Clinical Characteristics And Molecular Epidemiology Of Methicillin-resistant Staphylococcus Aureus Infection In Children’s Intensive Care Unit

Objective To analyze the clinical characteristics of Staphylococcus aureus infection in the children’s intensive care unit(ICU)in this region,to explore the risk factors of Methicillin-resistant Staphylococcus aureus(MRSA)infection in pediatric ward,and to analyze the resistance and virulence gene carrying status for MRSA which separated from clinical to explore the correlation between the dominat MRSA strains and their molecular typing,so as to provide the scientific knowledge for the prevention and treatment of MRSA in children’s intensive care unit.Methods(1)Retrospective analysis of medical records on infection in patients with Staphylococcus aureus children intensive care unit during 3 years was conducted.Univariate analysis and multivariate logistic regression were used to analyze the risk factors including age,gender and 17 other clinical related factors.(2)The bacterial identification was performed with VITEEK-2.(3)The Kirby-Bauer method was used to test the strain’s drug resistance to pediatric commonly used antibiotics.(4)The broth microdilution method was used to detect MRSA’s minimum inhibitory concentration(MIC).(5)Vancomycin damage test to detect the presence of heterogeneous vancomycin-mediated Staphylococcus aureus(hVISA)and vancomycin-mediated Staphylococcus aureus(VISA)was performed.(6)Polymerase chain reaction(PCR)method was performed to detect the prevalence of the gene mecA,enterotoxin genes sea and seb,leukocidin gene PVL,hemolysin genes hla and hlb,enterotoxin regulatory genes agrl-4,toxic shock syndrome toxin gene tst,as well as exfoliation toxin genes eta and etb in MRSA.(7)Molecular typing of MRSA by bacterial molecular typing methods including staphyloccal protein A gene polymorphism,pulsed field gel electrophoresis(PFGE)and multilocus sequence typing(MLST).Results(1)There were 102 cases of Staphylococcus aureus infection in this study.Overall,64.7%of cases were birth-1 years old,61.7%were diagnosed with pneumonia(63 cases),and the mortality rate was 9.8%(10/102).(2)Univariate analysis showed that gastric tube,suction,endotracheal intubation/incision,ventilator,catheterization,antibiotic use(≥ 3types),antibiotic use time(≥ 2 weeks),immunosuppressant/hormone,gamma globulin and hospitalization time(≥30 days)were closely related to the occurrence of MRSA infection.Noninvasive logistic regression analysis showed that mechanical endotracheal intubation/incision therapy,ventilator therapy and antibiotic use were all the independent risk factors of MRSA infection in children.(3)A total of 102 Staphylococcus aureus isolates were identified.The isolation source of sputum accounted for 59.8%,followed by nasal swab and throat swab,accounting for 21.6%and 9.8%,respectively(4)Up to 38(37.3%)isolates were proved to be MRSA.The resistance rates for common antibiotics in MRSA were erythromycin(92.1%),clindamycin(94.7%),streptomycin(52.6%),gentamicin(26.3%),tetracycline(18.4%),chloramphenicol(71.1%),ciprofloxacin(55.3%),moxifloxacin(28.9%),levofloxacin(39.5%)and sulfamethoxazole(5.3%),respectively.The resistance to rifampicin,linezolid,nitrofurantoin and vancomycin were not detect.VISA and hVISA were not found.Compared with the resistance rates in methicillin-sensitive Staphylococcus aureus(MSSA),the resistance rates in MRSA to macrolides,clindamycin,aminoglycosides and tetracyclines were significantly higher(P<0.05).(5)The carrier rates for following virulence genes in MRSA were found:sea(47.4%),seb(47.4%),hla(97.4%),hlb(76.3%),agrl(42.1%),agr2(2.6%),agr3(10.5%),and PVL(21.2%).Others gene like agr4,eta,etb and tst were not detected.The ioslates with two types,three types,four types,and five types of virulence genes accounted for 21.1%(8/38),26.3%(10/38),34.2%(13/38),and 15.8%(6/38)of all MRSA isolates,respectively.(6)Spa polymorphism analysis results showed,a total of 7 spa types in 38 MRSA,mainly t172(15 strains,39.5%),followed by t437(10 strains,26.3%).(7)PFGE results showed that 35 MRSA(3 isolates failed)were classfied into two clusters:cluster 3(25/35)(similarity>80%)and cluster 4(6/35)(similarity>85%),and four sporadic strains.(8)MLST typing results showed that 38 MRSA could be classified into 6 ST types,the dominant type being ST59(n = 31,81.6%),the other five ST types being ST1(n = 1,2.6%),ST88(n=1,2.6%),ST398(n = 3,7.9%),ST965(n = 19 2.6%).No new STs were found.Conclusions(1)The detection rate for MRSA in Staphylococcus aureus infection was 37.3%in this study.(2)The emergence of MRSA was caused by multiple factors,including mechanical tracheal intubation/incision therapy,ventilator therapy and multiple antibiotic use which were independent risk factors for MRSA infections.(3)Clinical isolation of drug-resistant Staphylococcus aureus is common,Resistance rate in MRSA to macrolides,tetracyclines and lincomycin was significantly higher than in MSSA.(4)Virulence gene detection results demonstrated that virulence genes in MRSA were complex.Most strains contained multiple virulence genes.(5)Molecular biology studies showed that ST59-t172(39.5%)and ST59-t437(26.3%)were prevalent strains,ST-59 MRSA were dominantly detected(81.6%)which suggested a possibly outbreak.Measures for the prevention and control of MRSA infectios should include scientific and rational use of antibiotics,strict use of invasive treatment,monitoring of drug resistance genes and other contributing risk factors.