COMMON SOURCES OF PATHOGENS

Human Patients

Human Carriers

Animals

Classification of Micro Organisms

A. Bacteria

B. Virus

C. Fungi

D. Protozoa

Common Means of Transfer

Direct contact

Fomites

Air

Dust

Insects

Food

Water

Soil

Common Portals of Entry into new Hosts

SKIN

Usually via abrasions, bites, wounds, glands, burns, follicles

RESPIRATORY TRACT

Following Inhalation

ALIMENTARY TRACT

Following injestion

GENITAL TRACT

Following Sexual Intercourse

PLACENTA

From Mother to Foetus

Some materials which may contain pathogens

Skin scales, scabs

Hairs

Droplets

Sputum

Discharge from wounds, lesions, urethra, vagina et.,

Blood

Faeces

urine

Animal Flesh

Eggs Milk

BACTERIA

Very small organisms

More bacteria than any other form of organisms, found everywhere

eg., in one gram of fertile soil 1,000 million bacteria

Structure

Very simple, one cell only

A small bacterium is only 1 mm in diameter

occur in a number of shapes

GENERALISED BACTERIUM

Capsule

Rigid cell wall

Semipermeable cell plasma membrane

Cytoplasm - containing food stores

Nuclear material

Flagellum (sometimes) for locomotion

Bacteria are named according to shape

Spherical - coccus

Rods - bacillus

Curved cylindrical rod - vibrio

Bacteria also tend to join in groups after division eg., 2 cells together - Diplococcus

Forming a line - Streptococcus

Forming irregular collections - Staphylococcus

Factors affecting growth of bacteria

is there a suitable food supply

Presence or absence of Oxygen

Aerobic bacteria - must had O2

Anaerobic - cannot live with O2

Temperature ) for enzymic activity

pH acidity ) water Time .20 minutes division

How are bacteria killed?

Heat

Cold - no this will only suspend them

Chemicals

1. Antiseptics

Prevents division

i.e., Bacteriostatic

2. Disinfectants

Kill bacteria

Bacteriocidal

3. Antibiotics

Kills bacteria in the body, but is non-toxic to the patient - allergies?

Radiation - Ultra violet rays from the sun, man produced radiation

Visit to `A' level prep room

Relationship to Humans

Two types of bacteria

Those which cause disease Pathogenic Bacteria, Pathogens.

Those which do not cause disease Non-pathogens.

Some diseases caused by bacterial infection

ie,. bacteria growing in the body - blood, bronchus, gut

Bronchitis

Typhoid Syphilis Food poisoning

Pneumonia