FDSCI 600 - Microorganisms

What are lactic acid bacteria (LAB)?

Bacteria responsible for many lactic acid fermentations; the slides identify them as important food fermenters.

What are the main types of lactic acid fermentation?

Homolactic fermentation and heterolactic fermentation.

What is homolactic fermentation?

Glycolysis breaks glucose down with lactic acid as the only fermentation end product.

What is heterolactic fermentation?

Glucose is broken down into lactic acid along with other compounds such as ethanol and CO2.

Which microorganisms are listed as common homolactic fermenters?

Lactobacillus acidophilus; Lactococcus lactis; Streptococcus thermophilus.

Which microorganisms are listed as common heterolactic fermenters?

Leuconostoc mesenteroides; Lactobacillus brevis; Weissella species; Oenococcus oeni.

What is Lactobacillus?

A genus of lactic acid bacteria widely used in food because of fermentation metabolism, probiotic benefits, and ease of use.

What are common Lactobacillus species listed in the slides?

Lactobacillus acidophilus; Lactobacillus plantarum; Lactobacillus casei; Lactobacillus rhamnosus.

What is the morphology of Lactobacillus?

Rod-shaped, non-spore-forming, usually non-motile, Gram-positive.

What metabolic pathways can Lactobacillus use?

Homofermentative or heterofermentative, depending on the species.

What are the growth conditions of Lactobacillus?

Facultatively anaerobic/aerotolerant; acid tolerant around pH 4–6; species-dependent temperature, with mesophilic species around 25–40°C.

What products can Lactobacillus fermentation produce?

Lactic acid, ethanol, acetic acid, and CO2.

What foods are associated with Lactobacillus?

Yogurt, kefir, sourdough, fermented pickles, cheeses, fermented sausages, sauerkraut, and kimchi.

What taxonomy note does the slide give for Lactobacillus?

Historically many were grouped as Lactobacillus; as of 2020, modern taxonomy divides these LAB among several genera.

What is Streptococcus thermophilus?

A lactic acid bacterium widely used in dairy fermentation for yogurt and cheese.

What is the morphology of Streptococcus thermophilus?

Cocci in chains; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Streptococcus thermophilus?

Homofermentative; ferments lactose primarily to lactic acid.

What are the growth conditions of Streptococcus thermophilus?

Facultatively anaerobic/aerotolerant; acid tolerant; optimal growth near pH 6–7; thermophilic, with optimum around 40–45°C.

Why is Streptococcus thermophilus important in dairy fermentation?

It rapidly acidifies milk and contributes to yogurt and cheese flavor and texture.

What foods are associated with Streptococcus thermophilus?

Yogurt, mozzarella, provolone, Asiago, Parmigiano-Reggiano, and Swiss-type/other thermophilic-culture cheeses.

What is Lactococcus?

A genus of lactic acid bacteria widely used in the dairy industry for cheese and buttermilk production.

What Lactococcus species are listed?

Lactococcus lactis; Lactococcus lactis subsp. diacetylactis; Lactococcus cremoris.

What is the morphology of Lactococcus?

Cocci in pairs or chains; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Lactococcus?

Homofermentative; sugars are converted primarily to lactic acid.

What are the growth conditions of Lactococcus?

Facultatively anaerobic/aerotolerant; acid tolerant around pH 5.5–6.5; mesophilic, with optimum around 30°C.

What is an important role of Lactococcus in dairy fermentation?

Rapid milk acidification; some strains also produce important flavor compounds.

What foods are associated with Lactococcus?

Buttermilk, cream cheese, cottage cheese, Gouda, Colby cheese, and sour cream.

What is Leuconostoc?

A genus of lactic acid bacteria important in fermented vegetables and some dairy fermentations.

What Leuconostoc species are listed?

Leuconostoc mesenteroides; Leuconostoc citreum; Leuconostoc kimchii.

What is the morphology of Leuconostoc?

Cocci in chains or clusters; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Leuconostoc?

Obligately heterofermentative; sugars produce lactic acid + CO2 + ethanol and/or acetate.

What are the growth conditions of Leuconostoc?

Facultatively anaerobic/aerotolerant; acid tolerant around pH 5.5–6.5; mesophilic, around 20–30°C.

Why is Leuconostoc important in vegetable fermentation?

It is especially important early in fermentation, producing acid, CO2, and flavor compounds and contributing to microbial competition.

What other important compound can some Leuconostoc strains produce?

Diacetyl, an important flavor/aroma compound.

What foods are associated with Leuconostoc?

Sauerkraut, kimchi, and fermented pickles.

What is Pediococcus?

A genus of lactic acid bacteria widely used in fermented meat production for development of tangy flavors.

What Pediococcus species are listed?

Pediococcus acidilactici; Pediococcus pentosaceus; Pediococcus damnosus.

What is the morphology of Pediococcus?

Cocci in pairs, triads, or clusters; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Pediococcus?

Homofermentative; sugars are converted primarily to lactic acid.

What are the growth conditions of Pediococcus?

