New pathogen implicated in ocular infections

M. massiliense has emerged in the form of keratitis and can be properly identified with multiple gene sequencing, a report said.

Issue: September 2012

Mycobacterium massiliense nontuberculous mycobacterium, first isolated in 2004, has recently been identified as causing keratitis in a Chinese man, the first-ever reported instance, according to a recently published case report.

“M. massiliense is a newly emerged pathogen that had never been involved in ocular infections prior to this report,” Qin Long, MD, PhD, said in an interview with Primary Care Optometry News.

“There are two reasons for that,” Long continued. “First, it is difficult to distinguish M. massiliense from other group members grossly by regular 16S rRNA gene sequencing, which means it could be misinterpreted as M. abscessus due to the less accurate differential methods. Second, M. massiliense had similar clinical characteristics as other nontuberculous mycobacterium (NTM) keratitis cases, including history and ophthalmic signs and symptoms.”

A 23-year-old Chinese male shipbuilder presented to a local hospital with intractable redness and vision loss in his right eye. When obtaining the patient history, the clinicians discovered that he had suffered an instance of metal foreign body trauma in the right eye 2 months prior.

Four days after self-removal of the foreign body, the eye showed severe redness and tearing. A diagnosis of keratitis was made and a treatment regimen of both topical and systemic antibiotics, including penicillin, ofloxacin, chloramphenicol and erythromycin ointment, and antiviral and antifungal eye drops was begun. However, the keratitis remained unresolved over the next 2 months. The patient was then referred to the Peking University Medical College hospital, where pathogen and drug susceptibility testing were performed, according to the report.

Corneal scraping and culture showed acid-fast staining positive bacilli, and polymerase chain reaction and sequencing confirmed the diagnosis, the authors said.

“Because the typical clinical features in M. massiliense keratitis were not specific compared to other NTM keratitis at the onset of the disease, making the diagnosis was challenging,” Long said.

According to the report, because M. massiliense and M. bolletti appear identical to M. abscessus through 16S rRNA sequencing, differentiating M. massiliense from M. abscessus is best achieved by analyzing polymorphisms in either the rpoB, hsp65, sodA or recA genes or in the 16S-23S rRNA internal transcribed sequence. In this case, correct identification of M. massiliense NTM was achieved with the analysis of the rpoB and hsp65 genes.

A new treatment regimen was initiated, and the disease responded positively to topical amikacin and levofloxacin, Long said.

Although the neovascularization worsened under the treatment regimen, the corneal ulcer was ultimately cured in 2 months.

“We recommend multiple gene sequencing on patients with NTM keratitis, especially in cases in which M. abscessus is suspected, for the identification and early diagnosis of M. massiliense. Prompt treatment with combined antibiotic therapy will minimize the risk of sequelae such as corneal scarring and neovascularization,” Long said.

The authors reported that amikacin and ciprofloxacin are considered the treatment of choice for NTM infections, but less than 50% of cases have responded well to this therapy. Therefore, they said, “more than half of the reported cases need treatment of three or more antibiotics working together, including clarithromycin, amikacin, sulfacetamide, tobramycin, ciprofloxacin, ofloxacin, cefazolin and azithromycin.” – by Daniel R. Morgan

Reference:

Liu X, Zhao Y, Yang Y, et al. Mycobacterium massiliense keratitis. Optom Vis Sci. 2012;89(6):944-947.

For more information:

Qin Long, MD, PhD, can be reached at the Department of Ophthalmology, Peking Union Medical College Hospital, 1 Shuaifuyuan, Dongdan Street, Beijing 100730, People’s Republic of China; longqinbj@hotmail.com.