[Detection of bla(CTX-M) beta-lactamase genes in extended-spectrum beta-lactamase producing gram-negative bacteria]

Widespread production of CTX-M type extended-spectrum beta-lactamases (ESBL) in Enterobacteriaceae strains which are resistant to extended-spectrum cephalosporins is the most remarkable example for rapid and global spread of plasmid mediated antimicrobial resistance in bacteria. Consecutive 200 ESBL producing Enterobacteriaceae strains out of 1640 isolates that were obtained from clinical samples (167 urine, 11 wound, 7 bronchoalveolar lavage, 3 peritoneal fluid, 2 cerebrospinal fluid, 2 biopsy, 2 tracheal aspirate, 2 conjunctiva, 1 abscess, 1 catheter) between February to July 2009 in our laboratory were included to this study. Among the 200 ESBL positive isolates 141 (70.5%) were Escherichia coli, 51 (26%) were Klebsiella pneumoniae, 5 (2.5%) were Enterobacter spp. and one of each (0.5%) Citrobacter freundii, Klebsiella oxytoca and Proteus mirabilis. ESBL positivity was 11% among the 123 community-acquired strains and 13% among the 77 hospital acquired strains, the statistical difference being insignificant (p > 0.05). The prevalence of bla(CTX-M) beta-lactamase genes were detected by multiplex polymerase chain reaction with the use of two general primer sets: CTX-MA1 and CTX-MA2 primers for the amplification of CTX-M-1, CTX-M-2 and CTX-M-9 enzymes group, and CTX825-F and CTX825-R primers for the amplification of CTX-M-8 and CTX-M-25 enzymes group. bla(CTX-M) genes were detected in 167 out of 200 strains (83.5%). CTX-M production rates in community and hospital acquired strains were found as 86.2% and 79.2%, respectively and no statistically significant difference was detected (p > 0.05). CTX-M producing strains were either E. coli (n = 132) or Klebsiella spp. (n = 35) and were expressing one of the enzymes from CTX-M-1, CTX-M-2 or CTX-M-9 groups. No strains carrying CTX-M-8 or CTX-M-25 group enzymes were detected. CTX-M production rates in ESBL producing E. coli strains in community and hospital were found as 92.5% and 95.7%, respectively, whereas the same rates for ESBL producing Klebsiella spp. strains were 67.8% and 66.7%. The difference between the CTX-M production rates of community and hospital acquired strains was not statistically significant (p > 0.05). In conclusion, CTX-M prevalence was found high in ESBL producing strains of both E. coli and Klebsiella spp. Since bla(CTX-M) gene acquisition usually results in the emergence of multiple drug-resistant Enterobacteriaceae strains, screening for CTX-M type ESBL production in the laboratory has an important impact on monitoring the resistant strains which have endemic potential.