Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) have been found on German dairy farms and may be the cause of difficult-to-treat bovine mastitis. Considering the one health approach, MRSA might be transmitted from animals to humans raising the risk for severe infections. On 17 German dairy farms with a history of MRSA detection, MRSA strains were isolated from quarter milk, bulk tank milk, and swab samples of calves, heifers, pigs, and the environment. A selection of 33 isolates was analyzed using whole-genome sequencing and antimicrobial resistance testing. All detected MRSA strains were attributed to the livestock-associated sequence type 398. Methicillin-resistance was associated with the mecA gene in the staphylococcal cassette chromosome (SCC)mec types IVa (7/33) or V (26/33). The MRSA strains across the German federal states showed large allelic differences indicating independent development and distribution. On one farm, a clonal MRSA isolate was widely spread among different animals and the milking equipment. Moreover, MRSA transmission between two dairy farms in one federal state seems to be likely. In depth studies indicated that the resistance gene prediction and phenotypic resistance are in good agreement. Twenty eight strains were determined to exhibit a non-wildtype phenotype (resistant) against up to seven antimicrobial substances with an overall resistance to β-lactams and tetracycline. Ten different phenotypic antimicrobial resistance patterns were found among the MRSA strains. The strains harbored a wide virulence gene repertoire, of which some of them are related to bovine mastitis. However, the isolates lacked typical human infection associated factors such as the immune evasion cluster genes, staphylococcal enterotoxin genes, or Panton-Valentine leukocidin genes leading to the assumption for a low risk for severe human infections and foodborne diseases.
Highlights
Methicillin-resistant Staphylococcus (S.) aureus (MRSA) were repeatedly detected on German dairy farms (Tenhagen et al, 2018; Kadlec et al, 2019) and may be a cause of bovine mastitis (Holmes and Zadoks, 2011)
All strains were characterized as ST398 LA-Methicillin-resistant Staphylococcus aureus (MRSA), a sequence type, which is often found on dairy farms (Feßler et al, 2012; Kadlec et al, 2019) and which is the most widely disseminated Livestock-associated MRSA (LA-MRSA) sequence type (Cuny et al, 2015b)
The lack of toxic shock syndrome toxin (TSST), Panton-Valentine leucocidin (PVL), and immune evasion clusters (IECs) genes in the strains from the farms investigated in our study indicates a low risk for severe human infections
Summary
Methicillin-resistant Staphylococcus (S.) aureus (MRSA) were repeatedly detected on German dairy farms (Tenhagen et al, 2018; Kadlec et al, 2019) and may be a cause of bovine mastitis (Holmes and Zadoks, 2011). MRSA infections are hard to cure since these bacteria are resistant against β-lactam antibiotics, which are widely used for S. aureus mastitis treatment. Antibiotic resistance and virulence genes, are often encoded on mobile genetic elements (MGEs) giving the possibility to spread resistance or virulence between different strains. Livestock-associated MRSA (LA-MRSA) often lack the potential for causing severe human infections due to a lack of IEC genes or genes encoding the toxic shock syndrome toxin (TSST) or Panton-Valentine leucocidin (PVL; Cuny et al, 2015a). Frequent monitoring of LA-MRSA strains from different livestock farms and the respective environment are necessary, since the genetic repertoire of MRSA strains might change spontaneously due to horizontal gene transfer leading to more harming strains with regard to animal and human health (Kraushaar et al, 2017)
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