What is Mycobacterium chelonae Infection?
Mycobacterium chelonae is a type of bacteria that is not associated with tuberculosis (known as a nontuberculous mycobacterium or NTM). It’s classified as rapidly growing, meaning it reproduces quickly in the body. M. chelonae was first discovered in a turtle in 1903. This group of bacteria makes up half of all known mycobacterial species and is split into six groups.
There was a time when M. chelonae and another bacterium called M. abscessus were thought to be the same. But in 1992, M. chelonae was recognized as a separate species. Both can be differentiated based on their unique gene sequences. However, it’s not easy to tell the difference just by looking at how susceptible they are to different medicines.
These bacteria are common in the environment and can be found in soil, water, and aquatic animals. M. chelonae prefers temperatures between 30 to 32 degrees Celsius and may take a long time to develop. It often causes skin infections, particularly in the arms and legs (like cellulitis and abscesses). The bacteria may also cause severe infections around areas where medical procedures occurred – like where a catheter was inserted, after surgery involving implants, transplants, or injections. It can invade the eyes as well.
Lung infections from this bacterium are less common compared to M. abscessus. However, in people with weak immune systems, such as those taking certain drugs post-transplant or those with cancer or chronic kidney disease, more severe infections can occur. They may spread throughout the skin, affect the bones, or cause internal abscesses.
What Causes Mycobacterium chelonae Infection?
M. chelonae is a type of bacteria that is non-spore-forming, non-moving, and gram-positive, meaning it retains a certain stain used in lab testing. It’s a large bacteria and often appears beaded under a microscope. This bacteria is part of a group known as rapidly growing mycobacterium. However, unlike other bacteria in this group that form colonies within seven days, M. chelonae takes a bit longer to grow – around 15 days or even up to six to eight weeks. It also prefers temperature conditions between 30-32 degrees Celsius for its optimal growth.
M. chelonae, along with M. abscessus and its three subspecies, belong to the same bacterial family. Biochemically, M. chelonae doesn’t nitrify, can’t tolerate 5% salt solution, and doesn’t turn dark brown when grown on a substance called ferric ammonium citrate, which is used to test for iron uptake. We can differentiate between M. chelonae and M. abscessus via their different responses to citrate, a substance involved in energy production of cells. M. chelonae is 100% citrate positive while M. abscessus is mostly negative. Also, M. chelonae is catalase positive, indicating it can break down harmful substances in cells, but it’s oxidase negative, meaning it lacks a specific enzyme for the oxidation process. However, these biochemical methods aren’t very effective in diagnosing infections in a clinical setting. Nowadays, more advanced molecular techniques are often used for identifying atypical bacterial infections.
Of all rapidly growing mycobacteria, M. chelonae is one of the most harmful. This bacteria usually causes local skin infections in otherwise healthy individuals, especially after an invasive medical procedure or due to a catheter-related infection. Lung infections caused by M. chelonae are rare, although it can frequently colonize cystic fibrosis patients’ lungs. It can cause widespread and invasive infections in people with weakened immune systems. However, there’s no known instance of it spreading from person to person. Though it’s rare, M. chelonae can cause lymph node inflammation in the neck of children. However, other bacteria like Mycobacterium avium intracellulare and Mycobacterium hemophilum are usually more associated with this condition in children than M chelonae.
Risk Factors and Frequency for Mycobacterium chelonae Infection
Reports of infections caused by M.chelonae and other related RGM are not required in the United States, so we don’t have an exact number of cases. However, it is observed that non-tuberculous mycobacteria (NTM), which includes M.chelonae, are more common in the southern states such as Florida, Georgia, Louisiana and Texas. Based on a national survey completed between 1981 and 1983, the annual instances of NTM were about 1.78 cases per 100,000 people. In this same survey, M.chelonae was recorded at a rate of 0.08 case per 100,000 people.
A more recent study conducted in Oregon from 2005 to 2006 found 7.2 cases of NTM per 100,000 people annually, with M.chelonae making up 0.2 of these cases. The majority of these infections were found in the skin and soft tissue. This bacteria has been reported globally, including the Americas, Eurasia, and Australia. Again, most instances were skin and soft tissue infections.
There is a worldwide upward trend in infection rates from NTM. No specific age, sex, or race has been determined to be more prone to these infections. The bacteria does not seem to have a seasonal trend, i.e., it can show up any time of the year. M.chelonae has been found in water systems that we drink from as it can resist the effects of chlorine. It is reported more often than M.abscessus, but less than M.fortuitum or M.gordanae, with the latter being the most commonly found mycobacteria in drinking water systems.
Signs and Symptoms of Mycobacterium chelonae Infection
Mycobacterial infections, including M. chelonae, can affect various parts of the body and cause different health issues. They can lead to lung disease, skin and soft tissue infections, musculoskeletal infections, widespread disease throughout the body, catheter-associated disease, and swollen glands (lymphadenitis). Of these, skin and soft tissue infections are the most common. These types of infections can happen to anyone, healthy or with weakened immune systems. M. chelonae generally targets the limbs because it grows well at lower temperatures.
Outcomes of these infections on the skin vary widely. There might be nodules (hard lumps), small raised rashes, and a pattern of infection similar to Sporotrichosis. Some reported cases tie skin lesions from M. chelonae to various treatments like sclerotherapy, acupuncture tattoos, and other injection processes. Skin lesions may worsen resulting in pus-filled sores, blood-filled crusts, and abscesses (pockets full of pus). In some cases, M. chelonae can cause Nodular lymphangitis, which involves painful nodules along the lymphatic vessels in the limbs. In patients with weak immune systems, these ailments can spread and lead to serious skin issues.
Skin manifestations may look like other disorders. For instance, a condition called Sweet syndrome, which typically impacts the limbs, can be a sign of M. chelonae. Similarly, M. chelonae infection can mimic lupus vasculitis. A widespread infection may cause multiple sores or complex ones likely to occur in more central parts of the body. Facts indicate that pimples or pus-filled sores on the face and upper body may also happen.
M. chelonae can also invade bones, joints, and muscles. This is prevalent in patients with weakened immune systems, and following joint injections or surgery. It can survive in endoscopes too. Infections caused by catheters can lead to fever, serious infections in the bloodstream, or skin sores distributed throughout the body. Cases of such infections were found in patients with weak immune systems, including pregnant women.
Testing for Mycobacterium chelonae Infection
An infection with a bacterium known as M. chelonae may not cause any symptoms. It’s pretty common for this bacteria to settle in the lungs of patients with cystic fibrosis. Another related bacterium, M. abscessus, often leads to lung infections.
If someone has unexplainable or ongoing skin or under-the-skin infections on their limbs, especially if the condition hasn’t been responding to antibiotics, a skin biopsy and culture tests can help to figure out what’s going on. This is particularly important for people who have recently had injections or for those who have weakened immune systems.
Standard lab tests may not be enough to identify these bacteria and determine the most effective treatment. Instead, more advanced techniques, like the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), can help to identify these bacteria, including M. chelonae.
M. chelonae bacteria can sometimes be resistant to certain drugs. Nonetheless, most are sensitive to antibiotics called macrolides and aminoglycosides. Testing to see which drugs the bacteria are most sensitive to is recommended as it helps doctors to decide on the best treatment.
Mixing up M. chelonae and M. abscessus can be easy, as the common technique of high-performance liquid chromatography (HPLC) is not enough to tell them apart. Further DNA analysis is required. However, DNA probes specifically for M. chelonae have not yet been given the green light.
Another method, known as PRA, is often used for distinguishing between different types of these bacteria. It uses a technique that targets a heat shock protein (HSP) followed by a process that identifies distinct length fragments of genetic material—these lengths are specific to each type of bacteria. Although this method can tell the difference between M. chelonae and M. abscessus, it might not be sufficient for identifying new species of these bacteria.
Treatment Options for Mycobacterium chelonae Infection
M. chelonae, a type of bacteria, strongly resists the drug cefoxitin. Instead, imipenem is usually the prefered choice. Tobramycin is more effective than another medication known as amikacin. These bacteria are most susceptible to tobramycin and clarithromycin, and somewhat susceptible to linezolid, imipenem, amikacin, clofazimine, doxycycline, and ciprofloxacin.
For skin infections, therapy with clarithromycin alone might be sufficient. However, sometimes resistance develops during treatment because of a single change (mutation) in the 23S rRNA of the bacteria. In case of lung disease, spread infections, or invasive diseases affecting bones and soft tissues, long-term therapy of at least six months is recommended. The therapy typically includes a macrolide (a type of antibiotic) and another drug adjusted based on what the bacteria are susceptible to.
Surgery to clean out infected tissue (called debridement), remove foreign objects, and remove catheters may be helpful. The best treatment plan for lung infections caused by this bacteria is not entirely sure, but is likely similar to other NTM (non-tuberculous mycobacteria) infections. This would include 12 months of continued therapy until no more bacteria are found in sputum (mucus) cultures.
In people with suppressed immune systems who are infected with M. chelonae, successful treatment often involves a combination of a macrolide and amikacin. For infections of the cornea (the clear front portion of the eye), both topical and systemic treatments are used. These could include eye drops containing macrolides, aminoglycosides (another type of antibiotic), and fluoroquinolones (yet another type of antibiotic). As always, the treatment should be based on which drugs the bacteria are susceptible to, if possible.
What else can Mycobacterium chelonae Infection be?
These are some medical conditions that a doctor may consider when making a diagnosis:
- Actinomycosis
- Blastomycosis
- Cryptocosis
- Histoplasmosis
- Mycetoma
- Mycobacterium abscesses
- Mycobacterium kansasii
- Mycobacterium marinum infection
- Mycobacterium xenopi
- Nocardiosis
