for disk diffusion testing. Results All ten isolates demonstrated phenotypic resistance to aztreonam, amoxicillin-clavulanate, and piperacillin–tazobactam, and eight were resistant to ceftazidime–avibactam (CLSI breakpoints). The zone diameter observed for aztreonam in combination with ceftazidime–avibactam was greater than for either antimicrobial on its own for nine isolates. Seven isolates (70%) had susceptibility to aztreonam restored (zone diameter ≥21 mm) in the presence of avibactam. Aztreonam in combination with amoxicillin-clavulanate demonstrated in increase in zone diameter for all isolates relative to the zone for each antimicrobial alone, but only two (20%) had aztreonam susceptibility restored. Aztreonam susceptibility was not restored for any of the isolates in combination with piperacillin–tazobactam. Conclusion Of the three β-lactam/β-lactamase inhibitor-aztreonam combinations evaluated, ceftazidime–avibactam plus aztreonam demonstrated the greatest in vitro activity vs. NDM-producing Enterobacteriaceae. Disclosures All authors: No reported disclosures.

Background Commonly reported penicillin allergies result in limited treatment options, increased healthcare costs, and increasing resistance with the use of broad-spectrum agents. By providing penicillin skin testing (PST) to patients with a penicillin allergy, there is potential to reduce the use of carbapenems, aztreonam, vancomycin, and other broad-spectrum agents, resulting in cost savings and unnecessary overuse. This study examined clinical and economic outcomes of antimicrobials prescribed before and after PST. Methods This nonrandomized, observational chart review examined adult patients admitted over an open enrollment period of 100 patients who completed PST for a self-reported penicillin allergy. The study included all patients who met inclusion criteria and completed the test per protocol. Administration of the test utilized a stewardship pharmacist-driven, nursing administered, protocol that has three phases: puncture, intradermal, and oral challenge (optional phase). The primary outcome assessed was change made to antimicrobial regimen directly related to PST. A secondary outcome assessed was cost savings associated with PST. Results Over 13 months, 116 patients were consulted for PST with 100 patients completing PST per protocol. Self-reported allergies consisted of IgE-mediated and unknown in 52% and 30% of patients respectively. Seventy-one of 98 patients who tested negative (73%) had changes directly made to their antimicrobial regimens related to PST after intervention from the stewardship pharmacist. Thirty-four patients who had received carbapenems were changed directly to a penicillin or cephalosporin. A previous evaluation at our institution showed an average total antimicrobial acquisition cost savings per patient to be $314.75, which would result in $22,347.25 in direct savings for all patients evaluated. Conclusion PST led to immediate antimicrobial de-escalation in the majority of patients who tested negative. Most of these patients were transitioned to optimal therapy or de-escalated from carbapenem therapy. A total direct cost savings for the institution over the course of 13 months exceeded $20,000. Our study confirmed the overall utility of PST as a cost effective antimicrobial stewardship tool, especially as a carbapenem-sparing strategy. Disclosures B. Jones, ALK: Consultant, Grant Investigator and Scientific Advisor, Consulting fee, Grant recipient and Speaker honorarium; C. Bland, ALK: Grant Investigator and Scientific Advisor, Grant recipient and Speaker honorarium

Background Targeting “low-hanging fruit” is a pillar of antimicrobial stewardship (AMS). Β-lactam allergies (BLA) frequently restrict clinical decision-making and lead to utilization of alternative, less preferred antimicrobials making them an ideal AMS target. Prior studies have demonstrated that BLA are grossly over reported by patients. This study aimed to calculate the excess pharmaceutical expenditures incurred by utilization of aztreonam in patients who had previously (or subsequently) tolerated a β lactam (BL). Methods Retrospective chart review was performed on inpatients >18 years old at our institution who received at least one dose of aztreonam during the 2017 calendar year. Data collected included: BLA, both prior and subsequent BL classes tolerated, number of doses and days of aztreonam administered. Patients were excluded from the analysis if they did not have a documented BLA or if they received aztreonam as targeted/de-escalation therapy. Cost of aztreonam therapy was then compared with the cost of alterative BL agents based on prior and subsequently tolerated classes of BLs. Comparator agents included: pipericillin/tazobactam (penicillin), cefepime (cephalosporin) and meropenem (carbapenem). Wholesale acquisition costs were used for each agent and comparator regimens were based on our health system-wide dosing guidelines adjusted for renal function. Results One hundered thirty-two patients met inclusion criteria. Of those patients, 88/132 (66.7%) had demonstrated tolerance of a BL agent. Specifically 69/132 (52.3%) previously and 19/132 (14.4%) subsequently tolerated a β-lactam. Across the study, $40,768.84 was spent on aztreonam for patients with prior/subsequent BL tolerance. Cost for alternative therapy was estimated at $13,143.25 total; with an estimated cost difference of $27,625.59. Estimated cost difference for prior tolerance was $21,987.87 and subsequent tolerance $5,637.72. Conclusion Aztreonam is an uncommon but costly antimicrobial. This study demonstrated that reduction in aztreonam utilization based on prior tolerance of β-lactam agents could lead to a meaningful reduction in pharmaceutical expenditures and serve as low-hanging fruit for an antimicrobial stewardship program. Disclosures All authors: No reported disclosures.

