Important bacteria found in milk

Krishna: Yes, lots of them! But I am mentioning only a few important ones here.

Microorganisms present in raw milk, including milk from cows, sheep, goats and humans:

Milk, due to its high nutritional content, can support a rich microbiota. These microorganisms enter milk from a variety of sources and, once in milk, can play a number of roles, such as facilitating dairy fermentations (e.g. Lactococcus, Lactobacillus, Streptococcus, Propionibacterium and fungal populations), causing spoilage (e.g. Pseudomonas, Clostridium, Bacillus and other spore-forming or thermoduric microorganisms), promoting health (e.g. lactobacilli and bifidobacteria) or causing disease (e.g. Listeria, Salmonella, Escherichia coli, Campylobacter and mycotoxin-producing fungi).(1)

Milk provides a favorable environment for the growth of microorganisms. Yeasts, moulds and a broad spectrum of bacteria can grow in milk, particularly at temperatures above 16°C.

Microbes can enter milk via the cow, air, feedstuffs, milk handling equipment and the milker. Once microorganisms get into the milk their numbers increase rapidly. It is more effective to exclude microorganisms than to try to control microbial growth once they have entered the milk. Milking equipment should be washed thoroughly before and after use rinsing is not enough. Bacterial types commonly associated with milk are given below (2):

Bacterial types commonly associated with milk.

Pseudomonas: Spoilage

Brucella: Pathogenic

Enterobacteriaceae:Pathogenic and spoilage

Staphylococci, Staphylococcus aureus: Pathogenic

Streptococcus, S. agalactiae: Pathogenic

S. thermophilus: Acid fermentation

S. lactis: Acid fermentation

S. lactis-diacetyllatic: Flavour production

S. cremoris: Acid fermentation

Leuconostoc lactis: Acid fermentation

Bacillus cereus: Spoilage

Lactobacillus, L. lactis: Acid production

L. bulgaricus: Acid production

L. acidophilus: Acid production

Propionibacterium: Acid production

Mycobacterium tuberculosis: Pathogenic

Pathogenic Bacteria in Milk

Pathogenic bacteria are transmissible to humans through milk and milk products. Recently, attention is focused on milk, cheese, and ice cream contaminated with pathogenic bacteria, viz., Listeria monocytogenes, Yersinia enterocolitica, Campylobacter jejuni, and enteropathogenic Escherichia coli. (3)

Footnotes:

1. complex microbiota of raw milk
2. Milk composition and microbiology
3. Pathogenic Bacteria in Milk — A Review