Lack of activity of transferrins towards Streptococcus spp

Human milk glycoproteins protect infants against human pathogens

Breastfeeding protects the neonate against pathogen infection. Major mechanisms of protection include human milk glycoconjugates functioning as soluble receptor mimetics that inhibit pathogen binding to the mucosal cell surface, prebiotic stimulation of gut colonization by favorable microbiota, immunomodulation, and as a substrate for bacterial fermentation products in the gut. Human milk proteins are predominantly glycosylated, and some biological functions of these human milk glycoproteins (HMGPs) have been reported. HMGPs range in size from 14 kDa to 2,000 kDa and include mucins, secretory immunoglobulin A, bile salt-stimulated lipase, lactoferrin, butyrophilin, lactadherin, leptin, and adiponectin. This review summarizes known biological roles of HMGPs that may contribute to the ability of human milk to protect neonates from disease.

Comparative antibacterial activity of avian egg white protein extracts

1. Egg white proteins from the eggs of domestic chicken (Gallus gallus), turkey (Meleagris gallopavo), duck (Anas platyrhynchos) and goose (Anser anser) were analysed in order to compare the antimicrobial activity of these products. 2. Albumen from each species was sampled and analysed by SDS-PAGE and Western blotting. Antimicrobial activity and lysozyme activity were measured. 3. Ovotransferrin and ovalbumin were identified in all species while c-type lysozyme was present in chicken, turkey and duck egg white samples, but not in goose. 4. Galliformes appear to possess albumens with greater antimicrobial activity than those of the Anseriformes. This can be attributed to higher concentrations of ovotransferrin and the broad acting c-type lysozyme.

Antimicrobial activity of cuticle and outer eggshell protein extracts from three species of domestic birds

1. The eggshell cuticle is the proteinaceous outermost layer of the eggshell which regulates water exchange and protects against entry of micro-organisms. In this study, we investigated the hypothesis that the cuticle may also reduce microbial contamination by providing a chemical defence. 2. Outer eggshell and cuticle protein was extracted from domestic chicken (Gallus gallus), duck (Anas platyrhynchos) and goose (Anser anser) eggs by HCl and urea treatment, respectively. Antimicrobial activity of the extracts against Gram-positive and Gram-negative bacteria was evaluated. 3. C-type lysozyme, ovotransferrin and ovocalyxin-32 were identified in all extracts by Western blotting. All extracts from all species demonstrated lysozyme enzymatic activity. Immobilised c-type lysozyme retained some enzymatic activity. Protein extracts demonstrated activity against Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis suggesting the action of antimicrobial proteins in addition to lysozyme. 4. The results suggest that the antimicrobial outer eggshell and cuticle proteins present in a number of avian species may be a mechanism which enhances avian reproductive success.

Mn2+-dependent regulation of multiple genes in Streptococcus pneumoniae through PsaR and the resultant impact on virulence

The concentration of Mn2+ is 1,000-fold higher in secretions than it is at internal sites of the body, making it a potential signal by which bacteria can sense a shift from a mucosal environment to a more invasive site. PsaR, a metal-dependent regulator in Streptococcus pneumoniae, was found to negatively affect the transcription of psaBCA, pcpA, rrgA, rrgB, rrgC, srtBCD, and rlrA in the presence of Mn2+. psaBCA encode an ABC-type transporter for Mn2+. pcpA, rrgA, rrgB, and rrgC encode several outer surface proteins. srtBCD encode a cluster of sortase enzymes, and rlrA encodes a transcriptional regulator. Steady-state RNA levels are high under low Mn2+ concentrations in the wild-type strain and are elevated under both high and low Mn2+ concentrations in a psaR mutant strain. RlrA is an activator of rrgA, rrgB, rrgC, and srtBCD (D. Hava and A. Camilli, Mol. Microbiol. 45:1389-1406, 2002), suggesting that PsaR may indirectly control these genes through rlrA, while PsaR-dependent repression of psaBCA, pcpA, and rlrA transcription is direct. The impact of Mn2+-dependent regulation on virulence was further examined in mouse models of pneumonia and nasopharyngeal carriage. The abilities of DeltapsaR, pcpA, and DeltapsaR DeltapcpA mutant strains to colonize the lung were reduced compared to those of the wild type, confirming that both PcpA-mediated gene regulation and PsaR-mediated gene regulation are required for full virulence in the establishment of pneumonia. Neither PcpA nor PsaR was found to be required for colonization of the nasopharynx in a carriage model. This is the first demonstration of Mn2+ acting as a signal for the expression of virulence factors within different host sites.

Iron content of Streptococcus suis and evidence for a dpr homologue

The type strain of Streptococcus suis was investigated for features that might help the organism to tolerate the H2O2 that is produced during growth. Enzyme assays, using soluble extracts, revealed that the type strain, which lacks catalase, lacks NADH peroxidase in both the mid-exponential and stationary phases of the growth cycle. Although iron could not be detected colourimetrically in dense cell suspensions, determination of the cellular iron content following growth to early stationary phase in the presence of 55FeCl3 demonstrated that S. suis does contain iron and hence is incapable of iron exclusion. Gene amplification, using oligonucleotide primers based on dpr of Streptococcus mutans, followed by nucleotide sequencing, revealed in S. suis, the presence of a gene that encodes a Dpr homologue. It is concluded that in S. suis, tolerance of H2O2 is due to iron sequestration by Dpr and the consequent effect of this process on the extent of Fenton chemistry.

Effects of iron and manganese availability on growth and production of superoxide dismutase by Streptococcus suis

A complex medium supported good growth of the type strain of Streptococcus suis irrespective of the presence or absence of a high concentration (1 microM) of the iron chelating agent, ethylenediamine di-o-hydroxyphenylacetic acid. Good growth was also obtained using a complex medium that had been treated with Chelex-100 to reduce the iron content, but only if this medium was supplemented with manganese; supplementation with iron had little effect. Collectively, these results indicate that S. suis requires manganese, but not iron, for growth. Polyacrylamide gel electrophoresis of cell extracts followed by activity staining revealed the presence of a single manganese-cofactored superoxide dismutase; activity staining and enzyme assays revealed that manganese availability during growth affected the activity of the superoxide dismutase in cell extracts. The results are discussed with respect to the capacity of S. suis to avoid damage by reactive oxygen species.

Human transferrin as a source of iron for Streptococcus intermedius

Streptococcus intermedius is well known to produce severe infections in various areas of the body. In this study, we evaluated the ability of S. intermedius to utilise human transferrin as a source of iron and investigated the mechanism by which iron can be obtained from this plasma protein. Adding either ferrous sulfate or holotransferrin to an iron-deficient culture medium allowed growth of S. intermedius. Cultivation of S. intermedius under an iron-poor condition was associated with the over expression of a 58 kDa cell surface protein. Neither siderophore activity nor reductase activity could be detected. Moreover, cells of S. intermedius did not show transferrin-binding activity or proteolytic activity toward transferrin. It was found that S. intermedius could rapidly decrease the pH of the medium during cell growth, resulting in a release of iron from holotransferrin. When the buffering capacity of the culture medium was significantly increased, the holotransferrin could not support growth of S. intermedius. It is suggested that under certain circumstances, S. intermedius may migrate from its normal niche (oral cavity), reach a particular site and create a localised environment where the pH can be lowered with the subsequent release of iron from transferrin. This would allow bacterial growth and initiation of the infectious process.