Adhesion of Enterococcus faecalis 1131 grown under subinhibitory concentrations of ampicillin and vancomycin to a hydrophilic and a hydrophobic substratum

The effect of two subinhibitory antibiotic concentrations of ampicillin and vancomycin during growth on the adhesion of Enterococcus faecalis 1131 to glass and silicone rubber was studied in a parallel plate flow chamber. Initial deposition rates and numbers of adhering bacteria after 4 h were higher on hydrophilic glass than on hydrophobic silicone rubber, regardless of growth conditions. The presence of 1/4 minimal inhibitory concentration (MIC) of ampicillin during growth reduced enterococcal adhesion to both substrata, but growth in the presence of 1/4 MIC vancomycin did not affect the adhesion of E. faecalis. Moreover, enterococcal adhesion increased after growth in the presence of 1/8 MIC vancomycin. The increased adhesion after growth in the presence of subinhibitory concentrations of vancomycin may have strong implications for patients living with implanted biomaterials, as they may suffer adverse effects from use of this antibiotic, especially since bacteria once adhered are less sensitive to antibiotics.     

Silicone rubber membrane bioreactors for bacterial cellulose production

Cellulose production byAcetobacter pasteurianus was investigated in static culture using four bioreactors with silicone rubber membrane submerged in the medium. The shape of the membrane was flat sheet, flat sack, tube and cylindrical balloon. Production rate of cellulose as well as its yield on consumed glucose by the bacteria grown on the flat type membranes was approximately ten-fold greater than those on the non-flat ones in spite of the same membrane thickness. The membrane reactor using flat sacks of silicone rubber membrane as support of bacterial pellicle can supply greater ratio of surface to volume than a conventional liquid surface culture and is promising for industrial production of bacterial cellulose in large scale.     

Microflora on explanted silicone rubber voice prostheses: taxonomy, hydrophobicity and electrophoretic mobility

Silicone rubber voice prostheses are implants which are inserted in a non-sterile environment and therefore become quickly colonized by micro-organisms. The micro-organisms exist on the medical grade silicone rubber as mixed biofilms of bacteria and yeasts. A total of 79 bacterial and 39 yeast strains were isolated from these biofilms by soft ultrasonic treatment. Gram-positive/catalase-negative and Gram-positive/catalase-positive cocci represented the dominant bacterial strains. The yeasts were mainly Candida species. Further characterization of cell surface properties such as hydrophobicity by microbial adhesion to hexadecane and electrophoretic mobility showed a distinct difference when the bacterial strains were compared with the yeasts. The bacterial hydrophobicities ranged from 0 to 100% adhesion to hexadecane, whereas the yeast strains, especially the Candida albicans strains, all had markedly hydrophilic cell surfaces. A comparison of the electrophoretic mobilities showed also differences between bacteria and yeast. The values for the bacteria were found to be between -2.5 to -0.5 (10^-8 m² V^-1 s^-1), whereas for the yeasts electrophoretic mobilities were more positive. Based on the adhesive properties of the isolated micro-organisms, strategies can now be developed to modify the properties of the silicone rubber to reduce biofilm formation on such prostheses.     

Growth inhibition due to aged silicone rubber tubing

Growth of the obligately methylotrophic Bacterium B6/2 in continuous culture was inhibited when the mineral salts-methylamine medium was supplied through silicone rubber tubing which had been autoclaved more than 50 times. The growth inhibition was removed when the medium was supplied through new silicone rubber tubing. Growth in small-scale batch cultures was delayed or inhibited after the medium passed through the former tubing but not when it had passed through the latter. It is recommended that silicone rubber medium supply lines to chemostats are replaced periodically.     

