ABSTRACT
Background: As there is no molecular-based assays available for the detection of hVISA and VISA. However, increasing amounts of data support a number of methods for the screening and confirmation of heterogeneous vancomycin intermediate S. aureus [hVISA] and vancomycin intermediate S. aureus [VISA] infection. The vancomycin MIC result alone is unable to accurately distinguish hVISA from VSSA isolates, and the use of MIC testing alone will fail to detect h VISA strains that are relatively common among isolates of Staphylococcus aureus [S. aureus] with broth MICs of 2g per ml. of Staphlococcus aureus [S. aureus] with broth MICs of 2 g per ml
Objective: The aim of the present work was to detect the efficacy of phenotypic and automated methods for detection of MRSA with reduced susceptibility to vancomycin. It aimed also, to determine the best MIC concentration in vancomycin screening agar for detection of VISA among MRSA isolates
Methods: one hundred MRSA isolated were obtained from 100 patients from different departments of Ain Shams University Hospitals during the period from October 2015 to the end of April 2016. They were isolated from different clinical specimens; sputum, wound swabs, blood, pus, urine, and body fluid that were referred to central microbiology laboratory for routine culture and sensitivity. Detection of S. aureus with reduced susceptibility to vancomycin was done by vancomycin screening agar with different concentrations 2,4,6 ug/ml with and without casein, MIC broth microdilution method for vancomycin according to CLSI
Results: Out of 100 MRSA isolates, vancomycin screening agar 2 ug/ml with casein showed highest detection rate for VISA isolates [48%] among other screening agars. Vancomycin screening agar 6 ug/ml without casein gave the lowest detection rate [29%]. So, adding casein to vancomycin screening agar did not increase detection of VISA in any of vancomycin screening agar except for that with 2 ug/ml vancomycin. Vancomycin screening agar 2 ug/ml with casein gave the best sensitivity among all vancomycin screening agar tested. VITEK 2 system failed to detect any isolates with reduced susceptivility to vancomycin. They were sensitive to linezolid [100%] followed by tigecyclin [99%] then Quinupristin-dalfopristin [91%]. However, most of the isolates were resistant to tetracycline [85%] followed by gentamicin [80%] then ciprofloxacin [63%]
Conclusion: BHI agar with 2 ug/ml vancomycin and 16 g/l casein is a reliable, easy to perform, and inexpensive method to screen large number of S. aureus isolates for detection of reduced susceptibility to vancomycin on a daily basis. Applying quadruplicate technique in vancomycin screening agar may increase the yield for detection of VISA isolates. Although vancomycin screening agar 6 ug/ml is recommended by CLSI as a screening method for detection of VISA, yet it did not perform well and underestimated VISA isolates. VITEK 2 system is not an appropriate method for detection of S. aureus with reduced susceptibility to vancomycin [VISA]. MRSA isolates with reduced susceptibility to vancomycin can be treated effectively with Linezolid
ABSTRACT
Enterohemorrhagic E. coli [EHEC] cause non bloody, bloody diarrhea and hemolytic uremic syndrome [HUS] which is a major cause of acute renal failure in children. This study aimed at detection of EHEC in fecal specimens of children with bloody diarrhea, comparing the conventional methods to PCR as a gold standard method. A total of 50 stool specimens collected from children with bloody diarrhea were cultured on Sorbitol Mac Conkey agar culture [SMAC] plates as a specific medium for E. coli, O157:H7, ELISA for detection of shiga toxins and multiplex PCR for detection of stx[1], stx[2] eaeA and EHEC hlyA genes. Six samples out of 50 yielded non-sorbitol fermenting colonies on SMAC, none of them gave positive agglutination with O157: H7 latex antisera. While ELISA gave two positive cases [4%] out of the 50 studied cases with one false positive result, compared to PCR which gave one positive sample [2%] for stx[2] and eaeA genes, however this sample was not one of the those which gave non sorbitol fermenting colonies on SMAC. Culture on SMAC is a simple method for screening for EHEC O157, but can not be used for identification of non O157 serotypes. ELISA is a sensitive, but less specific method for detection of STEC as it detects stx produced by other species. Multiplex PCR for detection of stx[1], stx[2] eaeA and EHEC hlyA genes, is advantageous as it rapidly detects EHEC pathogenicity factors in fecal specimens