Exam 5: Microbial Growth and Its Control

An agar plate for counting colonies and maximizing statistical validity should ideally contain

Explain why a hyperthermophile is unlikely to be a human pathogen.

When viable cell concentrations are too high to count on an agar plate, it is common to use larger sized plates to increase the surface area for counting the colonies.

A common antimicrobial chemical (or chemicals) used as both an antiseptic and a general disinfectant is

Microbial growth is generally described as an increase in cell number rather than the expansion in size of an individual microbial cell.

Enumerating the viable and total cell concentration of a population of a microbial isolate can be a laborious task for a microbiologist, especially when studying the same isolate for several years. It is often more practical to determine the relationship between optical density (OD) and cell concentration. Once this relationship (determined by a standard curve) is determined, the OD of an isolate in a broth can be used to determine the populationʹs concentration. Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve.