# Epidemiological Investigation on Pathogenic Bacteria of Buffalo Subclinical Mastitis and Their Antibiotic Resistance and Virulence Characteristics in Guangxi, China

## TL;DR

This study identifies common bacteria causing subclinical mastitis in buffalo milk in China and finds they are highly resistant to antibiotics.

## Contribution

The first systematic investigation of pathogenic bacteria in buffalo subclinical mastitis in Guangxi, China, with insights into antibiotic resistance and virulence.

## Key findings

- Coagulase-negative Staphylococci, Enterococcus faecalis, Escherichia coli, and Klebsiella pneumoniae were the most frequently isolated pathogens.
- E. faecalis and Lactococcus garvieae showed resistance to all 12 tested antibiotics.
- Levofloxacin was effective against several PSM strains, suggesting potential as a treatment.

## Abstract

Subclinical mastitis (SCM) is a major but often neglected issue in dairy farming, affecting milk yield and quality. Identification of pathogenic bacteria of subclinical mastitis (PSM) in dairy cows is crucial for implementing effective prophylactic and control measures. This paper highlights the first systematic study to investigate the PSM in buffalo farms in Guangxi, China. It also analyzes the antibiotic resistance and virulence characteristics of typical PSM. A total of 1659 bacterial strains were isolated from 132 milk samples with SCM, among which 1058 were identified as PSM. Coagulase-negative Staphylococci (55.30%), Enterococcus faecalis (51.52%), Escherichia coli (31.82%), and Klebsiella pneumoniae (28.03%) were frequently isolated PSM in total samples. All PSM strains showed multiple-antibiotic resistance. E. faecalis and Lactococcus garvieae were resistant to all 12 antibiotics. E. coli exhibited the strongest mortality of Galleria mellonella. These results highlight that the prevention and control of PSM in buffalo farms should be strengthened.

Subclinical mastitis (SCM) is one of the most common and detrimental diseases affecting dairy cows, causing lower milk yield and quality. Identification of pathogenic bacteria of subclinical mastitis (PSM) in dairy cows is crucial for selecting suitable antibiotic treatments and implementing effective prophylactic measures. This paper highlights the first systematic study to investigate the PSM in buffalo farms in Guangxi, China. It also analyzes the antibiotic resistance and virulence characteristics of typical PSM. The bacteriological characteristics of 132 milk samples collected from buffaloes with SCM across 3 representative buffalo farms in Guangxi, China were investigated. A total of 1659 bacterial strains were isolated and classified into 46 genera and 183 species, where 1058 bacterial strains were identified as PSM, representing 64% of the total isolates. The frequently isolated PSM in total samples were coagulase-negative Staphylococci (55.30%), Enterococcus faecalis (51.52%), Escherichia coli (31.82%), and Klebsiella pneumoniae (28.03%). All PSM strains showed multiple antibiotic resistance. Notably, E. faecalis and Lactococcus garvieae were resistant to all 12 antibiotics, whereas Staphylococcus chromogenes (95.24%), E. coli (89.19%), K. pneumoniae (83.87%), and Staphylococcus epidermidis (83.33%) were sensitive to levofloxacin (LEV). Additionally, E. coli exhibited the strongest mortality of Galleria mellonella. This study concluded that multiple PSM are present in the milk of buffaloes suffering from SCM in Guangxi, China. LEV may be a suitable antibiotic for the treatment of PSM. In the future, it is necessary to monitor the prevalence of PSM in buffalo farms and develop control strategies to prevent their spread.