THE BACTERIAL-DNA CONTENT OF MOUSE ORGANS IN THE CORNELL MODEL OF DORMANT TUBERCULOSIS

Setting: The Cornell model of murine tuberculosis has proved useful fo r demonstrating and studying dormancy. However, it has not previously been used to investigate the molecular aspects of dormancy. Objective: To obtain a profile of the amount of Mycobacterium tuberculosis DNA a t various stages of the Cornell model. Design: BALB/C mice were infect ed intravenously with 2.7 x 10(6) cfu M. tuberculosis strain H37Rv; th ey were left for two weeks, treated for 14 weeks,vith isoniazid and py razinamide and left untreated for a further 14 weeks. Spleens and lung s at start of treatment and at 8, 12, 14, 18, 24 and 28 weeks thereaft er were examined by culture, and DNA in tissue homogenates was quantit ated by polymerase chain reaction (PCR) and dot blot hybridisation. Re sults: Culture and quantitative PCR estimated initial bacillary conten t at about 10(7) per organ. Thereafter, organ cultures rapidly decline d and were usually negative between 14 and 28 weeks. However, during t his period quantitative PCR consistently estimated about 5.5 log(10) b acilli equivalents in spleens and lungs, Dot blot hybridisation sensit ive to about 10 ng bacillary DNA was usually positive pretreatment and occasionally during and after treatment, hence confirming the PCR res ults. Conclusions: There is persistence of significant quantities of M . tuberculosis DNA throughout the various stages of the model. This ma y represent dead bacilli, free DNA or dormant forms.