An in vitro model to assess pneumococcal adherence to nasopharyngeal cells under competition conditions

Simultaneous Quantification and Differentiation of Streptococcus suis Serotypes 2 and 9 by Quantitative Real-Time PCR, Evaluated in Tonsillar and Nasal Samples of Pigs

Invasive Streptococcus suis (S. suis) infections in pigs are often associated with serotypes 2 and 9. Mucosal sites of healthy pigs can be colonized with these serotypes, often multiple serotypes per pig. To unravel the contribution of these serotypes in pathogenesis and epidemiology, simultaneous quantification of serotypes is needed. A quantitative real-time PCR (qPCR) targeting cps2J (serotypes 2 and 1/2) and cps9H (serotype 9) was evaluated with nasal and tonsillar samples from S. suis exposed pigs. qPCR specifically detected serotypes in all pig samples. The serotypes loads in pig samples estimated by qPCR showed, except for serotype 9 in tonsillar samples (correlation coefficient = 0.25), moderate to strong correlation with loads detected by culture (correlation coefficient > 0.65), and also in pigs exposed to both serotypes (correlation coefficient > 0.75). This qPCR is suitable for simultaneous differentiation and quantification of important S. suis serotypes.

PcpA of Streptococcus pneumoniae mediates adherence to nasopharyngeal and lung epithelial cells and elicits functional antibodies in humans

Streptococcus pneumoniae (pneumococci) adhere to human nasopharyngeal (NP) epithelial cells as a first step in colonization and adherence of pneumococci to lung epithelia may be required to establish pneumonia. We sought to determine if PcpA can serve as an adhesin to human NP (D562) and lung (A549) epithelial cells and whether PcpA mediated adherence can be inhibited by human anti-PcpA antibodies. A PcpA isogenic mutant was constructed in a pneumococcal TIGR4 background. When the mutant and wild type strains were compared for their adherence to D562 and A549 cell lines, a reduction in adherence by the mutant was observed (p = 0.0001 for both cell types). PcpA was ectopically expressed on the surface of minimally-adherent heterologous host Escherichia coli resulting in augmented adherence to D562 (p = 0.002) and A549 (p = 0.015) cells. Total IgG was purified from a pool of 6 human sera having high IgG titers of anti-pneumococcal proteins. The purified IgG reduced TIGR4 adherence to D562 cells but we determined that this effect was largely due to bacterial cell aggregation as determined by flow cytometry and confocal microscopy. Fab fragments were prepared from pooled IgG sera. Inhibition of TIGR4 adherence to D562 cells was observed using the Fab fragments without causing bacterial aggregation (p = 0.0001). Depletion of PcpA-specific Fab fragments resulted in an increase in adherence of TIGR4 to D562 cells (p = 0.028). We conclude that PcpA can mediate adherence of pneumococci to human NP and lung epithelial cells and PcpA mediated adherence can be inhibited by human anti-PcpA antibodies.

Mechanistic exploration of AhR-mediated host protection against Streptococcus pneumoniae infection

Streptococcus pneumoniae is a primary cause of invasive bacterial infection and pneumonia and is one of the leading causes of death worldwide. In prior studies we showed that pre-treating mice with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent agonist of the aryl hydrocarbon receptor (AhR), protects against S. pneumoniae-induced mortality and reduces pulmonary bacterial burden. The current studies were conducted to help elucidate the mechanism for this protective effect, and to characterize the response in the lung during the first 10h following infection. C57Bl/6 mice were treated with TCDD one day prior to intranasal infection with serotype 3 S. pneumoniae. Monitoring of bacteria in the lung airways revealed that bacterial growth was inhibited in the TCDD-treated animals within 10h of infection. To address the mechanism of this rapid protective response, macrophages, neutrophils, and invariant Natural Killer T (iNKT) cells were quantified, and levels of natural antibodies produced by B-1 B cells were evaluated. Functional assays addressed whether AhR activation reduced the capacity of lung epithelial cells to bind bacteria, and whether TCDD treatment enhanced production of antimicrobial agents in the lung or blood. None of the hypothesized mechanisms was able to explain the protective effect. Finally, the exposure paradigm was manipulated to test whether administration of TCDD after instillation of the bacteria was also protective. Results showed that TCDD must be administered in advance of exposure to bacteria, suggesting that the lung environment is rendered inhospitable to the pathogens.