Phenotypic factors correlated with the absence of virulence among gentamicin-resistant Pseudomonas aeruginosa strains.

Previous reports have suggested that clinical strains of gentamicin-resistant Pseudomonas aeruginosa (GRPA) generally produce only superficial infections (wounds, urinary tract infections) in contrast to their more invasive gentamicin-susceptible counterparts (GSPA). In view of this finding, a comparative study of a number of phenotypic properties of 20 GRPA and GSPA strains (10 isolates) was assessed to determine how closely related these two populations are and how their phenotypic properties might reflect virulence. GRPA isolates were found to be more adherent to buccal cells than their susceptible counterparts (P = 0.0001). Motility, however, was generally restricted in the GRPA population when compared with GSPA isolates (P = 0.02), although on the basis of zone diameters, some strains overlapped into the other group. Enzymatically, GSPA isolates produced significantly more lipase activity against C-14 lipids than GRPA strains (P = 0.04). No differences were recorded between the two populations in dye sensitivity or in their ability to grow on minimal media at 37 and 42 degrees C. Only 35% of the GRPA isolates agglutinated in 1 of the 17 monospecific antisera reactive for P. aeruginosa. The results of this study suggest that in vivo-generated GRPA strains possess phenotypic properties intermediate between those described for in vitro-derived GRPA isolates and their progenitor GSPA strains. The increased adherence of clinical GRPA isolates to buccal cells may explain their predilection to produce wound and urinary tract infections, whereas their lack of systemic dissemination may be partially due to decreased motility and to reduced lipase production.