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Streptococcus pneumoniae Enhances Human Respiratory Syncytial Virus Infection In Vitro and In Vivo.

Nguyen DT, Louwen R, Elberse K, van Amerongen G, Yüksel S, Luijendijk A, Osterhaus AD, Duprex WP, de Swart RL - PLoS ONE (2015)

Bottom Line: Intranasal HRSV infection three days later resulted in strain-specific enhancement of HRSV replication in vivo.However, neither pneumococci nor HRSV were found to spread from the upper to the lower respiratory tract, and neither pathogen was transmitted to naive cage mates by direct contact.These results demonstrate that pneumococcal colonization can enhance subsequent HRSV infection, and provide tools for additional mechanistic and intervention studies.

View Article: PubMed Central - PubMed

Affiliation: Department of Viroscience, Erasmus MC, Rotterdam, The Netherlands.

ABSTRACT
Human respiratory syncytial virus (HRSV) and Streptococcus pneumoniae are important causative agents of respiratory tract infections. Both pathogens are associated with seasonal disease outbreaks in the pediatric population, and can often be detected simultaneously in infants hospitalized with bronchiolitis or pneumonia. It has been described that respiratory virus infections may predispose for bacterial superinfections, resulting in severe disease. However, studies on the influence of bacterial colonization of the upper respiratory tract on the pathogenesis of subsequent respiratory virus infections are scarce. Here, we have investigated whether pneumococcal colonization enhances subsequent HRSV infection. We used a newly generated recombinant subgroup B HRSV strain that expresses enhanced green fluorescent protein and pneumococcal isolates obtained from healthy children in disease-relevant in vitro and in vivo model systems. Three pneumococcal strains specifically enhanced in vitro HRSV infection of primary well-differentiated normal human bronchial epithelial cells grown at air-liquid interface, whereas two other strains did not. Since previous studies reported that bacterial neuraminidase enhanced HRSV infection in vitro, we measured pneumococcal neuraminidase activity in these cultures but found no correlation with the observed infection enhancement in our model. Subsequently, a selection of pneumococcal strains was used to induce nasal colonization of cotton rats, the best available small animal model for HRSV. Intranasal HRSV infection three days later resulted in strain-specific enhancement of HRSV replication in vivo. One S. pneumoniae strain enhanced HRSV both in vitro and in vivo, and was also associated with enhanced syncytium formation in vivo. However, neither pneumococci nor HRSV were found to spread from the upper to the lower respiratory tract, and neither pathogen was transmitted to naive cage mates by direct contact. These results demonstrate that pneumococcal colonization can enhance subsequent HRSV infection, and provide tools for additional mechanistic and intervention studies.

No MeSH data available.


Related in: MedlinePlus

In vivo transmission study HRSV infection in S. pneumoniae colonized cotton rats.(A) Schematic representation of the time course of the experiment. Animals were initially housed in pairs. One of each pair was pneumococcus- or mock-colonized, and infected with HRSV three days later. Another two days later the matching naive contact animals were added to their cage, reuniting the original pairs. Index and contact animals were euthanized at day 8 or 11, respectively. (B) Bacterial titer of index and contact animals. The geometric mean titer (GMT) was about 2x105 CFU/ml for the index group, but no bacteria were isolated in the contact animals. Each data symbol represents one animal, bars represent GMT. (C) Virus titers of index and contact animals. Significantly higher virus loads were detected in the index group colonized with strain 19F, as compared to mock-colonized. In both contact groups no virus could be isolated out of the nose and lungs. * p ≤ 0.05; 2-tailed Mann-Whitney U test.
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pone.0127098.g004: In vivo transmission study HRSV infection in S. pneumoniae colonized cotton rats.(A) Schematic representation of the time course of the experiment. Animals were initially housed in pairs. One of each pair was pneumococcus- or mock-colonized, and infected with HRSV three days later. Another two days later the matching naive contact animals were added to their cage, reuniting the original pairs. Index and contact animals were euthanized at day 8 or 11, respectively. (B) Bacterial titer of index and contact animals. The geometric mean titer (GMT) was about 2x105 CFU/ml for the index group, but no bacteria were isolated in the contact animals. Each data symbol represents one animal, bars represent GMT. (C) Virus titers of index and contact animals. Significantly higher virus loads were detected in the index group colonized with strain 19F, as compared to mock-colonized. In both contact groups no virus could be isolated out of the nose and lungs. * p ≤ 0.05; 2-tailed Mann-Whitney U test.

