In recent years,methicillin-resistant Staphylococcus aureus(MRSA)has been repeatedly detected in livestock and animal foods,which poses a serious threat to human and animal health.In order to understand the bacterial pathogens carried by sheep with respiratory diseases in Aksu area of Xinjiang,a total of 280 nasal swab samples(136 sick sheep and 144 healthy sheep)were collected from 6 large-scale sheep farms in Aksu.The samples were inoculated on BHI defibered sheep blood plate and high-salt mannitol agar plate,and the isolated bacteria were identified by Gram staining microscopy and biochemical identification.The results showed that 34 and 62 strains of Staphylococcus aureus(SA)were isolated from 136 sick sheep and 144 healthy sheep nasal swab samples,respectively.PCR was used to amplify the specific genes nuc and mecA of SA and MRSA,respectively.The results showed that 96 strains of SA were isolated,of which 24 strains(25.0％)were MRSA,and all of MRSA were isolated from sick sheep.Six common virulence genes of MRSA were detected by PCR.The results showed that the detection rates of clfa,hla and pvl in 24 strains of MRSA were 100.0％,and the detection rates of tst,fnbB and sec were 41.2％(10/24),45.7％(11/24)and 33.6％(8/24),respectively.Mice were infected with 24 strains of MRSA at 104cfu/mL-108cfu/mL.The pathogenicity of isolated MRSA to mice was evaluated by observing clinical symptoms,calculate the mortality rate of mice in each group,necropsy of organs of dead mice and the isolation of bacteria from organs of mice in each group.The results showed that the mice in each group began to show clinical symptoms after 8 hours after infection.All the mice in the 108cfu/mL and 107cfu/mL infection groups died at different times after infection.The mortality rates of mice in 106cfu/mL-104cfu/mL infection groups were 83.3％,83.3％and 33.3％,respectively.The mice in the control group were all alive within 72 hours.The lungs of the dead mice had extensive bleeding and the liver and spleen were enlarged.No significant changes were observed in other organs.MRSA was isolated again from the lungs,spleen and other organs of the dead mice.Finally,22 strains of MRSA were confirmed to be pathogenic to mice.The sensitivity of 24 strains of MRSA to 15 drugs in 9 categories was detected by K-B disk method.The resistance genes mecC,blaZ(β-lactams),ermA(macrolides),Aac(6')/aph(2','),aph(3')-III,Ant(4')-Ia(aminoglycosides),qnrA(quinolones)and tetM(tetracyclines)of 24 MRSA strains were detected by PCR.The results of drug sensitivity test showed that 24 strains of MRSA were all resistant to penicillin and aztreonam of β-lactam class,ampicillin of cephalosporins class.14 strains of MRSA were multi-drug resistant(58.3％,14/24),among which strains resistant to 3 drugs accounted for 42.8％(6/14),followed by strains resistant to 4,5 and 6 drugs account for 28.6％(4/14),14.3％(2/14),and 14.3％(2/14),respectively.Some strains were sensitive to tetracycline,erythromycin,clindamycin and ciprofloxacin.The drug resistance gene detection results showed that 6 drug resistance genes were detected in 24 strains of MRSA,among which the detection rate of mecC and blaZ reached 100％;the detection rate of tetM was 79.2％(19/24);the detection rate of ermA was 37.5％(9/24);the detection rates of Aac(6')/aph(2','),aph(3')-Ⅲ and Ant(4')-Ia were all 25.0％(6/24),and these MRSA carried at least three and up to six drug resistance genes.Analysis showed that there was a positive correlation between the drug resistance phenotype and drug resistance genes of 24 strains of MRSA,and the quinolone resistance gene qnrA was not detected,which was consistent with the result that MRSA was sensitive to this drug ciprofloxacin.The results of this study showed that MRSA was isolated from sheep suffering from respiratory diseases in Aksu area of Xinjiang.The bacteria carrying a variety of virulence genes and multiple drug resistance genes had strong pathogenicity to mice and resistance to multiple drugs and carried multiple drug resistance genes,which may be related to sheep suffering from respiratory diseases.This study provides a reference for the etiology research and clinical medication of sheep respiratory diseases in Aksu area of Xinjiang.
respiratory tract of sheepmethicillin-resistant Staphylococcus aureusvirulence genepathogenicitydrug resistance
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