Minimum inhibitory concentrations of standard and novel antimicrobials for isolates from bacterial keratitis.
OBJECTIVE
To determine the minimum inhibitory concentrations (MICs) of 12 antimicrobials in current ophthalmic use and 4 potentially new alternatives against isolates from bacterial keratitis.


METHODS
Bacteria were collected from cases of bacterial keratitis in six centers in the United Kingdom between 2003 and 2006. MICs were measured by using susceptibility strips containing a concentration gradient of the antimicrobials penicillin, cefuroxime, ceftazidime, chloramphenicol, gentamicin, amikacin, vancomycin, teicoplanin, ciprofloxacin, ofloxacin, levofloxacin, moxifloxacin, meropenem, linezolid, tigecycline, and daptomycin.


RESULTS
Isolates (n = 772) were collected including coagulase negative Staphylococcus (CNS) (30%), Pseudomonas aeruginosa (23%), Staphylococcus aureus (14%), Enterobacteriaceae (14%), and streptococci (13%). Meropenem had low MICs for most isolates. All isolates except P. aeruginosa were susceptible to tigecycline. Linezolid was active against the majority of Gram-positive pathogens. Ten percent of S. aureus and 20% of CNS isolates were methicillin resistant. When systemic breakpoints were used, 84% of S. aureus isolates were susceptible to ciprofloxacin and 98% to moxifloxacin. Of the P. aeruginosa isolates, 99% were susceptible to ceftazidime, 96% to gentamicin, 99% to ciprofloxacin and 100% to moxifloxacin. More than 97% of Enterobacteriaceae isolates were susceptible to ceftazidime, gentamicin, ciprofloxacin, and moxifloxacin.


CONCLUSIONS
Based on systemic breakpoint data, resistance to commonly used antimicrobials was apparent. Meropenem is a potentially effective agent for ophthalmic use, with low MICs throughout all the bacterial subgroups. Tigecycline and linezolid showed good activity against particular groups and may be useful for treating bacterial keratitis resistant to current antimicrobials. Of the fluoroquinolones, moxifloxacin showed the lowest MICs and resistance for both Gram-positive and -negative bacteria.
Sueke
Henri
H
Department of Ophthalmology, Royal Liverpool University Hospital, School of Infection and Host Defence, University of Liverpool, Liverpool, United Kingdom. hsueke@gmail.com
Kaye
Stephen
S
Neal
Timothy
T
Murphy
Conor
C
Hall
Amanda
A
Whittaker
Dianne
D
Tuft
Stephen
S
Parry
Christopher
C
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D003320:Corneal Ulcer / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D015818:Eye Infections, Bacterial / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009883:Ophthalmic Solutions / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D009883:Ophthalmic Solutions