In what type of sample would you expect to identify the presence of mesophilic bacteria?

Mesophilic bacteria typically thrive at moderate temperatures, generally within the range of 20°C to 45°C. Environmental samples, such as soil and water, are natural habitats for these types of bacteria. In these settings, they play significant roles in nutrient cycling and organic matter decomposition. Soil and water provide a conducive environment for mesophiles, as they can find ample organic materials and favorable conditions for growth.

The other options—fresh frozen plasma, urine samples, and exhaled breath condensate—do not primarily serve as environments conducive to the growth of mesophilic bacteria. Fresh frozen plasma is a human blood product that is preserved at very low temperatures to prevent bacterial growth. Urine samples from patients may contain bacteria, but they are not a natural environment where mesophilic bacteria are expected to flourish compared to the rich diversity found in environmental samples. Exhaled breath condensate, while containing microorganisms, is primarily composed of respiratory droplets and may not provide the right conditions or nutrients for mesophilic bacterial populations.

Therefore, environmental samples like soil and water are the most likely to show the presence of mesophilic bacteria due to their natural habitat and suitable growth conditions.