Comparison of in vitro fosfomycin susceptibility testing methods with agar dilution for carbapenem resistant Klebsiella pneumoniae and Escherichiacoli.

PURPOSE: The emergence of Extensively drug resistant (XDR) pathogens like Carbapenem Resistant Klebsiella pneumoniae (CR Kpn) and Carbapenem Resistant Escherichia coli (CR Eco) has limited therapeutic options for treating them. Fosfomycin a broad-spectrum antibiotic, has emerged as a potential treatment option in combination with other agents. It is therefore important that accurate drug susceptibility testing (DST) results of fosfomycin should be available to all clinical microbiology laboratories. Agar dilution which is the recommended method for fosfomycin DST is not convenient to adopt in a routine set-up. This study aimed to determine the susceptibility pattern of CR Kpn and CR Eco to fosfomycin and to evaluate the discrepancies of the available manual MIC based alternative methods. METHODS: Agar dilution (AD), broth microdilution (BMD), E-test and Ezy MIC test were performed on 235 CR-Kpn and Eco isolates respectively. RESULTS: Of 177 CR Kpn, 31.63% (n â€‹= â€‹56/177) of the isolates were susceptible by AD. Categorical Agreement (CA) by BMD, E-test and Ezy MIC were lower than the acceptable limit while Very Major Errors (VMEs) and Major Errors (MEs) were beyond the acceptable limits. In the case of CR Eco, 96.55% (n â€‹= â€‹56/58) were susceptible by AD. CA of 100% (n â€‹= â€‹58/58) was shown by both BMD and Ezy MIC while 86.20% (n â€‹= â€‹50/58) was shown by E-test, with no VME observed for CR Eco. ME was only observed for E-test method. CONCLUSION: The alternative methods were in poor agreement with AD method for CR Kpn and for CR Eco, BMD and Ezy MIC have shown reliable results.

Minimum inhibitory concentration (MIC) of Ceftriaxone and Azithromycin for blood culture isolates of Salmonella enterica spp.

INTRODUCTION: Enteric fever caused by Salmonella enterica continues to be a major public health problem worldwide. In the last decade, ceftriaxone and azithromycin have become the drugs of choice for treating enteric fever caused by Nalidixic acid resistant Salmonella (NARS) enterica. This has led to reports of drug resistance to both drugs. Since enteric fever is endemic in India, accurate drug susceptibility surveillance is crucial to ensure empiric management of enteric fever is appropriate. The aim of this study is to evaluate the minimum inhibitory concentration (MIC) of ceftriaxone and azithromycin for blood culture isolates of NARS isolated at our centre. METHODOLOGY: This is a retrospective study conducted in a tertiary care center in Mumbai for blood culture isolates of NARS from 2016 to 2018. Isolates were tested for antimicrobial susceptibility testing (AST) against ceftriaxone and azithromycin using a manual broth microdilution method (BMD). RESULTS: Of 155 blood culture isolates of NARS: S. Typhi (n = 112) and S. Paratyphi A (n = 43) were included in the study. 81.9% (127 / 155) isolates were susceptible, 6.4% (10 / 155) isolates were intermediate while 11.6% (18 / 155) isolates were resistant to ceftriaxone. 100% susceptibility of NARS was observed to azithromycin. CONCLUSIONS: This study documents an alarming increase in resistance to ceftriaxone among NARS in Mumbai while azithromycin continues to be susceptible in vitro. It is essential to know MICs to understand epidemiological trends and choose appropriate treatment regimens for treating enteric fever.