Indian Journal of Pathology and Microbiology

ORIGINAL ARTICLE
Year
: 2010  |  Volume : 53  |  Issue : 2  |  Page : 281--286

Prevalence of bacterial pathogens causing ocular infections in South India


S Ramesh1, R Ramakrishnan2, M Jayahar Bharathi2, M Amuthan1, S Viswanathan1,  
1 Postgraduate Department of Microbiology, Sri Paramakalyani College, Alwarkuruchi, Tirunelveli, Tamil Nadu-627 412, India
2 Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Tirunelveli, Tamil Nadu- 627001, India

Correspondence Address:
M Jayahar Bharathi
Aravind Eye Hospital & Postgraduate Institute of Ophthalmology, Tirunelveli, Tamil Nadu-627 001
India

Abstract

Background / Aims: The eye may be infected from external sources or through intra-ocular invasion of micro-organisms carried by the blood stream. This study was undertaken to isolate and identify the specific bacterial pathogens causing ocular infections and to determine their in-vitro antibacterial susceptibilities to commonly used antibacterial agents. Materials and Methods: A retrospective analysis of all patients with clinically diagnosed bacterial ocular infections such as blepharitis, conjunctivitis, internal and external hordeolum, suppurative scleritis, canaliculitis, keratitis, dacryocystitis, preseptal cellulitis, endophthalmitis and panophthalmitis presenting between January 2005 and December 2005 was performed. Extra-ocular and intra-ocular specimens were collected and were subjected to direct microscopy and culture. Results: A total of 756 patients with bacterial ocular infections were analyzed, of which 462(61%) eyes had adnexal bacterial infection, 217(28.7%) had corneal infection, 6 (0.8%) had scleral involvement and the remaining 71(9.39%) eyes had infection of the intra-ocular tissues. The predominant bacterial species isolated was S. aureus (195 of 776; 25%) followed by S. pneumoniae (169 of 776; 21.78%) and coagulase negative staphylococci (142 of 776; 18.3%). The largest number of gram-positive isolates were susceptible to cefazolin (545 of 624; 87.34%), chloramphenicol (522 of 624; 83.65%) and gatifloxacin (511 of 624; 81.89%) and gram-negative isolates were to amikacin (127 of 136; 93.38%), gatifloxacin (125 of 136; 91.91%) and ofloxacin (119 of 136; 87.5%), while aerobic actinomycetes were to amikacin (100%), gatifloxacin (14 of 16; 87.5%), chloramphenicol (14 of 16; 87.5%) and ofloxacin (13 of 16; 81.25%). Conclusions: S. aureus frequently causes infections of eyelids and conjunctiva, S. pneumoniae of lacrimal apparatus and cornea and coagulase negative staphylococci causes intra-ocular infections. Of all routinely used antibacterials tested, flouroquinolones, especially gatifloxacin and ofloxacin represented a good choice for treating bacterial ocular infections.



How to cite this article:
Ramesh S, Ramakrishnan R, Bharathi M J, Amuthan M, Viswanathan S. Prevalence of bacterial pathogens causing ocular infections in South India.Indian J Pathol Microbiol 2010;53:281-286


How to cite this URL:
Ramesh S, Ramakrishnan R, Bharathi M J, Amuthan M, Viswanathan S. Prevalence of bacterial pathogens causing ocular infections in South India. Indian J Pathol Microbiol [serial online] 2010 [cited 2023 Feb 7 ];53:281-286
Available from: https://www.ijpmonline.org/text.asp?2010/53/2/281/64336


Full Text

 Introduction



The eye is a unique organ that is almost impermeable to almost all external agents. Continuous tear flow aided by the blink reflex mechanically washes substances from the ocular surface and prevents the accumulation of microorganisms. In addition, lysozyme, lactoferrin, secretory immunoglobulins, and defensins, which are present at high levels in tears, can specifically reduce bacterial colonization of the ocular surface. Under normal circumstances the conjunctiva and eyelids support a population of bacteria that do not cause diseases. [1] Although it is claimed that practically every conjunctival sac exhibitis some flora. Bacteria cultured from the conjunctival sac are usually similar to those found in the upper respiratory tract and the skin, with majority being gram-positive bacteria, most commonly Staphylococcus sp. and Corynebacterium sp. In addition, the eyelid margins and conjunctival sacs of healthy subjects can also contain gram-negative pathogens. [2] However, infections occur when microbes overwhelm host defense mechanisms.

