In Vitro Efficacy of Third Generation Cephalosporins against Nalidixic Acid Resistant and Multi Drug Resistant Salmonella Typhi and Paratyphi via E-strip Method

Abstract

Background: Samonella typhi and paratyphi are the strains causing typhoid which carries significant mortality in our region. There have been reports of fluoroquinolone treatment failure due to resistance. After fluoroquinolones, cephalosporins have reliable efficacy against these bacteria. We aimed to find the minimum inhibitory concentrations of cefixime and ceftriaxone against nalidixic acid resistant and multi drug resistant Salmonella typhi and paratyphi in clinical isolates of a tertiary care setting to detect the rising minimum inhibitory concentrations.

Materials and methods: This prospective, cross-sectional study was carried out in Microbiology laboratory of Army Medical College, Rawalpindi from 2010-2011. Blood cultures were dealt via standard microbiological techniques for detection of Salmonella typhi and paratyphi. Isolates were then tested against antibiotic disks of nalidixic acid, chloramphenicol, ampicillin and cotrimoxazole. Minimum inhibitory concentration of cefixime and ceftriaxone were determined by E-strip method against multidrug resistant and nalidixic acid resistant Salmonella typhi and paratyphi according to CLSI guidelines. This is an ongoing
study.
Results: In the first part of this study one hundred and fifty-six isolates of nalidixic acid resistant and multidrug resistant typhoidal salmonellae were included in our study. Among these eightyone (51.92%) were Salmonella typhi and seventy-five (48.08%) were Salmonella paratyphi A. All the isolates had minimal inhibitory concentrations of cefixime and ceftriaxone in
susceptible range.

Conclusion: Both ceftriaxone and cefixime prove very effective antibiotics against nalidixic acid resistant and multidrug resistant typhoidal Salmonellae. Ceftriaxone is the therapeutic agent of choice for inpatients. While cefixime, can be given on outpatient basis due to its convenient oral administration till full emergence of cephalosporin resistant typhoidal Salmonella.

Key words: Cephalosporins, Multidrug resistant Salmonella, Nalidixic acid resistant Salmonella.