Beer altered by microorganisms: Detection / of microorganism / s involved / s by molecular methods (PCR), and species identification by sequencing
Beer is an alcoholic beverage that is made from time immemorial. Since the late nineteenth century is known that bacteria can alter it . However, the microorganisms that can alter are scarce due to inhibition exerted on them beer, and hygienic measures taken into account during their preparation. However, the introduction of new techniques has changed the ecosystem that is generated during processing, and some contaminating bacteria that alter their properties may appear.

Gram - negative bacteria are strict anaerobes involved more often in their alterations. This is due to the reduction of the oxygen content in the preparation of the packaged beer since the late 1970s, and the elimination of the final pasteurization. Today, the need to expand production chains, stay in the market, the tendency to produce products with minimal amounts or free of alcohol, is prompting new situations that favor spoilage by microorganisms. This entails very significant economic losses as industrial processing is done in large volumes. Therefore, there is a need to safeguard the microbiological quality and safety of the beer produced.

The finished beer has some antimicrobial activity factors that exert a natural protection against the growth of microorganisms, such as: acid pH (pH 3.8 to 4.7), ethanol content (0.5 to 10%), sulfur dioxide content, low oxygen content (<0.1 ppm) and nutrients, the high concentration of carbon (0.5%) and the presence of hop extracts (Humulus lupulus). These factors lead to a natural protection against the proliferation of microorganisms. The compounds of hops, mainly iso-alpha acids, having antibacterial activity against Gram - positive bacteria. The iso-alpha acids act as ionophores, changing gradient existing pH through the cytoplasmic membrane of bacteria, reducing the protonic force (PMF: proton motive force), so that the bacteria can not incorporate nutrients and dies .
There are two factors to consider: 1) on the one hand, being manufactured free of alcohol (0%) lacking the protective effect of alcohol, and 2) beer hops not only provides aromas and flavors, but also provides fatty acids alpha-iso (iso-alpha-acids), which act as inhibitors of microbial proliferation, but currently being detected strains of various species of gram - positive bacteria (Lactobacillus spp.) resistant hops. These strains contain the hour gene encoding an efflux pump of compounds, among these, hops, and therefore bacteria that contain not suffer the action of inhibitors present in the hops. The presence of lactic acid bacteria resistant hops is crucial, because that allows them to develop resistance in beer.
In the methods of quality control of beer, anaerobic bacteria are the most difficult contaminants to detect and identify its sensitivity to oxygen. However, to be detected but only a viable bacteria is present. In normal practice, in most industries producing beer, the enrichment culture is the only method available for detection. This method takes time (1-6 weeks) to provide adequate results, and sometimes does not provide identification to species or strain, it may be necessary to know the source of contamination and to plan and implement the measures corresponding corrective.
Contamination of the beer may come from various sources, but are divided into two groups: 1) pollution in the production area, which usually affect the entire production and 2) contamination in the filling area, which usually involves some containers unpasteurized beers.
The type of microbial disrupters vary during the manufacturing process, when the oxygenates make beer ingredients in an anaerobic environment with limited nutrients, and a high concentration of natural antimicrobial. Only some Gram - positive or Gram - negative bacteria are able to grow in beer during manufacturing or upon completion: Acetobacter spp. Bacillus spp., Brevibacillus spp., Clostridium spp., Gluconobacter spp., Enterobacter, Lactobacillus spp., Megasphaera spp., Pectinatus spp., Pediococcus spp., Selenomonas spp., Zymomonas spp., And Zymophilus spp. From these bacteria, Lactobacillus strains and Pediococcus, universal distribution, they are resistant hops and cause most cases of disturbance. The effects caused by microbial spoilage manifest from minimal changes to its aroma, other important organoleptic alterations, presence of turbidity, etc. In domestic beer production they were detected contamination by Bacillus cereus and Bacillus licheniformis, some strains of which can cause food poisoning. Moreover, some contaminants can produce dangerous bacteria metabolites, such as N-nitrosamine or biogenic amines, both during processing and in the finished packaging.
The main species involved are:
  • Megasphaera genre (gram - negative)
Megasphaera cerevisiae
Megasphaera paucivorans
Megasphaera sueciensis

  • Gender pectinatus (gramnegativo)
pectinatus cerevisiiphilus
pectinatus frisingensis
pectinatus haikarae

  • Pediococcus genus (Gram - positive)
Pediococcus damnosus
Pediococcus parvulus
Pediococcus acidilactici

  • Genus Lactobacillus (Gram - positive)
Lactobacillus brevis
Lactobacillus lindneri
Lactobacillus coryniformis
Lactobacillus casei
Lactobacillus plantarum

  • Selenomonas genre (gram - negative)
Selenomonas lacticifex
  • Zymophilus genre (gram - negative)
Zymophilus paucivorans
Zymophilus raffinosivorans

Tests in IVAMI

  • Molecular detection of each genus of bacteria by PCR (polymerase chain reaction).
  • Species identification by sequencing.
  • Detection Time gene, resistance hops (hop resistance) by PCR.

Delivery of results

The minimum necessary for carrying out the methods according to the number of bacteria that is sought to detect (usually 48 to 72 hours).

Sample Type:

Altered packaging beer.

Preservation and shipment of sample:

Refrigerated (preferred) for a maximum time of 24 to 48 hours.

Cost of the test: Consult