Inhibition of microbial adhesion to silicone rubber treated with biosurfactant from Streptococcus thermophilus A

Microbial adhesion of four bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber before and after conditioning with a biosurfactant obtained from the probiotic bacterium Streptococcus thermophilus A was investigated in a parallel plate flow chamber. The silicone rubber with and without an adsorbed biosurfactant layer was characterized using contact angle measurements. Water contact angles indicated that the silicone rubber surface with adsorbed biosurfactant was more hydrophilic (58 degrees) than bare silicone rubber (109 degrees). The results obtained showed that the biosurfactant was effective in decreasing the initial deposition rates, and the number of bacterial cells adhering after 4 h, for all microorganisms tested. A decrease in the initial deposition rate was observed for Rothia dentocariosa GBJ 52/2B and Staphylococcus aureus GB 2/1 from 1937+/-194 to 179+/-21 microorganisms cm(-2) s(-1) and from 1255+/-54 to 233+/-26 microorganisms cm(-2) s(-1), respectively, accounting for an 86% reduction of the initial deposition rate for both strains. The number of bacterial cells adhering to the silicone rubber with preadsorbed biosurfactant after 4 h was further reduced by 89% and 97% by the two strains, respectively. The two yeast strains tested showed less reduction in adhesion after 4 h, to values between 67% and 70%. Such a pretreatment with surface-active compounds may constitute a promising strategy to reduce the microbial colonization rate of silicone rubber voice prostheses.     

Plant growth-altering effects of Azospirillum brasilense and Bacillus C–11–25 on two wheat cultivars

The effect of Azospirillum brasilense Cd, Bacillus C–11–25, indole acetic acid, gibberellic acid and cytokinin on plant growth characteristics of two wheat ( Triticum aestivum L. emend Thell) cultivars was studied under laboratory and greenhouse conditions. Responses of wheat plants to bacterial inoculation were similar to those caused by the addition of gibberellic acid in growth pouches. Chester and Fielder wheat varieties differed in responses to the bacteria and hormone additions. When added to growth pouches, bacterial culture filtrates and dead bacterial cells caused plant growth responses similar to those caused by the addition of live cells. Bacteria and hormone additions resulted in increased permeability of Fielder wheat to ¹⁵Nlabelled nitrate, and decreased nitrate permeability of Chester wheat. Bacterial inoculation of soil in pots caused ¹⁵N isotope dilution in Fielder but not in Chester wheat. Hormone addition to pots caused isotope dilution in Chester wheat. It appeared that genetic differences between cultivars affected plant growth responses. The accuracy of estimates of N₂ fixation by associative bacteria based on ¹⁵N isotope dilution calculations may be reduced if control plants differ in plant response to these bacteria.     

Effects of Cephenemyia spp. (Diptera: Oestridae) on the nasopharynx of black-tailed deer (Odocoileus hemionus columbianus)

A study was conducted to determine gross and microscopic tissue changes in the nasopharynx of black-tailed deer (Odocoileus hemionus columbianus) infected with nasal bot fly larvae (Cephenemyia spp.). Paired retropharyngeal recesses were the preferred sites for the growing second and third stage larvae of two species of Cephenemyia (C. apicata and C. jellisoni). Retropharyngeal recesses distended into "pouches" that harbored up to 30 larvae. Pouches were oriented caudal-laterally toward the basisphenoid bone of the cranium. Lateral support of the pouch mass was provided by the stylohyoid bone. The laryngeal orifice was never occluded by the enlarged recesses. The distal pouch wall was relatively thin and remained uniform in thickness as expansion progressed. Occasionally, aberrant larvae were found protruding through the distal wall of the pouch. Disruption of the epithelium and submucosa by larval mouth hooks and integumentary spines were examined by scanning electron microscopy. Histological examination of infected recesses revealed substantial loss of epithelium and mucous glands. Enlargement of recesses into pouches resulted from fibrosis. Healing occurred after larvae egressed from the pouches. Degenerating mucous glands, epithelial metaplasia, epithelial desquamation, and intense inflammation were found near larvae. An eosinophilic exudate with a mixture of macrophages and erythrocytes was present in the lumen of the pouch. The presence of larvae within the pouch inhibited secondary bacterial infection and suppuration. Infection by larvae caused severe local trauma and intense tissue response.     

