Microbiological Studies on the Prevalence of Staphylococcus Spp., Involved in the Etiology of Mastitis in Cattle and their Susceptibility to Antimicrobial Agents
Volume 80, Issue 2 (2022): Veterinarija ir Zootechnika, pp. 29–36
Pub. online: 27 February 2023
Type: Research Article
Open Access
Open Access
Received
25 October 2022
25 October 2022
Revised
23 November 2022
23 November 2022
Accepted
9 December 2022
9 December 2022
Published
27 February 2023
27 February 2023
Abstract
For the period between June 2020 and -March 2022, a total of 8 dairy cattle farms were surveyed in terms of the prevalence of clinical and subclinical mastitis. Four of them were located in Northern Bulgaria (Targovishte, Shumen and Dobrich districts) and another four in Southern Bulgaria (Stara Zagora, Plovdiv and Haskovo districts). In these target farms, a rapid mastitis screening test was initially performed to detect the presence of subclinical mastitis or samples with high somatic cell counts. A total of 312 milk samples were obtained from milk quarters who reacted with 3+ or 4+ to which 34 samples of inflammatory exudate from cows with clinical mastitis were added. During the microbiological investigation of the 346 samples, 272 of them (79.1%) were bacteriologically positive. Streptococcus spp., were isolated from 151 samples (55.5%). The second most common species was Staphylococcus spp., detected in 110 (40.4%) of the tested samples. In total, the Grampositive cocci finding exceeded 95% of the microbial species. The remaining 11 (4.0%) isolates belonged
to another 6 taxa. These included four strains identified by prior phenotypic identification as Trueperella pyogenes, three Escherichia coli isolates, and one strain of each Pasteurella multocida, Nocardia asteroides, Klebsiella pneumoniae, and Acinetobacter spp. Staphylococci were also studied for their sensitivity to 11 chemotherapeutic agents. The highest percentage of resistance (50%) was determined to lincomycin, followed by that to tetracycline (37.3%), and beta-lactams ampicillin (24.5%), and oxacillin (13.6%). The resistance rates to cefoxitin and cephalotin were 5.5% and 0.9% respectively. Also, lower values of resistant strains were observed for the combination
of trimethoprim/sulfonamides (7.3%), ciprofloxacin (1.8%), and rifampicin (0.9%). Resistance to gentamicin and amoxicillin/ clavulanic acid was not established. Minimum inhibitory concentrations were determined for the studied chemotherapeutics, with the highest MIC90 values of 128 μg/mL and 2 μg/mL for tetracycline and lincomycin, and the lowest MIC90 values of 0.001 μg/mL for rifampicin and ciprofloxacin, respectively. A MIC90 of 0.125 μg/mL was obtained for oxacillin, 1.5 μg/mL for trimethoprim/sulfonamides and 1.0 μg/mL for ampicillin, cephalotin and cefoxitin.