Introduction:
Mycobacterial infections cause many infections, and tuberculosis is the most common. Nontuberculous mycobacteria are classified according to their growth rates. Mycobacteria are a group of aerobic bacteria that produce filamentous pellicles that mimic molds when grown in a liquid medium. The mycobacteria are a family of a single genus and appear thin, curved to straight, non-spore-forming, and acid-fast bacilli. The genus has more than 190 species in tap water, soil, animals, plants, and food products. Mycobacterium fortuitum is reported to be found in commensal human skin. They are also seen as colonizers in medical equipment such as surgical solutions and endoscopes.
How Are Mycobacterial Infections Classified?
Mycobacterial infections are classified into three types:
1) Tuberculosis - It is a systemic infectious illness caused by the Mycobacterium tuberculosis complex that affects the respiratory, genitourinary, and lymphatic systems (Mycobacterium tuberculosis, M. bovis, M. africanum, and M. microti).
2) Nontuberculous Mycobacteriosis - Nontuberculous mycobacteria (NTM) have frequently been identified as opportunistic pathogens in patients with underlying illnesses or immunosuppression, such as AIDS. The most frequent nontuberculous mycobacterial pathogens in humans are M. avium complex (M. avium and M. intracellulare) and M. kansasii.
3) Leprosy - M. leprae is the cause of leprosy, a skin, mucous membrane, and peripheral nerve infection.
What Is the Pathophysiology of Mycobacterial Infections?
In humans, the mycobacterial species affect various anatomical species because they enter through the skin and mucosal barriers, which commonly cause cutaneous or pulmonary infections. Mycobacterial infections are common in immunocompromised individuals, those on tumor necrosis factor (TNF- alpha inhibitors), and transplant recipients. Individuals with normal host defense mechanisms prevent acquiring nontuberculous mycobacteria infection. The lungs are the most common site of infection, and nontuberculous mycobacteria can also infect organs, including skin, lymph nodes, ears, eyes, sinuses, central nervous system, urinary tract, and bones. A major host-derived risk factor involves a preexisting lung disease which includes asthma, chronic obstructive pulmonary disease, alpha one antitrypsin deficiency, cystic fibrosis, non-cystic fibrosis bronchiectasis, allergic bronchopulmonary aspergillosis, or primary ciliary dyskinesia which predisposes to nontuberculous mycobacteria infection.
What Is the Etiology of Mycobacterial Infections?
Tap water is one of the major causes of mycobacterial infections as it is a major reservoir of pathogens and is raising public health concerns. It was reported that piped water contains up to 90 % of mycobacteria species. Exposure to injections, contaminated water, cosmetic and surgical procedures, and trauma lead to infections with mycobacteria. Common immunosuppressive drugs involve oral and systemic steroids, tumor necrosis factor alpha inhibitors, solid organ transplantation, and cancer chemotherapy which predispose to mycobacterial infections. Cockroach infestations have been reported as one of the causes as cockroaches were infected with the following mycobacteria species:
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M.kansasii.
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M.xenopi.
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M.gordonae.
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M.haemophilum.
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M.fortuitum.
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M.avium.
How Common Is Mycobacterial Infection?
The following describes the epidemiology of the disease:
Frequency:
The most common mycobacterial species causing human disease are the evolving M.avium complex, M.kansasii, and M.abscesses, rapidly growing mycobacteria. M.kansasii is the second most common cause of lung diseases, followed by M.avium complex. M.kansasii is the most virulent among the other species of mycobacteria. Detecting single M.kansasii in sputum can be a clinically significant finding. 85% of infections involve the pulmonary organs, 15 % involve lymph nodes, skin, bones, and soft tissue, and less often, ears, eyes, and disseminated infection. Cutaneous infections are rarely reported. They are all reported in immunocompromised individuals, particularly in human immunodeficiency virus (HIV), immunosuppressive therapy, and leukemia.
Race:
No difference in race exists concerning mycobacterial infections.
Sex:
Mycobacterial infections have been reported to be more common in men than women. Middle-aged white men of urban origin are predominantly affected by skin, soft tissue, and pulmonary diseases.
Age:
Mycobacterial infections are common in older individuals. Hence it relates to the reduction in health and other predisposing factors. The predominant mycobacterial infections in children involve cervical lymphadenopathy caused by M.avium complex and M.scrofulaceum and cutaneous diseases due to M.ulcerans and M.marinum. Nontuberculous mycobacterium affects children below the age of five years.
What Is the Prognosis of Mycobacterial Infections?
Mycobacterial infections have a good prognosis with prompt medical care and surgical treatment. The mortality rate for mycobacterial infection is low. Mycobacterial infections can cause morbidity if they are not diagnosed and treated promptly. Occasionally cutaneous mycobacterial infections resolve independently and do not need any intervention. Children affected by mycobacterial infection may have facial nerve injury, which may also lead to hypertrophic scarring.
What Are the Signs and Symptoms of Mycobacterial Infections?
Humans are prone to mycobacterial infections because of their ubiquity in the environment. The pathogenic mechanism includes crossing the first line barrier defenses of the innate immune system and activating the phagocytes, which cause the disease in the respiratory tract, skin, and soft tissues. The signs and symptoms include:
1. Pulmonary Diseases: Chronic pulmonary diseases in HIV-infected individuals. The signs and symptoms include:
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Chronic cough.
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Sputum.
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Hemoptysis.
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Fatigue.
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Malaise.
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Weight loss.
2. Lymphadenitis: Commonly seen in children aged one to five years, with female predominance. It can lead to complications like fistula, scarring, and sinus tracts. A definitive diagnosis is obtained through tissue cultures.
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Visceral Disseminated Disease: Commonly seen in immunocompromised individuals. It frequently presents as disseminated lesions. The M.avium complex causes the majority of the cases reported. M.kansasii and M.haemophilum are common causative agents.
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Skin and Soft Tissue Disease: It presents as isolated or multiple nodules following blood and lymphatic distributions in a linear distribution. Clinically specific entities involve:
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Fish tank granuloma.
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Other symptoms include subcutaneous nodules, folliculitis, papules, abscesses, cellulitis, panniculitis, and ulcerations. Lesser common signs and symptoms include:
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Hepatosplenomegaly.
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Colonic ulcers.
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Mesenteric involvement.
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Abscess formation.
What Is the Differential Diagnosis for Mycobacterial Infection?
The differential diagnosis includes:
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Cat scratch disease.
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Acute complications of sarcoidosis.
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Cellulitis.
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Cutaneous fungal infections.
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Cutaneous manifestations of HIV.
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Cutaneous tuberculosis.
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Coccidioidomycosis.
What Is the Treatment for Mycobacterial Infections?
The treatment involves:
Medical Care:
A wide range of antibiotics is available for mycobacterial infections. However, as the species are becoming resistant, the treatment remains challenging. The choice of regimen may depend on the personal choice of the health care provider.
Surgical Approach:
Surgical modalities include drainage, debridement, excision, and extended treatment with antimicrobials. Cervicofacial lymphadenitis in children may be treated with selective cervical lymphadenectomy. Split-thickness skin grafting can be used to cover large wounds.
Conclusion:
Mycobacterial infections cause many infections, and tuberculosis is the most common. In humans, the mycobacterial species affect various anatomical species because they enter through the skin and mucosal barriers, which commonly cause cutaneous or pulmonary infections. Mycobacterial infections are common in older individuals. Treatment involves a medical approach or surgical modalities depending on the extent of the infection.
