Comparative in-vitro efficacy of fluoroquinolones against Streptococcus pneumoniae recovered from bacterial keratitis as determined by E-test.
OBJECTIVE
The advent of new fluoroquinolones has drawn the attention for reliable methods on the in-vitro susceptibility testing of Streptococccus pneumoniae. This study attempts to determine the minimum inhibitory concentration (MIC) of second-generation (ciprofloxacin and ofloxacin), third-generation (levofloxacin) and the fourth-generation (moxifloxacin and gatifloxacin) fluoroquinolones against S. pneumoniae recovered from bacterial keratitis.


METHODS
In retrospect, the MICs of 50 strains of S. pneumoniae isolated from the corneal scrapes of patients with bacterial keratitis were determined against ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin and moxifloxacin using E-tests. The National Committee of Clinical Laboratory Standards (NCCLS) susceptibility patterns and the potencies of the MICs were statistically compared.


RESULTS
The median MIC of ciprofloxacin (0.25microg/ml) was found to be lower than the median MICs of ofloxacin (0.5microg/ml) (P < 0.449) and levofloxacin (1.0microg/ml) (P < 0.001). The median MICs of gatifloxacin (0.1microg/ml) was lower than the median MICs of ciprofloxacin (0.25microg/ml) (P < 0.001), ofloxacin (0.5microg/ml) (P < 0.001) and levofloxacin (1.0microg/ml) (P < 0.001). Moxifloxacin (0.06microg/ml) had showed lower median MICs than gatifloxacin (0.1microg/ml) (P < 0.001) levofloxacin (1.0microg/ml) (P < 0.001), ofloxacin (0.5microg/ml) (P < 0.001) and ciprofloxacin (0.25microg/ml) (P < 0.001). Moxifloxacin (0.06microg/ml) had a lower MIC50 (microg/ml) than gatifloxacin (0.1microg/ml), levofloxacin (1.0microg/ml), ciprofloxacin (0.25microg/ml) and ofloxacin (0.5microg/ml). MIC90 (microg/ml) of moxifloxacin (0.06microg/ml) was found to be lower than the MIC90 (microg/ml) of gatifloxacin (0.5microg/ml), levofloxacin (1.0microg/ml), ofloxacin (0.5microg/ml) and ciprofloxacin (0.5microg/ml).


CONCLUSIONS
Based on in-vitro testing, the five portrayed fluoroquinolones 100% sensitivity to S. pneumoniae. However, the fourth-generation fluoroquinolone, moxifloxacin appeared to be more effective against S. pneumoniae than gatifloxacin, levofloxacin, ofloxacin and ciprofloxacin.
Ramakrishnan
R
R
Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli, Tamil Nadu- 627 001, India.
Ramesh
S
S
Bharathi
M Jayahar
MJ
Amuthan
M
M
Viswanathan
S
S
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D007634:Keratitis / Q000382:microbiology*; D008826:Microbial Sensitivity Tests / Q000379:methods; D008853:Microscopy; D011008:Pneumococcal Infections / Q000382:microbiology*; D012189:Retrospective Studies; D013296:Streptococcus pneumoniae / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones