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Antibiotic resistance is a global threat, with a disproportionate burden of mortality in low- and middle-income countries. It is increasing in both the public and private healthcare sectors within South Africa, especially in Gram-negative organisms, and is associated with increased use of World Health Organization watch and reserve antibiotics. There is a need for improved access to new antibiotics to treat infections caused by drug-resistant organisms in order to limit side-effects and improve patient outcomes of currently available antibiotics. We propose the responsible introduction of these new antibiotics with both administrative and clinical oversight in order to preserve the longevity of these precious antibiotics.

Objectives: To report the in vitro susceptibility of Enterobacterales (n = 3905) and Pseudomonas aeruginosa (n = 1,109) isolates, collected from patients in sub-Saharan Africa (four countries) in 2017-2021, to a panel of 10 antimicrobial agents with a focus on ceftazidime-avibactam activity against resistant phenotypes and β-lactamase carriers., Methods: MICs were determined by CLSI broth microdilution and interpreted using both 2022 CLSI and EUCAST breakpoints. β-lactamase genes were identified in select β-lactam-nonsusceptible isolate subsets using multiplex PCR assays., Results: Among Enterobacterales, 96.2% of all isolates were ceftazidime-avibactam-susceptible (MIC 90 , 0.5 µg/mL), including all serine carbapenemase-positive (n = 127), 99.6% of ESBL-positive, carbapenemase-negative (n = 730), 91.9% of multidrug resistant (MDR; n = 1817), and 42.7% of DTR (difficult-to-treat resistance; n = 171) isolates. Metallo-β-lactamase (MBL) genes were identified in most (n = 136; 91.2%) ceftazidime-avibactam-resistant isolates (3.5% of all Enterobacterales isolates). Ceftazidime-avibactam percent susceptible values ranged from 99.5% (Klebsiella species other than Klebsiella pneumoniae) to 92.5% (K. pneumoniae) for the various Enterobacterial taxa examined. Greater than 90% of Enterobacterales isolates from each country (Cameroon, Ivory Coast, Nigeria, South Africa) were ceftazidime-avibactam-susceptible. Among P. aeruginosa, 88.9% of all isolates were ceftazidime-avibactam-susceptible (MIC 90 , 16 µg/mL). Most (88.5%) MBL-negative, meropenem-resistant (n = 78), 68.1% of MDR (n = 385), and 19.2% of DTR isolates (n = 99) were ceftazidime-avibactam-susceptible. MBL genes were identified in 43.1% of ceftazidime-avibactam-resistant isolates (n = 53; 4.8% of all P. aeruginosa isolates). Country-specific ceftazidime-avibactam percent susceptible values for P. aeruginosa ranged from 94.1% (Cameroon) to 76.2% (Nigeria)., Conclusion: Reference in vitro antimicrobial susceptibility testing demonstrated that most recent Enterobacterales (96%) and P. aeruginosa (89%) clinical isolates from four sub-Saharan African countries were ceftazidime-avibactam susceptible., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Minimum inhibitory concentration (MIC) values are useful in guiding appropriate antimicrobial therapy however, routine provision and interpretation of MIC values to guide clinical decision-making is challenging., Objectives: This proof of concept study aims to demonstrate the clinical utility and application of Vitek ® -derived MIC values through categorisation of clinical isolates as wild type., Method: A random selection of clinically relevant Gram negative isolates routinely tested on the Vitek ® instrument were included. The Vitek ® MIC values, for selected antimicrobials at the lowest calling range of that card, were compared to the broth microdilution reference method. The specified end-point was concordance between the two results if the reference MIC was less than or equal to the EUCAST-defined epidemiological cut-off value (ECOFF) for that drug-bug combination., Results: A total of 525 isolates were included (468 Enterobacterales and 57 Pseudomonas aeruginosa ), with an overall concordance rate of 96.4% (508/525). Correct ECOFF categorisation by the Vitek ® was highest for ceftazidime and piperacillin (100%, n = 48 and n = 55, respectively) and lowest for cefepime (81.8%, n = 66)., Conclusion: Vitek ® -derived MIC values can be used to categorise organisms as wild-type if the MIC is reported at the card's lowest calling range (≤) as there is high likelihood that the MIC is at or below the ECOFF. This has important implications for antimicrobial management, assisting in choice of agent and in improving probability of target attainment for desired pharmacodynamic targets which can translate into improved clinical outcomes., Contribution: Minimum inhibitory concentration data from an automated antimicrobial susceptibility testing instrument can be used to guide clinical decisions., Competing Interests: The author declares that he has no financial or personal relationships that may have inappropriately influenced him in writing this article., (© 2023. The Author.)