Mentions: S. pneumoniae strain 19F had enhanced HRSV infection both in vitro and in vivo. We hypothesized that higher virus loads could facilitate transmission of virus or bacteria to naive cage mates by direct contact. To test this hypothesis, and confirm the pneumococcal enhancement of HRSV infection in vivo, we designed a transmission experiment in cotton rats (Fig 4A). Two groups of index animals (n = 6) were mock-treated or intra-nasally inoculated with S. pneumoniae strain 19F, with each animal being housed solitarily. Three days later all index animals were infected intra-nasally with rHRSVB05EGFP(5). At day 5 naive contact animals were added to each cage permitting direct physical contact between the index and contact animals for 72 hours, including the anticipated peak of HRSV replication in the index animals. Index and contact animals were euthanized at days 8 and 11, respectively (Fig 4A). Bacterial and viral loads were determined in nasopharyngeal lavages and lung homogenates. In the colonized index group S. pneumoniae was cultured from the nasopharyngeal lavage of all animals, with a geometric mean titer of 2.1x105 CFU/ml (Fig 4B). In addition, significantly higher virus loads were detected in the colonized index animals as compared to the mock control index animals (Fig 4C; p<0.05). On day 11 all contact animals were euthanized, and bacterial culture and HRSV re-isolation procedures were repeated. However, no S. pneumoniae or HRSV was detected in either the nose or the lungs of any of these animals (Fig 4C). Thus, in vivo enhancement of HRSV infection by nasal colonization of cotton rats with S. pneumoniae strain 19F proved to be reproducible, but we could not detect bacterial or viral transmission.


Streptococcus pneumoniae Enhances Human Respiratory Syncytial Virus Infection In Vitro and In Vivo.

Nguyen DT, Louwen R, Elberse K, van Amerongen G, Yüksel S, Luijendijk A, Osterhaus AD, Duprex WP, de Swart RL - PLoS ONE (2015)

In vivo transmission study HRSV infection in S. pneumoniae colonized cotton rats.(A) Schematic representation of the time course of the experiment. Animals were initially housed in pairs. One of each pair was pneumococcus- or mock-colonized, and infected with HRSV three days later. Another two days later the matching naive contact animals were added to their cage, reuniting the original pairs. Index and contact animals were euthanized at day 8 or 11, respectively. (B) Bacterial titer of index and contact animals. The geometric mean titer (GMT) was about 2x105 CFU/ml for the index group, but no bacteria were isolated in the contact animals. Each data symbol represents one animal, bars represent GMT. (C) Virus titers of index and contact animals. Significantly higher virus loads were detected in the index group colonized with strain 19F, as compared to mock-colonized. In both contact groups no virus could be isolated out of the nose and lungs. * p ≤ 0.05; 2-tailed Mann-Whitney U test.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4430531&req=5

