Molecular architecture of Streptococcus pneumoniae surface thioredoxin-fold lipoproteins crucial for extracellular oxidative stress resistance and maintenance of virulence

The respiratory pathogen Streptococcus pneumoniae has evolved efficient mechanisms to resist oxidative stress conditions and to displace other bacteria in the nasopharynx. Here we characterize at physiological, functional and structural levels two novel surface-exposed thioredoxin-family lipoproteins, Etrx1 and Etrx2. The impact of both Etrx proteins and their redox partner methionine sulfoxide reductase SpMsrAB2 on pneumococcal pathogenesis was assessed in mouse virulence studies and phagocytosis assays. The results demonstrate that loss of function of either both Etrx proteins or SpMsrAB2 dramatically attenuated pneumococcal virulence in the acute mouse pneumonia model and that Etrx proteins compensate each other. The deficiency of Etrx proteins or SpMsrAB2 further enhanced bacterial uptake by macrophages, and accelerated pneumococcal killing by H₂O₂ or free methionine sulfoxides (MetSO). Moreover, the absence of both Etrx redox pathways provokes an accumulation of oxidized SpMsrAB2 in vivo. Taken together our results reveal insights into the role of two extracellular electron pathways required for reduction of SpMsrAB2 and surface-exposed MetSO. Identification of this system and its target proteins paves the way for the design of novel antimicrobials.

Complement regulator Factor H mediates a two-step uptake of Streptococcus pneumoniae by human cells

Streptococcus pneumoniae, a human pathogen, recruits complement regulator factor H to its bacterial cell surface. The bacterial PspC protein binds Factor H via short consensus repeats (SCR) 8-11 and SCR19-20. In this study, we define how bacterially bound Factor H promotes pneumococcal adherence to and uptake by epithelial cells or human polymorphonuclear leukocytes (PMNs) via a two-step process. First, pneumococcal adherence to epithelial cells was significantly reduced by heparin and dermatan sulfate. However, none of the glycosaminoglycans affected binding of Factor H to pneumococci. Adherence of pneumococci to human epithelial cells was inhibited by monoclonal antibodies recognizing SCR19-20 of Factor H suggesting that the C-terminal glycosaminoglycan-binding region of Factor H mediates the contact between pneumococci and human cells. Blocking of the integrin CR3 receptor, i.e. CD11b and CD18, of PMNs or CR3-expressing epithelial cells reduced significantly the interaction of pneumococci with both cell types. Similarly, an additional CR3 ligand, Pra1, derived from Candida albicans, blocked the interaction of pneumococci with PMNs. Strikingly, Pra1 inhibited also pneumococcal uptake by lung epithelial cells but not adherence. In addition, invasion of Factor H-coated pneumococci required the dynamics of host-cell actin microfilaments and was affected by inhibitors of protein-tyrosine kinases and phosphatidylinositol 3-kinase. In conclusion, pneumococcal entry into host cells via Factor H is based on a two-step mechanism. The first and initial contact of Factor H-coated pneumococci is mediated by glycosaminoglycans expressed on the surface of human cells, and the second step, pneumococcal uptake, is integrin-mediated and depends on host signaling molecules such as phosphatidylinositol 3-kinase.

Biological activities of suilysin: role in Streptococcus suis pathogenesis

Streptococcus suis is an important swine and zoonotic pathogen equipped with several virulence factors. The pore-forming toxins are the most abundant bacterial toxins and classified as critical virulence (associated) factors of several pathogens. The role of suilysin (SLY), a pore-forming cholesterol-dependent cytolysin of S. suis, as a true virulence factor is under debate. Most of the bacterial toxins have been reported to modulate the host immune system to facilitate invasion and subsequent replication of bacteria within respective host cells. SLY has been demonstrated to play an important role in the pathogenesis of S. suis infection and inflammatory response in vitro and in vivo. This review highlights the contributions of SLY to the pathogenicity of S. suis. It will address its role during the development of S. suis meningitis in pigs, as well as humans, and discuss SLY as a potential vaccine candidate.

