| Mastitis has been one of the tough problems in dairy cows.The economic losses and potential hazards caused by subclinical mastitis as much as clinical mastitis. Investigating the prevalence of subclinical mastitis, studying the resistance and resistance mechanisms of Streptococcus isolated from dairy cows with subclinical mastitis,So as to provide theoretical guidance for the effective prevention and treatment of subclinical mastitis cows in Liaoning province.In total,306 lactating cows were sampled from 6 different dairy farms. Then milk samples were analyzed for somatic cells count (SCC). The positive samples were submitted for pathogen isolation, identification and susceptibility testing.The objectives of this study were to study Streptococcus, which is one of the most important pathogens causing subclinical mastitis.Based on SCC, Overall prevalence of SCM was 34.31% in cattle. And the highest prevalence was 76.67%, The lowest was 10% by means of the API Strep identification,55 streptococcus were identified, including Enterococcus faecium(39), Enterococcus avium(13), Enterococcus faecalis(1), and Streptococcus uberis(2). The average detection rate was 52.4%.The micro two-fold dilution method was selected to detect the in vitro antibacteri al activity of 55 strains of Streptococcus to 21 antibacterial drugs.The results indicated that Streptococcus showed a very high proportion of isolates resistant to sulfonamide, lincosamides, Cephalexin and Oxacillin, and the resistance rate was 100%,100%,90.9% and 90.9%, respectively. Resistance todoxyc ycline,erythromycin and azithromycin was found above 85%; Resistance to Amoxicillin, penicillin, ceftiofur, tylosin, enrofloxacin was found above 60%.55 Streptococcus isolates were sensitive for ofloxacin,ciproflox acin and amikacin,the sensitive rate were 65.5%,63.6% and 47.3%, respectively.So,th-ese three drugs can be the first choise for clinical treatment. There were 33drug resis-tance spectras in 55 Streptococcus,All the pathogens were resistant to at least 3 kinds of antimicrobial agents, and 8 for the most.By the PCR screening for the integrons,45.5%(25/55) Streptococcus isolates carried class 1 integrons and 14.5% (8/55) isolates carried class 2 integrons. Moreover,10.9% isolates carried both class 1 and class 2 integrons. No class 3 integrons were found 16 of the class 1 integron positive isolates harbored gene cassette, including micro multi-drug resistance gene (smr), and those encoding resistance to aminoglycosides (aadA1, aadA2), trimethoprim (dfrA15), ADP ribose transferase gene (arr-3) and Aminoglycoside acetyltransferase gene(aacA4). Two class 2 integrons isolates were not detected resistance gene cassette, and the kinds of the resistance gene cassette carried by class 2 integrons positive isolates were not detected at the same time.The objective of the present study was to find out the the prevalence of the subclinical mastitis in Liaoning province, and in terms of the results of antimicrobial susceptibility testing, It provides a reasonable theoretical basis for the clinical prevention and treatment of subclinical mastitis. Meanwhile, by studying the mechanism of resistance of Streptococcus, laying a strong foundation for the further study of the Molecular mechanisms of drug resistance of the Streptococcus in dairy subclinical mastitis. |
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