Distribution of Staphylococcus aureus drug resistance genes, biofilm formation and cell wall characteristics in dairy cattle from dairy farms in Northeast China

The spread of drug-resistant Staphylococcus aureus(S.aureus) in cattle herds not only threatens livestock production but also becomes an important route for the transmission of drug-resistant bacteria to humans, posing significant public health risks and epidemiological significance. In this study, a total of 282 clinical samples were collected form cattle farms in Heilongjiang, Jilin, and Inner Mongolia, and isolation of S. aureus from 62 samples. Through spa typing and disk diffusion assays of 62 isolates, the predominant spa type was identified as t034. Notably, 54 isolates exhibited multidrug resistance, with a penicillin resistance rate as high as 87.1%, and 34 isolates were identified as methicillin-resistant S. aureus (MRSA). Among the 11 resistance genes tested, the detection rate of tetM gene was 100%. The Congo red plates and crystal violet staining assay showed that the isolated strains all produced biofilms, with no significant changes in the cell wall. In addition, icaA, SarA, and CidA genes identified as critical regulators of biofilm formation. Results from this study suggest that the feces and milk of dairy cows in Northeast China were contaminated with S. aureus including MRSA strains, and these strains carry a variety of resistance genes and have the ability to form biofilms, showing a resistance phenotype to a variety of antimicrobial agents.