The eye may be infected from external sources or through intra-ocular invasion of micro-organisms carried by the blood stream. [3] External bacterial infections of the eye are usually localized but may frequently spread to adjacent tissue, from the conjunctiva to the cornea, the inner eye, the orbit and the brain. The conjunctival sac and lid margins of the eye harbor a variety of micro-organisms; the bacteria present in the conjunctival sac form a constant source of infection to other parts of the eye. [4] The common eye infections caused by bacterial pathogens are blepharitis, conjunctivitis, internal and external hordeolum, microbial scleritis, canaliculitis, keratitis, dacryocystitis, preseptal cellulitis, orbital cellulitis, endophthalmitis and panophthalmitis. [4] Timely institution of appropriate therapy must be initiated to control the infections and thereby minimize the ocular morbidity. If they are not treated promptly, it may lead to sight threatening condition. In addition, some of the bacterial diseases such as orbital cellulitis and panophthalmitis may lead to life threatening conditions. For specific antibacterial treatment, isolation and identification of bacterial pathogens along with antibiotic susceptibility spectrum is essential. The bacterial aetiology and their susceptibility as well as resistant patterns may vary with geographical location according to the local population. [5],[6],[7],[8],[9],[10] Thus the current trends in the etiology of the bacterial ophthalmic infections and their susceptibilities must be updated to make a rational choice of initial antibiotic therapy. The purpose of this study was to identify the specific bacterial pathogens responsible for the development of ocular infections and to determine their in-vitro susceptibilities to commonly used antibacterial agents.

 Materials and Methods



A retrospective analysis included all patients with clinically diagnosed bacterial ocular infections such as blepharitis, conjunctivitis, internal and external hordeolum, suppurative scleritis, canaliculitis, keratitis, dacryocystitis, preseptal cellulitis, endophthalmitis and panophthalmitis treated in the period from January 2005 to December 2005. All patients were examined on the slit-lamp bio-microscope and bacterial infections included in this study were diagnosed by a group of ophthalmologist using standard protocols. [11],[12] After detailed ocular examinations, using standard techniques, specimens for culture and smear were obtained by scraping and swabbing the eyelid margin using sterile blade (# 15) on Bard-Parker handle and sterile broth-moistened cotton swabs in case of blepharitis. [4],[13],[14] Similarly, specimens were also obtained from scraping the corneal ulcers. For cases of suppurative scleritis, specimens were collected by scraping and swabbing the area of the suppurative abscess. Conjuctival cultures were obtained by wiping a broth-moistened swab across the lower conjunctival cul-de-sac in conjunctivitis cases and thick, tenacious purulent punctal discharge was collected from the canaliculus by pressure applied over the area of the eyelid that overlies the canaliculus in cases of canaliculitis. In cases of external and internal hordeolum, the abscesses were incised and the drained pus was obtained. For cases of dacryocystitis purulent material was collected from everted punta by pressure applied over the lacrimal sac area, and surgically exised lacrimal sac was also collected. Specimens from cases of pre-septal cellulitis were obtained after stab incision or through an open wound or drainage site, if present. Patients suspected of infectious endophthalmitis and panophthalmitis, lid and conjunctival specimens along with anterior chamber and vitreous fluids were obtained.

The obtained extra-ocular and intra-ocular specimens were subjected to culture onto the sheep blood agar, chocolate agar, non-nutrient agar, Sabouraud's dextrose agar, potato dextrose agar, thioglycollate medium and brain heart infusion broth, and direct microscopic examinations such as 10% KOH wet mounting, Gram-stain, Giemsa-stain, Kinyoun's acid-fast stain. Microbial cultures were considered significant if growth of the same organism was demonstrated on more than one solid phase medium, and/or if there was a confluent growth at the site of inoculation on one solid medium, and/or if growth of one medium to be consistent with direct microscopy findings (that is, appropriate staining and morphology with Gram-stain) and/or if the same organism was grown from repeated specimens. [14] The isolated bacterial strains were identified up to species level by using standard biochemical tests. [15] In-vitro susceptibility testing was performed by Kirby-Bauer disc diffusion method and interpreted using National Committee for Clinical Laboratory Standards (NCCLS) serum standards. [16]

