Detection and characterisation of ESBLs in German Escherichia coli, isolated from animal, foods, and human origin between 2001–2006

Abstract number: 1733_511

Guerra B., Avsaroglu M.D., Junker E., Schroeter A., Beutin L., Helmuth R.

Objectives: Detection and characterisation of ESBLs in E. coli isolates, from animal, foods, and human origin and isolated between 2001–2006. Characterisation of the host structures.

Methods: About 2000 E. coli isolates (2001–2006) mostly from animal and food origin have been analysed in the NRL-Salm (BfR) for their susceptibility to 17 antimicrobial agents (including the b-lactams ampicillin and ceftiofur, and amoxycillin/clavulanic acid) by broth microdilution. Isolates showing ceftiofur-R were further tested for a panel of 11 b-lactams by disc diffusion. According to the R-patterns found, the strains were screened for different ESBL genes. The complete R-repertoire of the strains was characterised by molecular methods (R-genes, class 1 and 2 integrons and mutations in the quinolone-R determining regions). Strains were typed by XbaI-PFGE and plasmid profile analysis. Location of ESBLs was determined by hybridisation.

Results: Only two isolates were completely resistant (MIC ≥ 8 mg/mL) to ceftiofur. Three isolates showed intermediate resistance values (MIC = 1–2 mg/mL) and their resistance phenotypes to other b-lactams indicated mechanisms different than ESBLs. The two resistant isolates showed resistance patterns which suggested the presence of CTX-M enzymes (cefotaxime 22 and 21 mm, ceftriazone 20 and 17 mm, cefuroxime-R, cefpodoxime-R, aztreonam 25 and 26 mm, respectively). After PCR and sequencing CTX-M15 was found in one human isolate (Ont:H4) which also showed resistance to kanamycin-neomycin, nalidixic acid, ciprofloxacin, streptomycin, spectinomycin, sulfadiazine, tetracycline, trimethoprim and trimethoprim/sulfamethoxazole. The other isolate (Ont:H-) was isolated from milk from a cow with mastitis, and carried CTX-M1. The strains showed different PFGE patterns and plasmid profiles. Both CTX-M15 and CTX-M1 were located on big plasmids (aprox. sizes 160–180 kb). These plasmids could not be transferred.

Conclusions: While in many countries the presence and spread of ESBLs is of concern, their prevalence still remains low among German E. coli isolates. However, presence of ESBLs in multiresistant strains (more than 7 different classes of antimicrobials) including fluoroquinolone resistance is worrying and should be prevented by prudent use of extended-spectrum b-lactams.