Dual role for pilus in adherence to epithelial cells and biofilm formation in Streptococcus agalactiae

Prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections

Osteomyelitis is a devastating disease caused by microbial infection in deep bone tissue. Its high recurrence rate and impaired restoration of bone deficiencies are major challenges in treatment. Microbes have evolved numerous mechanisms to effectively evade host intrinsic and adaptive immune attacks to persistently localize in the host, such as drug-resistant bacteria, biofilms, persister cells, intracellular bacteria, and small colony variants (SCVs). Moreover, microbial-mediated dysregulation of the bone immune microenvironment impedes the bone regeneration process, leading to impaired bone defect repair. Despite advances in surgical strategies and drug applications for the treatment of bone infections within the last decade, challenges remain in clinical management. The development and application of tissue engineering materials have provided new strategies for the treatment of bone infections, but a comprehensive review of their research progress is lacking. This review discusses the critical pathogenic mechanisms of microbes in the skeletal system and their immunomodulatory effects on bone regeneration, and highlights the prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections. It will inform the development and translation of antimicrobial and bone repair tissue engineering materials for the management of bone infections.

An opportunistic pathogen under stress: how Group B Streptococcus responds to cytotoxic reactive species and conditions of metal ion imbalance to survive

Group B Streptococcus (GBS; also known as Streptococcus agalactiae) is an opportunistic bacterial pathogen that causes sepsis, meningitis, pneumonia, and skin and soft tissue infections in neonates and healthy or immunocompromised adults. GBS is well-adapted to survive in humans due to a plethora of virulence mechanisms that afford responses to support bacterial survival in dynamic host environments. These mechanisms and responses include counteraction of cell death from exposure to excess metal ions that can cause mismetallation and cytotoxicity, and strategies to combat molecules such as reactive oxygen and nitrogen species that are generated as part of innate host defence. Cytotoxicity from reactive molecules can stem from damage to proteins, DNA, and membrane lipids, potentially leading to bacterial cell death inside phagocytic cells or within extracellular spaces within the host. Deciphering the ways in which GBS responds to the stress of cytotoxic reactive molecules within the host will benefit the development of novel therapeutic and preventative strategies to manage the burden of GBS disease. This review summarizes knowledge of GBS carriage in humans and the mechanisms used by the bacteria to circumvent killing by these important elements of host immune defence: oxidative stress, nitrosative stress, and stress from metal ion intoxication/mismetallation.

Invasive Streptococcus agalactiae (group B streptococcus) infection with toxic shock-like syndrome: A report of a fatal non-pregnant case and a review of the literature

Streptococcus agalactiae (group B streptococcus; GBS) is a Gram-positive coccus. It has emerged as a cause of significant infections in non-pregnant adults, particularly neonates and individuals aged 65 years or older, which can lead to fatal outcomes. Streptococcal toxic shock-like syndrome (STSS) is an acute illness, which is mainly caused by exotoxin-producing strains of Streptococcus pyogenes and may result in death. In this report, we present a fatal non-pregnant case of STSS induced by GBS in a 45-year-old healthy female. The patient presented with fever, polyarthralgia, myalgia, and skin erythema. Matrix Assisted Laser Desorption/Ionization‒Time of Flight Mass Spectrometry (MALDI-TOF-MS) and PCR identified GBS in colonies from her blood and urine cultures, and she was diagnosed with septicemia and STSS. On the sixth day of her illness, she died from acute respiratory distress syndrome and multiple organ dysfunction syndrome. Whole-genome sequencing revealed the presence of several virulence genes in the genome of the GBS strain detected in the blood cultures, which may have contributed to the development of STSS and the patient's death.

Identification of a DNA-cytosine methyltransferase that impacts global transcription to promote group B streptococcal vaginal colonization

IMPORTANCE

Group B Streptococcus (GBS) colonizes the female reproductive tract (FRT) in one-third of women, and carriage leads to numerous adverse pregnancy outcomes including the preterm premature rupture of membranes, chorioamnionitis, and stillbirth. The presence of GBS in the FRT during pregnancy is also the largest predisposing factor for the transmission of GBS and invasive neonatal diseases, including pneumonia, sepsis, and meningitis. The factors contributing to GBS colonization are still being elucidated. Here, we show for the first time that GBS transcription is regulated by an orphan DNA cytosine methyltransferase (Dcm). Many GBS factors are regulated by Dcm, especially those involved in carbohydrate transport and metabolism. We show that GBS persistence in the FRT is dependent on the catabolism of sugars found on the vaginal mucin MUC5B. Collectively, this work highlights the regulatory importance of a DNA methyltransferase and identifies both host and bacterial factors required for GBS colonization.

Bacterial biofilms in the human body: prevalence and impacts on health and disease

Bacterial biofilms can be found in most environments on our planet, and the human body is no exception. Consisting of microbial cells encased in a matrix of extracellular polymers, biofilms enable bacteria to sequester themselves in favorable niches, while also increasing their ability to resist numerous stresses and survive under hostile circumstances. In recent decades, biofilms have increasingly been recognized as a major contributor to the pathogenesis of chronic infections. However, biofilms also occur in or on certain tissues in healthy individuals, and their constituent species are not restricted to canonical pathogens. In this review, we discuss the evidence for where, when, and what types of biofilms occur in the human body, as well as the diverse ways in which they can impact host health under homeostatic and dysbiotic states.

Feature architecture aware phylogenetic profiling indicates a functional diversification of type IVa pili in the nosocomial pathogen Acinetobacter baumannii

The Gram-negative bacterial pathogen Acinetobacter baumannii is a major cause of hospital-acquired opportunistic infections. The increasing spread of pan-drug resistant strains makes A. baumannii top-ranking among the ESKAPE pathogens for which novel routes of treatment are urgently needed. Comparative genomics approaches have successfully identified genetic changes coinciding with the emergence of pathogenicity in Acinetobacter. Genes that are prevalent both in pathogenic and a-pathogenic Acinetobacter species were not considered ignoring that virulence factors may emerge by the modification of evolutionarily old and widespread proteins. Here, we increased the resolution of comparative genomics analyses to also include lineage-specific changes in protein feature architectures. Using type IVa pili (T4aP) as an example, we show that three pilus components, among them the pilus tip adhesin ComC, vary in their Pfam domain annotation within the genus Acinetobacter. In most pathogenic Acinetobacter isolates, ComC displays a von Willebrand Factor type A domain harboring a finger-like protrusion, and we provide experimental evidence that this finger conveys virulence-related functions in A. baumannii. All three genes are part of an evolutionary cassette, which has been replaced at least twice during A. baumannii diversification. The resulting strain-specific differences in T4aP layout suggests differences in the way how individual strains interact with their host. Our study underpins the hypothesis that A. baumannii uses T4aP for host infection as it was shown previously for other pathogens. It also indicates that many more functional complexes may exist whose precise functions have been adjusted by modifying individual components on the domain level.

Engineered skin bacteria induce antitumor T cell responses against melanoma

Certain bacterial colonists induce a highly specific T cell response. A hallmark of this encounter is that adaptive immunity develops preemptively, in the absence of an infection. However, the functional properties of colonist-induced T cells are not well defined, limiting our ability to understand anticommensal immunity and harness it therapeutically. We addressed both challenges by engineering the skin bacterium Staphylococcus epidermidis to express tumor antigens anchored to secreted or cell-surface proteins. Upon colonization, engineered S. epidermidis elicits tumor-specific T cells that circulate, infiltrate local and metastatic lesions, and exert cytotoxic activity. Thus, the immune response to a skin colonist can promote cellular immunity at a distal site and can be redirected against a target of therapeutic interest by expressing a target-derived antigen in a commensal.

The Determination, Monitoring, Molecular Mechanisms and Formation of Biofilm in E. coli

Biofilms are cell assemblies embedded in an exopolysaccharide matrix formed by microorganisms of a single or many different species. This matrix in which they are embedded protects the bacteria from external influences and antimicrobial effects. The biofilm structure that microorganisms form to protect themselves from harsh environmental conditions and survive is found in nature in many different environments. These environments where biofilm formation occurs have in common that they are in contact with fluids. The gene expression of bacteria in complex biofilm differs from that of bacteria in the planktonic state. The differences in biofilm cell expression are one of the effects of community life. Means of quorum sensing, bacteria can act in coordination with each other. At the same time, while biofilm formation provides many benefits to bacteria, it has positive and negative effects in many different areas. Depending on where they occur, biofilms can cause serious health problems, contamination risks, corrosion, and heat and efficiency losses. However, they can also be used in water treatment plants, bioremediation, and energy production with microbial fuel cells. In this review, the basic steps of biofilm formation and biofilm regulation in the model organism Escherichia coli were discussed. Finally, the methods by which biofilm formation can be detected and monitored were briefly discussed.

