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   Table of Contents      
Year : 2005  |  Volume : 53  |  Issue : 1  |  Page : 59-60

Speciation of Coagulase Negative Staphylococcus causing Bacterial Keratitis

Department of Microbiology, Aravind Eye Hospital, Coimbatore, India

Date of Submission07-Jun-2003
Date of Acceptance18-Nov-2003

Correspondence Address:
M Bhaskar
Department of Microbiology, Aravind Eye Hospital, Avinashi Road, Coimbatore- 641 014, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0301-4738.15288

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Thirty-five coagulase negative Staphylococcus (CoNS) cultured from corneal ulcer were speciated and antibiotic sensitvity tested. S epidermidis was the commonest isolate and it was sensitive to ampicilin and vanconycin.

Keywords: Coagulase Negative Staphylococcus, bacterial keratitis, antibiotic susceptibility

How to cite this article:
Manikandan P, Bhaskar M, Revathy R, John RK, Narendran K, Narendran V. Speciation of Coagulase Negative Staphylococcus causing Bacterial Keratitis. Indian J Ophthalmol 2005;53:59-60

How to cite this URL:
Manikandan P, Bhaskar M, Revathy R, John RK, Narendran K, Narendran V. Speciation of Coagulase Negative Staphylococcus causing Bacterial Keratitis. Indian J Ophthalmol [serial online] 2005 [cited 2020 Dec 3];53:59-60. Available from: https://www.ijo.in/text.asp?2005/53/1/59/15288

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Staphylococci are gram-positive, non-motile, non-sporulating and capsulated spherical organisms. Detection of the enzyme coagulase distinguishes them as Staphylococcus aureus , a coagulase-positive pathogen, and coagulase-negative Staphylococci . The latter are the indigenous flora of our skin and mucous membrane. Coagulase-negative Staphylococci are isolated in large numbers from diverse ophthalmic conditions like chronic blepharitis, purulent conjunctivitis and suppurative keratitis. As they form the part of the normal flora, effective management may not be aimed at curtailing coagulase-negative Staphylococci (CoNS). Moreover, if CoNS is isolated along with another organism, its pathogenic potential may be totally neglected. Hence, it is necessary to speciate CoNS and understand the pathogenic potential of individual CoNS. This study was framed as a pilot study to determine the prevalence and resistance patterns of specific CoNS in bacterial keratitis.

  Materials and Methods Top

All the coagulase-negative Staphylococci isolated from infected corneal ulcers between May and November 2002 in the Microbiology Diagnostic Laboratory, Aravind Eye Hospital, Coimbatore were included in this study. Standard procedures were followed for specimen collection and culture isolation.[1] Specimens showing growth of the white non-haemolytic colonies in more than one streak on blood agar, with direct microscopy showing gram-positive cocci in clusters were considered significant. All these organisms were labelled CoNS after reconfirmation with the coagulase test. The strains were streaked on to nutrient agar for further biochemical tests. Speciation was done based on biochemical tests,[2] which included coagulase production, oxidase, acetoin production and susceptibility to novobiocin and a set of sugars (lactose, maltose, mannitol, fructose, sucrose, trehalose, xylose, cellobiose, raffinose and mannose). Antibiotic susceptibility testing was done by the Kirby-Bauer disc diffusion method for ampicillin, cefazolin, cephotaxime, chloramphenicol, ciprofloxacin, gentamicin, ofloxacin, and vancomycin. The susceptibility of the organisms to these antibiotics was based on NCCLS standards.[3]

  Results Top

In the study period we isolated 35 strains of clinically significant coagulase-negative Staphylococcus . This accounted for 20.9 % (35 of 167) of the total bacterial isolation. Nineteen (54.2%) of 35 patients were males and 30 (85.7%) patients were above the age of 40. Incidence of CoNS was significantly higher among those 60 and older. Staphylococcus epidermidis was the predominant CoNS (57.1 %) isolate followed by Staphylococcus hominis (22.8 %). The details are shown in the [Table - 1]. Three strains (8.5%) (S.epidermidis , S.lugdunensis , and S. simulans ′ (one each) were sensitive to all the antibiotics used. Four (11.4%) strains (S.epidermidis , n=3, and S.hominis n = 1) were resistant to all the antibiotics used. Others showed variable sensitivity. Sensitivity to ciprofloxacin, the commonly used second line antibiotic was 60% [Table - 2].

  Discussion Top

Coagulase-negative Staphylococci are a leading cause of infected corneal ulcers in elderly patients. Since CoNS form a part of the normal flora and are ubiquitous, the significance of these isolates in the pathogenesis of corneal ulcer is unjustifiably disregarded.

Similar to other studies,[4],[5] Staphylococcus epidermidis was the most common isolate in our study, accounting for more than half (57.1%) the cases. CoNS infections may be more prevalent in elderly patients due to low immunity. But contrary to the Hyderabad study[5] we did not isolate CoNS from patients below 19 years of age.

In our study 62.8% of organisms were sensitive to ciprofloxacin though increasing resistance to ciprofloxacin is reported in India and USA studies.[6],[7] Multidrug resistance of ciprofloxacin-resistant strains to other drugs is a significant problem.[8] In our study 40% of ciprofloxacin resistant strains were also resistant to cefazolin, and four (11.4%) strains were resistant to all the antibiotics tested. This is of concern because the spread of such strains in hospitals could be alarming to immuno-compromised patients.

Though it is too early to draw any conclusion from this study, it clearly suggest, that all CoNS are not Staphylococcus epidermidis , and bacterial keratitis is caused by CoNS other than Staphylococcus epidermidis too which are equally pathogenic. Hence speciation of CoNS is important for appropriate management. Future studies are needed to assess their pathogenic potentials.

  References Top

Wilhelmus KR. Bacterial keratitis In: Pepose JS, Holland GN, Wilhelmus KR, editors, Ocular infection and Immunity. St. Louis: Mosby; 1996. pp 970-1031.  Back to cited text no. 1
Barrow GI, Feltham RKA. Characters of Gram-positive bacteria. In: Cowan and Steel's Manual for the identification of Medical bacteria. 3rd edition. UK: Cambridge University Press; 1993.p 50.  Back to cited text no. 2
Villanova PA. Performance standards for antimicrobial disk susceptibility tests. In: National Committee for Clinical Laboratory Standards. Approved Standard. 7th ed. National Committee for Clinical Laboratory Standards; 2000;20:M2-A7.  Back to cited text no. 3
Kunimoto DY, Sharma S, Garg P, Gopinathan U, Miller D, Rao GN. Corneal ulceration in the elderly in Hyderabad, south India. Br J Ophthalmol 2000;84:54-59.  Back to cited text no. 4
Kunimoto DY, Sharma S, Reddy MK, Gopinathan U, Jyothi J, Miller D, et al. Microbial Keratitis in children. Ophthalmology 1998;105:252-57.  Back to cited text no. 5
Kunimoto DY, Sharma S, Garg P, Garg P, Rao GN. In vitro susceptibility of bacterial keratitis pathogens to ciprofloxacin. Emerging resistance. Ophthalmology 1999;106:80-85.  Back to cited text no. 6
Goldstein MH, Kowalski RP, Gordon J. Emerging flurocqunolone resistance in bacterial keratitis. A 5-year review. Ophthalmology 1999;106:1313-18.  Back to cited text no. 7
Pinna A, Zanetti S, Sotgiu M, Sechi LA, Fadda G, Carta F. Identification and antibioic susceptibility of coagulase negative staphylococci isolated in corneal/external infections. Br J Ophthalmol 1999;83:771-73.  Back to cited text no. 8


  [Table - 1], [Table - 2]

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