pone.0127098.g004: In vivo transmission study HRSV infection in S. pneumoniae colonized cotton rats.(A) Schematic representation of the time course of the experiment. Animals were initially housed in pairs. One of each pair was pneumococcus- or mock-colonized, and infected with HRSV three days later. Another two days later the matching naive contact animals were added to their cage, reuniting the original pairs. Index and contact animals were euthanized at day 8 or 11, respectively. (B) Bacterial titer of index and contact animals. The geometric mean titer (GMT) was about 2x105 CFU/ml for the index group, but no bacteria were isolated in the contact animals. Each data symbol represents one animal, bars represent GMT. (C) Virus titers of index and contact animals. Significantly higher virus loads were detected in the index group colonized with strain 19F, as compared to mock-colonized. In both contact groups no virus could be isolated out of the nose and lungs. * p ≤ 0.05; 2-tailed Mann-Whitney U test.
Mentions: S. pneumoniae strain 19F had enhanced HRSV infection both in vitro and in vivo. We hypothesized that higher virus loads could facilitate transmission of virus or bacteria to naive cage mates by direct contact. To test this hypothesis, and confirm the pneumococcal enhancement of HRSV infection in vivo, we designed a transmission experiment in cotton rats (Fig 4A). Two groups of index animals (n = 6) were mock-treated or intra-nasally inoculated with S. pneumoniae strain 19F, with each animal being housed solitarily. Three days later all index animals were infected intra-nasally with rHRSVB05EGFP(5). At day 5 naive contact animals were added to each cage permitting direct physical contact between the index and contact animals for 72 hours, including the anticipated peak of HRSV replication in the index animals. Index and contact animals were euthanized at days 8 and 11, respectively (Fig 4A). Bacterial and viral loads were determined in nasopharyngeal lavages and lung homogenates. In the colonized index group S. pneumoniae was cultured from the nasopharyngeal lavage of all animals, with a geometric mean titer of 2.1x105 CFU/ml (Fig 4B). In addition, significantly higher virus loads were detected in the colonized index animals as compared to the mock control index animals (Fig 4C; p<0.05). On day 11 all contact animals were euthanized, and bacterial culture and HRSV re-isolation procedures were repeated. However, no S. pneumoniae or HRSV was detected in either the nose or the lungs of any of these animals (Fig 4C). Thus, in vivo enhancement of HRSV infection by nasal colonization of cotton rats with S. pneumoniae strain 19F proved to be reproducible, but we could not detect bacterial or viral transmission.

Bottom Line: Intranasal HRSV infection three days later resulted in strain-specific enhancement of HRSV replication in vivo.However, neither pneumococci nor HRSV were found to spread from the upper to the lower respiratory tract, and neither pathogen was transmitted to naive cage mates by direct contact.These results demonstrate that pneumococcal colonization can enhance subsequent HRSV infection, and provide tools for additional mechanistic and intervention studies.

View Article: PubMed Central - PubMed

Affiliation: Department of Viroscience, Erasmus MC, Rotterdam, The Netherlands.

ABSTRACT
Human respiratory syncytial virus (HRSV) and Streptococcus pneumoniae are important causative agents of respiratory tract infections. Both pathogens are associated with seasonal disease outbreaks in the pediatric population, and can often be detected simultaneously in infants hospitalized with bronchiolitis or pneumonia. It has been described that respiratory virus infections may predispose for bacterial superinfections, resulting in severe disease. However, studies on the influence of bacterial colonization of the upper respiratory tract on the pathogenesis of subsequent respiratory virus infections are scarce. Here, we have investigated whether pneumococcal colonization enhances subsequent HRSV infection. We used a newly generated recombinant subgroup B HRSV strain that expresses enhanced green fluorescent protein and pneumococcal isolates obtained from healthy children in disease-relevant in vitro and in vivo model systems. Three pneumococcal strains specifically enhanced in vitro HRSV infection of primary well-differentiated normal human bronchial epithelial cells grown at air-liquid interface, whereas two other strains did not. Since previous studies reported that bacterial neuraminidase enhanced HRSV infection in vitro, we measured pneumococcal neuraminidase activity in these cultures but found no correlation with the observed infection enhancement in our model. Subsequently, a selection of pneumococcal strains was used to induce nasal colonization of cotton rats, the best available small animal model for HRSV. Intranasal HRSV infection three days later resulted in strain-specific enhancement of HRSV replication in vivo. One S. pneumoniae strain enhanced HRSV both in vitro and in vivo, and was also associated with enhanced syncytium formation in vivo. However, neither pneumococci nor HRSV were found to spread from the upper to the lower respiratory tract, and neither pathogen was transmitted to naive cage mates by direct contact. These results demonstrate that pneumococcal colonization can enhance subsequent HRSV infection, and provide tools for additional mechanistic and intervention studies.

No MeSH data available.


Related in: MedlinePlus