Examples of bacteria in everyday life include Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Bacteria are single-celled organisms that are too small to see without a microscope, yet they surround us and are inside our bodies. Here’s a closer look at some of the bacteria we encounter in daily life, their characteristics, and the diseases they sometimes cause.
Normal Flora
Many of the bacteria we encounter everyday have a commensal or mutualistic symbiotic relationship with humans. That is, they either do no harm or else provide us with some benefit in exchange for food and a comfortable environment in which to live. These bacteria are part of the normal flora of the body. Examples include Staphylococcus aureus on human skin and Escherichia coli in the gut. Usually, the normal flora co-exists peacefully with us, but an injury or a problem with the immune system can lead to an infection.
Types of Bacteria
In order to distinguish between bacteria encountered everyday, it helps knowing the main types of bacteria. One way of classifying bacteria is by their shape.
- Spherical: Round or spherical bacteria are called cocci (singular bacterium is a coccus). Typically, the bacterium’s name includes its shape. For example, Streptococcus and Staphylococcus are two groups of bacteria with spherical cells.
- Rod: Rod-shaped bacteria are called bacilli (singular bacillus). Examples include species that include the shape in their names, such as Bacillus and Lactobacillus, and other bacteria, such as Escherichia and Pseudomonas.
- Spiral: Spiral or corkscrew-shaped bacteria are spirilla (singular spirillus) or spirochetes. For the most part, spiral bacteria are not part of the normal flora of the human body. They do cause diseases, however, such as Lyme disease (Borrelia sp.) and syphilis (Treponema pallidum).
Another way of categorizing bacteria is according to their response to the Gram stain. The Gram stain is a protocol that stains bacteria different colors according to the chemistry of their cell wall. Gram-positive bacteria stain purple because their cell walls have a thick coating of peptidoglycan that holds the stain crystal violet. Gram-negative bacteria stain pink (the color of the counterstain) because they lack this layer of peptidoglycan and don’t retain the purple color of crystal violet. Staphylococcus and Streptococcus are examples of Gram-positive cocci. Neisseria is an example of a group of Gram-negative cocci. Escherichia and Pseudomonas are Gram-negative bacilli. Bacillus and Clostridium are Gram-positive rods.
Other ways of classifying bacteria include whether or not they form spores or capsules, whether they are aerobic or anaerobic, whether they produce the enzyme catalase, and whether they contain the enzyme coagulase. Microbiologists and doctors use tests that group bacteria according to their characteristics to predict which environments are suitable for growing certain bacteria and identifying antibiotics for successfully treating infections.
Examples of Bacteria
Here are some examples of bacteria common in everyday life, where you find them, and diseases they can cause.
- Bifidobacterium: Bifidobacterium is a group of Gram-positive gut bacteria. These bacilli are probiotic and don’t typically cause disease. However, some people are allergic to certain species.
- Escherichia coli: E. coli is a Gram-negative, facultatively anaerobic rod that lives in the large intestine of warm-blooded animals. The particular strain that lives in your gut is beneficial and helps produce vitamin K2. However, eating food contaminated with a different strain results in food poisoning. This occurs when food is contaminated with fecal matter.
- Lactobacillus acidophilus: Lactobacillus is a Gram-positive bacillus. This species is part of the normal gut flora of humans and other animals. It also occurs in fermented foods and acts as a probiotic when ingested. Lactobacillus is almost always a “friendly” kind of bacteria, but it can cause dental caries (cavities), endocarditis, meningitis, and abscesses when it colonizes other parts of the body besides the intestines.
- Pseudomonas aeruginosa: P. aeruginosa is a capsule-forming, anaerobic Gram-negative bacillus. It lives in skin, water, soil, and on surfaces, where it isn’t normally harmful. However, it’s an opportunistic organism that causes disease in both animals and plants when given a chance. In humans, it is a significant cause of hospital-acquired infections, including sepsis and pneumonia. It resists a variety of drugs, so infections are challenging to treat.
- Staphylococcus aureus: S. aureus is a Gram-positive coccus. These bacteria live on the skin and help defend against pathogenic organisms. However, they can cause Staph infections when they colonize wounds, including MRSA (Methicillin-resistant Staphylococcus aureus) infections.
- Streptococcus mutans: S. mutans is another Gram-positive coccus. This species lives in the mouth and is a significant cause of tooth decay.
References
- Eleyan, L.; Khan, A.A.; et al. (2021). “Infective endocarditis in paediatric population”. European Journal of Pediatrics. 180 (10): 3089–3100. doi:10.1007/s00431-021-04062-7
- Martin, M.O. (2002). “Predatory Prokaryotes: An Emerging Research Opportunity”. Journal of Molecular Microbiology and Biotechnology. 4 (5): 467–77.
- Pommerville, J.C. (2014). Fundamentals of Microbiology (10th ed.). Boston: Jones and Bartlett. ISBN 978-1-284-03968-9.
- Wheelis, M. (2008). Principles of Modern Microbiology. Sudbury, Mass: Jones and Bartlett Publishers. ISBN 978-0-7637-1075-0.