Heme regulation of the cytolytic enterotoxin/aerolysin/hemolysin expression in Aeromonas hydrophila and prevalence of the toxin gene amongst Aeromonas coastal water populations

Aeromonas hydrophila, an opportunistic human pathogen, produces hemolysin/cytolytic enterotoxin (Act) under stress in order to obtain iron needed for growth. Iron, an essential nutrient for microorganisms, is a limiting factor in bacterial growth during infection. Presence of Act has been associated to A. hydrophila strains isolated from patients. This dissertation examined: (1) the potential health risk to bathers from aeromonad infections and (2) the induction/suppression of the Act gene in A. hydrophila isolates.; The occurrence of Aeromonas species and prevalence of virulence factors (Act gene and serine protease activator (sp) gene) in the coastal water populations of Southern California's major river mouths and associated beaches were determined using a most probable number method and single polymerase chain reaction (PCR) assays to detect the targeted genes. Overall, 94% and 82% of all samples had the Act and the sp genes, respectively with Aeromonas counts ranging from 102 to 105 cfu/100 ml in the majority of the environmental waters. Furthermore, 50% of the beach samples had a high toxin prevalence, between 1:1 and 1:10 (Aeromonas carry the trait : number of Aeromonas cell). The high toxin prevalence presents a potential health risk to bathers using our beaches.; In addition, to increase detection sensitivity of the virulence factors, quantitative PCR (qPCR) with a dual labeled probe was implemented on samples that were toxin negative by single PCR method. 22.4% of dilutions that gave negative results by the MPN-single PCR assay became positive using qPCR.; Finally, three A. hydrophila strains were selected for Act gene expression study in brain heart infusion broth (BHIB), 2% red blood cell/seawater (2% RBC/seawater), and nutrient broth (NB). Act gene expression increased in BHIB for 2 of the 3 isolates while there was no significant change in NB. In 2% RBC/seawater, 1.3 to 3.5-fold increased in Act expression was observed. The strain, isolated from environmental water, transcribed the fastest (1.5-fold increase in 2 hours), but the food borne outbreak strain had the highest expression (3.5-fold in 6 hours). Overall the data illustrated that the ability to express the toxin gene in marine water may present a potential health risk to Aeromonas infection.