SUSCEPTIBILITY OF PSEUDOMONAS-AERUGINOSA TO SERUM BACTERICIDAL ACTIVITY - A COMPARISON OF 3 METHODS WITH CLINICAL CORRELATIONS

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  • 1 January 1981
    • journal article
    • research article
    • Vol. 98  (4) , 511-518
Abstract
Twenty-nine blood culture isolates of P. aeruginosa were tested by 3 established methods to determine the effect of in vitro conditions on the survival of this organism in human serum. Clinical correlations were made to determine the relationship of serum resistance as defined by each method to clinical outcome. Major differences of bacterial survival in the presence of pooled normal human serum and in classification of isolates (sensitive, intermediate, resistant) were observed among the 3 methods. Isolates grown in broth for preparation of inocula demonstrated significantly greater sensitivity to serum bactericidal activity than those grown on agar. The use of organisms in early logarithmic growth phase or increased concentrations of serum augmented the serum sensitivity of these isolates. No correlation was observed between serum bactericidal activity and antibiotic susceptibility, pyocine type, patient mortality or underlying disease. All strains of serotype 6 or 11 (immunotype 1 or 2) were serum-sensitive by 1 of the 3 methods. Thus, by testing isolates of P. aeruginosa under a variety of in vitro conditions, it is evidently possible to identify a few isolates that are highly sensitive or resistant to serum under all conditions. The survival of the majority of strains of P. aeruginosa in human serum is highly dependent on in vitro conditions. Conclusions regarding the role of serum bactericidal activity in host defense must be drawn cautiously when based solely on in vitro tests.