What is Mycobacterium marinum Infection?
Mycobacterium marinum is a bacteria that was first discovered in 1926 from lesions on dead saltwater fish in a Philadelphia aquarium. This bacteria causes a disease in fish that’s similar to tuberculosis. Humans can get infected with this bacteria if they have a skin injury which comes into contact with water that’s contaminated with the bacteria.
The infection caused by Mycobacterium marinum leads to the development of small lumps known as nodules and inflammation in the body tissue, technically referred to as granulomatous disease. This can spread in the body in a manner similar to sporothrix infection, which is another type of skin infection usually caused by a fungus in soil or plants.
Mycobacterium marinum is found in environments including plants, soil, and fish. Infections usually occur in healthy people and mostly affect the skin and soft tissues. Rarely, more widespread infections have been reported in people with HIV/AIDS, where the immune system is significantly weakened.
What Causes Mycobacterium marinum Infection?
M. marinum is a type of bacteria that doesn’t move or produce spores. It’s marked by its ability to stain bright with certain dyes, due to its makeup. It grows slowly and belongs to a group called Runyon group 1. This bacteria produces a yellow pigment when it’s exposed to light. It finds it easiest to grow on a special substance called Lowenstein-Jensen medium, at a temperature of 32 degrees Celsius.
It’s worth noting that M. marinum has a hard time growing at the temperature of the human body, 37 degrees Celsius. This is different from another bacteria, Mycobacterium tuberculosis (the bacteria that causes tuberculosis) that grows well at this temperature. However, from an evolutionary perspective, M. marinum is closely related to M. ulcerans and Mycobacterium tuberculosis.
In places like a fish’s or frog’s body, M. marinum can cause diseases that resemble tuberculosis. Just like the tuberculosis bacteria, M. marinum can survive inside the cells of its host, so it can be used as a model to study the tuberculosis bacteria. If you get an M. marinum infection, you might even test positive for a tuberculosis skin test.
M. marinum has one part of its DNA strand (called an rRNA operon) that controls how fast it produces proteins. When looked at genetically, this rRNA operon part isn’t so different in M. marinum and the tuberculosis bacteria. But interestingly, even though M. marinum grows faster, we don’t know why this is the case. When it’s in the body, M. marinum divides and doubles every 24 hours, just like the tuberculosis bacteria. But in a lab, at 32 degrees Celsius, it’s much speedier, taking just 4 hours to divide. Meanwhile, the tuberculosis bacteria doubles every 24 hours when grown at the body temperature of 37 degrees Celsius in a lab.
Lastly, while dealing with M. marinum is hard as there’s no flawless antibiotic regimen to tackle it.
Risk Factors and Frequency for Mycobacterium marinum Infection
The first case of M. marinum, a type of bacteria, in humans was reported in Sweden in 1951. The bacteria were found on skin lesions of swimmers who had been in a contaminated pool. These days, you don’t need to worry about catching M. marinum from swimming pools, as they’re usually cleaned with chlorine. The main ways people get M. marinum now are through working in wet areas, doing water sports, or cleaning fish tanks. In the United States, the rate of M. marinum infection is pretty low, with only about 0.27 cases per 100,000 people each year.
Getting a M. marinum infection usually requires two things: an injury or scraped skin, and exposure to water that’s been contaminated with the bacteria. One study found that roughly half of all M. marinum infections were linked to home aquariums. Other common sources of infection were injuries from fish or shellfish, and injuries related to saltwater or brackish water. People with HIV have the same risk factors and can potentially develop a widespread infection if their immune system is weakened.
- First case of M. marinum reported in Sweden in 1951, from contaminated swimming pools.
- Cleaned swimming pools do not carry M. marinum bacteria.
- Main risk factors for M. marinum include working in wet areas, water sports, or cleaning fish tanks.
- About 0.27 cases per 100,000 people happen each year in the United States.
- Two conditions for infection: skin injury and exposure to contaminated water.
- Half of M. marinum infections are linked to home aquariums.
- Injuries from fish or shellfish, and saltwater exposure are also risk factors.
- People with HIV have the same risk factors.
- Weak immune system can lead to widespread infection.
Signs and Symptoms of Mycobacterium marinum Infection
Mycobacterium marinum, or M. marinum, is a type of bacteria often found in water, plants, and soil. It can cause skin infections especially if the skin has been scratched, cut or otherwise injured. Skin infections from M. marinum usually appear as a single blue-red lesion or lump. These lumps may have a crusty or wart-like surface, and often contain pus. The bacteria can also cause an infection that spreads along the lymph nodes and appears similar to sporotrichosis.
Infections with M. marinum should be considered if a person has a lump or lesion on their skin that doesn’t heal, even with antibiotic treatment. This is particularly true for lumps on the upper limbs. However, such lesions might as well appear on the lower limbs, depending on where the person was exposed to the M. marinum bacteria. Rarely, M. marinum can cause widespread infections, usually in people with weakened immune systems like HIV patients, but this has become less common due to advances in HIV treatment.
Testing for Mycobacterium marinum Infection
To diagnose a potential M. marinum infection, which is a type of bacterial infection, good communication with the lab team is crucial. The lab conducts tests using a type of growing medium called “Lowenstein-Jensen agar”, and these tests need to be kept under certain temperature conditions (28 to 32 degrees Celsius) and observed for six weeks. Although only 70%-80% of these tests turn out positive, they’re still worth conducting even if initial microscopic observation doesn’t show signs of the bacteria. This is because the infection can have a very low concentration of the bacteria causing the disease.
