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The effect of feeding to cockroaches the antimicrobial agent metronidazole, which acts specifically against anaerobes, was assessed by light and scanning electron microscopy, bacteriological examination, and methane formation. Types of organisms and total numbers were greatly reduced from controls. The health of mature adults was unaffected, but stunting occurred in subadult animals maintained on the antibiotic from hatching. The intracellular bacteria of the fat body were not affected by the drug. The results are discussed with respect to a proposed microbe-host extracellular symbiosis.Studies of the alimentary canal of the cockroach indicate the presence of an elaborate hindgut microflora (7). Many of the attached microbes and unusual morphological forms have been refractory to isolation. As an alternative to the isolation and characterization of all the anaerobes possible, we have approached the problem of interactions of the hindgut flora with the animal via the possibilities of transport of microbial products across the hindgut wall (J. W. Bracke and A.

Previous investigators have suggested that opsonization of two Bacteroides species is mediated exclusively by the alternative complement pathway and requires immunoglobulins. In this study, the nature of the opsonic factors in nonimmune human serum for four species of Bacteroides was investigated by measuring uptake of [3H]thymidine-labeled bacteria by human polymorphonuclear leukocytes. Normal human serum, C2-deficient serum, immunoglobulindeficient serum, and serum chelated with ethylene glycol-bis(,f-aminoethyl ether)-N,N-tetraacetic acid (EGTA), MgEGTA, and ethylenediaminetetraacetic acid (EDTA) were used as opsonic sources. Heat inactivation of each of these sera significantly reduced its opsonic activity for all four Bacteroides species, suggesting that serum complement was essential for effective opsonization. All strains were opsonized in the absence of the classical complement pathway; however, kinetics studies revealed that opsonization proceeded at a significantly faster rate when the classical complement pathway was intact. Although two strains were opsonized in immunoglobulin-deficient sera, opsonization was less efficient and appeared to occur via the alternative complement pathway. Unexpectedly, all strains were well opsonized by the classical complement pathway in 10% serum which had been effectively chelated with EGTA or EDTA. The explanation for this finding is unknown; however, it is possible that cell wall cations of Bacteroides species may participate in the activation of complement in chelated serum, resulting in effective opsonization. It was also found that Bacteroides, when incubated with an Escherichia coli strain in normal serum, could compete for opsonins and thereby reduce phagocytosis ofE. coli. It is possible that competition for opsonins among bacterial species contributes to the synergistic role these organisms share in mixed floral infections. An effective osponic source including complement or immunoglobulin is required to prepare bacteria for maximal phagocytosis by polymorphonuclear leukocytes (PMNL). Anderson et al.(1) have shown that encapsulated strains of Haemophilus influenzae are opsonized in immune serum by the classical complement pathway, whereas Quinn and co-workers (26) found that these same strains were opsonized by the alternative complement pathway in nonimmune serum. Other investigators (31, 34) have shown that several bacterial species can be opsonized by the complement system in the relative absence of immunoglobulin. In contrast to unencapsulated organisms, encapsulated bacteria appear to require specific antibodies for optimal opsonization (3, 24).Casciato et al. (4) were the first to study opsonization and phagocytosis of Bacteroides species. They demonstrated that B. thetaiotaomicron could be opsonized only by heat-la-bile serum opsonic factors and that phagocytosis by PMNL occurred equally well under anaerobic and aerobic conditions. Recently, Bjornson and Bjornson (2) studied two species of Bacteroides and concluded that optimal opsonization required bot...

A morphological study employing scanning and transmission electron microscopy was made of the alimentary tract of the American cockroach, Periplaneta americana L. A complex microbiota of diverse morphology, which could not be readily dislodged, was observed and found to be restricted to the hindgut, particularly the colon. Numerous filamentous forms were noted, and some are described, including the morphologically distinct Methanospirillum. Flora was noted attached to the cuticular lining and cuticular filaments of the colon, and several spiral forms were observed in the luminal contents from the colon.

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Serum, gingival crevicular fluid, and parotid, submandibular, and labial minor gland saliva from four individuals stimulated glucan formation from sucrose by the Streptococcus mutans strain 6715 dextransucrase (EC 2.4.1.5). At final dilutions of 1:10 all of the fluids stimulated crude enzyme preparations approximately 1.8-fold. The fluids stimulated the purified water-insoluble glucan-synthesizing form of the dextransucrase approximately 3.2-fold and the water-soluble glucanproducing form of the enzyme approximately 2.4-fold. The fluids all contained concentrations of stimulatory material that could be reduced to undetectable levels only after dilutions of greater than 1:1,000. The increased rates of glucan formation caused by the fluids and dextran were additive, indicating that stimulation by the fluids was primarily due to interactions with entities other than glucan primer molecules. In contrast, the elevated levels of glucan formation in the presence of the fluids was not further enhanced by the addition of lysophosphatidylcholine. Lysophosphatidylcholine purified from parotid and submandibular saliva by solvent extraction and thin-layer chromatography stimulated the dextransucrase as effectively as egg yolk lysophosphatidylcholine. Thus, phospholipids normally found in human oral fluids can enhance the activity of an enzyme believed to be directly associated with the cariogenic potential of S. mutans.

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