RESUMO

Pseudomonas aeruginosa is an opportunistic pathogen found in a wide variety of environments, including soil, water, and habitats associated with animals, humans, and plants. From a One Health perspective, which recognizes the interconnectedness of human, animal, and environmental health, it is important to study the virulence characteristics and antibiotic susceptibility of environmental bacteria. In this study, we compared the virulence properties and the antibiotic resistance profiles of seven isolates collected from the Gulf of Mexico with those of seven clinical strains of P. aeruginosa. Our results indicate that the marine and clinical isolates tested exhibit similar virulence properties; they expressed different virulence factors and were able to kill Galleria mellonella larvae, an animal model commonly used to analyze the pathogenicity of many bacteria, including P. aeruginosa. In contrast, the clinical strains showed higher antibiotic resistance than the marine isolates. Consistently, the clinical strains exhibited a higher prevalence of class 1 integron, an indicator of anthropogenic impact, compared with the marine isolates. Thus, our results indicate that the P. aeruginosa marine strains analyzed in this study, isolated from the Gulf of Mexico, have similar virulence properties, but lower antibiotic resistance, than those from hospitals.

RESUMO

Salmonella enterica serovar Typhimurium causes gastroenteritis and systemic infections in humans. For this bacterium the expression of a type III secretion system (T3SS) and effector proteins encoded in the Salmonella pathogenicity island-1 (SPI-1), is keystone for the virulence of this bacterium. Expression of these is controlled by a regulatory cascade starting with the transcriptional regulators HilD, HilC and RtsA that induce the expression of HilA, which then activates expression of the regulator InvF, a transcriptional regulator of the AraC/XylS family. InvF needs to interact with the chaperone SicA to activate transcription of SPI-1 genes including sicA, sopB, sptP, sopE, sopE2, and STM1239. InvF very likely acts as a classical activator; however, whether InvF interacts with the RNA polymerase alpha subunit RpoA has not been determined. Results from this study confirm the interaction between InvF with SicA and reveal that both proteins interact with the RNAP alpha subunit. Thus, our study further supports that the InvF/SicA complex acts as a classical activator. Additionally, we showed for the first time an interaction between a chaperone of T3SS effectors (SicA) and the RNAP.

Assuntos

RESUMO

In many bacteria, the BarA/SirA and Csr regulatory systems control expression of genes encoding a wide variety of cellular functions. The BarA/SirA two-component system induces the expression of CsrB and CsrC, two small non-coding RNAs that sequester CsrA, a protein that binds to target mRNAs and thus negatively or positively regulates their expression. BarA/SirA and CsrB/C induce expression of the Salmonella Pathogenicity Island 1 (SPI-1) genes required for Salmonella invasion of host cells. To further investigate the regulatory role of the BarA/SirA and Csr systems in Salmonella, we performed LC-MS/MS proteomic analysis using the WT S. Typhimurium strain and its derived ΔsirA and ΔcsrB ΔcsrC mutants grown in SPI-1-inducing conditions. The expression of 164 proteins with a wide diversity, or unknown, functions was significantly affected positively or negatively by the absence of SirA and/or CsrB/C. Interestingly, 19 proteins were identified as new targets for SirA-CsrB/C. Our results support that SirA and CsrB/C act in a cascade fashion to regulate gene expression in S. Typhimurium in the conditions tested. Notably, our results show that SirA-CsrB/C-CsrA controls expression of proteins required for the replication of Salmonella in the intestinal lumen, in an opposite way to its control exerted on the SPI-1 proteins. SIGNIFICANCE: The BarA/SirA and Csr global regulatory systems control a wide range of cellular processes, including the expression of virulence genes. For instance, in Salmonella, BarA/SirA and CsrB/C positively regulate expression of the SPI-1 genes, which are required for Salmonella invasion to host cells. In this study, by performing a proteomic analysis, we identified 164 proteins whose expression was positively or negatively controlled by SirA and CsrB/C in SPI-1-inducing conditions, including 19 new possible targets of these systems. Our results support the action of SirA and CsrB/C in a cascade fashion to control different cellular processes in Salmonella. Interestingly, our data indicate that SirA-CsrB/C-CsrA controls inversely the expression of proteins required for invasion of the intestinal epithelium and for replication in the intestinal lumen, which suggests a role for this regulatory cascade as a molecular switch for Salmonella virulence. Thus, our study further expands the insight into the regulatory mechanisms governing the virulence and physiology of an important pathogen.

