Scanning electron microscopy of the H37Ra strain of Mycobacterium tuberculosis exposed to isoniazid

The morphology of cells of the H37Ra strain of Mycobacterium tuberculosis exposed to 0.5 mug of isonicotinic acid hydrazide (isoniazid) per ml was examined by scanning electron microscopy (SEM). Cells that were exposed to isoniazid for 3 h showed no detectable change, whereas cells exposed to the drug for 24 h exhibited diverse morphological features. From our examination of these SEM pictures, we have reconstructed the probable sequence of morphological changes to be as follows: (i) the wrinkling of the cell surface was ascribed as the earliest observable change, (ii) the cell surface then became very rough and ragged, (iii) eventually the cytoplasmic material was extruded from the cell, (iv) this event produced a collapsed cell, (v) the cells began to fragment, (vi) the fragmented cells then coalesced to form an amorphous mass of cell debris.

Relationship between the uptake of isoniazid and its action on in vivo mycolic acid synthesis in Mycobacterium tuberculosis

A direct relationship was established between the rate of uptake of isoniazid and the action of this drug on in vivo mycolic acid synthesis in Mycobacterium tuberculosis H37Ra. The rate of uptake of isoniazid increased linearly with its external concentration and appeared to reach a maximal value of 52 pmoles per hr per 10(9) cells at an external concentration of about 13 mum. Correspondingly, the rate of inhibition of mycolic acid synthesis increased with the rise in the rate of uptake of the drug. A 50% inhibition of mycolic acid synthesis occurred when the uptake of isoniazid reached 5.2 pmoles per 10(9) cells. Calculations showed that this level of drug uptake represents an internal cellular concentration of 9 mum. These results show clearly that the action of isoniazid on the mycolate synthetase system of M. tuberculosis is rapid and that this enzyme system is highly sensitive to the drug.

Effect of isoniazid on the in vivo mycolic acid synthesis, cell growth, and viability of Mycobacterium tuberculosis

When an actively growing culture of the H37Ra strain of Mycobacterium tuberculosis was exposed to isoniazid at a concentration of 0.5 mug/ml, the cells began to lose their ability to synthesize mycolic acids immediately. After 60 min, the cells had completely lost this ability. The synthesis of the three mycolate components-alpha-mycolate, methoxymycolate, and beta-mycolate-was inhibited. The viability of the isoniazid-treated cells was unaffected up to about 60 min of exposure, after which time there was a gradual decline in the viability to about 18% after 180 min. Correspondingly, growth of the drug-treated cells slowed down and stopped after 24 hr. The inhibition of the synthesis of mycolic acids was reversible if the drug was removed before the loss of viability set in. Incubation of the viable cells in the absence of the drug for 24 hr restored the mycolate synthesis. These results strongly suggest that the inhibition of the synthesis of the mycolic acids is closely associated with the primary mechanism of action of isoniazid on the tubercle bacilli. The sequence of events which leads to the loss of viability of cells exposed to isoniazid is described.

New multichannel optical correlator

This paper describes a multichannel optical correlator that uses two spatial dimensions to achieve multi-channel capability and operates in real time. Given I signals, r(i)(t), and J signals, s(j)(t), it can produce the I x J cross products, r(i)(t)s(j)(t), averaged over some interval. Multiplication is based on the fact that the square of the sum of two signals contains their cross product. Light fields modulated by the signals are added and their sum squared by measuring its intensity. An experimental correlator and its performance are described along with applications.

Elongation of fatty acids in Mycobacterium tuberculosis

Cell-free extracts of the H37Ra strain of Mycobacterium tuberculosis contain a soluble enzyme system which catalyzes an elongation reaction of long-chain fatty acids. The predominant reaction involves the addition of a single C(2) unit to the acceptor fatty acid; the elongation takes place exclusively at the carboxyl end of the acceptor molecule. The endogenous acceptor lipid can be removed by solvent extraction of the enzyme system. The lipid-depleted enzyme can be fully reactivated with external acyl coenzyme A, after which elongation with acetyl coenzyme A takes place. The elongation reaction is avidin-insensitive and does not require adenosine triphosphate. Reduced nicotinamide adenine dinucleotide is the source of reducing equivalent, whereas reduced nicotinamide adenine dinucleotide phosphate is without effect.

Repression of thiaminase I by thiamine and related compounds in Bacillus thiaminolyticus

The extracellular enzyme thiaminase I from Bacillus thiaminolyticus is repressible by thiamine. Either one of the heterocyclic moieties of this vitamin supported limited growth of this organism but had no effect on thiaminase I production. However, a combination of these two resulted in optimal growth and partial repression of this enzyme. The products of the base exchange reaction catalyzed by thiaminase I are not functional in repression when present alone. The simultaneous presence of both reaction products, i.e., N-[5-(4-amino-2-methylpyrimidinyl)] methyl aniline and 5-(2′-hydroxy-ethyl)-4-methylthiazole, can replace the vitamin B1 requirement for growth and give the same degree of enzyme repression. Neither pyrithiamine nor oxythiamine inhibited growth of the organism when present in a 100:1 molar ratio to thiamine. Pyrithiamine and vitamin B1 repressed thiaminase I to approximately the same extent, whereas oxythiamine was only partially functional in this process.