Polymeric immunoglobulin receptor-mediated invasion of Streptococcus pneumoniae into host cells requires a coordinate signaling of SRC family of protein-tyrosine kinases, ERK, and c-Jun N-terminal kinase

Streptococcus pneumoniae are commensals of the human nasopharynx with the capacity to invade mucosal respiratory cells. PspC, a pneumococcal surface protein, interacts with the human polymeric immunoglobulin receptor (pIgR) to promote bacterial adherence to and invasion into epithelial cells. Internalization of pneumococci requires the coordinated action of actin cytoskeleton rearrangements and the retrograde machinery of pIgR. Here, we demonstrate the involvement of Src protein-tyrosine kinases (PTKs), focal adhesion kinase (FAK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) but not p38 mitogen-activated protein kinases (MAPK) in pneumococcal invasion via pIgR. Pharmacological inhibitors of PTKs and MAPKs and genetic interference with Src PTK and FAK functions caused a significant reduction of pIgR-mediated pneumococcal invasion but did not influence bacterial adhesion to host cells. Furthermore, pneumococcal ingestion by host cells induces activation of ERK1/2 and JNK. In agreement with activated JNK, its target molecule and DNA-binding protein c-Jun was phosphorylated. We also show that functionally active Src PTK is essential for activation of ERK1/2 upon pneumococcal infections. In conclusion, these data illustrate the importance of a coordinated signaling between Src PTKs, ERK1/2, and JNK during PspC-pIgR-mediated uptake of pneumococci by host epithelial cells.

Contamination of ready-to-eat street food in Pakistan with Salmonella spp.: Implications for consumers and food safety

OBJECTIVES

Ready-to-eat (RTE) food sold in Quetta, Pakistan was assessed for microbial contamination.

METHODS

Equal numbers of samples were collected from four categories of RTE food - burgers, shawarma, pizza and sandwiches - from January 2018 to December 2018. Microbial contamination of individual food samples was assessed by quantifying the total aerobic count obtained from plating samples on bacterial growth medium. Salmonella spp. serovars were identified using polymerase chain reaction.

RESULTS

Approximately 38% (121/320) of RTE food samples were not fit for human consumption. The most contaminated type of RTE food was shawarma (49%). Microbial contamination of food samples was higher in summer compared with the other seasons. Approximately 40% (49/121) of food samples that were not fit for human consumption were contamined with Salmonella spp. Salmonella enteritidis (69%) and Salmonella typhimurium (31%) were the only serovars among the samples testing positive for Salmonella spp. Of the 49 samples with high microbial counts, S. enteritidis was present in 34 samples and S. typhimurium was present in 15 samples. The antibiotic sensitivity results demonstrated that both S. enteritidis and S. typhimurium were resistant to amoxicillin. In addition, S. enteritidis was resistant to chloramphenicol and erythromycin, and S. typhimurium presented high resistance to erythromycin. Both S. typhimurium and S. enteritidis were highly sensitive to kanamycin.

CONCLUSION

RTE food sold by street vendors in Quetta was found to be contaminated with Salmonella spp. and poses a great health risk to consumers. As such, consumption should be avoided, and the health authorities should take stringent action to ensure the quality of street food in order to reduce the healthcare burden.

Impact of calcium signaling during infection of Neisseria meningitidis to human brain microvascular endothelial cells