Local and Systemic Effects of Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a gram-negative anaerobe, is a leading etiological agent in periodontitis. This infectious pathogen can induce a dysbiotic, proinflammatory state within the oral cavity by disrupting commensal interactions between the host and oral microbiota. It is advantageous for P. gingivalis to avoid complete host immunosuppression, as inflammation-induced tissue damage provides essential nutrients necessary for robust bacterial proliferation. In this context, P. gingivalis can gain access to the systemic circulation, where it can promote a prothrombotic state. P. gingivalis expresses a number of virulence factors, which aid this pathogen toward infection of a variety of host cells, evasion of detection by the host immune system, subversion of the host immune responses, and activation of several humoral and cellular hemostatic factors.

Antibacterial activity and metabolomic analysis of linalool against bovine mastitis pathogen Streptococcus agalactiae

Streptococcus agalactiae is among the major causative pathogens of bovine mastitis, as well as crucial pathogen leading to human morbidity and mortality. Being a promising natural antibacterial agent, linalool has been broadly applied in medicine and food processing. However, its antibacterial effect against S. agalactiae has barely been elucidated. This study is the first to investigate the antibacterial activity and action mechanism of linalool against S. agalactiae causing bovine mastitis. Linalool exhibited significant antibacterial activity against S. agalactiae, with an inhibition zone diameter of 23 mm and a minimum inhibitory concentration of 1.875 μL/mL. In addition, linalool damaged cell structural integrity of S. agalactiae, leading to the leakage of intracellular components (alkaline phosphatase, nucleic acids and protein). Linalool also exhibited a scavenging effect on biofilm. Moreover, untargeted metabolomics analysis revealed that linalool stress substantially disrupted intracellular metabolism of S. agalactiae. Linalool caused energy metabolism disorder, and obstructed nucleic acid synthesis in S. agalactiae. Furthermore, downregulation of amino acids (e.g., proline, alanine) and upregulation of saturated fatty acids provide strong evidence for linalool induced cell wall and membrane damage. Overall, linalool exhibited strong antibacterial activity against S. agalactiae by destroying the cell structure and disrupting intracellular metabolism. This study provides a new insight and theoretical foundation for linalool application in preventing S. agalactiae infection.

Group B Streptococcus: Virulence Factors and Pathogenic Mechanism

Group B Streptococcus (GBS) or Streptococcus agalactiae is a major cause of neonatal mortality. When colonizing the lower genital tract of pregnant women, GBS may cause premature birth and stillbirth. If transmitted to the newborn, it may result in life-threatening illnesses, including sepsis, meningitis, and pneumonia. Moreover, through continuous evolution, GBS can use its original structure and unique factors to greatly improve its survival rate in the human body. This review discusses the key virulence factors that facilitate GBS invasion and colonization and their action mechanisms. A comprehensive understanding of the role of virulence factors in GBS infection is crucial to develop better treatment options and screen potential candidate molecules for the development of the vaccine.

Structural Identification of Lipid-α: A Glycosyl Lipid Involved in Oligo- And Polysaccharides Metabolism in Streptococcus agalactiae (Group B Streptococcus)

Streptococcus agalactiae (group B Streptococcus, GBS) is a gram-positive bacterium that is an asymptomatic colonizer commonly found in the gastrointestinal and genitourinary tract of healthy adults. GBS is also the most common cause of life-threatening bacterial infections in newborns and is emerging as a pathogen in immunocompromised and diabetic adults. The GBS cell wall and covalently linked capsular polysaccharides (CPS) are vital to the protection of the bacterial cell and act as virulence factors. GBS-CPS have been successfully used to produce conjugate vaccines for all currently identified GBS serotypes. However, the mechanisms of biosynthesis and assembly of CPS and the other cell wall components remain poorly defined due to their complex surface structures. In this biosynthetic study of the GBS cell wall-CPS complex, glycolipids with varying lengths of glycosyl-chains were discovered. Among those, one of the smallest glycolipids (named GBS Lipid-α) was structurally characterized. Lipid-α is involved in GBS saccharide metabolism and presumably acts as a glycosyl acceptor to elongate the glycosyl chain. GBS Lipid-α was determined to be a 3-monosaccharide 1,2 acyl glycerol with a molecular mass in the range of m/z = 724-808. GBS Lipid-α is highly heterogenic with various acyl groups and glycosyl moieties. This knowledge will pave the way for future studies to elucidate the entire metabolic pathway and genes involved. The Lipid-α pathway may also exist in other bacterial species and has the potential to be a biomarker for future drug development.

McaA and McaB control the dynamic positioning of a bacterial magnetic organelle

Magnetotactic bacteria are a diverse group of microorganisms that use intracellular chains of ferrimagnetic nanocrystals, produced within magnetosome organelles, to align and navigate along the geomagnetic field. Several conserved genes for magnetosome formation have been described, but the mechanisms leading to distinct species-specific magnetosome chain configurations remain unclear. Here, we show that the fragmented nature of magnetosome chains in Magnetospirillum magneticum AMB-1 is controlled by genes mcaA and mcaB. McaA recognizes the positive curvature of the inner cell membrane, while McaB localizes to magnetosomes. Along with the MamK actin-like cytoskeleton, McaA and McaB create space for addition of new magnetosomes in between pre-existing magnetosomes. Phylogenetic analyses suggest that McaA and McaB homologs are widespread among magnetotactic bacteria and may represent an ancient strategy for magnetosome positioning.

The In Vitro Replication Cycle of Achromobacter xylosoxidans and Identification of Virulence Genes Associated with Cytotoxicity in Macrophages

Achromobacter xylosoxidans is an opportunistic pathogen implicated in a wide variety of human infections including the ability to colonize the lungs of cystic fibrosis (CF) patients. The role of A. xylosoxidans in human pathology remains controversial due to the lack of optimized in vitro and in vivo model systems to identify and test bacterial gene products that promote a pathological response. We have previously identified macrophages as a target host cell for A. xylosoxidans-induced cytotoxicity. By optimizing our macrophage infection model, we determined that A. xylosoxidans enters macrophages and can reside within a membrane bound vacuole for extended periods of time. Intracellular replication appears limited with cellular lysis preceding an enhanced, mainly extracellular replication cycle. Using our optimized in vitro model system along with transposon mutagenesis, we identified 163 genes that contribute to macrophage cytotoxicity. From this list, we characterized a giant RTX adhesin encoded downstream of a type one secretion system (T1SS) that mediates bacterial binding and entry into host macrophages, an important first step toward cellular toxicity and inflammation. The RTX adhesin is encoded by other human isolates and is recognized by antibodies present in serum isolated from CF patients colonized by A. xylosoxidans, indicating this virulence factor is produced and deployed in vivo. This study represents the first characterization of A. xylosoxidans replication during infection and identifies a variety of genes that may be linked to virulence and human pathology. IMPORTANCE Patients affected by CF develop chronic bacterial infections characterized by inflammatory exacerbations and tissue damage. Advancements in sequencing technologies have broadened the list of opportunistic pathogens colonizing the CF lung. A. xylosoxidans is increasingly recognized as an opportunistic pathogen in CF, yet our understanding of the bacterium as a contributor to human disease is limited. Genomic studies have identified potential virulence determinants in A. xylosoxidans isolates, but few have been mechanistically studied. Using our optimized in vitro cell model, we identified and characterized a bacterial adhesin that mediates binding and uptake by host macrophages leading to cytotoxicity. A subset of serum samples from CF patients contains antibodies that recognize the RTX adhesion, suggesting, for the first time, that this virulence determinant is produced in vivo. This work furthers our understanding of A. xylosoxidans virulence factors at a mechanistic level.

