Study On The Characteristics Of Drug Resistance And Virulence Of Staphylococcus Aureus Isolated From The Skin Sites With Suppurative Infection

Objective:1.To analyze the characteristics of drug resistance of Staphylococcus aureus isolated from the skin sites with suppurative infection,so as to provide experimental basis for clinicians to use anti-infective drugs.2.To understand the virulence and molecular epidemiological characteristics of Staphylococcus aureus isolated from the skin sites with suppurative infection.Methods:1.Samples of skin suppurative infection and nasal secretions from dermatology inpatients in the affiliated Hospital of Inner Mongolia Medical University from May 2020 to December 2020 were collected for isolation and culture.Suspected Staphylococcus aureus colonies were identified by MALDI-TOF MS mass spectrometer.2.The sensitivity of Staphylococcus aureus strains to common antibiotics was detected by microbroth dilution method.3.Six kinds of virulence-related genes of Staphylococcus aureus were amplified by polymerase chain reaction(PCR),including enterotoxin gene(sea,seb,sec,sed,see),toxic shock syndrome toxin gene(tsst-1),exfoliative toxin gene(eta and etb),leukocidin gene(pvl),hemolysin gene(hla,hlb,hld,mpHLG1 and mpHLG2),adhesin gene(clfA and clfB).4.The real-time fluorescent quantitative PCR method was used to detect the relative expression levels of the four virulence genes of tsst-1,pvl,hla,and clfA in Staphylococcus aureus strains from different sources.5.Staphylococcus aureus strains were genotyped by multilocus sequence typing(MLST).Results:1.A total of 85 strains of Staphylococcus aureus were isolated from 210 inpatients in the dermatology department of our hospital from May 2020 to December2020.The source of the specimen is divided into two parts,that is,54 strains were isolated from the skin sites with suppurative infection(63.53%,54/85),and 31 strains were isolated from the nasal cavity(36.47%,31/85),corresponding to the strains of the case group and the control group respectively.2.The results of drug sensitivity test showed that a total of 14 strains of methicillin-resistant Staphylococcus aureus(MRSA)were detected in 85 strains of Staphylococcus aureus,including 9strains in the case group and 5 strains in the control group.The resistance rate of 85 strains to penicillin was the highest(90.59%).The resistance rates to clindamycin and erythromycin were 60.00% and 61.18% respectively,and to moxifloxacin,levofloxacin,tetracycline,oxacillin,gentamicin and sulfamethoxazole were 9.41%,10.59%,14.12%,16.47%,18.82% and 21.18%,respectively.No resistant strains to rifampicin,vancomycin and linezolid were found.The resistance rates of MRSA to levofloxacin,moxifloxacin and tetracycline were 42.86%,42.86% and 35.71%,respectively.The resistance rates of the above three antibiotics were significantly higher than those of methicillin-sensitive Staphylococcus aureus(MSSA)(P <0.05).3.The detection rate of 4 virulence genes of hla,hld,clfA and clfB in the case group was 100%.The detection rates of other virulence genes sea,seb,sec,sed,tsst-1,eta,pvl,hlb,mpHLG1 and mpHLG2 were 7.41%,11.11%,25.93%,11.11%,20.37%,3.70%,33.33%,35.19%,61.11%,53.70%,respectively.See and etb were not detected.Compared with the control group,the detection rate of pvl gene in the case group was higher than that in the control group(P<0.05).4.The results of real-time fluorescence quantitative PCR showed that there was no significant difference in the relative expression of 4 virulence genes of pvl,tsst-1,hla and clfA virulence genes m RNA between MRSA and MSSA.The relative expression of clfA in the control group(3.87(2.30 ～ 5.94))was higher than that in the case group(1.63(0.95～2.62)),P=0.007<0.05.There was no significant difference in the relative expression of other virulence genes between the two groups.5.A total of 17 ST types were obtained from 85 strains of Staphylococcus aureus,namely ST398(25.88%,22/85)、 ST22(21.18%,18/85)、 ST25(10.59%,9/85)、ST72(9.41%,8/85)、 ST7(8.24%,7/85)、 ST5(4.71%,4/85)、 ST121(3.53%,3/85)、ST4849(3.53%,3/85)、ST30(2.35%,2/85)、ST59(2.35%,2/85).The other 7 rare types were ST15,ST45,ST188,ST630,ST1027,ST3268,and ST4867,each of which accounted for 1.18%.The main dominant types are ST398-MSSA and ST22-MRSA.However,the detection rate of virulence gene pvl of ST22-MRSA strains was significantly higher than that of non-ST22 strains.Conclusion:1.Staphylococcus aureus strains isolated from the skin sites with suppurative infection had high resistance to penicillin,clindamycin and erythromycin and should not be used as the first choice for clinical experience,while the overall resistance rate of Staphylococcus aureus strains to levofloxacin,moxifloxacin and tetracycline antibiotics was low.No resistant strains to rifampicin,vancomycin and linezolid were found.2.The carrying rate of virulence gene pvl of Staphylococcus aureus isolated from the skin sites with suppurative infection was higher than that of the strains isolated from nasal cavity.3.The expression level of virulence gene clfA m RNA of Staphylococcus aureus isolated from nasal cavity was significantly higher than that from skin suppurative infection,suggesting that nasal colonization may be related to clfA gene.4.The dominant clones of Staphylococcus aureus isolated from the skin sites with suppurative infection of dermatology inpatients in our hospital were ST398-MSSA and ST22-MRSA,and the carrying rate of pvl gene of ST22-MRSA isolates was significantly higher than that of non-ST22 strains.5.At present,there is no active screening program for Staphylococcus aureus or MRSA in non-ICU patients to reduce the infection rate of Staphylococcus aureus or MRSA in inpatients.The positive rate of Staphylococcus aureus in the control group was higher in this study.According to the results of this study,active screening of Staphylococcus aureus in nasal cavity could be carried out to identify carriers as early as possible and give appropriate intervention to reduce the rate of hospitalization infection or the proportion/possibility of colonization to infection.