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Updated: Jul 24, 2026
Experimental Human Pneumococcal Carriage
Published on: February 15, 2013
Egg-based media for delayed processing of nasopharyngeal swabs in colonization studies of Streptococcus pneumoniae
1University of Illinois College of Medicine at Peoria, 531 NE Glen Oak Avenue, Peoria, IL 61637, USA. lizanne140@hotmail.com
Abstract:
This report describes the development and evaluation of a selective egg-based medium for ambient-temperature storage and transport of nasopharyngeal (NP) swabs in colonization studies of Streptococcus pneumoniae. Egg-thioglycolate-antibiotic (ETA) medium is based on Dorset's egg medium but made with thioglycolate broth and the addition of gentamicin (3 mg/l), nalidixic acid (15 mg/l), and amphotericin B (2.5 mg/l). Laboratory studies were conducted using mock swabs from 34 NP samples with known colony counts of pneumococci, which had previously been frozen in STGG (skim milk, tryptone, glucose, glycerol) broth. ETA facilitated better recovery of pneumococci than did either Stuart's or Amies' transport media. In a field study of 117 children, NP swabs were placed in ETA, after being vortexed in STGG and direct-plated for colony counts. Of 52 swabs that were culture positive for pneumococci, all 52 grew pneumococci after 4 days of storage in ETA, and 49 isolates were recovered after 7 days. Transport media such as Stuart's and Amies' require the processing of swabs within about 24 h, and storage in STGG broth requires freezing at -70 degrees C. ETA should be a useful addition to the storage media available for use in epidemiological studies of pneumococcal colonization, especially in situations where prompt processing, rapid transport, or low-temperature storage are not possible.
Insights
A new Egg-thioglycolate-antibiotic (ETA) medium allows for Streptococcus pneumoniae detection from nasopharyngeal swabs without refrigeration. This novel medium supports bacterial viability for up to 7 days, aiding colonization studies.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Epidemiology
Background:
- Nasopharyngeal swabs are crucial for diagnosing Streptococcus pneumoniae colonization.
- Current transport media have limitations, requiring prompt processing or cold storage.
Purpose of the Study:
- To develop and evaluate a selective egg-based medium for ambient-temperature storage and transport of nasopharyngeal swabs.
- To assess the efficacy of the Egg-thioglycolate-antibiotic (ETA) medium for Streptococcus pneumoniae recovery.
Main Methods:
- Development of Egg-thioglycolate-antibiotic (ETA) medium incorporating gentamicin, nalidixic acid, and amphotericin B.
- Laboratory evaluation using mock nasopharyngeal swabs with known pneumococcal colony counts.
- Field study involving 117 children's nasopharyngeal swabs stored in ETA.
Main Results:
- ETA demonstrated superior recovery of pneumococci compared to Stuart's and Amies' transport media in laboratory settings.
- In a field study, all positive nasopharyngeal swabs (52/52) yielded pneumococci after 4 days in ETA.
- High recovery rates (49/52) were maintained after 7 days of storage in ETA at ambient temperature.
Conclusions:
- The Egg-thioglycolate-antibiotic (ETA) medium is effective for preserving Streptococcus pneumoniae viability in nasopharyngeal swabs at ambient temperatures.
- ETA offers a valuable alternative for epidemiological studies, particularly when rapid processing or cold storage is not feasible.
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