Adhesive interactions between voice prosthetic yeast and bacteria on silicone rubber in the absence and presence of saliva

Biofilms on silicone rubber voice prostheses are the major cause for frequent failure and replacement of these devices. The presence of both bacterial strains and yeast has been suggested to be crucial for the development of voice prosthetic biofilms. Adhesive interactions between Candida albicans, Candida krusei, and Candida tropicalis with 14 bacterial strains, all isolated from explanted voice prostheses were investigated in a parallel plate flow chamber. Bacteria were first allowed to adhere to silicone rubber, after which the flow chamber was perfused with yeast, suspended either in saliva or buffer. Generally, when yeast were adhering from buffer and saliva, the presence of adhering bacteria suppressed adhesion of yeast. In saliva, Rothia dentocariosa and Staphylococcus aureus enhanced adhesion of yeast, especially of C. albicans. This study shows that bacterial adhesion mostly reduces subsequent adhesion of yeast, while only a few bacterial strains stimulate adhesion of yeast, provided salivary adhesion mediators are present. Interestingly, different clinical studies have identified R. dentocariosa and S. aureus in biofilms on explanted prostheses of patients needing most frequent replacement, while C. albicans is one of the yeast generally held responsible for silicone rubber deterioration.     

Interference in adhesion of bacteria and yeasts isolated from explanted voice prostheses to silicone rubber by rhamnolipid biosurfactants

AIMS: The effects and extent of adhesion of four different bacterial and two yeast strains isolated from explanted voice prostheses to silicone rubber with and without an adsorbed rhamnolipid biosurfactant layer obtained from Pseudomonasaeruginosa DS10-129 was studied. METHODS AND RESULTS: The ability of rhamnolipid biosurfactant to inhibit adhesion of micro-organisms to silicone rubber was investigated in a parallel-plate flow chamber. The anti-adhesive activity of the biosurfactant at different concentrations was significant against all the strains and depended on the micro-organism tested. The results showed an effective reduction in the initial deposition rates, and the number of bacterial cells adhering after 4 h, for all micro-organisms tested at the 4 g l(-1) undiluted rhamnolipid solution. Maximum initial reduction of adhesion rate (an average of 66%) occurred for Streptococcus salivarius GB 24/9 and Candida tropicalis GB 9/9. The number of cells adhering after 4 h on silicone rubber conditioned with biosurfactant was reduced to 48% for Staphylococcus epidermidis GB 9/6, Strep. salivarius GB 24/9, Staphylococcus aureus GB 2/1 and C. tropicalis GB 9/9 in comparison to controls. Perfusing the flow chamber with biosurfactant containing solution followed by the passage of a liquid-air interface, to investigate detachment of micro-organisms adhering to silicone rubber, produced high detachment (96%) of adhered cells for all micro-organisms studied, except for Staph. aureus GB 2/1 (67%). SIGNIFICANCE AND IMPACT OF THE STUDY: It is concluded that biosurfactant represent suitable compounds that should be considered in developing future strategies to prevent the microbial colonization of silicone rubber voice prostheses.     

Glutaraldehyde: its uptake by sporing and non-sporing bacteria, rubber, plastic and an endoscope

Uptake of glutaraldehyde to bacterial spores, germinating and outgrowing spores, vegetative cells (sporing and non-sporing bacteria), various types of rubber, plastic and an endoscope was investigated. Escherichia coli NCTC 10418 exhibited greatest uptake, followed by Bacillus subtilis NCTC 8236 vegetative cells and Staphylococcus aureus NCTC 6571. Germinated and outgrowing B. subtilis spores adsorbed more glutaraldehyde than resting spores, but less than vegetative cells. Low concentrations of alkaline and acid glutaraldehyde increased the surface hydrophobicity and inhibited the germination of bacterial spores, the alkaline solution to a greater extent in both cases.
Rubbers exhibited varying degrees of uptake and are listed in decreasing order of uptake: red rubber, fluorinated rubber (Vinescol), silicone rubber (Silescol), butyl rubber (Butyl XX). Polypropylene, the only plastic examined, was found not to adsorb any glutaraldehyde. The endoscope adsorbed more glutaraldehyde (per gram) than fluorinated rubber but less than red rubber. No damage was observed.     

