Soil particles inhibit colony formation of Escherichia coli on the surface of agar media

• Published in: Soil science and plant nutrition (Tokyo) Vol. 49; no. 6; pp. 867 - 872
• Main Authors: Ohtomo, R. (National Inst. of Livestock and Grassland Science, Tsukuba, Ibaraki (Japan)), Minato, K, Saito, M
• Format: Journal Article
• Language: English
• Published: Tokyo Taylor & Francis Group 01.12.2003; Japanese Society of Soil Science and Plant Nutrition
• Subjects: AGAR; Agronomy. Soil science and plant productions; Biological and medical sciences; CELL COUNTING; colony-formation unit (CFU); CULTURE MEDIA; ESCHERICHIA COLI; Fundamental and applied biological sciences. Psychology; MICROBIOLOGICAL ANALYSIS; most probable number (MPN); pour-plating; SOIL; soil particles; surface-plating; soil particles; Escherichia coli; Agar; colony-formation unit (CFU); Soils; pour-plating; surface-plating; Bacteria; Colony; Soil science; Formation; Enterobacteriaceae; most probable number (MPN)
• ISSN: 0038-0768; 1747-0765
• DOI: 10.1080/00380768.2003.10410349

When enumerating Escherichia coli in serial dilution of soil using selective media, soils was found to exert an inhibitory effect on colony formation on the surface of the agar plates. The inhibitory effect did not appear to be due to either soil bacteria or soluble chemicals but to the soil particles themselves. No inhibition was observed when the cells were enumerated by the most probable number (MPN) method. Some alternative plating methods, such as pour-plating or overlaying, were effective in removing the inhibitory effect. Removal of soil particles by simple sedimentation was also effective in enhancing the enumeration efficiency. These observations would be practically important for enumerating bacteria in the soil environment.