**1. Introduction**

year review. Ophthalmology.2012: May 23.[Epub ahead of print] ISSN 0161-6420/12/

[17] Conville PS, Witebsky FG. Nocardia, Rhodococcus, GordoniaActinomadura,Strepo‐ tomyces and other aerobic Actinomycetes In Vesalovic J, Carroll KC, Funke G, Jor‐ gensen JH, Landry ML, Warnock. Manual of Clinical Microbiology. 10th Ed. Vol.

[18] Sridhar MS, Gopinathan U, Garg P, Sharma S, Rao GN. Ocular Nocardiainfections with special emphasis on the cornea. Surv of Ophtlmol. 2001: 45(5); 361-378.

[19] Das S, Constantinou M, Daniell M, Taylor H. Moraxella keratitis: predisposing fac‐ tors and clinical review of 95 cases. Br. Jour. Ophthalmol 2006; 90: 1236-1238.

[20] Ando N, Takatori K. Fungal Flora of the Conjunctival Sac. Am Jour Ophthalmol1982;

[21] Gopinathan U, Garg P, Fernandes M, Sharma S, Athmanathan S. The epidemiologi‐ calfeatures and laboratory results of fungal keratitis. Cornea 2002; 21(6): 555-559.

[22] Perez-Balbuena AL, Vanzzini-Rosano V, Valadez-Virgen JJ, Campos Muller X. Fusa‐

[23] Dursun D, Fernandez V, Miller D, Alfonso EC. Advanced Fusarium keratitis pro‐

[24] Marangon FB, Miller D, Giaconi J, Alfonso EC. In vitro investigation of Voriconazole‐ susceptibility for keratitis and endophthalmitis fungal pathogens. Am Jour Ophthal‐

[25] Vanzzini VZ. Manzano-Gayoso P, Hernandez-Hernandez F, Gomez-Leal A, Mendez-Tovar LJ, Lopez-Martinez R, Queratomicosisen un centro de atenciónoftalmológica

[26] Srinivasan M, Gonzalez CA, George C, Cevallos V, Mascareñas JM, Asokan B, Wil‐ kins J, Smolin G, Whitcher JP. Epidemiology and etiological diagnosis of corneal ul‐

[27] Baine PK, Reddy AK, Kodiganti M, Gorli SR, Garg P. Evaluation of three PCR assays for the detection of fungi in patient with mycotic keratitis.. Br J. Ophthalmol

[28] Goldschmidt P, Degorge S, Benallaoua D, Semoun O, Borsali E, Le Bouter A, Battelier L, Borderie V, Laroche L, Chaumeil C. New strategy for rapid diagnosis andcharacte‐

[29] Vanzzini Z. Alcantara-Castro M, Naranjo TR, Support of the laboratory of fungal oc‐ ular infections. Int Jour. Inflam.Vol 2012 article ID. 643104doc.10.1155/2012/643104.

cerations inMadurai south India. Br. J. Ophthalmol. 1997; 81(11): 965-971.

rium Keratitis in Mexico. Cornea 2009; 28(6): 626-630.

gressing to endophthalmitis. Cornea 2003: 23(4); 300-303.

enla Ciudad de México. Rev. IberoamerMicol. 2010; 27(2): 57-61.

rization of keratomicosis. Ophthalmology 2012; 119: 945-950.

Shttp//dx.doi.org/10.106/j.ophtha.2012.03.031.

1;2011: 443-471.

84 Common Eye Infections

94(1): 67-74.

mol. 2004; 137:820-825.

2012.96:911-912.

#### **1.1. Epidemiology**

Microbial keratitis is a potentially serious corneal infection and a major cause of visual im‐ pairment worldwide. A conservative estimate of the number of corneal ulcers occurring annually in the developing world alone is 1.5–2 million [1]. The incidence of this condi‐ tion varies from 11.0 per 100 000 person years in the United States to 799 per 100 000 per‐ son years the developing nation of Nepal [2, 3]. Microbial keratitis is thus a significant public health problem, and numerous studies have been performed describing the micro‐ biology of corneal infection. Wide geographical variation exists in the epidemiology of mi‐ crobial keratitis based on economic and climate factors. To some degree, this variation is explained by economic factors as well as contact-lens wear. A high proportion of bacterial ulcers were reported from centres in developed countries (North America, Australia and Western Europe). In these countries, patients are far less likely to be agricultural workers, and so have a reduced risk of trauma from organic matter, which is known to be a risk factor for fungal infection.

Almost any microorganism can invade the corneal stroma if the normal corneal defense mechanisms are compromised. A wide spectrum of microbial organisms can produce cor‐ neal infections and, consequently, the therapeutic strategies adopted for its treatment may be varied. As there is no definite pathognomonic clinical feature, it is difficult to establish the aetiology of corneal ulcer merely on the basis of clinical features. Hence, microbiological evaluation is a must in order to attain a definitive diagnosis and to ensure specific therapy for keratitis.

© 2013 Robles-Contreras et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Robles-Contreras et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Regarding bacterial keratitis there are several potential risk factors such as contact lenses, trauma, aqueous tear deficiencies, neurotrophic keratopathy, eyelid alterations or malposi‐ tion, decreased immunologic defenses, use of topical corticoid medications and surgery [4]. Trauma is a major risk factor for corneal infection in developing countries. In Paraguay, the percentage of cases with preceding trauma was 48%, in Madurai, South India, 65% and 83% in Eastern India [5, 6, 7]. By far the most common cause of trauma to the corneal epithelium and the main risk factor for bacterial keratitis in developed countries is the use of contact lenses, particularly extended-wear contact lenses. Patients with bacterial keratitis, 19-42% are contact lens wearers; incidence of bacterial keratitis secondary to use of extended-wear contact lenses is about 8,000 cases per year. The annual incidence of bacterial keratitis with daily-wear lenses is 3 cases per 10,000 [8].

Traditionally the more common groups responsible for bacterial keratitis are: *Streptococcus sp.*, *Pseudomonas sp.*, *Enterobacteriaceae* (including *Klebsiella*, *Enterobacter*, *Serratia*, and *Proteus*), and *Staphylococcus sp.* Although there is also a wide variation depending on the setting of the series reported. A high percentage of *Staphylococcus sp.* (79%) was recorded in a study from Para‐ guay, although the reason for this is not clear. Another study found the highest proportion of *Streptococcus sp.* (46.8%), the authors noted that this figure was only 18.5% in 1986 and suggest that the trend might represent a genuine change in the bacterial flora owing to changes in the climate and environment [9]. A study from Bangkok [10] had the highest proportion of *Pseudo‐ monas* infections (55%). Interestingly, this study did not have the highest proportion of con‐ tact-lens wearers. Other studies reported far higher proportions of contact-lens wearers—for example, 44% in a study from Taiwan [11] and 50% in a study from Paris [12]. When compared the percentage of contact-lens wearers with the percentage of pseudomonal infections, the Spearman correlation coefficient was not statistically significant. Cohen et al. at Wills Eye Hos‐ pital reported a decline in contact lens-related ulcers: during 1991 to 1998, contact-lens wear accounted for 44% of all ulcers, but during 1992 to 1995, it accounted for only 30%. Liesegang reports the following risk factors for development of bacterial keratitis among contact lenses wearers: overnight wear, smoking, male sex, and socioeconomic status. The risk with thera‐ peutic contact lenses is much higher: approximately 52/10,000 per year [13].

Jeng [14] commented on the emerging resistance of bacterial infections to fluoroquinolones. In addition to changes in resistance patterns, studies have also demonstrated changing pat‐ terns of causative organisms over time in a given geographical location. Varaprasathan et al [15] reported that the proportion of S*treptococcus pneumoniae* and *Pesudomonas aeruginosa* ul‐ cers in Northern California had decreased over a 50-year period, while that of *Serratia mar‐ cescens* had increased over the same period. Sun et al [16] reported a rise in the percentage of Gram positive (+) cocci in North China from 25% in 1991 to 70.8% in 1997, as well as a de‐ crease in Gram negative (-) bacilli from 69% to 23.4% over a similar period. Hsiao et al [17] reported on a 10 year follow up that there was a significant decrease in the percentage of Gram(+) microorganisms over time. The sensitivity of Gram(-) isolates to tested antimicrobi‐ als was >97% response for all the reported antibiotics; this was not the case for Gram(+) iso‐ lates, in which resistance to the antibiotics was more common, methicillin-resistant organisms accounted for 29.1% of all Gram(+) cultures.

The overview of bacterial keratitis is quite extensive, from the epidemiological point of view is important to consider the wide variety of presentations even within the same regions of a country. Microbiological studies are essential to determine the casuistry of each center in a given time. A common problem throughout the world is the ever increasing resistance to an‐ tibiotics including the new fluoroquinolones.
