Tinctorial Properties of Spherical Bodies in Broth Cultures of Nocardia asteroides GUH-2

In yeast extract-supplemented brain heart infusion (BHI) broth cultures of Nocardia asteroides GUH-2, many spherical bodies (SBs) were frequently seen nearby filamentous cells. They showed no Gram-positivity when Gram stain was applied. When acridine orange stain was applied, many of them showed different green fluorescence from bright orange fluorescence of the filamentous nocardiae under ultraviolet light. Their acid-fastness appeared to depend on the presence of paraffin. Using the polymerase chain reaction (PCR) method, 16S rRNA genes were detected in SB-containing broth cultures inoculated with culture filtrates from broth cultures of the strain and identical to that of N. asteroides. These results suggest that SBs are cell wall-defective (CWD) forms which result from the spontaneous mutation of N. asteroides GUH-2.     

Kinetic Properties of Purified Pseudomonas aeruginosa Phosphorylcholine Phosphatase Indicated That This Enzyme May Be Utilized by the Bacteria to Colonize in Different Environments

A protein oligomer with an approximate molecular weight of its 37-kDa monomer form was purified from the cell envelope fraction of Vibrio damsela cells. This oligomer exhibited strong porin activity when reconstituted into proteoliposomes with phosphatidyl choline. The functional properties for the 37-kDa protein suggest that it is a nonspecific or general porin, with an apparent pore size of 1.6 nm. This porin allows penetration of a variety of hydrophilic solutes according to their molecular mass. After electroelution, the oligomer was partially dissociated into monomers, whereas treatment with EDTA did not affect its dissociation. The monomers of the 37-kDa protein were not active in the reconstitution assay. The effect of culture media on the composition of the outer membrane protein of V. damsela was examined. Only one outer membrane protein with an apparent molecular weight of 37 kDa (37-kDa protein) was formed in cells grown in 3% NaCl–BHI broth and in 3% NaCl–nutrient broth with the addition of 2% glucose. Three outer membrane proteins, with apparent molecular weights of 37 kDa, 40 kDa, and 46 kDa, were produced in cells grown in 3% NaCl–nutrient broth. An additional outer membrane protein with an apparent molecular weight of 44 kDa (44-kDa protein) was found in cells grown in 3% NaCl–nutrient broth with the addition of 2% maltose. This protein was found to exhibit specificity to maltose derivatives. The results obtained in this study confirm the porin-like character of discussed proteins and give a basis for advanced study of those proteins. Received: 16 June 1998 / Accepted: 18 July 1998     

Unstable Expression and Thermal Instability of a Species-Specific Cell Surface Epitope Associated with a 66-Kilodalton Antigen Recognized by Monoclonal Antibody EM-7G1 within Serotypes of Listeria monocytogenes Grown in Nonselective and Selective Broths

Conditions that resulted in unstable expression and heat instability of a cell surface epitope associated with a 66-kDa antigen in Listeria monocytogenes serotypes were identified with the probe monoclonal antibody (MAb) EM-7G1 in an enzyme-linked immunosorbent assay. This epitope appeared to be absent in three serotypes (serotypes 3b, 4a, and 4c), which did not react with MAb EM-7G1 irrespective of the enrichment broth tested. The remaining 10 serotypes were detected by MAb EM-7G1 only when cells were grown in nonselective brain heart infusion broth (BHI) or selective Listeria enrichment broth (LEB). When cells were grown in Listeria repair broth (LRB), only 6 of the 13 serotypes were detected by MAb EM-7G1, and recognition of serogroup 4 was completely lost. None of the 13 serotypes was detected by MAb EM-7G1 when cells were grown in two other commonly used Listeria-selective media, UVM1 broth and Fraser broth (FRB), indicating that possible loss of epitope expression occurred under these conditions. MAb EM-7G1 maintained species specificity without cross-reacting with live or heat-killed cells of six other Listeria spp. (Listeria ivanovii, Listeria innocua, Listeria seeligeri, Listeria welshimeri, Listeria grayi, and Listeria murrayi) irrespective of the enrichment conditions tested. Due to heat instability of the cell surface epitope when it was exposed to 80 or 100°C for 20 min, MAb EM-7G1 is suitable for detection of live cells of L. monocytogenes in BHI or LEB but not in LRB, UVM1, or FRB enrichment medium.     

