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Introduction to plant pathogenic microorganism
Learn Agricultural Microbiology with Braimy – B.Sc. agriculture
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  • Proteolytic : break protein
  • Saccharolytic : break sugar
  • Lipolytic : break lipids


  • Streptococcus lactis ferments lactose of milk into lactic acid. Other Saccharolytic forms are:
  1. Streptococcus cremaris
  2. Leuconostoc citrovorum etc. which also produce lactic acid in milk.
  • Several species of Lactobacillus are commonly found in milk. They are :

Lactobacillus acidophilus

Lactobacillus bulgaricus

Lactobacillus brevis

Lactobacillus fermentum

Lactobacillus thermophilus etc.

  • The main end product is lactic acid in several of the cases but in some of the cases, other acids and alcohol may also be produced.
  • Microbacterium lacticum, Micrococcus luteus, Micrococcus varians, Micrococcus freudenreichii are also the bacterial fermenters present in milk.
  • Some bacteria ferment milk and produce gas.
  • Clostridium butyricum, Candida pseudotrophicalisare some of the organisms which produce gas in the milk, fermenting lactose.


  • Several microorganisms which are Lipolytic enter into the milk thorough various sources
  • g.: Enterobacter aerogenes cause ropiness in milk, in which case, the milk becomes viscous (slimy) or stringy and produce a gummy substance in the milk.
  • Some organisms split the fat in milk & produce glycerol and fatty acid resulting in a rancid taste and soul milk.

Pseudomonas fluorescens

Candida lipolytica

  • Penicillium spp.are some of the microorganisms responsible for such action.
  • Besides this some bacteria like Serratia marcescens produce red coloration, Pseudomonas synxanthia produce yellow coloration.
  • Pseudomonas syncyanea produce blue coloration in milk.



  • Milk is coagulated or curdled without acid production when the casein contained is coagulated.
  • This is brought about by bacteria like Bacillus subtilis, Bacillus cereus var. mycoidea, Pseudomonas viscosa and Streptococcus lignaefaciens.
  • When milk is stored for longer period, certain characteristic bacteria multiply depending upon the condition of storage.
  • If stored at low temperature psychrophilic bacteria multiply whereas at higher temperature (above 600C) thermophilic bacteria multiply and spoil the milk.
  • These bacteria survive pasteurization so they are harmful.

Bacillus stearothermophilus

Mycobacterium lacticum

Micrococcus luteus

  • Streptococcus thermophilus are some of the microorganisms found to cause severe damage at higher storage temperature.
  • Several pathogenic microorganisms may spread through milk and cause disease outbreaks.
  • Pathogenic organism from infected cow may pass to milk and through milk to man or calves. Some examples of the disease that spread through milk are:

Tuberculosis               – Mycobacterium bovis

Brucellosis                  – Brucella abortus

  1. fever – Coxialla burnetti

Typhoid fever – Salmonella typhii

  • Beside these some humane pathogens may find their way to milk, through which, they spread from one place to another place and from one individual to another individual.
  • Typhoid, Depthera, Dysentery are some examples of these disease.
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