Characterization of non-tuberculosis mycobacteria by neutron radiography

The genus Mycobacterium shares many characteristics with Corynebacterium and Actinomyces genera, among which the genomic guanine plus cytosine content and the production of long branched-chain fatty acids, known as mycolic acids are enhanced. Growth rate and optimal temperature of mycobacteria are variable. The genus comprises more than 140 known species; however Mycobacterium fortuitum, a fast growing nontuberculous mycobacterium, is clinically significant, because it has been associated to several lesions following surgery procedures such as liposuction, silicone breast and pacemaker implants, exposure to prosthetic materials besides sporadic lesions in the skin, soft tissues and rarely lungs. The objective of the present study is to reduce the time necessary for M. fortuitum characterization based on its morphology and the use of the neutron radiography technique substituting the classical biochemical assays. We also aim to confirm the utility of dendrimers as boron carriers. The samples were sterilized through conventional protocols using 10% formaldehyde. In the incubation process, two solutions with different molar ratios (10:1 and 20:1) of sodium borate and PAMAM G4 dendrimer and also pure sodium borate were used. After doping and sterilization procedures, the samples were deposited on CR-39 sheets, irradiated with a 4.6×105 n/cm2 s thermal neutron flux for 30 min, from the J-9 irradiation channel of the Argonauta IEN/CNEN reactor. The images registered in the CR-39 were visualized in a Nikon E400 optical transmission microscope and captured by a Nikon Coolpix 995 digital camera. Developing the nuclear tracks registered in the CR-39 allowed a 1000× enlargement of mycobacterium images, facilitating their characterization, the use of more sophisticated equipment not being necessary. The use of neutron radiography technique reduced the time necessary for characterization. Doping with PAMAM dendrimer improved the visualization of NTM in neutron radiography images.

► We aimed to characterize morphologically nontuberculous mycobacterium by neutron radiography.
► This methodology greatly reduced the time to identify of NTM compared to conventional microbiological assays.
► Images of NMT resulted magnified 1000x and are displayed on a conventional optical microscope.
► Doping with PAMAM dendrimer and sodium borate improved the visualization of NTM by NR.