Background
Among bacterial pathogens, Staphylococcus aureus which lives in the mammary gland is the leading cause of bovine mastitis worldwide, which causes enormous economic losses to the dairy industry.
Objectives and methods
The study was carried out cross‐sectionally to determine the occurrence of methicillin‐resistant S. aureus (MRSA) and the risk factors for mastitis infection in dairy cows in and around Adama from October 2014 to June 2015. This particular study included 384 animals. Milk samples were collected and screened with California mastitis test. Then bacteria were cultured and identified using biochemical tests and disc diffusion test was used to determine the antimicrobial sensitivity for MRSA.
Results
The prevalence of mastitis was 121 (31.5%). Among them, 37 cases (30.6%) were clinical mastitis and 84 cases (69.4%) were subclinical mastitis. Among these positive cases, 37 cases (30.6%) of S. aureus were isolated. The prevalence of mastitis was significantly related to the breed, age, floor type and sanitation status of the milking (p <0.05). The Kirby–Bauer disc diffusion method was performed on Mueller Hinton agar medium according to NCCLS guidelines to test antibiotic sensitivity. The 32.4% of S. aureus isolates were resistant to oxacillin. Isolates of MRSA are more resistant to amoxicillin (75%), oxytetracycline (66.7%) and sulfa (50%). However, they were sensitive to kanamycin (75%), streptomycin (58.3%) and nalidixic acid (50%). Insufficient dosage, short treatment time and chronic infection in dairy cows in the herd are the main reasons for the large number of resistant strains.
Conclusion and recommendation
Generally, mastitis was prevalent in the area, and it was resistant to commonly used antibiotics. Therefore, hygienic, prevention and alternative treatment methods should be implemented.
From January to May 2018, a cross-sectional study was undertaken on lactating dairy cows in Bishoftu town to isolate Corynebacterium bovis, determine the prevalence and risk factors, and evaluate the effectiveness of several antibiotics in lactating dairy farms. Study animals were selected randomly from selected dairy farms in the area. Collecting milk samples from mastitic cows, cultivating, and then performing an antibiotic sensitivity test were the procedures followed. A total of 384 lactating dairy cows were examined with inspection and California Mastitis Test (CMT), in which 86 of them were found to be CMT positive. Accordingly, prevalence was 3.9% and 18.5% for cows affected by clinical and subclinical mastitis respectively. The prevalence of mastitis showed statistically significant difference between, lactation stage, breed, age and washing (p > 0.05). However, there was no statistically significant difference noted in animal husbandry practice (p > 0.05). A total of 384 lactating dairy cows were examined with inspection and CMT, in which 86 of them were found to be CMT positive. Out of the 86 mastitis positive samples (sample indicates milk from one cow) sent to microbiology laboratory for microbiological examination, 7 bacterial isolates were identified as Corynebacterium bovis. The biochemical and morphological characteristics of 7 (1.8%) C. bovis isolated from bovine milk samples and the C. bovis reference strains were found to be uniform. Valuable criteria for identification were presence of catalase and oxidase, production of acid from glucose and a requirement for enriched basal media. C. bovis isolates have revealed a higher sensitivity to the kanamycin and streptomycin (71.4% each). A certain resistance has been noted to oxytetracycline (71.4%) and nalidixic acid (42.8%). Higher number of isolates showed moderate sensitivity or resistance to amoxicillin (51.1%). Regarding to multidrug resistance, the study reflects that only one isolate (14.3%) shows multidrug resistance to four drugs namely kanamycin, amoxicillin, nalidixic acid and oxytetracycline. This study demonstrated that mastitis due to C. bovis is rare in lactating dairy farms in Bishoftu. Some of the risk factors for mastitis can be addressed by practical management of dairy cows. Farm owners should selectively use the antibiotics to which the bacteria do not show resistance, such as streptomycin and kanamycin.
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