New techniques for assessing pathogenicity of quinolone-resistant bacteria

Ciprofloxacin and ofloxacin-resistant variants of Staphylococcus aureus and Pseudomonas aeruginosa have been compared with their original drug-sensitive progenitor strains with respect to their susceptibility to opsonophagocytosis by human polymorphonuclear leucocytes. For strains exhibiting low level resistance to each quinolone some depression of chemiluminescence (respiratory burst) was recognized whereas for strains exhibiting high level resistance some potentiation of chemiluminescence occurred. There was no difference in terms of the phagocytic ingestion of each of the strains. This study provides only limited evidence to suggest that changes in bacterial virulence are associated with the development of resistance to the quinolone antimicrobials.