Ocular Flora Research Articles

Changes in bacterial and fungal ocular flora of clinically normal horses following experimental application of topical antimicrobial or antimicrobial-corticosteroid ophthalmic preparations

To determine effects of topical antimicrobial and antimicrobial-corticosteroid preparations on the ocular flora of horses. animals: 40 horses. One eye was treated 3 times daily for 2 weeks with one of the following ointments: (1) neomycin-bacitracin-polymyxin B, (2) 0.6% prednisolone-0.3% gentamicin, (3) neomycin-polymyxin B-0.05% dexamethasone, or (4) treated (artificial tears) control. Contralateral eyes of treated control eyes served as untreated control eyes. Corneal and conjunctival specimens for bacterial and fungal cultures were collected prior to initiation of treatment, after 1 and 2 weeks of treatment, and 2 weeks after concluding treatment. Changes in culture growth quantity scores of bacterial and fungal species were analyzed. The most common species before treatment were the following: gram-positive bacteria included Streptomyces spp (66%), Staphylococcus spp (46%), Bacillus spp (32%), and Streptococcus spp (32%); gram-negative bacteria included Moraxella spp (28%), Escherichia coli (24%), Acinetobacter spp (18%), and Enterobacter spp (14%); and fungi included Aspergillus nidulans (56%), Cladosporium spp (32%), and Aspergillus fumigatus (22%). In all groups, the percentage of positive bacterial culture results, growth quantity score of gram-positive bacteria, and number of bacterial species isolated decreased at week 1 and increased at week 2, whereas growth quantity score of gram-negative bacteria decreased throughout treatment. Differences were not significant among groups. Fungal growth quantity score decreased during treatment in all groups. Repopulation of bacterial and fungal species occurred. All interventions decreased the number of microorganisms. Repopulation of normal flora occurred during and after treatment.

Role of Contact Lens Wear, Bacterial Flora, and Mannose-Induced Pathogenic Protease in the Pathogenesis of Amoebic Keratitis

The ocular surface is continuously exposed to potential pathogens, including free-living amoebae. Acanthamoeba species are among the most ubiquitous amoebae, yet Acanthamoeba keratitis is remarkably rare. The pathogenesis of Acanthamoeba keratitis is a complex, sequential process. Here we show that Acanthamoeba keratitis is profoundly affected by mannosylated proteins on the ocular surface, which stimulate the amoebae to elaborate a 133-kDa pathogenic protease. The mannose-induced protease (MIP133) mediates apoptosis of the corneal epithelium, facilitates corneal invasion, and degrades the corneal stroma. We show that contact lens wear upregulates mannosylated proteins on the corneal epithelium, stimulates MIP133 secretion, and exacerbates corneal disease. Corynebacterium xerosis, a constituent of the ocular flora, contains large amounts of mannose and is associated with Acanthamoeba keratitis. The present results show that amoebae exposed to C. xerosis produce increased amounts of MIP133 and more severe corneal disease. Oral immunization with MIP133 mitigates Acanthamoeba keratitis and demonstrates the feasibility of antidisease vaccines for pathogens that resist immune elimination.

Presurgical antimicrobial prophylaxis: effect on ocular flora in healthy patients.

Evaluation of presurgical antimicrobial prophylaxis for reduction of ocular flora. Ophthalmology Section, Department of Medicine and Surgery, University of Catania, Italy. Three days before photorefractive keratectomy (PRK), conjunctiva of 70 healthy patients (100 eyes) were swabbed. After 3 days of instillation of ofloxacin 0.3% (3 times daily), conjunctival swabs were taken again. Bacteria were isolated and identified from each swab. A total of 191 independent isolates were obtained prior to antimicrobial treatment. Bacteria were isolated from all 100 eyes sampled. Gram-positive species predominated, with Staphylococcus epidermidis and Staphylococcus aureus cultured from 69% and 25% of eyes sampled, respectively. Species of the anaerobic genera Peptococcus and Peptostreptococcus were found in 22% and 14% of eyes, respectively. After prophylaxis with ofloxacin, bacteria could be cultured from only 7% of eyes (10 independent isolates). All isolates were sensitive to ofloxacin except 5 strains of S. epidermidis, which displayed intermediate sensitivity. No infections occurred after PRK. Prophylaxis by instillation of ofloxacin 0.3% 3 times daily for 3 days substantially reduced the ocular flora of 100 healthy eyes prior to refractive surgery.

