Staphylococcus aureus
Gram positive, Spherical cocci .
Measuring 0.8 to 1.0 um in diameter.
Arranged characteristically in ‘Grape like’ clusters. 
Cluster formation is due to cell division occurring in more than one plane with daughter cells remaining               closer together.
Non-spore forming,
 Non-motile,
Non-capsulated (Exceptions rare strains).
 
 Streptococcus pyogenes
Gram-positive cocci (In older cultures decolorized).
Streptococcus pyogenes is a coccus 0.5 um to 1 um in size arranged in chains, chains made up of many                      diplococci. (Division in one plane.)
Chains are shorter in artificial medium.
Length of chain is increased by the presence of specific antibodies and is decreased in the absence of abs.
Non-motile, Non- sporulating.
Capsule producing strain – Streptococcus epidemicus.
Corynebacterium bovis
Gram-positive slender rods with a tendency to clubbing at one or both ends;
Non-sporing,
Non-motile,
Non-capsulated,
Non-acid fast,
The granules are more strongly Gram positive than the rest of the bacterial cell.
Stained with Loeffler’s methylene blue, the granules take up a reddish purple color and hence they are                         called metachromatic granules.They are called as volutin or Babes Ernst Granules, often situated at the                       poles of the bacilli and are called polar bodies.
Special stains, such as Albert’s, Neisser’s and Ponder’s have been devised for demonstrating the granules.
Stained smears from animal tissues often reveal groups of cells in parallel (Palisades) or cells at sharp                       angles to each other (Chinese letter or Cuneiform arrangement).
Bacillus anthracis
Largest pathogenic Bacteria, 1-1.5 X4-8 u in size.
Rod shaped bacilli with truncated ends , Arranged in chain ‘Bamboo’ like appearance
Gram Positive,
Non-motile,
Capsulated(D-glutamic acid-polypeptide),
McFadyeans reaction,
Spore forming.
 
 Pasteurella multocida
 Small coccoid rod .
Measuring 0.25-0.4 u by 0.6-2.6u.
Pleomorphic.
Gram negative rods with characteristic ‘Bipolar’ appearance in the stained smears.
Possess capsule (Hyaluronic acid) when recently isolated from the disease process.On subculturing looses the capsule.
Non-sporulating,
Non-motile.
 
 Escherichia coli
Gram negative rods, measuring 1-3um x 0.4-0.7um in size varying from coccid bipolar to filamentous forms, occurs singly or in short chains.
Fimbriae are present in 80% of the strains,
Motile by means of peritrichous flagella,
Non-capsulated, few extra-intestinal strains possess polysaccharide capsule,
Non-spore forming.
Salmonella Pullorum
Gram-negative short plump rods, measuring 0.4-0.6um x 0.8-1.6um in size.
Occur singly or in short chains,
Non-motile,
Non-spore forming,
Non-capsulated, Long filamentous forms occur.
Mycobacterium tuberculosis
Slender rod, 0.2-0.6um X 1.5-4.0um in size.
Non-spore forming.
Non-motile.
Extremely pleomorphic.
Acid fast (resist acid fast decolourization-due to waxy substances which prevents the ready absorption of dyes.)
Exercise
Q1. Prepare the smear stain with Gram’s staining and write the shape, size, arrangement, and staining reaction of the given bacteria.