Characterization of the plasmids harbouring the florfenicol resistance gene floR in Glaesserella parasuis and Actinobacillus indolicus

Strict relationship between phenotypic and plasmid-associated genotypic of multidrug-resistant Escherichia coli isolated from Taihe Black-Boned Silky Fowl farms

Taihe Black-Boned Silky Fowl (TBSF) is a unique breed in China, characterized by a high concentration of melanin deposited throughout its body. Compared to broiler chickens, many antibiotics exhibit significantly longer withdrawal periods in TBSF. Given that antibiotic exposure is widely recognized as the primary selective pressure driving the persistence and dissemination of antibiotic resistance genes (ARGs) across diverse environments, it is crucial to investigate the occurrence and prevalence of ARGs within TBSF farming systems. In this study, 34 Escherichia coli strains isolated from 22 TBSF farms were subjected to phenotypic and genotypic analyses. The isolates were tested for susceptibility to 28 antimicrobial drugs representing nine antibiotic classes to determine their antimicrobial resistance phenotypes. Draft genome sequences of these E. coli strains were obtained, and the ARGs carried by mobile genetic elements, particularly plasmids, were analyzed for their association with susceptibility phenotype. The genetic context of key ARGs in these E. coli isolates was further characterized. Network analysis was employed to investigate the correlations between ARGs, phenotypes, and drug residues. The results demonstrated that high rates of antimicrobial resistance were observed, with 100 % and 29.4 % of isolates exhibiting resistance to four or more and eight or more antibiotic classes, respectively. According to whole-genome sequencing, a total of 143 ARGs were identified. The antimicrobial resistance phenotypes were consistently correlated with the presence of corresponding ARGs in the 34 E. coli genomes. 100 % of the β-lactams antibiotics resistant mechanism could be attributed to the presence of the resistance gene blaTEM and/or blaOXA-10. Similarly, resistance to tetracyclines, chloramphenicols, aminoglycosides, and fluoroquinolones was fully explained by the presence of tetR and/or tetA, floR and/or cmlA, ant(3'')-IIa, aph(3'')-Ib, aph(6)-Id, aac(3)-IId, and aadA, and qnrS and/or mutant gyrA/parC/mdtH. The majority of these key ARGs were found to be plasmid-associated. This study verified and highlighted the prevalent horizontal gene transfer of ARGs in TBSF farms. Factors such as hygiene status, biosecurity measures, and other environmental conditions might play a more significant role than antimicrobial usage in facilitating the horizontal gene transfer of ARGs in TBSF farms. Appropriate measures should be taken to control the transmission and dissemination of these mobile genetic elements associated ARGs and prevent their entry into the human clinical environment from TBSF breeding environment.

Prevalence, detection of virulence genes and antimicrobial susceptibility of Escherichia coli isolated from arbor acres broilers feeding cycle in China

The prevalence of antimicrobial resistance originating from animals presents a significant threat to the treatment of animal disease, public health, and food safety. Researchers have focused on antibiotic resistance in Escherichia coli (E. coli), yet there are few reports on the resistance change during the feeding cycle. The purpose of this study was to investigate the prevalence and antibiotic resistance changes of E. coli in animal, environmental, and human samples during the broiler feeding cycle. Epidemiological surveys were performed in a farm with feeding AA broilers in Yangzhou, Jiangsu Province, China. Results showed that during a 42-days feeding cycle, 128 E. coli isolates were obtained from the cloaca of white-feathered broilers (n = 140), with an isolation rate of 91.4%, 27 E. coli isolates were obtained from Feed (n = 70) and 35 E. coli isolates were obtained from cage swabs (n = 70). A workers' hands swabs sample isolation rate of 68.6% (24/35) was observed. Antibiotic susceptibility testing revealed that out of 214 E. coli isolates, varying degrees of resistance were observed against 14 antibiotics. Most strains were resistant to ampicillin, cephalothiophene, ciprofloxacin, tetracycline, sulfamisoxazole, sulfamethoxazole and florfenicol, with a resistance rate exceeding 80%. The resistant strains demonstrated relatively stable patterns in their resistance to various antibiotics. Of the six antibiotic resistance genes tested, the floR gene showed the highest detection rate (72.4%), followed by qnrS (43.0%), mcr-1 (35.0%), aadE-Sat4-aphA-3 (28.0%), blaNDM (8.4%), aac(6')-lb (3.7%), and cfr (0). The highest detection rate for virulence genes was yijp. In summary, the isolation rate of E. coli and antibiotic resistance profile in broiler chickens remained stable throughout their feeding cycle. These findings can serve as a reference for the rational use of antibiotics in clinical settings, they can guide the use of veterinary drugs in poultry breeding.

Molecular characterization of the integrative and conjugative elements harbouring multidrug resistance genes in Glaesserella parasuis

It is widely known that integrative and conjugative elements (ICEs) play an important role in the transmission of resistance genes and other exogenous genes. The present study aimed to characterize the three novel ICEs including ICEGpa76, ICEGpa44, and ICEGpa11, from Glaesserella parasuis. The ICEs from G. parasuis strains d76, Z44, and XP11 were predicted and identified by whole-genome sequencing (WGS) analysis, ICEfinder, and PCR. Characterization of G. parasuis strains carrying ICEs were determined by conjugation assay, antimicrobial susceptibility testing, WGS, phylogenetic analysis, and comparative sequence analysis.The WGS results showed that three ICEs from G. parasuis have a common genetic backbone belonging to characteristics ofthe ICEHpa1 family. The sequence comparison showed that the ICEHpa1 family has five hot spots (HSs) determined by IS6, IS110, and IS256. Moreover, two variable regions (VRs), VR1 and VR2 were determined by multidrug resistance genes and the rearrangement hotspot (rhs) family, respectively. VR1 consists of multidrug resistance genes, ISApl1s, and other accessory genes, while VR2 is composed of IS4, rhs family, transposase, and hypothetical protein genes. Conjugation experiments and MICs revealed that three ICEs could be transferred to G. parasuis strain IV52, indicating these three ICEs could be transmitted horizontally among G. parasuis strains. Additionally, the difference in resistance genes from ICEs might be due to the insertion function of the ISApl1s in VR1, and the rhs family in VR2 might evolve andthen be stably inherited in G. parasuis. These results further elucidated the transmission mechanism of exogenous genes in G. parasuis.