Human oral defenses against gram-negative rods

Gram-negative rods are unusual pharyngeal isolates in normal man, which suggests the presence of effective oral defense mechanisms against these organisms. To understand this protection better, we studied the elimination of gram-negative rods from the mouth after gargle challenge. Suspensions of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis (108 organisms per ml) were gargled by normal volunteers, and pharyngeal swabs for serial quantitative cultures were taken for 3 hours. Initial swabs yielded approximately 10(5) organisms. Bacterial counts rapidly decreased, and less than 1 per cent of the original inoculum was still recoverable 3 hours later. Studies of tongue, pharynx, and buccal mucosa samples showed the most rapid decrease in buccal mucosa samples and the slowest decrease in tongue swabs. To evaluate physical clearance, gargle challenges were performed using E. coli radiolabeled with technetium-99m. External counts of the oral cavity decreased rapidly, with 21.8, 14.7, 8.9, and 7.8 percent of the initial counts remaining at 30, 60, 120, and 180 min, respectively. Nonpiliated E. coli adhered poorly to buccal epithelial cells in vitro, in contrast to good adherence when piliated strains were tested. Despite these findings, no differences in radiolabel clearance was noted in vivo using piliated and nonpiliated E. coli for gargle challenges. Normal oral defenses against gram-negative rods are highly effective and seem to involve both physical clearance and local bactericidal activity.

Chloroplast genes in Chlamydomonas affecting organelle ribosomes. Genetic and biochemical analysis of analysis of antibiotic-resistant mutants at several gene loci

Six chloroplast gene mutants of Chlamydomonas reinhardtii resistant to spectinomycin, erythromycin, or streptomycin have been assessed for antibiotic resistance of their chloroplast ribosomes. Four of these mutations clearly confer high levels of antibiotic resistance on the chloroplast ribosomes both in vivo. Although one mutant resistant to streptomycin and one resistant to spectinomycin have chloroplast ribosomes as sensitive to antibiotics as those of wild type in vivo, these mutations can be shown to alter the wildtype sensitivity of chloroplast ribosomes in polynucleotide-directed amino acid incorporation in vitro. Genetic analysis of these six chloroplast mutants and three similar mutants (Sager, 1972), two of which have been shown to affect chloroplast ribosomes (Mets and Bogorad, 1972; Schlanger and Sager, 1974), indicates that in Chlamydomonas at least three chloroplast gene loci can affect streptomycin resistance of chloroplast ribosomes and that two can affect erythromycin resistance. The three spectinomycin-resistant mutants examined appear to be alleles at a single chloroplast gene locus, but may represent mutations at two different sites within the same gene. Unlike wild type, the streptomycin and spectinomycin resistant mutants which have chloroplast ribosomes sensitive to antibiotics in vivo, grow well in the presence of antibiotic by respiring exogenously supplied acetate as a carbon source, and have normal levels of cytochrome oxidase activity and cyanide-sensitive respiration. We conclude that mitochondrial protein synthesis in these mutants is resistant to these antibiotics, whereas in wild type it is sensitive. To explain the behavior of these two chloroplast gene mutants as well as other one-step mutants which are resistant both photosynthetically and when respiring acetate in the dark, we have postulated that a mutation in a single chloroplast gene may result in alteration of both chloroplast and mitochondrial ribosomes. Mitochondrial resistance would appear to be the minimal necessary condition for survival of all such mutants, and antibiotic-resistant chloroplast ribosomes would be necessary for survival only under photosynthetic conditions.

Genetic control of chlorophyll biosynthesis in Chlamydomonas. Analysis of mutants at two loci mediating the conversion of protoporphyrin-IX to magnesium protoporphyrin

In this report we describe two nonallelic Mendelian protoporphyrin accumulating mutants br(s)-1 and br(c)-1. Results of experiments with these mutants lead us to postulate that porphyrin biosynthesis branches into light and dark steps between protoporphyrin-IX and magnesium protoporphyrin. We hypothesize that the br(c) locus controls a dark step while the br(s) locus either controls a step in the main pathway before the branch or mediates the preparation of the magnesium ion for its insertion into protoporphyrin-IX. The br(s)-1 mutant is thought to be light sensitive because a block prior to the branch point in the porphyrin pathway prevents chlorophyll formation in either the light or the dark. The br(c)-1 mutant, which also accumulates protoporphyrin in the dark, forms chlorophyll and chloroplast lamellae when transferred to the light, showing that function of the porphyrin pathway is normal in the light.