الفهرس 
StaphylococciOnly 14 pages are availabe for public view
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Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) has become the leading nosocomial pathogen worldwide and seems to have spread into the community . The prevalence of CA-MRSA continues to rise; a meta-analysis published in 2003 reported a pooled CA-MRSA prevalence rate of 30.2% in retrospective studies and a colonisation rate of 1.3% .
CA-MRSA infections tend to be less severe and less invasive than healthcare associated MRSA infections. This could be due to the fact that CA-MRSA strains are susceptible to drugs other than -lactams in contrast to the HA-MRSA strains which are usually multi-resistant . However, CA-MRSA infections are generally more aggressive and result in more adverse outcomes as compared to methicillin sensitive Staph. aureus (MSSA) infections . Moreover, recurrences of CA-MRSA infections may be more common than CA-MSSA infections
Methicillin resistance in Staphylococcus species is due to altered penicillin binding protein production mediated by the mecA gene, although less commonly the phenotype is due to either hyperproduction of -lactamase or the production of altered intrinsic PBP
There are several methods available to laboratories for detecting methicillin resistance. These include oxacillin disk test, automated susceptibility testing systems, and oxacillin agar screen plate. In addition, the cefoxitin disk test was recently recommended by the Clinical and Laboratory Standards Institute for prediction of mec A–mediated resistance .
More rapid alternative methods for the detection of MRSA have been developed including the use of chromogenic media, which have been shown to be comparable or superior in sensitivity and specificity to traditional selective media . The use of mannitol salt agar supplemented with oxacillin and the use of the oxacillin resistance screening agar (ORSA) are two of the most commonly used culured methods nowadays .
MIC is generally regarded as the most basic laboratory measurement of the activity of an antimicrobial agent against an organism , including MICs by broth microdilution and MIC by Epsilometer-test (E-test). Molecular techniques for the detection of mec A gene are viewed as the gold standard for determining MRSA including Polymerase chain reaction (PCR) for amplification of the mec A gene.
Traditional antibiotics used in the treatment are not effective against MRSA as it has become resistant to multiple other antimicrobial agents including Vancomycin. Tigecycline and linezolid have been used in clinical practice for resistant Gram-positive infections and ceftobiprole is in phase 3 of clinical development
New drugs are available in France (i.e. daptomycin, ertapenem, and doripenem) as well as those of antibacterial drugs currently in development (i.e. ceftaroline, dalbavancin, telavancin, oritavancin, iclaprim, and ramoplanin) or available in other countries (i.e. garenoxacin, sitafloxacin, and temocillin).
Linezolid in combination with ertapenem showed in vitro synergy against methicillin-resistant Staphylococcus aureus strains. This interaction was confirmed by using a rabbit endocarditis experimental model and simulation of the human pharmacokinetics in animals for both antibiotics. Linezolid plus ertapenem exhibited highly synergistic activity in vivo after 4 days of treatment.
In our study a total number of 200 MRSA isolates were collected from different clinical specimens received at the microbiology laboratory of Ain Shams University Hospitals from June 2012 to December 2012. Specimens studied were pus specimens , blood culture samples , throat swabs , sputum and knee aspiration.
Our study shows that 20% of isolates were resistant by Linezolid disc diffusion method .
E-test is performed to the LZD resistant isolates by disc diffusion,which shows that 25 were sensitive and 15 were resistant. This means that E-test is more sensitive than disc diffusion method.