Sensing and adaptation to low pH mediated by inducible amino acid decarboxylases in Salmonella.

Laboratoire de Chimie Bactérienne, Institut de Microbiologie de la Méditerranée, CNRS (UPR-CNRS 9043), Marseille, France.
PLoS ONE (Impact Factor: 3.73). 01/2011; 6(7):e22397. DOI: 10.1371/journal.pone.0022397
Source: PubMed

ABSTRACT During the course of infection, Salmonella enterica serovar Typhimurium must successively survive the harsh acid stress of the stomach and multiply into a mild acidic compartment within macrophages. Inducible amino acid decarboxylases are known to promote adaptation to acidic environments. Three low pH inducible amino acid decarboxylases were annotated in the genome of S. Typhimurium, AdiA, CadA and SpeF, which are specific for arginine, lysine and ornithine, respectively. In this study, we characterized and compared the contributions of those enzymes in response to acidic challenges. Individual mutants as well as a strain deleted for the three genes were tested for their ability (i) to survive an extreme acid shock, (ii) to grow at mild acidic pH and (iii) to infect the mouse animal model. We showed that the lysine decarboxylase CadA had the broadest range of activity since it both had the capacity to promote survival at pH 2.3 and growth at pH 4.5. The arginine decarboxylase AdiA was the most performant in protecting S. Typhimurium from a shock at pH 2.3 and the ornithine decarboxylase SpeF conferred the best growth advantage under anaerobiosis conditions at pH 4.5. We developed a GFP-based gene reporter to monitor the pH of the environment as perceived by S. Typhimurium. Results showed that activities of the lysine and ornithine decarboxylases at mild acidic pH did modify the local surrounding of S. Typhimurium both in culture medium and in macrophages. Finally, we tested the contribution of decarboxylases to virulence and found that these enzymes were dispensable for S. Typhimurium virulence during systemic infection. In the light of this result, we examined the genomes of Salmonella spp. normally responsible of systemic infection and observed that the genes encoding these enzymes were not well conserved, supporting the idea that these enzymes may be not required during systemic infection.

  • [Show abstract] [Hide abstract]
    ABSTRACT: This study aimed to evaluate the possible impact of acid adaptation of Listeria monocytogenes cells on their attachment to stainless steel (SS) during long-term incubation under either low or moderate temperature conditions and on the subsequent recalcitrance of attached cells to lethal acid treatments. Initially, nonadapted or acid-adapted stationary phase L. monocytogenes cells were used to inoculate (ca. 10(8)CFU/ml) brain-heart infusion (BHI) broth in test tubes containing vertically placed SS coupons. Incubation was carried out at either 5 or 30°C for up to 15days, under static conditions. On the 5th, 10th and 15th days of incubation, attached cells were subjected to lethal acid treatments by exposing them, for either 6 or 60min, to pH2, adjusted with either hydrochloric or lactic acid. Following the acid treatments, remaining viable cells were detached (through strong vortexing with glass beads) and enumerated by agar plating, and also indirectly quantified by conductance measurements via their metabolic activity. Results obtained from both quantification techniques, employed here in parallel, revealed that although the numbers of attached cells for nonadapted and acid-adapted ones were similar, the latter were found to present significantly (p<0.05) increased recalcitrance to all the acid treatments for both incubation temperatures and all sampling days. In addition and regardless of acid adaptation, when long (60min) acid treatments were applied, conductance measurements revealed that the weak organic lactic acid exhibited significantly (p<0.05) stronger antilisterial activity compared to the strong inorganic hydrochloric acid (at the same pH value of 2). To conclude, present results show that acid adaptation of L. monocytogenes cells during their planktonic growth is conserved even after 15days of incubation under both low and moderate temperature conditions, and results in the increased recalcitrance of their sessile population to otherwise lethal acid treatments. This "stress hardening" should be severely taken into account when acidic decontamination interventions are used to kill attached to equipment surfaces cells of this important pathogenic bacterium.
    International journal of food microbiology 11/2013; 171C:1-7. · 3.01 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Salmonella Gallinarum biovar Pullorum (S. Gallinarum biovar Pullorum) is the causative agent of pullorum disease (PD) in chickens which results in considerable economic losses to the poultry industries in developing countries. PCR-Signature Tagged Mutagenesis was used to identify virulence determinants of S. Gallinarum biovar Pullorum and novel attenuated live vaccine candidates for use against this disease. A library of 1800 signature-tagged S. Gallinarum biovar Pullorum mutants was constructed and screened for virulence-associated genes in chickens. The attenuation of 10 mutants was confirmed by in vivo and in vitro competitive index (CI) studies. The transposons were found to be located in SPI-1 (2/10 mutants), SPI-2 (3/10), the virulence plasmid (1/10) and non-SPI genes (4/10). One highly attenuated spiC mutant persisted in spleen and liver for less than 10 days and induced high levels of circulating antibody and protective immunity against oral challenge in young broiler chickens. The spiC mutant is a potential new vaccine candidate for use with chickens against this disease.
    Veterinary Microbiology 11/2013; · 3.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The low pH of the stomach serves as a barrier to ingested microbes and must be overcome or bypassed when delivering live bacteria for vaccine or probiotic applications. Typically, the impact of stomach acidity on bacterial survival is evaluated in vitro, as there are no small animal models to evaluate these effects in vivo. To better understand the effect of this low pH barrier to live attenuated Salmonella vaccines, which are often very sensitive to low pH, we investigated the value of the histamine mouse model for this application. A low pH gastric compartment was transiently induced in mice by the injection of histamine. This resulted in a gastric compartment of approximately pH 1.5 that was capable of distinguishing between acid-sensitive and acid-resistant microbes. Survival of enteric microbes during gastric transit in this model directly correlated with their in vitro acid resistance. Because many Salmonella enterica serotype Typhi vaccine strains are sensitive to acid, we have been investigating systems to enhance the acid resistance of these bacteria. Using the histamine mouse model, we demonstrate that the in vivo survival of S. Typhi vaccine strains increased approximately 10-fold when they carried a sugar-inducible arginine decarboxylase system. We conclude that this model will be a useful for evaluating live bacterial preparations prior to clinical trials.
    PLoS ONE 01/2014; 9(1):e87411. · 3.73 Impact Factor

Full-text (2 Sources)

Available from
Jun 2, 2014