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Comparative in-vitro efficacy of fluoroquinolones against Streptococcus pneumoniae recovered from bacterial keratitis
R Ramakrishnan1, S Ramesh, M Jayahar Bharathi
1Aravind Eye Hospital and Postgraduate Institute of Ophthalmology, Tirunelveli, Tamil Nadu- 627 001, India.
Background And Objectives:
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.
Materials And 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).
Conclusion:
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.
