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Epidemiological studies of Streptococcus pneumoniae in infants: methods of isolating pneumococci
Insights
Gentamicin agar is a superior method for detecting Streptococcus pneumoniae carriers in infants compared to traditional sheep blood agar and mouse inoculation. This enhanced recovery aids in identifying pneumococcal carriage more effectively.
Area of Science:
- Microbiology
- Pediatric Infectious Diseases
- Diagnostic Microbiology
Background:
- Streptococcus pneumoniae (pneumococcus) is a significant cause of infant infections.
- Accurate identification of pneumococcal carriers is crucial for understanding transmission and developing control strategies.
Purpose of the Study:
- To compare the efficacy of different culture methods for isolating Streptococcus pneumoniae from infants.
- To evaluate gentamicin agar and mouse inoculation for detecting pneumococcal carriage.
Main Methods:
- Prospective study involving serial cultures from infant nasopharynges and throats.
- Comparison of sheep blood agar, sheep blood agar with gentamicin, and mouse inoculation.
- Analysis of carrier rates and recovery efficiency for each method.
Main Results:
- Gentamicin agar significantly improved pneumococcal recovery from throat cultures compared to plain sheep blood agar.
- Gentamicin agar demonstrated superior recovery rates of carrier strains from nasopharyngeal samples versus mouse inoculation.
- A substantial percentage of pneumococcal strains (25%) would have been missed using mouse inoculation alone.
Conclusions:
- Sheep blood agar with gentamicin sulfate offers a simple, cost-effective, and superior method for isolating S. pneumoniae.
- This method is ideal for identifying pneumococcal carriers and recovering strains from clinical samples.
- Gentamicin agar enhances the detection of pneumococcal carriage in infants, surpassing traditional methods.
Abstract:
A prospective study of the natural history of pneumococcal infection, which involves serial culture studies in healthy infants from 6 weeks of age onward, is in progress in our laboratory. This report describes results of a comparison of several methods for the isolation and identification of Streptococcus pneumoniae from the nasopharynges and throats of these infants. Sheep blood agar, sheep blood agar with gentamicin sulfate (gentamicin agar), and mouse inoculation with 4-h broth cultures were used. Gentamicin agar proved superior to plain sheep blood agar as a solid culture medium, especially in enhancing the recovery of pneumococci from throat cultures. With gentamicin agar, similar carrier rates were found for both culture sites (nasopharynx and throat). In addition, gentamicin agar proved superior to mouse inoculation for the recovery of carrier strains from 131 nasopharyngeal culture samples processed by both methods. Sixty of 131 samples were positive for pneumococci, 25% of which would have been missed had mouse inoculation alone been used. In only three instances did we recover a strain by mouse inoculation that failed to grow on gentamicin agar; conversely, 15 strains were isolated on gentamicin agar but could not be recovered from mice. The latter observation might be explained by the fact that certain carrier strains may be relatively mouse avirulent. The use of blood agar containing gentamicin appears to offer a simple and inexpensive method for the recovery of S. pneumoniae and, in our opinion, provides an ideal method for the identification of pneumococcal carriers as well as for the recovery of these strains from clinical material such as sputum or ear exudates, where other and less fastidious organisms may also be present.