Micro-organisms in Action
Growth of micro-organisms is defined as increase in size, mass or number of cells. Micro-organisms like all living things, increase in size and multiply in number of cells using culture medium or any suitable surface such as moist bread as source of food.
If environmental conditions of growth such as food, adequate temperature and humidity are favorable, such an increase in mass, size and number of cells of the colony is an index of growth of micro-organisms.
Growth in micro-organisms
Bacteria reproduce by binary fission in which a single cell divides into two. This process is called asexual reproduction. The time interval required for the cell to divide into two is called generation time. This time varies from one organism to another. It strongly depends upon nutrient availability, temperature, gaseous requirement and pH. There are different phases in the growth of bacteria. A growth curve can be used to describe the growth of micro-organisms in an environment with limited resources. It is a typical sigmoid curve. The four stages of the growth curve are:
- Lag Phase: Growth is slow as the micro-organisms are adapting to the conditions in the environment.
- Exponential/ Log phase: The micro-organisms reproduce rapidly and their numbers increase exponentially.
- Stationary phase: Eventually, the nutrients are exhausted. Toxic by-products have also accumulated in the medium. At this stage, the net growth is zero and the number of micro-organisms stabilizes.
- Death Phase: In this stage, cells die faster than they are replaced and the microbial decreases in size rapidly.
There are two major ways of measuring growth in micro-organisms. These are:
- A bacterial sample is inoculated into a nutrient agar (i.e. a clear liquid culture medium). As the bacterial population increases, the clear liquid medium becomes cloudy or turbid. Progressive increase in turbidity indicates a related increase in number of bacterial cells. This is used to measure bacterial growth. In laboratory, turbidity can be measured with spectrophotometer.
- In this method, small samples of bacteria are taken from the nutrient agar at regular intervals of time. Each sample is diluted several times. Each diluted sample is inoculated on to a nutrient agar medium in a petri- dish and incubated. The number of colonies formed in each petri-dish is counted. A colony is formed by the multiplication of a single bacterium, the number of colonies indicates the number of living bacterial cells in the diluted sample and this can be used to calculate the actual number of bacterial in the original sample.
Benefits and disadvantages of Micro-organisms
Some micro-organisms especially bacteria and fungi are beneficial to man in three major ways: in nature, medicine and in industries.
Benefits
- Bacteria help to digest cellulose in herbivores
- Bacteria and fungi are widely used in the synthesis of antibiotics
- Micro-organisms help in maintaining some cycles in nature e.g. the nitrogen cycle and carbon cycle. They also help in recycling phosphates and sulphate
- Some bacteria are used in curdling of milk, brewing of wine and in butter and cheese making.
- Saprophytic micro-organisms decompose sewage into harmless inorganic compounds
- Most decomposers are micro-organisms and they help to maintain soil fertility
- Some bacteria living in the rumen of ruminants like sheep, goat, cattle help to digest cellulose in their food (grasses / vegetation)
- Some bacteria are also useful in silage making which involves the preservation of pasture crops for future use.
- Bacteria are useful in the curing or ripening of tobacco leaves
Harmful Effects
- Materials like wood, paper, textiles, rubber and metals are destroyed by microbes
- Bacteria cause decay and spoilage of food items
- They cause diseases of different types
- Micro-organisms can also cause the death of plants and animals
Disease-Causing Micro-Organisms
There are 4 types of microbes (micro-organisms) that cause diseases
- Bacteria: Not all bacteria cause disease; some are very useful “in nature”. When bacteria infect the body, they can reproduce quite fast. Often they produce chemicals called toxins which have the actual effect which causes an illness. Bacteria can usually be killed by antibiotics such as penicillin.
- Fungi: Not all fungi cause disease; some are very useful “in nature”.
- Virus: Viruses are inactive when outside of a living cell, but once their nucleic acid is inside they take over the cell’s activities. Usually they make many copies of themselves inside the cell, then break out of the cell and infect others. Viruses cannot be killed by antibiotics such as penicillin.
- Protozoa: generally single celled organisms with true nuclei and a cell membrane, so they are quite like our body cells.
Micro-organisms can spread or transmit diseases through the following ways:
- Food and Water
- Air
- Animal Vectors
- Personal or direct skin contact
Food and water borne diseases
| Disease | Pathogen | Symptoms | Transmission | Treatment/ control |
|---|---|---|---|---|
| Cholera | Vibrio Cholerae | Watery diarrhea, vomiting, leg cramps | flies, food , Faeces | Personal hygiene |
| Food poisoning | Salmonella spp | diarrhea, stomach pain or cramps, nausea, vomiting, and fever | Infected meat, Poultry, eggs, milk and contaminated food | resolves without treatment. Ensuring adequate hydration is important |
| Diarrhoea | Giardia intestinalis | A sore throat, hoarseness, painful swallowing, swollen glands (enlarged lymph nodes) in your neck, thick, difficulty breathing or rapid breathing | Contact | Use antibiotics and avoid contacts |
| Typhoid | Salmonella Typhi | Abdominal tenderness, agitation, bloody stools, chills,confusion, difficulty paying attention, fluctuating | Flies, food etc | Treat water before drinking. Maintain personal hygiene |
| Amoebic dysentery | Protozoan (Entamoeba histolytica) | Abdominal pain, heavy vomiting and diarrhea | Food and water | antibiotics and IV fluids |
| Bacillary dysentery | Bacterium (shigella dysenteriae) | severe diarrhea, fever, stomach pain, nausea and vomiting | Water and food | fluid intake, rehydration solutions, IV fluids and antibiotics |
| Poliomyelitis | Polio Virus or Enterovirus | Fever, sore throat, headache, vomiting, fatigue, back pain or stiffness, neck pain or stiffness, pain or stiffness in the arms or legs | houseflies, food and water | Good hygiene and appropriate medication |
| Hepatitis A | hepatovirus A | Fatigue, jaundice, abdominal pain, nausea | contaminated water and food | Supportive care, rest, rehydration, and vaccination for prevention |
Air-borne Diseases
| Disease | Pathogen | Symptoms | Transmission | Treatment/ control |
|---|---|---|---|---|
| Common Cold | Rhino Virus | Cough, runny nose, shivering, etc | Contact | Taking appropriate medications |
| Tuberculosis | Mycobacterium tuberculosis | Malaise, weight loss, and night sweats | Bacteria transmission by cough | Isolate patients and use appropriate antibiotics |
| Whooping cough | Hameophilius Pertussis | Cough, whooping sound during breathing | coughing and sneezing | Isolate patients and use appropriate antibiotics |
| Smallpox | Variola Virus | High fever, vomiting, fatigue, backache, a raised spotted rash, etc | Contact | Take appropriate medication and avoid contact |
| Measles | Measles virus (ParaMyxoVirus) | A high temperature, sore eyes (conjunctivitis), runny nose, small white spots, dry coughs,tiredness, aches, pains, vomiting | Contact | Take appropriate medication and avoid contact |
| Pneumonia | Diplococcus pneumonia | High fever, shaking chills, cough with phlegm (a slimy substance) which doesn't improve or worsens, shortness of breath, chest pain when you breathe or cough | bacteria transmission by contact | Use of antibiotics and avoidance of contact |
| Chickenpox | Varicella Virus | Fever, tiredness, and an itchy, blistery rash | Contact | Isolate patient and use appropriate drugs |
Vector spread diseases
| Disease | Pathogen | Symptoms | Transmission | Treatment/ control |
|---|---|---|---|---|
| Malaria | Plasmodium | chills, headache,muscle aches, tiredness, nausea, vomiting and diarrhea | Bite from female Anophelex mosquitoes | Use of drugs, insecticides, etc. |
| Dengue | Dengue Virus (arbovirus) | Severe headache, severe eye pain (behind eyes), joint pain, muscle pain | Aedes Mosquito | Drain the water and clear the bushes around |
| Rabies | Rhabdovirus | Fever, cough, sore throat, etc | Animal bites | Treat dogs and seek urgent medical attention in cases of bites |
| Sleeping Sickness | Tryponosoma Brucei | drowsiness during the day,fever, headache, insomnia at night, mood changes, sleepiness, sweating, and swollen lymph nodes all over the body | transmission thru fly bites | Use insecticides and take appropriate medication |
sexually transmitted Diseases
| Disease | Pathogen | Symptoms | Transmission | Treatment/ control |
|---|---|---|---|---|
| Gonorrhea | Bacterium (Neisseria gonorrhea) | Inflamed urethra, burning sensation during urination, and a thick, yellowish discharge in male. In female, redness around the urinary opening, vaginal discharge or swelling of the vulva. | Sexual intercourse | Antibiotics |
| Syphilis | Treponema pallidum | A small painless sore or chancre appears on the penis or vulva. A mild fever, skin rashes, mouth ulcers and aching pains in the lymph node regions. | Sexual intercourse | Antibiotics |
| AIDS | HIV | High fever, loss of weight, chronic diarrhea, skin rashes, wasting away of muscles | Sexual intercourse, blood transfusion, injection needle | antiretroviral medicines |
| Staphylococcus | Staphylococcus | Itching around private parts, burning sensations around waist in male. In females, there are itching around private parts, burning sensation in waist and stomach, vaginal discharge, irregular menstruation | Sexual intercourse | Antibiotics |