Spore: These are highly resistant structures formed in response to adverse conditions. They has a thick keratin like coat, that is responsible for the remarkable resistance to heat, dehydration radiation and chemicals, spore has no metabolic activity and can remain dormant for many years, when they come contact of available water & food they comes to life. All bacteria cannot form spore. Mainly gram positive Bacillus and clostridium can form spore.

Classification of Bacteria

Bacteria are three types based on shape. They are –
Cocci: Round shaped Bacteria; i.e.-Gonococci, Diplococcus Pneumonia, Streptococci etc.
Bacillus: Rod shaped or stick shaped bacteria; Streptobacilli
Spirochetes: Spiral shaped, flexible, Coiled Bacteria.

Bacteria are two types based on gram staining
Lipid bilayer (Lipopolysaccharide) is found in Gram-negative bacteria but not in Gram-positive bacteria.
Gram-positive bacteria: Staphylococcus aureus, Streptococcus pneumonia, Clostridium botulinum, Clostridium titani, Streptococcus pyrogens etc.

Gram-negative bacteria : Eschericia coli , Salmonella spp, Shigella species, Vibrio spp., Neisseria gonorrhoea, Neisseria meningitides, Klepsiella spp etc.

Bacteria are four types based on Gaseous requirements. They are-
a) Aerobic bacteria: Require O2 for growth, (21% O2)
b) Anaerobic bacteria: Don’t use O2 to obtained energy. Some can tolerate low level of O2 but other cannot tolerate even low level of O2 and may die upon brief exposure to air.
c) Facultatively anaerobic bacteria: Don’t require O2 for growth, although they may use O2 for energy production.
d) Microaerophilic bacteria: Require low level of O2 for growth but cannot tolerate the level of O2 present in air (21% O2).

VIRUS

Virus: Non-cellular organisms. They are innate, but alive within the host. Diameter is 0.02 – 0.2mm. They have no Nucleus, Ribosome and Mitochondria.

Characteristics of Virus
Viruses depend upon living host for Replication.
Contain DNA or RNA but not both.
Use the living cell’s energy stores, substrates and Synthetic machinery.
Can have a benign or very destructive relationship with the host.

FUNGI

Fungi: Eukaryotic microorganisms. Most fungi are obligate aerobes some are facultatively aerobes. Diameter 3 – 10 mm. Size of ribosome is 80s. It comprises Mold and Yeast. Molds are filamentous and multi-cellular. Yeasts are unicellular. Example: Aspergillus, Candida, Trychophyton, etc.
Characteristics of Fungi
Fungi lack pigments to manufacture their own food and therefore depend upon other
organisms for life
Includes Yeast & Mushrooms
Suffix – mycosis refer to fungus
PROTOZOA

Protozoa: Eukaryotic microorganisms that have the following features.
More Complex Organism
Unicellular, Mobile, lacking cell wall
Examples: Trichomaniasis, Malaria, Entamoeba histolytica, Giardia lamblia etc.

Antiseptic: Agent that kills or inhibits the growth of microorganisms on the external surface of the body. Toxicity is very low for the host cells. It can be used directly on skin, mucous membrane and wounds.
Example: Alcohol, Iodine, Hydrogen peroxide, Boric Acid, etc.

Antibiotic: Agent, which kills or inhibits the growth of microorganisms internally, is called antibiotic. It is sufficiently nontoxic to the host. It is used in the treatment of infectious disease of man, animals and plants. Example: Tetracycline, Ciprofloxacin, Gentamicin, Mertonidazole, Penicillin etc.

Disinfectant: A chemical, which kills bacteria, virus and other microorganisms on a non-living surface. A complete disinfectant is able to kills spore of microorganisms.Infectious disease in human being is caused by Bacteria, Virus, Fungi, Protozoa and Helminths. Infectious pathogen may spread via water and food. Diarrhoea, Typhoid, Giardiasis, Amebiasis etc. are the common public health problem till today which are the consequence of contaminated water and food