Host-Nonspecific Iron Acquisition Systems and Virulence in the Zoonotic Serovar of Vibrio vulnificus

Abstract

dThe zoonotic serovar of Vibrio vulnificus (known as biotype 2 serovar E) is the etiological agent of human and fish vibriosis. The aim of the present work was to discover the role of the vulnibactin-and hemin-dependent iron acquisition systems in the pathogenicity of this zoonotic serovar under the hypothesis that both are host-nonspecific virulence factors. To this end, we selected three genes for three outer membrane receptors (vuuA, a receptor for ferric vulnibactin, and hupA and hutR, two hemin receptors), obtained single and multiple mutants as well as complemented strains, and tested them in a series of in vitro and in vivo assays, using eels and mice as animal models. The overall results confirm that hupA and vuuA, but not hutR, are host-nonspecific virulence genes and suggest that a third undescribed host-specific plasmid-encoded system could also be used by the zoonotic serovar in fish. hupA and vuuA were expressed in the internal organs of the animals in the first 24 h of infection, suggesting that they may be needed to achieve the population size required to trigger fatal septicemia. vuuA and hupA were sequenced in strains representative of the genetic diversity of this species, and their phylogenies were reconstructed by multilocus sequence analysis of selected housekeeping and virulence genes as a reference. Given the overall results, we suggest that both genes might form part of the core genes essential not only for disease development but also for the survival of this species in its natural reservoir, the aquatic environment.

Novel host‐specific iron acquisition system in the zoonotic pathogenVibrio vulnificus

“…immersion in a bacterial‐infected bath (Table ). Previous studies have shown that the hupA and vuuA double mutant (the receptors for vulnibactin and Hm) was avirulent for mice but retained some degree of virulence for i.p.‐injected eels (Pajuelo et al ., ) (Table ). We obtained the triple mutant strain Δ hupA Δ vuuA Δ vep20 to determine whether vep20 influenced this remaining virulence.…”

“…To determine whether vep20 was involved in iron acquisition from Hb, the strains were cultured with commercial Hm as the sole iron source. No significant differences in growth were observed among wild type, c vep20 and Δ vep20 strains, while the minimal Hm stimulatory concentration was higher than 10 μM for the negative control strain, Δ hupA Δ hutR , a mutant strain obtained in a previous study, unable to grow using Hm as the sole iron source (Pajuelo et al ., ) (Table ).…”

“…In addition, Pajuelo et al . () also suggested that Vep20 is under Fur control. To confirm that Vep20 is an IROMP, the OM proteins of the wild type and derivative strains (Δ vep20 , c vep20 ) were extracted from cultures grown in the absence and presence of iron, followed by immunostaining with antibodies against rVep20 (Fig.…”

“…The same results were obtained by Pajuelo et al . () for hupA and vuuA , indicating that these three genes are involved in response to iron starvation.…”

The Fish Pathogen Vibrio vulnificus Biotype 2: Epidemiology, Phylogeny, and Virulence Factors Involved in Warm-Water Vibriosis

“…The VuuA-and HupA-depending systems are involved in virulence of biotype 1 for mice (87,88,89), while the role of HutR-depending system in virulence has not been studied. In order to find out the role of the three systems in the virulence for eels and mice of the zoonotic serovar, Pajuelo et al (90) selected the strain CECT 4999 and obtained a series of single and multiple mutants in vuuA, hupA, and hutR, as well as the corresponding complemented strains that were used together with the wild type strain in a series of phenotypic assays performed in vitro and in vivo. The authors demonstrated that hutR is not involved in virulence, although it could collaborate in iron-uptake from hemin/hemoglobin.…”