Differential expression of InlB and ActA in Listeria monocytogenes in selective and nonselective enrichment broths

Aim: To investigate the effect of selective and nonselective media on the expression of ActA and InlB proteins in Listeria monocytogenes. Methods and Results: Polyclonal antibodies to InlB and ActA were used in western blotting to determine the effect of selective (BLEB, UVM, and FB) or nonselective (BHI and LB) enrichment broths or hotdog exudates. Of the 13 L. monocytogenes serotypes tested, 11 and 12 serotypes showed a strong InlB expression in brain heart infusion (BHI) and Luria‐Bertani (LB), respectively, while only seven and one serotypes showed a strong ActA expression in these two respective broths, and others showed a weaker or no expression. On the contrary, in selective broths, expression of InlB was either very weak or undetectable. However, ActA expression was stronger in 12 serotypes when grown in buffered Listeria enrichment broth (BLEB), 11 in University of Vermont medium (UVM), and 10 in Fraser broth (FB). When tested in hotdog exudates, InlB and ActA were detected in serotypes grown at 37°C but not at 4°C. Transmission electron microscopy, enzyme‐linked immunosorbent assay, and mRNA analysis further supported these observations. Conclusion: Overall, selective enrichment broths promote ActA while nonselective broths promote InlB expression. Significance and Impact of the study: As commonly recommended enrichment broths show differential InlB and ActA expression, proper media must be selected to avoid false results during antibody‐based detection of L. monocytogenes.     

Thermal injury of Yersinia enterocolitica

Procedures were developed to evaluate thermal injury to three strains of Yersinia enterocolitica (serotypes 0:3, 0:8, and 0:17). Serotype 0:17 (atypical strain) was more sensitive to bile salts no. 3 (BS) and to sublethal heat treatment than the typical strains, 0:3 and 0:8. When the 0:3, 0:8, and 0:17 serotypes were thermally stressed in 0.1 M PO4 buffer, pH 7.0, at 47 degrees C for 70, 60, and 12 min, respectively, greater than 99% of the total viable cell population was injured. Injury was determined by the ability of cells to form colonies on brain heart infusion (BHI) agar, but not on Trypticase soy agar (TSA) plus 0.6% BS for serotypes 0:3 and 0:8 and TSA plus 0.16% BS for 0:17. Heat injury of serotype 0:17 cells for 15 min in 0.1 M PO4 buffer caused an approximate 1,000-fold reduction in cell numbers on selective media as compared with cells heated in pork infusion (PI), BHI broth, and 10% nonfat dry milk (NFDM). The extended lag and resuscitation period in BHI broth was 2.5 times greater for 0:17 cells injured in 0.1 M PO4 than for cells injured in BHI or PI. The rate and extent of repair of Y. enterocolitica 0:17 cells in three recovery media were directly related to the heating menstruum used for injury. The use of metabolic inhibitors demonstrated that ribonucleic acid synthesis was required for repair, whereas deoxyribonucleic, cell wall, and protein synthesis were not necessary for recovery of 0:17 cells injured in 0.1 M PO4 buffer, BHI, or PI. Inhibition of respiration by 2,4-dinitrophenol slowed repair only for 0:17 cells injured in 0.1 M PO4 buffer, not for cells injured in PI or BHI.     

The sterol composition of Trypanosoma cruzi changes after growth in different culture media and results in different sensitivity to digitonin-permeabilization

Respiration, oxidative phosphorylation. and the corresponding changes in membrane potential (deltapsi) of Trypanosoma cruzi epimastigotes grown either in liver infusion-tryptose (LIT) or brain heart infusion (BHI) culture medium were assayed in situ using digitonin to render their plasma membrane permeable to succinate, ADP, safranine O, and other small molecules. When the cells were permeabilized with 64 microM digitonin, a concentration previously used with epimastigotes, the ability of the cells grown in LIT medium to sustain oxidative phosphorylation was demonstrated by the detection of an oligomycin-sensitive decrease in mitochondrial membrane potential induced by ADP. In contrast, the cells grown in BHI medium were not able to sustain a stable membrane potential and did not respond to ADP addition. Analyses of oxygen consumption by these permeabilized cells indicated that the rate of basal respiration, which was similar in both cell types, was significantly decreased by 64 microM digitonin. Addition of ADP to the permeabilized cells grown in LIT medium promoted an oligomycin-sensitive transition from resting to phosphorylating respiration in contrast to the cells grown in BHI medium, whose respiration decreased steadily and did not respond either to ADP or CCCP. Titration of the cells grown in BHI medium with different digitonin concentrations indicated that their mitochondria have higher sensitivity to digitonin than those grown in LIT medium. Analysis of the sterol composition of epimastigotes grown in the two different media showed a higher percentage of cholesterol in total and mitochondrial extracts of epimastigotes grown in BHI medium as compared to those grown in LIT medium, suggesting the involvement of this sterol in their increased sensitivity to digitonin-permeabilization.     

