Emergence of a bacterial clone with enhanced virulence by acquisition of a phage encoding a secreted phospholipase A2

A novel phospholipase A2 is a core component of the typhoid toxin genetic islet

Salmonella Typhi, the cause of typhoid fever, is a bacterial pathogen of substantial global importance. Typhoid toxin is a secreted AB-type toxin that is a key S. Typhi virulence factor encoded within a 5-gene genetic islet. Four genes in this islet have well-defined roles in typhoid toxin biology; however, the function of the fifth gene is unknown. Here, we investigate the function of this gene, which we name ttaP. We show that ttaP is cotranscribed with the typhoid toxin subunit cdtB, and we perform genomic analyses that indicate that TtaP is very highly conserved in typhoid toxin islets found in diverse salmonellae. We show that TtaP is a distant homolog of group XIV secreted phospholipase A2 (PLA2) enzymes, and experimentally demonstrate that TtaP is a bona fide PLA2. Sequence and structural analyses indicate that TtaP differs substantially from characterized PLA2s, and thus represents a novel class of PLA2. Secretion assays revealed that TtaP is neither cosecreted with typhoid toxin, nor is it required for toxin secretion. Although TtaP is a phospholipase that remains associated with the S. Typhi cell, assays that probed for altered cell envelope integrity failed to identify any differences between WT S. Typhi and a ttaP deletion strain. Collectively, this study identifies a biochemical activity for the lone uncharacterized typhoid toxin islet gene and lays the groundwork for exploring how this gene factors into S. Typhi pathogenesis. This study further identifies a novel class of PLA2, enzymes that have a wide range of industrial applications.

Streptococcus dysgalactiae subsp. equisimilis infection and its intersection with Streptococcus pyogenes

SUMMARYStreptococcus dysgalactiae subsp. equisimilis (SDSE) is an increasingly recognized cause of disease in humans. Disease manifestations range from non-invasive superficial skin and soft tissue infections to life-threatening streptococcal toxic shock syndrome and necrotizing fasciitis. Invasive disease is usually associated with co-morbidities, immunosuppression, and advancing age. The crude incidence of invasive disease approaches that of the closely related pathogen, Streptococcus pyogenes. Genomic epidemiology using whole-genome sequencing has revealed important insights into global SDSE population dynamics including emerging lineages and spread of anti-microbial resistance. It has also complemented observations of overlapping pathobiology between SDSE and S. pyogenes, including shared virulence factors and mobile gene content, potentially underlying shared pathogen phenotypes. This review provides an overview of the clinical and genomic epidemiology, disease manifestations, treatment, and virulence determinants of human infections with SDSE with a particular focus on its overlap with S. pyogenes. In doing so, we highlight the importance of understanding the overlap of SDSE and S. pyogenes to inform surveillance and disease control strategies.

Emergent emm4 group A Streptococcus evidences a survival strategy during interaction with immune effector cells

The major gram-positive pathogen group A Streptococcus (GAS) is a model organism for studying microbial epidemics as it causes waves of infections. Since 1980, several GAS epidemics have been ascribed to the emergence of clones producing increased amounts of key virulence factors such as streptolysin O (SLO). Herein, we sought to identify mechanisms underlying our recently identified temporal clonal emergence among emm4 GAS, given that emergent strains did not produce augmented levels of virulence factors relative to historic isolates. By creating and analyzing isoallelic strains, we determined that a conserved mutation in a previously undescribed gene encoding a putative carbonic anhydrase was responsible for the defective in vitro growth observed in the emergent strains. We also identified that the emergent strains survived better inside macrophages and killed macrophages at lower rates than the historic strains. Via the creation of isogenic mutant strains, we linked the emergent strain "survival" phenotype to the downregulation of the SLO encoding gene and upregulation of the msrAB operon which encodes proteins involved in defense against extracellular oxidative stress. Our findings are in accord with recent surveillance studies which found a high ratio of mucosal (i.e., pharyngeal) relative to invasive infections among emm4 GAS. Since ever-increasing virulence is unlikely to be evolutionarily advantageous for a microbial pathogen, our data further understanding of the well-described oscillating patterns of virulent GAS infections by demonstrating mechanisms by which emergent strains adapt a "survival" strategy to outcompete previously circulating isolates.

Emergent emm4 group A Streptococcus evidences a survival strategy during interaction with immune effector cells

The major gram-positive pathogen group A Streptococcus (GAS) is a model organism for studying microbial epidemics as it causes waves of infections. Since 1980, several GAS epidemics have been ascribed to the emergence of clones producing increased amounts of key virulence factors such as streptolysin O (SLO). Herein, we sought to identify mechanisms underlying our recently identified temporal clonal emergence amongst emm4 GAS, given that emergent strains did not produce augmented levels of virulence factors relative to historic isolates. Through the creation and analysis of isoallelic strains, we determined that a conserved mutation in a previously undescribed gene encoding a putative carbonic anhydrase was responsible for the defective in vitro growth observed in the emergent strains. We also identified that the emergent strains survived better inside macrophages and killed macrophages at lower rates relative to the historic strains. Via creation of isogenic mutant strains, we linked the emergent strain "survival" phenotype to the downregulation of the SLO encoding gene and upregulation of the msrAB operon which encodes proteins involved in defense against extracellular oxidative stress. Our findings are in accord with recent surveillance studies which found high ratio of mucosal (i.e., pharyngeal) relative to invasive infections amongst emm4 GAS. Inasmuch as ever-increasing virulence is unlikely to be evolutionary advantageous for a microbial pathogen, our data furthers understanding of the well described oscillating patterns of virulent GAS infections by demonstrating mechanisms by which emergent strains adapt a "survival" strategy to outcompete previously circulating isolates.

Categorizing sequences of concern by function to better assess mechanisms of microbial pathogenesis

To identify sequences with a role in microbial pathogenesis, we assessed the adequacy of their annotation by existing controlled vocabularies and sequence databases. Our goal was to regularize descriptions of microbial pathogenesis for improved integration with bioinformatic applications. Here, we review the challenges of annotating sequences for pathogenic activity. We relate the categorization of more than 2,750 sequences of pathogenic microbes through a controlled vocabulary called Functions of Sequences of Concern (FunSoCs). These allow for an ease of description by both humans and machines. We provide a subset of 220 fully annotated sequences in the supplemental material as examples. The use of this compact (∼30 terms), controlled vocabulary has potential benefits for research in microbial genomics, public health, biosecurity, biosurveillance, and the characterization of new and emerging pathogens.

Host phospholipid peroxidation fuels ExoU-dependent cell necrosis and supports Pseudomonas aeruginosa-driven pathology

Regulated cell necrosis supports immune and anti-infectious strategies of the body; however, dysregulation of these processes drives pathological organ damage. Pseudomonas aeruginosa expresses a phospholipase, ExoU that triggers pathological host cell necrosis through a poorly characterized pathway. Here, we investigated the molecular and cellular mechanisms of ExoU-mediated necrosis. We show that cellular peroxidised phospholipids enhance ExoU phospholipase activity, which drives necrosis of immune and non-immune cells. Conversely, both the endogenous lipid peroxidation regulator GPX4 and the pharmacological inhibition of lipid peroxidation delay ExoU-dependent cell necrosis and improve bacterial elimination in vitro and in vivo. Our findings also pertain to the ExoU-related phospholipase from the bacterial pathogen Burkholderia thailandensis, suggesting that exploitation of peroxidised phospholipids might be a conserved virulence mechanism among various microbial phospholipases. Overall, our results identify an original lipid peroxidation-based virulence mechanism as a strong contributor of microbial phospholipase-driven pathology.

