2025.04.20
Concept of bacteria
Bacteria are microscopic living organisms that have only one cell (the smallest unit of life). The word used to refer to one type of bacteria is Bacterium, while Bacteria generally refers to a collection of single-celled microbes. The word bacteria is derived from the Greek word Backerion, meaning stick, because the first bacteria observed were bacillus-shaped (rod-shaped). There are millions or perhaps billions of different types of bacteria, many of which live in various environments, including the human body.
Coliform bacteria
The name Coliform bacteria is a combination of two parts: Coli, which refers to the natural habitat of these bacteria in the digestive tract of mammals, especially the large intestine or colon, and form, meaning shape. This led to this group of bacteria being named this way. Since their discovery in the late nineteenth century by Theodor Escherich, coliform bacteria have been recognized as one of the most important indicators of microbial contamination in water and food. In 1885, Theodor Escherich, a German physician and microbiologist, first found Escherichia coli in the feces of healthy people and named it Bacterium coli commune. He described this bacterium as part of the normal flora (a collection of microscopic organisms such as bacteria, fungi, etc. that naturally live in parts of the body) of the digestive system and showed that some of their strains (a strain refers to a group of bacteria that are distinguished from each other based on specific characteristics such as bacterial type, growth pattern, and physiological characteristics such as metabolism or production of specific compounds) can become pathogenic in certain conditions such as a weakened immune system, stress and anxiety, increased numbers or changes in the microbial environment of the intestine, etc. Then, in 1895, Migula named this bacterium Bacillus coli, and later, in honor of Theodor Escherich, it was named E. coli. Coliform bacteria are defined as aerobic or facultative anaerobic, gram-negative (gram-negative is a type of bacteria that appears red when gram-stained), non-spore-forming (a spore is a resistant form of a bacterium that survives in conditions such as heat, reduced humidity, dryness, nutrient deficiency, etc.), rod-shaped, often flagellated, and motile microorganisms. Four genera, Citrobacter, Enterobacter, Klebsiella, and Escherichia, are the most important and common genera of coliform bacteria belonging to the Enterobacteriaceae family. These genera, due to their specific characteristics and higher prevalence, are of particular importance in the coliform group and studies related to fecal and sanitary contamination. In the 1960s, the name coliform bacteria was changed to total coliform in the United States.
Total coliform
Total coliform includes all bacteria that can ferment lactose (a natural sugar found in milk and dairy products) at 35 to 37 degrees Celsius and produce acid and gas. This group of bacteria is usually found in water, soil, plant surfaces, food, and the digestive tract of animals and is an overall indicator of environmental microbial contamination (such as water, soil, etc.). If these bacteria are found in drinking water, their presence does not necessarily mean that the drinking water is dangerous for human consumption; however, the presence of these organisms in drinking water should be investigated because it may indicate contamination and the possibility of other pathogenic microorganisms such as pathogenic strains of E. coli. The genus Enterobacter from total coliform, in addition to the intestine, exists in environments such as soil, water, plant surfaces, food, etc., and has two known species, E. aerogenes and E. cloacae. Other genera of this group include Citrobacter. Known species of this genus include C. freundii and C. koseri, which are found in various environments such as soil, water, food, human and animal intestines. Another genus belonging to total coliform is Klebsiella, which is found in the environment, food, the bodies of living organisms, etc. Two common species of this genus are K. pneumoniae and K. oxytoka.
Fecal coliform
Fecal coliform is a subset of total coliform bacteria that are usually found in the digestive tract (intestines) of warm-blooded organisms and are excreted through the feces of humans and warm-blooded animals. Their presence in drinking water sources indicates water contamination with fecal matter and may therefore be a threat to human health. This group of bacteria grows at 44.5 to 45.5 degrees Celsius (this temperature promotes the growth of fecal coliform bacteria and inhibits the growth of other total coliform bacteria and is specific for identifying fecal coliform) and produces acid and gas within 48 hours of lactose fermentation. E. coli is the most famous member of fecal coliform and is considered a specific indicator of fecal contamination. The presence of even small amounts of it indicates dangerous contamination. Not all E. coli strains are pathogenic, but some are a serious threat to human health. The presence of E. coli in a drinking water sample usually indicates fresh fecal contamination. A pathogenic strain of E. coli that has been widely studied is O157:H7.
Sources of coliform bacteria
Coliform bacteria can originate from various sources, including sewage or non-fecal contamination. This variety of sources indicates that coliforms can indicate different contamination indicators. The most common sources of contamination include:
- Human and animal sewage: Sewage from human and animal activities is the main source of fecal coliform and can be dangerous.
- Soil: Many non-fecal coliforms are naturally found in soil. These microorganisms live in moist environments rich in organic matter and unrelated to animal feces, such as soil, fresh water, and plants, and usually pose less risk to human health. These coliforms are usually known as environmental coliform and are different from fecal coliform that originates from the intestines of warm-blooded animals.
- Food: Foods that are more at risk of contamination with coliforms include fresh agricultural products, especially vegetables and fruits due to direct contact with soil and water, milk and other dairy products if not properly pasteurized, red meat and poultry due to contact with animal intestines during slaughter, etc.
- Contaminated surface and groundwater: Water sources such as rivers, lakes, and shallow wells may be contaminated with coliforms. This contamination usually occurs due to human sewage leaks, agricultural runoff, etc.