Thermal injury of Yersinia enterocolitica.

Procedures were developed to evaluate thermal injury to three strains of Yersinia enterocolitica (serotypes 0:3, 0:8, and 0:17). Serotype 0:17 (atypical strain) was more sensitive to bile salts no. 3 (BS) and to sublethal heat treatment than the typical strains, 0:3 and 0:8. When the 0:3, 0:8, and 0:17 serotypes were thermally stressed in 0.1 M PO4 buffer, pH 7.0, at 47 degrees C for 70, 60, and 12 min, respectively, greater than 99% of the total viable cell population was injured. Injury was determined by the ability of cells to form colonies on brain heart infusion (BHI) agar, but not on Trypticase soy agar (TSA) plus 0.6% BS for serotypes 0:3 and 0:8 and TSA plus 0.16% BS for 0:17. Heat injury of serotype 0:17 cells for 15 min in 0.1 M PO4 buffer caused an approximate 1,000-fold reduction in cell numbers on selective media as compared with cells heated in pork infusion (PI), BHI broth, and 10% nonfat dry milk (NFDM). The extended lag and resuscitation period in BHI broth was 2.5 times greater for 0:17 cells injured in 0.1 M PO4 than for cells injured in BHI or PI. The rate and extent of repair of Y. enterocolitica 0:17 cells in three recovery media were directly related to the heating menstruum used for injury. The use of metabolic inhibitors demonstrated that ribonucleic acid synthesis was required for repair, whereas deoxyribonucleic, cell wall, and protein synthesis were not necessary for recovery of 0:17 cells injured in 0.1 M PO4 buffer, BHI, or PI. Inhibition of respiration by 2,4-dinitrophenol slowed repair only for 0:17 cells injured in 0.1 M PO4 buffer, not for cells injured in PI or BHI.     

Plume height and surface coverage analysis of methicillin-resistant Staphylococcus aureus isolates grown in a CDC biofilm reactor

Biofilm formation is a dynamic process that leads to mature communities over time. Despite a general knowledge of biofilm community formation and the resultant limitations of antibiotic therapy, there is a paucity of data describing specific plume heights, surface coverage and rates of maturation. Furthermore, little is published on the effect that the broth medium might have on the degree of biofilm maturation. In this study, three strains of methicillin-resistant Staphylococcus aureus (MRSA) (USA300, USA400 and a clinical isolate) were grown in brain heart infusion broth (BHI) or tryptic soy broth (TSB). Following growth, SEM images were captured for 3-D analysis to assess plume height. TSB produced significantly higher plume heights of USA300 and USA400 compared to BHI. Broth type was less influential on the clinical isolate. The data indicate that broth type and time may be important factors to consider when assessing maturation and plume height formation of MRSA biofilms.     

Bacillus cereus-Induced Fluid Accumulation in Rabbit Ileal Loops

The usefulness of the ligated rabbit ileal loop as an experimental model of Bacillus cereus food poisoning was investigated. Positive responses, as measured by fluid accumulation in the loop, were obtained from 19 of 22 strains of B. cereus. Four of six strains of B. thuringiensis also elicited fluid accumulation, but eight strains of other Bacillus spp. failed to evoke a response. The growth medium employed markedly affected the ability of a given strain of B. cereus to provoke a response. Brain heart infusion broth (BHI) (Difco) proved to be best for this purpose. Loop fluid-inducing activity was produced by exponentially growing cells and was present in cell-free culture filtrates and associated with washed vegetative cells. Intraluminal growth of B. cereus did not elicit fluid accumulation. Cultures grown at temperatures in the range of 18 C to 43 C were loop active. When BHI cultures of selected loop positive strains were injected intraluminally into the normal ileum of rabbits, they failed to elicit diarrhea.     

