Comparative analysis of antimicrobial resistance phenotype and genotype of Riemerella anatipestifer

Riemerella anatipestifer is one of the important bacterial pathogens that threaten the waterfowl farming industry. In this study, 157 suspected R. anatipestifer strains were isolated from diseased ducks and geese from seven regions of China during 2019-2020, and identified using multiple polymerase chain reaction (PCR). Antimicrobial susceptibility tests and whole-genome sequence (WGS) analysis were then performed for comparative analysis of antimicrobial resistance phenotypes and genotypes. The results showed that these strains were susceptible to florfenicol, ceftriaxone, spectinomycin, sulfafurazole and cefepime, but resistant to kanamycin, amikacin, gentamicin, and streptomycin, exhibiting multiple antimicrobial resistance phenotypes. WGS analysis revealed a wide distribution of genotypes among the 157 strains with no apparent regional pattern. Through next-generation sequencing analysis of antimicrobial resistance genes, a total of 88 resistance genes were identified. Of them, 19 tetracycline resistance genes were most commonly found, followed by 15 efflux pump resistance genes, 11 glycopeptide resistance genes and seven macrolide resistance genes. The 157 R. anatipestifer strains contained 42-55 resistance genes each, with the strains carrying 47 different resistance genes being the most abundant. By comparing the antimicrobial resistance phenotype and genotype, it was observed that a high correlation between them for most antimicrobial resistance properties was detected, except for a difference in aminoglycoside resistance phenotype and genotype. In conclusion, 157 R. anatipestifer strains exhibited severe multiple antimicrobial resistance phenotypes and genotypes, emphasizing the need for improved antimicrobial usage guidelines. The wide distribution and diverse types of resistance genes among these strains provide a foundation for studying novel mechanisms of antimicrobial resistance.

Evaluation of culturable 'last-resort' antibiotic resistant pathogens in hospital wastewater and implications on the risks of nosocomial antimicrobial resistance prevalence

Antimicrobial resistance has been recognized as an important emerging environmental pollutant. 'Last-resort' antibiotics including tigecycline, polymyxin E, daptomycin, vancomycin and linezolid are the 'last line of defence' for antibiotic resistant pathogen infections. Therefore, the presence of 'last-resort' antibiotic resistant pathogens in hospital environments and the nosocomial transmission of 'last-resort' antibiotic resistance poses a grave threat to the well-being of patients. In this work, the extent of resistance to 'last-resort' antibiotics in culturable pathogens in hospital wastewater was investigated. Resistance to 'last-resort' antibiotics were quantified for 1384 culturable Enterobacteriaceae, Enterococcus, Staphylococcus, and Pseudomonas strains. With these investigations, several significant findings were made: (1) a very high level of resistance to 'last-resort' antibiotics was found; (2) multiple resistance to antibiotics, including 'last-resort' antibiotics, was prevalent; (3) a high level of 'last-resort' antibiotic resistance phenotype-genotype inconsistency was found, suggesting knowledge gap for resistance mechanisms; 4) tet(X4)-containing tigecycline-resistant Gram-positive pathogens were found for the first time; 5) wastewater treatment processes are effective in preventing the release of 'last-resort' antibiotic resistant pathogens to the environment. This investigation reveals the severe situation on 'last-resort' resistance in the hospital environment, and implies high risk for nosocomial transmission of 'last-resort' antibiotic resistant pathogens.