Population-Based Surveillance of Neisseria meningitidis Antimicrobial Resistance in the

Background. Antimicrobial treatment and chemoprophylaxis of patients and their close contacts is critical to reduce the morbidity and mortality and prevent secondary cases of meningococcal disease. Through the 1990’s, the prevalence of antimicrobial resistance to commonly used antimicrobials among Neisseria meningitidis was low in the United States. Susceptibility testing was performed to ascertain whether the proportions of isolates with reduced susceptibility to antimicrobials commonly used for N meningitidis have increased since 2004 in the United States. Methods. Antimicrobial susceptibility testing was performed by broth microdilution on 466 isolates of N men-ingitidis collected in 2004, 2008, 2010, and 2011 from an active, population-based surveillance system for suscept-ibility to ceftriaxone, ciprofloxacin, penicillin G, rifampin, and azithromycin. The molecular mechanism of reduced susceptibility was investigated for isolates with intermediate or resistant phenotypes. Results. All isolates were susceptible to ceftriaxone and azithromycin, 10.3 % were penicillin G intermediate (range, 8 % in 2008–16.7 % in 2010), and <1 % were ciprofloxacin, rifampin, or penicillin G resistant. Of the penicillin G intermediate or resistant isolates, 63 % contained mutations in the penA gene associated with reduced susceptibility to penicillin G. All ciprofloxacin-resistant isolates contained mutations in the gyrA gene associated with reduced susceptibility. Conclusions. Resistance of N meningitidis to antimicrobials used for empirical treatment of meningitis in th