A chemically defined and minimal medium for Clostridium difficile

A chemically defined medium (CDCDM) has been developed for Clostridium difficile. The medium contains nine amino acids, five mineral salts, N -acetylglucosamine and the growth factors riboflavin and nicotinic acid. Ten strains of C. difficile have been subcultured repeatedly in this medium with no apparent changes in colonial or cellular morphology. The metabolic end-products of strains grown in this medium were reproducible and yielded patterns similar to those produced by cells cultured in Brain Heart Infusion broth (BHI). The growth rates were approximately 40% slower than those in a complex medium and the growth rate constants ranged between 0·011 and 0·087 h^-1. When the defined medium was supplemented with proteose peptone, yeast extract or caesin hydrolysate at concentrations of 1%, growth increased. No such growth increase was observed when the medium was supplemented with casamino acids or glucose.     

Production of staphylococcal enterotoxin in mixed cultures

Two Staphylococcus aureus strains were grown in brain-heart infusion (BHI) broth and a meat medium with Bacillus cereus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. Both S. aureus strains grew well and produced enterotoxin in the presence of S. faecalis in BHI broth; however, enterotoxin production was observable in the meat medium only when the S. aureus inoculum was greater than the S. faecalis inoculum. S. aureus FRI-100 grown with B. cereus produced enterotoxin in both media only when the S. aureus inoculum was much higher than the B. cereus inoculum (10 versus 10(4) CFU), whereas S. aureus FRI-196E produced enterotoxin in both media at all inoculum combinations except in the meat medium, when the inocula of the two organisms were the same. S. aureus grown with E. coli in BHI broth produced enterotoxin at all inoculum combinations except when the E. coli inoculum was greater than the S. aureus inoculum; however, in the meat medium, enterotoxin was produced only when the S. aureus inoculum was much greater than the E. coli inoculum (10 versus 10(4) CFU), S. aureus FRI-100 grown with P. aeruginosa in either medium produced enterotoxin only when the S. aureus inoculum was much greater than the P. aeruginosa inoculum (10 versus 10(3) or 10(4) CFU). It can be concluded from these results that enterotoxin production is unlikely in mixed cultures unless the staphylococci outnumber the other contaminating organisms.     

Production of staphylococcal enterotoxin in mixed cultures.

Two Staphylococcus aureus strains were grown in brain-heart infusion (BHI) broth and a meat medium with Bacillus cereus, Streptococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa. Both S. aureus strains grew well and produced enterotoxin in the presence of S. faecalis in BHI broth; however, enterotoxin production was observable in the meat medium only when the S. aureus inoculum was greater than the S. faecalis inoculum. S. aureus FRI-100 grown with B. cereus produced enterotoxin in both media only when the S. aureus inoculum was much higher than the B. cereus inoculum (10 versus 10(4) CFU), whereas S. aureus FRI-196E produced enterotoxin in both media at all inoculum combinations except in the meat medium, when the inocula of the two organisms were the same. S. aureus grown with E. coli in BHI broth produced enterotoxin at all inoculum combinations except when the E. coli inoculum was greater than the S. aureus inoculum; however, in the meat medium, enterotoxin was produced only when the S. aureus inoculum was much greater than the E. coli inoculum (10 versus 10(4) CFU), S. aureus FRI-100 grown with P. aeruginosa in either medium produced enterotoxin only when the S. aureus inoculum was much greater than the P. aeruginosa inoculum (10 versus 10(3) or 10(4) CFU). It can be concluded from these results that enterotoxin production is unlikely in mixed cultures unless the staphylococci outnumber the other contaminating organisms.     

Isolation from poultry litter and characterization [corrected] of Staphylococcus spp. capable of growth in high phosphate conditions [corrected

AIMS: To isolate and characterize micro-organisms from poultry litter capable of growing under phosphate concentrations typical of poultry litter. METHODS AND RESULTS: Poultry litter extracts were plated onto brain-heart infusion medium (BHI) containing an additional 0.75 mol l(-1) phosphate (BHI-P). Colonies were screened for the presence of inclusion granules with five being selected for further study. All strains displayed identical biochemical characteristics consistent with Staphylococcus spp. and grouped with Staphylococcus spp. by comparative 16S rDNA analysis. Thus all five strains were identified as such. All strains displayed elevated intracellular phosphate levels when cultured in BHI-P broth (0.417-0.600 microg phosphate mg(-1) protein) vs BHI broth (0.075-0.093 microg phosphate mg(-1) protein). When grown using an austere semi-defined medium or BHI-P, Staph. sp. #7 displayed similar elevated intracellular phosphate levels compared with growth in BHI. CONCLUSIONS: Poultry litter contains novel Staphylococcus spp. capable of robust growth when exposed to phosphate levels comparable with that typically found in poultry litter. Data suggest intracellular phosphate levels in these strains increase in response to increasing phosphate in the medium or austere medium conditions. Intracellular phosphate did not reach levels comparable with known hyper-accumulating micro-organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: These data suggest poultry litter possesses a resident microflora that thrives and accumulates intracellular phosphate in response to high phosphate conditions.     

