Microbes cause infectious diseases such as flu and measles. There is also strong evidence that microbes may contribute to many non–infectious chronic diseases such as some forms of cancer and coronary heart disease. Different diseases are caused by different types of micro-organisms.
Bacteria that require oxygen to grow are called obligate aerobic bacteria. In fact, the presence of oxygen actually poisons some of their key enzymes. Some bacteria (S. pneumoniae) are microaerophilic or aerotolerant anaerobes because they grow better in low concentrations of oxygen.
Most bacteria grow best around neutral pH values (6.5 - 7.0), but some thrive in very acid conditions and some can even tolerate a pH as low as 1.0. Such acid loving microbes are called acidophiles.
Anaerobic habitats often have low pH and high concentrations of fermentation acids, and these conditions can inhibit the growth of many bacteria. The toxicity of fermentation acids at low pH was traditionally explained by an uncoupling mechanism.
Generally,an increase in temperature will increase enzyme activity. But if temperatures get too high, enzyme activity will diminish and the protein (the enzyme) will denature. Every bacterial species has specific growth temperature requirements which is largely determined by the temperature requirements of its enzymes.
E. coli O157:H7 has the ability to survive in acidic conditions (pH, > or = 4.0) for up to 56 days, but survival is affected by type of acidulant and temperature.
What bacteria need to grow and multiply
- Food (nutrients)
- Water (moisture)
- Proper temperature.
- Time.
- Air, no air, minimal air.
- Proper acidity (pH)
- Salt levels.
FAT TOM is a mnemonic device used in the food service industry to describe the six favorable conditions required for the growth of foodborne pathogens. It is an acronym for food, acidity, time, temperature, oxygen and moisture.
One of the most critical factors for microbial growth is the availability of nutrients and energy. Microbes need carbohydrates, fats, proteins, metals, and vitamins to survive, just like animals. The process of using nutrients and converting them into cellular material requires energy.
Conditions needed for bacterial growth
- Moisture – Bacteria need moisture in order to grow.
- Food – Food provides energy and nutrients for bacteria to grow.
- Time – If provided with the optimum conditions for growth, bacteria can multiply to millions over a small period of time via binary fission .
Bacteria are all around us, including those that can cause food poisoning. Food poisoning bacteria grow best at temperatures between 5°C and 60°C. This is called the Temperature Danger Zone. Keeping potentially hazardous foods cold (below 5°C) or hot (above 60°C) stops the bacteria from growing.
In order to grow successfully, microorganisms must have a supply of water as well as numerous other substances including mineral elements, growth factors, and gas, such as oxygen. Virtually all chemical substances in microorganisms contain carbon in some form, whether they be proteins, fats, carbohydrates, or lipids.
Pathogens can also be spread by indirect contact when an infected person touches a surface such as a doorknob, countertop, or faucet handle, leaving behind microbes that are then transferred to another person who touches that surface and then touches his or her eye, mouth, or nose.
Every species of microbe has evolved adaptations that enable them to live under specific environmental conditions, which we refer to as their niche. These include oxygen (O2) concentration, temperature, pH, light intensity, radiation, pressure, solute concentration (osmolarity) and water activity.
At lower temperatures molecules move slower, enzymes cannot mediate in chemical reactions, and eventually the viscosity of the cell interior brings all activity to a halt. As the temperature increases, molecules move faster, enzymes speed up metabolism and cells rapidly increase in size.
The word anaerobic indicates "without oxygen." The term has many uses in medicine. Anaerobic bacteria are germs that can survive and grow where there is no oxygen. For example, it can thrive in human tissue that is injured and does not have oxygen-rich blood flowing to it.
How does pH negatively affect the metabolism of microorganisms? causes proteins and enzymes to denature and causing a loss of enzymantic activity. Fermentation produces acids and would lower pH. Urea hydrolysis produces ammonia which would raise pH.
coli bacteria grow best at a near neutral pH of 6-8. They do not grow at a more acidic pH of 4 or 5. The advice to add acids to food appears to be a valid way to prevent the growth of E. coli.
These results affirm that the bacteria subjected to thermal stress at 35°C under slightly acidic environment (pH 6.0) required the highest increase in temperature to obtain the thermal death decimal reduction time.
TCS food supports growth of bacteria better than others this includes meat, poultry, dairy products, and eggs. Bacteria grow best in food that is neutral to slightly acidic (a pH of 7.5 to 4.6). Bacteria grows best in little or no acid.
The conditions affecting the growth of fungi are similar to those affecting bacteria. Both yeasts and molds are able to grow in an acidic environment (pH less than 7). The low pH of fruits is generally unfavourable for the growth of bacteria, but yeasts and molds can grow and cause spoilage in fruits.
What is the maximum pH that the bacteria can sustain in terms of alkalinity? Explanation: Operation outside of the pH range of 7.0 to 8.5 can be toxic to bacteria; however, if the change is gradual the micro-organisms can become acclimated to pH levels slightly beyond this range. 11.
Explain why microorganisms differ in their pH requirements. Differences in pH requirements among microorganisms are dependent upon the susceptibility of their individual enzyme systems due to denaturing at various pH levels. Many fungi grow best in an acidic environment, while soil bacteria may prefer an alkaline pH.
pH is a measure of how acidic/basic water is. The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic.
A bacterium is classified as acid-tolerant if it prefers pH above 5.5, but can grow at pH 5.5 or below, whereas an acidophilic bacterium actually experiences optimal growth at pH 5.5 or below.
Alkaliphiles are able to survive in an alkaline environment because of a membrane system that actively pumps H+ across the cell membrane into their cytoplasm and therefore able to maintain pH of about 8.0. obligate alkaliphiles, i.e. those requiring high pH.
psychrophilic or cryophilic) are extremophilic organisms that are capable of growth and reproduction in low temperatures, ranging from −20 °C to +10 °C. They are found in places that are permanently cold, such as the polar regions and the deep sea.
Acidophiles and chemoautotophic bacteria grow well in an acidic environment, molds and yeasts will to. Most bacteria do not grow well in an acidic environment. 15.
The optimum growth range is about 6.0 to 7.5, but growth can occur slowly at lower or higher pH levels. A pH of 4.6 and below or a pH above 11 will prevent pathogen growth. An example is pickled fish which is produced by adding vinegar to lower the pH and slow down the growth of spoilage and disease causing bacteria.
coli bacteria grow at a near neutral pH between 6.7-7.8. They do not grow or (weak growth) at a more acidic or more alkaline.
Maximum growth occurred over a pH range of 7.38 to 7.87. Cell growth declined precipitously on the alkaline side and more gradually on the acid side of the optimal pH range.
The pH scale ranges from 0 to 14 with ph 7 being neutral. The lower the pH reading, the more acid the food. In order to preserve foods with acidity, the regulation requires the pH to be 4.6 or below. At these levels, toxins formed by the deadly organism causing botulism are inhibited.