 Results



During the study period of one year, a total of 756 eyes with culture-positive bacterial infections were analysed, of which 462(61%) eyes had ocular adnexal bacterial infection, 217(28.7%) had corneal infection, 6(0.8%) had scleral involvement and the remaining 71(9.39%) eyes had infection of the intra-ocular tissues. Out of 756 eyes, 736(97.35%) had infection with single species of bacteria and the remaining 20(2.64%) had infection with two species bacteria and thus a total of 776 bacterial isolates were recovered. The most frequently isolated bacterial isolates were gram-positive cocci (545 of 776; 70%) followed by gram-negative bacilli (123 of 776; 15.85%) and gram-positive bacilli (79 of 776; 10%). The predominant bacterial species isolated was S. aureus (195 of 776; 25%). The bacterial isolates recovered from eyes with infections are presented in [Table 1]. Most of the bacterial isolates were susceptible to gatifloxacin (650 of 776; 83.76%) and ofloxacin (626 of 776; 80.67%). These are summarized in [Table 2].

 Discussion



The most common bacterial species isolated in this study is S. aureus (25.13%) followed by S. pneumoniae (21.78%) and coagulase-negative staphylococci (18.29%). S. aureus predominates in eyelids and conjunctival infections, S. pneumoniae in lacrimal sac and corneal infections, and coagulase-negative staphylococci in intra-ocular tissues infections. The reviews of literatures show that eyelid margins provide a favorable environment for infection and generally involve the skin, eyelashes, and associated glands anterior to the gray line or mucocutaneous junction. Acute and chronic infection of the eyelids margin and glands of the eyelid are reported predominantly by S. aureus and S. epidermidis. [17],[18],[19],[20] Although Staphylococcus spp. has been frequently recovered from eyes with lid infections, the current prevalence of Corynebacterium spp. is increased in causing eyelids infections. The conjunctiva is predisposed to infection by diverse micro-organisms. The principal routes of inoculation are airborne droplets, hand-to-eye contact, and spread from the ocular adnexa, including the lacrimal system, nose, and paranasal sinuses. [21] The prevalence of S. aureus in causing conjunctivitis has been reported to be higher in many parts of the world. [22],[23],[24]

The most common infection of the lacrimal apparatus is dacryocystitis. The basis for this infection is blockage of the lacrimal duct system resulting in accumulation of tears and creation of a fertile environment for secondary bacterial infection, and dacryolith formation. [12],[25] The proportion of S. pneumoniae (32%) isolated in this study from cases of dacryocystitis is found to be higher. Similarly, Bareja et al.[26] reported higher rate of S. pneumoniae (29%) in dacryocystitis in North India, where as Chaudhry et al.[27] (50%) and Brook et al.[28] (30%) reported higher prevalence of Staphylococcus spp. from eyes with acute dacryocystitis. In case of keratitis, S. pneumoniae (37.72%) is found to be the predominant cause followed by Staphylococcus spp. and (29%) and Pseudomonas spp. (17.72%) in this study. In contrast, predominance of Pseudomonas spp. has been reported in Ghana and Hong Kong and Staphylococcus spp. in South Florida and Switzerland. [29],[30],[31],[32] The rate of prevalence of Moraxella spp.(19%) and Corynebacterium spp. (16%) causing keratitis was reported to be higher in New Zealand. [33] The principal route of intra-ocular infection is exogenous and may come from the conjunctival flora or from outside contaminants. [34] Endogenous microbial endophthalmitis occurs most commonly due to Streptcoccus species, S. aureus, and B. cereus infections in compromised hosts or intravenous drug abusers and usually occurs through the posterior ocular circulation. [34],[35],[36] In this study there were three cases of endogenous endophthalmitis and these were due to Haemophilus sp., S. pneumoniae and Pseudomonas aeruginosa and their prevalence has been reported in many studies.[34],[37] Coagulase negative staphylococci are found to be predominant cause for post-operative and post-traumatic endophthalmitis in this series.

The analysis on in-vitro susceptibility testing shows that cefazolin, vancomycin and chloramphenicol demonstrated greatest efficacy against gram-positive isolates alone, while gatifloxacin and ofloxacin demonstrated greatest efficacy against both gram-positive and gram-negative isolates in this series. Frequent and routine use of antibiotics for all bacterial ocular infections in our population has decreased susceptibility to most of the tested antibiotics. [38] Besides that, all fluoroquinolones tested in this study, gatifloxacin and ofloxacin showed high efficacy against all bacterial isolates and proving that in our community quinolones, especially gatifloxacin and ofloxacin are a good choice for treating ocular infections at present. This report documents the bacterial etiology of ocular infections necessary for regional-wise evidence based understanding of the diseases.

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