Vancomycin resistance among MRSA

Sir,

The study by Thati et al1 brings to limelight an alarming situation of vancomycin resistance in methicillin resistant Staphylococcus aureus (MRSA) in south India. There are certain points mentioned in the article which need clarification.

• The authors have not mentioned how they screened the isolates for MRSA. There is no point in testing oxacillin and methicillin together and they require a different temperature of incubation.

• DNA extraction step in the PCR could have been elaborated.

• How did the authors validate the PCR? There is no mention of running a positive control.

• It is absurd to mention that MRSA isolates were also resistant to ceftazidime. MRSA by definition are considered resistant to all beta- lactam antibiotics irrespective of the zones of inhibition.

• The authors mention that all vancomycin resistant S. aureus (VRSA) isolates were inducible for clindamycin resistance but the Table shows that two of the isolates (VRSA3 & VRSA6) were susceptible to erythromycin. How did authors determine inducible resistance to clindamycin when the isolates were susceptible to erythromycin?

• How was the presence of mecA (PCR or latex agglutination) confirmed?

• The authors have described an alarming situation but fail to suggest an alternative for treatment. They should have tested linezolid and quinopristin/dalfopristin and reported their sensitivity.

• The authors have done MIC of vancomycin but failed to mention the MIC₉₀ and MIC₅₀ values.

• The authors should have highlighted the presence or absence of MIC creep in their isolates.

• The authors should have determined the correlation between the diameters of vancomycin disc diffusion and MIC especially when they were in the intermediate range.

• The authors have not mentioned about the VISA strains or their PCR results?

• The authors should have mentioned the clinical source of at least the VISA and VRSA isolates.