Cutaneous Mycobacterium fortuitum Infection: Successfully Treated with Amikacin and Ofloxacin Combination.

Cutaneous infections caused by atypical mycobacteria are uncommon and the diagnosis can be missed unless there is strong clinical suspicion supported by laboratory confirmation. We report a case of chronic discharging sinus caused by Mycobacterium fortuitum in a young healthy immunocompetent individual. The patient recovered completely following amikacin and ofloxacin therapy.

What was known?

Cutaneous infections caused by atypical mycobacteria that used to be considered unusual have become frequent nowadays, particularly in immunocompromised individuals.

Introduction

Skin and soft tissue infections caused by rapidly growing non-tuberculous mycobacteria (NTM) have become frequent nowadays, particularly in immunocompromised individuals. Among the rapidly growing mycobacteria, Mycobacterium fortuitum and Mycobacterium chelonae are known for producing a wide spectrum of clinical diseases.[1] Cutaneous and subcutaneous infections by M. fortuitum are caused by colonization of the tissue following accidental trauma, injection of drugs (cortisone), mesotherapy, surgical procedures, or domestic animal bites.[23] M. fortuitum is only occasionally associated with primary cutaneous infections in immunocompetent people. We here report a case of chronic discharging sinus caused by M. fortuitum in a young healthy immunocompetent individual.

Case Report

A 16-year-old male presented to the outpatient surgery department with a pus discharging lesion over abdomen. The lesion had started as a small painful swelling 3 months back, which after a period of 1 month ulcerated to form a discharging sinus. The discharge was very minimal and non-foul smelling. There was history of a similar swelling in left paraumbilical region, which was incised and drained about 7 days earlier at a private clinic. On local examination, there was a 0.5 cm × 0.5 cm sinus with minimal seropurulent discharge in right paraumbilical region and 1 cm × 0.5 cm healing incision wound on left side [Figure 1]. The surrounding skin was warm, indurated, and slightly tender. No regional lymphadenopathy was found. During the last 3 months the patient had received multiple courses of antibiotics without any improvement and had been started on antituberculous treatment (ATT) few days back. There was no history of fever, chronic cough, and loss of weight and appetite. There was no history of any trauma over the affected site. Systemic examination was within normal limits. Chest X-ray was normal. The patient's blood counts, sedimentation rate, and serum and urinary biochemistry were within normal limits. Enzyme-linked immunosorbent assay (ELISA) for HIV was negative. The Mantoux test gave size of induration. C-reactive protein (CRP) level was slightly raised.

Figure 1

Discharging sinus in right and the healing incision wound in left paraumbilical region

The sinus discharge was collected and subjected to microbiological evaluation that included Gram stain, Ziehl–Neelsen (ZN) stain, and stains to detect fungi. The specimen was cultured on to blood agar (Hi Media, Mumbai, India) and MacConkey agar (Hi Media, Mumbai, India) for aerobic and anaerobic bacteria, Lowenstein–Jensen (LJ) (Hi Media, Mumbai, India) medium for mycobacteria and Sabouraud's dextrose agar (Hi Media, Mumbai, India) for fungal isolation. ZN stain revealed acid fast bacilli (AFB) while other stains did not show any microorganism. Cultures for bacteria and fungi were negative. However, magenta colored colonies appeared on MacConkey agar after 48 h of incubation and small white colonies grew on the LJ media after 5 days of incubation. The isolate was identified as M. fortuitum based on growth on MacConkey agar, non-photochromogenic colonies, positive nitrate reduction, iron uptake, aryl sulfatase, tolerance to 5% NaCl and 68°C catalase. The isolate was subjected to minimum inhibitory concentration (MIC) testing by Mycobacterium Growth Indicator Tube MGIT 960 and was found to be sensitive to amikacin (MIC < 1 μg/ml), ofloxacin (MIC < 2 μg/ml), and capreomycin (MIC < 2.5 μg/ml) and resistant to rifampicin (MIC > 1 μg/ml), isoniazid (MIC > 0.1 μg/ml), ethambutol (MIC > 5 μg/ml), streptomycin (MIC > 1 μg/ml), and kanamycin (MIC > 1 μg/ml). The patient was advised to discontinue ATT and was started on a course of amikacin (15 mg/kg intramuscular daily for 1 month) and ofloxacin (400 mg oral daily for 4 months) therapy. The lesion healed completely after 4 months of therapy with no recurrence after 6 months follow-up.

Discussion

The rapidly growing mycobacteria are ubiquitous in the environment. In humans, M. fortuitum mainly causes infections of the skin, lungs, lymph nodes, and joints. In the skin the lesions tend to be subacute or chronic, occult, resistant to treatment, and recurrent. Cutaneous disease with environmental mycobacteria follows two patterns:[4] Following trauma (accidental or surgical) in immunocompetent patients, a single abscessed lesion appears in the damaged region 4-6 weeks later and heals spontaneously in 20-30% of patients. However, immunocompromised patients develop disseminated, multiple subcutaneous nodules and usually no previous trauma is described.

The histological findings due to rapidly-growing mycobacteria are varied, depending on the immune status of the patient and the amount of time the lesions have been developing. Thus the chance of overlooking these organisms is high unless microbiological confirmation is done. Culture is almost always needed for the definitive diagnosis.[5]

There are multiple reports of M. fortuitum infection after trauma and surgical procedures,[6] liposuction,[7] pedicure[8], and subcutaneous injections.[9] Isolation of M. fortuitum from soft tissue infections in immunocompetent individuals have also been reported.[5610]

Treatment of the fast-growing mycobacteria depends on the characteristic of each patient. Usually they are resistant to first line tuberculostatic drugs.[4] They are particularly sensitive to amikacin and also to the tetracyclines, first generation cephalosporins, quinolones, and the new macrolides. Monotherapy should not be used, since resistance to quinolones has already been found.

Our case is unusual because the patient was an immunocompetent young male with chronic sinus formation. The source of infection could not be traced. At the time of presentation, single sinus was present. Unfortunately, the swelling on the other side had already been debrided and thus could not be diagnosed.

Hence, a high degree of clinical suspicion followed by microbiological identification and susceptibility testing allows the timely and efficient therapy of such patients.

What is new?

Immunocompetent individuals are also prone to atypical mycobacteria, hence, every specimen received for pyogenic culture must be processed for AFB examination and culture also.