Analysis of glycerol and dihydroxyacetone metabolism in Enterococcus faecium

Glycerol (Gly) can be dissimilated by two pathways in bacteria. Either this sugar alcohol is first oxidized to dihydroxyacetone (DHA) and then phosphorylated or it is first phosphorylated to glycerol-3-phosphate (GlyP) followed by oxidation. Oxidation of GlyP can be achieved by NAD-dependent dehydrogenases or by a GlyP oxidase. In both cases, dihydroxyacetone phosphate is the product. Genomic analysis showed that Enterococcus faecium harbors numerous genes annotated to encode activities for the two pathways. However, our physiological analyses of growth on glycerol showed that dissimilation is limited to aerobic conditions and that despite the presence of genes encoding presumed GlyP dehydrogenases, the GlyP oxidase is essential in this process. Although E. faecium contains an operon encoding the phosphotransfer protein DhaM and DHA kinase, which are required for DHA phosphorylation, it is unable to grow on DHA. This operon is highly expressed in stationary phase but its physiological role remains unknown. Finally, data obtained from sequencing of a transposon mutant bank of E. faecium grown on BHI revealed that the GlyP dehydrogenases and a major intrinsic family protein have important but hitherto unknown physiological functions.

Molecular subtyping and antimicrobial susceptibility of Streptococcus dysgalactiae subspecies equisimilis isolates from clinically diseased pigs

Background

Streptococcus dysgalactiae subspecies equisimilis (SDSE) acts as an etiological agent for lameness, neurological signs, and high mortality in pigs. Despite its importance in pig industries and zoonotic potential, little is known about the effects of this pathogen.

Objectives

This study aimed to determine the molecular characteristics and antimicrobial resistance of SDSE strains isolated from diseased pigs.

Methods

A total 11 SDSE isolates were obtained from diseased pigs. Bacterial identification, PCR for virulence genes, emm typing, and antimicrobial resistance genes, multilocus sequence typing, and antimicrobial susceptibility test were performed.

Results

Nine isolates were from piglets, and 8 showed lameness, sudden death, or neurological signs. The isolates were PCR-positive for sla (100%), sagA (100%), and scpA (45.5%), and only 1 isolate amplified the emm gene (stL2764). Eight different sequence types were detected, categorized into 2 clonal complexes and 4 singletons. All the isolates in this study were included in a small cluster, which also contained other strains derived from humans and horses. The minimum inhibitory concentrations for the tested beta-lactams were low, while those for macrolides, tetracyclines, and fluoroquinolones were relatively high. PCR analysis of the macrolide and tetracycline resistance genes demonstrated that the isolates carried erm(B) (18.2%, n = 2), mef(A/E) (9.1%, n = 1), tet(M) (18.2%, n = 2), and tet(O) (90.2%, n = 10). Two isolates presented a mutation in parC, which is associated with fluoroquinolone resistance.

Conclusion

This study provided insight into swine-derived SDSE, as it is related to veterinary medicine, and elucidated its zoonotic potential, in the context of molecular epidemiology and antimicrobial resistance in public health.

Streptococcus pyogenes genes that promote pharyngitis in primates

Streptococcus pyogenes (group A streptococcus; GAS) causes 600 million cases of pharyngitis annually worldwide. There is no licensed human GAS vaccine despite a century of research. Although the human oropharynx is the primary site of GAS infection, the pathogenic genes and molecular processes used to colonize, cause disease, and persist in the upper respiratory tract are poorly understood. Using dense transposon mutant libraries made with serotype M1 and M28 GAS strains and transposon-directed insertion sequencing, we performed genome-wide screens in the nonhuman primate (NHP) oropharynx. We identified many potentially novel GAS fitness genes, including a common set of 115 genes that contribute to fitness in both genetically distinct GAS strains during experimental NHP pharyngitis. Targeted deletion of 4 identified fitness genes/operons confirmed that our newly identified targets are critical for GAS virulence during experimental pharyngitis. Our screens discovered many surface-exposed or secreted proteins - substrates for vaccine research - that potentially contribute to GAS pharyngitis, including lipoprotein HitA. Pooled human immune globulin reacted with purified HitA, suggesting that humans produce antibodies against this lipoprotein. Our findings provide new information about GAS fitness in the upper respiratory tract that may assist in translational research, including developing novel vaccines.

Characterization and genome analysis of B1 sub-cluster mycobacteriophage PDRPxv

Mycobacteriophages are viruses specific to mycobacteria that have gained attention as alternative therapeutic strategies for treating antibiotic-resistant infections. Mycobacteriophages are highly diverse and have been grouped into 29 clusters, 71 sub-clusters and 10 singletons based on the genome sequence. Here, we annotate the genome of PDRPxv, a lytic mycobacteriophage isolated from New Delhi; it belongs to the Siphoviridae family as determined by transmission electron microscopy. This phage survives at higher temperatures (up to 55 °C) and in alkaline conditions (up to pH11). PDRPxv phage genome is 69,171 bp in length with 66.35 % GC content and encodes 107 putative open reading frames and belongs to the B1 sub-cluster. Genome annotation indicated that genes for DNA encapsidation, structural proteins, replication/transcription and lysis of the host are present in functional clusters. Structural proteins encoded by Gp10-Gp12, Gp18, Gp25 and Gp28-Gp33 were identified by mass spectrometry. Interestingly, no gene encoding a holin function was found. Single-step growth curve revealed that PDRPxv has an adsorption time of 45 min, a latency time of 135 min and an average burst size of 99 phage particles per infected cell. The short latency period and the large burst size mark the lytic nature of the PDRPxv phage, which could therefore be a promising therapeutic candidate against pathogenic Mycobacterium species.

The Contribution of Genetic Variation of Streptococcus pneumoniae to the Clinical Manifestation of Invasive Pneumococcal Disease

Background

Different clinical manifestations of invasive pneumococcal disease (IPD) have thus far mainly been explained by patient characteristics. Here we studied the contribution of pneumococcal genetic variation to IPD phenotype.

Methods

The index cohort consisted of 349 patients admitted to 2 Dutch hospitals between 2000-2011 with pneumococcal bacteremia. We performed genome-wide association studies to identify pneumococcal lineages, genes, and allelic variants associated with 23 clinical IPD phenotypes. The identified associations were validated in a nationwide (n = 482) and a post-pneumococcal vaccination cohort (n = 121). The contribution of confirmed pneumococcal genotypes to the clinical IPD phenotype, relative to known clinical predictors, was tested by regression analysis.