Assuntos

RESUMO

Development of novel antibacterial strategies is required to tackle the alarming threat for global health due to antimicrobial resistance. In this issue of the Journal of Bacteriology, Boulanger et al. provide evidence supporting that the blocking of metabolic pathways to induce accumulation of toxic intermediates can be a possible approach to combat bacterial infections (E. F. Boulanger, A. Sabag-Daigle, M. Baniasad, K. Kokkinias, et al., J Bacteriol 204:e00344-22, 2022, https://doi.org/10.1128/jb.00344-22).

Assuntos

RESUMO

The acquisition of Salmonella pathogenicity island 2 (SPI-2) conferred on Salmonella the ability to survive and replicate within host cells. The ssrAB bicistronic operon, located in SPI-2, encodes the SsrAB two-component system (TCS), which is the central positive regulator that induces the expression of SPI-2 genes as well as other genes located outside this island. On the other hand, CpxRA is a two-component system that regulates expression of virulence genes in many bacteria in response to different stimuli that perturb the cell envelope. We previously reported that the CpxRA system represses the expression of SPI-1 and SPI-2 genes under SPI-1-inducing conditions by decreasing the stability of the SPI-1 regulator HilD. Here, we show that under SPI-2-inducing conditions, which mimic the intracellular environment, CpxRA represses the expression of SPI-2 genes by the direct action of phosphorylated CpxR (CpxR-P) on the ssrAB regulatory operon. CpxR-P recognized two sites located proximal and distal from the promoter located upstream of ssrA. Consistently, we found that CpxRA reduces the replication of Salmonella enterica serovar Typhimurium inside murine macrophages. Therefore, our results reveal CpxRA as an additional regulator involved in the intracellular lifestyle of Salmonella, which in turn adds a new layer to the intricate regulatory network controlling the expression of Salmonella virulence genes. IMPORTANCE SPI-2 encodes a type III secretion system (T3SS) that is a hallmark for the species Salmonella enterica, which is essential for the survival and replication within macrophages. Expression of SPI-2 genes is positively controlled by the two-component system SsrAB. Here, we determined a regulatory mechanism involved in controlling the overgrowth of Salmonella inside macrophages. In this mechanism, CpxRA, a two-component system that is activated by extracytoplasmic stress, directly represses expression of the ssrAB regulatory operon; as a consequence, expression of SsrAB target genes is decreased. Our findings reveal a novel mechanism involved in the intracellular lifestyle of Salmonella, which is expected to sense perturbations in the bacterial envelope that Salmonella faces inside host cells, as the synthesis of the T3SS-2 itself.

Assuntos

RESUMO

One important event for the divergence of Salmonella from Escherichia coli was the acquisition by horizontal transfer of the Salmonella pathogenicity island 1 (SPI-1), containing genes required for the invasion of host cells by Salmonella. HilD is an AraC-like transcriptional regulator in SPI-1 that induces the expression of the SPI-1 and many other acquired virulence genes located in other genomic regions of Salmonella. Additionally, HilD has been shown to positively control the expression of some ancestral genes (also present in E. coli and other bacteria), including phoH. In this study, we determined that both the gain of HilD and cis-regulatory evolution led to the integration of the phoH gene into the HilD regulon. Our results indicate that a HilD-binding sequence was generated in the regulatory region of the S. enterica serovar Typhimurium phoH gene, which mediates the activation of promoter 1 of this gene under SPI-1-inducing conditions. Furthermore, we found that repression by H-NS, a histone-like protein, was also adapted on the S. Typhimurium phoH gene and that HilD activates the expression of this gene in part by antagonizing H-NS. Additionally, our results revealed that the expression of the S. Typhmurium phoH gene is also activated in response to low phosphate but independently of the PhoB/R two-component system, known to regulate the E. coli phoH gene in response to low phosphate. Thus, our results indicate that cis-regulatory evolution has played a role in the expansion of the HilD regulon and illustrate the phenomenon of differential regulation of ortholog genes. IMPORTANCE Two mechanisms mediating differentiation of bacteria are well known: acquisition of genes by horizontal transfer events and mutations in coding DNA sequences. In this study, we found that the phoH ancestral gene is differentially regulated between Salmonella Typhimurium and Escherichia coli, two closely related bacterial species. Our results indicate that this differential regulation was generated by mutations in the regulatory sequence of the S. Typhimurium phoH gene and by the acquisition by S. Typhimurium of foreign DNA encoding the transcriptional regulator HilD. Thus, our results, together with those from an increasing number of studies, indicate that cis-regulatory evolution can lead to the rewiring and reprogramming of transcriptional regulation, which also plays an important role in the divergence of bacteria through time.

