Gram-negative bacillary infections. Pathogenic and pathophysiologic correlates.

Gram-negative bacillary infections continue to be extremely important. Escherichia coli is the single most frequently encountered pathogen, followed by organisms belonging to the tribe Klebsiella-Enterobacter-Serratia and Proteus-Providencia. Pseudomonas aeruginosa, although it receives considerable (perhaps excessive) attention, is found relatively less frequently, occurring principally in the hospitalized patient who is immunocompromised. Many factors, both host and microbial, are responsible for invasiveness, virulence, and pathogenicity of gram-negative bacilli, but their relative roles, importance, and the pathophysiologic reactions they trigger are yet to be precisely defined. Certain aspects of many (but certainly not all) of the pathogenic correlates considered important in gram-negative bacillary infections, such as microbial flora, local barriers, surface and serum antibodies, complement, cell-mediated immunity, slime production, capsules, pili, endotoxin, cell wall components, extracellular products, and inoculum size are discussed herein. Points at which preventive or therapeutic strategies might be developed are offered. The benefits of antibiotics in managing susceptible gram-negative bacillary infections appear to be plateauing. If further advances are to be made in the therapy of these infections, new approaches to rapidly identifying the responsible etiologic agent and a better understanding of the factors responsible for invasiveness, virulence, and pathogenicity are needed.