Facultatively anaerobic/aerotolerant; acid tolerant around pH 5.5–6.5; mesophilic, around 25–35°C.

What special compounds can some Pediococcus strains produce?

Bacteriocins called pediocins, which can help with food safety.

What foods are associated with Pediococcus?

Salami, pepperoni, fermented chorizo, summer sausage, and some fermented vegetables.

What is a beneficial role of Pediococcus?

It can serve as a starter/protective culture in fermented meats and vegetables.

What is a spoilage role of Pediococcus?

Pediococcus damnosus can contribute to beer and wine spoilage.

What is Enterococcus?

A genus of food-associated LAB; some species occur naturally in foods and can contribute to fermentation and flavor development.

What Enterococcus species are listed?

Enterococcus faecalis; Enterococcus faecium; Enterococcus durans.

What is the morphology of Enterococcus?

Cocci in pairs or short chains; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Enterococcus?

Homofermentative; converts sugar, especially glucose, into lactic acid.

What are the growth conditions of Enterococcus?

Facultatively anaerobic/aerotolerant; broad pH tolerance, with many strains growing at pH 9.6; many species grow around 10–45°C, with optimum around 35–37°C.

Why is Enterococcus unusual among food-associated LAB?

Some strains are opportunistic pathogens and may carry clinically important antibiotic-resistance or virulence traits.

What foods are associated with Enterococcus?

Traditional/artisanal cheeses, raw milk cheeses, Mediterranean-style cheeses, fermented sausages, and some fermented vegetables.

What environmental stresses can Enterococcus tolerate?

Salt, acid, and other environmental stresses.

What is Tetragenococcus?

A genus of LAB important in high-salt food fermentations, particularly in Asian foods.

What Tetragenococcus species is listed?

Tetragenococcus halophilus.

What is the morphology of Tetragenococcus?

Cocci in tetrads; non-spore-forming; usually non-motile; Gram-positive.

What is the metabolic pathway of Tetragenococcus?

Homofermentative; sugars are converted primarily to lactic acid; some species can produce small amounts of acetic acid.

What are the growth conditions of Tetragenococcus?

Facultative anaerobe; tolerates mildly acidic to neutral conditions; mesophilic with optimum around 30°C; highly salt tolerant.

What is a key characteristic of Tetragenococcus?

It is extremely halotolerant; some strains grow at very high NaCl levels.

What foods are associated with Tetragenococcus?

Soy sauce, miso, shoyu, fish sauce, fermented seafood, and high-salt vegetable fermentations.

Which genus is particularly associated with butyric acid fermentation?

Clostridium.

What is Clostridium?

A genus of bacteria in which certain species participate in butyric acid fermentation.

What are the key characteristics of the Clostridium group shown in the slides?

Rod-shaped, spore-forming, motile with peritrichous flagella, typically Gram-positive, and obligate anaerobes.

What is the metabolic pathway of Clostridium in butyric acid fermentation?

Pyruvate is converted to acetyl-CoA, then acetyl-CoA to butyryl-CoA, producing butyric acid and other products.

What are the growth conditions of Clostridium?

Obligate anaerobe; prefers near-neutral conditions around pH 6–7; spores survive adverse conditions.

Which Clostridium species are listed as food-fermenting species?

Clostridium butyricum and Clostridium tyrobutyricum.

Which Clostridium species are listed as foodborne pathogens?

Clostridium botulinum and Clostridium perfringens.

Why is Clostridium important in food processing?

Its ability to form endospores makes it particularly important; the genus includes both foodborne pathogens and spoilage organisms.

What products are formed in butyric acid fermentation?

Butanoic (butyric) acid, hydrogen, carbon dioxide, and small amounts of acetic acid.

What is propionic acid fermentation important for?

Dairy applications, particularly production of Swiss cheese and other fermented products.

What are the key characteristics of propionic acid bacteria shown in the slides?

Rod-shaped, non-spore-forming, non-motile, Gram-positive, fermentative, and anaerobic to aerotolerant.

What is the metabolic pathway of propionic acid bacteria?

Lactate is converted to pyruvate, then pyruvate is converted to propionate; propionic acid, acetic acid, and CO2 are produced.

What are the growth conditions of propionic acid bacteria?

Anaerobic to aerotolerant; optimum near neutral and acid tolerant; mesophilic with optimum around 30°C; able to tolerate cheese-ripening conditions.

What propionic acid bacteria species are listed?

Propionibacterium freudenreichii and Acidipropionibacterium acidipropionici.

What is Propionibacterium freudenreichii used for?

Propionic acid fermentation and dairy production, especially Swiss cheese.

What foods are associated with propionic acid bacteria?

Traditional Swiss cheese, Emmental Swiss cheese, Gruyere, Jarlsberg, and some bakery items.

What is the overall role of LAB in food production?

LAB have a wide range of applications and are rarely used independently; they are often used in combination.

Can LAB cause spoilage?

Yes. Depending on the product and species, certain LAB can create spoilage.