What is Bacteroides Fragilis?
Anaerobes are types of bacteria that don’t need oxygen to survive. They usually come in two types based on their appearance under a microscope – gram-positive or gram-negative, and they can be shaped like spheres (cocci) or rods (bacilli). A few known harmful strains that are rod-shaped and gram-negative include Prevotella, Fusobacterium, Bacteroides, and Porphyromonas.
Among these, the Bacteroides strain is a significant cause of illness and is involved in most infections caused by anaerobic bacteria. The infections from these bacteria are quite serious, with about 19% of infected people not surviving. Bacteroides fragilis, a rod-shaped and gram-negative type, is particularly noteworthy.
Believe it or not, the human colon (part of your digestive system) has the highest number of bacteria in our bodies – over ten organisms for each gram of its weight! A majority of these organisms are anaerobes, and about 25% of them are various forms of Bacteroides, including Bacteroides fragilis, which normally lives in our colon.
However, if the surface of the colon is damaged due to inflammation, injury, or surgery, and Bacteroides fragilis manages to get into the bloodstream or surrounding tissues, it can cause serious infections.
What Causes Bacteroides Fragilis?
The bacteria Bacteroides fragilis is part of our gut’s bacteria, though another bacteria called Bacteroides thetaiotaomicron is more common but doesn’t cause as many infections. We likely get Bacteroides fragilis when we’re born. In the first year of life, a child’s gut bacteria changes a lot and by the time they’re a year old, it starting to look more like an adult’s gut bacteria.
Infections from Bacteroides fragilis usually happen inside the abdomen. If tissue barriers inside our body break, it can result in the spread of this and other bacteria from the gut into surrounding tissue. This leads to an infection caused by multiple types of bacteria. This is why Bacteroides fragilis is rarely the only bacteria causing the infection, it’s usually found with other bacteria like Enterobacteriaceae.
Risk Factors and Frequency for Bacteroides Fragilis
The Bacteroides fragilis bacteria is usually found in the human colon and plays an important role in its health. In a study, 87% of healthy adults were found to have Bacteroides fragilis in their stool samples. Although the bacteria can be beneficial in the colon, if they somehow manage to get past a damaged or compromised lining of the colon, they can cause health problems.
- A medical study from Japan found that about 12.8% of surgical site infections were caused by Bacteroides species.
- In Greece, another study found that people who had undergone recent surgery had an increased risk of getting infected by Bacteroides fragilis. These infections had a mortality rate of 10.9%, especially when associated with bacteremia (bacteria in the blood) or cancer.
- From 1969 to 2012, there were 20 cases of joint infections linked to Bacteroides at Mayo Clinic in Rochester, MN, in 17 different patients.
Signs and Symptoms of Bacteroides Fragilis
Anaerobic infections, including those caused by Bacteroides fragilis, can arise due to various factors. People are more likely to develop these infections after recent surgery, trauma or if they have cancer. The symptoms of an anaerobic infection often include bad-smelling discharge and the formation of abscesses, or swollen areas filled with pus.
Bacteroides fragilis infections can manifest in different ways depending on which part of the body is affected. For instance, this type of bacteria can be found in chronic pressure ulcers and diabetic foot ulcers. Some strains of Bacteroides fragilis can also contribute to inflammatory diarrhea.
Furthermore, Bacteroides fragilis can be involved in severe conditions such as necrotizing fasciitis, which is a rapidly spreading infection that destroys tissue, and blood infections that occur following a transfer of a local infection into the bloodstream. Other cases have linked Bacteroides fragilis to septic abortions and infections of artificial joints.
There’s also a rare chance of encountering Bacteroides fragilis infections that cause inflammation of the heart’s inner lining, also known as endocarditis. This was recorded in a patient with Crohn’s, a type of inflammatory bowel disease. Another unusual clinical scenario involves the development of septic thrombophlebitis of a major abdominal vein.
So the symptoms of Bacteroides fragilis include:
- Foul-smelling discharge
- Formation of abscesses
- Presence in chronic pressure ulcers and diabetic foot ulcers
- Involvement in inflammatory diarrhea
- Possibility of causing necrotizing fasciitis
- Risk of causing bloodstream infections
- Link to septic abortions
- Infections of artificial joints
- Possibility of causing inflammation of the heart’s inner lining
- Risk of causing septic thrombophlebitis of a major abdominal vein
Testing for Bacteroides Fragilis
It’s really important to properly collect samples, in order to avoid any contamination from the usual microbes found in our bodies. To ensure proper testing, the sample should be transported to the lab as quickly as possible. In order to test for bacteria that don’t need oxygen to survive (anaerobic bacteria), the ideal samples are those taken using a needle aspiration or tissue biopsy.
