Lab 4: Enrichment Of Lactic Acid Bacteria Flashcards
What environmental conditions are used to enrich for lactic acid bacteria?
Low pH and presence of sodium azide, which favors acid-tolerant, non respiring LAB
List three common characteristics of LAB
- Non motile
- Acid tolerant
- Gram postive
Why are LAB not harmed by sodium azide?
They lack cytochromes and do not perform respiration, so sodium azide doesn’t affect them
How does pH affect LAB growth?
LAB grow well at low pH, which inhibits many competing microbes
Which of the following is not a LAB trait?
A. Non spore forming
B. Acid tolerant
C. Obligate aerobes
D. Gram positive
C
Give two ways LAB benefit humans or animals.
- Used in food fermentation and preservation
- Promote gut health and immune health as probiotics
What is assessed during macroscopic observations of colonies?
Purity of culture — colony morphology, color, and size
Why might gram staining LAB enrichment cultures be difficult?
The cultures may be too dilute to obtain enough cells for staining
Why is pH measured in LAB enrichment cultures?
To assess lactic acid production, a low pH indicates a successful LAB enrichment
How is the alternate plate inoculation method performed?
Smear broth onto plate using a moistened sterile swab, rotating the plate to ensure even coverage
What is the function of CaCO3 in APT-azide-CaCO3 plates?
It neutralizes acid and reveals acid production by creating clear zones around colonies
How do LAB preserve food and improve flavor?
They produce lactic acid and other byproducts that inhibit spoilage and enhance taste and texture
What does GRAS mean, and why is it important for LAB?
“Generally regarded as safe”, it ensures LAB can be used in food products without concern
Name 3 LAB genera and one function or product for each.
- Lactobacillus: yoghurt production
- Leuconostoc: sauerkraut and silage fermentation
- Streptococcus: some strains used in dairy; others can be pathogenic
How do LAB act as probiotics in the gut?
They may promote digestion, boost immunity, and outcompete harmful microbes by producing acid
What role does Leuconostoc mesenteroides play in plant fermentation?
Initiates natural fermentation in vegetables, like sauerkraut and silage
Which LAB species is used in acidophilus-style yoghurt?
Lactobacillus acidophilus
Why is streptococcus pyogenes an opportunistic pathogen?
It can be carried without symptoms but causes infections when immunity is compromised
What are the key steps for collecting a sample using eSwab?
Keep the swab sterile, collect the sample, insert into media vial, snap shaft, and seal
Why would you know the animals health history before sampling?
To determine potential antibiotic exposure or health conditions that may affect microbiotia
