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Decreased susceptibility to quinolones in methicillin-resistant Staphylococcus aureus isolated from ocular infections at a tertiary eye care centre
  1. B Bagga1,
  2. A K Reddy2,
  3. P Garg1
  1. 1Cornea and Anterior Segment Services, LV Prasad Eye Institute, Hyderabad, India
  2. 2Jhaveri Microbiology Centre, Prof Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, LV Prasad Eye Institute, Hyderabad, India
  1. Correspondence to Dr A K Reddy, Jhaveri Microbiology Centre, Hyderabad Eye Research Foundation, LV Prasad Eye Institute, Road No. 2 Banjara Hills, Hyderabad 500 034, India; ashokkumar{at}

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Methicillin-resistant Staphylococcus aureus (MRSA) is a serious cause of morbidity and mortality worldwide because of its multiple-drug resistance.1 In the past, MRSA infections were considered as hospital acquired; however, in the 1990s, serious MRSA infections were reported in patients with no previous contact with the healthcare system.2 Aggressive infections due to MRSA were observed in the eye and orbit in patients with no hospital exposure.3 There are very few reports on ocular MRSA infections, and to the best of our knowledge, there are no reports on MRSA in ocular infections from India. The present study was carried out to study the changing trends of methicillin susceptibility in S aureus isolated from different ocular infections and to analyse the susceptibility of MRSA to quinolones and vancomycin.

We performed a retrospective review of microbiology records from January 2006 through December 2008 to determine the susceptibility pattern of S aureus isolated from corneal scrapings, vitreous, conjunctival swabs and lacrymal sac and adnexa to oxacillin (methicillin). Staphylococcus was identified to species level by conventional biochemical tests and by using Mini API (bioMérieux, France). Antibiotic susceptibility of the isolates was determined by using the Kirby Bauer disk diffusion method on cation-adjusted Mueller Hinton agar to oxacillin, ciprofloxacin, ofloxacin, moxifloxacin gatifloxacin and vancomycin. Plates were incubated at 35°C for 16–18 h in non–carbon dioxide incubator. The results were interpreted as per the Clinical Laboratory Standards Institute guideline.

Statistical analysis

Changing the trends of oxacillin susceptibility in S aureus isolates was analysed by using χ2 test, and the susceptibility evaluation of MRSA to different antibiotics was done by correlation analysis.

A total of 199 S aureus isolates were isolated during the study period. Of these, 74 were isolated from the corneal scrapings; 43, from the conjunctival swabs; 11, from the vitreous and 71 from the lacrimal sac and adnexa. Of 199 isolates, 68 (34.1%) were resistant to methicillin. Of 68 MRSA isolates, 22 (32.3%) were isolated from the conjunctiva, 23 (33.8%) were isolated from the lacrimal sac and adnexa, 20 (29.4%) were isolated from the corneal scrapings and 3 (4.4%) were isolated from the vitreous. All the 199 (100%) S aureus isolates were sensitive to vancomycin.

Yearwise distribution of S aureus isolates and their susceptibility to methicillin are shown in table 1.

Table 1

Susceptibility of S aureus to methicillin

The susceptibility rates of methicillin-resistant and methicillin-susceptible S aureus (MSSA) to quinolones are shown in table 2.

Table 2

Susceptibility of methicillin-resistant and methicillin-susceptible S aureus to quinolones

Methicillin-resistant S aureus causes severe ocular infections,3 4 and prevalence of ocular MRSA infections varies from 3% to 30%.1 5 In this laboratory-based investigation, the proportion of MRSA ocular infections increased from 26% in 2006 to 38% in 2008. An annual increase in MRSA incidence was observed in our study.

Hospital-acquired MRSA strains are usually multidrug resistant.6 Community-acquired MRSA, though resistant to methicillin and other β lactam antibiotics (penicillin, cephalosporins and carbapenems), often remain sensitive to many other classes of antibiotics including trimethoprim sulfamethaxazole and tetracyclines.6 Resistance to macrolides, clindamycin and fluoroquinolones varies by region.6 In this study, the comparison of susceptibility of MRSA and MSSA isolates with different quinolones revealed that MRSA showed a statistically significant increase in resistance to ciprofloxacin, moxifloxacin, gatifloxacin and ofloxacin when compared with MSSA. Of all the quinolones tested, gatifloxacin showed the highest susceptibility (77%) to MRSA.

The drug of choice for MRSA infection is vancomycin. In our study, all the MRSA and MSSA isolates were sensitive to vancomycin, and vancomycin continues to be the drug of choice for MRSA. We observed that there is no significant difference in the incidence of MRSA isolated from different ocular infections.


The authors thank the Hyderabad Eye Research Foundation.


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  • Funding This study was funded by the Hyderabad Eye Research Foundation.

  • Competing interests None.

  • Provenance and peer review Not commissioned; not externally peer reviewed.

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