Investigation of Antibiotic Resistance, Phylogenetic Groups and Clonal Relationships of Colistin Resistant Escherichia coli Isolates Obtained from Broilers.

PHOENIX (Ariz.); TURKEY

The emergence of resistance mechanisms in bacteria that can be carried and spread through plasmids can lead to problems, particularly in densely populated poultry environments such as broilers, where the spread of antibiotic resistance and the reduction of treatment options can occur. The aims of this study were to investigate the antibiotic resistance profiles of Escherichia coli isolates obtained from broilers with colibacillosis, the presence of the most prevalent plasmid-mediated mobile colistin resistance gene-1 (mcr-1) and the phylogenetic groups and clonal relationships of colistin resistant isolates. The material for the study consisted of 184 E. coli isolates obtained from commercial broilers. Bacterial identification was performed using conventional methods. The susceptibility of the isolates to 20 antibiotics belonging to nine antimicrobial families was examined using the BD Phoenix™ M100 automated system and NMIC/ID 433 panels. Isolates resistant to at least three or more antibiotic classes were considered as multidrug-resistant (MDR). The presence of the mcr-1 in the isolates was investigated by polymerase chain reaction (PCR), while their phylogenetic groups were determined by quadruplex PCR and clonal relationships were analyzed using enterobacterial repetitive intergenic consensus sequences (ERIC) PCR. According to the results of the antibiotic susceptibility testing, the highest resistance was observed against tigecycline (100.0%), ampicillin (78.8%), and ciprofloxacin (53.8%), while the highest susceptibility was observed against amikacin, imipenem, and meropenem (100.0%). Of the isolates, colistin resistance was detected phenotypically in 4.4% (8/184) and genotypically in 5.4% (9/184). All phenotypically resistant isolates carried the mcr-1 gene. Of all the isolates, 72.8% were MDR, while 100.0% of the colistin-resistant isolates were MDR. Among the nine colistin-resistant E. coli isolates, eight (88.9%) were classified into four phylogenetic groups (B1, C, F, E), while one isolate (11.1%) could not be classified. Using ERIC typing, a total of seven ERIC types were identified, including six single and one multiple genotypes from seven farms. Two isolates obtained from the same farm had the same genetic background and one isolate obtained from a different farm was closely related. This indicates that there is clonal dissemination among isolates carrying the mcr-1 gene, and it suggests that this resistance gene can spread within the same farm. This study is the first research in Türkiye demonstrating the coexistence of low colistin resistance and high tigecycline resistance in APEC isolates obtained from broilers in the food chain. [ABSTRACT FROM AUTHOR]