ELECTRON-MICROSCOPIC EXAMINATION OF FACTORS INFLUENCING THE EXPRESSION OF FILAMENTOUS SURFACE-STRUCTURES ON CLINICAL AND ENVIRONMENTAL ISOLATES OF AEROMONAS-VERONII BIOTYPE SOBRIA

Strains of Aeromonas veronii biotype sobria isolated from clinical and environmental sources were examined for their expression of surface s tructures under a variety of culture conditions. When grown on solid m edia at 37 C, more than 95% of bacteria from the majority of strains i solated from human diarrheal feces and chicken carcasses were non-pili ated or expressed only a few pill of long, flexible morphology per cel l. Strains isolated from water or other foods were much more likely to express pill. Heavily piliated strains (all sources) possessed pill o f several morphological types, including long, flexible pill of varyin g widths and rigid pill of varying lengths. Expression of pill was fav ored by growth at temperatures ca, 20 C and below and growth in liquid medium. Most fecal strains expressed some pill Finder these condition s. In addition, other surface structures (fibrillar aggregates, fibril lar networks, bundle-forming pill) were seen on some strains from most sources. These were also seen most frequently when bacteria were grow n in liquid media at temperatures ca. 20 C and below. Pill expression was not dramatically influenced by growth under anaerobic conditions, or in iron-depleted media, or by combinations of the above conditions. The role of the above surface structures in Aeromonas pathogenicity r emains to be elucidated.