Bacteria are responsible for 80% of all food poisoning outbreaks.
So what effects do pathogens have on food? Do they affect the colour, taste, texture and appearance? Actually, food which is contaminated with food poisoning bacteria smells looks and tastes normal. Therein lies the problem, we do not know we have eaten contaminated food until it is too late. The type of bacteria that affect the taste, colour, smell and texture of food are known as spoilage bacteria. Spoilage bacteria affect food in the following way: Discolouration, texture change, off odours, damage to packaging, unusual taste, mould growth, slime and stickiness and the production of gas such as carbon dioxide or hydrogen. If these gases occur inside a sealed can they are classed as blown cans, which means the bulging of cans due to the increase in gas. You can also have blown packs such as bag in the box wine which can expand to the size of a large football. What are bacteria, where do they come from, how to they interact with us? Bacteria are living organisms, much like us. Humans are living organisms, bacteria are a lot smaller, in fact they are microscopic, you can only see them with the aid of a microscope. Bacteria are very similar to us; some scientists say we have evolved from bacteria. Their cellular processes and cellular contents are very similar to ours. Bacteria are found everywhere. The four major areas to find bacteria are:
- On and in the soil
- Water supplies
- Faeces
- Raw meat.
The major depository of bacteria on the planet is soil. The majority of bacteria are harmless. Without many microorganisms we would not be able to survive. Bacteria have many generic names including pathogenic bacteria, pathogens, and germs. These three names apply to bacteria that cause illness. Pathos is the Greek word for illness and therefore pathogens and pathogenic apply to bacteria that cause illness. Microorganisms and microbes apply to all bacteria, good and bad. When the Earth formed 4.6 billion years ago, the environment was far too hostile for any life to form. But as the Earth cooled it has been hypothesised and theorised (although nobody will ever know the answer) that life formed from the primordial soup that was flowing on the Earth’s surface.
How did this happen? Again, it can only be surmised that a chemical explosion occurred which brought together vital elements that fused to form life. Scientists in the 1950s conducted experiments which combined heated water and air and electricity to mimic conditions thought to exist when the Earth was cooling. The experiment concluded with the production of 5 amino acids, the building blocks of proteins and life. In 2008 a similar experiment was undertaken, but this time a further element was introduced, steam. These conditions were thought to mimic volcanoes erupting. The experiment resulted in the synthesis of 20 amino acids. That are all the amino acids in existence. During pre-life did the amino acids form proteins and did the proteins combine to form life?
It is thought that microbes have been around for 3.8 billion years and further life such as plants developed from the fusion of Amoeba and Cyanobacteria 1.9 billion years ago. Multicellular organisms are believed to have developed 630 million years ago. Organisms made the transition from sea to land 3.2 billion years ago. Some scientists think that life existed on Mars, many billions of years ago and came to Earth by way of meteorites and fused with terrestrial proteins to form life. Did we really come from Mars? We will never know. Some scientists believe that all life developed from bacteria, with fusion and mutation continually playing vital roles in the evolutionary process. They have reached this conclusion due the remarkable similarity between cells and cellular processes in bacteria, plants and animals. The tree of life splits all living organisms into 3 groups:
- Bacteria
- Archaea
- Eukarya.
Humans and other animals come under the Eukarya branch. There are more microbes than stars in the universe, so it has been suggested. Bacteria are ubiquitous, they are found in and on humans, in the soil, water and atmosphere. Dust clouds contain many species of bacterial and viral particles responsible for causing diseases such as meningitis, coral farm disease, pneumonia, septic shock, inflammation of the heart, sars, influenza, valley fever and foot and mouth. Whenever you are ready to take a shower, let it run for a minute before stepping in or risk getting a face full of bacteria. Scientists have found large numbers of Mycobacterium avium in the shower faucets. These bacteria cause respiratory diseases similar to TB. Two other strains of these bacteria actually cause TB and leprosy. Humans, along with other species, possess vast amounts of symbiotic bacteria in and on their bodies. Our skin, for example, is home to over 180 different species of bacteria and fungi. The majority of skin micro-flora is concentrated around our sweat glands, such as the underarms, genitalia, nipples and navel. Half of all these bacteria mainly belong to the genera Streptococcus, Corynebacterium, Staphylococcus and Propionibacterium (a species of which causes acne). Staphylococcus aureus are commensal bacteria which are part of the natural microflora of humans (and other animals). Any microbes which are not part of our natural flora are called transients. S aureus releases molecules which prevent skin cells from releasing chemicals that cause the inflammatory response. Although the inflammatory response is crucial to aid recovery from injury, too much, prolonged inflammation can cause skin diseases such as psoriasis.
