Abstract:
Objectives: To determine the prevalence and antimicrobial susceptibility of carbapenemase-producing Enterobacteriaceae
among hospitalized patients and outpatients attending two military hospitals in Rawalpindi,
Pakistan, and to compare the performance of two chromogenic culture media for the isolation of these organisms.
Methods: Stool samples from 200 distinct patients were cultured on MacConkey agar and subsequently on two
chromogenic media—Colorex KPC and a prototype chromogenic medium, ID Carba—designed for the isolation
of carbapenemase-producing Enterobacteriaceae. All Gram-negative isolates growing on either chromogenic
medium were investigated for carbapenemases by phenotypic and molecular methods. Producers were
subjected to susceptibility testing with 40 antimicrobials by VITEK 2 or agar dilution.
Results: In total, 64 NDM-1-positive isolates of Enterobacteriaceae, belonging to seven distinct species, were
recovered from 37 (18.5%) of the stool samples. No other carbapenemase types were confirmed. Nineteen
positive samples were identified among 70 from inpatients (prevalence 27.1%) and there were 18 positive
samples among 130 from outpatients (prevalence 13.8%). Fifty-six isolates (87.5%) harbouring the NDM-1
enzyme were recovered on ID Carba compared with 41 isolates (64.1%) on Colorex KPC (P¼0.012). Multidrug
resistance was prevalent, but no pan-resistant isolates were found, with most isolates susceptible in vitro to
colistin (97%), mecillinam (95%), fosfomycin (94%), tigecycline (89%) and nitrofurantoin (78%).
Conclusions: This study shows a high prevalence of multidrug-resistant Enterobacteriaceae with the NDM-1
enzyme in Rawalpindi. The new chromogenic medium, ID Carba, was more sensitive than Colorex KPC and
has potential as a screening medium for isolation of Enterobacteriaceae harbouring the NDM-1 enzyme.
