Characterisation of ß-lactamases implicated in resistance to ß-lactem antibiotics in urinary tract infections
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South Africa is not excluded from the problems encountered world-wide in the treatment of nosocomial urinary tract infections, commonly caused by enzyme-producing Enterobacteriaceae. These enzymes include the ß-lactamases and extended-spectrum ß-lactamases (ESBLs) capable of hydrolysing the ß-lactam agents and in particular the expanded-spectrum cephalosporins frequently used. The study was designed to determine the role of ß-lactamases in resistance development in commonly encountered pathogens implicated in urinary tract infections and to characterise the enzymes involved. Resistance to the ß-lactam agents amoxicillin, ceftriaxone, ceftriaxone, piperacillin and cefoxitin was suspected to involve the presence of one or more β-lactamases in the isolates from Bloemfontein hospitals. Diverse and complex β-lactamases were identified and ESBLs were detected in 80% of the isolates. These β-lactamases were characterised by isoelectric focusing (IEF) and genetic analysis (DNA amplification by PCR) to investigate the presence of possible genes responsible for resistance development. The production of blaTEM and blaSHV type genes was demonstrated. Isolates harbouring these genes were highly resistant to amoxicillin and piperacillin, with MIC90s of >128μg/ml. Resistance to these antibiotics was shown to be readily transferred between strains and there was an indication that the resistance genes are carried on plasmids and was transferred by conjugation. A plasmid of 9-10 kb was detected in 83% of the isolates and could be one of the mechanisms implicated in the transfer of ESBLs in uropathogenic bacteria. ß-Lactam resistance could be attributed to the presence and action of ß-lactamases such as the TEM and SHV type enzymes and this resistance can be transmitted between bacteria, causing problems specifically in the hospital environment. Further and continuous investigations are required to find a solution for this ever increasing problem.