Propionic bacteria in dairy products (Propionibacterium freudenreichii, P. jensenii, P. acidipropionici, P. thoenii) - qualitative or quantitative culture; Molecular diagnosis of the main species; Molecular species identification (sequencing).

Information 15/10/15.

Lactic bacteria which generate lactic acid from the milk sugars (lactic thermophilic bacteria) and propionic bacteria, which use the lactic acid generated by lactic acid bacteria for: in the manufacture of cheeses two types of bacteria can be used produce propionic acid, acetic acid and carbon dioxide (CO _2). When these bacteria are used to start making cheese, starter bacteria are considered. Propionic acid generated contributes to preserving cheese preventing multiplication of filamentous fungi (mold), but also provide other features aromatic cheeses, when used for manufacturing. For this reason it is used as an additive in other foods such as precooked foods.

There are several bacteria that can synthesize propionic acid. These bacteria include certain species of Clostridium, some Veillonella species, species Selenomonas, and all Propionibacterium species.

Among the Propionibacterium, there are 8 main species, four of them related to the human habitat (Propionibacterium acnes, P. granulosum, P. avidum, and P. lymphophilum), and four other related dairy products (Propionibacterium freudenreichii, P. jensenii, acidipropionici P., P. thoenii). These bacterial species are difficult to differentiate from one another by classical bacteriology methods, particularly P. jensenii, P. thoenii. Therefore in our laboratory we perform species identification by molecular methods (sequencing nucleic acids).

Propionibacteria are non-spore forming Gram - positive bacteria, bacillary motionless, strict anaerobic or aerotolerant, producing catalase, slow growing, fermenting lactate (lactic acid) resulting propionic acid, acetic acid and carbon dioxide ( CO _2).

These bacteria have today a considerable technological importance for the manufacture of certain types of cheese, such as cheese called type Swiss hard (Swiss type hard cheeses), such as Emmental cheese, among others, being responsible for the holes and flavor (sweet aroma and nuts or sweaty smell) generated during cheese ripening, which characterizes these cheeses. These aromas are generated during proteolysis to peptides and amino acids occur, particularly proline and leucine and lipolysis for the generated acid, which together with other metabolic products contribute to the characteristic aroma. Furthermore, propionibacteria are also considered human probiotics for positive impact on intestinal bifidobacteria and their ability to beneficially modify the activity of bacterial enzymes in the intestine. Some research has indicated its ability to induce cell apoptosis of colorectal carcinomas.

Said bacteria, commonly found in fresh milk in a concentration between 10 and 10 ⁴ CFU / mL due to environmental pollution. All species involved have been isolated from soil and plant silage, and some species of fodder and manure. During the conservation of cheese manufacturing temperature of 18 to 24ºC reach concentrations of 10 ⁹ CFU / g cheese.

Keep in mind that sometimes, their presence may result in altered cheeses, such as abnormal swelling or bursting (rupture) of the cheeses, and the appearance of brown spots due to pigmented strains of Propionibacterium jensenii and P. thoenii.

Tests in IVAMI:

• Culture on selective and differential media qualitative and quantitative.

• Molecular Diagnostics: specific for the four main species of dairy products (cheese, ...) PCR.

• Molecular identification of Propionibacterium species by nucleic acid sequencing.

• Performing one or another test depends on the purpose to be obtained, such as:

• Knowing the total amount of Propionibacterium spp. unidentified species: quantitative culture on selective and differential media;

• Knowing the total amount of each species: quantitative culture with molecular species identification;

• Knowing the presence of one or other species present in dairy products, without quantification: species-specific PCR;

• Knowing the amount of each species to be modified as desired l in the manufacture of cheese effect: quantitative culture with molecular quantitative identification of each species.

Recommended sample:

• Cheeses (minimum 25 grams, in suitable container protected).

• Other dairy products ( at least 25 grams, in suitable container protected).

Preservation and shipment of sample:

• Refrigerated (preferred) for less than 2 days.

Delivery term:

• Culture for isolation: propionibacteria are slow growing bacteria anaerobically, so that crops must be kept before making identification for at least 6 days and referiblemente 10 days, and then proceed to its generic identification by phenotypic characteristics, or molecular identification.

• PCR for molecular targets of each of the four species of importance in cheese industries: 48 to 72 hours.

• Molecular species identification by nucleic acid sequencing: 72 to 96 hours.

Cost of the test:

Consult ivami@ivami.com