title: Activity of newer fluoroquinolones against gram-positive and gram-negative bacteria isolated from ocular infections: an in vitro comparison.
abstract: BACKGROUND
  To determine the antibacterial activity of newer fluoroquinolones and compare their activity between ciprofloxacin-susceptible and resistant bacterial isolates from patients with keratitis and endophthalmitis.
  
  
  METHODS
  The minimum inhibitory concentration (MIC) of ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin and moxifloxacin was determined for 123 bacterial isolates, using E test. Among the 123 isolates, 68 were gram-positive (Staphylococcus spp, Streptococcus spp, Corynebacterium spp, Bacillus spp.) and 55 were gram-negative (Pseudomonas aeruginosa). The bacterial isolates were divided into three groups: susceptible/intermediate/resistant to ciprofloxacin. The MIC values for various fluoroquinolones were compared between the three groups and between gram-positive and gram-negative bacteria.
  
  
  RESULTS
  For gram-positive isolates, median MICs of fourth generation fluoroquinolones were lower than second generation. The median MIC was lowest for gatifloxacin and moxifloxacin (0.094 mg/ml) in ciprofloxacin-susceptible isolates of gram-positive bacteria. For ciprofloxacin-susceptible gram-negative bacteria, the median MIC of ciprofloxacin (0.19 mg/ml) was significantly lower than ofloxacin, levofloxacin, gatifloxacin and moxifloxacin (1.5, 0.5, 0.5 and 2 mg/ml respectively). Ciprofloxacin-resistant isolates of gram-positive bacteria showed higher MIC of levofloxacin, moxifloxacin and gatifloxacin though they remained susceptible to them. None of the fluoroquinolones were effective against ciprofloxacin-resistant gram-negative bacteria. Overall, for gram-positive bacteria, median MICs of levofloxacin, moxifloxacin and gatifloxacin were below ciprofloxacin, the MIC of gatifloxacin and moxifloxacin was equal for gram-positive bacteria.
  
  
  CONCLUSIONS
  Levofloxacin, gatifloxacin and moxifloxacin are statistically more effective against gram-positive bacteria, the latter two being equally effective. Ciprofloxacin remains the most effective fluoroquinolone against gram-negative bacteria.
authors.affiliation: Jhaveri Microbiology Centre, LV Prasad Eye Institute, Hyderabad, India.
authors.forename: Aparna
authors.initials: A
authors.lastname: Duggirala
authors.forename: Joveeta
authors.initials: J
authors.lastname: Joseph
authors.forename: Savitri
authors.initials: S
authors.lastname: Sharma
authors.forename: Rishita
authors.initials: R
authors.lastname: Nutheti
authors.forename: Prashant
authors.initials: P
authors.lastname: Garg
authors.forename: Taraprasad
authors.initials: T
authors.lastname: Das
mesh_terms: D015818:Eye Infections, Bacterial / Q000382:microbiology*; D024841:Fluoroquinolones / Q000494:pharmacology*; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology*; D006801:Humans; D066298:In Vitro Techniques; D008826:Microbial Sensitivity Tests
chemical_list: D024841:Fluoroquinolones