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Shigella , the etiological agent of bacillary dysentery (shigellosis), is a highly adapted human pathogen. It evolved from an innocuous ancestor resembling the Escherichia coli strain by gain and loss of genes and functions. While the gain process concerns the acquisition of the genetic determinants of virulence, the loss is related to the adaptation of the genome to the new pathogenic status and occurs by pathoadaptive mutation of antivirulence genes. In this study, we highlight that the SRRz/Rz 1 lambdoid lysis cassette, even though stably adopted in E. coli K12 by virtue of its beneficial effect on cell physiology, has undergone a significant decay in Shigella . Moreover, we show the antivirulence nature of the SRRz/Rz 1 lysis cassette in Shigella . In fact, by restoring the SRRz/Rz 1 expression in this pathogen, we observe an increased release of peptidoglycan fragments, causing an unbalance in the fine control exerted by Shigella on host innate immunity and a mitigation of its virulence. This strongly affects the virulence of Shigella and allows to consider the loss of SRRz/Rz 1 lysis cassette as another pathoadaptive event in the life of Shigella . [ABSTRACT FROM AUTHOR]

Abstract: Nicotinamide adenine dinucleotide (NAD) is a crucial cofactor in several anabolic and catabolic reactions. NAD derives from quinolinic acid (QUIN) which in Escherichia coli is obtained through a pyridine salvage pathway or a de novo synthesis pathway. In the latter case, two enzymes, l-aspartate oxidase (NadB) and quinolinate synthase (NadA), are required for the synthesis of QUIN. In contrast to its E. coli ancestor, Shigella spp., the causative agent of bacillary dissentery, lacks the de novo pathway and strictly requires nicotinic acid for growth (Nic− phenotype). This phenotype depends on the silencing of the nadB and nadA genes and its pathoadaptive nature is suggested by the observation that QUIN attenuates the Shigella invasive process. Shigella shares the pathogenicity mechanism with enteronvasive E. coli (EIEC), a group of pathogenic E. coli. On the basis of this similarity EIEC and Shigella have been grouped into a single E. coli pathotype. However EIEC strains do not constitute a homogeneous group and do not possess the complete set of characters that define Shigella strains. In this work we have analysed thirteen EIEC strains belonging to different serotypes and originating from different geographic areas. We show that, in contrast to Shigella, only some EIEC strains require nicotinic acid for growth in minimal medium. Moreover, by studying the emergence of the Nic− phenotype in all serotypes of S. flexneri, as well as in S. sonnei and S. dysenteriae, we describe which molecular rearrangements occurred and which mutations are responsible for the inactivation of the nadA and nadB genes. Our data confirm that the genome of Shigella is extremely dynamic and support the hypothesis that EIEC might reflect an earlier stage of the pathoadaptation process undergone by Shigella. [Copyright &y& Elsevier]

Abstract: Polyamines are small polycationic molecules found in almost all cells and associated with a wide variety of physiological processes. In recent years it has become increasingly clear that, in addition to core physiological functions, polyamines play a crucial role in bacterial pathogenesis. Considerable evidence has built up that bacteria have evolved mechanisms to turn these molecules to their own advantage and a novel standpoint to look at host–bacterium interactions emerges from the interplay among polyamines, host cells and infecting bacteria. In this review, we highlight how human bacterial pathogens have developed their own resourceful strategies to exploit polyamines or manipulate polyamine-related processes to optimize their fitness within the host. Besides contributing to a better understanding of the complex relationship between a pathogen and its host, acquisitions in this field have a significant potential towards the development of novel antibacterial therapeutic approaches. [Copyright &y& Elsevier]

Abstract: Stenotrophomonas maltophilia is a microorganism of environmental and clinical importance as well as a frequent airway colonizer of cystic fibrosis (CF) individuals. We combined 2-DE and MALDI-TOF MS to profile the protein expression in S. maltophilia K279a, a completely sequenced clinical isolate, grown at 37°C with respect to the strain grown at 26°C. Among the proteins up-regulated at 37°C, we identified GroEL, a molecular chaperone that mainly assist the folding and unfolding of proteins under both normal and stress conditions. A 2.4-kb groESL mRNA was detected independently by Northern blot analyses with a groES- and a groEL-specific probe, indicating that S. maltophilia groES and groEL form an operon. Primer extension analysis of S. maltophilia groESL done in Escherichia coli showed that 2 promoters, Pσ32 and Pσ70, were utilized under the heat-shock and normal condition, respectively, whereas S. maltophilia groEL was shown to act as a heat-shock gene at 37°C, 42°C, and, to a lesser extent, at 50°C by real-time RT-PCR analyses. Finally, immunoblot analyses revealed that S. maltophilia GroEL strongly reacted with sera from CF patients chronically infected by the microorganism, but did not with sera from CF patients with sporadic infection or uninfected. [Copyright &y& Elsevier]

Abstract: The genetic relatedness of 52 Stenotrophomonas maltophilia strains, collected from various environmental and clinical sources, including cystic fibrosis (CF) patients, as well as the presence and the expression of some virulence-associated genes were studied. Pulsed-field gel electrophoresis (PFGE) analysis identified 47 profiles and three clusters of isolates with an identical PFGE pattern considered to be indistinguishable strains. Restriction fragment length polymorphism of the gyrB gene grouped the 52 strains into nine different profiles. Most CF clinical isolates (29 out of 41) showed profile 1, while the analysis of the hypervariable regions of the 16S rRNA gene revealed five distinct allelic variations, with the majority of CF isolates (23 out of 41) belonging to sequence group 1. Furthermore, the strains were characterized for motility and expression of virulence-associated genes, including genes encoding type-1 fimbriae, proteases (StmPr1 and StmPr2) and esterase. All S. maltophilia strains exhibited a very broad range of swimming and twitching motility, while none showed swarming motility. A complete smf-1 gene was PCR-amplified only from clinically derived S. maltophilia strains. Finally, the virulence of representative S. maltophilia strains impaired in the expression of proteases and esterase activities was evaluated by infecting larvae of the wax moth Galleria mellonella. The results obtained strongly indicate that the major extracellular protease StmPr1 may be a relevant virulence factor of S. maltophilia. [ABSTRACT FROM AUTHOR]

