![]() ![]() During that time, each individual viable bacterial cell multiplies to form a readily visible colony. It reveals information related only to viable or live bacteria. Using this method, a small volume (0.1 - 1.0 mL) of liquid containing an unknown number of bacteria is spread over the surface of an agar plate, creating a "spread plate." The spread plates are incubated for 24-36 hours. The most common method of measuring viable bacterial cell numbers is the standard or viable plate count or colony count.This is a viable count, NOT a total cell count. In a microbiology lab, we frequently determine the total viable count in a bacterial culture. Many approaches are commonly employed for enumerating bacteria, including measurements of the direct microscopic count, culture turbidity, dry weight of cells, etc. coli suggests feces are present, indicating that serious pathogens, such as Salmonella species and Campylobacter species, could also be present (1). coli, are often used as indicator species, as they are not commonly found growing in nature in the absence of fecal contamination (1). A subset of these bacteria are the fecal coliforms, which are found at high levels in human and animal intestines. Coliform bacteria are Gram-negative non-spore forming bacteria that are capable of fermenting lactose to produce acid and gas. ![]() In general, small numbers of pathogenic bacteria are not dangerous, but improper storage and/or cooking conditions can allow these bacteria to multiply to dangerous levels (1).įecal contamination of water is another one of the ways in which pathogens can be introduced (1). For example, bacterial pathogens can be introduced into foods at any stage: during growth/production at the farm, during processing, during handling and packaging, and when the food is prepared in the kitchen (1). Often one needs to determine the number of organisms in a sample of material, for example, in water, foods, or a bacterial culture. ![]()
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