Antimicrobial resistance and molecular characteristics of bovine mastitis-associated methicillin-resistant Staphylococcus aureus: potential for cross-species transmission of ST59-MRSA

Abstract

Mastitis caused by methicillin-resistant Staphylococcus aureus (MRSA) is a common issue in dairy farming, with sequence types (STs) related to cows mainly including ST9 and ST97. ST59, the predominant community-acquired clone, is still less reported in dairy cows. This study investigated the antimicrobial resistance patterns and molecular characteristics of 77 Staphylococcus aureus isolates obtained from eight dairy farms in the mid-east of China during 2019-2020, focusing particularly on the bovine mastitis-related livestock-associated MRSA (LA-MRSA) clone ST59. Among the 77 isolates, 14 isolates were identified as MRSA. A total of 20 STs were identified, with ST59 being the most prevalent among MRSA isolates (35.7%). All MRSA isolates possessed various Staphylococcal cassette chromosome mec (SCCmec) types, including XII (n = 5), IV.a (n = 4), IV.c (n = 2), IV.g (n = 2), and V (n = 1). Three MRSA lineages were identified: MRSA-ST59-t437-SCCmec IV.a/IV.g (n = 5), MRSA-ST9-t899-SCCmec XII (n = 4), and MRSA-ST88-t3622-SCCmec IV.c (n = 2). Approximately 44.2% of isolates demonstrated multidrug resistance. MRSA isolates showed a higher prevalence of antimicrobial resistance compared to methicillin-sensitive Staphylococcus aureus (MSSA) isolates. Virulence factor assays revealed that all MRSA isolates carried at least hemolysin genes and enterotoxin genes. ST59-MRSA strains showed the closest genetic relationship with human-derived strains, indicating a potential public health risk due to transmission of Staphylococcus aureus between livestock and humans. This study highlights the significant prevalence of the bovine mastitis-related LA-MRSA clone ST59 in the mid-east of China. Therefore, reinforcing monitoring and implementing preventive measures are essential to combat LA-MRSA.

Importance: Obtained the prevalence and molecular characteristics of Staphylococcus aureus in dairy farms in the mid-east of China from 2019 to 2020. Recently identified livestock-associated methicillin-resistant S. aureus (LA-MRSA) clones in cattle, including ST59-MRSA, may have originated from human sources, suggesting a potential risk for interspecies transmission.

Keywords: ST59; bovine mastitis; livestock-associated Staphylococcus aureus; molecular characteristics; multidrug-resistant.

Fig 1

Phylogenetic analysis of 77 S. aureus strains. Different colored bar patterns represent different sequence types and spa types. HB, Hubei Province; HN, Hunan Province; and JX, Jiangxi Province. The red circular pattern indicates strains that harbored the mecA gene. ARGs and VFs: the filled squares (purple or blue) indicate the presence and empty squares the absence of individual genes indicated at the head of each column.

Fig 2

MST of 14 MRSA isolates. Each circle represents a strain, with colors corresponding to the legend STs, and distances labeled on each branch.

Fig 3

Antimicrobial susceptibility tests of 77 S. aureus strains. PEN, penicillin; AMC, amoxicillin/clavulanic acid; TIO, cftiofur; FOX, cefoxitin; OXA, oxacillin; ERY, erythromycin; TIL, timicosin; CLI, clindamycin; ENR, enrofloxacin; OFX, ofloxacin; SOX, sulfisoxazole; SXT, sulfamethoxazole; VAN, vancomycin; DOX, doxycycline; FFC, florfenicol; TIA, tiamulin; GEN, gentamicin; and LZ, linezolid.

Fig 4

Pairwise associations of the virulence gene in 77 S. aureus strains. Associations were computed using the Pearson coefficient. Color represents the types of associations (red, positive; blue, negative). The color intensity reflects the significant correlation.

Fig 5

Phylogenetic tree of ST59 S. aureus. The ST59 isolates in this study have an orange background color. Hosts: FD, food; HM, human; SW, swine; SH, sheep; CW, cow; CK, chicken; /, others. Locations: CHN, China; FRA, France; USA, United States of America; GER, Germany; Swit, Switzerland; KR, Korea; /, unknown. The red star pattern represents harbored the mecA gene. ARGs and VFs: the filled squares (purple or blue) indicate the presence and empty squares the absence of individual genes indicated at the head of each column.