Cortisol Promotes Surface Translocation of Porphyromonas gingivalis

Studies are showing that the stress hormone cortisol can reach high levels in the gingival sulcus and induce shifts in the metatranscriptome of the oral microbiome. Interestingly, it has also been shown that cortisol can influence expression levels of Type IX Secretion System (T9SS) genes involved in gliding motility in bacteria belonging to the phylum Bacteroidota. The objective of this study was to determine if cortisol impacts gene expression and surface translocation of Porphyromonas gingivalis strain W50. To conduct these experiments, P. gingivalis was stabbed to the bottom of soft agar plates containing varying cortisol concentrations (0 μM, 0.13 μM, 1.3 μM, and 13 μM), and surface translocation on the subsurface was observed after 48 h of incubation. The results show that when grown with certain nutrients, i.e., in rich medium with the addition of sheep blood, lactate, or pyruvate, cortisol promotes migration of P. gingivalis in a concentration-dependent manner. To begin to examine the underlying mechanisms, quantitative PCR was used to evaluate differential expression of genes when P. gingivalis was exposed to cortisol. In particular, we focused on differential expression of T9SS-associated genes, including mfa5, since it was previously shown that Mfa5 is required for cell movement and cell-to-cell interactions. The data show that mfa5 is significantly up-regulated in the presence of cortisol. Moreover, an mfa5 deletion mutant showed less surface translocation compared to the wild-type P. gingivalis in the presence of cortisol, and the defects of the mfa5 deletion mutant were restored by complementation. Overall, cortisol can stimulate P. gingivalis surface translocation and this coincides with higher expression levels of T9SS-associated genes, which are known to be essential to gliding motility. Our findings support a high possibility that the stress hormone cortisol from the host can promote surface translocation and potentially virulence of P. gingivalis.

Genotypic Characterization and Biofilm Production of Group B Streptococcus Strains Isolated from Bone and Joint Infections

Bone and joint infections (BJI) represent the second cause of invasive Group B Streptococcus (GBS) infections. Biofilm formation plays a major role in BJI. This study's aim was to analyze the genetic features and biofilm production of GBS strains. In six French laboratories, 77 GBS strains isolated from BJI and 57 strains from vaginal human colonization (Hcol) were characterized and compared by Multi-Locus Sequence Typing (MLST). PCR was used to search for the adhesins (bsaB, lmb, scpB, fbsA, fbsB, hvgA, bibA, bca, srr-1, and srr-2) and Pilus Islands (PI) related genes (PI-1, PI-2a, PI-2b). Biofilm production was studied by crystal violet assay. Strains were categorized into three groups, based on Specific Biofilm Formation (SBF) values defined as: weak, moderate, or strong producers. Molecular study revealed three major clonal complexes (CC) in BJI strains: CC1 (42%), CC23 (22%) and CC10 (14%). Several associations between CC and adhesin/pili were identified: CC1 with srr2, PI-1 + 2a; CC10 with srr-1, bca, PI-1 + 2a; CC17 with fbsB, hvgA, srr-2, PI-1+PI-2b; CC19 with bibA, srr-1, PI-1 + 2a; CC23 with fbsB, bibA, srr-1, PI-2a. The biofilm production was significantly different according to CC, adhesins and pili gene detection. CC10, CC23 and strains harboring fbsB produce more biofilm than CC1, PI-1 + 2a (independently). Finally, SBF values were significantly stronger for Hcol strains rather than for BJI strains (76% versus 40%). This study revealed that Hcol strains appeared to produce stronger biofilm than BJI strains, though they belonged to similar CCs and had the same adhesin and pili content. IMPORTANCE Bone and joint infections (BJI) are pathologies that can be life-threatening and result in compromised functional prognosis for patients. Relapses are common and often related to biofilm formation. Group B streptococci (GBS) BJI increased since the last decade. However, few data are available on this subject in the literature. Our study aims to highlight genotype and biofilm production of GBS isolates from BJI. Seventy-seven GBS strains isolated from BJI and 57 from asymptomatic human vaginal colonization were characterized by multilocus sequence typing (MLST), adhesins content, nature of the pili and the ability to form biofilm. Our results revealed that vaginal human colonization strains produced stronger biofilm than BJI strains, despite belonging to the same phylogenetic lineage and having the same adhesin and pili content.

Streptococcal bacterial components in cancer therapy

The incidence rate of cancer is steadily increasing all around the world, and there is an urgent need to develop novel and more effective treatment strategies. Recently, bacterial therapy has been investigated as a new approach to target cancer, and is becoming a serious option. Streptococcus strains are among the most common and well-studied virulent bacteria that cause a variety of human infections. Everyone has experienced a sore throat during their lifetime, or has been asymptomatically colonized by streptococci. The ability of Streptococcus bacteria to fight cancer was discovered more than 100 years ago, and over the years has undergone clinical trials, but the mechanism is not yet completely understood. Recently, several animal models and human clinical trials have been reported. Streptococcal strains can have an intrinsic anti-tumor activity, or can activate the host immune system to fight the tumor. Bacteria can selectively accumulate and proliferate in the hypoxic regions of solid tumors. Moreover, the bacteria can be genetically engineered to secrete toxins or enzymes that can specifically attack the tumors.

Proteome and strain analysis of cyanobacterium Candidatus "Phormidium alkaliphilum" reveals traits for success in biotechnology

Cyanobacteria encompass a diverse group of photoautotrophic bacteria with important roles in nature and biotechnology. Here we characterized Candidatus “Phormidium alkaliphilum,” an abundant member in alkaline soda lake microbial communities globally. The complete, circular whole-genome sequence of Ca. “P. alkaliphilum” was obtained using combined Nanopore and Illumina sequencing of a Ca. “P. alkaliphilum” consortium. Strain-level diversity of Ca. “P. alkaliphilum” was shown to contribute to photobioreactor robustness under different operational conditions. Comparative genomics of closely related species showed that adaptation to high pH was not attributed to specific genes. Proteomics at high and low pH showed only minimal changes in gene expression, but higher productivity in high pH. Diverse photosystem antennae proteins, and high-affinity terminal oxidase, compared with other soda lake cyanobacteria, appear to contribute to the success of Ca. “P. alkaliphilum” in photobioreactors and biotechnology applications.

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Closed genome of the cyanobacteria Ca. P. alkaliphilum from high-pH photobioreactor

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Genetic factors lead this Phormidium to outcompete other cyanobacteria in photobioreactor

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Adaptation to high pH and alkalinity is not linked to specific genes

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Strain-level diversity contributes Ca. P. alkaliphilum success in changing conditions

Type IV Pili of Streptococcus sanguinis Contribute to Pathogenesis in Experimental Infective Endocarditis

Streptococcus sanguinis is a common cause of infective endocarditis (IE). Efforts by research groups are aimed at identifying and characterizing virulence factors that contribute to the ability of this organism to cause IE. This Gram-positive pathogen causes heart infection by gaining access to the bloodstream, adhering to host extracellular matrix protein and/or platelets, colonizing the aortic endothelium, and incorporating itself into the aortic vegetation. While many virulence factors have been reported to contribute to the ability of S. sanguinis to cause IE, it is noteworthy that type IV pili (T4P) have not been described to be a virulence factor in this organism, although S. sanguinis strains typically encode these pili. Type IV pili are molecular machines that are capable of mediating diverse virulence functions and surface motility. T4P have been shown to mediate twitching motility in some strains of S. sanguinis, although in most strains it has been difficult to detect twitching motility. While we found that T4P are dispensable for direct in vitro platelet binding and aggregation phenotypes, we show that they are critical to the development of platelet-dependent biofilms representative of the cardiac vegetation. We also observed that T4P are required for in vitro invasion of S. sanguinis into human aortic endothelial cells, which indicates that S. sanguinis may use T4P to take advantage of an intracellular niche during infection. Importantly, we show that T4P of S. sanguinis are critical to disease progression (vegetation development) in a native valve IE rabbit model. The results presented here expand our understanding of IE caused by S. sanguinis and identify T4P as an important virulence factor for this pathogen.

IMPORTANCE This work provides evidence that type IV pili produced by Streptococcus sanguinis SK36 are critical to the ability of these bacteria to attach to and colonize the aortic heart valve (endocarditis). We found that an S. sanguinis type IV pili mutant strain was defective in causing platelet-dependent aggregation in a 24-h infection assay but not in a 1-h platelet aggregation assay, suggesting that the type IV pili act at later stages of vegetation development. In a rabbit model of disease, a T4P mutant strain does not develop mature vegetations that form on the heart, indicating that this virulence factor is critical to disease and could be a target for IE therapy.

