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Streptococcus pneumoniae is desiccation tolerant and infectious upon rehydration.

Walsh RL, Camilli A - MBio (2011)

Bottom Line: Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces.Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally.Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.

View Article: PubMed Central - PubMed

Affiliation: Graduate Program in Molecular Microbiology, Sackler School of Graduate Biomedical Science, Howard Hughes Medical Institute and Department of Molecular Biology and Microbiology, School of Medicine, Tufts University, Boston, Massachusetts, USA.

ABSTRACT

Unlabelled: Streptococcus pneumoniae (pneumococcus) is a frequent colonizer of the nasopharynx and one of the leading causative agents of otitis media, pneumonia, and meningitis. The current literature asserts that S. pneumoniae is transmitted person to person via respiratory droplets; however, environmental surfaces (fomites) have been linked to the spread of other respiratory pathogens. Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces. This study investigated the survival and infectivity of S. pneumoniae following desiccation under ambient conditions. We recovered viable bacteria after all desiccation periods tested, ranging from 1 h to 4 weeks. Experiments conducted under nutrient limitation indicate that desiccation is a condition separate from starvation. Desiccation of an acapsular mutant and 15 different clinical isolates shows that S. pneumoniae desiccation tolerance is independent of the polysaccharide capsule and is a species-wide phenomenon, respectively. Experiments demonstrating that nondesiccated and desiccated S. pneumoniae strains colonize the nasopharynx at comparable levels, combined with their ability to survive long-term desiccation, suggest that fomites may serve as alternate sources of pneumococcal infection.

Importance: Even with the advent of multivalent capsular polysaccharide conjugate vaccines, S. pneumoniae continues to be a major cause of morbidity and mortality worldwide. Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally. It is believed that the human upper respiratory tract is the sole niche of S. pneumoniae and, thus, that spread occurs via close contact with an infected individual. In this study, we characterized the desiccation tolerance of S. pneumoniae and found that it can survive for many weeks postdehydration and retain infectivity. Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.

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Murine nasopharyngeal colonization by desiccated versus nondesiccated S. pneumoniae. Shown are bacterial loads in nasal lavage fluid at 72 hours post-intranasal inoculation with 1.5 × 104 CFU (nondesiccated) and 3.2 × 104 CFU (desiccated) S. pneumoniae D39. Closed circles represent individual mice, and bars indicate the medians (P value determined by Mann-Whitney U test).
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f5: Murine nasopharyngeal colonization by desiccated versus nondesiccated S. pneumoniae. Shown are bacterial loads in nasal lavage fluid at 72 hours post-intranasal inoculation with 1.5 × 104 CFU (nondesiccated) and 3.2 × 104 CFU (desiccated) S. pneumoniae D39. Closed circles represent individual mice, and bars indicate the medians (P value determined by Mann-Whitney U test).

Mentions: To extrapolate the importance of fomites as a source of S. pneumoniae transmission, it first must be established that, upon rehydration, desiccated bacteria are capable of colonization. Because S. pneumoniae is naturally virulent in mice and can colonize the nasopharynx asymptomatically, as in humans, we used this murine model to test whether desiccation affects colonization. We intranasally inoculated 8- to 12-week-old female Swiss-Webster mice with 5 µl/nare of PBS (mock) or PBS-suspended nondesiccated S. pneumoniae D39 (grown overnight on blood agar plates) or desiccated S. pneumoniae D39 (for 48 h). Three days postinoculation, the mice were killed, and the nasal lavage fluid was plated on blood agar containing 3 µg/ml gentamicin, to which S. pneumoniae is naturally resistant. The mock group had no detectable S. pneumoniae colonies, but the bacteria desiccated for 48 h colonized the murine nasopharynx well (Fig. 5). In the nondesiccated wild-type group, 80% of mice (4/5) had detectable levels of colonization, while 75% of mice (6/8) in the desiccated group were measurably colonized. The relatively low dose of inoculum used (~1.5 × 104 to 3.2 × 104 CFU/mouse) likely increased the spread seen in the data, as the mice had a better chance of clearing the bacteria than if the dose used was higher. Although the median load of bacteria recovered was higher for the nondesiccated challenge group, there was no significant difference in colonization levels between it and the desiccated group (P = 0.27), indicating that desiccation does not exert a major negative impact on the ability of S. pneumoniae to colonize hosts.


Streptococcus pneumoniae is desiccation tolerant and infectious upon rehydration.

