Wild boars as reservoirs of extended-spectrum beta-lactamase (ESBL) producing Escherichia coli of different phylogenetic groups

ESBL-producing E. coli isolates have been isolated from eight of seventy seven faecal samples (10.4%) of wild boars in Portugal. The ESBL types identified by PCR and sequencing were bla(CTX-M-1) (6 isolates) and bla(CTX-M-1) + bla(TEM1-b) (2 isolates). Further resistance genes detected included tet(A) or tet(B) (in three tetracycline-resistant isolates), aadA (in three streptomycin-resistant isolates), cmlA (in one chloramphenicol-resistant isolate), sul1 and/or sul2 and/or sul3 (in all sulfonamide-resistant isolates). The intI1 gene encoding class I integrase was detected in all ESBL-producing E. coli isolates. One isolate also carried the intI2 gene, encoding class 2 integrase. The ESBL-producing E. coli isolates could be assigned to phylogenetic groups B1 (3 isolates), B2 (3 isolates) or A (2 isolates). Amino acid change in GyrA protein (Ser83Leu or Asp87Tyr) was detected in three nalidixic acid-resistant and ciprofloxacin-susceptible isolates. Two amino acid changes in GyrA (Ser83Leu + Asp87Asn) and one in ParC (Ser80Ile) were identified in two nalidixic acid- and ciprofloxacin-resistant isolates. As evidenced by this study wild boars could be a reservoir of antimicrobial resistance genes.