Indian Journal of Pathology and Microbiology

LETTER TO EDITOR
Year
: 2014  |  Volume : 57  |  Issue : 4  |  Page : 662--663

Changing trend in susceptibility to vancomycin of methicillin susceptible and resistant Staphylococcus aureus clinical isolates from a tertiary care centre


Munesh K Gupta, Tuhina Banerjee, Shampa Anupurba, Ragini Tilak 
 Department of Microbiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi - 221 005, Uttar Pradesh, India

Correspondence Address:
Dr. Tuhina Banerjee
Department of Microbiology, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh
India




How to cite this article:
Gupta MK, Banerjee T, Anupurba S, Tilak R. Changing trend in susceptibility to vancomycin of methicillin susceptible and resistant Staphylococcus aureus clinical isolates from a tertiary care centre.Indian J Pathol Microbiol 2014;57:662-663


How to cite this URL:
Gupta MK, Banerjee T, Anupurba S, Tilak R. Changing trend in susceptibility to vancomycin of methicillin susceptible and resistant Staphylococcus aureus clinical isolates from a tertiary care centre. Indian J Pathol Microbiol [serial online] 2014 [cited 2021 Nov 30 ];57:662-663
Available from: https://www.ijpmonline.org/text.asp?2014/57/4/662/142730


Full Text

Editor,

The problem with Staphylococcus aureus (S. aureus) is its ability to present various types of antimicrobial resistance along with widespread dissemination of multidrug-resistant (MDR) strains. Not only had this organism shown resistance to penicillin within 4 years of its introduction, but also acquired resistance to several classes of antibiotics. Present situations are such that virtually all S. aureus isolates are resistant to natural penicillin and derivatives, considerably resistant to methicillin with prevalence of MRSA (methicillin-resistant S. aureus) varying from 8% to 71% [1] and emerging as resistant to vancomycin with infrequent reports of VRSA (vancomycin-resistant S. aureus) and VISA (vancomycin-intermediate S. aureus) from the subcontinent. [2],[3] To tackle this grave situation, constant monitoring of these isolates is important. We tested the trend of vancomycin susceptibility of MRSA and MSSA (methicillin-susceptible S. aureus) isolates over a period of 1 year in a tertiary care center in North India.

A total of 152 non-duplicate S. aureus isolates were collected from clinical samples. All the S. aureus isolates were screened for methicillin resistance using a 30 μg cefoxitin disc (Hi Media, India) on Mueller Hinton agar according to CLSI guideline. [4] Determination of minimum inhibitory concentration (MIC) against vancomycin (Hi Media, India) was done by agar dilution method. [4] S. aureus ATCC 25923 was used as control. For statistical analysis, z-test for proportions was used to compare the MIC values between the methicillin-susceptible and -resistant isolates (P < 0.05).

Of the 152 S. aureus isolates, 70 (46.05%) were screened to be MRSA and 82 (53.94%) were MSSA. Most of the isolates were from pus samples isolated from the patients attending the indoor services (48.68%). For all the isolates, vancomycin MIC varied from 0.5 to 2 μg/ml and none were resistant [Table 1]. Majority of the isolates (73.2% of MRSA and 67.3% of MSSA) showed vancomycin MIC ≤0.5 μg/ml. Interestingly, isolates with higher vancomycin MIC values (1-2 μg/ml) were MSSA (38 of 82 isolates) as compared to MRSA (15 of 70 isolates) (P = 0.00132). {Table 1}

This observation is of importance because a statistically significant shift in vancomycin MIC from 1 to 2 μg/ml has previously been reported among the MRSA isolates but not in the MSSA isolates. [5] Widespread vancomycin use for treatment of MRSA infections have often been implicated in the emergence of higher MIC values. Simultaneously, owing to the broad spectrum activity of vancomycin against Gram-positive cocci, its empirical use especially in the intensive care units and the selective pressure thus caused might be another contributing factor, even in susceptible isolates. In this respect, it is often forgotten that in vitro activity of vancomycin against MRSA and MSSA is less effective as compared to any β lactam agent [3] and hence its empirical use is still debatable.

Lastly, whether a change in susceptibility of these isolates to vancomycin noted here reflects the actual situation or is an incidental finding can only be validated by long-term monitoring studies. However, based on these observations, a prudent approach would be besides limiting empirical use, determination of MIC values for all S. aureus isolates prior to administration of vancomycin, in order to avoid selection of resistant isolates in future.

References

1Bhattacharya S. Is screening patients for antibiotic-resistant bacteria justified in the Indian context? Indian J Med Microbiol 2011;29:213-7.
2Tiwari HK, Sen MR. Emergence of vancomycin resistant Staphylococcus aureus (VRSA) from a tertiary care hospital from northern part of India. BMC Infect Dis 2006;6:156.
3Assadullah S, Kakru DK, Thoker MA, Bhat FA, Hussain N, Shah A. Emergence of low level vancomycin resistance in MRSA. Indian J Med Microbiol 2003;21:196-8.
4Clinical Laboratory and Standards Institute, Performance standard for antimicrobial susceptibility testing; Twenty first informational supplement. 2011;M100:31(1, Clinical Laboratory and Standards Institute, Wayne, PA.
5Dhawan B, Gadepalli R, Rao C, Kapil A, Sreenivas V. Decreased susceptibility to vancomycin in meticillin-resistant Staphylococcus aureus: A 5 year study in an Indian tertiary hospital. J Med Microbiol 2010;59:375-6.