| Objective: Bloodstream infection is the main cause of high morbidity and mortality of hospitalized patients around the world.Coagulase-negative staphylococci(CNS)plays an important role in nosocomial bloodstream infection.The isolation rate of Staphylococcus haemolyticus(SH)in bloodstream infection is the second in CNS,second only to Staphylococcus epidermidis.SH had the highest level of antibiotic resistance in CNS,and most of them developed into multiple drug-resistant strains.In recent decades,with the wide use of antibiotics,the detection rate of methicillinresistant Staphylococcus haemolyticus(MRSH)is increasing,and the speed of transmission,epidemic and evolution is very fast,which brings a great threat to human health.The purpose of this study was to study the drug sensitivity,staphylococcal chromosome cassette mec(SCCmec)typing and clone relationship of MRSH isolated from patients with clinical bloodstream infection in this area,so as to provide a basis for clinical diagnosis and treatment.Methods: 78 strains of MRSH from patients with bloodstream infection in20 tertiary and first-class hospitals in Hunan Province from January 1,2013 to December 31,2014 were collected.The isolates were identified by MALDI-TOF MS,and the in vitro drug sensitivity test was carried out by microbroth dilution method.The D test recommended by CLSI was used to detect the induced resistance phenotype of erythromycin to clindamycin;the resistance gene and SCCmec gene were amplified by PCR,and the positive results were verified by Sanger sequencing;the homology of MRSH was detected by pulsed field gel electrophoresis(Pulsed-field gel electrophoresis,PFGE).Results: The drug sensitivity results showed that the resistance rates of 78 MRSH strains to oxacillin,cefoxitin and penicillin were 100%,and the resistance rates to erythromycin,levofloxacin,gentamicin and clindamycin were 94.9%,80.7%,75.6% and 53.8%,respectively.The induced resistance phenotype of erythromycin to clindamycin showed that D test of20.6%(7/34)MRSH was positive.The results of drug resistance genes showed that most of the strains resistant to methicillin and cefoxitin carried the mec A gene 94.8%(74/78)and the penicillin resistant strains carried the bla Z gene 94.8%(74/78).Among the isolates with tet K gene as the main genetic determinant,90.9%(20/22)were resistant to tetracycline.Among the compound sulfamethoxazole resistant strains,88.9%(24/27)carried dfr G gene,2 linezolid strains carried cfr A gene,but gry A gene was only found in 65.1%(41/63)levofloxacin resistant strains.Among the erythromycin resistant strains,erm C and msr A genes were the main genetic determinants,accounting for 41.9%(31/74)and 39.1%(29/74),respectively,and aph(3’)-III gene was the main genetic determinant in gentamicin resistant strains of 75.6%(59/78),accounting for 35.6%(21/59)of erythromycin resistant strains,respectively,among the erythromycin resistant strains,aph(3’)-Ⅲ gene was the main genetic determinant,accounting for 41.9%(31/74)and 39.1%(29/74),respectively.The results of SCCmec genotyping showed that SCCmec can be classified as typeable(50%,39/78)and untypeable(50%,39/78).Among the 39 genotypeable strains,type I was the main type of single SCCmec(18/39,46.2%),and type Ⅰ + Ⅱ was the main type of mixed SCCmec(13/39,30.8%).The PFGE banding patterns were scattered as a whole,but there were 100% homology among six groups of strains.However,there were 100% homology among 6 groups of strains.Conclusion: The situation of drug resistance of MRSH in bloodstream infection in this area is grim,and it is highly resistant to β-lactam antibiotics,especially to penicillin,and also has a high resistance rate to erythromycin,clindamycin,levofloxacin and gentamicin.The positive rate of D-test was 20.6%,which was beneficial to the rational use of MLS antibiotics(macrolipids,lincomides,streptomycin)in clinic.There is a great correlation between drug resistance and drug resistance genes of MRSH strains isolated from bloodstream infection,and drug-resistant strains carry a variety of drug resistance genes at the same time,among which erm C,aph(3’)-Ⅲ,ant(4 ",4"),tet K and gry A genes are the main genes causing macrolides,aminoglycosides,tetracyclines and quinolones,respectively.Among the strains that can be typed by SCCmec,I type SCCmec is the main type,and SCCmec is diverse and there are differences in drug resistance among different SCCmec types.MRSH in this area is mainly sporadic,but there is the possibility of inter-hospital and intrahospital cross-infection.Surveillance of MRSH should be strengthened to reduce the further spread of MRSH. |
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