Facilitated uptake of streptomycin by Kupffer cells during phagocytosis

Wolbachia from the planthopper Laodelphax striatellus establishes a robust, persistent, streptomycin-resistant infection in clonal mosquito cells

The obligate intracellular bacterium, Wolbachia pipientis (Rickettsiales: Anaplasmataceae), distorts reproduction of its arthropod hosts to facilitate invasion of naïve populations. This property makes Wolbachia an attractive "gene drive" agent with potential applications in the control of insect vector populations. Genetic manipulation of Wolbachia will require in vitro systems for its propagation, genetic modification, amplification, and introduction into target insects. Here we show that Wolbachia from the planthopper, Laodelphax striatellus, establishes a robust infection in clonal C7-10 Aedes albopictus mosquito cells. Infected cells, designated C/wStr, expressed radiolabeled proteins that were enriched in cells grown in the absence of antibiotics that inhibit Wolbachia, relative to cultures grown in medium containing tetracycline and rifampicin. Using mass spectrometry, we verified that tryptic peptides from an upregulated 24 kDa band predominantly represented proteins encoded by the Wolbachia genome, including the outer surface protein, Wsp. We further showed that resistance of Wolbachia to streptomycin is associated with a K42R mutation in Wolbachia ribosomal protein S12, and that the pattern of amino acid substitutions in ribosomal protein S12 shows distinct differences in the closely related genera, Wolbachia and Rickettsia.

Multiplication of Mycobacterium tuberculosis Within Normal and "Immune" Mouse Macrophages Cultivated With and Without Streptomycin

Acquired cellular immunity to infection with Mycobacterium tuberculosis is believed to reside in the capacity of mononuclear phagocytes of immunized animals to inhibit intracellular multiplication of the parasite. However, in macrophage tissue culture systems, it has been customary to employ streptomycin in the medium for the purpose of restricting extracellular, but not intracellular, growth of M. tuberculosis. In contrast, our data show that small amounts of streptomycin markedly inhibit intracellular as well as extracellular growth of M. tuberculosis in normal mouse peritoneal macrophages, and that the degree of this inhibition is directly proportional to the concentration of streptomycin used. In the absence of streptomycin, virulent tubercle bacilli grew as rapidly in "immune" macrophages as in normal macrophages. "Immune" macrophages, however, were slightly more resistant to destruction by the intracellularly multiplying mycobacteria. In the presence of streptomycin, however, intracellular mycobacterial growth was inhibited more in "immune" macrophages than in normal macrophages, and this effect also was directly proportional to the concentration of streptomycin used. Virulent mycobacteria grew somewhat more slowly within mouse peritoneal macrophages obtained after induction of a peritoneal exudate with glycogen than in noninduced cells. The rate of multiplication, though, was the same within normal and "immune" induced peritoneal cells except in the presence of streptomycin. As with noninduced macrophages, this drug inhibited the intracellular multiplication of virulent tubercle bacilli more effectively within "immune" induced than within normal induced cells. It would appear, therefore, that the greater inhibition of intracellular multiplication of virulent tubercle bacilli in "immune" macrophages in tissue culture noted by a number of investigators in the past may have been an artifact created by the use of streptomycin in the tissue culture medium.

Uptake of h-dihydrostreptomycin by macrophages in culture

Mouse peritoneal macrophages, in culture, concentrate significant amounts of (3)H-dihydrostreptomycin, provided that the incubation period is sufficiently extended. Macrophages cultured in vitro from both stimulated and unstimulated animals concentrate the antibiotic from growth or maintenance media. The increase in cell-associated radioactivity is linear for almost a week before a plateau is reached. Calculations based on intracellular volumes of the cells indicate that the intracellular concentration of dihydrostreptomycin may attain levels greater than five times that of the external milieu. No uptake is measurable at 4 C, suggesting an active mechanism of transport into the cell. Phagocytosis of killed bacteria during incubation did not increase uptake of the antibiotic nor did the addition of poly-l-ornithine to the medium augment uptake. A nonphagocytic cell line (BHK-21) concentrated (3)H-dihydrostreptomycin to a lesser extent than the macrophages. These observations suggest that a wide variety of mammalian cells may be permeable to the antibiotic, and thus potential bactericidal action on intracellular bacteria cannot be ignored.

Activity of antibiotics against microorganisms ingested by mononuclear phagocytes

The data available on the activity of antibiotics against microorganisms ingested by mononuclear phagocytes are reviewed. The antibacterial activity of penicillins against Staphylococcus aureus is enhanced by human monocytes. This enhancement is possibly brought about by a peptidoglycan-degrading enzyme that is produced and secreted by monocytes. Aminoglycosides affect bacteria ingested by mononuclear phagocytes, but their intracellular activity is limited as compared with that of non-phagocytosed bacteria. Clindamycin, erythromycin, ciprofloxacin and rifampicin are effective against intracellular bacteria. The first three of these antibiotics do not show enhanced activity against phagocytosed bacteria, contrary to what might be expected from their high cell-associated concentrations.

Role of the phagocyte in host-parasite interactions. XI. Relationship between stimulated oxidative metabolism and hydrogen peroxide formation, and intracellular killing

The increased respiratory and hexose monophosphate activities noted in phagocytizing cells results in the formation of hydrogen peroxide. This is brought about by the oxidation of reduced nicotinamide adenine dinucleotide phosphate by its oxidase. Evidence is presented which indicates that this H(2)O(2) is involved in the intracellular killing of bacteria. When molecular oxygen was excluded from phagocytizing leukocytes by anaerobiosis, thus inhibiting H(2)O(2) formation, reduced intracellular killing was observed. In some cases the impairment of leukocytic bactericidal activity by anaerobiosis could be partially reversed by the addition of H(2)O(2). Exogenous catalase also could reduce intracellular killing. In addition, when leukocytic isolates were dialyzed so as to reduce endogenous H(2)O(2), the bactericidal activity of the leukocytes was significantly decreased under both aerobic and anaerobic conditions. These results occurred with both guinea pig and human leukocytes and with several test microorganisms.

Autoradiographic evidence for the impermeability of mouse peritoneal macrophages to tritiated streptomycin

Cultured mouse peritoneal macrophages were found to be relatively impermeable to streptomycin. Based on radioactivity measurements and radioautographic evidence, macrophages were impermeable to tritiated dihydrostreptomycin for periods up to 20 hr of incubation. Little or no intracellular streptomycin could be detected even when incubation was carried out in the presence of therapeutic blood levels of carrier dihydrostreptomycin. When the cultured mouse macrophages were allowed to phagocytize staphylococci, yeast cells, or polystyrene latex particles in the presence of tritiated streptomycin, the impermeability of the cells to the antibiotic was not affected. These observations suggested that the process of phagocytosis does not facilitate the intracellular accumulation of streptomycin, as seems to be the case for the fixed phagocytic cells of the liver.