What is Anaerobic Infections?
Anaerobic bacteria are a type of bacteria that live naturally on our skin and in certain parts of our bodies. Most of the time, these bacteria cause infections at the same places where they normally live. These infections can range from simple abscesses (collections of pus) to severe, life-threatening conditions. One of the unique things about anaerobic bacteria is that they can’t live in environments with oxygen. This is because they lack certain enzymes (proteins that help speed up chemical reactions in the body), like catalase, superoxide dismutase, and peroxidase, which other bacteria have to protect themselves against oxygen. Anaerobic bacteria can be tricky to grow in a lab if the correct methods aren’t used. Identifying these bacteria and diagnosing an infection caused by them needs careful observation of symptoms and correct testing.
Bacteria can also be grouped depending on how they relate with oxygen:
1. Obligate aerobes: These bacteria must have oxygen to survive. They can’t get energy from any other source, like through the process called fermentation.
2. Obligate anaerobes: These bacteria get energy through fermentation, using organic compounds instead of oxygen.
3. Facultative anaerobes: These bacteria can grow whether there’s oxygen present or not.
Obligate anaerobes can be separated into two groups based on the amount of oxygen that can harm them. Strict obligate anaerobes can’t survive if there is more than half a percent of oxygen around them, while moderate obligate anaerobes can still grow even if there’s 2 to 8% oxygen in their environment.
What Causes Anaerobic Infections?
Anaerobic bacteria, which do not need oxygen to survive, can often lead to infections in various parts of the body. These areas commonly include the mouth, stomach, pelvic area, or even areas like the head, neck, and skin.
Specific types of these bacteria have different effects:
1. Clostridium: This type of bacteria can lead to serious infections and makes up about 10% of all infections caused by anaerobes. Notable forms of this bacteria include Clostridium difficile, which causes C. difficile infection, and Clostridium perfringens, which can lead to gas gangrene or soft tissue infections.
2. Actinomyces: This bacteria is often found in the human GI (gastrointestinal) tract but can cause infection if it breaches certain barriers in the body. The infections commonly affect the face and neck, chest, and abdominal area.
3. Propionibacterium: This bacteria is usually found on our skin. A significant member of this family, Propionibacterium acne, is known to contribute to the development of acne.
4. Bifidobacterium: Generally found in the intestinal tracts and usually harmless, but in some cases, it has been linked to infections in children, including chronic ear infections, abdominal abscesses, and peritonitis.
5. Lactobacillus: These bacteria are seen in the GI tract and can be found in some food products as well. They normally do not cause disease, but instances of abdominal abscesses, breathing pneumonia, and bacteremia, especially in newborns, have been recorded.
6. Peptococcus and Peptostreptococcus: These bacteria inhabit various parts of our body like the mouth, GI tract, upper respiratory tract, and skin, and can cause numerous infections such as chronic ear and sinus infections, aspiration pneumonia, and pelvic inflammatory disease.
7. Bacteroides: These are commonly found in our colon and female genital area and is often the cause of stomach-related infections. They can also cause infections beyond the stomach, such as breathing pneumonia and brain abscesses.
8. Fusobacterium: A specific type of this bacteria, Fusobacterium necrophorum, is usually identified as the cause of peritonsillar abscesses linked with a complication known as Lemierre syndrome affecting the internal jugular vein.
9. Campylobacter: This bacteria is one of the most common causes of acute bacterial gastroenteritis, which is an inflammation of the stomach and intestines that causes vomiting and diarrhea.
10. Prevotella: These bacteria often inhabit our mouth and intestinal tract and are linked to head and neck infections in children, such as peritonsillar abscesses and retropharyngeal abscesses, as well as skin infections in the butt area such as pilonidal abscesses.
11. Veillonella: This type is occasionally connected with abdominal abscesses and aspiration pneumonia in children.
Risk Factors and Frequency for Anaerobic Infections
Anaerobes, or a type of bacteria, naturally live in areas of our body like the mouth, bowel, and female genital tract. The type and number of these bacteria can depend on factors such as a person’s age, where in the body they are located, and their environment. For example, babies who are only breastfed have different gut bacteria, mainly Bifidobacterium, compared to babies who are fed cow’s milk, who have gut bacteria more like adults, with more types of bacteria such as gram-negative anaerobes.
These bacteria normally live in our bodies without causing problems, and can even help by fighting off harmful, foreign bacteria. But, infections can still occur, typically if the body’s protective barriers break down or the immune system is weakened. Some examples of infections that anaerobes can cause include:
- Brain abscesses
- Dental infections
- Aspiration pneumonia
- Lung abscesses
- Bite infections (from animals or humans)
- Abdominal abscesses
- Necrotizing infections of soft tissue
Signs and Symptoms of Anaerobic Infections
Anaerobic infections, or infections due to bacteria that can live without oxygen, are mostly localized in children and rarely enter the bloodstream. The management of these infections often includes identifying certain factors that make a child more susceptible, such as:
- Infections in organs close to an area home to bacteria (like the mouth or intestines)
- Blockage, like a foreign object in the nose or blockages in the appendix or intestines
- Perforation or tearing of a hollow organ like the intestines
- Difficulty clearing secretions, often seen in children with conditions like cerebral palsy, making them prone to pneumonia due to aspiration
- Bites from animals or humans causing deep wounds that oral anaerobes can infect
Other indicators of anaerobic infections include conditions that create an environment in which these bacteria thrive (like tissue death), foul-smelling fluids, infection-related vein inflammation, and lack of improvement with antibiotics often used for these infections. Doctors typically order a special culture test when they suspect an anaerobic infection.
Common infections where these bacteria play a role include:
- Head and neck infections: Anaerobic bacteria often contribute to dental infections (like abscesses, gum inflammation, and periodontitis), neck abscesses, inflammation of glands near the ear, tonsil abscesses, and neck lymph nodes infections. These bacteria also often team up with oxygen-using bacteria to infect the spaces behind the throat and the salivary glands. Additionally, one anaerobic bacterium, Fusobacterium, can cause a severe complication called Lemierre syndrome if involved in a tonsil abscess. In the ear, chronic infections can have anaerobes as well as bacteria like Staphylococcus aureus and Pseudomonas.
- Central nervous system infections: anaerobes like Fusobacterium, Prevotella, and Bacteroides are often found in brain abscesses, which usually result from complications of sinusitis, ear infections, or dental infections. They are also seen in infections of the area between the brain and skull.
- Abdominal infections: damage to the intestinal wall can allow gut bacteria to access the abdominal cavity, leading to a combination of anaerobic and aerobic bacteria forming an abscess. The most common anaerobe here is Bacteroides fragilis, followed by Lactobacillus and Clostridium species.
- Liver infections: anaerobes like Bacteroides and Fusobacterium species are common causes of liver abscesses.
- Pelvic infections: bacteria that do and don’t require oxygen are often implicated in pelvic inflammation in sexually active females. Prevotella, Porphyromonas, and Clostridium are commonly involved anaerobes.
- Lung infections: children with conditions like cerebral palsy or esophagus abnormalities often risk inhaling secretions into the lungs, leading to infections that can worsen to abscesses. The culprits include bacteria usually found in the mouth or throat, including Peptostreptococcus, Prevotella, Bacteroides fragilis, and Fusobacterium.
- Skin and soft tissue infections: anaerobes can cause abscesses near the rectum or on the face in children. Bacteroides fragilis and Clostridium species are commonly involved in rectal infections, whereas Prevotella, Porphyromonas, and Fusobacterium feature in oral infections.
Testing for Anaerobic Infections
Identifying serious anaerobic infections quickly is key to starting treatment as soon as possible. Life-threatening infections like tetanus, gas gangrene, or infant botulism are caused by certain types of bacteria called Clostridium tetanus, Clostridium perfringens, and Clostridium botulinum respectively.
When a child who has been immunized suffers an injury, such as a deep puncture wound from a nail, or has damaged tissue, they should be checked for tetanus.
