Propionic acid Bacteria Enrichment

Bruno FonsecaHopkins Microbiology Course 2010

Monterey, CA, USA

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 CO2.

If pH value is below 4.5 there is practically no growth

Clostridium Veillonella Selenomonas

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 CO2 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.

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 CO2) Incubate at 30 ºC

Day 1

2 days later …

Streaked the milk-white growth into a lactate-CaCO3 agar plate Incubated at 30ºC in an anaerobic jar

1 week later …

Brownish-red colored colonies

Probably due to having a cytochrome system

Catalase Activity test:

2H2O2 2H2O + O2Catalase Production of O2 Bubbles

Small non-motile rod-shapped bacteria

Looking at them under the microscope…

Propionic acid formationDicarboxylic acid pathway: Lactate

Vitamin B12

Lactate Dehydrogenase

NAD+

NADH

Succinate

methylmalonyl-CoA mutase

Propionic acid formationAcrylate pathway:

CoA-SH

CoA-SH

This pathway occurs namely in Clostridium propionicum

Propionic acid formationAcrylate pathway: