Classification of Dairy Bacteria

MORPHOLOGY AND CLASSIFICATION OF DAIRY BACTERIA

Introduction

Micro-organisms found in milk can be studied as groups possessing one or more major characteristics in common. These may be divided on the basis of their action on milk constituents, for example acid-former, proteolytic, saccharolytic etc. Another approach of classification is based on the morphology of these micro-organisms. These types of classification of dairy industrial microbes have been discussed in the following sections in this lesson.

Classification Based on Shape, Size and Arrangement of Cells

The bacteria have been classified as cocci, bacilli, spirilla based on the shape of the cells. However, some bacterial cells appear in different shapes or may be lacking uniform shape and are known as pleomorphic (e.g. Arthrobacter, Bifidobacterium). Further based on the arrangement of cells bacteria are also classified into different groups. The arrangement of cells linked side by side similar to that like matchsticks is known as palisade arrangement. 

Cocci

Bacterial cells with spherical or ellipsoidal shape are called as cocci and may have the following type of arrangement of cells:

a)      Diplococci: cells divide in one plane and remain attached in pairs (e.g. Neisseria)

b)      Streptococci: cells divide in one plane and remain attached after some divisions, in form of chains (e.g. Streptococcus)

c)      Tetrads: cells divide in two planes and form 4 cells (e.g. Pediococci)

d)      Sarcinae: cells divide in 3 planes and form a cuboidal arrangement

e)      Staphylococci: cells divide in 3 planes in an irregular pattern producing bunches of cocci.

Bacilli

Bacteria with cylindrical or rod like cells are called as bacilli and these may have the following type of arrangement of cells.

a)      Diplobacilli: cells divide in one plane and remain attached in pairs.  

b)      Streptobacilli: cells divide in one plane and remain attached after some divisions, in form of chains.

Ends may be rounded as in Lactobacillus bulgaricus or squamosed as in Bacillus anthracis.

Spirilla

Bacteria with spiral or helical shaped cells are called as spirilla and may have the following characteristic shape.

a)      Vibrio: rod shaped cells having single curves

b)      Spirochetes: rod shaped cells having many curves

c)      Few curves: true spirilla