Phenotypic and molecular characteristics of Escherichia coli strains producing ESBLs isolated in the Military Hospital of Tunis

Abstract

Betalactam resistance due to ESBL is increasing all over the world especially in Enterobacteriaceae. The new frequently community enzymes such as CTX-M are responsible for a global "pandemic" and at the same time the part of E. coli increase among the species represented. Our retrospective study concern a 64 strains of Escherichia coli producing ESBLs isolated in the laboratory of Microbiology of the Military Hospital of Tunis, from October 2009 to December 2010. The study of antibiotic sensiti-vity was done by the method of diffusion in agar and supplemented by measuring the MIC by E-test strips. Betalactamases were detected by PCR using primers specific genes TEM, SHV, CTX-M and CTX-M group 1. The strains were isolated from the neonatal unit of the Military Hospital of Tunis (17%), intensive care (16%), followed by pediatric service (14%), emergency (9%) and 23% of strains in external consultations. The E. coli studied were isolated from urine cultures (73%), followed by blood cultures (11%), pus and rectal swabs (6%). Twenty strains were isolated in 2009 and 44 in 2010. The resistance of the strains studied was 61% with amoxicillin + clavulanic acid, 53% to nalidixic acid, 48% to ofloxacin, 45% to ciprofloxa-cin, 81% to gentamicin, 31% to chloramphenicol, low resistance to cefoxitin 3% and no resistance to imipenem. All the strains studied had a double positive synergy test. MICs obtained for the different antibiotics are high except for imipenem. The blaCTX-M gene was detected in 95% of the strains studied, 87% were positive for blaCTX-M genes in group 1. BlaTEM genes (9%) and blaSHV (4%) are not significant in Escherichia coli strains studied. We noted the presence of multidrug-resistant strains that harbor two or three resistance genes blaTEM, blaSHV and blaCTXM-1, this association can be found in the same region of multidrug resistance often observed with strains producing CTX-M-15. Our study confirms the results found by other authors, namely the prevalence of ESBL CTX-M (probably M-15) Resistance to β-lac-tam antibiotics is associated with co-resistance to other antibiotics which often makes regimens traditionally used for the treatment ineffective. A better understanding of the epidemiology of resistance will improve the therapeutic management of patients while reducing the prescription of broad spectrum antibiotics.