Fimbriation, Pellicle Formation and the Amount of Growth of Salmonellas in Broth

Abstract

In aerobic static broth cultures grown at 37[degree], salmonellas of genotype Fim(l)+, i.e. bearing type-I (mannose-sensitive, hemagglutinating) fimbriae, formed a surface pellicle consisting of densely packed bacteria shortly after the cessation of logarithmic growth at about 6 hr. and then underwent a large secondary phase of growth during the next 24 hr. Salmonellas of genotype Fim(2)+, i.e. bearing type-2 (non-he magglutinating) fimbriae, and most Fim~(non-fimbriate) salmonellas did not form, a pellicle and gave only slight post-logarithmic growth; after 24-72 hr. the amount of their growth, i.e. bacterial concentration estimated turbidimetrically, was only 1/3-1/2 that of comparable type-I fimbriate bacteria. Fim- strains of Salmonella typhimurium differed from most other Fim- salmonellas by forming a pellicle and undergoing an associated secondary phase of growth, but they gave these effects 24-48 hr. later than the Fim(I)+ strains. A pellicle was not formed by any organism either in static cultures incubated anaerobically or in cultures aerated by continuous shaking, and the course and amount of growth were the same for the Fim(l)+ as for the Fim- bacteria in these 2 sets of conditions. The large secondary phase of growth shown by the Fim(l)+ bacteria in aerobic statis broth results from the free availability of atmospheric O2 to the bacteria growing in the pellicle. The presence of 0.2% (w/v) of the hemagglutination-inhibiting sugar, [alpha]-methylmannoside, which was not utilized within 6 days, delayed the formation of a pellicle and the onset of the secondary phase of growth in aerobic static cultures of the Fim(1)+ strain LT2 of S. typhimurium by more than 24 hr. Another hemagglutination-inhibiting sugar, D-mannose, utilized within 12 hr. delayed pellicle formation by only 2-3 hr. in cultures of strain LT2, but it caused a prolonged (> 24 hr.) delay in pellicle formation in cultures of 2 non-mannose -utilizing mutants of strain LT2. D-Glucose and L-sorbose, which do not inhibit hemagglutination, did not delay pellicle formation. These findings, together with the failure of Fim(2)+ bacteria to form a pellicle, suggest that the property of type-1 fimbriae that promotes early pellicle formation is the same as that responsible for the mannose-sensitive hemagglutinating activity.