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Effect of temperature on transport and plating media for enteric pathogens

W I Taylor, D Schelhart

    Journal of Clinical Microbiology
    |October 1, 1975
    PubMed

    Insights

    This study found that incubation time and temperature significantly impact the detection of Salmonella and Shigella in stool samples. Ambient temperatures in warm climates can yield satisfactory results for enteric bacteriology without specialized incubators.

    Area of Science:

    • Clinical Microbiology
    • Bacteriology
    • Diagnostic Microbiology

    Background:

    • Accurate detection of enteric pathogens like Salmonella and Shigella is crucial for diagnosing diarrheal diseases.
    • Standard laboratory protocols often rely on controlled incubation temperatures and specific incubation periods.

    Purpose of the Study:

    • To evaluate the impact of varying incubation temperatures and prolonged incubation times on the recovery of Salmonella and Shigella from clinical samples.
    • To determine the optimal conditions for transport and enrichment media, as well as plating methods for these enteric pathogens.

    Main Methods:

    • Analysis of 132 diarrheal stool samples for Salmonella and Shigella.
    • Use of multiple plating media (EMB, SS, XLD) and enrichment broths (Selenite F, GN, saline, CB).
    • Incubation at various temperatures (20°C, 35°C, 40°C, ambient) and durations (1-7 days), including simulated transport conditions.

    Main Results:

    • Direct plating was most effective for Salmonella at 2 days; enrichment broths were effective at 1-2 days. Shigella recovery declined significantly in broths after 2 days.
    • Salmonella preferred higher temperatures (35-40°C) for direct plating, while Shigella preferred ambient (28°C) or 35°C.
    • Gram-negative (GN) broth was the most effective enrichment medium for Salmonella, while GN and saline were preferred for Shigella. Xylose lysine deoxycholate (XLD) agar showed the best performance among plating media.

    Conclusions:

    • Incubation time and temperature significantly influence the detection rates of Salmonella and Shigella.
    • Ambient temperature incubation can be effective for enteric bacteriology in warm climates, reducing the need for constant-temperature incubators.
    • Enrichment broth choice and plating medium are critical factors for pathogen recovery, with Selenite F being unsuitable for Shigella.

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