THIN-SECTION ELECTRON MICROGRAPHS OF MONOCYTES INFECTED WITH BRUCELLA SUIS

Application of polymerase chain reaction to detect burkholderia pseudomallei and Brucella species in buffy coat from patients with febrile illness among rural and peri-urban population

Context:

Melioidosis and Brucellosis are important endemic infections among people in India, especially in rural settings. Conventional detection techniques have several limitations. Only a few studies exist on the prevalence of Melioidosis and Brucellosis in rural area especially in India.

Aim:

We sought to evaluate detection of Burkholderia pseudomallei and Brucella spp. among patients presenting febrile illness.

Material and Methods:

Previously described polymerase chain reaction (PCR) assays for both pathogens were evaluated with Deoxyribonucleic acid extracts of buffy coat samples collected from 301 patients recruited prospectively. Data was not amenable to statistical analysis.

Results:

The PCR showed specific amplification and no non-specific amplification with heterologous Gram-negative bacilli. The lower limit of detection of the assay for B. pseudomallei was determined to be 1 colony-forming unit /mL and for Brucella it was 1.95 × 10³ plasmids per microliter. Blood culture in automated blood culture system was negative for all the samples. This prospective study carried out in southern India for the first time. PCR for Brucella was positive in 1% of the patient samples whereas 0.3% was positive for B. pseudomallei.

Conclusion:

The finding of Brucella and Burkholderia infections in our populations leads us to suggest that tests for Brucella and B. pseudomallei should also form part of a diagnostic platform for patients with Pyrexia of unknown origin in tropical developing countries.

Electron microscopic study on phagocytosis of staphylococci by mouse peritoneal macrophages

Macrophages from the mouse peritoneal cavity were examined by electron microscopy at various time intervals up to 24 h after intraperitoneal administration of each of three strains of staphylococci different in virulence for mice: high-virulent, low-virulent, and avirulent strains. After engulfment, avirulent bacteria were highly liable to intracellular digestion, resulting in almost complete degradation within 24 h after injection, whereas high-virulent bacteria were more resistant to digestion, some showing figures suggestive of a dividing process; the gross configuration of most of the ingested bacteria was relatively well preserved over the 24-h period. Time-dependent morphological changes of low-virulent bacteria were intermediate. Among the most distinct cytoplasmic responses to the ingested bacteria was the formation of phagocytic vacuoles around them, the type of which was dependent on the staphylococcal strain infected; ingestion of avirulent bacteria led to formation of vacuoles in which the bacteria were surrounded by a halo of amorphous material of moderate density, which may be the lysosomal content. In contrast, larger vacuoles developed after ingestion of high-virulent bacteria and contained only a small quantity of such amorphous materials. Both types of phagocytic vacuoles were seen around the low-virulent bacteria ingested. Some degenerative changes were found in the macrophages ingesting high- or low-virulent bacteria, but were not in those ingesting avirulent bacteria. Thus, resistance to intracellular degradation, as well as cytotoxicity toward phagocytes of staphylococcal strains, can be correlated with their virulence.

Electron microscopy of tissue culture cells infected with Brucella abortus

Thin sections of hamster kidney tissue cultures were examined by electron microscopy over a 7-day period after infection with Brucella abortus 3183. Numerous bacteria and structures resembling L-forms were present both intracellularly and extracellularly after the first 24 hr of infection. Most intracellular microorganisms were enclosed by a cytoplasmic membrane, but in a few instances no limiting membrane was detected. After 4 to 7 days, fewer microorganisms were present, and most normal-appearing bacteria were intracellular, particularly in antibiotic-treated cultures. Structures typical of Brucella L-forms were extracellular at the latter time intervals. Several structures were observed in cells from infected cultures whose relationship to the infecting organisms is not known. These consisted of various membranous structures within cytoplasmic vacuoles, myelin-like structures surrounding occasional intracellular organisms, and small bodies present within vacuoles and extracellularly. The latter structures observed throughout the experimental period appeared to occur more frequently as the duration of the infection increased.

An examination of the cytotoxic effects of silica on macrophages

Effects of silica, diamond dust, and carrageenan on mouse macrophages were studied by phase-contrast cine-micrography, electron microscopy, histochemical techniques for lysosomal enzymes and measurements of the release of lysosomal enzymes into the culture medium. All added materials were rapidly taken up into phagosomes, to which lysosomes became attached. In all cases lysosomal enzymes were discharged into the phagosomes to form secondary lysosomes. Within 24 hr most of the silica particles and enzyme had escaped from the secondary lysosomes and lysosomal enzymes were found in the culture media. Most macrophages were killed by this time. With nontoxic particles (diamond dust, aluminium-coated silica, or silica in the presence of the protective agent polyvinyl-pyridine-N-oxide, PVPNO) ingested particles and lysosomal enzymes were retained within the secondary lysosomes for a much longer time, and cytotoxic effects were considerably delayed or absent altogether. It is concluded that silica particles are toxic because they are efficiently taken up by macrophages and can then react relatively rapidly with the membranes surrounding the secondary lysosomes. The particles and lytic enzymes can then escape into the cytoplasm, producing general damage, and thence into the culture medium. It is suggested that hydrogen bonding of silicic acid with lipid and protein constituents of the membrane accounts for the induced permeability. Protective agents such as PVPNO are retamed in lysosomes and preferentially form hydrogen bonds with silicic acid. Carrageenan is demonstrable within macrophages by its metachromatic reaction. It brings about release of enzymes from secondary lysosomes, but much more slowly than does silica. Silica released from killed macrophages is as cytotoxic as the original preparation. It is suggested that repeated cycles of macrophage killing in vivo leads to the mobilization of fibroblasts and fibrogenesis characterizing the disease silicosis.

Electron microscopy of Listeria monocytogenes-infected mouse spleen

Armstrong, B. A. (The University of Kansas, Lawrence), and C. P. Sword. Electron microscopy of Listeria monocytogenes-infected mouse spleen. J. Bacteriol. 91:1346-1355. 1966.-Mouse spleen infected with Listeria monocytogenes was observed during the acute phase of infection; 72 hr after infection, organisms were usually found within phagocytic vacuoles in the cytoplasm of macrophages. These vacuoles, which resembled phagosomes, often contained several organisms as well as varying amounts of amorphous electron-dense material, ferritin-like particles, membrane fragments, and vesicles of varying density. Breakdown of vacuolar membranes appeared to be accompanied by damage to the host cell cytoplasm. Nuclear membrane damage was occasionally observed when phagocytic vacuoles were close to the nucleus.

Tetracycline Fluorescence in Permeability Studies of Membranes around Intracellular Parasites

Certain protozoa, bacteria, and viruses when phagocytosed by host cells become surrounded by an intracytoplasmic boundary. This membrane prevents the fluorescent antibiotic tetracycline from entering the parasites when it is added to the medium, since they show no fluorescence, whereas extracellular parasites are immediately visible. As soon as the host cell dies, the intracellular parasites also become visible. This indicates that the boundary probably is of host origin. This phenomenon provides a means for selective permeability studies of such boundaries. A similar exclusion of tetracycline from certain extracellular parasites is seen in the presence of whole serum.