An electron microscopy study of intra-cellular mycobacteria in experimental mouse tuberculosis

The effects of disinfectant foam on microbial biofilms

This investigation examined the effects of common aqueous biocides and disinfectant foams derived from them on Pseudomonas aeruginosa biofilms. Biofilms were grown on stainless steel coupons under standardised conditions in a reactor supplemented with low concentrations of organic matter to simulate conditions prevalent in industrial systems. Five-day-old biofilms formed under ambient conditions with continuous agitation demonstrated a low coefficient of variation (5.809%) amongst viable biofilm bacteria from independent trials. Scanning electron microscopy revealed biofilms on coupons with viable biofilm bacteria observed by confocal microscopy. An aqueous solution of a common foaming agent amine oxide (AO) produced negligible effects on bacterial viability in biofilms (p>0.05). However, significant biofilm inactivation was noted with aqueous solutions of common biocides (peracetic acid, sodium hypochlorite, sodium ethylenediaminetetraacetic acid) with or without AO (p<0.05). Aereation of a mixture of AO with each of these common biocides resulted in significant reductions in the viability of biofilm bacteria (p<0.05). In contrast, limited effects were noted by foam devoid of biocides. A relationship between microbial inactivation and the concentration of biocide in foam (ranging from 0.1-0.5%) and exposure period were noted (p<0.05). Although, lower numbers of viable biofilm bacteria were recovered after treatment with the disinfectant foam than by the cognate aqueous biocide, significant differences between these treatments were not evident (p>0.05). In summary, the studies revealed significant biofilm inactivation by biocidal foam prepared with common biocides. Validation of foam disinfectants in controlled trials at manufacturing sites may facilitate developments for clean in place applications. Advantages of foam disinfectants include reductions in the volumes of biocides for industrial disinfection and in their disposal after use.

Triton WR-1339 as a biological-response modifier in mycobacterial infection

A non-ionic detergent, Triton WR-1339, prolonged markedly the survival time of mice infected fatally with virulent mycobacteria, though it exerted only a limited effect on the fate of tissue viable counts. The combined administration of Triton WR-1339 with lentinan (a glucan purified from the Japanese mushroom Lentinus edodes) was more effective than the single administration of each. This detergent was not lytic to red blood cells or lysosomes, but its substantial effect on the biomembrane was suggested by cold-shock experiment of hemolysis. It was considered that Triton WR-1339 is a biological-response modifier, possibly altering the interaction between the mycobacterial surface and the membrane structure of phagocytes.

Ultrastructural studies on the effect of Triton WR-1339 on macrophage-mycobacteria interaction

Mycobacterium bovis (BCG organisms) suspended in saline or a 5% solution of a non-ionic detergent, Triton WR-1339, was injected intraperitoneally into mice. Electron-microscopic observation was carried out on peritoneal exudate cells harvested therefrom. Electron-lucent vacuoles limited by the membrane structure were found in macrophages of the mice injected with BCG suspended in the detergent, but not in polymorphonuclear leukocytes or lymphocytes. Mycobacterial cells were present within such vacuoles. Without the detergent, the ingested mycobacterial cells were in close contact with the phagosomal membrane. Within the electron-lucent vacuoles, however, such close contact was not present. These observations, together with other collateral findings, led us to a view that Triton WR-1339 may inhibit the interaction between mycobacteria and the phagosomal membrane by intervening between them thus making the progress of infection delayed.

Bactericidal activity of the membrane fraction isolated from phagocytes of mice and its stimulation by melittin

The membrane fraction prepared from mouse peritoneal exudate cells was incubated with mycobacteria, staphylococci, or E. coli in acetate buffer of pH 5.6 to follow the fate of viable bacilli. The membrane fraction exhibited bactericidal effect on mycobacteria and staphylococci, but not on E. coli. The activity to kill mycobacteria, as well as the endogenous phospholipase A2 activity, of the membrane fraction was markedly enhanced by melittin, a basic peptide from bee venom, and inhibited by indomethacin and EDTA. The role of the enzyme activity in the bactericidal activity was discussed.

