[Variation in transfer resistance to cefotaxime, ceftazidime and aztreonam in strains of Acinetobacter sp., Enterobacter sp. and Citrobacter sp. isolated from the same university hospitals].

BACKGROUND: In the last decade were in SR documented new problems in resistance to the newer antibiotics that with regard to their structure and antibacterial properties resisted to the known mechanism of bacterial resistance. The emergence of multiple drug resistance to the new betalactams is connected both with frequent application of these drugs in the hospitals and transfer of R plasmids.

METHODS AND RESULTS: We studied composition and transferability of resistance to newer betalactam antibiotics in strains of Acinetobacter sp., Enterobacter sp, and Citrobacter sp. isolated during one month in patients from two teaching University Hospitals. All strains studied were resistant to cefotaxime (CTX), ceftazidime (CAZ) and aztreonam (ATM) but Acinetobacter strains, although resistant also to CAZ and ATM transferred the resistance to CTX only. Thus, resistance to CAZ and ATM has a chromosomal origin in these strains. A strain of Citrobacter sp., resistant to CTX, CAZ and ATM, produced a ESBL betalactamase detectable in a double-disk diffusion method (Fig. 1). An Enterobacter cloacae strain transfers directly the resistance to all new betalactams indicated. Their hydrolysis by these strains points to their production of new types of extended-spectrum beta-lactamases ESBL).

CONCLUSIONS: We strongly recommend to be strictly rational in the use of new betalactams of CTX, CZA or ATM type because it is suspected that, especially in so-called empirical prophylaxis or treatment, they exert a strong selective pressure toward the prevalence of mutants with transferable ESBL-producing nosocomial bacteria resistant to these drugs.