Walsh RL, Camilli A - MBio (2011)

Murine nasopharyngeal colonization by desiccated versus nondesiccated S. pneumoniae. Shown are bacterial loads in nasal lavage fluid at 72 hours post-intranasal inoculation with 1.5 × 104 CFU (nondesiccated) and 3.2 × 104 CFU (desiccated) S. pneumoniae D39. Closed circles represent individual mice, and bars indicate the medians (P value determined by Mann-Whitney U test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3101785&req=5

f5: Murine nasopharyngeal colonization by desiccated versus nondesiccated S. pneumoniae. Shown are bacterial loads in nasal lavage fluid at 72 hours post-intranasal inoculation with 1.5 × 104 CFU (nondesiccated) and 3.2 × 104 CFU (desiccated) S. pneumoniae D39. Closed circles represent individual mice, and bars indicate the medians (P value determined by Mann-Whitney U test).
Mentions: To extrapolate the importance of fomites as a source of S. pneumoniae transmission, it first must be established that, upon rehydration, desiccated bacteria are capable of colonization. Because S. pneumoniae is naturally virulent in mice and can colonize the nasopharynx asymptomatically, as in humans, we used this murine model to test whether desiccation affects colonization. We intranasally inoculated 8- to 12-week-old female Swiss-Webster mice with 5 µl/nare of PBS (mock) or PBS-suspended nondesiccated S. pneumoniae D39 (grown overnight on blood agar plates) or desiccated S. pneumoniae D39 (for 48 h). Three days postinoculation, the mice were killed, and the nasal lavage fluid was plated on blood agar containing 3 µg/ml gentamicin, to which S. pneumoniae is naturally resistant. The mock group had no detectable S. pneumoniae colonies, but the bacteria desiccated for 48 h colonized the murine nasopharynx well (Fig. 5). In the nondesiccated wild-type group, 80% of mice (4/5) had detectable levels of colonization, while 75% of mice (6/8) in the desiccated group were measurably colonized. The relatively low dose of inoculum used (~1.5 × 104 to 3.2 × 104 CFU/mouse) likely increased the spread seen in the data, as the mice had a better chance of clearing the bacteria than if the dose used was higher. Although the median load of bacteria recovered was higher for the nondesiccated challenge group, there was no significant difference in colonization levels between it and the desiccated group (P = 0.27), indicating that desiccation does not exert a major negative impact on the ability of S. pneumoniae to colonize hosts.

Bottom Line: Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces.Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally.Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.

View Article: PubMed Central - PubMed

Affiliation: Graduate Program in Molecular Microbiology, Sackler School of Graduate Biomedical Science, Howard Hughes Medical Institute and Department of Molecular Biology and Microbiology, School of Medicine, Tufts University, Boston, Massachusetts, USA.

ABSTRACT

Unlabelled: Streptococcus pneumoniae (pneumococcus) is a frequent colonizer of the nasopharynx and one of the leading causative agents of otitis media, pneumonia, and meningitis. The current literature asserts that S. pneumoniae is transmitted person to person via respiratory droplets; however, environmental surfaces (fomites) have been linked to the spread of other respiratory pathogens. Desiccation tolerance has been to shown to be essential for long-term survival on dry surfaces. This study investigated the survival and infectivity of S. pneumoniae following desiccation under ambient conditions. We recovered viable bacteria after all desiccation periods tested, ranging from 1 h to 4 weeks. Experiments conducted under nutrient limitation indicate that desiccation is a condition separate from starvation. Desiccation of an acapsular mutant and 15 different clinical isolates shows that S. pneumoniae desiccation tolerance is independent of the polysaccharide capsule and is a species-wide phenomenon, respectively. Experiments demonstrating that nondesiccated and desiccated S. pneumoniae strains colonize the nasopharynx at comparable levels, combined with their ability to survive long-term desiccation, suggest that fomites may serve as alternate sources of pneumococcal infection.

Importance: Even with the advent of multivalent capsular polysaccharide conjugate vaccines, S. pneumoniae continues to be a major cause of morbidity and mortality worldwide. Every year, there are approximately 7 million cases of pneumococcus-based otitis media in the United States alone, while pneumococcal invasive diseases are responsible for more than 1 million deaths globally. It is believed that the human upper respiratory tract is the sole niche of S. pneumoniae and, thus, that spread occurs via close contact with an infected individual. In this study, we characterized the desiccation tolerance of S. pneumoniae and found that it can survive for many weeks postdehydration and retain infectivity. Our results suggest that desiccation tolerance is an inherent trait of this genetically variable species and that fomites may be a source of transmission.

Show MeSH
Related in: MedlinePlus