Potential of Variovorax paradoxus isolate BFB1_13 for bioremediation of BTEX contaminated sites

Here, we report and discuss the applicability of Variovorax paradoxus strain BFB1_13 in the bioremediation of BTEX contaminated sites. Strain BFB1_13 was capable of degrading all the six BTEX-compounds under both aerobic (O₂ conc. 8 mg l⁻¹) and micro-aerobic/oxygen-limited (O₂ conc. 0.5 mg l⁻¹) conditions using either individual (8 mg‧l⁻¹) or a mixture of compounds (~ 1.3 mg‧l⁻¹ of each BTEX compound). The BTEX biodegradation capability of SBP-encapsulated cultures (SBP—Small Bioreactor Platform) was also assessed. The fastest degradation rate was observed in the case of aerobic benzene biodegradation (8 mg l⁻¹ per 90 h). Complete biodegradation of other BTEX occurred after at least 168 h of incubation, irrespective of the oxygenation and encapsulation. No statistically significant difference was observed between aerobic and microaerobic BTEX biodegradation. Genes involved in BTEX biodegradation were annotated and degradation pathways were predicted based on whole-genome shotgun sequencing and metabolic analysis. We conclude that V. paradoxus strain BFB1_13 could be used for the development of reactive biobarriers for the containment and in situ decontamination of BTEX contaminated groundwater plumes. Our results suggest that V. paradoxus strain BFB1_13—alone or in co-culture with other BTEX degrading bacterial isolates—can be a new and efficient commercial bioremediation agent for BTEX contaminated sites.

Hemolytic activity and biofilm-formation among clinical isolates of group B streptococcus causing acute urinary tract infection and asymptomatic bacteriuria

Streptococcus agalactiae, also known as group B Streptococcus, is an aetiological agent of urinary tract infection (UTI) in adults, including cystitis, pyelonephritis and asymptomatic bacteriuria (ABU). Whereas ABU-causing S. agalactiae (ABSA) have been shown to grow and achieve higher culture denstity in human urine compared to uropathogenic S. agalactiae (UPSA) other phenotypic distinctions between S. agalactiae isolated from different forms of UTI are not known. Here, we define the hemolytic activities and biofilm-formation of a collection of clinical isolates of UPSA, ABSA and recurrent S. agalactiae bacteriuria (rSAB) strains to explore these phenotypes in the context of clinical history of isolates. A total of 61 UPSA, 184 ABSA, and 47 rSAB isolates were analyzed for relative hemolytic activity by spot assay on blood agar, which was validated using a erythrocyte lysis suspension assay. Biofilm formation was determined by microtiter plate assay with Lysogeny and Todd-Hewitt broths supplemented with 1% glucose to induce biofilm formation. We also used multiplex PCR to analyze isolates for the presence of genes encoding adhesive pili, which contribute to biofilm formation. Comparing the hemolytic activities of 292 isolates showed, surprisingly, that ABSA strains were significantly more likely to be highly hemolytic compared to other strains. In contrast, there were no differences between the relative abilities of strains from the different clinical history groups to form biofilms. Taken together, these findings demonstrate a propensity of S. agalactiae causing ABU to be highly hemolytic but no link between clinical history of UTI strains and ability to form biofilm.

PilB from Streptococcus sanguinis is a bimodular type IV pilin with a direct role in adhesion

Type IV pili (T4P) are functionally versatile filaments widespread in prokaryotes, composed of type IV pilins and assembled by conserved multiprotein machineries. It remains unclear how such rather simple filaments can be so versatile. Our structure/function analysis of PilB, a minor pilin of Streptococcus sanguinis T4P, offers an elegant explanation for this paradox. We show that PilB is a modular pilin with a bulky module “grafted” onto a small pilin module, which directly mediates adhesion of S. sanguinis to host cells/proteins. This evolutionary tinkering strategy appears to be prevalent in bacteria since a global analysis reveals that modular pilins are widespread and exhibit an astonishing variety of architectures.

Type IV pili (T4P) are functionally versatile filamentous nanomachines, nearly ubiquitous in prokaryotes. They are predominantly polymers of one major pilin but also contain minor pilins whose functions are often poorly defined and likely to be diverse. Here, we show that the minor pilin PilB from the T4P of Streptococcus sanguinis displays an unusual bimodular three-dimensional structure with a bulky von Willebrand factor A–like (vWA) module “grafted” onto a small pilin module via a short loop. Structural modeling suggests that PilB is only compatible with a localization at the tip of T4P. By performing a detailed functional analysis, we found that 1) the vWA module contains a canonical metal ion–dependent adhesion site, preferentially binding Mg²⁺ and Mn²⁺, 2) abolishing metal binding has no impact on the structure of PilB or piliation, 3) metal binding is important for S. sanguinis T4P–mediated twitching motility and adhesion to eukaryotic cells, and 4) the vWA module shows an intrinsic binding ability to several host proteins. These findings reveal an elegant yet simple evolutionary tinkering strategy to increase T4P functional versatility by grafting a functional module onto a pilin for presentation by the filaments. This strategy appears to have been extensively used by bacteria, in which modular pilins are widespread and exhibit an astonishing variety of architectures.

12/111phiA Prophage Domestication Is Associated with Autoaggregation and Increased Ability to Produce Biofilm in Streptococcus agalactiae

CC17 Streptococcus agalactiae carrying group-A prophages is increasingly responsible for neonatal infections. To investigate the impact of the genetic features of a group-A prophage, we first conducted an in silico analysis of the genome of 12/111phiA, a group-A prophage carried by a strain responsible for a bloodstream infection in a parturient. This revealed a Restriction Modification system, suggesting a prophage maintenance strategy and five ORFs of interest for the host and encoding a type II toxin antitoxin system RelB/YafQ, an endonuclease, an S-adenosylmethionine synthetase MetK, and an StrP-like adhesin. Using the WT strain cured from 12/111phiA and constructing deleted mutants for the ORFs of interest, and their complemented mutants, we demonstrated an impact of prophage features on growth characteristics, cell morphology and biofilm formation. Our findings argue in favor of 12/111phiA domestication by the host and a role of prophage features in cell autoaggregation, glycocalyx and biofilm formation. We suggest that lysogeny may promote GBS adaptation to the acid environment of the vagina, consequently colonizing and infecting neonates.

AFM in cellular and molecular microbiology

The unique capabilities of the atomic force microscope (AFM), including super-resolution imaging, piconewton force-sensitivity, nanomanipulation and ability to work under physiological conditions, have offered exciting avenues for cellular and molecular biology research. AFM imaging has helped unravel the fine architectures of microbial cell envelopes at the nanoscale, and how these are altered by antimicrobial treatment. Nanomechanical measurements have shed new light on the elasticity, tensile strength and turgor pressure of single cells. Single-molecule and single-cell force spectroscopy experiments have revealed the forces and dynamics of receptor-ligand interactions, the nanoscale distribution of receptors on the cell surface and the elasticity and adhesiveness of bacterial pili. Importantly, recent force spectroscopy studies have demonstrated that extremely stable bonds are formed between bacterial adhesins and their cognate ligands, originating from a catch bond behaviour allowing the pathogen to reinforce adhesion under shear or tensile stress. Here, we survey how the versatility of AFM has enabled addressing crucial questions in microbiology, with emphasis on bacterial pathogens. TAKE AWAYS: AFM topographic imaging unravels the ultrastructure of bacterial envelopes. Nanomechanical mapping shows what makes cell envelopes stiff and resistant to drugs. Force spectroscopy characterises the molecular forces in pathogen adhesion. Stretching pili reveals a wealth of mechanical and adhesive responses.

