In vitro antibiotic susceptibility of rapidly growing nontuberculous mycobacteria isolated from patients with microbial keratitis.
OBJECTIVE
This study was undertaken to determine the antibiotic susceptibility and minimum inhibitory concentrations (MIC) of amikacin, tobramycin, ciprofloxacin, gatifloxacin, azithromycin, and clarithromycin against rapidly growing nontuberculous mycobacteria isolated from patients with keratitis.


METHODS
A total of 15 rapidly growing nontuberculous mycobacteria isolated from corneal scrapings of keratitis patients from January 1999 through December 2007 were subjected to antimicrobial susceptibility testing by the E-Test to amikacin, tobramycin, ciprofloxacin, gatifloxacin, azithromycin, and clarithromycin.


RESULTS
Out of 15 isolates, 13 were identified as Mycobacterium chelonae complex and 2 as Mycobacterium fortuitum complex. Based on minimum inhibitory concentration (MIC) cut off, all 15 (100%) isolates were sensitive to amikacin, azithromycin, and clarithromycin, 13 (86%) were sensitive to tobramycin, nine (60%) to gatifloxacin, and only 6 (40%) to ciprofloxacin. The MIC range was 0.25-4 microg/ml for amikacin, 0.5-1 microg/ml for azithromycin, 0.125-1 microg/ml for clarithromycin, 0.5-16 microg/ml for ciprofloxacin, and 0.25-16 microg/ml for tobramycin. MIC(90) for amikacin was 2 microg/ml, azithromycin 1 microg/ml, clarithromycin 0.75 microg/ml, ciprofloxacin 8 microg/ml, gatifloxacin 8 microg/ml, and for tobramycin it was 4 microg/ml.


CONCLUSIONS
All the isolates were sensitive to amikacin, azithromycin, and clarithromycin, but the MIC values of clarithromycin and azithromycin were lower than amikacin. Based on in vitro susceptibility results it appears that the topical amikacin in combination with oral clarithromycin or azithromycin is the best treatment option for rapidly growing nontuberculous mycobacterial keratitis.
Reddy
Ashok Kumar
AK
Jhaveri Microbiology Centre, Prof Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, Hyderabad, India. ashokkumar@lvpei.org
Garg
Prashant
P
Babu
K Hari
KH
Gopinathan
Usha
U
Sharma
Savitri
S
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003320:Corneal Ulcer / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D015818:Eye Infections, Bacterial / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009165:Mycobacterium Infections, Nontuberculous / Q000382:microbiology*; D016926:Mycobacterium chelonae / Q000187:drug effects* / Q000302:isolation & purification; D019907:Mycobacterium fortuitum / Q000187:drug effects* / Q000302:isolation & purification
D000900:Anti-Bacterial Agents