Culture media will sometimes contain dead organisms that will be evident on a Gram stain. Other sources of non-viable organisms include slides, staining reagents, immersion oil, or the original specimen.

Culture media for biochemical, serological, and other confirmatory tests require inoculation with pure cultures.

Organisms differ in their requirements for humidity, temperature, atmosphere (levels of oxygen), and duration of incubation. These requirements must be observed in order to successfully culture the desired organism.

Selective media may at times permit certain strains of organisms to grow that are intended to be inhibited; conversely, certain strains may be inhibited that are intended to grow. It is therefore advisable to use a non-selective medium in parallel with a selective one to increase the chances of recovery of a pathogen.

Other variations of intended results may be due to improper specimen collection and transport, improper execution of procedures, improper exposure to temperatures or atmospheres, strain mutation or variation, or interference from other chemicals or inhibitors.

Incubators that have been recently cleaned and disinfected have been known to inhibit the growth of cultures due to toxic fumes and vapors. Consult appropriate reference texts for further information.(8,16,18,20)


The medium should not be used if it shows signs of microbial contamination, dehydration (shrinking or cracking of the medium), hemolysis, discoloration, or is beyond the expiration date. Refer to "Problem Reporting".


Hardy Diagnostics products are warranted in accordance with the standard warranty located at