Clostridium perfringens Produces an Adhesive Pilus Required for the Pathogenesis of Necrotic Enteritis in Poultry

Clostridium perfringens type G strains cause necrotic enteritis (NE) in poultry, an economically important disease that is a major target of in-feed antibiotics. NE is a multifactorial disease, involving not only the critically important NetB toxin but also additional virulence and virulence-associated factors. We previously identified a C. perfringens chromosomal locus (VR-10B) associated with disease-causing strains that is predicted to encode a sortase-dependent pilus. In the current study, we sought to provide direct evidence for the production of a pilus by C. perfringens and establish its role in NE pathogenesis. Pilus structures in virulent C. perfringens strain CP1 were visualized by transmission electron microscopy (TEM) of immunogold-labeled cells. Filamentous structures were observed extending from the cell surface in wild-type CP1 but not from isogenic pilin-null mutant strains. In addition, immunoblotting of cell surface proteins demonstrated that CP1, but not the null mutant strains, produced a high molecular weight ladder-like pattern characteristic of a pilus polymer. Binding to collagen types I, II, and IV was significantly reduced (Tukey's test, P < 0.01) in all three pilin mutants compared to CP1 and could be specifically blocked by CnaA and FimA antisera, indicating that these pilins participate in adherence. Furthermore, fimA and fimB null mutants were both severely attenuated in their ability to cause disease in an in vivo chicken NE challenge model. Together, these results provide the first direct evidence for the production of a sortase-dependent pilus by C. perfringens and confirm its critical role in NE pathogenesis and collagen binding.IMPORTANCE In necrotic enteritis (NE), an intestinal disease of chickens, Clostridium perfringens cells adhere tightly to damaged intestinal tissue, but the factors involved are not known. We previously discovered a cluster of C. perfringens genes predicted to encode a pilus, a hair-like bacterial surface structure commonly involved in adherence. In the current study, we have directly imaged this pilus using transmission electron microscopy (TEM). We also show that inactivation of the pilus genes stops pilus production, significantly reducing the bacterium's ability to bind collagen and cause disease. Importantly, this is the first direct evidence for the production of a sortase-dependent pilus by C. perfringens, revealing a promising new target for developing therapeutics to combat this economically important disease.

Genome-Wide fitness analysis of group B Streptococcus in human amniotic fluid reveals a transcription factor that controls multiple virulence traits

Streptococcus agalactiae (group B Streptococcus; GBS) remains a dominant cause of serious neonatal infections. One aspect of GBS that renders it particularly virulent during the perinatal period is its ability to invade the chorioamniotic membranes and persist in amniotic fluid, which is nutritionally deplete and rich in fetal immunologic factors such as antimicrobial peptides. We used next-generation sequencing of transposon-genome junctions (Tn-seq) to identify five GBS genes that promote survival in the presence of human amniotic fluid. We confirmed our Tn-seq findings using a novel CRISPR inhibition (CRISPRi) gene expression knockdown system. This analysis showed that one gene, which encodes a GntR-class transcription factor that we named MrvR, conferred a significant fitness benefit to GBS in amniotic fluid. We generated an isogenic targeted deletion of the mrvR gene, which had a growth defect in amniotic fluid relative to the wild type parent strain. The mrvR deletion strain also showed a significant biofilm defect in vitro. Subsequent in vivo studies showed that while the mutant was able to cause persistent murine vaginal colonization, pregnant mice colonized with the mrvR deletion strain did not develop preterm labor despite consistent GBS invasion of the uterus and the fetoplacental units. In contrast, pregnant mice colonized with wild type GBS consistently deliver prematurely. In a sepsis model the mrvR deletion strain showed significantly decreased lethality. In order to better understand the mechanism by which this newly identified transcription factor controls GBS virulence, we performed RNA-seq on wild type and mrvR deletion GBS strains, which revealed that the transcription factor affects expression of a wide range of genes across the GBS chromosome. Nucleotide biosynthesis and salvage pathways were highly represented among the set of differentially expressed genes, suggesting that MrvR may be involved in regulating nucleotide availability.

Group B Streptococcus (GBS) is a species of Gram-positive bacteria that often colonizes the healthy adult intestinal and reproductive tracts without causing serious symptoms. During pregnancy, however, GBS can invade the pregnant uterus, where it can cause infection of the placenta, fetal membranes, and fetus—a condition known as chorioamnionitis. Chorioamnionitis is associated with serious adverse pregnancy outcomes, including stillbirth, preterm labor, and severe infection of the newborn. GBS can survive in human amniotic fluid, which is low in bacterial nutrients and contains immune molecules that limit microbial persistence, and this ability likely contributes to GBS chorioamnionitis. This study is focused on a single GBS gene that encodes a genetic regulator we called MrvR, which we show is important for GBS resistance to human amniotic fluid. Using a series of genetic techniques combined with animal models of GBS colonization and infection, we show that MrvR also plays a key role in allowing GBS to invade the bloodstream and trigger the inflammatory responses that lead to preterm labor and stillbirth. The study concludes with a survey of other GBS genes whose activity is regulated by MrvR, which seems to be an important contributor to GBS virulence.

Complete Genome Sequence Analysis of Acidithiobacillus ferrivorans XJFY6S-08 Reveals Environmental Adaptation to Alpine Acid Mine Drainage

The present work reported the complete genome sequence analysis of Acidithiobacillus ferrivorans strain XJFY6S-08 isolated from acid mine drainage in Fuyun copper mine in Xinjiang, China, revealing the potential for extreme environmental adaptation. The strain XJFY6S-08 possesses 3,161,380 bp in length and 56.55% GC content. Genomic analysis revealed that this strain harbors metal-tolerant genes coding for the mer operon, arsRBC operon and a variety of metal assimilation and efflux proteins. Genes coding for K⁺/H⁺ transporting ATPase and the Na⁺/H⁺ antiporter gene nhaA for pH adaptation were identified. The presence of genes associated with various DNA repair enzymes and the synthesis of mycosporine-like amino acids precursor support the UVR resistance mechanisms. The genes related to membrane modifications (ppiBCD, slyD, surA, cfa and fabF) and resistance-nodulation-division (RND) family can play a crucial role in organic solvents tolerance. The strain XJFY6S-08 resists low-temperature conditions by a set of mechanisms such as changes of RNA metabolism, transmembrane transport, compatible solutes and transport, biofilm and EPS formation, chemotaxis and motility and ROS scavenging. These findings can provide important information for further studying the comparative genome and environmental adaptation mechanism of A. ferrivorans.

Force-Induced Changes of PilY1 Drive Surface Sensing by Pseudomonas aeruginosa

During biofilm formation, the opportunistic pathogen Pseudomonas aeruginosa uses its type IV pili (TFP) to sense a surface, eliciting increased second-messenger production and regulating target pathways required to adapt to a surface lifestyle. The mechanisms whereby TFP detect surface contact are still poorly understood, although mechanosensing is often invoked, with few data supporting this claim. Using a combination of molecular genetics and single-cell analysis, with biophysical, biochemical, and genomics techniques, we show that force-induced changes mediated by the von Willebrand A (vWA) domain-containing, TFP tip-associated protein PilY1 are required for surface sensing. Atomic force microscopy shows that TFP/PilY1 can undergo force-induced, sustained conformational changes akin to those observed for mechanosensitive proteins like titin. We show that mutation of a single cysteine residue in the vWA domain of PilY1 results in modestly lower surface adhesion forces, reduced sustained conformational changes, and increased nanospring-like properties, as well as reduced c-di-GMP signaling and biofilm formation. Mutating this cysteine has allowed us to genetically separate a role for TFP in twitching motility from surface-sensing signaling. The conservation of this Cys residue in all P. aeruginosa PA14 strains and its absence in the ∼720 sequenced strains of P. aeruginosa PAO1 may contribute to explaining the observed differences in surface colonization strategies observed for PA14 versus PAO1. IMPORTANCE Most bacteria live on abiotic and biotic surfaces in surface-attached communities known as biofilms. Surface sensing and increased levels of the second-messenger molecule c-di-GMP are crucial to the transition from planktonic to biofilm growth. The mechanism(s) underlying TFP-mediated surface detection that triggers this c-di-GMP signaling cascade is unclear. Here, we provide key insight into this question; we show that the eukaryote-like vWA domain of the TFP tip-associated protein PilY1 responds to mechanical force, which in turn drives the production of a key second messenger needed to regulate surface behaviors. Our studies highlight a potential mechanism that may account for differing surface colonization strategies.

In-hospital mortality among patients with invasive non-group A β-hemolytic Streptococcus treated with clindamycin combination therapy: a nationwide cohort study

Aim

Combination treatment with clindamycin is recommended in patients with invasive group A Streptococcus infection; however, whether the same treatment is effective in invasive group B Streptococcus and S. dysgalactiae subspecies equisimilis infections remains unknown. We aimed to investigate whether clindamycin added to standard of care therapy would be effective in patients with invasive non-group A β-hemolytic Streptococcus infections.

