Search

Objective: To compare the sensitivity and specificity of different phenotypic methods for detection of Amp C betalactamase producing bacteria., Study Design: Analytical study., Place and Duration of Study: Department of Microbiology, Army Medical College / National University of Sciences and Technology (NUST), Islamabad, Pakistan, from June 2010 to December 2010., Methodology: A total of 150 clinical isolates were screened for presence of Amp C beta-lactamase by using the cefoxitin disc. The confirmatory methods evaluated were inhibitor based assay (boronic acid), Amp C disc test and Amp C Etest. Three dimensional enzyme extract assay was used as the reference method for determining the sensitivity and specificity., Results: Among the total isolates tested, 62.8% bacteria showed the presence of Amp C beta-lactamase by standard three dimensional enzyme extract assay. Among the three methods compared, boronic acid disk test found out to be highly sensitive (88%) and specific (92%) for the detection of Amp C beta-lactamase producing bacteria., Conclusion: Detection of Amp C production is crucial in order to establish the antibiotic therapy and to attain the favourable clinical outcomes. Implementation of simple tests like boronic acid disk tests in the laboratories will help to alleviate the spread of Amp C beta-lactamase harboring organisms.

Fundamental and clinical evaluations were made on cefoxitin, a new cephamycin antibiotic, and the following results were obtained. 1) MIC of the drug to clinical isolates was determined and was higher than that of cefazolin to Gram-positive bacilli. Among Gram-negative rods, the drug showed a sufficient antibacterial activity even to cefazolin-resistant strains. However, the MIC of cefoxitin to cefazolin-sensitive strains tended to be higher than that of cefazolin. 2) As to the passage of cefoxitin in experimental staphylococcal meningitis in rabbits, a percentage of CSF/serum ratio of AUC was 10.7% up to 3 hours and CSF/serum ratio of T1/2 was 1.78 of which value was an intermediate between those of ampicillin and cefazolin. There were, however, larger individual differences. 3) Blood concentrations and urinary recovery rates were determined in 2 children. In 1 patient, in whom the drug was given intravenously at a dose of 25 mg/kg, a blood concentration after 30 minutes was 50 microgram/ml, T1/2 was 57.2 minutes. This patient, however, showed a slight renal dysfunction. In another patient, who received an intravenous injection of 12.5 mg/kg, a 30 minutes blood concentration was 14.6 microgram/ml and T1/2 was 31.8 minutes. Urinary recovery rates up to 6 hours were 85.8% and 73.5%, respectively. 4) Thirty patients with the following bacterial infections were treated with cefoxitin, i.e., urinary tract infection (24 cases), respiratory tract infection (4 cases), each one case of peritonitis and suspected sepsis. An overall efficacy rate was 93.3%, i.e., excellent in 13 cases, good in 15, and failure in 2. Disappearance rate of the causative organism of the 23 clinical isolates was 87.0%, i.e., that the causative organism disappeared in 20 strains, reduced in 1 and persisted in 2. 5) Based on the above results, it was concluded that cefoxitin is a potent new antibiotic in bacterial infections in children, particularly respiratory and urinary tract infections. The optimal recommended dose will be about 25 mg/kg which should be given 3-4 times daily intravenously or by drip infusion.

The authors have carried out the laboratory and clinical studies of cefoxitin. The results were as follows: The sensitivity was estimated by plate dilution method on 26 strains of S. aureus, 25 strains of E. coli, 24 strains of K. pneumoniae, 27 strains of Serratia and 17 strains of Salmonella isolated from patients. The distribution of sensitivity of S. aureus was 1.56-3.13 microgram/ml and the peak of distribution was 3.13 microgram/ml. The strains of 76.0% of E. coli was inhibited at concentration of less than 3.13 microgram/ml. The strains of 91.7% of K. pneumoniae was inhibited at concentration of less than 3.13 microgram/ml. The distribution of sensitivity of Serratia was 6.25-more than 100 microgram/ml and the peak of distribution was 100 microgram/ml. The all strains of Salmonella were inhibited at concentration of less than 3.13 microgram/ml. Cefoxitin was given by intravenous administration for 5 minutes at a single dose of 25 mg/kg of cefoxitin to 2 children, and by drip infusion for 60 minutes at a single dose of 25 mg/kg of cefoxitin to 4 children. After intravenous administration of cefoxitin, the mean peak of serum level was 67.3 +/- 6.3 microgram/ml at 15 minutes, and at 4 and 6 hours after administration was not detected. Half-life time was 22 minutes. And after drip infusion of cefoxitin for 60 minutes, the mean peak of serum level was 35.7 +/- 5.3 microgram/ml at 1 hour, and at 4 and 6 hours after administration was not detected. Half-life time was 20 minutes. The mean urinary recovery rate was 82.4 +/- 3.0% and 90.2 +/- 6.8% up to 6 hours after intravenous administration and drip infusion respectively. Cefoxitin was effective in all of 15 cases with bacterial infections. No side effects was observed.

