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Published on: November 4, 2016
Genetic and Phenotypic Characterization of Subclinical Mastitis-Causing Multidrug-Resistant Staphylococcus aureus
Amanda Thaís Ferreira Silva1, Juliano Leonel Gonçalves2, Stéfani Thais Alves Dantas3,4
1Department of Veterinary Medicine, Federal Rural University of Pernambuco, Recife 52171-900, Brazil.
Abstract:
The core objective of this study was to genetically and phenotypically characterize subclinical mastitis-causing multidrug-resistant Staphylococcus aureus (MDRSA). In addition, risk factors associated with subclinical mastitis caused by MDRSA were investigated. Bacterial cultures were performed on 2120 mammary quarters, 40 swabs of milk utensils, 5 bulk tank milk samples, and 11 nostril and 11 hand swabs from milkers from five dairy farms. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was conducted for S. aureus identification. Antimicrobial resistance was screened phenotypically using the disk diffusion test in all S. aureus isolates. A biofilm formation assay; detection of genes associated with beta-lactam resistance, efflux pump, and biofilm formation; and pulsed-field gel electrophoresis (PFGE) were performed in all MDRSA isolates. Multi-locus sequence typing (MLST) was carried out in cefoxitin-resistant MDRSA isolates. A total of 188 S. aureus isolates from milk as well as two from milking utensils and one from bulk tank milk were identified. Most of the isolates (92.7%; 177 of 191) showed beta-lactam resistance, and 7% (14 of 191) were MDRSA. Interestingly, 36% (5 of 14) of MDRSA isolates were cefoxitin-resistant, but none carried mecA or mecC genes. Based on PFGE results, it was observed that S. aureus strains were more likely to be unique to a specific herd. Two clonal complexes were identified, CC97 (ST126; commonly livestock-associated) and CC1 (ST7440; usually community-associated). To the best of our knowledge, this is the first report of ST7440 isolated from bovine mastitis in Brazil. The risk factor results underscored the importance of considering parity, stage of lactation, SCC, milk production, and herd size when studying the risk of subclinical mastitis and antimicrobial resistance in S. aureus. Thus, to implement effective strategies to prevent subclinical mastitis in dairy herds and to minimize MDRSA spread, it is important to understand MDRSA strains' distribution and their antimicrobial resistance profile.
Insights
This study characterized multidrug-resistant Staphylococcus aureus (MDRSA) in dairy cows, identifying risk factors for subclinical mastitis. Findings highlight the need for understanding MDRSA strain distribution and resistance profiles for effective prevention strategies.
Area of Science:
- Veterinary Microbiology
- Antimicrobial Resistance
- Bovine Health
Background:
- Subclinical mastitis in dairy cows is a significant economic concern.
- Multidrug-resistant Staphylococcus aureus (MDRSA) poses a growing threat to animal and public health.
- Characterization of MDRSA and associated risk factors is crucial for effective control.
Purpose of the Study:
- To genetically and phenotypically characterize MDRSA causing subclinical mastitis in dairy cattle.
- To investigate risk factors associated with subclinical mastitis caused by MDRSA.
- To determine the prevalence and genetic diversity of MDRSA in Brazilian dairy farms.
Main Methods:
- Bacterial cultures from milk, utensils, and milkers.
- Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for identification.
- Antimicrobial resistance screening, biofilm assays, gene detection, pulsed-field gel electrophoresis (PFGE), and multi-locus sequence typing (MLST).
Main Results:
- 188 Staphylococcus aureus isolates identified; 7% were MDRSA.
- 36% of MDRSA isolates were cefoxitin-resistant but lacked mecA/mecC genes.
- PFGE indicated herd-specific strains; CC97 (ST126) and CC1 (ST7440) were identified. ST7440 is newly reported in bovine mastitis in Brazil.
- Parity, lactation stage, SCC, milk production, and herd size were significant risk factors.
Conclusions:
- MDRSA strains in dairy herds exhibit diverse genetic profiles and resistance mechanisms.
- Understanding the distribution and antimicrobial resistance of MDRSA is vital for developing targeted prevention and control strategies.
- The identification of novel MDRSA strains and associated risk factors provides critical data for improving dairy herd management and reducing antimicrobial resistance spread.
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