Results

Among IPD patients, the presence of pneumococcal gene slaA was a nationwide confirmed independent predictor of meningitis (odds ratio [OR], 10.5; P = .001), as was sequence cluster 9 (serotype 7F: OR, 3.68; P = .057). A set of 4 pneumococcal genes co-located on a prophage was a confirmed independent predictor of 30-day mortality (OR, 3.4; P = .003). We could detect the pneumococcal variants of concern in these patients' blood samples.

Conclusions

In this study, knowledge of pneumococcal genotypic variants improved the clinical risk assessment for detrimental manifestations of IPD. This provides us with novel opportunities to target, anticipate, or avert the pathogenic effects related to particular pneumococcal variants, and indicates that information on pneumococcal genotype is important for the diagnostic and treatment strategy in IPD. Ongoing surveillance is warranted to monitor the clinical value of information on pneumococcal variants in dynamic microbial and susceptible host populations.

Structural analysis of a Vibrio phospholipase reveals an unusual Ser-His-chloride catalytic triad

Phospholipases can disrupt host membranes and are important virulence factors in many pathogens. VvPlpA is a phospholipase A₂ secreted by Vibrio vulnificus and essential for virulence. Its homologs, termed thermolabile hemolysins (TLHs), are widely distributed in Vibrio bacteria, but no structural information for this virulence factor class is available. Herein, we report the crystal structure of VvPlpA to 1.4-Å resolution, revealing that VvPlpA contains an N-terminal domain of unknown function and a C-terminal phospholipase domain and that these two domains are packed closely together. The phospholipase domain adopts a typical SGNH hydrolase fold, containing the four conserved catalytic residues Ser, Gly, Asn, and His. Interestingly, the structure also disclosed that the phospholipase domain accommodates a chloride ion near the catalytic His residue. The chloride is five-coordinated in a distorted bipyramid geometry, accepting hydrogen bonds from a water molecule and the amino groups of surrounding residues. This chloride substitutes for the most common Asp/Glu residue and forms an unusual Ser-His-chloride catalytic triad in VvPlpA. The chloride may orient the catalytic His and stabilize the charge on its imidazole ring during catalysis. Indeed, VvPlpA activity depended on chloride concentration, confirming the important role of chloride in catalysis. The VvPlpA structure also revealed a large hydrophobic substrate-binding pocket that is capable of accommodating a long-chain acyl group. Our results provide the first structure of the TLH family and uncover an unusual Ser-His-chloride catalytic triad, expanding our knowledge on the biological role of chloride.

Identification of novel genes associated with anti-phagocytic functions in Streptococcus equi subsp. zooepidemicus

The anti-phagocytic abilities of bacteria often affect bacterial pathogenicity. Here, random mutant library of Streptococcus equi subsp. zooepidemicus (SEZ) was constructed using transposon mutagenesis. After careful screening, 30 transposon mutants with different transposon insertion sites were identified by conducting quantitative phagocytosis and insertion-site confirmation assays, whose anti-phagocytic abilities were significantly reduced relative to the wild-type strain. Insertion sites of 19 strains were monocistronic, including genes coding membrane proteins, transporters, and enzymes with unknown pathological function, such as sadM, adhP, purD, guaA, alpha-galactosidase coding gene, ABC transporter permease coding gene, metallo-beta-lactamase coding gene, and three secreted enzyme coding genes spuZ, slaB, and endoS, as well as known virulence factor coding genes, such as hasA and szM. The insertion sites of another 11 strains were polycistronic. We focused on four monocistronic-mutant strains: MhtpZ, MspuZ, MslaB, and MendoS. The anti-phagocytic abilities of not only the mutants that were precoincubated with the recombinant proteins, but also the complement strains were significantly more pronounced than those of all four corresponding mutants. The polyclonal antiserum against SlaB or EndoS also significantly decreased the anti-phagocytic capacity of wild-type SEZ. All four mutants exhibited significantly decreased viability in whole blood and reduced lethality in mice relative to the wild-type strain. Thus, we identified a variety of new anti-phagocytic factors, particularly multiple SEZ secreted enzymes. These factors are instrumental in the phagocytic resistance of SEZ in the absence of opsonin. Our results provide a framework for further studies of SEZ pathogenesis and relevant vaccine development for novel potential targets.

Lipid Droplets: A Significant but Understudied Contributor of Host⁻Bacterial Interactions

Lipid droplets (LDs) are cytosolic lipid storage organelles that are important for cellular lipid metabolism, energy homeostasis, cell signaling, and inflammation. Several bacterial, viral and protozoal pathogens exploit host LDs to promote infection, thus emphasizing the importance of LDs at the host–pathogen interface. In this review, we discuss the thus far reported relation between host LDs and bacterial pathogens including obligate and facultative intracellular bacteria, and extracellular bacteria. Although there is less evidence for a LD–extracellular bacterial interaction compared to interactions with intracellular bacteria, in this review, we attempt to compare the bacterial mechanisms that target LDs, the host signaling pathways involved and the utilization of LDs by these bacteria. Many intracellular bacteria employ unique mechanisms to target host LDs and potentially obtain nutrients and lipids for vacuolar biogenesis and/or immune evasion. However, extracellular bacteria utilize LDs to either promote host tissue damage or induce host death. We also identify several areas that require further investigation. Along with identifying LD interactions with bacteria besides the ones reported, the precise mechanisms of LD targeting and how LDs benefit pathogens should be explored for the bacteria discussed in the review. Elucidating LD–bacterial interactions promises critical insight into a novel host–pathogen interaction.

Comparative Genomics of Environmental and Clinical Burkholderia cenocepacia Strains Closely Related to the Highly Transmissible Epidemic ET12 Lineage

The Burkholderia cenocepacia epidemic ET12 lineage belongs to the genomovar IIIA including the reference strain J2315, a highly transmissible epidemic B. cenocepacia lineage. Members of this lineage are able to cause lung infections in immunocompromised and cystic fibrosis patients. In this study, we describe the genome of F01, an environmental B. cenocepacia strain isolated from soil in Burkina Faso that is, to our knowledge, the most closely related strain to this epidemic lineage. A comparative genomic analysis was performed on this new isolate, in association with five clinical and one environmental B. cenocepacia strains whose genomes were previously sequenced. Antibiotic resistances, virulence phenotype, and genomic contents were compared and discussed with an emphasis on virulent and antibiotic determinants. Surprisingly, no significant differences in antibiotic resistance and virulence were found between clinical and environmental strains, while the most important genomic differences were related to the number of prophages identified in their genomes. The ET12 lineage strains showed a noticeable greater number of prophages (partial or full-length), especially compared to the phylogenetically related environmental F01 strain (i.e., 5–6 and 3 prophages, respectively). Data obtained suggest possible involvements of prophages in the clinical success of opportunistic pathogens.

