# Prevalence and Characterization of Staphylococcus aureus and Methicillin-Resistant Staphylococcus aureus Isolated from Guangxi Dairy Farms

## TL;DR

This study found a high rate of antibiotic-resistant Staphylococcus aureus in dairy farms in Guangxi, China, highlighting potential health risks from contaminated milk.

## Contribution

The study provides new insights into the prevalence and characteristics of MRSA in Guangxi dairy farms, including virulence genes and biofilm formation.

## Key findings

- 15.3% of samples tested positive for S. aureus, with 67.5% of these being MRSA.
- Most isolates carried virulence genes like sea, ser, and seh, and 78.4% showed antibiotic resistance.
- Over half of the isolates exhibited strong biofilm-forming ability, and spa typing identified 11 distinct types.

## Abstract

Staphylococcus aureus (S. aureus) is a major pathogen responsible for mastitis in dairy cows and can contaminate raw milk, thereby posing significant health risks to consumers. The emergence of methicillin-resistant S. aureus (MRSA) has further heightened public health concerns due to its antibiotic resistance and infectious potential. In this study, we examined the prevalence, virulence genes, antimicrobial resistance, spa types, and biofilm formation of S. aureus isolates from dairy farms in Guangxi Province, China. Among 242 randomly selected samples, 37 S. aureus strains were identified (15.3% infection rate), including 67.5% MRSA. Antibiotic resistance was observed in 78.4% of isolates, with 35.1% exhibiting multidrug resistance (MDR). Enterotoxin gene analysis showed sea as the most common (67.6%), followed by ser (54.1%) and seh (51.4%), whereas seb and selj were absent. All isolates formed biofilms in vitro, with 64.8% showing strong biofilm-forming ability. Staphylococcal protein A (spa) typing classified the 37 S. aureus strains into 11 spa types, with t030 being the most prevalent (43.2%). These findings indicate that S. aureus is moderately prevalent in raw milk, often carrying multiple virulence genes, forming robust biofilms, and showing antimicrobial resistance. The MRSA that is “latent” in raw milk reminds us of the need for monitoring at the farm level.