Micobacterias en muestras de autopsias / Mycobacteria in autopsy samples

Se estudiaron bacteriológicamente 83 muestras provenientes de autopsias (34 tejido ganglionar y 24 leptomeninges) correspondientes a 34 pacientes fallecidos y clínica de tuberculosis y/o VIH. En el 10,8 por ciento (9/83) hubo crecimiento de micobacterias: cuatro de M. tuberculosis y cinco micobacterias no tuberculosas (MNT): M. gordonae (1), M. vaccae (1) y tres que no pudieron ser identificadas bioquímicamente. Seis de estos aislados fueron estudiados por PCR, mediante amplificación de la secuencia IS6110. Se reconfirmaron como micobacterias del complejo tuberculoso (MCT) tres aislados (50 por ciento). En los tres aislados restantes, correspondientes a MNT, no se obtuvo amplificación de la secuencia IS6110. Sin embargo, utilizando la amplicación seguida de un análisis polimórfico de restricción (PRA) de un segmento del gen hsp65, éstos pudieron ser identificados como M. porcinum, M. vaccae y M. gordonae tipo II

[Transcription regulation in the ribosomal RNA operon of mycobacteria]. / Regulación de la transcripcion en el operon de ARN ribosomal en micobacterias.

Tuberculosis is a extremely important infectious disease, caused by the bacilli Mycobacterium tuberculosis. One of the characteristic of this bacteria is its very slow rate of growth, that allows it to survive for long periods of time inside the host cells. Among the genetic elements involved in growth regulation the operon rrn is of extreme importance. This operon contains the genes that code the three rRNA molecules, essential components of the bacterial ribosome. The tuberculosis bacilli, differently from most of the microorganisms, has a single copy of the rrn operon per genome, meaning that it must be submitted to very strict control mechanisms. Another important conclusion is that the sequences of the rrn operon constitute ideal targets for anti-mycobacterial drugs. In this work we have studied some of the elements involved in transcription control in M. tuberculosis, particularly those present in the leader region of the operon. By using basic molecular biology techniques we have identified sequence elements in the leader region that seem to be involved in the control of transcription elongation, by a mechanism related to anti-termination.

Schistosoma mansoni infection in owl monkeys (Aontus nancymai): evidence for the early elimination of adult worms.

Detailed parasitologic, serologic, clinical and histopathologic studies were conducted in owl monkeys (Aotus nancymai) exposed to varying numbers of cercariae of Schistosoma mansoni. All the experimental animals had clinical symptoms suggestive of infection (weight loss diarrhoea, mucus in stools, etc.) which were not seen in uninfected individuals. The only A. vociferans included in this study passed S. mansoni eggs 8 weeks after infection. None of the A. nancymai passed eggs in their faeces. No adult worms were recovered following perfusion of the sacrificed experimental monkeys, suggesting that they were early eliminated. Serological techniques (ELISA-SEA and COPT) allowed diagnosis of infection, starting 9 weeks post challenge, in all but one A. nancymai exposed to 100 cercariae. Granulomas containing eggs were observed predominantly in liver and less extensively in intestine, suggesting that adult worms were mainly lodged in the intrahepatic portal system. We conclude that A. nancymai is susceptible to infection with S. mansoi, with the worms reaching sexual maturity, but being eliminated shortly after oviposition.

Strategies used by pathogenic and nonpathogenic mycobacteria to synthesize rRNA.

One rRNA operon of all mycobacteria studied so far is located downstream from a gene thought to code for the enzyme UDP-N-acetylglucosamine carboxyvinyl transferase (UNAcGCT), which is important to cell wall synthesis. This operon has been designated rrnAf for fast-growing mycobacteria and rrnAs for slow growers. We have investigated the upstream sequences and promoter activities of rrnA operons of typical fast growers which also possess a second rrn (rrnBf) operon and of the rrnA operons of the fast growers Mycobacterium abscessus and Mycobacterium chelonae, which each have a single rrn operon per genome. These fast growers have a common strategy for increasing the efficiency of transcription of their rrnA operons, thereby increasing the cells' potential for ribosome synthesis. This strategy involves the use of multiple (three to five) promoters which may have arisen through successive duplication events. Thus we have identified a hypervariable multiple promoter region (HMPR) located between the UNAcGCT gene and the 16S rRNA coding region. Two promoters, P1 and PCL1, appear to play pivotal roles in mycobacterial rRNA synthesis; they are present in all of the species examined and are the only promoters used for rRNA synthesis by the pathogenic slow growers. P1 is located within the coding region of the UNAcGCT gene, and PCL1 has a characteristic sequence that is related to but distinct from that of the additional promoters. In fast-growing species, P1 and PCL1 produce less than 10% of rRNA transcripts, so the additional promoters found in the HMPR are important in increasing the potential for rRNA synthesis during rapid growth. In contrast, rrnB operons appear to be regulated by a single promoter; because less divergence has taken place, rrnB appears to be younger than rrnA.