Methods

This was a nationwide retrospective cohort study using the Japanese Diagnosis Procedure Combination inpatient database focusing on the period between 2010 and 2018. We extracted data on patients diagnosed with sepsis due to non-group A β-hemolytic Streptococcus. One-to-four propensity score-matching was undertaken to compare patients who were treated with clindamycin within 2 days of admission (clindamycin group) and those who did not (control group). The primary outcome was in-hospital mortality.

Results

We identified 3754 eligible patients during the study period. The patients were divided into the clindamycin (n = 296) and control groups (n = 3458). After one-to-four propensity score matching, we compared 289 and 1156 patients with and without clindamycin, respectively. In-hospital mortality did not significantly differ between the two groups (9.7% versus 10.3%; risk difference 0.3%; 95% confidence interval, -3.5% to 4.2%).

Conclusions

This nationwide database study showed that combination therapy involving the use of clindamycin was not associated with lower in-hospital mortality in patients with invasive non-group A β-hemolytic Streptococcus.

Molecular epidemiology, antimicrobial activity, and virulence gene clustering of Streptococcus agalactiae isolated from dairy cattle with mastitis in China

Streptococcus agalactiae is a contagious pathogen that causes bovine mastitis worldwide, resulting in considerable economic losses. In this study, we isolated 42 S. agalactiae strains in 379 milk samples from cows with subclinical mastitis on 15 dairy farms in 12 Chinese provinces. Analysis based on capsular typing and multilocus sequence typing, combined with patterns of virulence gene scanning and antimicrobial resistance, identified the lineages and populations of the isolates. We grouped the 42 isolates into 7 sequence types belonging to 6 clonal complexes, mainly CC103 (31/42 isolates; 73.8%). We identified an ST-23 strain named Sa 129 for the first time on Chinese dairy farms-this strain is usually associated with human isolates. Capsular types Ia and II were predominant in capsular typing. The prevalence of virulence profile 1 (bibA, cfb, cspA, cylE, fbsA, fbsB, hylB, and pavA) was 64.3%, and represented the main trend in China. With respect to antimicrobial resistance, most isolates were susceptible to β-lactams, rifamycin, glycopeptides, and oxazolidone; resistance to several antimicrobial agents, including lincomycin, clindamycin, and doxycycline, varied in 4 different regions. Our research provides a profile for the molecular epidemiology, multilocus sequence typing, antimicrobial resistance, and virulence gene clustering of S. agalactiae, and may be beneficial for the clinical monitoring, prevention, and control of mastitis in dairy cattle.

Collagen Binding Proteins of Gram-Positive Pathogens

Collagens are the primary structural components of mammalian extracellular matrices. In addition, collagens regulate tissue development, regeneration and host defense through interaction with specific cellular receptors. Their unique triple helix structure, which requires a glycine residue every third amino acid, is the defining structural feature of collagens. There are 28 genetically distinct collagens in humans. In addition, several other unrelated human proteins contain a collagen domain. Gram-positive bacteria of the genera Staphylococcus, Streptococcus, Enterococcus, and Bacillus express cell surface proteins that bind to collagen. These proteins of Gram-positive pathogens are modular proteins that can be classified into different structural families. This review will focus on the different structural families of collagen binding proteins of Gram-positive pathogen. We will describe how these proteins interact with the triple helix in collagens and other host proteins containing a collagenous domain and discuss how these interactions can contribute to the pathogenic processes.

Singularities of Pyogenic Streptococcal Biofilms - From Formation to Health Implication

Biofilms are generally defined as communities of cells involved in a self-produced extracellular matrix adhered to a surface. In biofilms, the bacteria are less sensitive to host defense mechanisms and antimicrobial agents, due to multiple strategies, that involve modulation of gene expression, controlled metabolic rate, intercellular communication, composition, and 3D architecture of the extracellular matrix. These factors play a key role in streptococci pathogenesis, contributing to therapy failure and promoting persistent infections. The species of the pyogenic group together with Streptococcus pneumoniae are the major pathogens belonging the genus Streptococcus, and its biofilm growth has been investigated, but insights in the genetic origin of biofilm formation are limited. This review summarizes pyogenic streptococci biofilms with details on constitution, formation, and virulence factors associated with formation.

Deciphering Streptococcal Biofilms

Streptococci are a diverse group of bacteria, which are mostly commensals but also cause a considerable proportion of life-threatening infections. They colonize many different host niches such as the oral cavity, the respiratory, gastrointestinal, and urogenital tract. While these host compartments impose different environmental conditions, many streptococci form biofilms on mucosal membranes facilitating their prolonged survival. In response to environmental conditions or stimuli, bacteria experience profound physiologic and metabolic changes during biofilm formation. While investigating bacterial cells under planktonic and biofilm conditions, various genes have been identified that are important for the initial step of biofilm formation. Expression patterns of these genes during the transition from planktonic to biofilm growth suggest a highly regulated and complex process. Biofilms as a bacterial survival strategy allow evasion of host immunity and protection against antibiotic therapy. However, the exact mechanisms by which biofilm-associated bacteria cause disease are poorly understood. Therefore, advanced molecular techniques are employed to identify gene(s) or protein(s) as targets for the development of antibiofilm therapeutic approaches. We review our current understanding of biofilm formation in different streptococci and how biofilm production may alter virulence-associated characteristics of these species. In addition, we have summarized the role of surface proteins especially pili proteins in biofilm formation. This review will provide an overview of strategies which may be exploited for developing novel approaches against biofilm-related streptococcal infections.

The impact of the ancillary pilus-1 protein RrgA of Streptococcus pneumoniae on colonization and disease

The Gram-positive bacterium Streptococcus pneumoniae, the pneumococcus, is an important commensal resident of the human nasopharynx. Carriage is usually asymptomatic, however, S. pneumoniae can become invasive and spread from the upper respiratory tract to the lungs causing pneumonia, and to other organs to cause severe diseases such as bacteremia and meningitis. Several pneumococcal proteins important for its disease-causing capability have been described and many are expressed on the bacterial surface. The surface located pneumococcal type-1 pilus has been associated with virulence and the inflammatory response, and it is present in 20%-30% of clinical isolates. Its tip protein RrgA has been shown to be a major adhesin to human cells and to promote invasion through the blood-brain barrier. In this review we discuss recent findings of the impact of RrgA on bacterial colonization of the upper respiratory tract and on pneumococcal virulence, and use epidemiological data and genome-mining to suggest trade-off mechanisms potentially explaining the rather low prevalence of pilus-1 expressing pneumococci in humans.

Precision Medicine in the Diagnosis and Management of Orthopedic Biofilm Infections

Orthopedic biofilm infections are difficult to treat and require a multidisciplinary approach to diagnostics and management. Recent advances in the field include methods to disrupt biofilm, sequencing tools, and antibiotic susceptibility tests for bacteria residing in biofilm. The observation of interclonal differences in biofilm properties of the causative microorganisms, together with considerations of comorbidities and polypharmacy in a growing aging population, calls for a personalized approach to treat these infections. In this article, we highlight aspects of precision medicine that may open new perspectives in the diagnosis and management of orthopedic biofilm infections.

More than a feeling: microscopy approaches to understanding surface-sensing mechanisms

The mechanisms by which bacteria sense and respond to surface attachment have long been a mystery. Our understanding of the structure and dynamics of bacterial appendages, notably type IV pili (T4P), provided new insights into the potential ways that bacteria sense surfaces. T4P are ubiquitous, retractable hair-like adhesins that until recently were difficult to image in the absence of fixation due to their nanoscale size. This review focuses on recent microscopy innovations used to visualize T4P in live cells to reveal the dynamics of their retraction and extension. We discuss recently proposed mechanisms by which T4P facilitate bacterial surface sensing, including the role of surface-exposed PilY1, two-component signal transduction pathways, force-induced structural modifications of the major pilin, and altered dynamics of the T4P motor complex.

