Study On Clinical Features And Molecular Characteristics Of Methicillin-resistant Staphylococcus In Children

Objective The aim of this study was to study the clinical and molecular characteristics of methicillin-resistant staphylococcus(MRSA) infection in children of Shanghai Area, and to determine the relationship between phenotypic and genotypic resistance profiles.Methods In this study, a total of37MRSA strains were isolated from hospitalized patients in Children’s Hospital of Fudan University from March2009to November2011. We studied the clinical characteristics by a cohort study. Furthermore, the mecA、ermB、aac(6’)/aph(2")、aph(3’)-Ⅲ、ant(4’,4")、qacA、pvlgenes were detected by polymerase chain reaction(PCR), and the genotypes of SCCmec were determined by multiplex polymerase chain reaction(PCR). Resistance to antibiotics was detected by agar dilution.Results (1) Among37MRS A isolates,21isolates(56.80%) were acquired from hospital(HA-MRSA), and16isolates(43.20%) were acquired from community(CA-MRSA). In the study,MRSA frequently caused respiratory tract infection, and most of the strains were isolated from Intensive care unit(ICU). CA-MRSA was most frequently associated with skin and soft tissue infections(SSTI), suppurative tonsillitis, even pneumonia and septicemia. HA-MRSA infection was more aggressive, most frequently associating with pneumonia, septicemia, even central nervous system(CNS) infections, such as meningitis. In children with fever caused by HA-MRSA or CA-MRSA infection, HA-MRSA showed a longer duration of fever, for10.5days. C-reactive protein(CRP) level caused by HA-MRSA was higher than CA-MRSA, and there were statistically significant differences between the groups. However, There were no statistically significant differences between the groups in White blood cell count(WBC) or procalcitonin(PCT) level.(2) Among37MRS A isolates, the whole isolates were mecA gene positive(100%). SCCmec genotyping results showed that the most frequent SCCmec types were type111(45.95%), the others including type IV(21.62%), type11(2.70%), nontype(29.73%). type I and type V were not found in this group. Thereinto, among21HA-MRSA isolates, SCCmec Ⅲ was the most common,15isolates(71.42%), type Ⅳ1isolates(4.76%), nontype5isolates (23.82%); Among16CA-MRSA isolates, SCCmec type Ⅳ was the most common,7isolates (43.75%), type Ⅲ2isolates (12.50%), type Ⅱ1isolates(6.25%), nontype6isolates(37.50%). Among37MRSA isolates,28isolates were pvl gene positive(75.70%); And among21HA-MRSA isolates,17isolates were pvl gene positive(80.95%); Among16CA-MRSA isolates,11isolates were pvl gene positive(68.75%); There were no statistically significant differences between the groups (P=0.244)(3) Among37MRSA isolates,37(100%) were resistant to penicillin, Unasyn, cefazolin, cefuroxime. And gentamicin, erythromycin, clindamycin, sulfamethoxazole, fosfomycin, rifampicin, levofloxacin resistance rates were51.35%(19/37),81.08%(30/37)51.35%(19/37),16.22%(6/37),27.03%(10/37),37.84%(14/23),54.05%(20/37). Teicoplanin,vancomycin, linezolid resistance rates were0. Thereinto,among16CA-MRSA isolates, gentamicin, erythromycin, clindamycin, sulfamethoxazole, fosfomycin, rifampicin, levofloxacin resistance rates were12.50%,75.00%,62.50%,12.50%,12.50%,6.25%,31.25%; and among21HA-MRSA isolates, gentamicin, erythromycin, clindamycin, sulfamethoxazole, fosfomycin, rifampicin, levofloxacin resistance rates were80.95%,85.71%,42.86%,19.05%,38.10%,61.90%,71.43%;For gentamicin, levofloxacin, and rifampin resistance, HA-MRSA was significantly higher than that CA-MRSA, the difference was statistically significant (P=0.000,0.015,0.001).(4) Among37MRSA isolates, the whole isolates were mecA gene positive(100%),9isolates were ermB gene positive(24.30%),21isolates were aac(6’)/aph(2") gene positive(56.80%),10isolates were aph(3’)-Ⅲ gene positive(27.00%),6isolates were ant(4’,4") gene positive(16.20%),9isolates were qacA gene positive(24.30%). Among the aminoglycoside resistance genes,the most frequent combination of genes was aac(6’)/aph(2") with aph(3’)-Ⅲ (16.20%). The second dominant gene combination was aac(6’)/aph(2") with ant(4’,4")(5.40%). The ant(4’,4") and aph(3’)-Ⅲ combination existed only in2.7%MRSA isolates.Among16CA-MRSA isolates,the positive rate of ermB、aac(6’)/aph(2")、aph(3’)-Ⅲ、 ant(4’,4")、QacA gene were25.00%、18.75%、31.25%,25.00%,25.00%; And Among21HA-MRSA isolates,the positive rate of ermB、aac(6’)/aph(2")、aph(3’)-Ⅲ、 ant(4’,4")、QacA was23.81%、85.71%、23.81%、9.52%、23.81%; for the positive rate of aac(6’)/aph(2"), HA-MRSA was significantly higher than that CA-MRSA, the difference was statistically significant (P=0.000).(5) By contrast the carrying of resistance genes with antibiotic resistance, for the rate of erythromycin resistant, ermB gene carrying strains is not significantly higher than others, the difference was not statistically significant (P=0.160); For the rate of Gentamicin resistant, aac(6’)/aph(2") gene carrying strains is significantly higher than others, the difference was statistically significant (P=0.000), aph(3’)-Ⅲ、ant(4’,4") gene carrying strains is not significantly higher than others, the difference was not statistically significant (P=0.920、0.405).Conclusions Compared with CA-MRSA, HA-MRSA infection was more aggressive, and induced inflammatory index(C reactive protein) higer; MRS A in children carry a variety of drug-resistant genes, showed multi-drug resistance. Carrying mecA gene is mainly due to the beta-lactam antibiotic resistance, and carrying aac (6’)/aph (2") gene is an important mechanism of aminoglycoside-resistant.The dominant epidemic strains of CA-MRSA is SCCmec type Ⅳ, and HA-MRSA is SCCmec type Ⅲ; By comparison between HA-MRSA and CA-MRSA,The rate of resistance genes carrying and resistance to antimicrobial medicines is higher.The positive rate of pvl and qacA gene is high.