- Industrial and agricultural sources: Industrial and agricultural activities can lead to the entry of coliforms into the environment. The use of industrial wastewater such as wastewater from food industries, meat industries, slaughterhouses (possibility of contact with fecal matter and animal residues), etc., without proper treatment can contain coliform bacteria and contaminate water and soil sources. In addition, the use of animal manure in agriculture can be a major source of coliform contamination. When these fertilizers are added to the soil from animals contaminated with coliform bacteria, coliforms can easily penetrate groundwater or be transferred to surface water sources through rainfall. Irrigating farms with water contaminated with sewage or water sources containing coliforms can also lead to contamination of agricultural products and soil.
Prevalence of diseases caused by coliform bacteria
The prevalence of diseases caused by coliform bacteria usually increases during warm seasons, especially summer, which may be due to the following reasons:
- Increased temperature: In warm seasons, the temperature of water and aquatic environments (rivers, pools, etc.) increases significantly. This condition is more suitable for the growth of bacteria, including coliforms.
- More rainfall and runoff: In some areas, heavy rainfall and floods are more common in summer. In addition, surface runoff that passes through agricultural areas, residential areas, or livestock farms can transfer coliform bacteria to drinking water sources.
- Increased human contact with water sources: In summer, water activities such as swimming, fishing, and agriculture increase. This increases the likelihood of contact with water sources contaminated with coliform bacteria.
Health problems caused by coliform bacteria
Total coliform bacteria are not directly a direct threat to human health, and most of their species are non-pathogenic. However, some specific strains can cause serious and even fatal diseases by producing dangerous toxins. One of the most well-known species of coliform is E. coli, which is widely found in water and food. While many strains of this bacterium are harmless, Shiga toxin-producing E. coli or Verotoxin-producing E. coli strains can lead to serious diseases in humans. One of the strains that produces Shiga toxin and may pose significant risks to human health is the O157:H7 strain. Shiga toxin can cause dangerous complications such as blockage of small blood vessels, destruction of blood cells, organ dysfunction, kidney failure, severe diarrhea (sometimes bloody), nausea, vomiting, jaundice, headache, fatigue, infection of various organs such as the lungs, etc.
Vulnerable groups
High-risk groups include children under 5, the elderly, pregnant women, and people with weakened immune systems, such as patients with cancer, diabetes, patients undergoing organ transplantation, etc., who show the highest vulnerability to infections caused by pathogenic coliform strains. These groups may face more serious consequences if infected.
Importance of coliform bacteria in the food iundustry
Coliform bacteria belonging to the genera Escherichia and others are used as indicators of sanitary conditions during food processing. Because coliform bacteria are usually found in water sources and food, to ensure the quality of raw materials and water used, their number in food products can be used as a warning to identify microbial contamination, and the presence of these bacteria may indicate contamination from human or animal sources. One of the key aspects of food quality control is monitoring the level of microbial contamination. Controlling the number of coliform bacteria during food production and storage, especially in dairy industries including the production of various products such as milk, yogurt, cheese, butter, etc., meat including the processing and production of various meat products such as red meat, poultry, sausages and bologna (meat contamination usually occurs due to contact with animal feces during slaughter or packaging), beverages including the production of various beverages including mineral water, carbonated drinks, fruit juices, etc., is essential to ensure the safety and quality of the final product. For example, according to the Iranian National Standard No. 2406, entitled Microbiology of Milk and Its Products - Characteristics and Test Methods, the maximum probable number of coliform bacteria in each milliliter of milk is 10, and it is negative for E. coli. In addition, according to National Standard No. 1011, Microbial Characteristics of Drinking Water, neither thermotolerant (heat-resistant) coliforms nor E. coli should be detectable in 100 milliliters of water. According to National Standard No. 5690, Peanut Butter - Characteristics and Test Methods, the maximum colony (a collection of identical bacteria) of coliform bacteria in peanut butter is 10 units per gram of peanut butter, and it is negative for E. coli. Or, according to National Standard 10080, Pre-Packaged Fresh-Cut and Frozen Ready-to-Eat Vegetables - Characteristics and Test Methods, the number of coliform bacteria colonies is 100 units per gram, and E. coli is considered negative.
Providing solutions to prevent contamination from coliform bacteria at home
To prevent contamination from coliform bacteria at home, observing some measures can help maintain the safety and quality of water and food:
1- Washing hands before preparing food, after contact with raw meat or pets, etc., is one of the most effective ways to prevent the transmission of coliform bacteria. For proper handwashing, spend at least 20 seconds.
2- To ensure food safety, especially for meats that are more likely to be contaminated (especially ground meat), cook them thoroughly, and it is best to avoid consuming undercooked meat.
3- To prevent the transfer of bacteria from one surface to another, use separate cutting boards for raw meat and vegetables, and after use, wash and disinfect all tools and surfaces that came into contact with raw meat.
4- Wash and disinfect fruits and vegetables thoroughly before consumption, especially those that are consumed raw.
5- If you suspect the quality of your drinking water, boiling water is one of the simplest and most effective ways to kill bacteria. Water should be boiled for at least 1 to 3 minutes to kill pathogenic bacteria.
6- Home water purification filters, such as reverse osmosis filters, can improve water quality by removing some bacteria, etc.