Programme Hospitalier Recherche Clinique, Institut Pasteur, Inserm, French Public Health Agency.

No abstract

This study evaluated the virulence potential of Escherichia coli isolates producing CTX-M beta-lactamases. During a 24-month period, 33 extended-spectrum beta-lactamase (ESBL)-producing E. coli, including 14 CTX-M-producers, were isolated from urinary tract infections at Nîmes University Hospital, France. The prevalence of 14 major virulence factors (VFs) was investigated by PCR and compared with the prevalence in a group of 99 susceptible E. coli isolates. Ten VFs were less prevalent (p <0.05) in the ESBL isolates than the susceptible E. coli, while iutA and traT were more prevalent in ESBL isolates (p <0.05). Moreover, the CTX-M-producing isolates had significantly fewer VFs than TEM-producing isolates. A novel infection model using the nematode Caenorhabditis elegans was developed to assess the virulence properties of extra-intestinal pathogenic E. coli (ExPEC) strains in vivo. C. elegans infection assays, using 14 ESBL-producing E. coli and ten susceptible E. coli isolates, indicated that the ability to kill nematodes correlated with the presence of VFs, and that CTX-M-producing isolates had relatively low virulence in vivo. Overall, the results suggested that hospital-acquired CTX-M-producing E. coli, although adapted for survival in an antibiotic-rich environment such as the hospital milieu, have a relatively low intrinsic virulence potential.

Twelve cases of infections caused by extended-spectrum beta-lactamase (ESBla)-producing Klebsiella pneumoniae were reported between August 1991 and March 1993 in the Geriatric Department of the Nimes University Hospital, where these bacteria had not been previously isolated. Restriction profiles of total genomic DNAs cleaved byXMal and Spel were compared by pulsed-field gel electrophoresis. The strains that were tested included the 12 isolates from K. pneumoniae-infected patients, strains recovered from rectal swabs of asymptomatic patients in the same ward, and strains isolated in other hospitals in Nimes at the same time. The restriction profiles of the 12 isolates and those recovered from asymptomatic patients in the same ward were very similar. Over a period of more than 1 year, extended-spectrum beta-lactamases were not detected in K. pneumoniae isolates with restriction patterns different from that of the epidemic strain. It seems, therefore, that there was no transfer of a plasmid or a gene coding for ESBla to strains of K. pneumoniae that were different from the epidemic strain. At the same time, ESBla-producing K. pneumoniae isolates exhibiting restriction endonuclease proffles very different from that of the epidemic strain were isolated from other hospitals in Nimes. None of these strains caused an outbreak. Pulsed-field gel electrophoresis, which allows precise characterization of strains beyond the species level, is a useful tool for studying the ESBla-producing K. pneumoniae strains involved in nosocomial outbreaks.