Antibiotic stewardship of hospital-acquired infections because of difficult-to-treat resistant (DTR) Gram-negative bacteria is a global challenge. Their increasing prevalence in South Africa has required a shift in prescribing in recent years towards colistin, an antibiotic of last resort. High toxicity levels and developing resistance to colistin are narrowing treatment options further. Recently, two new β-lactam/β-lactamase inhibitor combinations, ceftazidime-avibactam and ceftolozane-tazobactam were registered in South Africa, bringing hope of new options for management of these life-threatening infections. However, with increased use in the private sector, increasing levels of resistance to ceftazidime-avibactam are already being witnessed, putting their long-term viability as treatment options of last resort, in jeopardy. This review focuses on how these two vital new antibiotics should be stewarded within a framework that recognises the resistance mechanisms currently predominant in South Africa's multi-drug and DTR Gram-negative bacteria. Moreover, the withholding of their use for resistant infections that can be treated with currently available antibiotics is a critical part of stewardship, if these antibiotics are to be conserved in the long term., Competing Interests: The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article., (© 2022. The Authors.)

Acinetobacter baumannii is an opportunistic pathogen and causes various infections in patients. This study aimed to describe the clinical, epidemiological and molecular characteristics of A. baumannii isolated from BCs in patients at a tertiary-level hospital in South Africa. Ninety-six isolates from bloodstream infections were collected. Clinical characteristics of patients were recorded from patient files. Organism identification and AST was performed using automated systems. PCR screening for the mcr-1 to mcr -5 genes was done. To infer genetic relatedness, a dendrogram was constructed using MALDI-TOF MS. All colistin-resistant isolates ( n = 9) were selected for WGS. The patients were divided into three groups, infants (<1 year; n = 54), paediatrics (1-18 years; n = 6) and adults (≥19 years; n = 36) with a median age of 13 days, 1 and 41 years respectively. Of the 96 A. baumannii bacteraemia cases, 96.9% (93/96) were healthcare-associated. The crude mortality rate at 30 days was 52.2% (48/92). The majority of the isolates were multidrug-resistant (MDR). All isolates were PCR-negative for the mcr -1 to mcr -5 genes. The majority of the isolates belonged to cluster 1 (62/96) according to the MALDI-TOF MS dendrogram. Colistin resistance was confirmed in nine A. baumannii isolates (9.4%). The colistin-resistant isolates belonged to sequence type (ST) 1 (5/6) and ST2 (1/6). The majority of ST1 isolates showed low SNP diversity (≤4 SNPs). All the colistin-resistant isolates were resistant to carbapenems, exhibited an XDR phenotype and harboured the bla OXA- 23 gene. The bla NDM gene was only detected in ST1 colistin-resistant isolates ( n = 5). The lps B gene was detected in all colistin-resistant isolates as well as various efflux pump genes belonging to the RND, the MFS and the SMR families. The lipooligosaccharide OCL1 was detected in all colistin-resistant ST1 and ST2 isolates and the capsular polysaccharide KL3 and KL17 were detected in ST2 and ST1 respectively. This study demonstrated a 9.4% prevalence of colistin-resistant ST1 and ST2 A. baumannii in BC isolates. The detection of the lps B gene indicates a potential threat and requires close prospective monitoring., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Lowe, Singh-Moodley, Ismail, Thomas, Chibabhai, Nana, Lowman, Ismail, Chan and Perovic.)