I am at a facility that currently incubates all MacConkey plates in a non-CO2 incubator for the first 24 hours. I have never seen this practice, in my experience MAC has always been incubated w/all other agar in a C02 environment. The manufacturer does suggest incubation in a non CO2, but simply states 'for enhanced recovery of some enteric GNR'.

 

I understand the rationale for stool cultures (recovery of salmonella and shigella) but which GNR are enhanced for other routine cultures? (urine/wound/fluid/etc)

 

Additionally, does anyone know the mechanism that allows for enhanced growth in a non CO2 environment?

Actually it is not an enhancement of growth, but rather a reduction in presence of CO2 (5% and above). I think it was mainly Pseudomonas aeruginosa and some non-specified Enterobacteriaceaethat got inhibited, presumably due to a decrease in pH. It was based on a old study in the 80s and I am not sure whether it got updated. I am only aware of clinical stool isolates that were obtained under ambient conditions.