CEFOTAXIME-RESISTANT ENTEROBACTERIACEAE ISOLATES FROM A HOSPITAL IN WARSAW, POLAND - IDENTIFICATION OF A NEW CTX-M-3 CEFOTAXIME-HYDROLYZINGBETA-LACTAMASE THAT IS CLOSELY-RELATED TO THE CTX-M-1 MEN-1 ENZYME/

A group of cefotaxime-resistant Citrobacter freundii and Escherichia c oli isolates were collected by a clinical laboratory in a hospital in Warsaw, Poland, in July 1996. Detailed analysis has shown that all of these produced a beta-lactamase (pi, 8.4) belonging to the CTX-M famil y, one of the minor extended-spectrum beta-lactamase families with a s trong cefotaxime-hydrolyzing activity. Sequencing has revealed that C. freundii isolates produced a new CTX-M-3 enzyme which is very closely related to the CTX-M-1/MEN-1 beta-lactamase, sporadically identified in Europe over a period of 6 years. Amino acid sequences of these two beta-lactamases differ at four positions: Val77Ala, Asp114Asn, Ser140A la, and Asn288Asp (the first amino acid of each pair refers to CTX-M-1 /MEN-1 and second refers to CTX-M-3). The partial sequence of the E. c oli CTX-M gene was identical to the corresponding region of bla(CTX-M- 3), but a transconjugant of the E. coli isolate expressed higher level s of resistance to beta-lactams than did C. freundii transconjugants. These resistance differences correlated with differences in plasmid DN A restriction patterns. Our results suggest that CTX-M genes have been spread among different species of the family Enterobacteriaceae in th e hospital and that the CTX-M-3-expressing C. freundii strain causing routine urinary tract infections has been maintained for a relatively long time in the hospital environment.