Antibiotic resistance patterns of ocular bacterial flora: A prospective study of patients undergoing anterior segment surgery

Purpose To determine the antibiotic susceptibility patterns of conjunctival bacterial flora isolated preoperatively from patients undergoing anterior segment surgery. Design Prospective observational study. Participants One hundred fifty-six eyes from 139 patients scheduled for anterior segment surgery were enrolled over a 6-month period from August 2001 to February 2002. Methods Conjunctival cultures were obtained on the day of surgery before povidone-iodine or antibiotic application. Main outcome measures Bacterial isolates were identified and tested for antibiotic susceptibility using the Kirby-Bauer disc-diffusion technique. Results Among the 156 eyes studied, 36 were from patients who had undergone either bilateral surgery or more than one surgery in the same eye. Only the first eyes of the 120 patients that underwent initial ocular surgery were included in our analysis. Of these 120 eyes, 21 (18%) showed no bacterial growth. Of the 143 bacterial strains isolated from the remaining 99 eyes, 112 (78%) were coagulase-negative staphylococci (CNS). Among the CNS, greater than 90% were susceptible to cefotaxime, levofloxacin, imipenem, meropenem, vancomycin, and each of the aminoglycosides except neomycin. Between 70% and 90% of the CNS were susceptible to cefazolin, neomycin, ciprofloxacin, ofloxacin, norfloxacin, and chloramphenicol. Less than 70% of the isolated CNS were sensitive to the penicillin analogues, ceftazidime, erythromycin, and tetracycline. Conclusions Preoperative conjunctival isolates of CNS seem to be most sensitive to vancomycin, the aminoglycosides (except neomycin), and levofloxacin.

Effects of minocycline on the ocular flora of patients with acne rosacea or seborrheic blepharitis.

To assess the effect of minocycline on the ocular flora in patients with acne rosacea or blepharitis. A total of ten patients were enrolled in this prospective study, with six patients diagnosed with acne rosacea with concomitant meibomianitis, two patients with acne rosacea without concomitant ocular involvement, and two patients with seborrheic blepharitis. The eyelids and conjunctiva of both eyes were cultured before the initiation of systemic minocycline therapy, after 3 months of active therapy, and 3 months after the discontinuation of therapy. Isolated bacteria were identified and quantified, and antibiotic susceptibility was determined. The colony-forming units (CFU) isolated from the eyelids significantly decreased after a 3-month treatment with minocycline (P = 0.0013). The CFU significantly increased to approach that of the baseline with the discontinuation of minocycline (P = 0.0275). The most common isolated bacteria, including coagulase-negative Staphylococcus (CNS), Staphylococcus aureus (S. aureus), and Propionibacterium acne (P. acne), except for corynebacterium, had a significant decrease in bacterial count with minocycline therapy compared with baseline (P < 0.05). There was a trend in the decrease of bacterial CFU isolated from the conjunctiva with minocycline therapy, although this was not statistically significant (P = 0.1955). Four of the ten patients carried tetracycline-resistant CNS strains, but none of the S. aureus or P. acne isolated at baseline was resistant to tetracycline. All six patients with acne rosacea and concomitant meibomianitis had marked clinical improvement. Minocycline effectively decreased eyelid bacterial flora in patients with acne rosacea or blepharitis. One of the mechanisms of newer generation tetracycline analogues may be a decrease or elimination of bacterial flora from the eyelids.

Minocycline effect on meibomian gland lipids in meibomianitis patients

The objective of this research was to determine the effect of oral minocycline on the meibomian gland nonpolar and free fatty acid lipids of chronic blepharitis patients. Patients – seborrheic blepharitis (SBBL), acne rosacea (AR) without ocular involvement, and acne rosacea with meibomianitis (AR-MKC). Minocycline treatment – 50 mg orally for 2 weeks followed by 100 mg to the end of 3 months; this was followed by 3 more months with no treatment. Meibomian gland secretions (meibum) were collected before treatment, at the end of the 3 months on treatment, and 3 months after stopping treatment. Lipids were separated and analyzed for wax and sterol esters, triglycerides, diglycerides, free cholesterol and free fatty acids. Data were analyzed statistically by ANOVA. Minocycline treatment resulted in decreased diglycerides and free fatty acids in the group AR-MKC, which continued into the second 3 months (off treatment) and was significant. Cholesterol decreased, but triglycerides initially decreased with treatment and then increased when treatment in the group was discontinued (second 3 months); these results, however, were not significant. Thus, minocycline has its greatest effect on lipid types, which result from degradation (lipase) reactions, suggesting a lipase inhibition effect and/or direct effect on ocular flora. This minocycline effect continues even after treatment is discontinued, suggesting a more lasting effect on ocular microflora. Minocycline may be most effective when the treatment period is longer than 3 months. These results give insight into disease mechanisms associated with chronic blepharitis.

