1. Propionic acid Bacteria Enrichment Bruno Fonseca Hopkins Microbiology Course 2010 Monterey, CA, USA

2.  Propionic acid has numerous applications in various food and chemical industries, and is mainly used as a mold inhibitor for animal feeds and as a preservative for foods such as cheeses and baked goods.  Propionic acid is produced mainly by Propionibacterium, but this isn’t the only genera that has this ability:  Propionibacterium are slow-growing, non-sporeforming, rod-shaped, Gram-positive, anaerobic heterotrophic bacteria.  These microorganisms usually possess catalase.  Ferment lactate and produce acetate, propionate and CO 2.  If pH value is below 4.5 there is practically no growth  Clostridium  Veillonella  Selenomonas

3.  First observed in the cheese manufacture, dating back to the beginning of the nineteenth century.  Propionic acid is what partly gives Swiss cheese its characteristic flavor and the CO 2 is what produces its characteristic holes.  Propionibacterium have been granted GRAS (Generally Recognized As Safe) status by FDA.  However, certain species of Propionibacterium are known for causing infections including the common skin disease acne vulgaris (caused by P. acnes).  van Niel named some species of Propionibacterium.

4. Inoculum:  Swiss-cheese Media:  40 gr Sodium-lactate  5 gr Yeast extract Selective technique:  Lactate as the major carbon/electron source  Anaerobic growth (screw capped tubes gently bubbled with CO 2 )  Incubate at 30 ºC Day 1

5. 2 days later …  Streaked the milk-white growth into a lactate-CaCO 3 agar plate  Incubated at 30ºC in an anaerobic jar

6. 1 week later … Brownish-red colored colonies Probably due to having a cytochrome system Catalase Activity test: 2H 2 O 2 2H 2 O + O 2 Catalase Production of O 2 Bubbles

7. Small non-motile rod-shapped bacteria Looking at them under the microscope…

8. Propionic acid formation Dicarboxylic acid pathway: Lactate Vitamin B 12 Lactate Dehydrogenase NAD+ NADH Succinate methylmalonyl-CoA mutase

9. Propionic acid formation Acrylate pathway: CoA-SH This pathway occurs namely in Clostridium propionicum

10. Propionic acid formation Acrylate pathway: