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. Through the air 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.