The microbiology of the eye

Infection of the external structures of the eye is one of the commonest types of eye disease worldwide. In addition, although relatively impermeable to microorganisms, infection within the eye can result from trauma, surgery or systemic disease. This article reviews the general biology of viruses, bacteria, fungi and protozoa and the major ocular infections that they cause. In addition, the effectiveness of the various antimicrobial agents in controlling ocular disease is discussed. Because of changes in the normal ocular flora, continuous monitoring of the microbiology of the eye will continue to be important in predicting future types of eye infection. Basic research is also needed into the interactions of microbes at the ocular surface. There is increasing microbial resistance to the antimicrobial agents used to treat ocular infections and hence, new antimicrobial agents will continue to be needed together with new methods of drug delivery to increase the effectiveness of existing antimicrobial agents.

The microbiology of the eye

Infection of the external structures of the eye is one of the commonest types of eye disease worldwide. In addition, although relatively impermeable to microorganisms, infection within the eye can result from trauma, surgery or systemic disease. This article reviews the general biology of viruses, bacteria, fungi and protozoa and the major ocular infections that they cause. In addition, the effectiveness of the various antimicrobial agents in controlling ocular disease is discussed. Because of changes in the normal ocular flora, continuous monitoring of the microbiology of the eye will continue to be important in predicting future types of eye infection. Basic research is also needed into the interactions of microbes at the ocular surface. There is increasing microbial resistance to the antimicrobial agents used to treat ocular infections and hence, new antimicrobial agents will continue to be needed together with new methods of drug delivery to increase the effectiveness of existing antimicrobial agents.

Ocular Flora of Patients with AIDS Compared with Those of HIV-Negative Patients

To determine whether there are quantitative or qualitative differences in the ocular flora of patients with acquired immunodeficiency syndrome (AIDS) compared with human immunodeficiency virus (HIV)-negative patients. Forty patients with AIDS and 42 HIV-negative controls were sex and age matched. All subjects had a detailed anterior segment examination, including Schirmer's test, rose bengal staining, and quantitative cultures of the conjunctiva and lids. Statistical evaluation of the relation between AIDS, keratoconjunctivitis sicca (KCS), and ocular flora was performed. No differences were observed in the types or numbers of organisms isolated from the conjunctiva or lids of patients with AIDS and HIV-negative subjects. Ocular flora was not influenced by use of systemic antibiotics, level of immunosuppression as measured by CD4 lymphocyte counts, KCS, or other ocular-surface disease. One AIDS patient was colonized by large numbers of Haemophilus influenzae OU with minimal clinical signs of inflammation or infection. There do not appear to be any differences in the ocular flora of HIV-negative patients and patients with AIDS. Presence of KCS and level of immunosuppression do not appear to affect the ocular flora in patients with AIDS.

Ocular bacterial flora in contact lens wearers

In this study, ocular bacterial flora was determined for 126 healthy subjects before and after wearing soft contact lenses for 3, 6, and 9 months. The lenses were polyhydroxyethyl methacrylate with a water content of 55%. The care system used polyaminopropyl biguinide as the preservative. Our results indicate the presence of microorganisms such as Staphylococcus epidermidis (40.03%), Corynebacterium xerosis (2.78%), Corynebacterium acne (0.79%), and Bacillus subtilis (3.17%), before the wearing of contact lenses. A statistically insignificant decrease ( p > 0.05) was recorded in conjunctival flora at 3, 6, and 9 months after wearing the contact lenses. In addition, we demonstrated the presence of pathogens in the conjunctival flora of contact lens wearers at 9 months, such as Staphylococcus aureus (2.38%) and Streptococcus viridans (0.79%). We believe that these microorganisms may come from the contamination of the contact lenses, lens cases, and maintenance liquids.

Ocular Surface Flora in Drowning Victims

Contaminated allograft donor tissue represents a potential source of infection unique to keratoplasty. We prospectively studied perilimbal cultures of drowning victims over 30 months to determine if the ocular surface flora of drowning victims was unique. Twenty-eight donor eyes were cultured from 14 drowning victims. Ninety-three percent of limbal cultures were positive for one or more organisms, compared to results of a previous study of surface contamination of donor globes in which 65% were found to be culture positive. Fifty-seven percent (16 of 28) of donor eyes grew at least one streptococcal species, while 46% (13 of 28) grew two or more streptococcal species. A previous study identified streptococcal species in 7.9% of perilimbal cultures from nondrowning donor eyes, which demonstrates the unique effect of drowning on the ocular flora. The incidence of gram-negative isolates was also markedly higher in drowning victims, compared to previous studies of donor globes. This prospective study has shown that the ocular surface flora of drowning victims harbors markedly increased numbers of streptococcal species as well as gram-negative organisms. These findings demand careful globe decontamination, and emphasize the need for appropriate antibiotic coverage in corneal storage media.

Anaerobic flora of the conjunctival sac in patients with AIDS and with anophthalmia compared with normal eyes.

Relatively few investigations of anaerobic bacteria as ocular flora have been conducted, and their results have been contradictory. The conjunctival sacs of 22 normal subjects and of 14 patients with acquired immunodeficiency syndrome, and 22 anophthalmic sockets were cultured for anaerobic bacteria Thirty-four (77.3%) of the 44 eyes of normal subjects harbored anaerobic bacteria; Propionibacterium acnes was present in 28 eyes (63.6%), Lactobacillus species in 6 eyes (13.6%), and Veillonella species in 7 eyes (15.9%). The finding were very similar for anophthalmic sockets (p = 0.01), with 17 (77.3%) of the 22 sockets harboring anaerobes; Propionibacterium acnes was the organism identified in 16 (72.7%) of these sockets; Veillonella was identified in 4 (18.1%), Peptococcus niger in 3 (13.6%) and P. granulosum in 2 (9.0%) of these sockets. Acquired immunodeficiency syndrome patients had the highest incidence of anaerobic organisms, with positive cultures obtained from 24 (85.7%) of the 28 eyes. Propionibacterium species were isolated from 16 (57.1%) of these eyes. Clostridium species from 10 (35.7%) eyes and Actinomyces species from 8 (28.6%) eyes. It thus appears that anaerobic organisms are common flora in normal conjunctival sacs and in anophthalmic sockets, as well as in the sacs of acquired immunodeficiency syndrome patients, but the latter group had a higher incidence (x2 = 0.87) and a spectrum of organisms that was different from that of the other two groups.

Tear lactoferrin levels and ocular bacterial flora in HIV positive patients.

Keratoconjunctivitis Sicca(4) has recently been reported to occur at a greater rate in HIV-positive symptomatic patients. We looked at HIV positive asymptomatic patients, compared to age matched HIV negative patients to study external ocular resistant factors, namely lactoferrin levels in tears, bacterial flora in lid margins, conjunctiva and tears, and evidence of dry eyes using a Schirmer test and tear osmolarity. Eighteen eyes of nine HIV positive patients and eighteen eyes of HIV negative controls were studied. Results showed markedly decreased lactoferrin levels in HIV positive asymptomatic patients with a mean of 85.8 mgs/dcl compared to HIV negative patients with a mean 156 mgs/dcl (P < 0.01). There were increased numbers of colonies of bacterial flora on the lids of HIV positive asymptomatic patients with an average colony count 4.1 colonies/patient compared to 1.5 colonies/patients in the control group (P < 0.025). Seventy eight percent of the study group had bacterial growth compared to 33% in the control group. The tear osmolarity in both groups had no significant difference; mean in HIV positive being 312 mosml/litre; mean in control 306 mosml/litre. The Schirmer test also showed no significant difference, with the mean in HIV positive patients being 11 mm wetting, and in control patients being 12.7 mm wetting. Therefore, despite no symptomatic or clinical evidence of dry eyes, asymptomatic HIV-positive patients had markedly decreased levels of lactoferrin in tears and increased colony counts of bacterial flora in the lids.

Microbial flora in eyes of current and former contact lens wearers.

Microbial flora from the right eye conjunctival sac of 84 consecutively presenting contact lens patients were compared with cultures from both surfaces of their lens after aseptic removal and with the flora of their storage cases. Similar results were obtained from contact lens and conjunctival cultures of each individual; however, there was no correlation between storage case isolates and lens or conjunctival flora, suggesting that in uncomplicated lens wear, the eye is highly efficient in eradicating microorganisms introduced via handling. Conjunctival flora during daily contact lens wear was similar to the conjunctival flora of a matched control group of non-lens wearers. However, bacteria that are considered to be part of the normal ocular flora were isolated significantly more often from former contact lens wearers. The data also indicated that the use of nonperoxide chemical lens disinfection was associated with a higher proportion of positive cultures for pathogenic microorganisms than the use of other forms of disinfection, for both current and former contact lens wearers. The isolation of potential pathogens was particularly common among elderly subjects using thick contact lenses for extended wear. These changes to conjunctival flora may contribute to the increased risk of ocular infection associated with contact lens wear.

Microbiology of the Canine and Feline Eye

Knowledge of the microbiology of the canine and feline eye in normal and pathologic states is an important aspect of the clinician's assessment of external ocular disease. Gram-positive bacteria predominate in surveys of microbial flora in normal and diseased eyes. These same organisms are routinely isolated from skin and the upper respiratory tract. Injury to the eye may result in proliferation and potential pathogenicity of normal ocular flora. A variety of bacterial, fungal, viral, and other microbial isolates affect the diagnosis and treatment of external ocular disease.

Antimicrobial preparation of the eye for surgery

An important source of postoperative eye infection is the indigenous flora in and around the eye. Therefore, proper preparation of the operative field is crucial. Through an international survey we determined that ophthalmic surgeons used widely varying techniques in the pre-operative antimicrobial preparation of the eye. On the basis of these survey responses we have studied to date the effect on the bacterial flora of the conjunctiva of three regimens. Irrigation of the conjunctiva with saline tended to increase the ocular flora; instillation of silver protein solution had no significant effect. Povidone-iodine drops (5%) significantly reduced both colony and species counts.

Donor Cornea Contamination with Mccarey-Kaufman Medium Preservation

A patient had corneal infection with Staphylococcus aureus after keratoplasty from tissue preserved in McCarey-Kaufman medium. The small, successfully treated corneal infection was from the same organism cultured from the tissue culture medium at the time of transplantation. Possible sources of donor-tissue contamination included the increase in ocular flora seen in postmortem eyes, blood-borne bacteria, lack of sterile technique in securing donor tissue, inadequate irrigation of the tissue, and inadequate use of topical antibiotics on the tissue. Preservation medium and specimens from medium-preserved and refrigerated corneas should be cultured before and during surgery.

Ocular flora in the severely burned patient.

One hundred six eyes of 53 patients with severe thermal burns were studied with serial conjunctival cultures during a four-month period. A dramatic shift of the normal conjunctival flora from the preponderance of Staphylococcus epidermidis and Corynebacterium to S aureus and Gram-negative bacilli was observed. This commonly occurred on the fifth to sixth postburn day and represented colonization of the conjunctiva by bacteria recovered from other sites in the body. Despite the high incidence of Pseudomonas aeruginosa isolates (34%) of these eyes, deleterious effects were noted in only three eyes in two patients in whom infectious corneal ulcers developed before these patients died.

Microbiology of the Eye

Of the 20 chapters of this text, eight are contributed by the senior authors and the remaining 12 by others who range in experience from the Harkness Professor of Ophthalmology at Columbia University to an Assistant Resident in Ophthalmology at the University Hospital. Books on ocular microbiology are not plentiful and an authoritative contribution like the present one is most welcome. One would feel even happier with the result if the book were more finely attuned to the realities of ocular microbiology in the 1970s. Chapters 16 through 19, which deal with viral infections of the eye, serve present needs admirably. However, rather than a no-decision chapter on the flora of the healthy eye and the scholarly chapter on inhibitory properties of ocular flora, present-day realities call for a section on antibacterial drugs and their interaction with microorganisms. Such a chapter is not present. The section on the cytology of

Further studies on the incidence of antibiotic-producing micro-organisms of the ocular flora.

The possibility that inhibitory organisms of the normal microflora of superficial human tissues may be significant in resistance to or recovery from infections in these areas was suggested many years ago. 1-3 Until the recent expansion of our knowledge with regard to antibiotic substances, such studies were usually somewhat indeterminate. Reexamination of the problem since that time has shed much light on the prevalence and characteristics of such antibioticproducing organisms and has provided much circumstantial evidence implicating them in resistance or recovery mechanisms. The antibiotic activities of the microflora have been especially studied in the intestinal tract 4-9 and in the ocular flora. 10-13 In addition, such behavior has been found to be frequent in the organisms of the nose and throat, 14,15 oral cavity, 16,17 and skin. 18-20 Numerous antibiotics seem to be involved, 3, 21-24 and many of them seem to be of polypeptide nature. These antibiotic properties