Glycerol metabolism and its implication in virulence in Mycoplasma

Glycerol and glycerol-containing compounds such as lipids belong to the most abundant organic compounds that may serve as nutrient for many bacteria. For the cell wall-less bacteria of the genus Mycoplasma, glycerol derived from phospholipids of their human or animal hosts is the major source of carbon and energy. The lipids are first degraded by lipases, and the resulting glycerophosphodiesters are transported into the cell and cleaved to release glycerol-3-phosphate. Alternatively, free glycerol can be transported, and then become phosphorylated. The oxidation of glycerol-3-phosphate in Mycoplasma spp. as well as in related firmicutes involves a hydrogen peroxide-generating glycerol-3-phosphate oxidase. This enzyme is a key player in the virulence of Mycoplasma spp. as the produced hydrogen peroxide is one of the major virulence factors of these bacteria. In this review, the different components involved in the utilization of lipids and glycerol in Mycoplasma pneumoniae and related bacteria are discussed.

How to become a killer, or is it all accidental? Virulence strategies in oral streptococci

Streptococci are a diverse group of Gram-positive microorganisms sharing common virulence traits and similar strategies to escape the oral niche and establish an infection in other parts of the host organism. Invasive infection with oral streptococci is "a perfect storm" that requires the concerted action of multiple biotic and abiotic factors. Our understanding of streptococcal pathogenicity and infectivity should probably be less mechanistic and driven not only by the identification of novel virulence factors. The observed diversity of the genus, including the range of virulence and pathogenicity mechanisms, is most likely the result of interspecies interactions, a massive horizontal gene transfer between streptococci within a shared oral niche, recombination events, selection of specialized clones, and modification of regulatory circuits. Selective pressure by the host and bacterial communities is a driving force for the selection of virulence traits and shaping the streptococcal genome. Global regulatory events driving niche adaptation and interactions with bacterial communities and the host steer research interests towards attempts to define the oral interactome on the transcriptional level and define signal cross-feeding and co-expression and co-regulation of virulence genes.

Streptococcus pyogenes Phospholipase A2 Induces the Expression of Adhesion Molecules on Human Umbilical Vein Endothelial Cells and Aorta of Mice

The Streptococcus pyogenes phospholipase A₂ (SlaA) gene is highly conserved in the M3 serotype of group A S. pyogenes, which often involves hypervirulent clones. However, the role of SlaA in S. pyogenes pathogenesis is unclear. Herein, we report that SlaA induces the expression of intercellular adhesion molecule 1 (ICAM1) and vascular cell adhesion molecule 1 (VCAM1) via the arachidonic acid signaling cascade. Notably, recombinant SlaA induced ICAM1 and VCAM1 expression in human umbilical vein endothelial cells (HUVECs), resulting in enhanced adhesion of human monocytic leukemia (THP-1) cells. However, C134A, a variant enzyme with no enzymatic activity, did not induce such events. In addition, culture supernatants from S. pyogenes SSI-1 enhanced the adhesion of THP-1 cells to HUVECs, but culture supernatants from the ΔslaA isogenic mutant strain had limited effects. Aspirin, a cyclooxygenase 2 inhibitor, prevented the adhesion of THP-1 cells to HUVECs and did not induce ICAM1 and VCAM1 expression in HUVECs treated with SlaA. However, zileuton, a 5-lipoxygenase inhibitor, did not exhibit such effects. Furthermore, pre-administration of aspirin in mice intravenously injected with SlaA attenuated the transcriptional abundance of ICAM1 and VCAM1 in the aorta. These results suggested that SlaA from S. pyogenes stimulates the expression of adhesion molecules in vascular endothelial cells. Thus, SlaA contributes to the inflammation of vascular endothelial cells upon S. pyogenes infection.

Immunogenicity of phospholipase A2 toxins and their role in Streptococcus equi pathogenicity

Streptococcus equi subsp. equi (S. equi) is the causative agent of strangles, one of the most frequently diagnosed infectious diseases of horses worldwide. Phospholipase A₂ toxins (PLA₂) cleave phospholipid molecules at position sn-2 contributing to the production of leukotrienes that are important inflammatory mediators. Two homologous phospholipases, SlaA and SlaB are encoded by the S. equi genome suggesting that PLA₂ toxins may contribute to its pathogenicity. Here we report the immunogenicity and role of PLA₂ toxins during natural and experimental infection of horses with S. equi. The levels of anti-PLA₂ specific antibodies in serum from horses naturally exposed to S. equi or without exposure were measured by indirect ELISA. Furthermore, the importance of PLA₂ was determined during experimental infection of Welsh Mountain ponies with a mutant strain of S. equi lacking slaA and slaB. Our results show that PLA₂ toxins are immunogenic, which supports their production during natural S. equi infection, but that these toxins are not essential for the development of strangles in a susceptible natural host.

Prevalence of M75 Streptococcus pyogenes Strains Harboring slaA Gene in Patients Affected by Pediatric Obstructive Sleep Apnea Syndrome in Central Italy

Recently we reported an association between pediatric obstructive sleep apnea syndrome (OSAS) and Group A streptococcus (GAS) sub-acute chronic tonsil colonization. We showed that GAS may contribute to tonsil hyperplasia via a streptolysin O (SLO)-dependent cysteinyl leukotrienes (CysLTs) production, which can trigger T and B cell proliferation. In the present study, we characterized the GAS strains isolated from pediatric OSAS patients in comparison with a panel of age and sex matched GAS strains unrelated to OSAS, but isolated in the same area and during the same period ranging from 2009 to 2013. We found that slaA gene, previously reported to be associated to CysLTs production pathway, was significantly associated to GAS OSAS strains. Moreover, the most numerous group (32%) of the GAS OSAS strains belonged to M75 type, and 6 out of 7 of these strains harbored the slaA gene. Multilocus Sequence Typing (MLST) experiments demonstrated that the clone emm75/ST49/ smeZ, slaA was associated to OSAS cases. In conclusion, we found an association between slaA gene and the GAS OSAS strains, and we showed that the clone emm75/ST49 harboring genes smeZ and slaA was exclusively isolated from patients affected by OSAS, thus suggesting that this genotype might be associated to the pathogenesis of OSAS, although further studies are needed to elucidate the possible role of SlaA in tonsil hypertrophy development.

Streptococcus pyogenes adhesion and colonization

Streptococcus pyogenes (group A Streptococcus, GAS) is a human-adapted pathogen responsible for a wide spectrum of disease. GAS can cause relatively mild illnesses, such as strep throat or impetigo, and less frequent but severe life-threatening diseases such as necrotizing fasciitis and streptococcal toxic shock syndrome. GAS is an important public health problem causing significant morbidity and mortality worldwide. The main route of GAS transmission between humans is through close or direct physical contact, and particularly via respiratory droplets. The upper respiratory tract and skin are major reservoirs for GAS infections. The ability of GAS to establish an infection in the new host at these anatomical sites primarily results from two distinct physiological processes, namely bacterial adhesion and colonization. These fundamental aspects of pathogenesis rely upon a variety of GAS virulence factors, which are usually under strict transcriptional regulation. Considerable progress has been made in better understanding these initial infection steps. This review summarizes our current knowledge of the molecular mechanisms of GAS adhesion and colonization.

