Anti Microbial Activity

B.
Tech (Dairy Technology) 1st Year

DM 121 (Microbiology of Milk)
Chapter: Antimicrobial Components of Milk
R K Malik
ANTIMICROBIAL COMPONENTS IN MILK
Germicidal properties of milk known for many years
Milk from a healthy animals contains different levels of inhibitory

substances
Restrict the normal development of certain bacteria and sometimes
even kill them
The degree of inhibitory activity varies considerably in milk of
different species
Maximum activity present in Human Milk
Two groups of antimicrobial substances in milk

1. Inherent, naturally secreted in milk
2. Non-inherent compounds, that gain entry into milk from other
sources
Antimicrobial components in milk.....
Naturally occurring antimicrobial substances in milk

 A. Specific factors: Immunoglobulins, Complement, Macrophages, and
Bifidus factor
 B. Non specific: Iron binding protein-Lactoferrin, Lysozyme, Lactanins,
Lactoperoxidase, Vitamin binding proteins and fatty acids
Specific Factors
1. Immunoglobulins (Igs): Responsible for the immunological
protection of the neonates/infants
 In humans, prenatal immunity (Immunoglobulins) transferred from
mother across placenta to the foetus
 In animals(Buffalo, cow)-Transfer of Igs from colostrum post-
natally
 Gastro-intestinal tract is permeable to intact proteins molecules
 IgA is the Chief immunoglobulin in milk: Confers Passive
immunity (Colostrum: 50mg/ml; Mature milk: 1mg/ml)
ANTIMICROBIAL COMPONENTS IN MILK.......
Functions of SIgA
 Neutralizes toxins and viruses
 Inhibits bacterial adhesion
 Prevents absorption of food antigens
 Suppresses bacterial growth
 Aids in phagocytosis by bringing about attachment of bacteria to
macrophages
In human milk, anti E.coli IgA has been identified, prevents against
Infantile diarrhoea
2. Complement: Small amounts of several (nine) components of

complement detected in human milk
 Associated with bactericidal properties of milk
 Add to defence mechanism due to lysis of potentially
pathogenic microorganisms
ANTIMICROBIAL COMPONENTS IN MILK....
3. Viable Leucocytes (Macrophages):

 Present at a concentratin of 2 million cells/ml in colostrum
(reduced to 2% of it in mature milk)
 Associated with phagocytosis i.e. Engulfing and subsequent
killing of bacteria including pathogens
4. Bifidus Factor: Human milk contains bifidus factor responsible

for the dominance of the bacterium Bifidobacterium bifidus in
infants
Three beneficial effects
i. Inhibition of enteropathogenic strains of E coli, Shigella and other
pathogens due to production of lactic and acetic acid
ii. Acidic pH in stools necessary for absorption of Ca, Fe and P
iii. Synthesis of Vitamin B complex helps in infant growth
Non-specific factors
1. Lactanins: Lactanin L1 and Lactanin L2: Concentration varies
 Bovine colostrum rich in L1
 Normal milk contains higher concentrations of L2
 On heating raw milk to 70C/20 min, completely destroys L1
 L1 and L2 jointly more bactericidal than either alone
 Activity of lactanins lasts longer at low temperature
 Lactanins active against Streptococcus pyogenes
2. Lysozyme: Different amounts in milks of different species

 Avg. Content in human milk: 30mg/100ml (3000x more than bovine milk)
 Physiological and nutritional implications in infant feeding: Greater resistance
to enteric infections
 Lytic action of lysozyme due to hydrolysis of β-1,4-glycosidic linkage of the
peptidoglycan component of cell wall in Gm+ve bacteria
 Gram -ve bacteria normally lysozyme resistant
3. Lactoferrin (Iron binding protein):

One of the important antimicrobial substances in milk
It is a red glycoprotein
Human milk has higher concentration of this protein than cow/buffalo milk
-Human colostrum: 1.2 g/100ml
-Buffalo colostrum: 100mg/100ml
 The inhibitory effect of Lactoferrin is based on its ability to squeeze

out iron from the medium, thereby making it unavailable to the
bacteria-essential for growth.
Antibacterial property against:
Staphylococcus aureus
Pseudomonas aeruginosa
Vibrio cholerae
Clostridium tyrobutyricum
Bacillus stearothermophilus, B. subtilis
Lactoperoxidase:
Lactoperoxidase is present in milk in considerable amount (30mg/l) but
is absent in human milk; (Identical to L2 fraction of lactanin)
Inhibitory action is due to the formation of antimicrobial system:
LP System: Lactoperoxidase/Thiocynate/Hydrogen peroxide system
 Thiocynate secretion depends upon nutrition of the cow
 Hydrogen peroxide is either contributed by polymorpho-nucear-
leucocytes or by Hydrogen peroxide producing udder microflora
(e.g. strptococci)
The LP system is bacteriostatic for organisms like lactococci.
Bactericidal to Group A streptococci, E .coli, Salmonella Typhimurium
etc.
-Protects calf against enteritis problem
-May have some role in protecting udder against infections
Lactoperoxidase-Thiocyanate-Hydrogen Peroxide Antimicrobial System
 In raw milk, thiocyanate (SCN-) at a conc. of 1-10ppm, can be

oxidized by lactoperoxidase in the presence of about 10nmol/L
hydrogen peroxide to the putative antibacterial agent
Hypothiocyanate (OSCN-)
SCN- + H2O2 OSCN- + H2O
 Inhibition of Gm –ve organisms: Salmonella spp. Campylobacter

spp., Escherichia coli, & Ps. aeruginosa; Gm+ve organisms such as
Staph. aureus and Listeria monocytogenes
5. Vitamin binding proteins

 Certain proteins in the milk of some species that bind some
essential vitamins making them unavailable for the growth of
bacteria.
 Particularly bind with Vit B12 and Folic Acid
 Regulate bacterial growth in the intestinal tract of suckling
animals
 Aid in absorption of vitamins in the gut
6. Fatty Acids
 Free Fatty Acids in appreciable concentrations
 Generally medium chain saturated fatty acids (octanoic and
decanoic) and some unsaturated long chain fatty acids (C18:1
and C18:2) are more active against Gm+ve organisms
 Released due to action of lipases: at higher conc of FFAs,
growth of bacteria inhibits

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B.

Tech (Dairy Technology) 1st Year

Chapter: Antimicrobial Components of Milk

Germicidal properties of milk known for many years

Milk from a healthy animals contains different levels of inhibitory

Two groups of antimicrobial substances in milk

Naturally occurring antimicrobial substances in milk

2. Complement: Small amounts of several (nine) components of

3. Viable Leucocytes (Macrophages):

4. Bifidus Factor: Human milk contains bifidus factor responsible

2. Lysozyme: Different amounts in milks of different species

3. Lactoferrin (Iron binding protein):

 The inhibitory effect of Lactoferrin is based on its ability to squeeze

Lactoperoxidase-Thiocyanate-Hydrogen Peroxide Antimicrobial System

 In raw milk, thiocyanate (SCN-) at a conc. of 1-10ppm, can be

SCN- + H2O2 OSCN- + H2O

 Inhibition of Gm –ve organisms: Salmonella spp. Campylobacter

5. Vitamin binding proteins

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