There are 17 known genera of bacteria known to belong to the Bacterial Phylogenetic Tree. Each genus (genera = plural) can have many different species. Salmonella is a genus; there are over 2,500 known species of Salmonella, for example S typhi. The amount of bacteria present on the skin depends on several factors including the weather, age of host (young children harbour more bacteria, especially pathogens, than adults) and personal hygiene. The mouth does not harbour any micro-flora, due to the anti-bacterial qualities of lysozyme, a constituent of saliva. However, if one has poor dental hygiene, allowing the build-up of plaque, then transient bacteria can inhabit and grow. Plaque is a very good growth medium for several different genera of bacteria, causing such disorders as dental caries, gingivitis and periodontal disease. The gastrointestinal tract (GI) is a single long tube running from the mouth to the anus. It starts at the mouth. Between the oesophagus and anus there are up to 30 different species of bacteria present. Some studies have shown a bacteria cell count of 1014 in the GI tract. That is a lot of bacteria, considering that 106 is a million! The bacteria are responsible for:
- Steroid metabolism (modifying steroids released from the gall bladder after synthesis in the liver. The modified steroids are then absorbed by the gut)
- Synthesis of vitamins such as B1, B2, B6, B12 and K
- Breakdown of fibre (the digestible elements)
- Production of gas such as methane, hydrogen and carbon dioxide. Without bacteria present, we would not be able to digest food. The upper respiratory tract (sinuses – larynx) of a healthy individual contain many micro-flora. The lower respiratory tract (trachea – lungs) should contain few, if any. The uro-genital tract in both male and females contain a few resident bacteria. Urine is held in a sterile environment in the bladder. The bacteria inhabit the urethra. One such species, Lactobacillus acidophilus, is a resident of the vagina, where it ferments glycogen, releasing lactic acid. The acidic condition prevents disease, caused by pathogens, from developing. The body supports a diverse range of bacteria in many different environmental and nutritional conditions. The range depends on the diet (carnivores have a different range of bacteria compared to vegetarians) and the different physical conditions of the various anatomical areas. Where do these micro-organisms come from, since we develop in utero, in a sterile environment? The bacteria start to inhabit us as soon as we are born.
Escherichia coli are one species of our symbiotic bacteria. They are responsible for synthesising Vitamin K. Vitamin K is a blood clotting co-factor and is responsible for preventing us from bleeding to death if we sustain a cut or injury. It is one essential species that we can ill afford to be without. In developing countries, E coli inhabit the gut several days after birth, in developed countries it can take several months.
S aureus is more likely to inhabit the guts of individuals in developed countries before E coli. This is because it depends on the locality, environmental conditions and diet. It has been discovered that some bacteria can cause rain! They secrete chemicals which act as surfactants (detergents), causing rain to develop from clouds. Perhaps this is a self-survival mechanism, developed from the past as a way of helping them to combat dehydration.
Bacteria can be very environmentally resistant, especially extremophiles. Polaromonas vacuolata is a psychrophile, which grows optimally at 4°C. The “Lazarus Bug” was recently brought back to life after hibernating for 120,000 years under 3 Km of ice.
Most bacteria are mesophiles, which includes the majority of pathogens and our symbiotic bacteria. These prefer to grow at body temperature (37°C).
Pyrolobus fumarii prefers to grow at 106°C, that’s higher than the boiling point of water! These conditions are found near hydrothermal vents on the sea bed, where temperatures exceed 350 degrees Celsius.
Bacteria such as Thermus aquaticus, which are commonly found in hot springs, survive at temperatures of 80°C. Scientists have found this organism very interesting and have extracted an enzyme, Taq Polymerase, for studies involving heat resistant enzymes.
Halophiles are bacteria that can survive in high concentrations of salt.
Barophiles exist in high pressure environments, for example in deep sea.
Xerophiles exist in very dry conditions.
Acidophiles prefer an acidic environment, where most bacteria prefer a neutral pH Alkaliphiles opt for the more alkaline surroundings.
It has been suggested that when the Earth formed, 4.6 billion years ago, no life existed until the temperature of the cooling planet was such as to warrant life proliferation. It is also believed that conditions during the first evolution of life was anoxic and could not support oxygen breathing organisms. Bacteria must therefore have started out as anaerobes (living without oxygen). As oxygen became more readily available from the cyanobacteria photosynthesising carbon dioxide to produce oxygen and the evolution of plants, bacteria once again adapted. As there was little oxygen to start with they probably developed as facultative microbes (can survive with or without oxygen). Micro-aerophiles are bacteria, for example, Campylobacter, that require small amounts of oxygen (about 5%). Aerobic bacteria can only survive in oxygen.