Mycobacterium abscessus

Mycobacterium abscessus complex (MABSC) is a group of rapidly growing, multidrug-resistant non-tuberculous mycobacteria (NTM) species that are common soil and water contaminants. Although M. abscessus complex most commonly cause chronic lung infection and skin and soft tissue infection (SSTI), the complex can also cause infection in almost all human organs, mostly in patients with suppressed immune systems. Amongst NTM species responsible for disease, infection caused by M. abscessus complex are more difficult to treat due to antimicrobial drug resistance. M. abscessus cells are gram-positive, nonmotile, acid-fast rods about 1.0–2.5 µm long by 0.5 µm wide. They may form colonies on Löwenstein–Jensen media that appear smooth or rough, white or greyish and nonphotochromogenic. M. abscessus shows growth at 28 °C and 37 °C after 7 days but not at 43 °C. It may grow on MacConkey agar at 28 °C and even 37 °C.It shows tolerance to saline media (5% NaCl) as well as 500 mg/l hydroxylamine (Ogawa egg medium) and 0.2% picrate (Sauton agar medium). Strains of the species have been shown to degrade the antibiotic p-aminosalicylate. M. abscessus has also been shown to produce arylsulfatase but not of nitrate reductase and Tween 80 hydrolase.It shows a negative result for the iron uptake test and no utilisation of fructose, glucose, oxalate or citrate as sole carbon sources. M. abscessus and M. chelonae can be distinguished from M. fortuitum or M. peregrinum by their failure to reduce nitrate and to take up iron.Tolerance to 5% NaCl in Löwenstein-Jensen media, tolerance to 0.2% picrate in Sauton agar, and non-utilisation of citrate as a sole carbon source are characteristics that distinguish M. abscessus from M. chelonae. M. abscessus and M. chelonae sequevar I share an identical sequence in the 54-510 region of 16S rRNA, though both species can be differentiated by their hsp65, ITS or rpoB gene sequences. A draft genome sequence of M. abscessus subsp. bolletii BDT was completed in 2012. Since then, a large number of strains from this subspecies have had their genomes sequenced, leading to a clarification of subspecies boundaries. In 1992, M. abscessus was first recognised as a distinct species. In 2006, this group was separated into three subspecies: abscessus, bolletii and massiliense. In 2011, massiliense and bolletii were briefly merged into a single subspecies, but were subsequently separated again following greater availability of genome sequence data, which showed the three subspecies formed genetically distinct groups. These distinct groups also correspond to important biological differences. Clinically important differences include differing susceptibilities to antibiotics. M. abscessus subsp. abscessus and bolletii carry a common antibiotic resistance gene which confers resistance to macrolide antibiotics, while massiliense is thought to carry a non-functional copy, and is therefore more susceptible to antibiotics and more easily treated. M. abscessus can cause lung disease, skin infections, central nervous system infections, bacteremia, eye infections, and other, less common diseases. Chronic lung disease occurs most commonly in vulnerable hosts with underlying lung disease such as cystic fibrosis, bronchiectasis, and prior tuberculosis. Clinical symptoms of lung infection vary in scope and intensity but commonly include chronic cough, often with purulent sputum. Haemoptysis may also be present. Systemic symptoms include malaise, fatigue, and weight loss in advance disease. The diagnosis of M. abscessus pulmonary infection requires the presence of symptoms, radiologic abnormalities, and microbiologic cultures.