Corynebacterium Species of the Conjunctiva and Nose: Dominant Species and Species-Related Differences of Antibiotic Susceptibility Profiles

Clinical and bacteriological characteristics of Corynebacterium keratitis

PURPOSE

Corynebacterium species are commensals of human skin and mucous membranes and are recognized as important pathogens in ocular infections. This study investigated the clinical characteristics of Corynebacterium keratitis.

METHODS

We retrospectively reviewed cases of bacterial keratitis in which Corynebacterium species were solely isolated from corneal scraping cultures collected at Ehime University Hospital between January 2010 and February 2024. The clinical findings of Corynebacterium keratitis were divided into two types: adherent and infiltrative, which are defined as adhesion to the corneal surface or stromal infiltration, respectively.

RESULTS

Of the 232 culture-positive cases of bacterial keratitis, 23 (9.9%) were positive for Corynebacterium species alone. The mean patient age was 60.1 ± 21.0 years, and the cohort included 12 males and 11 females. Adherent type was found in 13 patients (56.5%) and infiltrative type was observed in 10 patients (43.5%). Fluoroquinolone eye drops were used by 14 (60.9%) patients and steroid eye drops by 12 (52.2%). Corynebacterium macginleyi was the most commonly identified species (85.7%). 91% of Corynebacterium isolates were resistant to fluoroquinolones. All of C. macginleyi isolates were fluoroquinolone-resistant, and 93.3% of the isolates were highly resistant (minimal inhibitory concentrations > 32 µg/mL). All cases were treated with frequent antimicrobial eye drops, mainly cephalosporins, and the mean treatment duration was 21.6 days. Although no patient required therapeutic keratoplasty, five adherent types required multiple therapeutic debridements to physically remove the bacteria.

CONCLUSIONS

Corynebacterium keratitis presented as adherent and infiltrative types of lesions. The main characteristics of the patient included the use of fluoroquinolone and steroid eye drops.

Relationship Between Fluoroquinolone Resistance and Mutations in the Quinolone Resistance-Determining Region in Corynebacterium macginleyi

Purpose

The purpose of this study was to investigate the bacterial composition in the conjunctiva and to determine the relationship between fluoroquinolone resistance and mutations in the quinolone resistance-determining region (QRDR) in Corynebacterium macginleyi (C. macginleyi).

Methods

Bacteria isolated from conjunctival swabs of patients awaiting ophthalmic surgery or patients with presumed keratoconjunctivitis were included in this study. For C. macginleyi isolates from 49 samples, the minimum inhibitory concentrations (MICs) of second- to fourth-generation fluoroquinolones were determined by broth microdilution. Additionally, we determined the sequence of the QRDR in the gyrA gene of C. macginleyi-positive isolates by direct sequencing and investigated the relationship between the QRDR mutation and the MICs of fluoroquinolones for C. macginleyi.

Results

Among 423 eyes of 296 preoperative patients who underwent conjunctival culture testing, 105 eyes of 89 patients were culture-positive, and among 148 eyes of 147 patients with keratoconjunctivitis, 55 eyes of 54 patients were culture-positive. C. macginleyi accounted for the largest proportion of cultured organisms (34.8%). C. macginleyi-positive isolates were found in 45 eyes of 37 preoperative patients and in 4 eyes of 4 patients with keratoconjunctivitis. Direct sequencing revealed that 91.8% of C. macginleyi-positive isolates had amino acid mutations in the QRDR and 95.5% of mutations were found at Ser-87 and Asp-91. Isolates harboring double mutations at Ser-87 and Asp-91 were resistant to second- to fourth-generation fluoroquinolones. One isolate with double mutations at Ser-87 and Ala-88 but no mutation in Asp-91 showed intermediate susceptibility to moxifloxacin, a fourth-generation fluoroquinolone.

Conclusions

C. macginleyi isolated from conjunctiva harboring QRDR amino acid mutations were resistant to second- to fourth-generation fluoroquinolones.

Interpretable metric learning in comparative metagenomics: The adaptive Haar-like distance

Random forests have emerged as a promising tool in comparative metagenomics because they can predict environmental characteristics based on microbial composition in datasets where β-diversity metrics fall short of revealing meaningful relationships between samples. Nevertheless, despite this efficacy, they lack biological insight in tandem with their predictions, potentially hindering scientific advancement. To overcome this limitation, we leverage a geometric characterization of random forests to introduce a data-driven phylogenetic β-diversity metric, the adaptive Haar-like distance. This new metric assigns a weight to each internal node (i.e., split or bifurcation) of a reference phylogeny, indicating the relative importance of that node in discerning environmental samples based on their microbial composition. Alongside this, a weighted nearest-neighbors classifier, constructed using the adaptive metric, can be used as a proxy for the random forest while maintaining accuracy on par with that of the original forest and another state-of-the-art classifier, CoDaCoRe. As shown in datasets from diverse microbial environments, however, the new metric and classifier significantly enhance the biological interpretability and visualization of high-dimensional metagenomic samples.

Does corneal tattooing affect the conjunctival microbiota?

PURPOSE

This study aimed to investigate the effects of commercial tattoo inks used in corneal tattooing on conjunctival microbiota.

