Learning Goals:

To be able to differentiate between different types of diseases.

To understand important aspects of bacteria.

To be able to classify bacteria based on shape.

Causes of disease can be grouped into 2 main categories:

1. Congenital diseases: inherited and passed down from parent to offspring.

2. Acquired diseases –contracted at some stage over a lifetime

- can be subdivided into 2 types:a. Lifestyle diseases - caused by an unhealthy

lifestyle e.g. heart disease; type 2 diabetes.b. Infectious disease – disease caused by a

pathogen.

Verne Troyer has Achondroplasia

• One of the main causes of disease in an organism is the presence of another organism in or on it. Such an invading organism is called a parasite.

• The organism that they ‘feed’ on is called the host.

• If a parasite causes a disease state (i.e. if it makes the host sick in any way) it is said to be a pathogen.

• Pathology is the branch of science involved in the study of disease and diseased tissue.

Pathogens may be a microorganism such as bacteria, viruses, fungi or prion; or may be a multicellular organism such as worms.

Most pathogens, and their associated infectious disease, can be transmitted from person to person (i.e. are contagious).

Many infectious diseases result in death.

Bacteria

T4 Bacteria

Candida albicansPrions

• Traumatic illnesses are injuries,

• Inflammatory diseases cause fever and swelling,

• Neoplastic conditions involve tumours or cancerous growths.

• Malignant cancers are those that spread active cancer cells throughout the body,

Classification of diseases

Hand with gout

Tumour on the palate

• Benign cancers are those where cancer cells form tumours at one site.

• Acute relates to a short, sudden episode of disease,

• Chronic relates to a continuing occurrence of the disease.

1. BacteriaBacteria are unicellular, prokaryotic organisms.

Bacteria are found everywhere and only a few cause diseases.

Most bacteria are saprophytes – they obtain their nutrients from dead and decaying organisms.

In humans, bacteria live in the intestine and help break down food.

Infectious diseases - Pathogens

Bacteria sample from the human tongue

Pond Bacteria

• Bacteria vary greatly in size and morphology (shape).

• Bacteria are generally between 1/1000 and 1/20 of a mm in length.

Bacteria Photo No.

Bacteria Shape (baccilus, spirochaete, coccus, staphylococcus, streptococcus, diplococcus)

Special features(flagella, capsule)

A

B

C

D

E

F

G

H

I

J

Baccilus Anthrax is the bacteria involved in the infection commonly known as anthrax. It affects the function of the lungs, the digestive system and the skin of mammals

A

Borellia bergdorferi is a spirochete bacteria responsible for Lyme disease. Although the first symptom of a rash seems minor, the disease can result in damage to the heart, nerves, brain, and facial paralysis.

D

Ticks are the vector of spread for this bacteria

Escherichia coli is a baccilis normally found in the intestines of mammals. Some strains are responsible for causing food poisoning, and the reason for mass recall of some food products.

E

Neisseria meningitides is a coccus bacteria responsible for meningitis; inflammation of the protective membrane of the brain.

F

Yersinia pestis is a cocco-baccillus bacteria which was responsible for Black Death which was responsible for loss of at least 1/3rd of the population of Europe between 1347 and 1353.

• Bacteria that need oxygen for their survival are called aerobic bacteria.

• Bacteria that do not require oxygen for survival are called anaerobic bacteria.

• Facultative anaerobes can survive wether in oxygen or not.

• Obligate anaerobes grow and reproduce only in the absence of oxygen.

Classifying bacteria on oxygen requirement

Group Characteristic Examples and the disease they cause

Aerobes Grow in presence of oxygen

Pseudomonas aeruginosa – external ear infection

Facultative anaerobes Grow wether oxygen is present or not

Streptococcus pyogenes – tonsillitis

Obligate anaerobes Grow only in absence of oxygen

Clostridium botulinum – botulismC. tetani – tetanusC. perfringens - gangrene

• Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method, in which an agent is used to bind to the cell wall of the bacteria.

