Toll-like receptor 2 contributes to antibacterial defence against pneumolysin-deficient pneumococci

Toll-like receptors (TLRs) are pattern recognition receptors that recognize conserved molecular patterns expressed by pathogens. Pneumolysin, an intracellular toxin found in all Streptococcus pneumoniae clinical isolates, is an important virulence factor of the pneumococcus that is recognized by TLR4. Although TLR2 is considered the most important receptor for Gram-positive bacteria, our laboratory previously could not demonstrate a decisive role for TLR2 in host defence against pneumonia caused by a serotype 3 S. pneumoniae. Here we tested the hypothesis that in the absence of TLR2, S. pneumoniae can still be sensed by the immune system through an interaction between pneumolysin and TLR4. C57BL/6 wild-type (WT) and TLR2 knockout (KO) mice were intranasally infected with either WT S. pneumoniae D39 (serotype 2) or the isogenic pneumolysin-deficient S. pneumoniae strain D39 PLN. TLR2 did not contribute to antibacterial defence against WT S. pneumoniae D39. In contrast, pneumolysin-deficient S. pneumoniae only grew in lungs of TLR2 KO mice. TLR2 KO mice displayed a strongly reduced early inflammatory response in their lungs during pneumonia caused by both pneumolysin-producing and pneumolysin-deficient pneumococci. These data suggest that pneumolysin-induced TLR4 signalling can compensate for TLR2 deficiency during respiratory tract infection with S. pneumoniae

Prognostic factors related to sequelae in childhood bacterial meningitis: Data from a Greek meningitis registry

<p>Abstract</p> <p>Background</p> <p>Bacterial meningitis (BM) is a life-threatening disease, often related with serious complications and sequelae. Infants and children who survive bacterial meningitis often suffer neurological and other sequelae.</p> <p>Methods</p> <p>A total of 2,477 patients aged 1 month to 14 years old hospitalized in a Children's Hospital in Greece diagnosed with acute bacterial meningitis were collected through a Meningitis Registry, from 1974 to 2005. Clinical, laboratory and other parameters (sex, age, pathogen, duration of symptoms before and after admission) were evaluated through univariate and multivariate analysis with regard to sequelae. Analysis of acute complications were also studied but not included in the final model.</p> <p>Results</p> <p>The rate of acute complications (arthritis and/or subdural effusion) was estimated at 6.8% (152 out of 2,251 patients, 95%CI 5.8-7.9) while the rate of sequelae (severe hearing loss, ventriculitis, hydrocephalus or seizure disorder) among survivors was estimated at 3.3% (73 out of 2,207 patients, 95%CI 2.6-4.2). Risk factors on admission associated with sequelae included seizures, absence of hemorrhagic rash, low CSF glucose, high CSF protein and the etiology of meningitis. A combination of significant prognostic factors including presence of seizures, low CSF glucose, high CSF protein, positive blood culture and absence of petechiae on admission presented an absolute risk of sequelae of 41.7% (95%CI 15.2-72.3).</p> <p>Conclusions</p> <p>A combination of prognostic factors of sequelae in childhood BM may be of value in selecting patients for more intensive therapy and in identifying possible candidates for new treatment strategies.</p

Predicting sequelae and death after bacterial meningitis in childhood: A systematic review of prognostic studies

Background: Bacterial meningitis (BM) is a severe infection responsible for high mortality and disabling sequelae. Early identification of patients at high risk of these outcomes is necessary to prevent their occurrence by adequate treatment as much as possible. For this reason, several prognostic models have been developed. The objective of this study is to summarize the evidence regarding prognostic factors predicting death or sequelae due to BM in children 0-18 years of age. Methods: A search in MEDLINE and EMBASE was conducted to identify prognostic studies on risk factors for mortality and sequelae after BM in children. Selection of abstracts, full-text articles and assessment of methodological quality using the QUIPS checklist was performed by two reviewers independently. Data on prognostic factors per outcome were summarized. Results: Of the 31 studies identified, 15 were of moderate to high quality. Due to substantial heterogeneity in study characteristics and evaluated prognostic factors, no quantitative analysis was performed. Prognostic factors found to be statistically significant in more than one study of moderate or high quality are: complaints > 48 hours before admission, coma/impaired consciousness, (prolonged duration of) seizures, (prolonged) fever, shock, peripheral circulatory failure, respiratory distress, absence of petechiae, causative pathogen Streptococcus pneumoniae, young age, male gender, several cerebrospinal fluid (CSF) parameters and white blood cell (WBC) count. Conclusions: Although several important prognostic factors for the prediction of mortality or sequelae after BM were identified, the inability to perform a pooled analysis makes the exact (independent) predictive value of these factors uncertain. This emphasizes the need for additional well-conducted prognostic studie

Frequency-dependent selection in vaccine-associated pneumococcal population dynamics