Laboratory and clinical studies were performed on a newly introduced antibiotic of the cephamycin series, cefoxitin (CFX), and the results obtained were as follows: 1. Employing clinical isolates, MICs were determined and comparisons made with those of cephalosporins. The MICs of CFX against S. aureus and S. pyogenes slightly inferior to those of the cephalosporins, while the MICs of CFX against Gram-negative bacilli such as E. coli, Proteus sp. and Klebsiella sp. were considerably superior to those of CER and CET, and slightly superior to those of CEZ. 2. The peak serum concentrations were 34.7 mcg/ml and 67.6 mcg/ml at 30 minutes after an intravenous injection in doses of 12.5 mg/kg and 25 mg/kg, respectively. The peak serum concentration was 40.8 mcg/ml at the end of 60 minutes intravenous drip infusion when it was given in a dose of 25 mg/kg. In these cases, the serum half life were 25.8-51.2 minutes, and their urinary recovery were 67-90%. 3. Clinically, CFX was given to the 29 children with a total of 31 of varying bacterial infections: 6 cases of urinary tract infection (U.T.I.), 19 of respiratory tract infection (R.T.I.), 2 of staphylococcal scalded skin syndrome (S.S.S.S.), 2 of purulent lymphadenitis and 2 cases of soft tissue dermatological infections. Overall efficacy rate was 83.9% (26 cases). No significant adverse reaction was noted except for 1 case of rash. Abnormal laboratory findings observed were elevation of GOT and GPT in 1 patient and of GPT in 1 patient.

Cefoxitin is a beta-lactam antibiotic derived from cephamycin C, a naturally occurring substance produced by Streptomyces lactamdurans. Its resistance to destruction by beta-lactamases results in a broad spectrum of antibacterial activity which includes anaerobic as well as Gram-positive and Gram-negative aerobic bacteria, including many resistant to cephalothin and other cephalosporins. Given by intravenous or intramuscular injection, cefoxitin is effective against a wide variety of infections caused by Gram-positive or Gram-negative aerobes as well as by anaerobic bacteria. It is generally well tolerated, thrombophlebitis, skin rash and some degree of discomfort after intramuscular injection, being the most commonly reported side effects. Cefoxitin has not been shown to cause adverse effects on renal function.

The antimicrobial activity of three 7-alpha-methoxy beta-lactams were compared to cefoperazone and ceftriaxone. All had a similar spectrum of activity against the Enterobacteriaceae, except cefoxitin. Cefotetan was only slightly less active than moxalactam against the Enterobacter spp. Ceftriaxone was most effective on Neisserias, Haemophilus spp, nonenterococcal Streptococcus spp, and Acinetobacter spp. Cefoperazone generally inhibited more pseudomonads while all of the "cephamycins" showed activity against Bacteroides fragilis and B. thetaiotaomicron. Beta-lactamase hydrolysis studies of six substrates having pharmacologic serum half lives of greater than or equal to 2 hrs were performed by bioassay and automated procedures. Excellent correlations were found between methods up to 24 hrs. A "lag-phase" was observed for several drug/enzyme combinations before initiation of significant substrate hydrolysis. The 7-alpha-methoxy beta-lactams were routinely more stable to the six representative enzymes (Richmond-Sykes types I-V) than other "stable" cephalosporins. Substrate hydrolysis rates resulting in greater than 50% drug loss in less than or equal to 1 hr generally produced resistant in vitro test results. Cefotetan, cefoxitin, moxalactam, ceftriaxone, and dicloxacillin were potent inhibitors of Type I (P99) beta-lactamases. Moxalactam demonstrated significant inhibition and affinity for the Type V enzyme while cefoperazone uniquely possesses affinity (so-called inhibition) for all tested beta-lactamases. Cefotetan appears to be a promising, beta-lactam compound with some in vitro characteristics comparable to the 1-oxa-beta-lactams and alpha-methoxyimino cephalosporins.