Liposomes-mycobacteria incubation systems as a partial model of host-parasite interaction at cell membrane level

The multilamellar lecithin-cholesterol liposomes entrapping carboxyfluorescence as a specific marker were prepared to be incubated with mycobacteria. The extent of resulting liposomal lysis was measured by marker release. Mycobacteria were highly active in this respect regardless of the species. Staphylococci were much less active and E. coli was completely inactive. Molecular species of lecithin and their ratio to cholesterol were related with the liposome sensitivity to mycobacteria. Ultrastructural and biochemical study showed that liposomes can be in close contact with mycobacteria and lecithins are degraded so that released fatty acids are incorporated into bacterial lipids, especially in virulent species. Liposomes-mycobacteria interaction was discussed as a partial model of the phagocyte-parasite interaction at the membrane level.

Mechanism of bactericidal activity of lysolecithin and its biological implication

Lysolecithin exhibited bactericidal effect on mycobacteria and staphylococci, but not on E. coli. The effect on staphylococci was manifested shortly after exposure, but that on mycobacteria was of the delayed type. The mycobactericidal activity was dependent on the fatty acid moiety of the chemical structure reflecting the cytotoxicity of the free form. The activity on staphylococci was not, however, of such fatty acid dependency and showed the same pattern of molecular species in hemolytic activity. These and other collateral findings suggest that the mycobactericidal effect of lysolecithin is due to the free fatty acids released therefrom by the enzymatic activity of the exposed bacterial cells, but that staphylococci are killed by the detergent effect of the whole lysolecithin molecule.

Purification and characterization of beta-glucuronidase inhibitor from Mycobacterium tuberculosis

Factors inhibitory to beta-glucuronidase were found in the culture filtrate and in a bacillary extract of Mycobacterium tuberculosis H37Rv grown for 6 weeks on Sauton medium. The inhibitors were purified by ammonium sulfate fractionation, treatment with n-butanol and streptomycin, and chromatography on DEAE-Sepharose CL-6B. Two inhibitors were obtained from the culture filtrate. The molecular weights were estimated to be 25,500 and 15,500 by gel filtration on a Sephadex G-75 column. Three inhibitors were purified from the bacillary extract, two of which were similar to those from the culture filtrate. The molecular weight of the third inhibitor was 21,000. However, the molecular weight of all the denatured inhibitors was 8,600 in the presence of sodium dodecyl sulfate. The inhibitors contained extremely high amounts of glutamic and aspartic acids and had a highly acidic isoelectric point of pH 2.5. The inhibitors acted noncompetitively against beta-glucuronidase of guinea pig origin at an optimal pH 4.5. beta-Glucuronidases from human peripheral leukocytes and beef liver were partially sensitive to the inhibitors; all the other enzymes tested for sensitivity were unaffected by the inhibitors.

Electron microscopic demonstration of close contact between intracellular mycobacteria and the phagosomal membrane

Ultrathin sections of granulomatous lung lesions of tuberculous mice were subjected to electron microscopy to observe the intraphagosomal behaviour of mycobacteria. The close contact between the external surface of the bacterial cell wall and the phagosomal membrane was a characteristic feature, This was also observed with ultrathin sections of a mycobacterial specimen harvested from the homogenate of such lungs. The significance of this event was interpreted in relation to the mechanism of mycobacterial infection.

A novel type of lymphocyte-macrophage association revealed electron microscopically in tuberculous lung lesions of mice

Electron microscopic survey of tuberculous lung lesions of mice revealed a novel type of lymphocyte-macrophage association. The finger-like projections with sharp or blunt tips of lymphocytes area formed as if pushing deeply the macrophage membrane to form pockets matching the shape of the projections. Intimate membrane contact occurs between these two cells, particularly at the leading edges. The biological significance of this morphological event remains to be a subject for future study.