Background Challenges due to multidrug resistant Gram-negative bacterial pathogens such as P. aeruginosa (PSA) are increasing globally. Suboptimal antimicrobial therapy of infections caused by PSA is associated with increased morbidity and mortality. As a result, antimicrobial susceptibility (%S) studies are pivotal to identifying trends in antimicrobial resistance that inform decisions regarding choice of antimicrobial therapy. This study assessed the in vitro potency of 7 antipseudomonal agents including ceftolozane/tazobactam against PSA collected from numerous sites across the United States. Methods Multiple U.S. hospitals provided nonduplicate respiratory and blood isolates of PSA for potency testing. MICs against PSA were determined using broth microdilution methods according to CLSI for seven antimicrobials with antipseudomonal activity: aztreonam, cefepime, ceftazidime, ceftolozane/tazobactam, imipenem, meropenem and piperacillin/tazobactam. Susceptibility (%S) was defined per CLSI or FDA breakpoint criteria. Results Fourteen hospitals geographically spread across the United States provided total of 560 PSA isolates. Of the antibiotics assessed, %S to C/T was the highest at 95% with an MIC50 of 1 µg/mL and MIC90 of 2 µg/mL. In comparison, other %S (MIC50/MIC90) were as follows: ceftazidime 76% (4/64); cefepime 75% (4/32); piperacillin/tazobactam 73% (8/128), meropenem 72% (0.5/16); aztreonam 65% (8/32) and imipenem 65% (2/16). Conclusion For this geographically diverse PSA population, ceftolozane/tazobactam demonstrated the highest overall susceptibility (95%). Other antipseudomonal agents inclusive of the carbapenems displayed susceptibilities of 65–76%. In the era of escalating PSA resistance to the β-lactams, the potency of ceftolozane/tazobactam may represent an important clinical option. Disclosures D. P. Nicolau, Merck: Consultant, Grant Investigator and Speaker’s Bureau, Consulting fee, Research grant and Speaker honorarium.

Background Novel antibiotics will not be available to combat the threat of MBLs until 2021. One strategy to overcome MBLs is to combine CAZ-AVI + ATM. ATM is not hydrolysed by MBLs and AVI offers protection for ATM and CAZ vs. ESBLs and AmpCs. The combination also offers a theoretical advantage to inactivating multiple PBPs by using dual β-lactam therapy. Our objective was to define optimal dosing profiles for clinical use of ATM to add to CAZ-AVI in the hollow fiber infection model (HFIM). Methods E. coli ARLG-1013 (blaNDM-1, blaCTX-M, blaCMY, blaTEM) and K. pneumoniae ARLG-1002 (blaNDM-1, blaCTXM-15, blaDHA, blaSHV, blaTEM) were studied at a 7.5 log10 CFU/mL in the HFIM. Human dosing regimens of CAZ-AVI 2 g/0.5 g q8h (2 hours infusion) and ATM 2 g q8h (2 hours infusion) were simulated in alone and in combination. Continuous infusion (CI) regimens of CAZ-AVI 6 g/1.5 g per day CI + ATM 6 g/day CI and q8h regimens were given simultaneously and sequentially (ATM given 2 hours after CAZ-AVI). Resistant subpopulations were profiled on single (ATM), double (CAZ/AVI) and triple (ATM/CAZ/AVI) drug plates containing 2/2/4, 8/8/4, or 32/32/4 mg/L over 7 days. Results Against E. coli ARLG-1013, ATM alone mirrored growth control (+3.14 at 168 hours) (All units Log10 CFU/mL change vs. baseline). CAZ-AVI alone showed some intrinsic activity (+1.19 at 168 hours). CAZ-AVI 2g/0.5g q8h (2 hours infusion) + ATM 2g q8h (2 hours infusion) given sequentially resulted regrowth and stasis (+0.34 at 168 hours) vs. the simultaneous combination resulted initial bactericidal activity (-3.53 killing within 28 hours) which regrew at (−0.90 at 168 hours). All CI regimens were effective. CAZ-AVI 6g/1.5g per day CI + ATM 6 g/day CI resulted in dramatic killing (up to -5.78 killing within 50 hours) which was sustained (up to -3.90 killing at 168 hours). Comparing the infusion time of CAZ/AVI + ATM on bacterial killing: CI + CI > 2 hours + 2 hours > 30 minutes + 30 minutes. CI + CI resulted in complete suppression of resistance over 7 days. Against K. pneumoniae ARLG-1002, CAZ/AVI (CI) + ATM (CI) resulted in early synergy (>5.0 log killing within 24 hours) and suppression of resistance for more than 168 hours. Conclusion The combination of CAZ-AVI + ATM was highly synergistic and suppressed resistance against MBL Enterobacteriaceae in HFIM. ATM efficacy in combination was driven by %T > MIC. A Phase I study will assess safety to provide patients a critically important solution against “untreatable” Gram negatives. Disclosures T. P. Lodise, paratek: Consultant and Scientific Advisor, Consulting fee. B. T. Tsuji, Nabriva: Consultant, Consulting fee. Achaogen: Grant Investigator, Educational grant. ARLG, DCRI: Grant Investigator, Grant recipient. NIH/NIAID: Grant Investigator, Grant recipient.