The activity of cefbuperazone, a 7 alpha-methoxy ureido cephalosporin, was determined against 726 clinical isolates. Ninety percent of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter diversus, Proteus mirabilis, Enterobacter aerogenes, Proteus vulgaris, Morganella morganii, Salmonella, and Shigella species were inhibited by less than or equal to 6.3 micrograms/ml. Cefbuperazone was more active than cefamandole, cefoxitin and piperacillin against these species. Concentrations of 25 micrograms/ml of cefbuperazone were needed to inhibit Serratia marcescens and Providencia species, and 50% of Enterobacter cloacae had MICs greater than 25 micrograms/ml. Cefbuperazone was less active by 8 to 32-fold than cefotaxime or moxalactam against most Enterobacteriaceae. Cefbuperazone did not inhibit Acinetobacter or Pseudomonas species. Hemolytic streptococci were inhibited by 12.5 micrograms/ml and staphylococci by 25 micrograms/ml. Cefbuperazone had activity comparable to cefoxitin and moxalactam against Bacteroides fragilis with MIC90s of 6.3 micrograms/ml. Cefbuperazone was not hydrolyzed by plasmid or chromosomal beta-lactamases and was an inhibitor of the P99 E. cloacae beta-lactamase with an I50 of 1 microgram/ml. It was a less effective inhibitor of the K. oxytoca K1 and E. coli TEM-1 beta-lactamases than was clavulanic acid. Cefbuperazone induced beta-lactamases in P. aeruginosa and resistant E. cloacae. A permeability barrier in E. cloacae, C. freundii and P. aeruginosa is suggested by the potentiation of cefbuperazone's activity by EDTA.

Antibiotic levels in serum are commonly used to guide antibiotic therapy. The antibiotic levels in interstitial fluid are a more accurate reflection of the efficacy of antibiotic penetration into the tissues. Although there are experimental models for determining interstitial fluid levels, there is no model for measuring the in vivo killing of bacteria, which is the endpoint of antibiotic therapy. We developed an accurate, reliable animal model which allows measurement of the in vivo killing of bacteria along with a determination of antibiotic levels in tissues. Modified Sykes-Moore chambers were applied to the dissected external oblique muscle of 14 dogs. The chambers were inoculated with clinical isolates of Staphylococcus aureus or Escherichia coli. The dogs were treated with cefoxitin or gentamicin. Quantitative cultures were performed, and the antibiotic levels in interstitial fluid were determined.

Studies on antimicrobial activity, absorption and excretion and clinical use of cefoxitin in pediatric field were performed. 1. MIC of cefoxitin was compared with that of cefazolin and/or ampicillin for clinical isolates of Staphylococcus aureus (36 strains), Escherichia coli (35 strains), Klebsiella pneumoniae (34 strains) and Haemophilus influenzae (80 strains). MIC of cefoxitin against S. aureus was approximately 1-2 tubes higher than that of cefazolin. Many strains of E. coli and K. pneumoniae that showed high MIC to cefazolin were sensitive to cefoxitin. It is presumed that the results are due to the strong resistance of cefoxitin to beta-lactamase degradation. MIC of cefoxitin against H. influenzae was approximately 1-2 tubes lower than that of cefazolin, but approximately 4 tubes higher than that of ampicillin. 2. Serum level and urinary recovery rate of cefoxitin after one shot i.v. injection of 25 mg/kg were examined. The serum mean levels were 33.8 microgram/ml at 1/2 hour, 7.0 microgram/ml at 1 hour and 2.9 microgram/ml at 2 hours after the injection, respectively, and the drug was not detected in serum at 4 and 6 hours after the injection. The mean half-life of serum level was 27.1 minutes. The mean urinary recovery rate within 6 hours after injection was 96.0% and most of the drug were excreted into urine within 2 hours after the injection. 3. In order to evaluate clinical response, bacteriological response and side effects, cefoxitin was applied to 19 cases, i.e., 12 cases of either acute lobar pneumonia or acute bronchopneumonia, 2 cases of acute pyelitis, 1 case each of acute bronchitis, acute purulent tonsillitis, acute purulent arthritis, acute orbital phlegmon and acute buccal abscess. As for clinical response, the overall efficacy rate (the percentage of cases showed excellent and good efficacy) was 88.9%. As for bacteriological response, among the 13 strains which were determined or supposed to be causative organisms, i.e., 6 strains of Streptococcus pneumoniae, 2 strains of H. influenzae and 1 strain each of streptococcus pyogenes, alpha-Streptococcus, Enterococcus, E. coli and Neisseria sp., all strains were disappeared except for Enterococcus which was reduced by the treatment with cefoxitin. No side effect was observed in any case. Abnormalities of laboratory findings were observed in 3 cases, i.e., 1 case each of reduction of RBC and Hb, elevation of GOT and GPT and elevation of GPT, but all of them returned to normal following completion of the dosage term.