METHOD

This prospective case control study consisted of 125 participants divided in the following three groups: 35 patients with corneal tattoos, 40 patients with corneal leukoma, and 50 healthy subjects. Corneal tattooing was performed in all the cases in this study using a tattoo pen machine and commercial tattoo ink. A total of 500 cultures were taken from 250 eyes of 125 individuals on chocolate and sheep blood agar. Bacteriological samples were taken from the inferior eyelid conjunctiva using a sterile cotton swab. Without any contact elsewhere, the swabs were smeared on bedside chocolate agars and 5% sheep blood agar.

RESULTS

In tattooed eyes, bacterial growth was detected in 42.9% of the chocolate and sheep blood agar samples. In other healthy eyes of patients with corneal tattoos, 54.5% bacterial growth on chocolate agar and 57.1% on sheep blood agar were detected. No statistical difference was detected in the conjunctival microbiota of chocolate and sheep blood agar (p = 0.254, p = 0.134, respectively) in the tattooed eyes compared to the other eye of the individual. No statistically significant difference was found in terms of bacterial growth in tattooed, leukoma, or healthy eyes on chocolate and sheep blood agar (p = 0.408, p = 0.349). The growth rate of Staphylococcus epidermidis decreased by 33.3% (from 12 to 8) on chocolate agar in 35 tattooed eyes, and it decreased by 28.5% (from 14 to 10) on sheep blood agar, while gram-negative bacteria Brevundimonas diminuta, Acinetobacter lwoffii, and Psychrobacter faecalis were detected in three patients.

CONCLUSION

Corneal tattooing using commercial dye does not affect conjunctival microbiota. In the past 3 years, 120 patients have been tattooed with commercial tattoo ink in Istanbul Medeniyet University Göztepe Training and Research Hospital. No complications related to infection were found in the 3-year follow-up. The gram-negative bacteria detected in the healthy control group and tattooed eyes were bacteria found on normal skin or in the respiratory tract. Although some gram-negative bacteria do not cause infection, careful eye examination, follow-up, and culture are required in suspicious cases.

Ocular surface microbiota dysbiosis contributes to the high prevalence of dry eye disease in diabetic patients

People with diabetes mellitus (DM) are at an increased risk for developing dry eye disease (DED). However, the mechanisms underlying this phenomenon remain unclear. Recent studies have found that the ocular surface microbiota (OSM) differs significantly between patients with DED and healthy people, suggesting that OSM dysbiosis may contribute to the pathogenesis of DED. This hypothesis provides a new possible explanation for why diabetic patients have a higher prevalence of DED than healthy people. The high-glucose environment and the subsequent pathological changes on the ocular surface can cause OSM dysbiosis. The unbalanced microbiota then promotes ocular surface inflammation and alters tear composition, which disturbs the homeostasis of the ocular surface. This "high glucose-OSM dysbiosis" pathway in the pathogenesis of DED with DM (DM-DED) is discussed in this review.

Ocular microbiome changes in dry eye disease and meibomian gland dysfunction

The most common and chronic ocular problem of aging is dry eye disease (DED) and the associated condition of meibomian gland dysfunction (MGD). The resident ocular surface bacteria may have a role in maintaining homeostasis and perturbation may contribute to disease development. The aim of this study was to compare the microbiomes of the conjunctiva and eyelid margin in humans with mild and moderate DED and controls using 16 S rRNA gene sequencing. The conjunctiva and lid margin of three cohorts (N = 60; MGD, MGD with lacrimal dysfunction [MGD + LD] and controls) were swabbed bilaterally three times over three months. Microbial communities were analysed by extracting DNA and sequencing the V3-V4 region of the 16 S ribosomal RNA gene using the Illumina MiSeq platform. Sequences were quality filtered, clustered into amplicon sequence variants (ASVs) using UNOISE algorithm and taxonomically classified using a Bayesian Last Common Ancestor (BCLA) algorithm against the GTDB 2207 database. The overall microbial communities of the MGD, MGD + LD and control groups were significantly different from each other (P = 0.001). The MGD and MGD + LD dry eye groups showed greater variability between individuals compared to the control (PERMDISP, P < 0.01). There was decreased richness and diversity in females compared to males for the conjunctiva (P < 0.04) and eyelid margin (P < 0.018). The conjunctiva in the MGD + LD group had more abundant Pseudomonas azotoformans, P. oleovorans and Caballeronia zhejiangensis compared to MGD and control (P < 0.05), while the MGD group had more abundant Corynebacterium macginleyi and C. kroppenstedtii compared to control (P < 0.05). The lid margin in MGD was more abundant in C. macginleyi, C. accolens, and C. simulans compared to the MGD + LD and control (P < 0.05). There were differences in the overall microbial community composition and certain taxa, including increased levels of lipophilic bacteria, on the conjunctiva and eyelid margin in mild to moderate DED/MGD compared to controls. DED/MGD was also associated with a reduced bacterial richness and diversity in females.