Fluid leaks (exudates), swabs from burns, wounds, and skin abscesses (boils) are typically not used for these types of bacterial cultures. This is because they often have microbes from the surrounding skin, which can interfere with the test. One type of anaerobic bacteria, Bacteroides fragilis, can also be diagnosed using a test that amplifies its DNA, known as PCR.
Treatment Options for Bacteroides Fragilis
The bacteria Bacteroides fragilis is known to resist antibiotics, especially penicillin, because it produces an enzyme that inactivates the drug. Some commonly used antibiotics including cefoxitin, moxifloxacin, and clindamycin may not be very effective against this bacteria, while others such as Piperacillin/tazobactam, meropenem, and metronidazole often work well. Metronidazole is typically the preferred choice for treating infections caused by bacteria that grow without oxygen, like Bacteroides fragilis.
However, there’s a small probability that Bacteroides fragilis may also resist metronidazole. The resistance could be attributed to a variety of complicated mechanisms, including the presence of specific genes that counteract the drug’s action.
Other bacteria in the Bacteroides group are found to be resistant to certain antibiotics, including meropenem and cefotetan. Infections caused by Bacteroides fragilis typically occur as a part of larger, mixed infections that arise when the body’s natural barriers are compromised due to surgery, inflammation, or trauma. These infections are often found in the abdomen. Treatment should consider antibiotics that can act against a range of bacteria including Bacteroides fragilis as well as other common bacteria such as Enterobacteriaceae, Pseudomonas aeruginosa, and Enterococcus faecalis.
Newer antibiotics are also under study for these types of infections. For example, eravacycline, has shown good initial results when tested against a mix of oxygen-requiring and non-oxygen-requiring bacterial infections within the abdomen. The efficacy and safety of tazobactam/ceftolozane combination with metronidazole has also been assessed and showed a promising response rate against Bacteroides fragilis infections among Japanese patients.
What else can Bacteroides Fragilis be?
The importance of detecting the bacteria Bacteroides fragilis can vary greatly, depending on where it was found in the body. For instance, finding this bacteria in a swab from a foot ulcer in a person with diabetes or a bed sore wouldn’t really mean much, because these types of sores usually have a lot of different bacteria growing in them. However, if we find Bacteroides fragilis in a fluid sample taken from inside a person’s belly, that suggests an infection in the abdominal area.
Such an infection should be treated with specific anti-bacterial medicines, and efforts should be made to eliminate the source of the infection. The presence of Bacteroides fragilis may be particularly significant in individuals who have recently had surgery (especially in the belly area), have suffered a physical injury, or have cancer.
What to expect with Bacteroides Fragilis
According to past research by Cheng C.W. and his team, almost 31% of people with Bacteroides fragilis— a type of bacteria found in the blood—didn’t survive, and cancer was the most common coexisting condition. Some studies suggest that the mix of bacteria in the colon may contribute to the development of colorectal cancer. For example, a study in Hong Kong found a higher risk of colorectal cancer among people with blood infections caused by B. fragilis or Streptococcus gallolyticus. These bacteria might infiltrate the bloodstream due to an imbalance of gut flora and compromised gut barrier.
But the connection isn’t clear-cut. A recent review from Denmark found that neither Fusobacterium nucleatum nor B. fragilis were definitively linked with tumors in colorectal cancer patients. They discovered that both these bacteria were barely present in the precancerous growths known as adenomas.
Possible Complications When Diagnosed with Bacteroides Fragilis
Bacteroides, a type of bacteria, are mostly involved in infections that develop in the absence of oxygen. These infections can cause health issues, leading to more than 19% of the cases resulting in death. Sometimes, a severe infection can develop due to a Bacteroides fragilis causing tubo-ovarian abscess, a pus-filled infection in a woman’s reproductive system. This exact situation can prompt a surgical procedure that includes removal of the uterus and both ovaries.
Preventing Bacteroides Fragilis
Bacteroides fragilis is a type of bacteria that is commonly found in the human colon. It can cause illness under certain circumstances. The human colon is protected by a kind of wall or barrier that stops bacteria from getting into body tissues. However, if this barrier is damaged due to injury, surgery, or tumors, the bacteria can break through and start causing infections.
Once this happens, our body’s immune system starts fighting back against the infection, causing inflammation which is our body’s way to get rid of the infection. This can result in pockets of pus forming in the area, and someone might feel systemic symptoms like fever and chills. If the infection is very severe, it can even lead to a serious condition called sepsis.
The usual treatment for a Bacteroides fragilis infection is to control the source of the infection. This could mean draining the pus, or, in some cases, using specific antibiotics that are effective against this particular bacteria.
