Phenotypic and molecular characteristics of methicillin-resistant and methicillin-susceptible isolated from pigs: implication for livestock-association markers and vaccine strategies.

BACKGROUND

Routine non-therapeutic antimicrobial use and overcrowding in animal farming may facilitate the propagation of methicillin-resistant (MRSA). This study aimed to examine the carriage prevalence and phenotype-genotype characteristics of MRSA and methicillin-susceptible isolated from pigs.

METHODS

Nasal swabs were collected from 1,458 pigs in 9 pig farms and 3 slaughterhouses. All strains were tested for antimicrobial susceptibility, resistance genes, and virulence genes, and characterized by multilocus sequence typing. The correspondence analysis was conducted to explore the relationships between multiple phenotypic and molecular characteristics of isolates.

RESULTS

In the 1,458 pigs, the carriage prevalence was 9.5% for , 3.3% for MRSA, and 9.3% for multidrug-resistant . Notably, 97.1% isolates were multidrug resistant, and the predominant resistance pattern was non-susceptible to clindamycin, tetracycline, and erythromycin. The predominant genotype was CC9 (ST9) for and MRSA isolates. Importantly, all isolates were negative for the gene and resistant to tetracycline. Notably, all 9 linezolid-resistant isolates were classified as multidrug resistance, including 1 expressing the gene and 6 expressing the gene. The correspondence analysis showed a significant relationship between clonal complexes and resistance pattern or virulence genes. For example, CC9 was associated with extensive drug-resistance and co-carrying , , and , and CC1 was associated with multidrug resistance and co-carrying and .

CONCLUSION

The significant correspondence relationship between multiple characteristics provides some implication for vaccine strategies and new ideas for monitoring new epidemiologic clones.