Many bacterial species are composed of multiple lineages distinguished by extensive variation in gene content. These often cocirculate in the same habitat, but the evolutionary and ecological processes that shape these complex populations are poorly understood. Addressing these questions is particularly important for Streptococcus pneumoniae, a nasopharyngeal commensal and respiratory pathogen, because the changes in population structure associated with the recent introduction of partial-coverage vaccines have substantially reduced pneumococcal disease. Here we show that pneumococcal lineages from multiple populations each have a distinct combination of intermediate-frequency genes. Functional analysis suggested that these loci may be subject to negative frequency-dependent selection (NFDS) through interactions with other bacteria, hosts or mobile elements. Correspondingly, these genes had similar frequencies in four populations with dissimilar lineage compositions. These frequencies were maintained following substantial alterations in lineage prevalences once vaccination programmes began. Fitting a multilocus NFDS model of post-vaccine population dynamics to three genomic datasets using Approximate Bayesian Computation generated reproducible estimates of the influence of NFDS on pneumococcal evolution, the strength of which varied between loci. Simulations replicated the stable frequency of lineages unperturbed by vaccination, patterns of serotype switching and clonal replacement. This framework highlights how bacterial ecology affects the impact of clinical interventions.Accessory loci are shown to have similar frequencies in diverse Streptococcus pneumoniae populations, suggesting negative frequency-dependent selection drives post-vaccination population restructuring

NERAZLIKOVNOST RAZLIKA

Analiziraju se leksikološko-leksikografska polazišta i metodološki postupci u izradi Razlikovnog rječnika srpskog i hrvatskog jezika Vladimira Brodnjaka

Metabolism of sucrose and its five isomers by Fusobacteriummortiferum. Microbiology 148:843

Fusobacterium mortiferum utilizes sucrose [glucose-fructose in α(1 2) linkage] and its five isomeric α-D-glucosyl-D-fructoses as energy sources for growth. Sucrose-grown cells are induced for both sucrose-6-phosphate hydrolase (S6PH) and fructokinase (FK), but the two enzymes are not expressed above constitutive levels during growth on the isomeric compounds. Extracts of cells grown previously on the sucrose isomers trehalulose α(1 1), turanose α(1 3), maltulose α(1 4), leucrose α(1 5) and palatinose α(1 6) contained high levels of an NAD M plus metal-dependent phospho-α-glucosidase (MalH). The latter enzyme was not induced during growth on sucrose. MalH catalysed the hydrolysis of the 6&apos;-phosphorylated derivatives of the five isomers to yield glucose 6-phosphate and fructose, but sucrose 6-phosphate itself was not a substrate. Unexpectedly, MalH hydrolysed both α-and β-linked stereomers of the chromogenic analogue p-nitrophenyl glucoside 6-phosphate. The gene malH is adjacent to malB and malR, which encode an EII(CB) component of the phosphoenolpyruvate-dependent sugar :phosphotransferase system and a putative regulatory protein, respectively. The authors suggest that for F. mortiferum, the products of malB and malH catalyse the phosphorylative translocation and intracellular hydrolysis of the five isomers of sucrose and of related α-linked glucosides. Genes homologous to malB and malH are present in both Klebsiella pneumoniae and the enterohaemorrhagic strain Escherichia coli O157 :H7. Both these organisms grew well on sucrose, but only K. pneumoniae exhibited growth on the isomeric compounds

Multiple Mutations Modulate the Function of Dihydrofolate Reductase in Trimethoprim-Resistant Streptococcus pneumoniae

Trimethoprim resistance in Streptococcus pneumoniae can be conferred by a single amino acid substitution (I100-L) in dihydrofolate reductase (DHFR), but resistant clinical isolates usually carry multiple DHFR mutations. DHFR genes from five trimethoprim-resistant isolates from the United Kingdom were compared to susceptible isolates and used to transform a susceptible control strain (CP1015). All trimethoprim-resistant isolates and transformants contained the I100-L mutation. The properties of DHFRs from transformants with different combinations of mutations were compared. In a transformant with only the I100-L mutation (R12/T2) and a D92-A mutation also found in the DHFRs of susceptible isolates, the enzyme was much more resistant to trimethoprim inhibition (50% inhibitory concentration [IC(50)], 4.2 μM) than was the DHFR from strain CP1015 (IC(50), 0.09 μM). However, K(m) values indicated a lower affinity for the enzyme's natural substrates (K(m) for dihydrofolate [DHF], 3.1 μM for CP1015 and 27.5 μM for R12/T2) and a twofold decrease in the specificity constant. In transformants with additional mutations in the C-terminal portion of the enzyme, K(m) values for DHF were reduced (9.2 to 15.2 μM), indicating compensation for the lower affinity generated by I100-L. Additional mutations in the N-terminal portion of the enzyme were associated with up to threefold-increased resistance to trimethoprim (IC(50) of up to 13.7 μM). It is postulated that carriage of the mutation M53-I—which, like I100-L, corresponds to a trimethoprim binding site in the Escherichia coli DHFR—is responsible for this increase. This study demonstrates that although the I100-L mutation alone may give rise to trimethoprim resistance, additional mutations serve to enhance resistance and modulate the effects of existing mutations on the affinity of DHFR for its natural substrates