title: Antimicrobial susceptibility and molecular subtypes of Staphylococcus aureus isolated from pig tonsils and cow's milk in China.
abstract: This study investigated and compared the antimicrobial resistance patterns and ribotypes of Staphylococcus aureus isolated from pig tonsils and cow's milk in China. A total of 90 isolates of S. aureus was included: 42 strains were isolated from tonsils of pigs and 48 from half-udder milk. The broth microdilution method and the double-disc diffusion test (D test) were used for antimicrobial susceptibility testing. The mecA gene for methicillin-resistant S. aureus (MRSA) and the ermA, ermB, ermC, and msrA genes for erythromycin-resistant strains were detected by polymerase chain reaction (PCR). The isolates were ribotyped with the Riboprinter system. The highest frequency of resistance was observed with clindamycin (91.1%), followed by penicillin (90.0%), and erythromycin (85.6%). All strains were susceptible to vancomycin and trimethoprim-sulfamethoxazole. The D test showed that 54.5% (42/77) of erythromycin-resistant isolates had the constitutive resistance phenotype and 45.5% (35/77) had the inducible resistance phenotype to clindamycin. A higher proportion of resistance to cephalosporins, macrolides, fluoroquinolones, and pleuromutilins was observed in pig isolates than in milk isolates (P < 0.05). The mecA gene was detected in all MRSA isolates; 89.6% of erythromycin-resistant strains harbored the ermC gene and 16.9% harbored the ermB gene. A total of 35 different ribogroups was found among the isolates investigated; 83.3% of pig strains belonged to 1 cluster with a similarity coefficient of 0.84. In contrast, 3 main clusters were observed among 68.8% of milk strains, which indicates a high degree of host specificity.
authors.affiliation: Department of Inspection Technology Research, China Institute of Veterinary Drug Control, Beijing, China 100081.
authors.forename: Chunping
authors.initials: C
authors.lastname: Zhang
authors.forename: Li
authors.initials: L
authors.lastname: Song
authors.forename: Huijuan
authors.initials: H
authors.lastname: Chen
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Yuling
authors.initials: Y
authors.lastname: Qin
authors.forename: Yibao
authors.initials: Y
authors.lastname: Ning
mesh_terms: D000818:Animals; D002417:Cattle / Q000382:microbiology*; D002681:China; D024901:Drug Resistance, Multiple, Bacterial; D005260:Female; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008892:Milk / Q000382:microbiology*; D014066:Palatine Tonsil / Q000382:microbiology*; D021521:Ribotyping / Q000662:veterinary; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D013552:Swine / Q000382:microbiology*
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