Abstract: A typical pathoadaptive mutation of Shigella and enteroinvasive Escherichia coli (EIEC) is the inactivation of the cad locus which comprises the genes necessary for lysine decarboxylation, an enzyme involved in pH homoeostasis. In E. coli, the cadBA operon, encoding lysine decarboxylase (CadA) and a lysine cadaverine antiporter (CadB), is submitted to the control of CadC, a positive activator whose gene maps upstream the operon, and is transcribed independently from the same strand. CadC is an integral inner membrane protein which acts both, as signal sensor and as transcriptional regulator responding to the low pH and lysine signals. Analysis of the molecular rearrangements responsible for the loss of lysine decarboxylase activity in Shigella and EIEC has revealed that the inactivation of the cadC gene is a common feature. The 3 major adaptive acid resistance (AR) systems – AR1, AR2, and AR3 – are known to be activated at low pH by Shigella and E. coli, allowing them to withstand extremely acid conditions. In this study, evaluating the survival of S. flexneri, S. sonnei, and EIEC strains complemented with a functional cadC gene and challenged at low pH, we present evidence that CadC negatively regulates the expression of the arginine-dependent adaptive acid-resistance system (AR3), encoded by the adi locus while it has no effect on the expression of AR1 and AR2 systems. Moreover, since our results indicate that in enteroinvasive strains the presence of CadC reduces the expression of the arginine decarboxylase encoding gene adiA, it is possible to hypothesize that the loss of functionality of lysine decarboxylase is counterbalanced by a higher expression of the adi system, and that CadC, besides specifically affecting the regulation of the cadBA operon, is also relevant to other systems responding to low pH. [Copyright &y& Elsevier]

Abstract: The whole DNA sequences of 2 Stenotrophomonas maltophilia strains isolated from the blood of a cancer patient (K279a) and the poplar Populus trichocarpa (R551-3) have been compared. The 2 chromosomes exhibit extensive synteny, but each is punctuated by about 40 genomic islands (GEIs), which vary in size from 3 to 70kb, and may encode up to about 50 proteins. A large set of smaller DNA sequences, encoding strain-specific ‘solo’ orfs, contributes to genetic heterogeneity in a significant manner. S. maltophilia GEIs potentially encode several proteins mediating interactions with the environment such as transmembrane proteins, haemagglutinins, components of type I and IV secretion systems, and efflux proteins having a role in metal and/or drug resistance. The presence of specific GEIs in the S. maltophilia population was monitored by PCR and slot-blot analyses. Data suggest that some islands are present at sites different from those identified in K279a and that alternative islands may be integrated at mapped sites. [Copyright &y& Elsevier]

Abstract: Shigella, the etiological agent of the bacillary dysentery, belongs to the extremely diverse species of Escherichia coli. In the evolutionary route of Shigella from commensal E. coli ancestors towards a pathogenic lifestyle, the critical events have been the acquisition of the pINV plasmid, through horizontal transfer and the inactivation of pre-existing genes. These so-called pathoadaptive mutations affect the expression of genes negatively interfering with the newly acquired functions necessary for the colonization of the host niche. Cadaverine, a small polyamine resulting from decarboxylation of lysine, has been shown to hamper the full expression of Shigella invasiveness mainly by altering the inflammatory response. Recent analysis of the evolution of the Shigella and enteroinvasive E. coli (EIEC) cad region indicates that silencing of the cad locus has been attained with several strategies. The increasing relevance of S. sonnei in both, developing and industrial countries, prompted us to analyze the molecular origin of the LDC? phenotype in these strains. The results obtained on several S. sonnei strains reveal that despite the difference in geographic origin and antibiotic resistance patterns, all the strains have undergone the same modifications. Multiple IS insertions into the cadBA operon have interrupted gene continuity without inducing deletions or inversions of the cadA and cadB genes which are remained entirely conserved. Moreover, by functional analysis we show that all the strains carry a defective cadC gene, thus strengthening the hypothesis that inactivation of the regulatory cadC gene might have been the first step towards a complete lack of the cad locus. [Copyright &y& Elsevier]

Abstract: Pathoadaptive mutations are evolutionary events leading to the silencing of specific anti-virulence loci. This reshapes the core genome of a novel pathogen, adapts it to the host and boosts its harmful potential. A paradigmatic case is the emergence of Shigella, the causative agent of bacillary dysentery, from its innocuous Escherichia coli ancestor. Here we summarize current views on how pathoadaptation has allowed Shigella to progressively increase its virulence. In this context, modification of the polyamine pattern emerges as a crucial step towards full expression of the virulence program in Shigella. [Copyright &y& Elsevier]

Abstract: In enterobacteria, acid stress induces expression of the cad system which is involved in maintaining intracellular pH at levels compatible with cell survival. Despite its crucial role, the cad operon is silenced in Shigella and in other pathogenic Escherichia coli. In the present review, we will address the question of why and how the cad locus has been sacrificed for the sake of optimal expression of virulence traits. [Copyright &y& Elsevier]

The contribution of histone-like proteins to the transcriptional regulation of virulence gene networks is a common feature among pathogenic bacteria. In this article we review current knowledge about the regulative role of major histone-like proteins in the silencing/activation of the invasivity phenotype of Shigella, the etiological agent of bacillary dissentery. [Copyright &y& Elsevier]