Tackling Multidrug Resistance in Streptococci - From Novel Biotherapeutic Strategies to Nanomedicines

The pyogenic streptococci group includes pathogenic species for humans and other animals and has been associated with enduring morbidity and high mortality. The main reason for the treatment failure of streptococcal infections is the increased resistance to antibiotics. In recent years, infectious diseases caused by pyogenic streptococci resistant to multiple antibiotics have been raising with a significant impact to public health and veterinary industry. The rise of antibiotic-resistant streptococci has been associated to diverse mechanisms, such as efflux pumps and modifications of the antimicrobial target. Among streptococci, antibiotic resistance emerges from previously sensitive populations as result of horizontal gene transfer or chromosomal point mutations due to excessive use of antimicrobials. Streptococci strains are also recognized as biofilm producers. The increased resistance of biofilms to antibiotics among streptococci promote persistent infection, which comprise circa 80% of microbial infections in humans. Therefore, to overcome drug resistance, new strategies, including new antibacterial and antibiofilm agents, have been studied. Interestingly, the use of systems based on nanoparticles have been applied to tackle infection and reduce the emergence of drug resistance. Herein, we present a synopsis of mechanisms associated to drug resistance in (pyogenic) streptococci and discuss some innovative strategies as alternative to conventional antibiotics, such as bacteriocins, bacteriophage, and phage lysins, and metal nanoparticles. We shall provide focused discussion on the advantages and limitations of agents considering application, efficacy and safety in the context of impact to the host and evolution of bacterial resistance.

Streptococcus agalactiae clinical isolates in Northwest Iran: antibiotic susceptibility, molecular typing, and biofilm formation

Background: Group B Streptococcus (S. agalactiae) is one of the colonizing bacteria in pregnant women which can be a causative agent of meningitis and neonatal sepsis. This organism has also been increasingly related to invasive infections in non-pregnant adults. Objective: In present study, we aimed to characterize the clonality of biofilm-producing S. agalactiae isolates from various sources from two different clinical laboratories in Tehran, Iran. Materials and Methods: S. agalactiae isolates were collected from community-acquired (CA) and hospital-acquired (HA) infections in pregnant and non-pregnant adults. The antimicrobial susceptibility patterns and biofilm formation ability were determined. In addition, pulse field gel electrophoresis (PFGE) was used to verify the clonal diversity of isolates. Results: Out of the 87 isolates, 15 (16.6%) formed biofilm. The antibiotic resistance rate was 98.85% for clindamycin, 98.85% for tetracycline, followed by 29.88% for erythromycin, 9.19% for moxifloxacin and 6.89% for levofloxacin. The PFGE patterns revealed a total of 16 different clusters consisting of 6 single types (STs). Conclusion: This study evaluated the biofilm formation of clinical S. agalactiae, which may be a step towards understanding its role in pathological processes. Biofilm formation was significant only in the hypervirulent ST-17 clone. Intraclonal spread of isolates indicates that a local lineage of isolates is responsible for infection by these bacteria.

Biofilm formation by ST17 and ST19 strains of Streptococcus agalactiae

Bacterial biofilms are an important virulence factor with a vital role in evasion from the host immune system, colonization and infection. The aim of the present study was to evaluate in vitro the effects of three environmental factors (H⁺, glucose and human plasma) in biofilm formation, by carrier and invasive Streptococcus agalactiae strains of ST17 and ST19 sequence types, including DNase producers and non-producers. Bacteria ability to assemble biofilms was classified based on crystal violet assay. Biofilm formation was also monitored by scanning electron microscopy. Depending on the growth medium used, each bacterial isolate could fit in different biofilm production categories. Our data showed that optimal conditions for S. agalactiae biofilm assembly were reached after 48 h incubation at pH 7.6 in the presence of glucose and inactivated human plasma. In the presence of inactivated human plasma, the biofilm biomass of ST19 strains experienced a higher increase than ST17 strains. The composition of the extracellular polymeric matrix of the three strongest biofilm producers (all from ST17) was accessed by enzymatic digestion of mature biofilms and proteins were shown to be the predominant component. The detailed identification of the extracellular protein components should contribute to the development of new therapeutic strategies to fight S. agalactiae infections.

Molecular characterization of pathogenic group B streptococcus from a tertiary hospital in Shanxi, China: High incidence of sequence type 10 strains in infants/pregnant women

BACKGROUND

Group B streptococcus (GBS) is a leading cause of serious infection in infants. Understanding its regional molecular epidemiology is helpful for regulating efficient prevention practice.

METHODS

A retrospective study was conducted to collected data from infants and pregnant women with culture-proven GBS disease in the largest women and children's medical center in Shanxi between January 2017 and September 2019. All GBS isolates were analyzed by multi-locus sequence typing (MLST) as well as distribution of pilus island (PI) genes.

RESULTS

A total of 54 GBS isolates were obtained from 36 (66.7%) pregnant women and 18 (33.3%) infants with invasive disease. Among invasive GBS strains, the most common sequence type was ST10 (72.2%, P < 0.05), followed by ST23 and ST19. The ST10 strain was also the leading sequence type in colonizing pregnant women (44.4%, P < 0.05). All of the isolates carried at least one pilus island. The most frequently detected pilus island was PI-1+PI-2a (85.2%, P < 0.05), followed in turn by PI-2a and PI-2b.

CONCLUSIONS

Our study demonstrates that one hypervirulent clone, sequence type 10, accounts for a large proportion of invasive GBS disease in infants and colonizing pregnant women, and the PI-1+PI-2a sub-lineages should be noted in infant infections.

Pan-GWAS of Streptococcus agalactiae Highlights Lineage-Specific Genes Associated with Virulence and Niche Adaptation

GBS is a leading cause of mortality in newborn babies in high- and low-income countries worldwide. Different strains of GBS are characterized by different degrees of virulence, where some are harmlessly carried by humans or animals and others are much more likely to cause disease. The genome sequences of almost 2,000 GBS samples isolated from both animals and humans in high- and low- income countries were analyzed using a pan-genome-wide association study approach. This allowed us to identify 279 genes which are associated with different lineages of GBS, characterized by a different virulence and preferred host. Additionally, we propose that the GBS now carried in humans may have first evolved in animals before expanding clonally once adapted to the human host. These findings are essential to help understand what is causing GBS disease and how the bacteria have evolved and are transmitted.

Streptococcus agalactiae (group B streptococcus; GBS) is a colonizer of the gastrointestinal and urogenital tracts, and an opportunistic pathogen of infants and adults. The worldwide population of GBS is characterized by clonal complexes (CCs) with different invasive potentials. CC17, for example, is a hypervirulent lineage commonly associated with neonatal sepsis and meningitis, while CC1 is less invasive in neonates and more commonly causes invasive disease in adults with comorbidities. The genetic basis of GBS virulence and the extent to which different CCs have adapted to different host environments remain uncertain. We have therefore applied a pan-genome-wide association study (GWAS) approach to 1,988 GBS strains isolated from different hosts and countries. Our analysis identified 279 CC-specific genes associated with virulence, disease, metabolism, and regulation of cellular mechanisms that may explain the differential virulence potential of particular CCs. In CC17 and CC23, for example, we have identified genes encoding pilus, quorum-sensing proteins, and proteins for the uptake of ions and micronutrients which are absent in less invasive lineages. Moreover, in CC17, carriage and disease strains were distinguished by the allelic variants of 21 of these CC-specific genes. Together our data highlight the lineage-specific basis of GBS niche adaptation and virulence.

The genome sequences of almost 2,000 GBS samples isolated from both animals and humans in high- and low- income countries were analyzed using a pan-genome-wide association study approach. This allowed us to identify 279 genes which are associated with different lineages of GBS, characterized by a different virulence and preferred host. Additionally, we propose that the GBS now carried in humans may have first evolved in animals before expanding clonally once adapted to the human host.

These findings are essential to help understand what is causing GBS disease and how the bacteria have evolved and are transmitted.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

Microarray Analysis of Group B Streptococci Causing Invasive Neonatal Early- and Late-onset Infection

BACKGROUND

Group B Streptococcus is the leading cause of meningitis and sepsis in newborns. Until now, there is no data of fast and simple typing of group B Streptococcus virulence factors using a genetic microarray and comparing these data to clinical manifestations.

METHODS

A prospective active surveillance study was conducted via 2 independent and nationwide reporting systems, the German Pediatric Surveillance Unit (ESPED) and the Laboratory Sentinel Group at Robert Koch-Institute. Surveillance was performed between 2001 and 2003 and between 2008 and 2010. Typing of virulence factors, serotypes, pilus islands and alpha-like proteins was done by means of a newly developed microarray method.

