Investigation of antimicrobial resistance of the bacteria isolated from cows with latent mastitis

The main problem of dairy farms is mastitis – inflammation of the mammary gland. Resistance of bacteria causing latent mastitis to antibiotics is increasing every year. Bacteria that have resistance genes to antibiotics are transmitted from one animal to another and through food chains or direct contacts from animals to humans. Latent mastitis is 15–40 times more frequent than clinical mastitis, which is more difficult to detect and is the major source of pathogens for the whole herd of cattle. The aim of this study was to isolate bacteria which cause mastitis from cow milk and determine their susceptibility to antimicrobials. Milk samples from two dairy farms (farm A and farm B) in Anykščiai District were taken in July 2018. Microbiological assays were performed at the Microbiology Laboratory of the Institute of Biomedical Sciences, Faculty of Medicine, Vilnius University. In total, 36 cows were tested. Using common methods of cultivation and identification tests, strains of Streptococcus spp., coagulase negative Staphylococcus spp. and Staphylococcus aureus were identified. Susceptibility of all isolated strains to neomycin, tetracycline, erythromycin, kanamycin, clindamycin, penicillin, ampicillin, streptomycin, gentamicin, rifampin, cefoxitin and oxacillin was performed using the disc diffusion method according to the guidelines of the Clinical Labaratory Standards Institute. It was concluded that the most frequent agent of mastitis was Staphylococcus spp. Also, a high level of resistance to penicillin, ampicillin and tetracycline in S. aureus strains was determined. All isolated bacteria were susceptible to neomycin, erythromycin, kanamycin, clindamycin, gentamycin, rifampin, cefoxitin and oxacillin.