Louis Pasteur(1822-1895)

• Father of microbiology.
• Established fermentation was caused by microbial agents.
• Intro sterilization technique.
• Developed steam sterilizer, hot air oven and autoclave.  
• Growth needs of different bacteria
• Vaccine for rabies and anthrax

• Father of bacteriology
• Intro staining techniques and methods to obtaining bacteria in pure culture using solid media
• Discovered Tubercle bacilli & Vibro cholerae
• Koch's postulates & phenomenon
• bacteriological techniques

A microorganism can be accepted as the causative agent of an infectious disease only if the following conditions are met.

1. Finding the bacterium in all cases of the disease.
2. Isolate the bacterium in pure culture from the lesions. 
3. Inducing the disease in a healthy organism by infecting them with the isolated bacterium.
4. Reisolate the same bacterium from the newly infected organism.
5. The specific antibody against the bacterium shld be present patients with the disease.

Types of staining methods 

• simple stains
• _ve staining
• impregnation methods
• differential staining 

gram +ve stain & gram _ve gram

• acid fast stain

1. Cocci- Oral /spherical cells
2. Bacilli- Rod shaped cells Coccobacilli- length is same as width ex: Brucella

• Chinese letter /Cuneiform pattern
• Comma shaped ex: vibrio
• Spirilla- rigid spiral form ex: spirillum 

1. Spirochetes- slender, flexuous spiral forms ex: treponema
2. Actinomycetes- branched, filamentous bacteria
3. Mycoplasma- cell wall deficient forms, hence do not possess a stable shape.
4. Rickettsiae and chalmydiae- small obligate parasites

Strong, protective layer surrounding bacteria, providing resistance against osmotic pressure, maintaining cell shape, aiding in cell division, and protecting against toxic substances.

Gram +ve cell wall

Gram _ve cell wall

1. Peptidoglycan Layer:

   • Thin layer (much thinner than in Gram-positive bacteria).
   • Made of mucopeptide chains, cross-linked by tetrapeptides (L-alanine, D-glutamine, meso-diaminopimelic acid, and D-alanine).
   • No pentaglycine bridge.

2. Outer Membrane:

   • Phospholipid bilayer, connected to the peptidoglycan by Braun’s lipoprotein.
   • Contains porin proteins that allow small molecules to pass.
   • Acts as a protective barrier against harmful substances and antibiotics.

3. Lipopolysaccharide (LPS):

   • Unique to Gram-negative bacteria.
   • Composed of three parts:
     • Lipid A (endotoxin) causes fever, toxicity, and immune response.
     • Core polysaccharide (stabilizes the outer membrane).
     • O side chain (used for serotyping, varies between strains).