Ocular infection by P. glucanolyticus causing Keratitis and Corneal Perforation: Case report
Paenibacillus glucanolyticus is a facultative anaerobic, gram-negative, thin, rod-shaped bacteria which is spore forming and included in the genus Paenibacillus (lit. almostbacillus). Paenibacillus species are mostly rhizobacteria, found in soil and often associated with plants roots where they serve useful roles in breaking down environmental materials into forms accessible to plants. Paenibacillus has been reported causing a human infection in only 1 other case, that of a cardiac device-related endocarditis.
A 56-year-old musician presented with a 5-day history of severe pain, photophobia, and redness affecting the right eye. There was no history of trauma or contact lens wear. The only previous ophthalmic history reported was of styes. His medical history was significant for hepatitis C with liver function derangement, bronchiectasis, and pneumonia requiring intensive care admissions on 2 previous occasions.
The patient was on a methadone program for heroin withdrawal and reported a daily alcohol consumption of approximately 2 units but denied any smoking or current drug use.
- The right eye Snellen visual acuity was "Hand Movements," and the left eye 6/9.
- Slit-lamp biomicroscopic examination showed a large area of right corneal epithelial loss measuring 8x 8 mm. A white dense abscess measuring 5x6 mm was seen in the para central superior cornea. In addition, the cornea showed an area of inferior paracentral stromal keratolysis and thinning. Superiorly, the anterior chamber seemed formed and inflammatory activity was noted (3+ cells, 1+ flare).
- A hypopyon was not clearly visible, given the inferior keratolysis and stromal haze. Corneal swab and scrape sampling was performed under topical anesthesia. Samples were mounted on a glass slide and inoculated onto blood, chocolate, and Sabouraud dextrose agar and sent to Microbiology Department for incubation. In addition, a swab was taken for pan-bacterial, pan-fungal, and herpetic virus' polymerase chain reaction analysis. Initial microscopic gram staining examination revealed white cells with no organisms.
Topical moxifloxacin (0.5%) every hour was started along with cyclopentolate (1%) 3 times per day and oral doxycycline 100 mg once daily in an attempt to retard further stromal keratolysis. The patient was initially followed every 2 days to ensure treatment compliance.
After 48 hours of incubation smooth, white colonies were observed on the blood and chocolate agar plates. A gram stain of the colonies revealed long and thin Gram-negative rods, and P. glucanolyticus was identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The isolated pathogen was confirmed sensitive to ceftriaxone and gentamicin and showed intermediate sensitivity to fluoroquinolones. Gentamicin 1.5% fortified eye drops hourly were then added. All polymerase chain reaction analysis was negative, and blood tests showed only a mild decrease in liver function.
Dexamethasone 0.1% eye drops 4 times daily were added after 48 hours of antimicrobial treatment to reduce ocular inflammation. A slow response to therapy was observed with reduction in the size of the infiltrate and reepithelialization of the superior cornea. After 1 week, gentamycin 1.5% was decreased to 4 times per day to minimize ocular surface toxicity. At day 14, the patient presented with multiple pinpoint leaks from the inferior stromal thinning with shallowing of the anterior chamber and an unrecordable intraocular pressure. This was managed with cyanoacrylate glue tectonic patch and 18 mm diameter bandage contact lens. The tectonic glue patch came off after 1 week during bandage contact lens replacement, and the underlying thinned stroma was found to be covered by epithelium.
The infection responded well to the treatment regimen, and by week 6, the inflammation had reduced significantly. Although complete corneal reepithelialization occurred, significant scarring and distortion remained because of the inferior thinning. Cataract and posterior iris synechiae had also developed, and the visual acuity remains Hand Movements in the right eye. Penetrating keratoplasty and extracapsular extraction can be considered for future visual rehabilitation.
Microbial keratitis still remains an important cause of corneal opacification and sight loss worldwide. Such continuous changes are because of developments in microbiological diagnostic testing methods such as gene sequencing techniques and matrix-assisted laser desorption/ ionization time-of-flight mass spectroscopy that offer accurate identification of rare pathogens such as P. glucanolyticus.
This is the first reported case of microbial keratitis by P. glucanolyticus. This infection occurred in a male patient with no history of contact lens wear or ocular trauma. The patient reported that the symptoms had developed over the preceding 5 days, becoming severe 2 days before presentation. This indicated the infection progressed rapidly; however, the use of methadone may have played a role in delaying the presentation by dampening the initial symptoms of pain. Methadone is also known to lower eye blink rate, and alongside the lid margin disease, both are likely to have precipitated ocular surface exposure in this patient.
It is unclear how the cornea became inoculated in this case because the patient did not report any trauma or other contamination from environmental sources; however, the patient did display signs of poor general hygiene, which makes contamination possible because this microorganism is environmentally ubiquitous being commonly found in soil.
Despite intensive treatment, a slow response was observed with progression of stromal keratolysis that eventually resulted in corneal perforation. Paenibacillus species isolated from humans have demonstrated a variety of strain-dependent drug resistance including to quinolones. Moreover, Paenibacillus species have the ability to break down complex organic polymers such as cellulose, hemicellulose, collagen, and lignin into their component compounds. Authors hypothesized that the specific antibiotic sensitivity profile along with the enzymatic properties of Paenibacillus may have slowed the response to therapy and led to rapid keratolysis and perforation seen in this case.
This case also highlights the use of mass spectrometry as a rapid and accurate method to identify rare pathogens such as P. glucanolyticus for which previous diagnostic techniques may be misleading.
Source: Hassan et al; Cornea 2021;40:1062–1064