Characterization of antibiotic resistance in Escherichia coli isolates from Black-headed gulls (Larus ridibundus) present in the city of Novi Sad, Serbia.

Despite common resistance to antimicrobials in Escherichia coli isolates from farm animals in Serbia, no data are currently accessible on its occurrence in E. coli isolated from gulls. Therefore, 67 cloacal swabs and 70 fecal samples from black-headed gulls were investigated for the presence of antibiotic-resistant E. coli isolates. Ninety-nine isolates were obtained during the study. Resistotyping and resistance gene typing has shown that 44 isolates harbor resistance to one or more antibiotics. Multidrug resistance was detected in 24 E. coli isolates. Ten isolates were resistant to extended-spectrum cephalosporin antibiotics and were studied in detail including virulence gene typing, phylogenetic and multilocus sequence typing, and mating. These ten isolates belonged to phylogenetic groups B2 (five isolates), D (four isolates) and B1 (one isolate). Five different sequence types (ST38, ST2307, ST224, ST162 and ST34) were detected in E. coli isolates with AmpC phenotype and genotype. One isolate carried the Inc I2/FIB replicon type plasmid with the blaCTX-M-1 gene. Nine isolates had blaCMY-2 genes, which were detected on conjugative plasmids in seven isolates. The virulence genes hly, iroN, iss, ompT and cvaC were detected in one transconjugant. Ten isolates were found to be resistant to ciprofloxacin, whose MIC ranged from 4 to 32 mg/L. Genotyping revealed single or double mutations in the quinolone resistance determining region (QRDR) of the gyrA or gyrA, parC and parE genes, respectively. So, Black-headed gulls from Serbia may be colonized by multidrug-resistant E. coli, some of which are resistant to critically important antibiotics in medicine.