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    • br Materials and methods br Results br Discussion The

    2018-11-03


    Materials and methods
    Results
    Discussion The patients in burn wards are more susceptible to infection than those in other common wards, and wound infection in burn patients is a difficult problem. The previous study illustrated that the patients in younger ages and owned larger burn sizes are inclined to infect MRSA because of the physical destruction of normal skin barrier, which would reduce the cell-mediated immunity. MRSA is one of the main pathogens that caused nosocomial infection, especially for burn patients. This infection is one of the most common reasons of mortality and morbidity. Therefore, it is necessary to investigate the prevalence of MRSA and their resistance mechanism for further prevention and treatment of burn patients who acquired MRSA infections. This study revealed the prevalence of MRSA in burn patients and detected the antimicrobial susceptibility profile. Moreover, the molecular and virulence characteristics and nucleotide homology of MRSA isolates was also analyzed in this study. In the past few years, MRSA has been spread around the world and its infection has becoming a serious problem in the world. With the wide application of antimicrobial agents, the susceptibility of Staphylococcus aureus is ever-changing. Thus, it is necessary to evaluate the resistance patterns of Staphylococcus aureus and the antibiotic therapy should be guided by susceptibility test. In this study, 365 Staphylococcus aureus strains were isolated in burn patients in our hospital from January 2008 to December 2014, including 85 MRSA and 280 MSSA and the corresponding constituent ratios of MRSA and MSSA were 23.9% and 76.1%. The rate of MRSA in the study was lower than that previous reports, which may be caused by the fact that our hospital has been strengthening the management of infection control in past few years. From the resistance patterns of the isolated MRSA, we realized that the resistant rates of MRSA stains were obvious higher than that of MSSA strains, which was similar with other studies. This result may be induced by the unreasonable use of broad spectrum antibiotic. The drug resistance of MRSA is mainly because that the gene encoding regulates the Sunitinib Malate of Penicillin Binding Protein (PBP2a), which is encoded by mecA gene, and arisen on the surface, which lies on the Staphylococcus gene cassette of SCCmec. Thus, the detection of mecA gene can be used to confirm diagnosis of MRSA isolates. PCR was performed to detect mecA gene in this study, and the results showed that the mecA-positive rate reached 100.0%, which were in accordance with other reports such as reported by Hossein Motamedi. These results are well in agreement with the conclusion that resistance in S. aureus mainly involves two mechanisms for the expression of b-lactamase and mecA gene. MRSA exhibits strong virulence and invasiveness, and the main pathogenic toxins are shock toxins, hemolytic toxins, kill IL, plasma coagulase, et al. These virulence factors have different biological characteristics, thus behaving different pathogenic characteristics. Also, the difference of virulence factors between MRSA and MSSA were analyzed in this study and showed a variety of distribution. The seizure rates of enterotoxin se and seb in MRSA were higher than that in MSSA, which was similar with previous report. PVL is a necrotizing toxin. Its high expression could lead to necrosis of monocytes, necrotic monocytes release inflammatory mediators, and host tissue damage, while the low expression could result in monocyte apoptosis. The carrying rates of PVL in MSSA were significantly higher than that in MRSA, which was lower than previous report. Other virulence factors’ carrying rates, such as hla and fabA, were higher in MSSA than that in MRSA. These results indicated that although MSSA is weaker in drug resistance than MRSA, it may be more pathogenic than MRSA in terms of virulence. Typing of MRSA is an essential prerequisite for initiation of targeted hospital infection control measures, allowing detection of nosocomial transmissions and outbreak situations. In order to treat and control MRSA infection of burn patients in a better way, nucleotide homology analysis was performed in this study. Currently, the S. aureus protein A (spa) typing, multilocussequence typing (MLST), and PFGE are the primary molecular typing ways for MRSA typing. Among these techniques, PFGE was regarded as the “gold standard” for outbreak investigations, which was mainly due to its excel-lent discriminatory power in short-term epidemiology. In this study, 16 MRSA isolates were classified into 3 different clone types by PFGE technology: A, B and C, and the corresponding amounts were 13 (81.25%), 2 (12.5%), and 1 (6.25%). Further researches are needed in order to reduce or control the outbreak of nosocomial infection caused by MRSA strains.