The pili and outer membrane proteins of Neisseria meningitidis (meningococci) facilitate bacterial adhesion and invasion into host cells. In this context expression of meningococcal PilC1 protein has been reported to play a crucial role. Intracellular calcium mobilization has been implicated as an important signaling event during internalization of several bacterial pathogens. Here we employed time lapse calcium-imaging and demonstrated that PilC1 of meningococci triggered a significant increase in cytoplasmic calcium in human brain microvascular endothelial cells, whereas PilC1-deficient meningococci could not initiate this signaling process. The increase in cytosolic calcium in response to PilC1-expressing meningococci was due to efflux of calcium from host intracellular stores as demonstrated by using 2-APB, which inhibits the release of calcium from the endoplasmic reticulum. Moreover, pre-treatment of host cells with U73122 (phospholipase C inhibitor) abolished the cytosolic calcium increase caused by PilC1-expressing meningococci demonstrating that active phospholipase C (PLC) is required to induce calcium transients in host cells. Furthermore, the role of cytosolic calcium on meningococcal adherence and internalization was documented by gentamicin protection assay and double immunofluorescence (DIF) staining. Results indicated that chelation of intracellular calcium by using BAPTA-AM significantly impaired PilC1-mediated meningococcal adherence to and invasion into host endothelial cells. However, buffering of extracellular calcium by BAPTA or EGTA demonstrated no significant effect on meningococcal adherence to and invasion into host cells. Taken together, these results indicate that meningococci induce calcium release from intracellular stores of host endothelial cells via PilC1 and cytoplasmic calcium concentrations play a critical role during PilC1 mediated meningococcal adherence to and subsequent invasion into host endothelial cells.

Streptococcus pneumoniae infection of host epithelial cells via polymeric immunoglobulin receptor transiently induces calcium release from intracellular stores

The pneumococcal surface protein C (PspC) is a major adhesin of Streptococcus pneumoniae (pneumococci) that interacts in a human-specific manner with the ectodomain of the human polymeric immunoglobulin receptor (pIgR) produced by respiratory epithelial cells. This interaction promotes bacterial colonization and bacterial internalization by initiating host signal transduction cascades. Here, we examined alterations of intracellular calcium ([Ca(2+)](i)) levels in epithelial cells during host cell infections with pneumococci via the PspC-hpIgR mechanism. The release of [Ca(2+)](i) from intracellular stores in host cells was significantly increased by wild-type pneumococci but not by PspC-deficient pneumococci. The increase in [Ca(2+)](i) was dependent on phospholipase C as pretreatment of cells with a phospholipase C-specific inhibitor U73122 abolished the increase in [Ca(2+)](i). In addition, we demonstrated the effect of [Ca(2+)](i) on pneumococcal internalization by epithelial cells. Uptake of pneumococci was significantly increased after pretreatment of epithelial cells with the cell-permeable calcium chelator 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid-tetraacetoxymethyl ester or use of EGTA as an extracellular Ca(2+)-chelating agent. In contrast, thapsigargin, an inhibitor of endoplasmic reticulum Ca(2+)ATPase, which increases [Ca(2+)](i) in a sustained fashion, significantly reduced pIgR-mediated pneumococcal invasion. Importantly, pneumococcal adherence to pIgR-expressing cells was not altered in the presence of inhibitors as demonstrated by immunofluorescence microscopy. In conclusion, these results demonstrate that pneumococcal infections induce mobilization of [Ca(2+)](i) from intracellular stores. This may constitute a defense response of host cells as the experimental reduction of intracellular calcium levels facilitates pneumococcal internalization by pIgR-expressing cells, whereas elevated calcium levels diminished bacterial internalization by host epithelial cells.

Endocytosis of Streptococcus pneumoniae via the polymeric immunoglobulin receptor of epithelial cells relies on clathrin and caveolin dependent mechanisms

