Correction: Zinc is required to ensure the expression of flagella and the ability to form biofilms in Salmonella enterica sv Typhimurium

: Correction for 'Zinc is required to ensure the expression of flagella and the ability to form biofilms in Salmonella enterica sv Typhimurium' by Serena Ammendola et al., Metallomics, 2016, DOI: 10.1039/c6mt00108d

Salmonella enterica serovar typhimurium exploits inflammation to modify swine intestinal microbiota

Salmonella enterica serovar Typhimurium is an important zoonotic gastrointestinal pathogen responsible for foodborne disease worldwide. It is a successful enteric pathogen because it has developed virulence strategies allowing it to survive in a highly inflamed intestinal environment exploiting inflammation to overcome colonization resistance provided by intestinal microbiota. In this study, we used piglets featuring an intact microbiota, which naturally develop gastroenteritis, as model for salmonellosis. We compared the effects on the intestinal microbiota induced by a wild type and an attenuated S. Typhimurium in order to evaluate whether the modifications are correlated with the virulence of the strain. This study showed that Salmonella alters microbiota in a virulence-dependent manner. We found that the wild type S. Typhimurium induced inflammation and a reduction of specific protecting microbiota species (SCFA-producing bacteria) normally involved in providing a barrier against pathogens. Both these effects could contribute to impair colonization resistance, increasing the host susceptibility to wild type S. Typhimurium colonization. In contrast, the attenuated S. Typhimurium, which is characterized by a reduced ability to colonize the intestine, and by a very mild inflammatory response, was unable to successfully sustain competition with the microbiota

Zinc is required to ensure the expression of flagella and the ability to form biofilms in: Salmonella enterica sv Typhimurium

Zinc is known to play a central role in bacterial physiology and pathogenesis. Here, we report that the accumulation of FliC, the structural subunit of Salmonella phase 1 flagella, is sharply reduced in a znuABC Salmonella enterica sv. Typhimurium strain grown in zinc-poor media. Consequently, this mutant strain lacks motility, unless it grows in zinc-replete environments. This phenotype is the consequence of a general downregulation of all the genes involved in the biosynthesis of flagella, suggesting that zinc is the cofactor of proteins involved in the initiation of the transcriptional regulatory cascade leading to flagella assembly. Competition experiments in mice demonstrated that aflagellated (fliBfljC) and znuABC strains are outcompeted by the wild type strain in the gastrointestinal tract. The fliBfljC strain overgrows a fliCfljBznuABC mutant strain, but the difference in gut colonization between these two strains is less striking than that between the wild type and the znuABC strains, suggesting that the downregulation of flagella contributes to the loss of virulence of Salmonella znuABC. The absence of either flagella or ZnuABC also impairs the ability of S. Typhimurium to produce biofilms. Zinc suppresses this defect in the znuABC mutant but not in the aflagellated strains, highlighting the role of flagella in biofilm organization. We have also observed an increased production of the quorum sensing signal AI-2 in the znuABC strain sensing zinc deprivation, that may further contribute to the reduced ability to form biofilms. On the whole, our study reveals novel roles of zinc in Salmonella motility and intercellular communication

S. Typhimurium and S. Typhimurium Monophasic variant attenuated vaccines. A comparison of efficacy in homologous and heterologous infection in piglets

Introduction: Salmonella Typhimurium and its monophasic variant (S. Typhimurium 1, 4, [5], 12:i-) are increasingly responsible of food borne infections in humans and pork represents the principal source of infection. Infection is generally sub-clinical in pigs and carrier pigs could introduce bacteria in the slaughterhouse. The aim of the study was to test the efficacy and safety of an attenuated vaccine of S. Typhimurium 1, 4, [5], 12:i- (S. Typhimurium Monophasic variant ΔznuABC) during an homologous and heterologous infection, with a field isolated strain of S. Typhimurium. The efficacy and safety of S. Typhimurium Monophasic variant ΔznuABC was compared to an attenuated strain of S. Typhimurium (S. Typhimurium ΔznuABC). Materials and Methods: Twenty eight weaned piglets were divided in 3 groups and acclimatized for a week. Group T was composed of 8 piglets vaccinated with an oral administration of S. Typhimurium ΔznuABC at the final dose of 5 х 107 CFU. Group M was composed of 10 piglets vaccinated with an oral administration of S. Typhimurium Monophasic variant ΔznuABC at the final dose of 5 х 107 CFU. Group C was composed of 10 unvaccinated piglets. At day 35 after vaccination, all piglets were challenged by an oral gavage with 5 х 108 CFU of S. Typhimurium Monophasic variant or S. Typhimurium. Particularly, piglets from group T were divided in 2 groups: 3 piglets were infected with S. Typhimurium, the other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Piglets from group M were divided in 2 groups: 5 piglets were infected with S. Typhimurium. The other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Unvaccinated piglets were divided in 2 groups: 5 piglets were infected with S. Typhimurium, the other 5 piglets were infected with S. Typhimurium 1, 4, [5], 12:i-. Analyzed parameters were weight, temperature, fecal shedding and organ colonization. Results: In control groups, the amount of S. Typhimurium in feces tends to be higher than S. Typhimurium 1, 4, [5], 12:i- from challenge to the end of the trial and temperature was significantly different at day 1 after infection indicating that S. Typhimurium was more virulent than S. Typhimurium 1, 4, [5], 12:i-. The safety of vaccine strains was monitored analyzing fecal shedding and growth of animals. Conclusion: Attenuated vaccines were safe, in fact they were not isolated in feces after three weeks from vaccination and did not affected growth of animals. Furthermore, both attenuated vaccines reduced the shedding of virulent strains in comparison to unvaccinated groups and S. Typhimurium ΔznuABC appeared more effective in homologous and heterologous challenge infections