Assuntos

RESUMO

Infection with Helicobacter pylori is one of the most important risk factors for developing gastric cancer (GC). The type IV secretion system (T4SS) encoded in the cag pathogenicity island is the main virulence factor of H. pylori associated with GC. Additionally, other virulence factors have been shown to play a role in the H. pylori virulence, such as vacuolizing cytotoxin (VacA), urease, flagella, and adhesins. Long-chain fatty acids (LCFAs) are signaling molecules that affect the transcription of virulence genes in several pathogenic bacteria such as Salmonella enterica, Vibrio cholerae, Pseudomonas aeruginosa and Mycobacterium tuberculosis. However, the effect of LCFAs on the transcription of H. pylori virulence and regulatory genes remains unknown. Here we analyzed whether the transcription of virulence genes that encode T4SS and cellular envelope components, flagellins, adhesins, toxins, urease, as well as the transcription of different regulatory genes of the H. pylori strain 26695, are altered by the presence of five distinct LCFAs: palmitic, stearic, oleic, linoleic, and linolenic acids. Palmitic and oleic acids up-regulated the transcription of most of the virulence genes tested, including cagL, cagM, flaB, sabA, mraY and vacA, as well as that of the genes encoding the transcriptional regulators NikR, Fur, CheY, ArsR, FlgR, HspR, HsrA, Hup, and CrdR. In contrast, the other LCFAs differentially affected the transcription of the virulence and regulatory genes assessed. Our data show that LCFAs can act as signaling molecules that control the transcription of the H. pylori virulome.

RESUMO

The genus Campylobacter groups 32 Gram-negative bacteria species, several being zoonotic pathogens and a major cause of human gastroenteritis worldwide. Antibiotic resistant Campylobacter is considered by the World Health Organization as a high priority pathogen for research and development of new antibiotics. Genetic elements related to antibiotic resistance in the classical C. coli and C. jejuni species, which infect humans and livestock, have been analyzed in numerous studies, mainly focused on local geographical areas. However, the presence of these resistance determinants in other Campylobacter species, as well as in C. jejuni and C. coli strains distributed globally, remains poorly studied. In this work, we analyzed the occurrence and distribution of antibiotic resistance factors in 237 Campylobacter closed genomes available in NCBI, obtained from isolates collected worldwide, in different dates, from distinct hosts and comprising 22 Campylobacter species. Our data revealed 18 distinct genetic determinants, genes or point mutations in housekeeping genes, associated with resistance to antibiotics from aminoglycosides, ß-lactams, fluoroquinolones, lincosamides, macrolides, phenicols or tetracyclines classes, which are differentially distributed among the Campylobacter species tested, on chromosomes or plasmids. Three resistance determinants, the bla OXA-493 and bla OXA-576 genes, putatively related to ß-lactams resistance, as well as the lnu(AN2) gene, putatively related to lincosamides resistance, had not been reported in Campylobacter; thus, they represent novel determinants for antibiotic resistance in Campylobacter spp., which expands the insight on the Campylobacter resistome. Interestingly, we found that some of the genetic determinants associated with antibiotic resistance are Campylobacter species-specific; e.g., the bla OXA-493 gene and the T86V mutation in gyrA were found only in the C. lari group, whereas genes associated with aminoglycosides resistance were found only in C. jejuni and C. coli. Additional analyses revealed how are distributed the resistance and multidrug resistance Campylobacter genotypes assessed, with respect to hosts, geographical locations, and collection dates. Thus, our findings further expand the knowledge on the factors that can determine or favor the antibiotic resistance in Campylobacter species distributed globally, which can be useful to choose a suitable antibiotic treatment to control the zoonotic infections by these bacteria.

