Transcript Helpful and Harmful Bacteria

Helpful and
Harmful Bacteria
Helpful Bacteria
• Most bacteria are harmless to humans.
• Many are useful:
– Aid in digestion
– Provide nutrients for plants by breaking
down dead material by decomposition
– Provide drugs and hormones
– Provide some types of food.
Yoghurt
• This is made by the action of a
particular type of bacteria on milk.
• Lactobacillus bulgaricus and
Streptococcus thermophilus
• These bacteria change milk sugar
(lactose) into lactic acid.
• The acid gives yoghurt its
characteristic sour flavour and also
causes the curd to separate from the
milk.
Yoghurt
• The resulting yoghurt is thick and
creamy.
• When it is eaten, the bacteria colonise
the intestinal tract where it is thought
that they aid the process of digestion.
Nutrient Cycles
• Decomposers break down dead plant and
animal material into simpler chemicals,
releasing essential nutrients into the
soil.
• These nutrients can then be used for
plant growth.
The Nitrogen Cycle
• Atmospheric nitrogen can be fixed by
lightning or certain nitrogen fixing
bacteria called Rhizobium.
• These Rhizobium live in a mutualistic
relationship in the root nodules of
leguminous plants such as lupins, gorse
and clover.
• Also some free-living soil bacteria “fix”
nitrogen.
The Nitrogen Cycle
• Denitrifying bacteria break down
nitrates to nitrogen, thus returning it to
the reservoir in the air.
• This is known as Denitrification.
The Nitrogen Cycle
The Carbon Cycle
Harmful Bacteria
Harmful Bacteria
• Micro-organisms that cause disease are
called Pathogens.
• An infectious disease is one that can be
passed on from person to person.
Catching Diseases
• Contaminated food and water.
– Salmonella spp, Clostridium botulinum
• Through the air
– Sneezing or coughing Staphylococcus and
Streptococcus
• Skin contact
– Particularly through broken skin
– Staphylococcus spp
Catching Diseases
• Contact with infected materials like
towels and handkerchiefs
• Contact with body fluids
– E.g. blood, semen, saliva
Harmful Bacteria
• Pathogenic bacteria make people feel
sick by getting into the body and
producing enzymes which break down
body tissues or by excreting very
strong poisons called toxins.
Bacterial Diseases
•
•
•
•
•
•
•
Diptheria - Corynebacterium diphtheriae
Syphillis - Treponema pallidum
Tetanus - Clostridium tetani
Typhoid - Salmonella typhi
Tuberculosis - Mycobacterium tuberculosis
Sore throat - Streptococcus
Salmonella – Salmonella spp
Bacterial Diseases
•
•
•
•
•
•
•
Meningitis - Neisseria meningitidis
Whooping cough - Bordetella pertussis
Cholera - Vibrio Cholerae
Gonorrhoea – Neisseria Gonorrhoeae
Chlamydia – Chlamydia trachomatis
Plague - Yersinia pestis
Pneumonia - Streptococcus pneumoniae
Harmful Bacteria
• When people are sick, samples of their
tissues, blood, or faeces may be taken
and placed onto agar plates to see if the
samples grow bacterial cultures.
• This will determine if a particular type
of bacteria is causing the illness and will
help the doctor prescribe an antibiotic
drug to kill the bacteria.