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Category: Clinical Microbiology; Bacterial Pathogenesis
Lurie’s Pulmonary Tubercle-Count Method, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815684/9781555813734_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555815684/9781555813734_Chap11-2.gifAbstract:
Lurie’s tubercle-count method consists of counting the number of grossly visible primary pulmonary tubercles, present 5 weeks after an aerosol infection of rabbits with virulent human-type tubercle bacilli. It is a quantitative measure of clinically apparent disease. At 5 weeks, the grossly visible primary tubercles are easily recognized, and many microscopic tubercles have regressed. Since human-type tubercle bacilli are not fully virulent for rabbits, the pulmonary-count method has a sensitivity that is not possible with fully virulent strains. The number of grossly visible pulmonary tubercles produced by human-type bacilli decreases (i) when rabbits are infected with bacilli of reduced virulence, (ii) when rabbits of high genetic (innate) resistance are used, and (iii) when rabbits are effectively immunized, so that they can rapidly activate macrophages and stop the development of early tubercles while they are still microscopic in size. Therefore, the pulmonary tubercle-count method can be used to assess (i) bacillary virulence, (ii) the genetic resistance of the host, and (iii) the efficacy of vaccines for tuberculosis.
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Formalin-fixed lungs of a commercial rabbit that inhaled about 33,000 virulent human-type tubercle bacilli (H37Rv) 5 weeks previously. Upon dissection, these lungs contained 131 grossly visible primary tubercles, with no apparent secondary tubercles. The ratio of the number of bacilli estimated as inhaled to the number of grossly visible primary tubercles produced was 250. Effective BCG (and other vaccines for tuberculosis) should increase this ratio at least fivefold (9, 12). Small areas of caseous necrosis are visible in many of the tubercles. On the left, this photograph shows the ventral surface of the right upper, middle, and azygous lobes; on the right, the entire left lung (upper and lower lobes) is shown. The right lower lobe had been removed for culture. This right lower lobe contained 23 grossly visible tubercles and 1.35 × 105 culturable tubercle bacilli. Magnification, ×1.1. Reproduced with permission from reference 3.
A tissue section of a primary lesion similar to the lesions shown in Fig. 1. From left to right are (i) one of the small sites of caseous necrosis, (ii) a surrounding area of large epithelioid macrophages, and (iii) an outside area that is densely infiltrated by smaller macrophages, lymphocytes, and plasma cells. Azure-eosin stain. Magnification, ×350. Reproduced with permission from reference 3.
The number of inhaled bovine-type tubercle bacilli (Ravenel) required to produce one primary pulmonary tubercle in Lurie’s inbred rabbits a
The relative resistance of inbred rabbit strains as determined by their response to quantitative inhalation of human-type bacilli (H37Rv) a
Number of inhaled virulent human-type bacilli (H37Rv) required to produce one grossly visible primary pulmonary tubercle (the ratio) in commercial outbred New Zealand White rabbits a
Virulence of two strains of human-type tubercle bacilli—H37Rv and CDC1551 (Oshkosh)—assessed in rabbits by Lurie’s tubercle-count method a
Variability in tubercle counts in two of Lurie’s inbred rabbit strains a
Vaccine efficacy: number of inhaled human tubercle bacilli (H37Rv) required to produce one grossly visible primary pulmonary tubercle in unvaccinated and vaccinated rabbits a