Bacterial Sphingomyelinases and Phospholipases as Virulence Factors

Bacterial sphingomyelinases and phospholipases are a heterogeneous group of esterases which are usually surface associated or secreted by a wide variety of Gram-positive and Gram-negative bacteria. These enzymes hydrolyze sphingomyelin and glycerophospholipids, respectively, generating products identical to the ones produced by eukaryotic enzymes which play crucial roles in distinct physiological processes, including membrane dynamics, cellular signaling, migration, growth, and death. Several bacterial sphingomyelinases and phospholipases are essential for virulence of extracellular, facultative, or obligate intracellular pathogens, as these enzymes contribute to phagosomal escape or phagosomal maturation avoidance, favoring tissue colonization, infection establishment and progression, or immune response evasion. This work presents a classification proposal for bacterial sphingomyelinases and phospholipases that considers not only their enzymatic activities but also their structural aspects. An overview of the main physiopathological activities is provided for each enzyme type, as are examples in which inactivation of a sphingomyelinase- or a phospholipase-encoding gene impairs the virulence of a pathogen. The identification of sphingomyelinases and phospholipases important for bacterial pathogenesis and the development of inhibitors for these enzymes could generate candidate vaccines and therapeutic agents, which will diminish the impacts of the associated human and animal diseases.

Targeted Curing of All Lysogenic Bacteriophage from Streptococcus pyogenes Using a Novel Counter-selection Technique

Streptococcus pyogenes is a human commensal and a bacterial pathogen responsible for a wide variety of human diseases differing in symptoms, severity, and tissue tropism. The completed genome sequences of >37 strains of S. pyogenes, representing diverse disease-causing serotypes, have been published. The greatest genetic variation among these strains is attributed to numerous integrated prophage and prophage-like elements, encoding several virulence factors. A comparison of isogenic strains, differing in prophage content, would reveal the effects of these elements on streptococcal pathogenesis. However, curing strains of prophage is often difficult and sometimes unattainable. We have applied a novel counter-selection approach to identify rare S. pyogenes mutants spontaneously cured of select prophage. To accomplish this, we first inserted a two-gene cassette containing a gene for kanamycin resistance (Kan^R) and the rpsL wild-type gene, responsible for dominant streptomycin sensitivity (Sm^S), into a targeted prophage on the chromosome of a streptomycin resistant (Sm^R) mutant of S. pyogenes strain SF370. We then applied antibiotic counter-selection for the re-establishment of the Kan^S/Sm^R phenotype to select for isolates cured of targeted prophage. This methodology allowed for the precise selection of spontaneous phage loss and restoration of the natural phage attB attachment sites for all four prophage-like elements in this S. pyogenes chromosome. Overall, 15 mutants were constructed that encompassed every permutation of phage knockout as well as a mutant strain, named CEM1ΔΦ, completely cured of all bacteriophage elements (a ~10% loss of the genome); the only reported S. pyogenes strain free of prophage-like elements. We compared CEM1ΔΦ to the WT strain by analyzing differences in secreted DNase activity, as well as lytic and lysogenic potential. These mutant strains should allow for the direct examination of bacteriophage relationships within S. pyogenes and further elucidate how the presence of prophage may affect overall streptococcal survival, pathogenicity, and evolution.

Hijacking and Use of Host Lipids by Intracellular Pathogens

Intracellular bacteria use a number of strategies to survive, grow, multiply, and disseminate within the host. One of the most striking adaptations that intracellular pathogens have developed is the ability to utilize host lipids and their metabolism. Bacteria such as Anaplasma, Chlamydia, or Mycobacterium can use host lipids for different purposes, such as a means of entry through lipid rafts, building blocks for bacteria membrane formation, energy sources, camouflage to avoid the fusion of phagosomes and lysosomes, and dissemination. One of the most extreme examples of lipid exploitation is Mycobacterium, which not only utilizes the host lipid as a carbon and energy source but is also able to reprogram the host lipid metabolism. Likewise, Chlamydia spp. have also developed numerous mechanisms to reprogram lipids onto their intracellular inclusions. Finally, while the ability to exploit host lipids is important in intracellular bacteria, it is not an exclusive trait. Extracellular pathogens, including Helicobacter, Mycoplasma, and Borrelia, can recruit and metabolize host lipids that are important for their growth and survival.Throughout this chapter we will review how intracellular and extracellular bacterial pathogens utilize host lipids to enter, survive, multiply, and disseminate in the host.

Serotype M3 and M28 Group A Streptococci Have Distinct Capacities to Evade Neutrophil and TNF-α Responses and to Invade Soft Tissues

The M3 Serotype of Group A Streptococcus (GAS) is one of the three most frequent serotypes associated with severe invasive GAS infections, such as necrotizing fasciitis, in the United States and other industrialized countries. The basis for this association and hypervirulence of invasive serotype M3 GAS is not fully understood. In this study, the sequenced serotype M3 strain, MGAS315, and serotype M28 strain, MGAS6180, were characterized in parallel to determine whether contemporary M3 GAS has a higher capacity to invade soft tissues than M28 GAS. In subcutaneous infection, MGAS315 invaded almost the whole skin, inhibited neutrophil recruitment and TNF-α production, and was lethal in subcutaneous infection of mice, whereas MGAS6180 did not invade skin, induced robust neutrophil infiltration and TNF-α production, and failed to kill mice. In contrast to MGAS6180, MGAS315 had covS G1370T mutation. Either replacement of the covS1370T gene with wild-type covS in MGAS315 chromosome or in trans expression of wild-type covS in MGAS315 reduced expression of CovRS-controlled virulence genes hasA, spyCEP, and sse by >10 fold. MGAS315 covSwt lost the capacity to extensively invade skin and to inhibit neutrophil recruitment and had attenuated virulence, indicating that the covS G1370T mutation critically contribute to the hypervirulence of MGAS315. Under the background of functional CovRS, MGAS315 covSwt still caused greater lesions than MGAS6180, and, consistently under the background of covS deletion, MGAS6180 ΔcovS caused smaller lesions than MGAS315 ΔcovS. Thus, contemporary invasive M3 GAS has a higher capacity to evade neutrophil and TNF-α responses and to invade soft tissue than M28 GAS and that this skin-invading capacity of M3 GAS is maximized by natural CovRS mutations. These findings enhance our understanding of the basis for the frequent association of M3 GAS with necrotizing fasciitis.

