A 75-year-old male belonging to the upper middle class presented with a history of a nonhealing sternal wound following a coronary artery bypass graft (CABG) in June 2010. CABG was done in the early part of May and the patient was discharged with the intact wound with an 8-h dose of amoxicillin and clavulanic acid combination (625 mg). The chest wound gradually progressed in size with a serosanguinous discharge despite the antibiotic cover. The patient was a known case of atherosclerotic heart disease with a history of myocardial infarction and chronic obstructive pulmonary disease. He had undergone percutaneous transluminal coronary angioplasty in March 2010. The patient was normotensive and nondiabetic with a family history of Koch's spine for which his wife was under antitubercular therapy (ATT).
The patient at admission was afebrile with a heart rate of 96 beats/min and BP of 120/80 mmHg. The chest was bilaterally clear, and clinically, all the systems were normal. Laboratory investigations revealed the following: hemoglobin: 10.6 gm%; total white blood cell (WBC) count: 10.39 x 103/mm3; differential WBC count: neutrophils 67%, lymphocytes 20%, monocytes 2%, eosinophils 0.2%, and basophils 0.3%; platelet count 4.4 lakhs/mm3. Tests for HbsAg, HCV, and HIV 1 and 2 antibodies were found to be nonreactive. Liver function tests and renal function tests were normal. Blood, pus from the wound, and sputum were sent for aerobic culture.
Blood cultures (BacT Alert; bioMeriux) sent in duplicate showed the presence of faint Gram-positive beaded, rod-shaped organisms after 4 days of incubation. Ziehl-Neelsen (ZN) staining of smears from signal positive blood culture bottles showed the presence of beaded acid-fast bacilli in chains. The blood was then inoculated onto blood agar, MacConkey agar, and Lowenstein-Jensen (LJ) medium. Blood and MacConkey agar did not show any growth till 48 h after aerobic incubation. The LJ medium showed the presence of tiny creamish colonies on the third day after incubation. ZN staining of the smears from these colonies showed the presence of acid-fast bacilli. The isolate was provisionally identified as atypical mycobacteria (rapid grower).
Gram staining of the pus smear showed plenty of Gram-variable bacilli. No growth was seen on blood and MacConkey agar till 2 days of aerobic incubation. Since the blood culture was positive for atypical mycobacteria, the pus sample was also subjected to ZN staining and mycobacterial culture. ZN staining of the pus smear showed the presence of numerous acid-fast bacilli. The culture on the LJ medium grew tiny creamish colonies on the fourth day of incubation. ZN staining of these colonies also showed the presence of acid-fast bacilli. This isolate was also provisionally identified as atypical mycobacteria (rapid grower).
The aerobic culture of the sputum on blood and MacConkey agar did not grow any respiratory pathogen. The sputum culture was negative for Mycobacterium tuberculosis after 6 weeks of incubation in the LJ medium, and PCR for the MTB complex of the sputum sample came negative.
The patient was started on second-line ATT comprising IV azithromycin 500 mg every 12 h, IV amikacin 1 g once daily, and tab ciplox 500 mg every 12 h. Sternal wound debridement was done 2 days later under general anaesthesia along with omentoplasty. The tissue was sent for aerobic culture, histopathological examination and MTB complex PCR to rule out M. Tuberculosis presence. The aerobic culture did not show any growth till 3 weeks after incubation and PCR for the MTB complex came negative. The mycobacterial culture grew similar colonies as mentioned above 7 days after incubation.
A histopathological examination of the biopsy sample showed chronic necrotizing, granulomatous osteomylitis of the sternum compatible with tuberculosis.
The atypical isolates (rapid growers) were later identified as M. abscessus by using the Genotype Mycobacterium CM kit (Hain Lifescience, Germany). This test is based on the DNA strip technology and permits the identification of common atypical mycobacteria along with the M. tuberculosis complex [Figure 1]. Antimicrobial sensitivity testing was done on Mueller-Hinton agar by the Kirby-Bauer disc diffusion method for amikacin, doxycycline, imipenem, ciprofloxacin, sulfonamide, erythromycin, cefoxitin, and clarithromycin. The strains were found to be sensitive to amikacin, erythromycin, ciprofloxacin, and clarithromycin.
Repeat blood and swab cultures for mycobacterium from the incision site sent 1 week after starting antibiotic therapy were negative. The sternal wound had completely healed and the patient was discharged on the 18th postoperative day with an advice to continue with the prescribed antibiotics for 6 months with regular follow-up.