When looking at the biopsy of the skin or nodules (lumps) under the microscope, the team may find that a typical pattern only shows up in two-thirds of cases. Sometimes, the pattern might even resemble that of rheumatoid nodules – lumps you get with rheumatoid arthritis. In one in five cases, the nodules might not look infectious at all under the microscope. In this scenario, the team could take samples from the deeper parts of the nodules or repeat the biopsy to gather more information.
Another important tool to diagnose an M. marinum infection is a technique known as Polymerase Chain Reaction (PCR). This technique is used to amplify and detect the presence of M. marinum bacteria in a biopsy sample. However, a method using a stain to detect the bacteria may not always work because the number of bacteria in the samples is usually quite low.
People who take certain types of medications, such as anti-tumor necrosis factor (TNF)-alpha and other biological drugs, may be more prone to contracting an M. marinum infection as these medications can weaken the immune system. Therefore, it’s important to check if a patient has a weakened immune system when diagnosing this infection. Skin tests using a substance called purified protein derivative are often positive in cases of M. marinum infection.
The lab may also use blood culture tests or other types of assays to aid in the diagnosis. More recently, in vivo imaging or imaging carried out inside the body has been proposed as an additional way to monitor treatment response for these types of infections.
Treatment Options for Mycobacterium marinum Infection
When treating infections caused by M. marinum, a type of bacteria, routine tests for drug susceptibility (how responsive the bacteria are to different antibiotics) are not generally recommended. This is because the results of these tests often do not correlate well with how the infection responds to treatment. There’s no ‘one-size-fits-all’ treatment and the therapy needs to be chosen on a case-by-case basis.
Rifampin is an antibiotic that works particularly well against M. marinum. However, it’s important to note that M. marinum is naturally resistant to another antibiotic, pyrazinamide. Other antibiotics like ciprofloxacin, levofloxacin, and linezolid also show varying degrees of effectiveness. Clarithromycin, in particular, has been found to be successful in treating these infections, regardless of the test results showing how susceptible the bacteria are to this drug.
Unfortunately, there’s no agreed-upon approach or duration of treatment for M. marinum infections. A variety of antibiotic plans have been used, often depending on the patient’s individual circumstances, such as their immune system status. For instance, single-drug therapy with an antibiotic called minocycline has been used for patients with a normal functioning immune system. In contrast, a combination of drugs is generally used for patients with suppressed immune systems. Response to treatment is usually slow, hence the selected therapy is usually given for three months before considering any changes. Often surgery is needed to physically remove infected tissue.
About a month after starting effective antibiotic therapy, all skin lesions typically heal. After this, individuals with a fully functional immune system should continue to take the medication for another two months. However, patients with suppressed immune systems need to continue dual drug treatment for at least six months. In severe cases, continuous treatment may have to be a life-long necessity.
In summary, when it comes to treating M. marinum infections in patients with a compromised immune system, it’s advisable to use a combination of two drugs, including clarithromycin. The exact duration of treatment can vary, but six months to a year is common. The best combination of drugs and duration will depend on the specifics of each patient’s condition.
What else can Mycobacterium marinum Infection be?
When diagnosing skin nodular infections, especially those caused by fungi and resulting in small lumps in the skin, different diseases need to be considered. They include:
- Blastomycosis
- Coccidioidomycosis
- Cryptococcosis
- Histoplasmosis
Additionally, other skin infections that could show similar symptoms include:
- Leishmaniasis
- Nocardiosis
- Sporotrichosis
What to expect with Mycobacterium marinum Infection
In most cases, M. marinum infection can be treated effectively, particularly in patients with a strong immune system. However, the treatment could be less successful if the infection has spread to deeper structures in the body or has led to open sores on the skin. Thankfully, these bacteria are not likely to become resistant to antibiotics.
It’s important to note that the treatment results for M. marinum infections are the same for both patients with and without HIV infections. However, if a patient’s immune system is compromised, or if they continue to be exposed to the bacteria, their risk for the disease can increase. As a result, some patients may need to continue treatment indefinitely to keep the infection at bay.
Possible Complications When Diagnosed with Mycobacterium marinum Infection
With a quick diagnosis and proper treatment, long-term problems from the disease are usually minor. However, some people can get ongoing ulcers at the spot where the disease first entered their body. If treatment is delayed or the wrong antibiotics are used for too short a time, deeper infections can occur. These include bone infections (osteomyelitis), inflammation of the tissue that surrounds tendons (tenosynovitis), and a more widespread disease, which might necessitate the removal of the affected tissue.
- Recurring ulcers at the site of initial exposure
- Deeper infections with delayed or improper treatment
- Bone infections (osteomyelitis)
- Inflammatory condition of the tissue around the tendons (tenosynovitis)
- More widespread disease
- Possible need for removal of affected tissue
Preventing Mycobacterium marinum Infection
Once doctors diagnose a patient with an M. marinum infection, it’s crucial to educate them on how to reduce their exposure to this bacterium. Importantly, people with this condition can’t spread it to others, a fact that often concerns them and their loved ones. The ideal way to minimize this risk involves avoiding any contact with water bodies when having cuts or scratches on the skin.
However, if these individuals need to be near saltwater due to their jobs, they are advised on how to clean their skin appropriately after being in the water, using a suitable antibacterial product. They should also cover any scratches with waterproof bandages to prevent infection. People who work with aquariums are encouraged to wear gloves at all times for their protection.