Streptococcus zooepidemicus and Streptococcus equi evolution: the role of CRISPRs

The host-restricted bacterium Streptococcus equi is the causative agent of equine strangles, the most frequently diagnosed infectious disease of horses worldwide. The disease is characterized by abscessation of the lymph nodes of the head and neck, leading to significant welfare and economic cost. S. equi is believed to have evolved from an ancestral strain of Streptococcus zooepidemicus, an opportunistic pathogen of horses and other animals. Comparison of the genome of S. equi strain 4047 with those of S. zooepidemicus identified examples of gene loss due to mutation and deletion, and gene gain through the acquisition of mobile genetic elements that have probably shaped the pathogenic specialization of S. equi. In particular, deletion of the CRISPR (clustered regularly interspaced short palindromic repeats) locus in the ancestor of S. equi may have predisposed the bacterium to acquire and incorporate new genetic material into its genome. These include four prophages and a novel integrative conjugative element. The virulence cargo carried by these mobile genetic elements is believed to have shaped the ability of S. equi to cause strangles. Further sequencing of S. zooepidemicus has highlighted the diversity of this opportunistic pathogen. Again, CRISPRs are postulated to influence evolution, balancing the need for gene gain over genome stability. Analysis of spacer sequences suggest that these pathogens may be susceptible to a limited range of phages and provide further evidence of cross-species exchange of genetic material among Streptococcus pyogenes, Streptococcus agalactiae and Streptococcus dysgalactiae.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Disease manifestations and pathogenic mechanisms of Group A Streptococcus

Streptococcus pyogenes, also known as group A Streptococcus (GAS), causes mild human infections such as pharyngitis and impetigo and serious infections such as necrotizing fasciitis and streptococcal toxic shock syndrome. Furthermore, repeated GAS infections may trigger autoimmune diseases, including acute poststreptococcal glomerulonephritis, acute rheumatic fever, and rheumatic heart disease. Combined, these diseases account for over half a million deaths per year globally. Genomic and molecular analyses have now characterized a large number of GAS virulence determinants, many of which exhibit overlap and redundancy in the processes of adhesion and colonization, innate immune resistance, and the capacity to facilitate tissue barrier degradation and spread within the human host. This improved understanding of the contribution of individual virulence determinants to the disease process has led to the formulation of models of GAS disease progression, which may lead to better treatment and intervention strategies. While GAS remains sensitive to all penicillins and cephalosporins, rising resistance to other antibiotics used in disease treatment is an increasing worldwide concern. Several GAS vaccine formulations that elicit protective immunity in animal models have shown promise in nonhuman primate and early-stage human trials. The development of a safe and efficacious commercial human vaccine for the prophylaxis of GAS disease remains a high priority.

Identification of new sphingomyelinases D in pathogenic fungi and other pathogenic organisms

Sphingomyelinases D (SMases D) or dermonecrotic toxins are well characterized in Loxosceles spider venoms and have been described in some strains of pathogenic microorganisms, such as Corynebacterium sp. After spider bites, the SMase D molecules cause skin necrosis and occasional severe systemic manifestations, such as acute renal failure. In this paper, we identified new SMase D amino acid sequences from various organisms belonging to 24 distinct genera, of which, 19 are new. These SMases D share a conserved active site and a C-terminal motif. We suggest that the C-terminal tail is responsible for stabilizing the entire internal structure of the SMase D Tim barrel and that it can be considered an SMase D hallmark in combination with the amino acid residues from the active site. Most of these enzyme sequences were discovered from fungi and the SMase D activity was experimentally confirmed in the fungus Aspergillus flavus. Because most of these novel SMases D are from organisms that are endowed with pathogenic properties similar to those evoked by these enzymes alone, they might be associated with their pathogenic mechanisms.

Functional analysis of a lipolytic protein encoded in phytoplasma phage based genomic island

Wall-less bacteria known as phytoplasmas are obligate transkingdom parasites and pathogens of plants and insect vectors. These unusual bacteria possess some of the smallest genomes known among pathogenic bacteria, and have never been successfully isolated in artificial culture. Disease symptoms induced by phytoplasmas in infected plants include abnormal growth and often severe yellowing of leaves, but mechanisms involved in phytoplasma parasitism and pathogenicity are little understood. A phage based genomic island (sequence variable mosaic, SVM) in the genome of Malaysian periwinkle yellows (MPY) phytoplasma harbors a gene encoding membrane-targeted proteins, including a putative phospholipase (PL), potentially important in pathogen-host interactions. Since some phytoplasmal disease symptoms could possibly be accounted for, at least in part, by damage and/or degradation of host cell membranes, we hypothesize that the MPY phytoplasma putative PL is an active enzyme. To test this hypothesis, functional analysis of the MPY putative pl gene-encoded protein was carried out in vitro after its expression in bacterial and yeast hosts. The results demonstrated that the heterologously expressed phytoplasmal putative PL is an active lipolytic enzyme and could possibly act as a pathogenicity factor in the plant, and/or insect, host.

Identification of residues involved in substrate specificity and cytotoxicity of two closely related cutinases from Mycobacterium tuberculosis

The enzymes belonging to the cutinase family are serine enzymes active on a large panel of substrates such as cutin, triacylglycerols, and phospholipids. In the M. tuberculosis H37Rv genome, seven genes coding for cutinase-like proteins have been identified with strong immunogenic properties suggesting a potential role as vaccine candidates. Two of these enzymes which are secreted and highly homologous, possess distinct substrates specificities. Cfp21 is a lipase and Cut4 is a phospholipase A2, which has cytotoxic effects on macrophages. Structural overlay of their three-dimensional models allowed us to identify three areas involved in the substrate binding process and to shed light on this substrate specificity. By site-directed mutagenesis, residues present in these Cfp21 areas were replaced by residues occurring in Cut4 at the same location. Three mutants acquired phospholipase A1 and A2 activities and the lipase activities of two mutants were 3 and 15 fold greater than the Cfp21 wild type enzyme. In addition, contrary to mutants with enhanced lipase activity, mutants that acquired phospholipase B activities induced macrophage lysis as efficiently as Cut4 which emphasizes the relationship between apparent phospholipase A2 activity and cytotoxicity. Modification of areas involved in substrate specificity, generate recombinant enzymes with higher activity, which may be more immunogenic than the wild type enzymes and could therefore constitute promising candidates for antituberculous vaccine production.

Strangles: taking steps towards eradication

Strangles, caused by the host adapted Lancefield group C bacterium Streptococcus equi sub-species equi (S. equi), is one of the oldest recognised infectious diseases of horses and continues to cause significant welfare and economic cost throughout the world. The ability of S. equi to establish sub-clinical persistent infections primarily in the guttural pouches of convalescent horses has been instrumental to its success. However, the implementation of simple control measures that permit the identification and treatment of persistently infected carriers can prevent further outbreaks of disease at a local level. This review summarises some of the molecular mechanisms exploited by S. equi to cause disease. New qPCR and iELISA diagnostic tests replace culture methodologies as the gold standard for the detection of infected animals. A strategy to maximise the effective application of these tests to direct management methods for the eradication of S. equi infection is presented and the role of preventative vaccines is discussed. In contrast to current understanding, emerging data illustrates the dynamism of the global S. equi population and potential consequences for the effectiveness of currently available vaccines. The ability to use modern vaccines alongside conventional biosecurity and screening procedures will be critical to the large-scale prevention and even eradication of strangles, providing an opportunity to finally break the stranglehold that this disease has on the world's equine industry.

