Author/Authors :
Akbariyeh، Hilda نويسنده Department of Microbiology, Faculty of Basic Sciences,
Ahar Branch, Islamic Azad University, Ahar, Iran , , Nahaei، Mohammad Reza نويسنده , , Hasani، Alka نويسنده Department of Microbiology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran. , , Pormohammad، Ali نويسنده Research Center of Infectious Diseases and Tropical Medicine, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran. ,
Abstract :
Staphylococcus aureus (S. aureus) is a bacterium responsible for a
variety of clinical conditions, ranging from skin diseases and pneumonia
to bloodstream infections. Methicillin-resistant S. aureus (MRSA) is a
perpetual concern in medical settings due to its resistance to many
antibiotics; accordingly, the periodic surveillance of antibiotic
susceptibility patterns is an everlasting concern in the clinical arena.
This quantitative study aimed to detect intrinsic and acquired
methicillin resistance precisely, testing for the effect of
beta-lactamase inhibitors and assessing the antibiotic sensitivity
patterns of clinical isolates for S. aureus. One hundred and five
isolates of S. aureus were ascertained for their resistance toward
methicillin by agar screening and agar dilution (minimal inhibitory
concentration [MIC]) methods. Acquired resistance was detected in
methicillin-resistant isolates by the addition of beta-lactamase
inhibitors. The tolerance phenomenon in these isolates was determined by
a ratio of their minimal bactericidal concentration (MBC) over their
MIC. Methicillin resistance was detected in 38% of S. aureus isolates,
confirmed by the agar dilution method and MIC > 8 µg/mL
(intrinsic resistance). These isolates were mostly collected from ICU
burn patients (32.5%). No isolate was found to have acquired resistance
or modified (MOD) type resistance. Tolerance was not observed in any
isolate. Antibiotic susceptibility toward other therapeutic agents
showed that all intrinsic methicillin-resistant isolates were
susceptible to vancomycin; however, methicillin-susceptible isolates
were the least sensitive (30%) to penicillin. Methicillin resistance is
a specialized concern in clinical studies, and it is mandatory to detect
this mechanism by an accurate method that is updated periodically.
Increasing the resistance of S. aureus to multiple antibiotics
underlines the need for intermittent resistance surveillance.