Background Aztreonam (AZT) is an alternative antibiotic for Gram-negative infections requiring IV therapy and anti-pseudomonal coverage in patients with an IgE mediated penicillin allergy. However, many reported allergic reactions to penicillins are either unknown or mis-categorized. In 2012, significant use of AZT was observed at our institution coupled with a 29% resistance rate for Pseudomonas aeruginosa (PA) to AZT. The aim of this study was to track and assess AZT use during a 5-year period during which antimicrobial stewardship interventions along with a hospital-wide allergy guideline were implemented to optimize antibiotic use. Methods A retrospective review of AZT use was conducted at RUSH University Medical Center from January 2012 to December 2017. September of 2012, AZT was restricted for use in patients with an immediate type-1 hypersensitivity reaction to a β-lactam (BL) with approval from the infectious diseases (ID) consult service. January 2015, a hospital-wide BL allergy guideline, including a clinical pathway for BL graded challenges, was implemented. November 2015 and April 2017, computerized order-sets for BL graded challenges and in-patient penicillin skin tests were executed, respectively. AZT usage was tracked yearly and stratified by the number of patient cases, total number of doses and average days of therapy (DOT) to assess for differences. AZT cost, PA susceptibility, BL graded challenges and ID consultations for approval were also tracked for assessment. Results Patient cases using AZT decreased by 76% in 2017. The total number of doses decreased by 84%. The mean DOT for AZT declined from 5.5 days in 2012 to 3.4 days in 2017. The expenditure of AZT reduced by 86%. Hospital-wide resistance rates for PA to AZT declined to 22% in 2017. Compliance with the BL allergy guideline improved post implementation as the number of BL graded challenges rose to a mean of 30 orders with an 82% decrease in ID consults in 2017. 2012 2017 % Decrease P value Patient cases (n) 259 62 76

Accepted manuscript version. Published version at http://doi.org/10.1093/jac/dku433. Objectives. To characterize the chromosome-encoded metallo-β-lactamase (MBL) from the psychrophilic, marine fish-pathogenic bacterium Aliivibrio salmonicida LFI1238 and check for the presence of the gene in other Aliivibrio isolates both connected to the fish-farming industry and from the environment. Methods. The MBL gene was cloned and intracellularly expressed in Escherichia coli. Kinetic parameters, NaCl dependence, pH optimum and temperature optimum were determined using purified enzyme. The VIM-2 enzyme from a Pseudomonas aeruginosa hospital isolate was used as a counterpart in comparative analysis. PCRs with degenerate MBL primers were used to screen different A. salmonicida isolates for the presence of the gene. Results. A. salmonicida MBL (ALI-1) is an Ambler class B β-lactamase sharing 39% and 29% amino acid identity with IMP-1 and VIM-2, respectively. ALI-1 hydrolysed all β-lactam antibiotics tested, except for the monobactam aztreonam and the penicillin piperacillin. A profound increase in activity was observed when adding NaCl to the assay mixture (60% active without addition of NaCl, increasing to 100% at 0.5 M NaCl). The increase was less noticeable for VIM-2 (100% active at 0.2 M NaCl). ALI-1 appears to be ubiquitous in nature as it is found in Aliivibrio isolates not affected by human activity. Conclusions. This work provides more data for the ever-expanding MBL group of enzymes. These periplasmic enzymes are activated by addition of NaCl, and the marine enzyme is highly salt tolerant and cold active. The observed enzyme properties very likely reflect the conditions that the enzymes face in situ.

The blaESBL and blaAmpC genes in Enterobacteriaceae are spread by plasmid-mediated integrons, insertion sequences, and transposons, some of which are homologous in bacteria from food animals, foods, and humans. These genes have been frequently identified in Escherichia coli and Salmonella from food animals, the most common being blaCTX-M-1, blaCTX-M-14, and blaCMY-2. Identification of risk factors for their occurrence in food animals is complex. In addition to generic antimicrobial use, cephalosporin usage is an important risk factor for selection and spread of these genes. Extensive international trade of animals is a further risk factor. There are no data on the effectiveness of individual control options in reducing public health risks. A highly effective option would be to stop or restrict cephalosporin usage in food animals. Decreasing total antimicrobial use is also of high priority. Implementation of measures to limit strain dissemination (increasing farm biosecurity, controls in animal trade, and other general postharvest controls) are also important.