Neutral genomic microevolution of a recently emerged pathogen, Salmonella enterica serovar Agona

Salmonella enterica serovar Agona has caused multiple food-borne outbreaks of gastroenteritis since it was first isolated in 1952. We analyzed the genomes of 73 isolates from global sources, comparing five distinct outbreaks with sporadic infections as well as food contamination and the environment. Agona consists of three lineages with minimal mutational diversity: only 846 single nucleotide polymorphisms (SNPs) have accumulated in the non-repetitive, core genome since Agona evolved in 1932 and subsequently underwent a major population expansion in the 1960s. Homologous recombination with other serovars of S. enterica imported 42 recombinational tracts (360 kb) in 5/143 nodes within the genealogy, which resulted in 3,164 additional SNPs. In contrast to this paucity of genetic diversity, Agona is highly diverse according to pulsed-field gel electrophoresis (PFGE), which is used to assign isolates to outbreaks. PFGE diversity reflects a highly dynamic accessory genome associated with the gain or loss (indels) of 51 bacteriophages, 10 plasmids, and 6 integrative conjugational elements (ICE/IMEs), but did not correlate uniquely with outbreaks. Unlike the core genome, indels occurred repeatedly in independent nodes (homoplasies), resulting in inaccurate PFGE genealogies. The accessory genome contained only few cargo genes relevant to infection, other than antibiotic resistance. Thus, most of the genetic diversity within this recently emerged pathogen reflects changes in the accessory genome, or is due to recombination, but these changes seemed to reflect neutral processes rather than Darwinian selection. Each outbreak was caused by an independent clade, without universal, outbreak-associated genomic features, and none of the variable genes in the pan-genome seemed to be associated with an ability to cause outbreaks.

Current insights in invasive group A streptococcal infections in pediatrics

A rising incidence of invasive group A Streptococcus infections (IGASI) has been noted in children in the past three decades. The relative frequency of the infection types showed marked differences to IGASI in adults, and severity of the disease resulted in a mortality rate usually comprising between 3.6% and 8.3%. The emm1-type group A Streptococcus (GAS) subclone displaying a particular pattern of virulence factors was widely disseminated and prevalent in children with IGASI while the emm3-type GAS subclone appeared as a recent emerging genotype. However, the implication of these hypervirulent clones in the increase of IGASI in children is still controversial. Recent advances in our knowledge on pathogenesis of IGASI underlined that deregulation of virulence factor production, individual susceptibility, as well as exuberant cytokine response are important factors that may account for the severity of the disease in children. Future changes in IGASI epidemiology are awaited from current prospects for a safe and effective vaccine against GAS. IGASI are complex infections associating septic, toxic, and immunological disorders. Treatment has to be effective on both the etiologic agent and its toxins, due to the severity of the disease associated to the spread of highly virulent bacterial clones. More generally, emergence of virulent clones responsible for septic and toxic disease is a matter of concern in pediatric infectiology in the absence of vaccination strategy.

Superantigenic activity of emm3 Streptococcus pyogenes is abrogated by a conserved, naturally occurring smeZ mutation

Streptococcus pyogenes M/emm3 strains have been epidemiologically linked with enhanced infection severity and risk of streptococcal toxic shock syndrome (STSS), a syndrome triggered by superantigenic stimulation of T cells. Comparison of S. pyogenes strains causing STSS demonstrated that emm3 strains were surprisingly less mitogenic than other emm-types (emm1, emm12, emm18, emm28, emm87, emm89) both in vitro and in vivo, indicating poor superantigenic activity. We identified a 13 bp deletion in the superantigen smeZ gene of all emm3 strains tested. The deletion led to a premature stop codon in smeZ, and was not present in other major emm-types tested. Expression of a functional non-M3-smeZ gene successfully enhanced mitogenic activity in emm3 S. pyogenes and also restored mitogenic activity to emm1 and emm89 S. pyogenes strains where the smeZ gene had been disrupted. In contrast, the M3-smeZ gene with the 13 bp deletion could not enhance or restore mitogenicity in any of these S. pyogenes strains, confirming that M3-smeZ is non-functional regardless of strain background. The mutation in M3-smeZ reduced the potential for M3 S. pyogenes to induce cytokines in human tonsil, but not during invasive infection of superantigen-sensitive mice. Notwithstanding epidemiological associations with STSS and disease severity, emm3 strains have inherently poor superantigenicity that is explained by a conserved mutation in smeZ.

Group a streptococcal vaccine candidates: potential for the development of a human vaccine

Currently there is no commercial Group A Streptococcus (GAS; S. pyogenes) vaccine available. The development of safe GAS vaccines is challenging, researchers are confronted with obstacles such as the occurrence of many unique serotypes (there are greater than 150 M types), antigenic variation within the same serotype, large variations in the geographical distribution of serotypes, and the production of antibodies cross-reactive with human tissue which can lead to host auto-immune disease. Cell wall anchored, cell membrane associated, secreted and anchorless proteins have all been targeted as GAS vaccine candidates. As GAS is an exclusively human pathogen, the quest for an efficacious vaccine is further complicated by the lack of an animal model which mimics human disease and can be consistently and reproducibly colonized by multiple GAS strains.

Invasive group A, C and G streptococcal disease in western Norway: virulence gene profiles, clinical features and outcomes

Invasive group A streptococcal (iGAS) disease is endemic in Norway, but data on invasive group C and group G streptococcal (iGCS/GGS) disease are lacking. We investigated the characteristics of iGAS and iGCS/GGS infections in western Norway from March 2006 to February 2009. Clinical information was retrospectively obtained from medical records. GAS and GCS/GGS isolates were emm typed and screened for the presence of 11 superantigen (SAg) genes and the gene encoding streptococcal phospholipase A₂ (SlaA). GCS/GGS isolates were also subjected to PCR with primers targeting speG(dys) . Sixty iGAS and 50 iGCS/GGS cases were identified, corresponding to mean annual incidence rates of 5.0 per 100,000 and 4.1 per 100,000 inhabitants, respectively. Skin and soft tissue infections were the most frequent clinical manifestations of both iGAS and iGCS/GGS disease, and 14 iGAS patients (23%) developed necrotizing fasciitis. The 30-day case fatality rates of iGAS and iGCS/GGS disease were 10% and 2%, respectively. emm1, emm3 and emm28 accounted for 53% of the GAS isolates, and these types were associated with severe clinical outcome. SAg gene and SlaA profiles were conserved within most of the GAS emm types, although five profiles were obtained within isolates of emm28. stG643 was the most prevalent GCS/GGS emm type, and speG(dys) was identified in 73% of the GCS/GGS isolates. Neither GAS SAg genes nor SlaA were detected in GCS/GGS. Our findings indicate a considerable burden of both iGAS and iGCS/GGS disease and a high frequency of necrotizing fasciitis caused by GAS in our community.