RESUMO

HilD is an AraC-like transcriptional regulator encoded in the Salmonella pathogenicity island 1 (SPI-1), which actives transcription of many genes within and outside SPI-1 that are mainly required for invasion of Salmonella into host cells. HilD controls expression of target genes directly or by acting through distinct regulators; three different regulatory cascades headed by HilD have been described to date. Here, by analyzing the effect of HilD on the yobH gene in Salmonella enterica serovar Typhimurium (S. Typhimurium), we further define an additional regulatory cascade mediated by HilD, which was revealed by previous genome-wide analyses. In this regulatory cascade, HilD acts through SprB, a LuxR-like regulator encoded in SPI-1, to induce expression of virulence genes. Our data show that HilD induces expression of sprB by directly counteracting H-NS-mediated repression on the promoter region upstream of this gene. Then, SprB directly activates expression of several genes including yobH, slrP and ugtL. Interestingly, we found that YobH, a protein of only 79 amino acids, is required for invasion of S. Typhimurium into HeLa cells and mouse macrophages. Thus, our results reveal a novel S. Typhimurium invasion factor and provide more evidence supporting the HilD-SprB regulatory cascade.

Assuntos

RESUMO

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

RESUMO

When Salmonella is grown in the nutrient-rich lysogeny broth (LB), the AraC-like transcriptional regulator HilD positively controls the expression of genes required for Salmonella invasion of host cells, such as the Salmonella pathogenicity island 1 (SPI-1) genes. However, in minimal media, the two-component system PhoP/Q activates the expression of genes necessary for Salmonella replication inside host cells, such as the SPI-2 genes. Recently, we found that the SL1344_1872 hypothetical gene, located in a S. Typhimurium genomic island, is co-expressed with the SPI-1 genes. In this study we demonstrate that HilD induces indirectly the expression of SL1344_1872 when S. Typhimurium is grown in LB; therefore, we named SL1344_1872 as grhD1 for gene regulated by HilD. Furthermore, we found that PhoP positively controls the expression of grhD1, independently of HilD, when S. Typhimurium is grown in LB or N-minimal medium. Moreover, we demonstrate that the grhD1 gene is required for the invasion of S. Typhimurium into epithelial cells, macrophages and fibroblasts, as well as for the intestinal inflammatory response caused by S. Typhimurium in mice. Thus, our results reveal a novel virulence factor of Salmonella, whose expression is positively and independently controlled by the HilD and PhoP transcriptional regulators.

Assuntos

RESUMO

BACKGROUND: Classical strains of Salmonella enterica serovar Typhimurium (Typhimurium) predominantly cause a self-limiting diarrheal illness in humans and a systemic disease in mice. In this study, we report the characterization of a strain isolated from a blood-culture taken from a 15-year old woman suffering from invasive severe salmonellosis, refractory to conventional therapy with extended-spectrum cephalosporin (ESC). RESULTS: The strain, named 33676, was characterized as multidrug-resistant Salmonella serogroup A by biochemical, antimicrobial and serological tests. Multilocus sequence typing (MLST) and XbaI macrorestrictions (PFGE) showed that strain 33676 belonged to the Typhimurium ST213 genotype, previously described for other Mexican Typhimurium strains. PCR analyses revealed the presence of IncA/C, IncFIIA and ColE1-like plasmids and the absence of the Salmonella virulence plasmid (pSTV). Conjugation assays showed that the ESC-resistance gene bla CMY-2 was carried on the conjugative IncF plasmid, instead of the IncA/C plasmid, as found in previously studied ST213 strains. Although the IncA/C plasmid conferred most of the observed antimicrobial resistances it was not self-conjugative; it was rather able to conjugate by co-integrating with the IncF plasmid. Strain 33676 was fully attenuated for virulence in BALB/c mice infections. Both type-three secretion system (T3SS), encoded in Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2), were functional in the 33676 strain and, interestingly, this strain produced the H2 FljB flagellin instead of the H1 FliC flagellin commonly expressed by S. enterica strains. CONCLUSIONS: Strain 33676 showed two main features that differentiate it from the originally described ST213 strains: 1) the bla CMY-2 gene was not carried on the IncA/C plasmid, but on a conjugative IncF plasmid, which may open a new route of dissemination for this ESC-resistance gene, and 2) it expresses the H2 FljB flagella, in contrast with the other ST213 and most Typhimurium reference strains. To our knowledge this is the first report of an IncF bla CMY-2-carrying plasmid in Salmonella.

Assuntos

RESUMO

Salmonella enterica can cause intestinal or systemic infections in humans and animals mainly by the presence of pathogenicity islands SPI-1 and SPI-2, containing 39 and 44 genes, respectively. The AraC-like regulator HilD positively controls the expression of the SPI-1 genes, as well as many other Salmonella virulence genes including those located in SPI-2. A previous report indicates that the two-component system CpxR/A regulates the SPI-1 genes: the absence of the sensor kinase CpxA, but not the absence of its cognate response regulator CpxR, reduces their expression. The presence and absence of cell envelope stress activates kinase and phosphatase activities of CpxA, respectively, which in turn controls the level of phosphorylated CpxR (CpxR-P). In this work, we further define the mechanism for the CpxR/A-mediated regulation of SPI-1 genes. The negative effect exerted by the absence of CpxA on the expression of SPI-1 genes was counteracted by the absence of CpxR or by the absence of the two enzymes, AckA and Pta, which render acetyl-phosphate that phosphorylates CpxR. Furthermore, overexpression of the lipoprotein NlpE, which activates CpxA kinase activity on CpxR, or overexpression of CpxR, repressed the expression of SPI-1 genes. Thus, our results provide several lines of evidence strongly supporting that the absence of CpxA leads to the phosphorylation of CpxR via the AckA/Pta enzymes, which represses both the SPI-1 and SPI-2 genes. Additionally, we show that in the absence of the Lon protease, which degrades HilD, the CpxR-P-mediated repression of the SPI-1 genes is mostly lost; moreover, we demonstrate that CpxR-P negatively affects the stability of HilD and thus decreases the expression of HilD-target genes, such as hilD itself and hilA, located in SPI-1. Our data further expand the insight on the different regulatory pathways for gene expression involving CpxR/A and on the complex regulatory network governing virulence in Salmonella.

RESUMO

Salmonella Typhimurium is the etiological agent of gastroenteritis in humans and enteric fever in mice. Inside these hosts, Salmonella must overcome hostile conditions to develop a successful infection, a process in which the levels of porins may be critical. Herein, the role of the Salmonella Typhimurium porin OmpD in the infection process was assessed for adherence, invasion and proliferation in RAW264.7 mouse macrophages and in BALB/c mice. In cultured macrophages, a ΔompD strain exhibited increased invasion and proliferation phenotypes as compared to its parental strain. In contrast, overexpression of ompD caused a reduction in bacterial proliferation but did not affect adherence or invasion. In the murine model, the ΔompD strain showed increased ability to survive and replicate in target organs of infection. The ompD transcript levels showed a down-regulation when Salmonella resided within cultured macrophages and when it colonized target organs in infected mice. Additionally, cultured macrophages infected with the ΔompD strain produced lower levels of reactive oxygen species, suggesting that down-regulation of ompD could favor replication of Salmonella inside macrophages and the subsequent systemic dissemination, by limiting the reactive oxygen species response of the host.