Colonization of Streptococcus pneumoniae (pneumococci) is a prerequisite for bacterial dissemination and their capability to enter the bloodstream. Pneumococci have evolved various successful strategies to colonize the mucosal epithelial barrier of humans. A pivotal mechanism of host cell invasion implicated with invasive diseases is promoted by the interaction of pneumococcal PspC with the polymeric Ig-receptor (pIgR). However, the mechanism(s) of pneumococcal endocytosis and the intracellular route of pneumococci upon uptake by the PspC-pIgR-interaction are not known. Here, we demonstrate by using a combination of pharmacological inhibitors and genetics interference approaches the involvement of active dynamin-dependent caveolae and clathrin-coated vesicles for pneumococcal uptake via the PspC-pIgR mechanism. Depleting cholesterol from host cell membranes and disruption of lipid microdomains impaired pneumococcal internalization. Moreover, chemical inhibition of clathrin or functional inactivation of dynamin, caveolae or clathrin by RNA interference significantly affected pneumococcal internalization suggesting that clathrin-mediated endocytosis (CME) and caveolae are involved in the bacterial uptake process. Confocal fluorescence microscopy of pIgR-expressing epithelial cells infected with pneumococci or heterologous Lactococcus lactis expressing PspC demonstrated bacterial co-localization with fluorescent-tagged clathrin and early as well as recycling or late endosomal markers such as Lamp1, Rab5, Rab4, and Rab7, respectively. In conclusion these data suggest that PspC-promoted uptake is mediated by both CME and caveolae. After endocytosis pneumococci are routed via the endocytic pathway into early endosomes and are then sorted into recycling or late endosomes, which can result in pneumococcal killing in phagolysosomes or transcytosis via recycling endosomes.

Heterologous expression of pneumococcal virulence factor PspC on the surface of Lactococcus lactis confers adhesive properties

Lactococcus lactis is a non-pathogenic bacterium that is used in the food industry but is also used as a heterologous host to reveal protein functions of pathogenic bacteria. The adhesin PspC from Streptococcus pneumoniae is a choline-binding protein that is non-covalently anchored to the bacterial cell wall. To assess the exclusive impact of pneumococcal surface protein C (PspC) on the interplay with its host we generated recombinant L. lactis producing a nisin-inducible and covalently anchored variant of PspC on the lactococcal cell surface. A translational fusion of the 5'-end of pspC3.4 with the 3'-end of hic (pspC11.4) was designed to decorate the surface of L. lactis with a chimeric PspC. The PspC3.4 part comprises the first 281 aa residues of PspC3.4, while the Hic sequence consists of the proline-rich and sortase-anchored domain. The results demonstrated that PspC is sufficient for adhesion and subsequent invasion of host epithelial cells expressing the human polymeric Ig receptor (hpIgR). Moreover, invasion via hpIgR was even more pronounced when the chimeric PspC was produced by lactococci compared with pneumococci. This study shows also for the first time that PspC plays no significant role during phagocytosis by macrophages. In contrast, recruitment of Factor H via the PspC chimer has a dramatic effect on phagocytosis of recombinant but not wild-type lactococci, as Factor H interacts specifically with the amino-terminal part of PspC and mediates the contact with phagocytes. Furthermore, L. lactis expressing PspC increased intracellular calcium levels in pIgR-expressing epithelial cells, thus resembling the effect of pneumococci, which induced release of Ca(2+) from intracellular stores via the PspC-pIgR mechanism. In conclusion, expression of the chimeric PspC confers adhesive properties to L. lactis and indicates the potential of L. lactis as a suitable host to study the impact of individual bacterial factors on their capacity to interfere with the host and manipulate eukaryotic epithelial cells.

Clinical Efficacy Comparison of Saccharomyces Boulardii and Lactic Acid as Probiotics in Acute Pediatric Diarrhea

OBJECTIVE

To compare the efficacy of Saccharomyces boulardii and lactic acid producing probiotics in addition to usual treatment regimen to cure diarrhea among children (6 months to 5 years of age).

STUDY DESIGN

Randomized controlled trial.

PLACE AND DURATION OF STUDY

Department of Pediatrics, Sheikh Zayed Hospital, Lahore, from February to July 2015.

METHODOLOGY

Children suffering from acute diarrhea were orally administered Saccharomyces boulardii and lactic acid producing probiotics for 5 days. The efficacy of administered probiotics was monitored. Patients were given Saccharomyces boulardii and lactic acid producing probiotics randomly to remove the bias.

RESULTS

Two hundred patients randomly selected for trials; out of which, 100 were treated with Saccharomyces boulardii while the other 100 were supplemented with lactic acid concomitantly along with conventional diarrhea treatment. Results indicated that Saccharomyces boulardii treatment group has significantly higher efficacy rate (45%) compared to lactic acid producing probiotics (26%).

