title: Heterogeneous vancomycin-intermediate among methicillin resistant Staphylococcus aureus.
abstract: BACKGROUND
  Hetero-resistance vancomycin intermediate Staphylococcus aureus (hVISA) is phenotype, which on in-vitro susceptibility test is vancomycin susceptible (VSSA) but has a minority population of vancomycin intermediate (VISA). hVISA is responsible for vancomycin treatment failure. Population Analysis Profile- Area under Curve (PAP-AUC) is a test for detection of hVISA; however, this test is unsuitable for clinical microbiology laboratory. Tests, such as Brain Heart Infusion Agar with 6 μg/ml vancomycin (BHIA6V), E test and Macromethod E Test (MET) are available; however reported to have variable results.
  
  
  METHODS
  58 clinical isolates of Methicillin resistant S aureus (MRSA) having MIC of vancomycin more than 1 μg/ml by E test and agar dilution were analyzed by PAP-AUC, BHIA6V and MET.
  
  
  RESULTS
  The prevalence of hVISA was 6.9%. hVISA isolates were having vancomycin E test MIC >2 μg/ml. Sensitivity of BHIA6V, MET and E test with MIC >2 μg/ml were 0.75, 0.67 and 1.0 respectively; however, positive predictive values (PPV) were 0.43, 0.4 and 0.27 respectively with PAP-AUC. PAP-AUC ratio correlated with MIC by E test and MET.
  
  
  CONCLUSIONS
  There is need for screening MRSA isolates showing in-vitro vancomycin susceptibility ≤2 μg/ml by agar dilution method for detection of hVISA. PAP-AUC test is unsuitable for routine laboratory testing. BHIA6V, MET and E test can be used for screening, however have low PPV.
authors.affiliation: Professor (Microbiology), INHS Asvini Colaba, Mumbai, India.
authors.forename: C N
authors.initials: CN
authors.lastname: Chaudhari
authors.affiliation: Medical Officer (Microbiology), Military Hospital Gwalior, India.
authors.forename: K
authors.initials: K
authors.lastname: Tandel
authors.affiliation: Associate Professor, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
authors.forename: N
authors.initials: N
authors.lastname: Grover
authors.affiliation: Senior Advisor (Pathology, Microbiology & Virology) Army Hospital (R&R), Delhi Cantt 10, India.
authors.forename: S
authors.initials: S
authors.lastname: Sen
authors.affiliation: Resident, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
authors.forename: P
authors.initials: P
authors.lastname: Bhatt
authors.affiliation: Professor & Head, Department of Microbiology, Armed Forces Medical College, Pune 411040, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Sahni
authors.affiliation: Professor & Head (Microbiology), AIIMS, Bhubaneswar, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Praharaj
keywords: MRSA; PAP-AUC; Vancomycin; hVISA