![]() If at all possible, we recommend discarding contaminated cultures immediately. Bacteria often produce toxins that disrupt cell function and ultimately destroy cell cultures. However, if the bacteria are anaerobic, the contamination will cause the medium to become basic and will appear pink. Most cases of bacterial contamination in the cell culture laboratory are caused by aerobes. If a culture is contaminated with aerobic bacteria, then the medium will become acidic and appear yellow. Characteristics in mammalian cell cultures: Bacterial contamination will usually cause sudden changes in pH. However, a regular particulate morphology and motility distinguish bacteria. Bacterial contamination is sometimes confused with precipitates of media constituents such as serum proteins or cellular debris. ![]() High power microscopy (~400X) allows the resolution of individual bacterium which typically reveals cocci or bacilli contamination in the cell culture environment. Also, flasks and cell culture reagents may become cloudy and develop a slight film on the surface of the growth vessel or reagent bottle that dissipates when the vessel is moved. The space between cells will appear uniformly granular and may shimmer from the movement of the bacteria. Bacteria are not easily distinguishable under low power microscopy (~100X), but some indications of contamination are notable. However, bacteria vary considerably in size ranging from 0.5 to 1.0 um in diameter to 10 to 20 um in length in some of the longer spiral forms. ![]() An average rod-shaped bacterium measures about 1 um in diameter and 4 um in length. Description: There are three principle forms of bacteria, round-shaped (cocci), rod-shaped (bacilli), and spiral-shaped (spirilla).
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