A nosocomial outbreak of fluoroquinolone-resistant Streptococcus pneumoniae

Over the course of a 20-month period, in a hospital respiratory ward in whi ch ciprofloxacin was often used as empirical antimicrobial therapy for lowe r respiratory tract infections (LRTIs), 16 patients with chronic bronchitis developed nosocomial LRTIs caused by penicillin- and ciprofloxacin-resista nt Streptococcus pneumoniae (serotype 23 F). The minimum inhibitory concent ration (MIC) of ciprofloxacin for all isolates from the first 9 patients wa s 4 mug/mL, in association with a parC mutation. Isolates from the subseque nt 7 patients all had a ciprofloxacin MIC of 16 mug/mL, in association with an additional mutation in gyrA. The MICs for this isolate were 8 mug/mL of levofloxacin (resistant), 2 mug/mL of moxifloxacin and gatifloxacin (inter mediately resistant), and 0.12 mug/mL of gemifloxacin. This outbreak demons trates the ability of S. pneumoniae to acquire multiple mutations that resu lt in increasing levels of resistance to the fluoroquinolones and to be tra nsmitted from person to person.