Question

When attempting to determine viable cell counts of a heat-sensitive bacterial isolate, which cell counting method should be avoided

Answer 1

The pour plate method should be avoided when determining viable cell counts of a heat-sensitive bacterial isolate, as the heat sensitivity of the bacteria can lead to inaccurate counts.

Step-by-step explanation:

When attempting to determine viable cell counts of a heat-sensitive bacterial isolate, the cell counting method that should be avoided is the pour plate method. This method involves mixing the sample in liquid warm agar, pouring it into a sterile Petri dish, and counting the resulting colonies. However, the heat sensitivity of the bacterial isolate may lead to inaccurate counts due to the high temperature of the agar.

Answer 2

For heat-sensitive bacterial isolates, the pour plate method should be avoided due to the potential for heat damage. Methods such as the spread plate method, membrane filtration, and indirect turbidity measurements are preferable alternatives that do not expose the bacteria to harmful temperatures.

Step-by-step explanation:

Understanding Viable Cell Counts in Heat-Sensitive Bacterial Isolates

When determining viable cell counts for a heat-sensitive bacterial isolate, an important consideration is the potential damage caused by heat during the counting process. The pour plate method, wherein samples are mixed with warm liquid agar at temperatures around 45-50 °C, should be avoided since it can harm heat-sensitive bacteria. Instead, alternative methods, such as the spread plate method or membrane filtration technique, can be used for such sensitive isolates. These methods do not expose bacteria to potentially harmful temperatures and enable accurate counting of viable cells. The spread plate method involves spreading a sample on the surface of an agar plate, potentially less harmful to heat-sensitive bacteria compared to the pour plate method.

It's also essential to recognize other methods for cell counting, such as the use of electronic particle counters like the Coulter particle counter, which do not require the culture to undergo any thermal stress. Additionally, indirect cell counts through measurements of turbidity via a spectrophotometer can provide estimations of cell density without direct exposure to heat. Direct microscopic cell counts using a Petroff-Hausser chamber are also a possibility, provided the culture is not diluted to the point where cell counts become unreliable.