OBJECTIVES: To determine the prevalence of class A extended spectrum β-lactamases (ESBL)-producing Escherichia coli and Klebsiella spp., and to investigate clonality among ESBL-producing isolates of nosocomial and community infections. METHODS: The study involved 354 nosocomial infections samples and 992 community infections samples, obtained between 2003 and 2006 at Caxias do Sul, RS. The detection of ESBL was performed by the disk-diffusion test. Presence of blaCTX-M, blaSHV and blaTEM β-lactamase genes was evaluated by PCR, and genomic typing was determined by pulsed-field gel electrophoresis analysis. RESULTS: Higher frequency of ESBL-producing isolates were detected among nosocomial samples of E. coli (6.7%) and Klebsiella (43.7%), than those obtained from community infections (0.4% and 2.6%). blaTEM and blaCTX were the most prevalent ESBL gene families in both E. coli and Klebsiella isolates. Different pulsotypes were obtained among ESBL-producing E. coli and 11 clones for Klebsiella spp., which occurred over the years and in different hospital wards. Among ESBL-producing K. pneumoniae, 74.3% transferred ESBL genes by conjugation and exhibited concomitant decreased aminoglycosides susceptibility. CONCLUSION: ESBL-producing E. coli, and especially K. pneumoniae are essentially a nosocomial problem, and their dissemination to the community is relatively limited. The great genetic variability observed among ESBL-producing bacteria indicates polyclonal spread and high transference of ESBL genes between bacteria in the hospital environment. This information is of paramount importance for nosocomial infection control.

Mutantes de Escherichia coli resistentes aos aminoglicosídios por seleção in vitro em meio de cultivo de alta osmolaridade contendo canamicina podem apresentar ausência da proteína periplásmica oligopeptídio permease (OppA). O comportamento desse mutante em presença de canamicina ou do peptídio tóxico triornitina sugere que a proteína OppA e um outro componente do envoltório bacteriano contribuem para a resistência osmodependente em E. coli.

The oligopeptide permease (OppA) protein was found to be missing in the periplasmic fractions of Escherichia coli kanamycin-resistant mutants selected under high osmotic conditions. The growth behavior of one mutant in media containing kanamycin or the toxic peptide triornithine suggests that OppA and another cell envelope component contribute to the osmolarity-dependent aminoglycoside resistance of E. Coli.