Attenuated mutant strain of salmonella typhimurium lacking the ZnuABC transporter contrasts tumor growth promoting anti-cancer immune response

Salmonella Typhimurium has been shown to be highly effective as antitumor agent. The aim of this study was to investigate the tumor targeting efficacy and the mechanism of action of a specific attenuated mutant strain of Salmonella Typhimurium (STM) devoid of the whole operon coding for the high-affinity zinc transporter ZnuABC, which is required for bacterial growth in environments poor in zinc and for conferring full virulence to different Gram-negative pathogens. We showed that STM is able to penetrate and replicate into tumor cells in in vitro and in vivo models. The subcutaneous administration of STM in mammary adenocarcinoma mouse model led to both reduction of tumor growth and increase in life expectancy of STM treated mice. Moreover, investigating the potential mechanism behind the favorable clinical outcomes, we provide evidence that STM stimulates a potent inflammatory response and a specific immune pattern, recruiting a large number of innate and adaptive immune cells capable to contrast the immunosuppressive environment generated by tumors

The capability of Pseudomonas aeruginosa to recruit zinc under conditions of limited metal availability is affected by inactivation of the ZnuABC transporter.

The ability of a large number of bacterial pathogens to multiply in the infected host and cause disease is dependent on their ability to express high affinity zinc importers. In many bacteria, ZnuABC, a transporter of the ABC family, plays a central role in the process of zinc uptake in zinc poor environments, including the tissues of the infected host. To initiate an investigation into the relevance of the zinc uptake apparatus for Pseudomonas aeruginosa pathogenicity, we have generated a znuA mutant in the PA14 strain. We have found that this mutant strain displays a limited growth defect in zinc depleted media. The znuA mutant strain is more sensitive than the wild type strain to calprotectin-mediated growth inhibition, but both the strains are highly resistant to this zinc sequestering antimicrobial protein. Moreover, intracellular zinc content is not evidently affected by inactivation of the ZnuABC transporter. These findings suggest that P. aeruginosa is equipped with redundant mechanisms for the acquisition of zinc that might favor P. aeruginosa colonization of environments containing low levels of this metal. Nonetheless, deletion of znuA affects alginate production, reduces the activity of extracellular zinc-containing proteases, including LasA, LasB and protease IV, and decreases the ability of P. aeruginosa to disseminate during systemic infections. These results indicate that efficient zinc acquisition is critical for the expression of various virulence features typical of P. aeruginosa and that ZnuABC also plays an important role in zinc homeostasis in this microorganism

Lack of AcrB efflux function confers loss of virulence to Salmonella Typhimurium

AcrAB-TolC is the paradigm resistance-nodulation-division (RND) multidrug resistance efflux system in Gram-negative bacteria, with AcrB being the pump protein in this complex. We constructed a non-functional AcrB mutant by substituting D408, a highly conserved residue essential for proton translocation. Western blotting confirmed that the AcrB D408A mutant had the same native level of expression of AcrB as the parental strain. The mutant had no growth deficiencies in rich or minimal media. However, compared with wild-type SL1344, the mutant had increased accumulation of the Hoechst 33342 dye, decreased efflux of ethidium bromide and was multidrug hyper-susceptible. The D408A mutant was attenuated in vivo in a mouse model and showed significantly reduced invasion into intestinal epithelial cells and macrophages in vitro. A dose dependent inhibition of invasion was also observed when two different efflux pump inhibitors were added to the wild-type strain during infection of epithelial cells. RNAseq revealed down-regulation of bacterial factors necessary for infection, including those in the Salmonella Pathogenicity Islands 1, 2 and 4, quorum sensing genes and phoPQ. Several general stress response genes were up-regulated, probably due to retention of noxious molecules inside the bacterium. Unlike loss of AcrB protein, loss of efflux function did not induce overexpression of other RND efflux pumps. Our data suggests that gene deletion mutants are unsuitable for studying membrane transporters and, importantly, that inhibitors of AcrB efflux function will not induce expression of other RND pumps