Fluoroquinolone Resistance
Serotypes 6A/B, 19F, and 23F accounted for 73% of 140 mucosal isolates of Streptococcus pneumoniae from Hong Kong. In pulsed-field gel electrophoresis analysis, a group of related patterns was shared by 14 of 15 ciprofloxacin-resistant and 12 of 16 ciprofloxacin-susceptible isolates. These strains exhibited capsular switching and were highly similar to the Spanish 23F clone.

Streptococcus pneumoniae, the most important cause of community-acquired pneumonia worldwide, particularly affects young children, elderly persons with chronic cardiopulmonary conditions, and immunosuppressed patients of all ages. Widespread emergence of antimicrobial resistance has become a concern in recent years. In many countries, rates of resistance to penicillin are >40%. Among penicillin-resistant S. pneumoniae, 60% to 90% are also resistant to the macrolides, tetracyclines, chloramphenicol, clindamycin, and cotrimoxazole. For this reason, newer fluoroquinolones with expanded activity against gram-positive bacteria have been recommended by the Infectious Disease Society of America as initial treatment of choice for community-acquired pneumonia.

Although resistance to the newer fluoroquinolones remains rare in most countries, the percentage of nonsusceptible S. pneumoniae has increased from <0.5% for ofloxacin to 5.5% for levofloxacin (MIC ≥4 µg/mL) from 1995 to 1998 in Hong Kong. Almost all strains of fluoroquinoline-resistant S. pneumoniae were isolated from respiratory tract specimens. Knowledge of the serotype distribution of S. pneumoniae, particularly strains with the emerging resistance pattern, is important for development of conjugate vaccines.

We studied the serotype distribution of recent isolates of drug-resistant pneumococci from Hong Kong, including isolates with resistance to the fluoroquinolones. To understand better the emergence of fluoroquinolone-resistant S. pneumoniae in this locality, we used pulsed-field gel electrophoresis (PFGE) to compare strains.