Studies on Escherichia coli associated with diabetic wounds; multi drug resistance and the occurrence of beta lactamase production in south-western Nigeria

The β-Lactam agents such as penicillins,2 cephalosporin’s, monobactams and carbapenems, are among the most frequently prescribed antibiotics worldwide. In Gram-negative pathogens, β-lactamases remain the most important contributing factor to β-lactam resistance,3 and their increasing prevalence as well as their alarming evolution seem to be directly linked to the clinical use of novel sub-classes of β-lactams.4 β-Lactamases are bacterial enzymes that inactivate β-lactam antibiotics by hydrolysis, which result in ineffective compounds.5 At least 400 different types of β-lactamases, originating from clinical isolates, have been described and a website has been created to monitor the latest developments among the newer types of b-lactamases.6 Several excellent reviews have recently been published describing the microbiology, characteristics, and structure, epidemiology and treatment options of organisms producing newer types of b-lactamases. This report does not aim to be comprehensive, but rather to illustrate that extended-spectrum b-lactamase-(ESBL) producing bacteria are emerging pathogens in the community, and that clinical laboratories play a critical role for their detection and control. Many genera of gram-negative bacteria possess a naturally occurring, chromosomally mediated β-lactamase. These enzymes are thought to have evolved from penicillin-binding proteins, with which they show some sequence homology. This development was likely due to the selective pressure exerted by β-lactam-producing soil organisms found in the environment.7 The first plasmid-mediated β-lactamase in gram-negatives, TEM-1, was described in the early 1960s.5 The TEM-1 enzyme was originally found in a single strain of E. coli isolated from a blood culture from a patient named Temoniera in Greece, hence the designation TEM.8,9 Being plasmid and transposon mediated has facilitated the spread of TEM-1 to other species of bacteria. Within a few years after its first isolation, the TEM1 β-lactamase spread worldwide and is now found in many different species of members of the family Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, and Neisseria gonorrhoeae. Another common plasmid-mediated β-lactamase found in Klebsiella pneumoniae and E. coli is SHV-1 (for sulphurhydryl variable). The SHV-1 β-lactamase is chromosomally encoded in the majority of isolates of K. pneumoniae but is usually plasmid mediated in E. coli.10