Comparison of the Ocular Microbiomes of Dry Eye Patients With and Without Autoimmune Disease

Purpose

The pathogenesis of dry eye concomitant with autoimmune disease is different from that of dry eye without autoimmune disease. The aim of this study was to explore differences in the microbiota diversity and composition in dry eye with and without autoimmune disease.

Methods

Swab samples from the inferior fornix of the conjunctival sac were obtained from dry eye patients without autoimmune disease (n = 49, dry eye group) and from those with autoimmune disease (n = 38, immdry eye group). Isolated bacterial DNAs from swabs were analyzed with 16S rRNA amplicon sequencing.

Results

Analysis of the alpha diversity revealed no significant differences between subjects in the dry eye and immdry eye groups. Those in the immdry eye group had a distinct microbial composition compared with those in the dry eye group. The combination of the genera Corynebacterium and Pelomonas distinguished subjects in the immdry eye group from those in the dry eye group, with an area under the curve of 0.73 (95% CI = 0.62-0.84). For the same bacteria, the correlations between microbe abundance and the ocular surface parameters were different in the two groups. In addition, the functions of the microbial communities were altered in the two groups.

Conclusions

Our study demonstrates changes in the composition and function of the ocular microbiome between subjects in the immdry eye and dry eye groups, which suggests that the potential pathogenesis is different.

Alternative Therapeutic Interventions: Antimicrobial Peptides and Small Molecules to Treat Microbial Keratitis

Microbial keratitis is a leading cause of blindness worldwide and results in unilateral vision loss in an estimated 2 million people per year. Bacteria and fungus are two main etiological agents that cause corneal ulcers. Although antibiotics and antifungals are commonly used to treat corneal infections, a clear trend with increasing resistance to these antimicrobials is emerging at rapid pace. Extensive research has been carried out to determine alternative therapeutic interventions, and antimicrobial peptides (AMPs) are increasingly recognized for their clinical potential in treating infections. Small molecules targeted against virulence factors of the pathogens and natural compounds are also explored to meet the challenges and growing demand for therapeutic agents. Here we review the potential of AMPs, small molecules, and natural compounds as alternative therapeutic interventions for the treatment of corneal infections to combat antimicrobial resistance. Additionally, we have also discussed about the different formats of drug delivery systems for optimal administration of drugs to treat microbial keratitis.

The effect of topical ocular moxifloxacin on conjunctival and nasal mucosal flora

To determine the short-term effect of topically administered ocular moxifloxacin on conjunctival and nasal bacterial mucosal flora. The study included 20 patients with newly diagnosed age-related macular degeneration. Each patient’s diseased eye was selected as the treatment eye and the fellow eye was selected as the control eye. All treatment eyes constituted the treatment group and all controls eyes constituted the control group. All patients received intravitreal injection of ranibizumab. Cultures were obtained from the inferior conjunctival fornix and the nostrils in all patients. Patients were instructed to administer moxifloxacin eye drops to the treatment eye 4 times daily for 1 week. The patients were instructed to come for a follow-up exam 1 week post intravitreal injection. The bacterial culture positivity rate and the bacteria isolated from the conjunctiva and nostrils were recorded in the 2 groups before and after use of topical ocular moxifloxacin. Mean age of the patients (12 female and 8 male) was 64.9 years. Before use of topical ocular moxifloxacin the conjunctival and nasal culture positivity rates in the treatment group were both 100%, versus 90% and 95%, respectively, in the control group. At the follow-up exam the conjunctival and nasal mucosa culture positivity rates in the treatment group decreased to 20% (4/20) and 30% (6/20), respectively (P < 0.001), versus 85% (17/20) and 80% (16/20), respectively, in the control group (P = 0.68 and P = 0.72 for conjunctival and nasal). This is the first study to show that moxifloxacin applied to the ocular surface topically has a significant effect on nasal flora. Daily administration of topical ocular moxifloxacin for 1 week significantly reduces the nasal bacterial flora in addition to conjunctival flora.

Current Evidence for Corynebacterium on the Ocular Surface

Corynebacterium species are commonly found in the conjunctiva of healthy adults and are recognized as non-pathogenic bacteria. In recent years, however, Corynebacterium species have been reported to be potentially pathogenic in various tissues. We investigated Corynebacterium species on the ocular surface and reviewed various species of Corynebacterium in terms of their antimicrobial susceptibility and the underlying molecular resistance mechanisms. We identified a risk for Corynebacterium-related ocular infections in patients with poor immunity, such as patients with diabetes or long-term users of topical steroids, and in those with corneal epithelial damage due to trauma, contact lens wear, lagophthalmos, and trichiasis. The predominant strain in the conjunctiva was C. macginleyi, and the species associated with keratitis and conjunctivitis were C. macginleyi, C. propinquum, C. mastitidis, C. pseudodiphtheriticum, C. accolens, C. striatum, C. xerosis, and C. bovis. Overall, Corynebacterium species present on the ocular surface were resistant to quinolones, whereas those in the nasal cavity were more susceptible. The prevalence of fluoroquinolone-resistant Corynebacterium has not changed in the past 10 years; however, Corynebacterium species remain susceptible to third-generation cephems. In conclusion, the use of third-generation cephems should be a reasonable and pragmatic approach for treatment of ocular infections caused by Corynebacterium species.