الفهرس 
ContentsOnly 14 pages are availabe for public view
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Abstract
The objective of control measures should be to improve patient care, minimise patient mortality and morbidity, and to help contain healthcare costs. In hospitals where MRSA is endemic, the objective is to minimise spread and in particular to avoid as far as possible the clinical impact of systemic or deep infection in high-risk patients such as those in the intensive care unit (ICU) or other key clinical areas. the number of patients with MRSA bacteraemia correlates with the hospital-wide prevalence of MRSA and that control measures have a substantial impact on both the reservoir of MRSA patients and the attack rate of MRSA bacteraemia or bloodstream infection. Rapid identification of S. aureus and detection of methicillin resistance are essential for early initiation of appropriate antimicrobial therapy and to limit the inappropriate use of glycopeptide agents. Current standard laboratory methods for detecting oxacillin resistance require at least 48 to 72 h for isolation, identification and susceptibility testing. In this work, we try to evaluate a rapid method for detection of methicillin resistant staphylococci directly from positive blood culture specimens. This method is a simple DNA extraction method followed by a multiplex PCR assay designed to detect the 16S rRNA gene (used as an internal control), the mecA gene (responsible for true methicillin resistance in staphylococci) and the nuc gene (found only in S. aureus and not in coagulase negative staphylococci). In this work, blood culture was done for all cases for isolation of the causative organisms. Staphylococcal isolates were then identified by standard methods including Gram stain, catalase, bacitracin susceptibility, tube coagulase and latex agglutination tests. This was followed by testing the staphylococcal isolates with oxacillin by disc diffusion method. All positive blood cultures were subjected to a multiplex PCR assay targeting 16S rRNA, nuc and mecA genes. The results were compared to the same multiplex PCR technique done on the bacterial isolates on culture plates. Our results revealed that blood cultures were positive for 85% of the patients. Staphylococci accounted for 58.8% of the positive cases. 52% of the isolated staphylococci were S. aureus and 48% were CoNS. 76.9% of S. aureus isolates were MRSA, 23.1% were MSSA. 91.7% of CoNS isolates were MRCoNS, 8.3% were MSCoNS. Our results showed that the sensitivity and specificity of latex agglutination test compared to tube coagulase test were 96.2% and 100.0%, respectively. It is worthy noting that the latex agglutination test used is one of the second generation agglutination kits that detect the presence of clumping factor and protein A. The sensitivity and specificity of oxacillin disk diffusion method in relation to mecA PCR were 95.2% and 87.5%. Our results showed also that the following factors were significantly associated with acquisition of methicillin resistant staphylococci: hospitalization or health care system contact, old age, increased severity of illness, CVC, mechanical ventilation, previous use of antibiotics. In our study the mortality associated with methicillin resistant staphylococci was significantly higher than methicillin susceptible staphylococci. As regards our multiplex PCR assay, significant agreement was found between direct multiplex PCR testing on blood cultures and PCR testing on bacterial isolates. However, few discrepant results were obtained. In 1 sample that grew MRCoNS, the 16S rRNA gene failed to amplify but PCR gave the correct mecA result. The assay was also successful in amplifying the 16S rRNA gene from other bacteria. Only two specimens initially failed to show a product after PCR. The assay also accurately distinguished S. aureus from coagulase-negative staphylococci. It has to be mentioned that the total time required to perform the multiplex PCR assay directly from positive blood cultures was 3 h. In our study assessing the efficacy of a control programme during the mid 2013s, the rate of MRSA infection decreased from 3.9 to 1.2/1,000 patient-days as did the prevalence of MRSA carriage and the ratio of MRSA to all Staphylococcus aureus. In a Spanish study, three time periods were studied, i.e. pre-outbreak, during an outbreak of MRSA. The experience in Finland, where two successive MRSA outbreaks in the early 1990s were successfully managed and where there is now no endemic MRSA. Efforts should be made to eradicate MRSA when it does arise in centres or units where it has not been previously. Consequently, specific measures to control MRSA as part of an overall strategy of hospital infection prevention will help reduce the number of patients likely to acquire both MRSA and also strains resistant to vancomycin.