Cheema K H, Javed I, Mushtaq S, Anwar M S.
Heteroresistant Vancompycin Intermediate Staphylococcus Aureus in a Tertiary Care Hospital.
Biomedica Jan ;33(3):192-6.

Background and Objectives: The burden of heteroresistant Vancomycin Intermediate Staphylococcus aureus (HVISA) and the issue of reduced vancomycin sensitivity are still unknown in Pakistan. This study was carried out to determine antimicrobial sensitivity and detect hVISA in clinical isolates of MRSA by Glycopeptide Resistance Detection (GRD) E test. This was a cross-sectional descriptive study, performed at the Pathology Department, Postgraduate Medical Institute, Lahore, from May 2014 to May 2015. Methods: The study was carried out on 41 MRSA isolates from different specimens collected from patients admitted in Lahore General hospital, Lahore. Antimicrobial susceptibility testing was performed on all isolates according to modified Kirby-Bauer method and interpreted according to CLSI 2015 criteria. After screening for methicillin resistance by cefoxitin disc method, MIC of vancomycin was determined by standard E test. Isolates with a vancomycin MIC of 1-2 mcg/ml were screened for heteroresistance by Glycopeptide Resistance Detection (GRD) E-test. Results: Majority of the MRSA isolates were recovered from pus 26 (63.4%) followed by tissue sample 04 (9.8%) and blood 03 (7.3%), two each form CVP tip, bronchoalveolar lavage and catheter tip (4.9%) and one each from CSF and pleural fluid (2.4%). Among the antibiotics, resistance to gentamicin was highest among MRSA isolates (73%), followed by TMP-SMZ (68%), ciprofloxacin (66%), erythromycin (51%), clindamycin (44%) and doxycycline (41%). All MRSA isolates in our study were sensitive to linezolid. Four (9.75%) MRSA isolates were confirmed as hVISA by E test GRD.The frequency of hVISA among MRSA isolates was higher in blood specimens (66.6%) followed by pus (7.69%). Conclusion: The issue of heteroresistance is still unknown in Pakistan. This study is the first attempt at detecting heteroresistance VISA (hVISA) in MRSA isolates. Patients suffering from MRSA infection should be screened for hVISA so that prompt antimicrobial therapy can be initiated in order to avoid treatment failures. Further studies are required to address this issue and its clinical relevance in our country.

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