Target gene sequencing to define the susceptibility of Neisseria meningitidis to ciprofloxacin

Abstract

Meningococcal gyrA gene sequence data, MICs, and mouse infection were used to define the ciprofloxacin breakpoint for Neisseria meningitidis. Residue T91 or D95 of GyrA was altered in all meningococcal isolates with MICs of ≥ 0.064 μg/ml but not among isolates with MICs of ≤ 0.032 μg/ml. Experimental infection of ciprofloxacin-treated mice showed slower bacterial clearance when GyrA was altered. These data suggest a MIC of ≥ 0.064 μg/ml as the ciprofloxacin breakpoint for meningococci and argue for the molecular detection of ciprofloxacin resistance.

Fig 1

Ciprofloxacin MICs for the 177 meningococcal isolates with MICs of ≤0.032 μg/ml and the 19 with MICs of ≥0.064 μg/ml examined in this study. The number of isolates with each MIC is shown above each bar. The MIC₅₀ and MIC₉₀ are also indicated.

Fig 2

(A) Dissemination of N. meningitidis in BALB/c mice infected by the intraperitoneal injection of a bacterial suspension of N. meningitidis (5 × 10⁶ CFU/ml). Clone 12lux (MIC of 0.006 μg/ml) and isogenic clone AS12lux (MIC of 0.125 μg/ml; GyrA T91I alteration) were used for infection. Two groups of four mice were infected with each strain. The fifth mouse in each group on the right is an uninfected control. One group of mice for each bacterial strain was treated with a single intramuscular injection of ciprofloxacin (5 mg/kg) after the acquisition of the images at 2.5 h. Mice were then analyzed for bioluminescence at the indicated times. Images (dorsal view) depict photographs overlaid with color representations of luminescence intensity, measured in photons per second and indicated on the scale at the right, where red is the most intense and blue is the least intense bioluminescence. (B) Bioluminescence was quantified and expressed as means ± standard deviations of four mice in each group at the indicated times by defining a specific representative region of interest encompassing the entire animal.