Virulence of serotype M3 Group A Streptococcus strains in wax worms (Galleria mellonella larvae)

Group A Streptococcus (GAS) causes human infections that range in severity from pharyngitis ("strep-throat") to necrotizing fasciitis ("flesh-eating disease").  To facilitate investigation of the molecular basis of host-pathogen interactions, infection models capable of rapidly screening for differences in GAS strain virulence are needed.  To this end, we developed a Galleria mellonella larvae (wax worm) model of invasive GAS infection and used it to compare the virulence of serotype M3 GAS strains.  We found that GAS causes severe tissue damage and kills wax worms in a dose-dependent manner.  The virulence of genetically distinct GAS strains was compared by Kaplan-Meier survival analysis and determining 50% lethal doses (LD 50).  Host-pathogen interactions were further characterized using quantitative culture, histopathology and TaqMan assays.  GAS strains known to be highly pathogenic in mice and monkeys caused significantly lower survival and had significantly lower LD 50s in wax worms than GAS strains associated with attenuated virulence or asymptomatic carriage.  Furthermore, isogenic inactivation of proven virulence factors resulted in a significantly increased LD 50 and decreased lesion size compared to the wild-type strain, a finding that also strongly correlates with animal studies.  Importantly, survival analysis and LD 50 determination in wax worms supported our hypothesis that a newly emerged GAS subclone that is epidemiologically associated with more human necrotizing fasciitis cases than its progenitor lineage has significantly increased virulence.  We conclude that GAS virulence in wax worms strongly correlates with the data obtained in vertebrate models, and thus, the Galleria mellonella larva is a useful host organism to study GAS pathogenesis.

emm gene diversity, superantigen gene profiles and presence of SlaA among clinical isolates of group A, C and G streptococci from western Norway

In order to investigate molecular characteristics of beta-hemolytic streptococcal isolates from western Norway, we analysed the entire emm gene sequences, obtained superantigen gene profiles and determined the prevalence of the gene encoding streptococcal phospholipase A2 (SlaA) of 165 non-invasive and 34 contemporary invasive group A, C and G streptococci (GAS, GCS and GGS). Among the 25 GAS and 26 GCS/GGS emm subtypes identified, only emm3.1 was significantly associated with invasive disease. M protein size variation within GAS and GCS/GGS emm types was frequently identified. Two non-invasive and one invasive GGS possessed emm genes that translated to truncated M proteins as a result of frameshift mutations. Results suggestive of recombinations between emm or emm-like gene segments were found in isolates of emm4 and stG485 types. One non-invasive GGS possessed speC, speG, speH, speI and smeZ, and another non-invasive GGS harboured SlaA. speA and SlaA were over-represented among invasive GAS, probably because they were associated with emm3. speG^dys was identified in 83% of invasive and 63% of non-invasive GCS/GGS and correlated with certain emm subtypes. Our results indicate the invasive potential of isolates belonging to emm3, and show substantial emm gene diversity and possible lateral gene transfers in our streptococcal population.

Comparison of rhesus and cynomolgus macaques in a Streptococcus pyogenes infection model for vaccine evaluation

Animal models predictive of human disease are generally difficult to establish and reproduce. In the case of the Group A Streptococcus (GAS) bacterium, which is predominantly a human pathogen, virulence assessment in animal models is problematic. We compared a monkey colonization and pharyngitis model of infection in two macaque species to determine the optimal model for vaccine candidate evaluation. Rhesus and cynomolgus macaques were intranasally infected with a streptomycin resistant (Str(r)) GAS strain. Monkeys were monitored for body weight and temperature changes, throat swabs and sera were collected, and clinical observations were noted throughout the study. Both species exhibited oropharyngeal colonization by GAS, with rhesus macaques demonstrating a more sustained colonization through day 28 post-challenge. Veterinary observations revealed no significant differences between GAS-infected rhesus and cynomolgus macaques. Mock-infected monkeys did not exhibit clinical symptoms or GAS colonization throughout the study. ELISA results demonstrated that both rhesus and cynomolgus macaques developed anti-streptolysin-O antibody titers, with cynomolgus generating higher titers. Sera from infected monkeys produced opsonophagocytic killing and bound to the bacterium in an immunofluorescence assay. Both rhesus and cynomolgus macaques can be used for colonization studies with this GAS M3 strain, yet only mild clinical signs of pharyngitis and tonsillitis were observed.

Moonlighting glutamate formiminotransferases can functionally replace 5-formyltetrahydrofolate cycloligase

5-Formyltetrahydrofolate (5-CHO-THF) is formed by a side reaction of serine hydroxymethyltransferase. Unlike other folates, it is not a one-carbon donor but a potent inhibitor of folate enzymes and must therefore be metabolized. Only 5-CHO-THF cycloligase (5-FCL) is generally considered to do this. However, comparative genomic analysis indicated (i) that certain prokaryotes lack 5-FCL, implying that they have an alternative 5-CHO-THF-metabolizing enzyme, and (ii) that the histidine breakdown enzyme glutamate formiminotransferase (FT) might moonlight in this role. A functional complementation assay for 5-CHO-THF metabolism was developed in Escherichia coli, based on deleting the gene encoding 5-FCL (ygfA). The deletion mutant accumulated 5-CHO-THF and, with glycine as sole nitrogen source, showed a growth defect; both phenotypes were complemented by bacterial or archaeal genes encoding FT. Furthermore, utilization of supplied 5-CHO-THF by Streptococcus pyogenes was shown to require expression of the native FT. Recombinant bacterial and archaeal FTs catalyzed formyl transfer from 5-CHO-THF to glutamate, with k(cat) values of 0.1-1.2 min(-1) and K(m) values for 5-CHO-THF and glutamate of 0.4-5 μM and 0.03-1 mM, respectively. Although the formyltransferase activities of these proteins were far lower than their formiminotransferase activities, the K(m) values for both substrates relative to their intracellular levels in prokaryotes are consistent with significant in vivo flux through the formyltransferase reaction. Collectively, these data indicate that FTs functionally replace 5-FCL in certain prokaryotes.

Functional characterization of a phospholipase A(2) homolog from Rickettsia typhi

Phospholipase A(2) (PLA(2)) has long been proposed to be involved in rickettsial entry into host cells, escape from the phagosome to evade destruction by lysosomal exposure, and lysis of the host cells. However, the corresponding rickettsial gene(s) encoding a protein with PLA(2) activity has not been identified or functionally characterized. Here, we report that the Rickettsia typhi genome possesses two genes encoding patatin-like PLA(2) proteins, RT0590 and RT0522. Sequence analysis of RT0522 and RT0590 reveals the presence of the conserved motifs essential for PLA(2) activity. Transcriptional analysis indicates that RT0522, but not RT0590, is transcribed at all stages of intracellular growth of R. typhi in Vero cells. The differential gene expression pattern of RT0522 at various stages of growth suggests its potential role during R. typhi infection of host cells. In silico, RT0522 is predicted to be noncytoplasmic and its gene does not encode a recognizable signal peptide sequence. However, our data indicate that RT0522 is secreted into the host cytoplasm. In addition, we observe that RT0522 protein expression is cytotoxic to both yeast and Vero cells. Importantly, we demonstrate that recombinant RT0522 possesses phospholipase A activity that requires a eukaryotic host cofactor for activation. Both cytotoxicity and phospholipase A activity associated with RT0522 were reduced by PLA(2) inhibitors. Site-directed mutagenesis of predicted catalytic Ser/Asp residues of RT0522 also eliminates cytotoxicity and phospholipase A activity. To our knowledge, RT0522 is the first protein identified from Rickettsia typhi with functional phospholipase A activity.