الفهرس 
Staphylococcus AureusOnly 14 pages are availabe for public view
 |  | from | 128 |  |  |
| | | from | 128 | | |
Abstract
Staphylococcus aureus is recognized to be causing nosocomial and community-acquired infection in every region of world, so the increasing prevalence of methicillin resistance among staphylococci is an increasing problem.
Once these organisms are recognized to be causing infections in a region, it is of interest to determine which of the alternatives to vancomycin are suitable for therapy.
Clindamycin is a frequent choice for some staphylococcal infections, particularly skin and soft-tissue infections, and as an alternative in the penicillin-allergic patient. However, therapeutic failure caused by MLS inducible resistance is being more commonly reported.
The MLS family of antibiotics has three different mechanisms of resistance: target site modification, enzymic antibiotic inactivation and macrolide efflux pumps.
The MLSB phenotype is inducible (iMLSB) or constitutive (cMLSB). Induction of resistance occurs in the presence of macrolide antibiotics but not lincosamides. Thus, isolates exhibiting iMLSB resistance appear susceptible to clindamycin by routine methods such as broth microdilution, disk diffusion, and agar dilution. However, treatment failures have occurred with such isolates when clindamycin is used, because of selection of mutations during therapy, leading to cMLSB resistance.
Inducible MLS resistance cannot be determined using standard susceptibility test method.
Double Disk diffusion is an easy method to detect iMLS phenotype, by placing an erythromycin disk in close proximity to a clindamycin disk on an agar plate.
In this study, 69 Erythromycin resistant Staphylococcal isolates were selected. They were identified by routine microbiological tests including macroscopic appearance on culture plate and hemolytic effect on blood agar, microscopic examination by Gram stain, biochemical reactions catalase, coagulase and DNAse tests and antibiotic susceptibility testing was done by disk diffusion method.
Clindamycin resistances (both constitutional and inducible) were tested in 69 Erythromycin resistant staphylococcal isolates by D- test.
In our results, the constitutive phenotype of MLSB resistance (EryR ClinR) was predominant 33/100 = 33%, while the inducible MLSB resistance (EryR ClinInd) was 17/100 = 17% and the MS phenotype (EryR ClinS) was 19/100 = 19%.
So it is clear that without the double-disk test, all Staphylococcus aureus isolates with inducible clindamycin resistance would have been misclassified as clindamycin susceptible; resulting in underestimated clindamycin resistance rate which may lead to therapeutic failure.
Also erythromycin resistant staphylococci should not be assumed to be clindamycin-resistant without prior testing. D-test is a simple test that can be used routinely in laboratories and can have reliable results.