Why obligate anaerobes are killed by free oxygen

Neisseria meningitidis , the causative agent of severe bacterial meningitis , and N. Many obligate anaerobes are found in the environment where anaerobic conditions exist, such as in deep sediments of soil, still waters, and at the bottom of the deep ocean where there is no photosynthetic life.

Anaerobic conditions also exist naturally in the intestinal tract of animals. Obligate anaerobes, mainly Bacteroidetes , represent a large fraction of the microbes in the human gut.

Transient anaerobic conditions exist when tissues are not supplied with blood circulation; they die and become an ideal breeding ground for obligate anaerobes. Another type of obligate anaerobe encountered in the human body is the gram-positive, rod-shaped Clostridium spp. Their ability to form endospores allows them to survive in the presence of oxygen.

One of the major causes of health-acquired infections is C. Prolonged use of antibiotics for other infections increases the probability of a patient developing a secondary C. Antibiotic treatment disrupts the balance of microorganisms in the intestine and allows the colonization of the gut by C. Other clostridia responsible for serious infections include C. In both cases, the infection starts in necrotic tissue dead tissue that is not supplied with oxygen by blood circulation.

This is the reason that deep puncture wounds are associated with tetanus. When tissue death is accompanied by lack of circulation, gangrene is always a danger. The study of obligate anaerobes requires special equipment.

Obligate anaerobic bacteria must be grown under conditions devoid of oxygen. The most common approach is culture in an anaerobic jar Figure 3. Anaerobic jars include chemical packs that remove oxygen and release carbon dioxide CO 2. An anaerobic chamber is an enclosed box from which all oxygen is removed. Gloves sealed to openings in the box allow handling of the cultures without exposing the culture to air Figure 3. Figure 3. Staphylococci and Enterobacteriaceae are examples of facultative anaerobes.

Staphylococci are found on the skin and upper respiratory tract. Enterobacteriaceae are found primarily in the gut and upper respiratory tract but can sometimes spread to the urinary tract, where they are capable of causing infections. It is not unusual to see mixed bacterial infections in which the facultative anaerobes use up the oxygen, creating an environment for the obligate anaerobes to flourish. Examples of aerotolerant anaerobes include lactobacilli and streptococci, both found in the oral microbiota.

Campylobacter jejuni , which causes gastrointestinal infections, is an example of a microaerophile and is grown under low-oxygen conditions. The optimum oxygen concentration , as the name implies, is the ideal concentration of oxygen for a particular microorganism.

The lowest concentration of oxygen that allows growth is called the minimum permissive oxygen concentration. The highest tolerated concentration of oxygen is the maximum permissive oxygen concentration.

The organism will not grow outside the range of oxygen levels found between the minimum and maximum permissive oxygen concentrations. Figure 4. This clinical photo depicts ulcers on the foot of a diabetic patient.

Dead tissue accumulating in ulcers can provide an ideal growth environment for the anaerobe C. Charles is a retired bus driver who developed type 2 diabetes over 10 years ago. Since his retirement, his lifestyle has become very sedentary and he has put on a substantial amount of weight. Because the sore did not bother him much, Charles figured it could not be serious until his daughter noticed a purplish discoloration spreading on the skin and oozing Figure 4. When he was finally seen by his physician, Charles was rushed to the operating room.

His open sore, or ulcer, is the result of a diabetic foot. The concern here is that gas gangrene may have taken hold in the dead tissue. The most likely agent of gas gangrene is Clostridium perfringens , an endospore-forming, gram-positive bacterium. It is an obligate anaerobe that grows in tissue devoid of oxygen.

Since dead tissue is no longer supplied with oxygen by the circulatory system, the dead tissue provides pockets of ideal environment for the growth of C. The wound will have to be surgically debrided debridement refers to the removal of dead and infected tissue and a sample sent for microbiological lab analysis, but Charles will not have to have his foot amputated.

Many diabetic patients are not so lucky. In , nearly 70, diabetic patients in the United States lost a foot or limb to amputation, according to statistics from the Centers for Disease Control and Prevention.

Aerobic respiration constantly generates reactive oxygen species ROS , byproducts that must be detoxified. Even organisms that do not use aerobic respiration need some way to break down some of the ROS that may form from atmospheric oxygen. Three main enzymes break down those toxic byproducts: superoxide dismutase, peroxidase, and catalase. Each one catalyzes a different reaction. Reactions of type seen in Reaction 1 are catalyzed by peroxidases. In these reactions, an electron donor reduced compound; e.

The enzymes play an important role by limiting the damage caused by peroxidation of membrane lipids. Reaction 2 is mediated by the enzyme superoxide dismutase SOD and breaks down the powerful superoxide anions generated by aerobic metabolism:. Figure 5. The catalase test detects the presence of the enzyme catalase by noting whether bubbles are released when hydrogen peroxide is added to a culture sample.

Compare the positive result right with the negative result left. Go over terms on page Tortora, Funke and Case. If you mix the bacteria with a lethal agent you get a progressive reduction in the number of survivors. Lysol, phenol carbolic acid , coal tar distillates Ichthamol , hexachlorophene. All are powerful disinfectants. Also a dehydration effect denatures proteins. Good for washing skin. Kills vegetative bacterial cells and enveloped viruses well. Not effective on endospores and non-enveloped viruses.

Silver sulfadiazine is also used on burn patients. Used in paint and used to treat swimming pools and fish tanks. Toxic to invertebrates. Chlorine widely used as a disinfectant to treat water and in dairy industry. Two to four drops of chlorox per liter of water will disinfect the water after 30 min.

Obligate aerobes and most facultative anaerobes have both superoxide dismutase and catalase. Some facultative and aerotolerant anaerobes have superoxide dismutase but lack catalase.

Most obligate anaerobes lack both enzymes. Last updated on June 21st, This bacterial growth curve reflects the events in bacterial population when they are grown in a closed system of microbial culture of fixed volume i. The typical […]. Last updated on June 21st, Microbes are loosely classified into several groups based on their preferred temperature ranges. Every organism has a range of permissive growth temperatures.

Unlike pH or osmolarity, microbes cannot regulate […]. Last updated on May 24th, pH scale is used to express the acidity or alkalinity of a solution on which neutrality is pH 7. The pH scale extends from pH 0. A question. Microaerophilic why they need low oxygen concentration?.

The high concentration of oxygen how it affects the microaerophils? I cannot ferment, but it can grow in lack of O2 if NO3 is available. A facultative anaerobe by definition is an organism that grows best in oxygen present environments, but can still grow in a lack of oxygen by utilizing fermentation.

So, since P. Why is Sexually Transmitted Bacteria for Mycology test be put inside the oxygen incubator but not in room temperature? Hi sir , nice details, my q is if u know a person who can write chemical reactions means phd chemistry. This site uses Akismet to reduce spam. Learn how your comment data is processed.

News Ticker. Contents 0. In a culture tube containing nutrient broth, obligate aerobes grow near the surface; where atmospheric oxygen diffuses into the medium; obligate anaerobes grow near the bottom of the tube, where little or no free oxygen reaches them.

Basic classification of Medically Important Bacteria. Factors affecting microbial growth.