Investigation of the Role of Type IV Aeromonas Pilus (Tap) in the Pathogenesis of Aeromonas Gastrointestinal Infection

Abstract

Although there is substantial evidence that type IV pili purified from diarrhea-associated Aeromonas species (designated Bfp for bundle-forming pilus) are intestinal colonization factors (S. M. Kirov, L. A. O'Donovan, and K. Sanderson, Infect. Immun. 67:5447-5454, 1999), nothing is known regarding the function of a second family of Aeromonas type IV pili (designated Tap for type IV Aeromonas pilus), identified following the cloning of a pilus biogenesis gene cluster tapABCD. Related pilus gene clusters are widely conserved among gramnegative bacteria, but their significance for virulence has been controversial. To investigate the role of Tap pili in Aeromonas pathogenesis, mutants of Aeromonas strains (a fish isolate of A. hydrophila and a human dysenteric isolate of A. veronii bv. sobria) were prepared by insertional inactivation of the tapA gene which encodes the type IV pilus subunit protein, TapA. Exotoxic activities were unaffected by the mutation in tapA. Inactivation of tapA had no effect on the bacterial adherence of these two isolates to HEp-2 cells. For the A. veronii bv. sobria isolate, adhesion to Henle 407 intestinal cells and to human intestinal tissue was also unaffected. There was no significant effect on the duration of colonization or incidence of diarrhea when the A. veronii bv. sobria strain was tested in the removable intestinal tie adult rabbit diarrhea model or on its ability to colonize infant mice. Evidence was obtained that demonstrated that TapA was expressed by both Aeromonas species and was present on the cell surface, although if assembled into pili this pilus type appears to be an uncommon one under standard bacterial growth conditions. Further studies into factors which may influence Tap expression are required, but the present study suggests that Tap pili may not be as significant as Bfp pili for Aeromonas intestinal colonization.

Distribution of virulence genes in Aeromonas spp. isolated from Sardinian waters and from patients with diarrhoea

“…The purpose of this study was to compare the virulence phenotype of different Aeromonas strains isolated from patients with diarrhoea, and from the aquatic environment of Sardinia. Furthermore, the presence of virulence genes previously reported and thought to be involved in pathogenicity was investigated (Barnett et al 1997;Kingombe et al 1999;Kirov et al 2000). The previously described enterobacterial repetitive intergenic consensus sequence PCR (ERIC-PCR) was used to differentiate the different Aeromonas spp.…”

Tissue Culture to Assess Bacterial Enteropathogenicity

“…The damage produced was demonstrated by the alterations of the integrity of intestinal microvilli, disruption of the epithelium and presence of mucosal microulcerations, which were brought about by the fact that this strain is an high cytotoxin producer and may possess other virulence factors [4,21] These strains belong to the A. caviae species and were considered of lesser virulence than other strains of this species [22].…”

“…[1,2,3] The genus Aeromonas comprises gram-negative bacteria that can be isolated from water and a diversity of foods. Some strains are important diarrhea producers, particularly in children under five years and in older adults [4,5].…”

An Aeromonas salmonicida type IV pilin is required for virulence in rainbow trout Oncorhynchus mykiss

“…In recent studies we and colleagues have described the isolation of genes encoding factors involved in the biogenesis of type IV pili and type II extracellular secretion of proteins from Aeromonas hydrophila (Pepe et al 1996, Barnett et al 1997, Barnett & Kirov 1999, Kirov et al 2000. Type IV pili are present on the surface of many Gram-negative pathogens and have been shown to be important virulence determinants .…”

“…While this is not proof of bacterial piliation, there are no known instances where a type IV pilin protein is expressed and not assembled into functional pili. Western blots do demonstrate that the amount of pilin protein expressed by A. salmonicida appears to be at a low level, and indeed similar low levels of expression under laboratory culture conditions have been demonstrated for the TapA type IV pili of A. hydrophila (Pepe et al 1996, Kirov et al 2000 and Vibrio vulnificus (R. N. Paranjpye & M. S. Strom unpubl.). However, low pilin expression could simply reflect a lack of appropriate environmental cues in the in vitro growth conditions used because it is known that expression of type IV pilins are under transcriptional control by members of protein-phosphorylating 2-component regulatory systems and the alternative RpoN sigma factor of RNA polymerase (Ishimoto & Lory 1989, Jin et al 1994.…”