الفهرس 
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Abstract
ethicillin-resistant Staphylococcus aureus (MRSA) has
emerged worldwide as a nosocomial pathogen of major
importance, and the incidence of infections caused by MRSA
continues to increase. As compared to methicillin-sensitive
Staphylococcus aureus strains, MRSA infection has been
associated with higher mortality and morbidity rates, longer
hospital stays, and higher hospital charges.
Biocides are critical components of intervention
strategies used in clinical medicine for preventing the
dissemination of nosocomial infections. However, MRSA
isolates with decreased biocide susceptibilities have been
isolated from clinical samples, and MRSA isolates carrying
antiseptic-resistance gene(s) have been prevalent worldwide.
This has raised concerns that, as for antibiotics, intensive
exposure of hospital pathogens to biocides may result in the
emergence of resistance to these agents.
The aim of the present work was to study the
susceptibility of methicillin-resistant isolates of Staph. Aureus,
obtained from different clinical samples, to commonly used
biocides and to determine the prevalence of the biocide
resistance genes, qacA/B and smr, among these isolates.
M
The study included 30 MRSA isolates as well as 30
isolates of methicillin-sensitive Staph. Aureus (MSSA) as
controls. Isolates were recovered from different clinical
samples submitted to the Microbiology Laboratory for routine
culture and susceptibility testing. All isolates were tested for
their susceptibility to commonly used biocides (PVP-I2,
gluteraldehyde, savlon, hypochlorite, and phenol) using the
broth macrodilution method; and for the presence of the
biocide resistance genes, qacA/B and qacC, using the
polymerase chain reaction method.
In the present study, both the MRSA and MSSA isolates
were effectively inhibited by the user’s defined concentrations
of PVP-I2 (10%), gluteraldehyde (2%), Savlon (3.3%) and
Phenol (10%). However, the MRSA isolates had statistically
higher MICs to PVP-I2, Savlon, and Phenol as compared to the
MSSA isolates.
Unlike the results obtained for the PVP-I2,
gluteraldehyde, savlon, and phenol, the MIC of hypochlorite
for the MRSA isolates were significantly higher than those for
the MSSA isolates. The MIC of the MRSA isolates exceeded
the user defined concentrations (MIC=0.825).
The qacA/B gene was detected in 43.3% of the studied
Staph. Aureus isolates. There was a statistically significant
difference between the MRSA isolates and the MSSA isolates
regarding the detection of the qacA/B gene since the gene was
detected in 63.3% of MRSA isolates and in 23.3% of MSSA
isolates. Also, the qacC gene was detected in 38.3% of the
studied Staph. Aureus isolates. The gene was detected in
63.3% of the MRSA isolates and in 13.3% of the MSSA
isolates.
A highly significant difference was found between the
qacA/B +ve isolates and the qacA/B -ve and qacC -ve isolates
regarding the MICs to savlon, hypochlorite and phenol. Yet,
no significant difference was observed between both groups
regarding the susceptibility to PVP-I2 and gluteraldehyde.
Furthermore, a highly significant difference was found
between the qacC +ve isolates and the qacA/B
-ve and qacC -ve isolates regarding the MICs to savlon,
hypochlorite and phenol. Yet, no significant difference was
observed between both groups regarding the susceptibility to
PVP-I2 and gluteraldehyde.
Finally, a significant difference was found between the
qacA/B +ve and the qacC +ve isolates regarding the MICs to
savlon with the qaCA/B +ve group being more resistant to
savlon than the qacC+ve group. No significant difference was
observed between both groups regarding their susceptibility to
PVP-I2, gluteraldehyde, hypochlorite and phenol.
We concluded that although the studied MRSA isolates
were susceptible to most of the commonly used biocides at the
user’s defined concentrations, there was a significant
difference between the MICs of MRSA isolates as compared
to the MSSA isolates. We call attention to the high prevalence
rate of biocide resistance genes detected in our studied MRSA
isolates. Carefulness of controlling their survival in the
hospital environment must be considered since the high
prevalence of these genes might be either due to selective
pressure imposed by the misuse of biocides in our hospitals or
due to the cross-resistance and co-resistance between biocides
and antibiotics.