| Staphylococcus aureus is widely exist in nature and it is a kind of important pathogens which can cause infectious diseases to people and animals. Macrolide antibiotics is a kind of antibiotic which containde macrolide basic chemical structure. It is often used in the treatment of Gram-positive infections caused by bacteria in clinical practice. With the use of macrolide antibiotics more frequently, the resistant strains were more and more and which lead treatment failure. Thus, the study on Staphylococcus aureus resistance, virulence genes, resistance genes and the detection of biofilm not only have guiding significance for clinical rational use of drug, but also was great importance in the veterinary clinical and public health.This study mainly aimed at Staphylococcus aureus isolate from dairy in Ningxia. First, the samples were collected form the clinical and subclinical bovine mastitis. The Staphylococcus aureus were isolated and identified by the methods including gram staining microscopy, CHROMagar Staphylococcus aureus agar and PCR amplification for 16S rDNA gene and nuc gene. Second, the MICs of 18 antimicrobial agents for Staphylococcus aureus isolates were determined by the broth microdilution method according to the guidelines recommended by the Clinical and Laboratory Standards Institute(CLSI).The results showed that 231 strains of Staphylococcus aureus were isolated and identified, and the isolation rate was 16.84%. The results of susceptibility testing showed that the highest proportion of resistance was ampicillin(79.2%), followed by Penicillin(77.9%), Sulfamethoxydiazine(65.4%). The resistance rates of macrolides and lincosamide antibiotics were about 40%. The relatively susceptible antimicrobials were Amoxicillin-clavulanic acid, Cefazolin, Amikacin, Doxycycle. The sensitive rates of cephalosporins and quinolones were 60%-89%. The 4,5,6,7-resistant strains were dominant, the proportions were 22.5%,12.1%,11.3%,12.1%, respectively. All isolates tolerated up to 16 kinds of antimicrobial agents. The multi-drug resistance rate was 84.8%.The virulence genes and resistant genes of macrolides among 231 strains of Staphylococcus aureus were determined by PCR. The results showed that the detecting rates of hla, hlb, clfa, pvl, sea, seb, sec were 99.1%(229/231),97.8%(226/231),98.7%(228/231),2.6%(6/231),27.7%(64/231),29.0%(69/231), 5.6%(13/231),respectively. The detection rates of msrA and ermC were 55.3%,67.5% respectively. The msrA can mediate active pumping system and ermC can change the action target. It can be seen, the hla, hlb, clfa were predominant virulence genes of Staphylococcus aureus isolated from cow in Ningxia.The induced resistance test was carried out aiming 31 Staphylococcus aureus which resistant to erythromycin and sensitive to clindamycin by double paper method. The results showed that the positive rate of D test was 90.3%(28/31).The biofilm formation ability of 231 Staphylococcus aureus were tested by Congo red method, of which 112 strains had the ability of biofilm formation and the positive rate is 48.5%.In conclusion,we analysed drug resistance of Staphylococcus aureus isolated from the NingXia region cow farms and detected the virulence genes and resistance gene of macrolides and biofilm. It revealed the drug resistance situation and the resistance characteristics of Staphylococcus aureus isolated from dairy farm in Ningxia. Provide theory basis for using antimicrobials rationaliy and controlling the spread of drug-resistant Staphylococcus aureus. And lay a solid foundation for the further study of bacterial resistance mechanisms. |
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