M. fortuitum and other nontuberculous mycobacteria are more susceptible in vivo and in vitro to the fluoroquinolones than are members of the M. abscessus–M. chelonae complex [47, 57, 58] (Table 1.2). Moshifar et al. reported a case of moxifloxacin-resistant M. chelonae recovered from a patient on Vigamox for prophylaxis post-LASIK [31]. De la Cruz reported two more cases unresponsive to gatifloxacin in vivo and documented resistance to both moxifloxacin and gatifloxacin in vitro [59].

Few new antibiotics are available for medical therapy or prophylaxis of mycobacterial keratitis. Those that have demonstrated both in vitro and in vivo include linezolid, telithromycin, and tigecycline. Linezolid has been used to treat M. tuberculosis and has >90% in vitro efficacy for most rapid growers [60, 61]. Telithromycin, a newer macrolide, had moderate (<90% in vitro efficacy) against the rapid growers and was not effective against M. tuberculosis and/or the slow-growing mycobacteria [45, 62]. Tigecycline a new type of tetracycline derivative had in vitro MICs of £1 ug/ml for the most common mycobacteria recovered from keratitis [56, 63, 64].

Clofazimine, an antileprosy drug, has been evaluated against rapidly growing mycobacteria with good in vitro results [65, 66]. Shen et al. evaluated clofazimine in vitro against rapidly growing mycobacteria. MIC90 for the most commonly recovered isolates was £1ug/ml (range 0.5–1.0 mg/ml). Susceptibility profiles were

M. abscessus (99.1%, N = 117), M. chelonae (100%, N = 20), and M. fortuitum

(91.7%, N = 48). Synergy with amikacin was documented for all M. abscessus and M. chelonae isolates and 48% of the M. fortuitum isolates. Results in vitro suggest that clofazimine alone or with amikacin may be effective against Group IV mycobacteria species [67]. No clinical data is available. The drug is not available in the United States and WHO discourages its widespread use for treating infections other than leprosy. It has been used as adjunctive therapy to treat M. avium complex pulmonary infections [65–67].

Besifloxacin is a new fluoroquinolone with similar or lower MIC90s against common ocular pathogens. No clinical or in vitro data are available for the treatment or in vitro susceptibility of mycobacterial species with this new fluoroquinolone [68, 69].

Corticosteroids should be used with caution in patients confirmed with mycobacterial keratitis. They may mask the disease progression, retard immune response, and accelerate growth and dissemination of the organisms [1, 3, 5–7, 15, 66, 70].

New drug delivery systems using liposomes and nanoparticles to deliver antituberculous drugs are in development. These systems are already used to deliver steroids and antiherpetic drugs to the eye. Mycobacterial keratitis might be an ideal disease to evaluate these two drug delivery systems [8].

Surgical Intervention

Surgical intervention is often necessary to affect a cure and control the progression of disease. Debridement reduces the microbial load which is an essential part of management and cure of mycobacterial keratitis [6, 7, 38, 71]. Huang et al. performed early keratectomy in 15/22 (68%) cases of nontuberculous keratitis