Assuntos

RESUMO

Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) have essential roles in the pathogenesis of Salmonella enterica. Previously, we reported transcriptional cross talk between SPI-1 and SPI-2 when the SPI-1 regulator HilD induces expression of the SsrA/B two-component system, the central positive regulator of SPI-2, during the growth of Salmonella to late stationary phase in LB rich medium. Here, we further define the mechanism of the HilD-mediated expression of ssrAB. Expression analysis of cat transcriptional fusions containing different regions of ssrAB revealed the presence of negative regulatory sequences located downstream of the ssrAB promoter. In the absence of these negative cis elements, ssrAB was expressed in a HilD-independent manner and was no longer repressed by the global regulator H-NS. Consistently, when the activity of H-NS was inactivated, the expression of ssrAB also became independent of HilD. Furthermore, electrophoretic mobility shift assays showed that both HilD and H-NS bind to the ssrAB region containing the repressing sequences. Moreover, HilD was able to displace H-NS bound to this region, whereas H-NS did not displace HilD. Our results support a model indicating that HilD displaces H-NS from a region downstream of the promoter of ssrAB by binding to sites overlapping or close to those sites bound by H-NS, which leads to the expression of ssrAB. Although the role of HilD as an antagonist of H-NS has been reported before for other genes, this is the first study showing that HilD is able to effectively displace H-NS from the promoter of one of its target genes.

Assuntos

RESUMO

A new mechanism for the turning-off of gene expression in Salmonella Pathogenicity Island 1 (SPI-1) is proposed by Espinosa and Casadesús, which involves the action of the LeuO quiescent regulator, by two different pathways. A major one through the activation of the hilE gene, where the HilE protein would in turn inactivate HilD, a major positive transcriptional regulator of SPI-1; and a minor HilE-HilD-independent pathway. This could constitute a back-up or an aid for the turn-off of SPI-1 genes mediated by the nucleoid protein H-NS.

Assuntos

RESUMO

Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) play key roles in the pathogenesis of Salmonella enterica. Previously, we showed that when Salmonella grows in Luria-Bertani medium, HilD, encoded in SPI-1, first induces the expression of hilA, located in SPI-1, and subsequently of the ssrAB operon, located in SPI-2. These genes code for HilA and the SsrA/B two-component system, the positive regulators of the SPI-1 and SPI-2 regulons respectively. In this study, we demonstrate that CsrA, a global regulatory RNA binding protein, post-transcriptionally regulates hilD expression by directly binding near the Shine-Dalgarno and translation initiation codon sequences of the hilD mRNA, preventing its translation and leading to its accelerated turnover. Negative regulation is counteracted by the global SirA/BarA two-component system, which directly activates the expression of CsrB and CsrC, two non-coding regulatory RNAs that sequester CsrA, thereby preventing it from binding to its target mRNAs. Our results illustrate the integration of global and specific regulators into a multifactorial regulatory cascade controlling the expression of virulence genes acquired by horizontal transfer events.

Assuntos

RESUMO

The acquisition of new genetic traits by horizontal gene transfer and their incorporation into preexisting regulatory networks have been essential events in the evolution of bacterial pathogens. An example of successful assimilation of virulence traits is Salmonella enterica, which acquired, at distinct evolutionary times, Salmonella pathogenicity island 1 (SPI-1), required for efficient invasion of the intestinal epithelium and intestinal disease, and SPI-2, essential for Salmonella replication and survival within macrophages and the progression of a systemic infection. A positive regulatory cascade mainly composed of HilD, HilA, and InvF, encoded in SPI-1, controls the expression of SPI-1 genes, whereas the two-component regulatory system SsrA/B, encoded in SPI-2, controls expression of SPI-2 genes. In this study, we report a previously undescribed transcriptional cross-talk between SPI-1 and SPI-2, where the SPI-1-encoded regulator HilD is essential for the activation of both the SPI-1 and SPI-2 regulons but at different times during the stationary phase of growth in Luria-Bertani medium. Our data indicate that HilD counteracts the H-NS-mediated repression exerted on the OmpR-dependent activation of the ssrAB operon by specifically interacting with its regulatory region. In contrast, HilD is not required for SPI-2 regulon expression under the in vitro growth conditions that are thought to resemble the intracellular environment. Our results suggest that two independent SPI-2 activation pathways evolved to take advantage of the SPI-2-encoded information at different niches and, in consequence, in response to different growth conditions.

Assuntos