CONCLUSION

This study concluded that Saccharomyces boulardii has a better efficacy compared to lactic acid and may be adopted as a probiotic of choice.

Neonatal Outcome of Pregnancies Complicated with Idiopathic Thrombocytopenia

OBJECTIVE

To determine the neonatal outcome with maternal idiopathic thrombocytopenia.

STUDY DESIGN

Descriptive study.

PLACE AND DURATION OF STUDY

Obstetrics and Gynecology Department, Liaqat National Hospital, Karachi, from January to June 2017.

METHODOLOGY

All 73 pregnant women diagnosed with idiopathic thrombocytopenia (ITP) during the study period were included. All the patients were kept under observation till birth of newborns. Neonates were assessed for thrombocytopenia, classified as mild, moderate and severe thrombocytopenia as outcome on the first post-natal day.

RESULTS

 Frequency of neonatal thrombocytopenia in 73 pregnant women complicated by idiopathic thrombocytopenia was 16.44% (12 neonates). Out of 12 cases, three (25%) neonates had mild thrombocytopenia, four (33.33%) neonates had moderate thrombocytopenia and five (41.66%) neonates had severe thrombocytopenia.

CONCLUSION

There are considerable chances of neonatal thrombocytopenia when mothers were suffering with idiopathic thrombocytopenia during pregnancy. These findings may be useful for the medical staff to counsel pre-pregnant or pregnant women with ITP as well as care required during delivery. Key Words: Thrombocytopenia, Idiopathic thrombocytopenia, Neonatal ITP, Pre-natal ITP.

Detection of Mutations in 81-bpRifampin Resistance Determining Region (RRDR) of rpoB gene in Mycobacterium tuberculosis using GeneXpert MTB/RIF in Clinical Specimens from Quetta, Pakistan

GeneXpert MTB/RIF has revolutionized the tuberculosis diagnosis by simultaneous detection of Mycobacterium tuberculosis and resistance to RIF (rifampicin), a surrogate marker for multidrug-resistant TB in less than two hours. The RIF-resistance pattern in Balochistan, Pakistan, is not documented. This study was aimed to detect RIF-resistant TB and mutations in RNA polymerase beta (rpoB) gene of M. tuberculosis within 81-bp RRDR in Quetta, Pakistan using GeneXpert® MTB/RIF assay. In total, 2300 clinical specimens were collected from suspected TB patients at Fatima Jinnah General and Chest Hospital Quetta, Pakistan between January and August 2017. These specimens were analyzed by GeneXpert® MTB/RIF assay. The data was statistically analyzed using SPSS software. Out of 2300 clinical specimens, M. tuberculosis was positive in in 899 (39.1%) cases by GeneXpert® MTB/RIF assay [positive respiratory cases 42.9% (871/2032) and non-respiratory 10.4% (28/268) with statistically significant difference (χ2= 104.5, p<0.001)]. Among 899 MTB positive cases, 46 (5.1%) were RIF-resistance caused by various rpoB gene mutations within 81-bp RRDR. Most of the RIF-resistant isolates were observed to harbor mutationsin Probe E 78.3% (n=36) whereas mutations in Probe A, B, D were observed 2.2% (n=1), 4.3% (n=2), and 6.5% (n=3), respectively. However, none of cases had RIF-resistance associated with Probe C. Out of 46 RRD cases, 21 (45.7 %) were males and 25 (54.3 %) were females. Additionally, Xpert® test showed higher detection rate than fluorescent microscopy (39.1% vs 31.2%, P<0.05) and detected MTB in 186 (11.8%) smear-negative specimens. Among 42 confirmed TB patients had MDR contact and eight patients were co-infected with HIV. In conclusion, 5.1% of the TB patients showed rifampicin resistance. The most frequent rpoB genetic mutations were observed in codons 531/533 (Probe E, 78.3%) whereas the least within the sequence 511 (Probe A, 2.2%).