Gas gangrene, caused by Clostridium perfringens or Clostridium septicum, is a medical emergency that requires immediate surgical intervention to remove the infected area, and antibiotics. Antibiotic therapy usually involves a combination of penicillin and clindamycin.
Botulism can cause gradual muscle weakness, especially in babies. Common signs to watch out for are difficulty feeding and problems with the gag reflex. It’s often linked to consuming damaged canned food, honey, or traveling to regions with high counts of the bacteria. If botulism is suspected, the California Department of Health provides expert reviews. Tests for the presence of Clostridium botulism spores in the baby’s stool may also be run. Treatment mainly involves taking care of the patient’s needs and could also include a medicine called botulism immunoglobulin (BabyBIG).
In teenagers, any throat pain, neck pain, or rapid heart rate that seems excessive when compared to a fever, could be a sign of Lemierre syndrome. In such cases, an ultrasound of the neck might be done to check for clotting and inflammation in the internal jugular veins, and a chest x-ray could be used to check for septic emboli, or infected clots in the bloodstream.
Abscesses, or collections of pus that can occur in the central nervous system (CNS), head, neck, or abdomen, can be diagnosed with a test that identifies anaerobic bacteria in cultures. Samples, preferably of tissue or fluid, must be collected from a sterile (germ-free) area and then, avoiding normal bacteria, samples are either aspirated (withdrawn with a needle) or collected during surgery. Unlike a swab, which may not capture the deeper bacteria, tissue or fluid samples tend to provide a more accurate result. This sample should be sent for testing in an anaerobic transport medium and inoculated (introduced) in an environment without oxygen.
Treatment Options for Anaerobic Infections
When managing an anaerobic infection, doctors take into account where the infection is in the body, the patient’s overall health, and whether the infection has resulted in an abscess (a pocket of pus). In general, if an abscess is present, it should be drained, and a sample should be taken for tests. Also, in serious cases, removal of dead tissue might be necessary. This is especially relevant in situations involving an infection by clostridium bacteria that causes a skin disease known as necrotizing fasciitis.
Once appropriate samples have been taken, it’s important to start antibiotics as soon as possible. These antibiotics need to be effective against anaerobic bacteria – the bacteria that grow in areas lacking oxygen. The selection of antibiotics includes:
- Metronidazole: This antibiotic works well against certain types of anaerobic bacteria but might not be as effective against others. It’s well-absorbed in the body and reaches various tissues effectively. It can sometimes leave a metallic taste in the mouth, which can lead to patients discontinuing use.
- Clindamycin: This antibiotic works well against many varieties of anaerobic bacteria. However, some types are becoming resistant to clindamycin, making it a less reliable choice. Clindamycin can reach different tissues in the body effectively but doesn’t reach the central nervous system (the brain and spinal cord).
- Penicillin/beta-lactamase inhibitor combination: This combination of drugs is effective against those anaerobic bacteria that do not produce an enzyme called beta-lactamase. Many anaerobic bacteria produce this enzyme which makes them resistant to penicillin alone.
- Second-generation cephalosporins: These antibiotics work well against certain anaerobic bacteria but due to increasing resistance, they’re not usually the first choice for treatment. They are often used to prevent infection during surgery.
- Carbapenems: These have excellent activity against both aerobic and anaerobic bacteria. They work particularly well in infections located in the abdomen and the central nervous system.
- Quinolones: These antibiotics are absorbed well when taken by mouth and effectively reach various tissues. However, due to increasing resistance, they’re usually reserved for patients who are allergic to beta-lactam antibiotics.
What else can Anaerobic Infections be?
Botulism can sometimes be mistaken for other conditions related to the nervous system. Some of these include:
- Guillain-Barre syndrome
- Infections that cause paralysis, like enterovirus infection
- Paralysis or muscle weakness caused by West Nile Virus
On the other hand, infections caused by bacteria such as Escherichia coli and Pseudomonas can lead to abscesses, which are collections of pus, springing up in different parts of the body. These may occur in specific areas like:
- The brain, leading to brain abscesses
- The head and neck
- The lungs
- Within the abdomen, leading to intra-abdominal infections