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

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