1.3 - Prevention and Treatment of Diseases Caused by Microorganisms

Pathogens, Prevention and Aseptic Technique

Pathogens are harmful microorganisms that cause diseases.
Aseptic technique refers to a healthcare procedure carried out to prevent infection by pathogens or to remove existing pathogens.
“Prevention is better than cure” means preventing a person from being infected by pathogens is better than treating the person after infection.
Aseptic techniques control the spread of pathogens through sterilisation, boiling, use of antiseptics, use of disinfectants and use of radiation.

Sterilisation is the process of killing or eliminating microorganisms from an object or a particular environment.
The method depends on the type of microorganism to be killed or eliminated.

Method	Example / action
Heat	An autoclave uses a temperature above 130°C to kill microorganisms and their spores.
Chemical substance	Soap.
Radiation	Ultraviolet rays.
High pressure	Pressure cooker.
Filtration	A micron filter removes fine particles and microorganisms measuring 0.1 μm–10 μm from water or other liquids.

An autoclave is more effective than boiling because its temperature above 130°C can kill both microorganisms and their spores.

An antiseptic is a chemical substance that can be applied to human skin or wounds to prevent pathogenic infection.
Acriflavine (yellow medicine) and povidone can kill microorganisms.
Proflavine blocks or prevents microorganism growth.
70% isopropyl alcohol (IPA) can act as both an antiseptic and a sterilising agent.

A disinfectant is a chemical substance applied to non-living things—such as bed sheets, toilets and swimming pools—to kill microorganisms, especially pathogens.
It is not suitable for skin or wounds.
Examples: bleach, hydrogen peroxide and liquid chlorine.

Antiseptic	Disinfectant
Applied to human skin or wounds.	Applied to non-living things.
Prevents pathogenic infection; may kill or prevent growth of microorganisms.	Kills microorganisms, especially pathogens.
Examples: acriflavine, povidone, proflavine, 70% IPA.	Examples: bleach, hydrogen peroxide, liquid chlorine.

Similarity: both use chemical substances to control microorganisms.

Ionising radiation, such as ultraviolet rays, X-rays and gamma rays, is used to kill microorganisms.
These rays penetrate microorganism cells and destroy them.
Example: ultraviolet lamps kill microorganisms in operating theatres.

An antibiotic is medicine used to treat infections caused by bacteria.
Antibiotics are not effective against viral infections, including common fever, cold and cough.
Antibiotic resistance occurs when an antibiotic loses its ability to kill bacteria and is no longer effective in treating bacterial infections.

Excessive use of antibiotics.
Inaccurate use—for example, using antibiotics to treat viral infections such as sore throat, fever, cold and common cough.
Not taking antibiotics for the prescribed duration or not completing the course.
Antibiotic resistance makes people vulnerable to more diseases.

Aim: Study the effect of penicillin concentration on the growth of Bacillus sp.
Problem statement: What is the effect of antibiotic concentration on bacterial growth?
Hypothesis: The higher the antibiotic concentration, the lower the bacterial growth.
Manipulated variable: Concentration of antibiotic.
Responding variable: Area of clear region.
Constant variable: Type of bacterium, Bacillus sp.
Materials: Bacillus sp. culture solution, sterile nutrient agar, four 6 mm filter-paper discs, 10%, 20% and 30% penicillin solutions (or 10-, 20- and 30-unit penicillin discs), distilled water, marker pen and cellophane tape.
Apparatus: Petri dish with lid, syringe, sterile forceps and transparent grid sheet.

Pour 1 cm³ of Bacillus sp. culture solution over sterile nutrient agar in a Petri dish.
Using sterile forceps, place four discs on the agar: one soaked in distilled water and three soaked in 10%, 20% and 30% penicillin solutions.
Cover and seal the dish with cellophane tape.
Keep it at room temperature in a dark cupboard for three days.
Observe the clear region around each disc and measure its area with a transparent grid sheet.

The distilled-water disc is the control.
A clear region contains no bacteria or shows where bacterial growth has been inhibited.
The clear region is larger around a disc with a higher penicillin concentration.
Conclusion: Increasing penicillin concentration increases the inhibition or killing of Bacillus sp.; bacterial growth decreases.
Sir Alexander Fleming studied the effect of Penicillium sp. on bacterial growth and was the first person to discover antibiotics.

Treatment must match the group of pathogen causing the disease.

Infectious disease and pathogen	Treatment
Pneumonia — Streptococcus pneumoniae (bacterium)	Antibiotic, for example penicillin.
Athlete’s foot — Trichophyton rubrum (fungus)	Antifungal, for example clotrimazole.
Shingles — Varicella-zoster (virus)	Antiviral, for example acyclovir.