الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
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 hVISA and VISA infection. According to
CLSI, broth microdilution is considered the gold standard to
determine vancomycin MIC. However, because it is time
consuming, a considerable number of clinical laboratories do
not use it as routine methodology. Other techniques have been
widely used, with variable sensitivity and specificity, such as Etest
and automated systems. The only CLSI vancomycin screen
agar method in place for clinical isolates for the detection of
vancomycin resistant S. aureus (VRSA) and possibly VISA is
BHI agar containing 6 mg/liter vancomycin (BHIA6V), a
method originally established for detection of vancomycin
resistance in enterococci , however this method have a very low
sensitivity for the detection of h-VISA. The CDC recommends
a supplemental test for VISA detection, with the caveat that
strains with vancomycin MICs of 4 ug/ml will not be reliably
identified and screen agar plates with a lower concentration of 3
mg/l vancomycin have a very high false positive rate.
In our study, One hunderds MRSA isolates were
subjected for detection of S.aureus with reduced susceptibility
to vancomycin by vancomycin screening agar with different
concentrations 2, 4, 6 ug/ml with and without casein, Vitek 2
Summary
104
automated system for determination of vancomycin MIC
(Biomerieux, France) and broth microdilution method for
detection of vancomycin MIC according to CLSI 2015 as
reference method. Out of 100 MRSA isolates, vancomycin
screening agar 2ug/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 2ug/ml
vancomycin.
Vancomycin screening agar 2ug/ml with casein gave the
best sensitivity among all vancomycin screening agar tested.
Vancomycin screening agar 2ug/ml with casein detected 30/30 of
isolates that were VISA by BMD with 100% sensitivity and
74.3% specificity. Vancomycin screening agar 2ug/ml without
casein detected 20/30 0f isolates that were VISA by BMD with
66.7% sensitivity and 85.7% specificity. Vancomycin screening
agar 4ug/ml with casein detected 20/30 0f isolates that were
VISA by BMD with 66.7% sensitivity and 84.3% specificity.
Vancomycin screening agar 4ug/ml without casein detected
20/30 0f isolates that were VISA by BMD with 66.7%
sensitivity and 85.7% specificity. Both vancomycin screening
agar 4 ug/ml with and without casein failed to detect 10 isolates
out of 30 (33.3%) that were VISA positive by BMD.
Vancomycin screening agar 6ug/ml with casein detected 20/30
Summary
105
0f isolates that were VISA by BMD with 66.7% sensitivity and
85.7% specificity. Vancomycin screening agar 6ug/ml without
casein detected 19/30 0f isolates that were VISA by BMD with
63.3% sensitivity and 85.7% specificity. VITEK 2 system
failed to detect any isolates with reduced susceptibolity to
vancomycin. They were sensitive to linezolid (100%) followed
by tigecyclin (99%) then Quinupristin-dalfopristin (91%).
However, most of the isolates were resistant to tetracyclin
(85%) followed by gentamicin (80%) then ciprofloxacin (63%).