Gram-positive bacteria take up the violet colour of the stain, Gram-negative bacteria stain pink.

• Some bacteria have a special polysaccharide called teichoic acid in their cell walls, and are susceptible to penicillin and sulfonamide drugs.

Gram Positive and Gram Negative bacteria:

Teichoic acid

Disaccharide and amino acid

Cell membrane

Lipid compounds

Disaccharide and amino acid

Cell membrane

The chemical components of the cell wall of Gram-positive and gram-negative bacterium

• The outer layer of lipid compounds in gram-negative bacteria enables the bacteria to resist drugs. • It also makes phagocytosis of the bacteria very difficult.

• Other drugs are effective against these types of bacteria.

Classification based on nutritional patternsThis is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction.

• Some bacteria are photosynthetic (autotrophs) use light as their energy source.

• Only some of these bacteria are able to use CO2 as their carbon source.

• Chemosynthetic organisms obtain their energy from oxidation reactions.

• Some of these can only oxidise organic compounds for their carbon source. Others can oxidise inorganic substances such as ammonia, sulfides and iron compounds. Other heterotrophic bacteria obtain carbon and/or sugar from the the living cells or organism they are in).

copy fig 7.8 p.193

• Based on the morphology, DNA sequencing, conditions required and biochemistry, scientists have classified bacteria into phyla.

• Each phylum further corresponds to number of species and genera of bacteria.

• The bacteria classification includes classification based on the habitat of the bacteria.

Classification based on Phyla:

• Bacteria can cause disease in humans if:1. They can enter a person who acts as a host2. They can reproduce in the host3. They act adversely on the tissue of the host.

Task: List several ways in which bacteria can be transmitted to a person.

How do bacteria cause disease?

• Transmission of bacteria (and other pathogens) occurs by:a) From one person to another through droplets if an infected

person coughs, sneezes or comes into body contactb) Contaminated water and foodc) Carried from one host to another by a vector (an animal

host such as a mosquito, rat or fly)

A carrier of a disease is someone who has the disease, be shows no symptoms, so passes it on to others unaware of doing so.

Transmission to a host

• In order to reproduce, bacteria need an environment with adequate nutrients and water, and an appropriate temperature and pH.• When conditions are favourable, bacteria reproduce

very quickly, about every 20 minutes or so.

Task: Q2 p.220

Reproduction of bacteria

Bacteria can damage the host in several ways:1. By producing enzymes that break down or digest tissues.2. By producing poisonous toxins.a) Exotoxins are released into the surroundings by bacteria as

they grow. Exotoxins are some of the most lethal substances known, and can (i) inhibit protein synthesis;(ii) Damage cell membranes or disrupt transport of materials across cell membranes; or(iii) Interfere with normal nerve function.Toxins retains their destructive powers after the bacteria dies.

Bacteria effects on tissues

b) Endotoxins are derived from the lipopolysaccharide layer in the cell wall of Gram-negative bacteria and are released after the cell lyses (breaks open).

Endotoxins resist the body’s defence system better than exotoxins.

Task: copy table 7.2 p.198

• Chemotherapy is the term used when a disease is treated with chemicals.

• Many chemicals are produced, or have been extracted from bacteria and fungi to fight disease-causing agents.

• Naturally occurring compounds which kill bacteria are called antibiotics.

• Some drugs are narrow-spectrum and act against a limited variety or microorganisms.

• Other drugs are broad-spectrum and act against many different kinds of pathogens.

Treatment of bacterial diseases

• Broad-spectrum antibiotics are useful when the doctor is not sure which bacterium is causing an infection.• Sensitivity tests are carried out to determine which drug is

most effective against the infecting bacteria.• A drug should be selectively toxic – it should kill the infecting

cells without destroying the host cells.• Some drugs have adverse effects (side effects) on a host.

Task: Copy table 7.3 p.200