Study On Clinical Features And Genotyping Of Methicillin-Resistant Stapholococci Isolated From Diabetic Foot Infections

OBJECTIVE:To study the distribution of pathogens and drug-resistant profiles of staphylococci isolated from the patients suffered with diabetic foot ulcers;to analyze the risk factors for the infections with methicillin-resistant staphylococcus aureus(MRSA)or methicillin-resistant Staphylococcus epidermidis(MRSE)in diabetic foot ulcers;to investigate SCCmec genotypes of MRSA and MRSE in the diabetic foot infections.Drug-resistant profiles in each SCCmec type and homologies of the strains were also explored.METHODS:388 diabetic-foot patients hosipitalized between Jan 2008 and Jun 2010 in the Tianjin Metabolic Diseases Hospital were included.The distribution of pathogens in foot infecions was summarized.Staphylococcus aureus(SA)and Staphylococcus epidermidis(SE)strains were screened for specimen identification.The drug-resistant profiles of staphylococci were analyzed.Patients infected with SA were divided into MRSA and MSSA groups.The patients suffered with SE infections were divided into MRSE and MSSE groups.The clinical features of the patients were compared between the groups.The risk factors for infections with MRSA or MRSE strains in diabetic foot ulcers were analyzed by non-conditional logistic regression methods.The DNAs of the MRSA and MRSE isolates were extracted,and mecA,pvl and lukE-lukD genes were detected by polymerase chain reaction.The MRSA and MRSE strains were also genotyped by SCCmec and pulsed-field gel electrophoresis(PFGE).Antibiotic-resistant profiles of each SCCmec type were also evaluated.RESULTS:Totally 362 strains were obtained from 388 diabetic foot patients.The predominant pathogens were gram-positive cocci(55.3%),gram-negative bacilli(39.2%)and fungi(3.6%).The most frequent isolates were SA(27.1%),SE(18.8%)and Pseudomonas aeruginosa(15.5%).The incidence of MRSA(24/98,to SA)and MRSE(18/68,to SE)was 24.5%and 26.5%,respectively.The resistance rates of MRSA and MRSE to p-lactams and macrolides were more than 70%,and to fluoroquinolones were between 50%and 79.2%.MRSE strains had a significantly higher resistance rate to trimethoprim-sulfamethoxazole than that of MRSA(P<0.01).MSSA and MSSE strains were sensitive to almost all the examined antimicrobials except penicillin G and macrolides.All MRSE strains were sensitive to rifampicin,but 33.3%MRSA strains were resistant to it.All the isolates were sensitive to vancomycin.Multivariate logistic regression analysis indicated that 5 factors were risk factors for infections of MRSA:drug usage in 6 months prior to admission,long course of the ulcers,osteomyelitis,hypoproteinemia and hypertension;HbA1c level was the only risk factor for MRSE infections.All the MRSA and MRSE isolates were mecA positive.24 MRSA strains were pvl negative and lukE-lukD positive.SCCmec I was detected in 5(20.8%)MRSA isolates,SCCmecⅡin 2(8.3%)isolates,SCCmecⅢ in 7(29.2%)isolates,SCCmecⅣ in 10(41.7%)isolates.Of the 18 MRSE isolates,2(11.1%)were SCCmecⅡ,8(44.4%)were SCCmecⅢ,8(44.4%)were SCCmecⅣ.None of the strains carried SCCmec V cassette.SCCmecⅣ isolates were all multi-drug resistant similar to the SCCmec I,II and Ⅲ strains.They were resistant to not only β-lactams but also non-β-lactams.The similarities of MRSA were 42%-97%.The MRSA isolates were classified into 11 PFGE types(A-K),12 were ty:pe A,2 were type B,2 were type C and the otber types only included one strain.The similarities of MRSE were 34%-100%and 14 PFGE types(A-N)were identified.Among MRSE srains,5 were type A,and the other types only included one strain.CONSILUTIONS:SA and SE are the commonest pathogens in the diabetic foot infections.MRSA and MRSE in the pateients are with multi-drug resistant characteristics.Risk factors for infections of MRSA are drug usage in 6 months prior to admission,long course of the ulcere,osteomyelitis,hypoproteinemia and hypertension;HbAlc level is the only risk factor for MRSE infections.All the MRSA isolates were pvl negative,but lukE-lukD positive.SCCmecⅢ and SCCmecⅣ are the dominant genotypes of the MRSA and MRSE.The SCCmecIVgenotype strains with multi-drug resistant profiles are prevalent in these patients.An outbreak of type A MRSA probably had happenned during the period from Jan 2008 to May 2008.No outbreak evidences have been identified from Jun 2008 to Jun 2010.