Characterization of intermediate phenotypes induced by chemically undefined laboratory media in virulent Bordetella bronchiseptica strains

The expression of many virulence factors of Bordetella bronchiseptica is regulated by the bvgAS locus and reduced in response to environmental signals called modulators. Virulent strains can alternate between virulent (Bvg(+)), intermediate (Bvg(i)), and modulated (Bvg(+)mod) phenotypes. Potential vaccine antigens can be expressed by Bvg1 strains grown only in the absence of modulators. In the present study we evaluated filamentous hemagglutinin (FHA) and outer membrane protein (OMP) expression in Bvg(+) B. bronchiseptica strains grown in chemically undefined media: nutrient agar (NA), tryptic soy agar (TSA), tryptose phosphate broth (TPB), and brain-heart infusion (BHI). Our results suggest that TSA and TPB usually induce semimodulation, since Bvg(+) strains cultured in these media retained the expression of FHA and virulence-associated OMPs in the 30 kDa region, but failed to express other virulence markers such as OMPs in the regions of 90 and 200 kDa, though they expressed flagellin (avirulence marker). On the other hand, NA and BHI usually induce modulation. Thus the assayed chemically undefined media should not be used in vaccine production. Semimodulation induced by TSA and TPB can be accurately detected by SDS-PAGE Sarkosyl-insoluble OMP-enriched profiles. The reduction or absence of OMPs in the regions of 90 and 200 kDa is the most sensitive marker, and in some cases the presence of flagellin in intermediate profiles is another trait of the Bvg(i) phenotypes. Therefore these markers could be useful for selecting media for vaccine production. We also characterized the phenotype of Bvg(+) strains grown in Stainer-Scholte broth, an expensive medium, with and without glutathione, and we have detected no differences; this is the first attempt to reduce the cost of a Bordetella growth medium for veterinary vaccine production.     

Increase of capsular material thickness following in vivo growth of virulent Streptococcus suis serotype 2 strains

Abstract Protein profile and capsular material thickness of Streptococcus suis serotype 2 strains were compared after in vitro and in vivo growth. Three virulent and one avirulent strains were used. These strains were grown in Brain Heart Infusion (BHI) broth, cells were collected by centrifugation, resuspended in a sterile saline solution and injected in diffusion chambers. The devices were then inserted in rat abdomens for 17 h. In vitro grown strains were also inoculated into fresh BHI broth and cultivated for 17 h at 37°C. In vivo as well as in vitro grown bacteria were harvested by centrifugation, processed in a French pressure cell, treated with lysozyme and centrifuged to collect cell proteins for SDS-PAGE analysis. Transmission electron microscopy using polycationic ferritin labeling to stabilize capsular material was also carried out. No significant modification was noted in the protein profile for any strain after in vivo growth except for a 39 kDa protein of one virulent strain. On the other hand, an increase in thickness of capsular material was noted for the three in vivo grown virulent strains while no change was noted for the avirulent strain. This increase in capsular material thickness of virulent strains was accompanied by an increased resistance to killing by pig polymorphonuclear leukocytes. The capacity to produce more capsular material in vivo seems to be an attribute of some virulent S. suis serotype 2 strains.     

Effects of nisin and temperature on survival, growth, and enterotoxin production characteristics of psychrotrophic Bacillus cereus in beef gravy.