RESULTS

We evaluated 475 isolates of invasive neonatal infections. Predominant virulence factors were serotype III (63%), pilus island 2b and pilus island 1 (50%) and alp rib (64%) (alp - alpha-like protein, rib -resistance to proteases, immunity, group B). There was no significant change over time or geographically within Germany. Serotype III, pilus island 2b + 1 and alp rib showed significant associations with late-onset disease and meningitis, whereas alp 5 had a significant association with early-onset disease. Based on serotypes, pilus islands and alpha-like proteins, it was possible to cluster 86% of all isolates into 5 genetic groups.

CONCLUSIONS

The molecular epidemiology of a large collection of invasive neonatal infections showed similar distributions, as shown in smaller cohorts before. The microarray used proved to be a fast and reliable technique. Using this new tool, we were able to cluster the isolates according to their virulence factors. The clusters showed a better association with clinical data than single virulence factors.

Role of luxS in immune evasion and pathogenicity of piscine Streptococcus agalactiae is not dependent on autoinducer-2

luxS-mediated autoinducer 2 (AI-2)-dependent quorum sensing (QS) has been demonstrated to affect many bacterial phenotypes, including virulence. Streptococcus agalactiae harbors a functional luxS gene required for the biosynthesis of AI-2. In this study, we investigated the regulation effect and mechanism of the luxS/AI-2 QS system in the pathogenicity of the piscine S. agalactiae strain GD201008-001. We found that inactivation of luxS caused a marked decrease in biofilm formation, hemolytic activity, antiphagocytosis and intracellular survival of S. agalactiae. Except for hemolytic activity, the altered phenotypes due to the luxS deletion were AI-2-independent. Further investigation indicated that high levels of the proinflammatory cytokines IL-1β and IL-6 could be induced in macrophages co-incubated with the luxS deletion mutant and synthetic AI-2, single or combined. Also, the results of tilapia infection showed that inactivation of luxS significantly decreased the virulence of S. agalactiae but upregulated the expression of cytokines in spleens and brains. Increased proinflammatory effects of the luxS mutant were restored in the luxS complemented strain but could not be restored by AI-2 addition. All the findings suggest that luxS is involved in virulence-associated phenotypes and immunological evasion of S. agalactiae, and furthermore, this involvement is mostly AI-2-independent. This study will provide valuable insights into our understanding of the role of the LuxS/AI-2 QS system in the pathogenesis of S. agalactiae.

The adhesive PitA pilus protein from the early dental plaque colonizer Streptococcus oralis: expression, purification, crystallization and X-ray diffraction analysis

PitA is the putative tip adhesin of the pilus islet 2 (PI-2)-encoded sortase-dependent pilus in the Gram-positive Streptococcus oralis, an opportunistic pathogen that often flourishes within the diseased human oral cavity. Early colonization by S. oralis and its interaction with Actinomyces oris seeds the development of oral biofilm or dental plaque. Here, the PI-2 pilus plays a vital role in mediating adherence to host surfaces and other bacteria. A recombinant form of the PitA adhesin has now been produced and crystallized. Owing to the large size (∼100 kDa), flexibility and complicated folding of PitA, obtaining diffraction-quality crystals has been a challenge. However, by the use of limited proteolysis with α-chymotrypsin, the diffraction quality of the PitA crystals was considerably enhanced to 2.16 Å resolution. These crystals belonged to space group P1, with unit-cell parameters a = 61.48, b = 70.87, c = 82.46 Å, α = 80.08, β = 87.02, γ = 87.70°. The anomalous signal from the terbium derivative of α-chymotrypsin-treated PitA crystals prepared with terbium crystallophore (Tb-Xo4) was sufficient to obtain an interpretable electron-density map via terbium SAD phasing.

Salivary dysbiosis and the clinical spectrum in anti-Ro positive mothers of children with neonatal lupus

Mothers giving birth to children with manifestations of neonatal lupus (NL) represent a unique population at risk for the development of clinically evident pathologic autoimmunity since many are asymptomatic and only become aware of anti-SSA/Ro positivity (anti-Ro+) based on heart block in their fetus. Accordingly, we hypothesized that the microbiome in saliva is associated with the development of autoreactivity and in some cases the progression in health status from benign to overt clinical disease including Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). The study comprised a clinical spectrum of anti-Ro+ mothers, all of whom gave birth to a child with NL: 9 were asymptomatic or had an undifferentiated autoimmune disease (Asym/UAS) and 16 fulfilled criteria for SS and/or SLE. Microbial diversity was reduced across all levels from kingdom to species for the anti-Ro+ mothers vs healthy controls; however, there were no significant differences between Asym/UAS and SS/SLE mothers. Relative abundance of Proteobacteria and more specifically class Betaproteobacteria decreased with clinical severity (healthy controls < Asym/UAS < SS/SLE). These ordered differences were maintained through the taxonomic hierarchy to three genera (Lautropia, Comamonas, and Neisseria) and species within these genera (L. mirabilis, N. flavescens and N. oralis). Biometric analysis comparing von Willebrand Factor domains present in human Ro60 with L. mirabilis proteins support the hypothesis of molecular mimicry. These data position the microbiome in the development of anti-Ro reactivity and subsequent clinical spectrum of disease.

Biofilm production under different atmospheres and growth media by Streptococcus agalactiae isolated from milk of cows with subclinical mastitis

Different methods to analyze Streptococcus agalactiae biofilm formation have been investigated, but standardized protocols have not been developed. We compared S. agalactiae biofilm production among different atmospheres and growth media. Biofilm formation was studied in 32 isolates from bovine mastitis cases grown in Tryptone Soy Broth (TSB), Todd Hewitt Broth (THB), Luria Bertani Broth (LB) and Brain Heart Infusion (BHI), under two atmospheres, aerobic and 5% CO₂. Regardless of the culture medium, growth under 5% CO₂ resulted in a greater proportion of biofilm formation (65.63%), as compared with aerobic conditions (39.84%). Regardless of the atmosphere, the chances of biofilm formation were greater for isolates grown in TSB, as compared with THB [Odds ratio (OR) = 3.02], BHI (OR = 4.57), or LB (OR = 10.20). Thus, we suggest the use of 5% CO₂ atmosphere and TSB in biofilm formation assays by Group-B streptococci (GBS) isolated from intramammary infections.

Biofilm production and distribution of pilus variants among Streptococcus agalactiae isolated from human and animal sources

Streptococcus agalactiae (group B Streptococcus, GBS) is a major pathogen in humans and animals. Pili and biofilm may be important virulence factors in this bacterial species. Here, biofilm production and the distribution of pilus variants among 134 GBS isolates from human and animal sources were evaluated. Biofilm production was significantly enhanced in 1% glucose-supplemented medium (p < 0.05). Using this medium, most GBS strains were strong biofilm producers. Biomass was mainly composed of proteins, followed by extracellular DNA, while polysaccharides represented a minor portion. All GBS strains presented at least one pilus variant. PI-2a was the most common among human GBS while PI-2b was the most common among animal isolates. Human GBS harboring PI-2b and animal GBS harboring PI-2a presented significantly reduced biofilm production (p = 0.0033). In conclusion, strong biofilm production seems to be a common characteristic in GBS, and association of the clinical source with the pilus variant may be crucial for this.

Morphological characterization of the adherence and invasion of Streptococcus agalactiae to the intestinal mucosa of tilapia Oreochromis sp.: An in vitro model

Streptococcosis in tilapia Oreochromis sp. is possibly the most important bacterial disease for fish production worldwide. In Colombia, streptococcosis is caused by Streptococcus agalactiae (GBS), but in other countries, Streptococcus iniae is also involved. Prevention of streptococcosis is required and must be addressed for economic, social, international trade and public health reasons. This research used an in vitro culture of tilapia intestine to detail the intestinal mucosal response once the pathogen contacts the epithelium. We show that S. agalactiae sheds off its capsule to adhere to the epithelium. The bacterium adheres as a single individuum, in groups or in chains and is able to divide on the apical border of enterocytes. GBS adheres at and invades exclusively through the apical portion of the intestinal folds, using the transepithelial route. Once within the cytoplasm of enterocytes, the bacteria continue to divide. On the basolateral side of the epithelium, the microorganisms leave the cells to reach the propria and travel through the microcirculation. No evidence of an immuno-inflammatory reaction or goblet cell response in the epithelium or the lamina propria was seen during the process of adherence and invasion of the pathogen.