Dairy Cows’ Udder Pathogens and Occurrence of Virulence Factors in Staphylococci

Abstract

This study investigated 960 Slovak and Czech spotted cattle from four different conventional (non-organic) dairy herds located in Eastern Slovakia and Czechia during early lactation (14–100 days after calving). Dairy cows were examined clinically; milk from fore-stripping of each udder quarter was subjected to sensory examination and assessed by the California mastitis test (CMT), and laboratory analyses of bacterial pathogens in milk, including virulence factors, were conducted. Positive CMT scores (1–3) for one or more quarters were detected in 271 (28.2%) of the examined animals. Out of 230 infected milk samples, representing 24.0% of all dairy cows, staphylococci (59.1% of positive findings) were the most commonly isolated organisms, followed by E. coli (11.3%), streptococci Str. uberis (9.1%) and Str. agalactiae (3.4%), and enterococci (6.1%). From 136 isolates of S. aureus (38 isolates) and non-aureus staphylococci (NAS; 98 isolates), virulence factors and their resistance to 14 antimicrobials were detected using the disk diffusion method, with PCR detection of the methicillin resistance gene, mecA. An increased incidence of clinical and chronic forms of mastitis has been reported in mastitic cows in which staphylococci, especially S. aureus and NAS (S. chromogenes, S. warneri, and S. xylosus), have been detected and compared to other isolated udder pathogens. From those species, S. aureus and isolates of NAS mentioned above showed multiple virulence factors that are more likely to hydrolyze DNA, hemolysis, produce gelatinase and biofilm, and have multi-drug resistance as compared to other less virulent staphylococci. Generally, the isolated staphylococci showed 77.2% resistance to one or more antimicrobials, in particular to aminoglycosides, β-lactams, macrolides, or cephalosporins. Isolates that showed the ability to form a biofilm were more resistant to more than one antimicrobial than isolates without biofilm production. Multi-drug resistance to three or more antimicrobial classes was recorded in 16 isolates (11.7%), and the presence of the mecA gene was also confirmed in two isolates of S. aureus and two species of NAS.

Occurrence of Mastitis in Dairy Herds and the Detection of Virulence Factors in Staphylococci

“…In isolated were validated when G ˃ χ 2 ; the independence was not statistically significant when G < χ 2 . Modified from Zigo et al [9].…”

“…In general, each mastitis case is believed to be caused by one primary pathogen, as in milk samples from the affected udder usually only one bacterial species has been identified. However, it is not rare to detect simultaneous infections by two different pathogen species, and even three pathogens have been found in a small proportion of samples [8,9].…”

“…According to Slovak studies [7,9,13], Staphylococcus chromogenes, Staphylococcus epidermidis, and Staphylococcus xylosus are the most common pathogens from CoNS causing mastitis, followed by Streptococcus agalactiae, Staphylococcus aureus, Streptococcus dysgalactiae, Escherichia coli, and Enterococci. Of the 42 monitored dairy farms, CoNS and S. aureus accounted for 36% and 12% of all positive mastitic cases, respectively.…”

“…Subclinical forms, which do not exhibit overt indications of inflammation but instead have elevated somatic cell counts (SCC) in the presence of the causative agents, are typically a serious silent issue and are the most common illnesses to result in significant financial loss for owners. Since they cannot be detected without a lab or field test, the subclinical types of IMI frequently become incurable in later stages [9].…”

Detection of Some Virulence Factors in Staphylococci Isolated from Mastitic Cows and Ewes

“…In general, each mastitis case is believed to be caused by one primary pathogen, as in milk samples from the affected udder usually only one bacterial species has been identified. However, it is not rare to detect simul taneous infections by two different pathogen species and even three pathogens have been found in a small propor tion of samples [32].…”