The expression of plasmid-mediated quinolone resistance (PMQR) genes confers low-level quinolone and fluoroquinolones resistance alone. However, the association to chromosomal resistance mechanisms determines an expressively higher resistance in Enterobacteriaceae. These mechanisms are horizontally disseminated within plasmids and have contributed to the emergence of bacteria with reduced susceptibility or resistant to therapies worldwide. The epidemiological characterization of PMQR dissemination is highly relevant in the scientific and medical context, to investigate the dissemination within enterobacteria, from different populations, including humans and food-producing animals. In the present study, 200 Enterobacteriaceae isolates were harvested from poultry with cloacal swabs and identified as Escherichia coli (90.5%), Escherichia fergusonii (5.5%), Klebsiella oxytoca (2.5%) and Klebsiella pneumoniae (1.5%). Among isolates evaluated, 46 (23%) harboured PMQR genes including qnrB (43/200), qnrS (2/200) and aac(6')-Ib-cr (1/200). All isolates carrying PMQR genes showed multidrug-resistance phenotype. The 36 E. coli isolates showed 18 different PFGE types. All E. fergusonii isolates showed the same PFGE type. The two Klebsiella oxytoca belonged to two different PFGE types. The phylogenetic groups A, B1, and D were found among the E. coli harboring PMQR genes. Based on the phylogenetic analysis and PFGE, the population structure of E. coli isolates was diverse, even within the same farm. All isolates carrying qnrB and qnrS genes also harboured ColE-like plasmids. The Southern blot hybridization using the S1-PFGE revealed that the qnrB genes were located on low molecular weight plasmids, smaller than 10Kb. Resistance plasmids were sequenced and showed 100% identity with plasmid pPAB19-3. The association of PMQR genes with mobile genetic elements, such as transferable plasmids, favours the selection and dissemination of (fluoro) quinolones resistant bacteria among food-producing animals, and may play an important role in the current increased prevalence of resistant bacteria in different environments reported worldwide.

There is an increasing number of reports worldwide about multidrug resistance (MDR) with potential of ExPEC in commensal E. coli. The present study evaluated the potential ExPEC in selected 44 MDR E.coli isolates, collected from livestock. ExPEC isolates were characterized by analysis of five main groups of virulence genes (papA and/or papC, sfa and/or foc, afa and/or dra, kpsMT II and iutA). We also determined the increased virulence potential analyzing other 29 virulence genes, the epidemiology of these isolates. Additionally, fifteen ExPEC isolates were selected to evaluate the adhesion and invasion capacity in vitro using Caco-2 cells. Based on the analysis of the five main virulence genes, 72.7% (32/44) strains were classified as ExPEC. The presence of each gene was iutA 88.6%, KpsMT II 70.4%, papC 25%, sfa/focDE 4.5%; afa/draBC genes were not found. All E. coli isolates were classified into: phylogenetic groups A (34%), B1 (10%), B2 (20%), and D (36%). MLST revealed 7 different STs among isolates, including a new ST identified (ST5687). The in vitro assay in Caco-2 cells showed that all isolates were capable to adhere or invade the epithelial cells, although this occurred at variable levels. The ExPEC isolate LO122 reached similar levels of invasion to the positive control strain Salmonella Typhimurium LT2. These results showed that the apparently commensal microbiota of poultry harbors MDR ExPEC isolates with high adhesion and invasion potential.