Probe on culture-negative lesions

Why it is important to pin down non-tuberculous mycobacteria species rapidly

Probe on culture-negative lesions

A 72-year-old woman presented with multiple painful lesions on the abdomen to the dermatology department at Amrita Institute of Medical Science, Kochi. The consulting dermatologist, Dr. Soumya Jagadeesan, noted that the lesions were purulent and the patient had previously undergone surgical drainage multiple times without any benefit. Gram staining of smears and routine cultures were negative and the patient had been treated with multiple courses of broad spectrum antibiotics, with no response even after several weeks. A skin biopsy had revealed a granulomatous inflammation and the patient was started on anti-tuberculosis treatment on the presumption that it might be an extra-pulmonary tuberculosis infection, as the chest X-ray was normal. At the time of her presentation to the centre, the patient had not responded to even anti-tuberculosis treatment. An atypical (non-tuberculous) mycobacterial infection was then suspected. While there was no history of trauma or surgery, the patient was taking insulin injections at the same site and admitted that she was not taking efforts to take these injections in an aseptic manner. Further testing including Ziehl–Neelsen staining of smears and mycobacterial cultures were done. Staining showed acid-fast bacilli. Nonpigmented colonies were observed on the 6th day in the cultures. Multiplex PCR was done and confirmed the presence of M. chelonae. The patient was then started on doxycycline and clarithromycin. Clarithromycin had to be substituted with linezolid as the patient had severe diarrhea due to the medication. The lesions healed within 4 weeks of starting this treatment and the treatment was continued for an additional 6 weeks. No recurrence was observed at the sixth-month follow up.
Incidence of non-tuberculous mycobacteria is on the rise. Non-tuberculous mycobacteria include mycobacterial species other than Mycobacterium tuberculosis, and contribute to causing infections in the lungs, lymph nodes, bone, brain, kidneys, genital tract as well as skin tissue. Different mycobacterial species respond to different treatment regimens and therefore rapid identification of the correct species is extremely important for appropriate treatment. Further, many non-tuberculous mycobacteria are resistant to typical M. tuberculosis treatments, making it essential to accurately determine the causative species. In India, the most prevalent non-tuberculous mycobacterial species include M. abscessus, M. fortuitum and M. chelonae in extrapulmonary tissue samples.
While rapid and accurate identification of these species is extremely important, diagnosis is challenging as they may not be identified via routine culture techniques. Recently, high performance liquid chromatography (HPLC) analysis of mycolic acids, probe-based tests and DNA sequencing have been used. However, they come with their own limitations. HPLC requires special expertise in interpreting the data generated and needs expensive equipment. Kit-based probe assays are costly and may not be readily available, while DNA sequencing is time consuming. Multiplex PCR options are also now available for accurate identification of rapid grower mycobacterium. It can differentially diagnose between M. abscessus, M. fortuitum,and M. chelonae, and is a useful diagnostic test in case rapid grower mycobacterium is suspected. Rapid identification is critical, since the treatment will depend on the species. For instance, M. chelonae responds well to medical management, however, M. abscessus may not and may require surgical management such as drainage of pus and removal of necrotic tissue to augment the treatment.
This case was one of four M.chelonae infected cases that came to Dr. Jagadeesan’s attention in the past one and a half years, and she advises that “a high index of suspicion is necessary if a patient presents with lesions that are culture negative and has a history of injury or surgical treatment.” She advocates that since these infections often occur at surgical sites, especially following laparoscopic procedures, inadequate sterilization practices at the hospitals maybe a source of the infection and doctors may need to be ready to inform the source sites to prevent further cases.
Dr. Jagadeesan is now quick to consider M. chelonaein case of culture-negative
cases and is prompt in carrying out the multiplex PCR to confirm her working diagnosis. Recently, a 42-year old lady presented with lesions on the abdomen. These lesions were at the site of a recent laparoscopic sterilization procedure. Multiplex PCR was done and M. chelonae was identified fairly quickly. The patient
was started on clarithromycin and ofloxacin tablets and recovered within 4 weeks. The treatment was however continued up to 12 weeks to prevent any recurrence. Thus, accurate early identification can substantially reduce the lag time in correct diagnosis and avoid inappropriate antibiotic use and anti-tuberculosis therapy that can result in adverse side effects and undue toxicity.

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