A simple micro-growth assay for enumerating bacteria.
A simple method for nonspecific determination of bacteria concentrations in a variety of liquid samples was developed. The assay was based on the time required for a sample grown in liquid media to reach a threshold turbidity. Samples were combined with media in a covered 96-well microwell plate and the turbidity was monitored in real time as the bacteria grew in a temperature-controlled plate reader. A significant problem with growth in microwells was condensation on the cover, which prevented accurate turbidity measurement. This problem was overcome by coating the cover with a small amount of surface-active agent. Salmonella and E. coli concentrations could be determined with a relative error of approximately 20% at levels from 10 to 10(6) cells/ml (eight replicates). An assay of 10 samples with standards required 10 min to set up and 20 min for data processing using a computer spreadsheet program. Growth time at 37 degrees C ranged from 4 h for samples at 10(7) cells/ml to 16 h for samples at 10 cells/ml.
Brewster
Jeffrey D
JD
United States Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 E. Mermaid Lane, Wyndmoor, Philadelphia, PA 19038, USA. jbrewster@arserrc.gov
D000465:Algorithms; D001419:Bacteria / Q000254:growth & development*; D001431:Bacteriological Techniques / Q000379:methods; D001666:Binding Sites, Antibody; D002138:Calibration; D002455:Cell Division; D015169:Colony Count, Microbial / Q000379:methods*; D012477:Salmonella enteritidis / Q000254:growth & development / Q000276:immunology / Q000302:isolation & purification