The presence of psychrotrophic enterotoxigenic Bacillus cereus in ready-to-serve meats and meat products that have not been subjected to sterilization treatment is a public health concern. A study was undertaken to determine the survival, growth, and diarrheal enterotoxin production characteristics of four strains of psychrotrophic B. cereus in brain heart infusion (BHI) broth and beef gravy as affected by temperature and supplementation with nisin. A portion of unheated vegetative cells from 24-h BHI broth cultures was sensitive to nisin as evidenced by an inability to form colonies on BHI agar containing 10 micrograms of nisin/ml. Heat-stressed cells exhibited increased sensitivity to nisin. At concentrations as low as 1 microgram/ml, nisin was lethal to B. cereus, the effect being more pronounced in BHI broth than in beef gravy. The inhibitory effect of nisin (1 microgram/ml) was greater on vegetative cells than on spores inoculated into beef gravy and was more pronounced at 8 degrees C than at 15 degrees C. Nisin, at a concentration of 5 or 50 micrograms/ml, inhibited growth in gravy inoculated with vegetative cells and stored at 8 or 15 degrees C, respectively, for 14 days. Growth of vegetative cells and spores of B. cereus after an initial period of inhibition is attributed to loss of activity of nisin. One of two test strains produced diarrheal enterotoxin in gravy stored at 8 or 15 degrees C within 9 or 3 days, respectively. Enterotoxin production was inhibited in gravy supplemented with 1 microgram of nisin/ml and stored at 8 degrees C for 14 days; 5 micrograms of nisin/ml was required for inhibition at 15 degrees C. Enterotoxin was not detected in gravy in which less than 5.85 log10 CFU of B. cereus/ml had grown. Results indicate that as little as 1 microgram of nisin/ml may be effective in inhibiting or retarding growth of and diarrheal enterotoxin production by vegetative cells and spores of psychrotrophic B. cereus in beef gravy at 8 degrees C, a temperature exceeding that recommended for storage or for most unpasteurized, ready-to-serve meat products.     

Iron repressibility of siderophore and transferrin-binding protein in Staphylococcus aureus

In order to investigate whether the iron acquisition mechanisms of Staphylococcus aureus are induced by iron restriction in vitro, we examined S. aureus ATCC 6538 for production of siderophore and expression of transferrin-binding protein (SA-tbp) in normal or deferrated brain heart infusion broth (BHI). Siderophore production was earlier and greater in the deferrated BHI. The SA-tbp, detected by ligand blot assay, was expressed only in the deferrated BHI. When human transferrin was added to the deferrated BHI, siderophore production was later and lower than when transferrin was not present. In conclusion, both iron acquisition mechanisms of S. aureus were found to be iron-repressible and via both of them, human transferrin-bound iron was utilized for growth under iron-restricted condition.     

Induction of release of tumor necrosis factor and IL-6 from human mononuclear cells by Bacteroides strains

The role of anaerobic Gram-negative bacteria in inducing cytokines during mixed infections involving aerobic and anaerobic bacteria is relatively poorly defined. The purpose of this study was to establish whether or not intact Bacteroides fragilis and related species, isolated from severe infections and from the faeces of healthy persons are capable of releasing tumor necrosis factor (TNF) and IL-6 from human mononuclear cells and whole blood. The purified lipopolysaccharides of Bacteroides fragilis strain (No. 7), extracted by the aqueous phenol method from BHI cultures and from BHI culture supplemented with 5% horse serum, were also tested. TNF release was detected by the WEHI 164-dependent bioassay and IL-6 production by the B-9 cell-dependent bioassay. Heat-inactivated Bacteroides strains belonging to different species were able to induce TNF (1x10(1)-5x10(2) U/mL) and IL-6 (1x10(1)-5x10(5) pg/mL) release from human mononuclear cells. When whole blood was used, the production of TNF and IL-6 was more pronounced (very probably because of the presence of certain serum factors). The culturing conditions (the presence of 5% horse serum in the BHI broth) influenced the inducing activity of almost all strains tested. The isolated lipopolysaccharide of Bacteroides fragilis strain No. 7 proved to have a rough profile on PAGE. There were no differences in TNF and IL-6 induction when the lipopolysaccharides of the strain was cultured in BHI or in BHI supplemented with 5% horse serum. Bacteroides strains often outnumber Enterobacteriaceae in the faeces and in mixed infections, and their role in inducing and/or modulating the host response in septic shock should not be overlooked.     

Filamentous growth ofPseudomonas aeruginosa

Summary The growth of two strains ofPseudomonas aeruginosa in stirred batch cultures was monitored by optical density, DNA concentration, and acridine orange direct cell count measurements. Growth of adherent bacteria in pure culture was also observed on suspended glass discs by light and scanning electron microscopy. Strain MUCOID produced significant numbers of filamentous cells in broth culture and in the adherent population, while strain PAO 381 did not produce elongated cells. Filamentous growth of MUCOID could be prevented by the addition of 5 × 10^–2 M Mg²⁺. However, the addition of 0.66 mM EDTA caused an increased proportion of the population (>50%) of MUCOID cells to become filamentous in broth culture. The results are discussed and related to theories regarding bacterial plasticity, and filamentation of normally bacillary cells.