Glutaraldehyde: its uptake by sporing and non-sporing bacteria, rubber, plastic and an endoscope

Uptake of glutaraldehyde to bacterial spores, germinating and outgrowing spores, vegetative cells (sporing and non-sporing bacteria), various types of rubber, plastic and an endoscope was investigated. Escherichia coli NCTC 10418 exhibited greatest uptake, followed by Bacillus subtilis NCTC 8236 vegetative cells and Staphylococcus aureus NCTC 6571. Germinated and outgrowing B. subtilis spores adsorbed more glutaraldehyde than resting spores, but less than vegetative cells. Low concentrations of alkaline and acid glutaraldehyde increased the surface hydrophobicity and inhibited the germination of bacterial spores, the alkaline solution to a greater extent in both cases. Rubbers exhibited varying degrees of uptake and are listed in decreasing order of uptake: red rubber, fluorinated rubber (Vinescol), silicone rubber (Silescol), butyl rubber (Butyl XX). Polypropylene, the only plastic examined, was found not to adsorb any glutaraldehyde. The endoscope adsorbed more glutaraldehyde (per gram) than fluorinated rubber but less than red rubber. No damage was observed.     

Response of spring rape (Brassica napus var. oleifera L.) to inoculation with plant growth promoting rhizobacteria containing 1-aminocyclopropane-1-carboxylate deaminase depends on nutrient status of the plant

Responses of rape (Brassica napus var. oleifera L.) to inoculation with plant growth promoting rhizobacteria, Pseudomonas putida Am2, Pseudomonas putida Bm3, Alcaligenes xylosoxidans Cm4, and Pseudomonas sp. Dp2, containing 1-aminocyclopropane-l-carboxylate (ACC) deaminase were studied using growth pouch and soil cultures. In growth pouch culture, the bacteria significantly increased root elongation of phosphorus-sufficient seedlings, whereas root elongation of phosphorus-deficient seedlings was not affected or was even inhibited by the bacteria. Bacterial stimulation of root elongation of phosphorus-sufficient seedlings was eliminated in the presence of a high ammonia concentration (1 mM) in the nutrient solution. Bacterial effects on root elongation of potassium-deficient and potassium-sufficient seedlings were similar. The bacteria also decreased inorganic phosphate content in shoots of potassium- and phosphorus-sufficient seedlings, reduced ethylene production by phosphorus-sufficient seedlings, and inhibited development of root hairs. The effects of treatment with Ag+, a chemical inhibitor of plant ethylene production, on root elongation, ethylene evolution, and root hair formation were similar to bacterial treatments. The number of bacteria on the roots of phosphorus-deficient seedlings was not limited by phosphorus deficiency. In pot experiments with soil culture, inoculation of seeds with bacteria and treatment with aminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis in plants, increased root and (or) shoot biomass of rape plants. Stimulation of plant growth caused by the bacteria was often associated with a decrease in the content of nutrients, such as P, K, S, Mo, and Ba, in shoots, depending on the strain used. The results obtained show that the growth-promoting effects of ACC-utilizing rhizobacteria depend significantly on the nutrient status of the plant.     

Effects of Quaternary Ammonium Silane Coatings on Mixed Fungal and Bacterial Biofilms on Tracheoesophageal Shunt Prostheses

Two quaternary ammonium silanes (QAS) were used to coat silicone rubber tracheoesophageal shunt prostheses, yielding a positively charged surface. One QAS coating [(trimethoxysilyl)-propyldimethyloctadecylammonium chloride] was applied through chemical bonding, while the other coating, Biocidal ZF, was sprayed onto the silicone rubber surface. The sprayed coating lost its stability within an hour, while the chemically bonded coating appeared stable. Upon incubation in an artificial throat model, allowing simultaneous adhesion and growth of yeast and bacteria, all coated prostheses showed significant reductions in the numbers of viable yeast (to 12% to 16%) and bacteria (to 27% to 36%) compared with those for silicone rubber controls, as confirmed using confocal laser scanning microscopy after live/dead staining of the biofilms. In situ hybridization with fluorescently labeled oligonucleotide probes showed that yeasts expressed hyphae on the untreated and Biocidal ZF-coated prostheses but not on the QAS-coated prostheses. Whether this is a result of the positive QAS coating or is due to the reduced number of bacteria is currently unknown. In summary, this is the first report on the inhibitory effects of positively charged coatings on the viability of yeasts and bacteria in mixed biofilms. Although the study initially aimed at reducing voice prosthetic biofilms, its relevance extends to all biomedical and environmental surfaces where mixed biofilms develop and present a problem.     

Effects of quaternary ammonium silane coatings on mixed fungal and bacterial biofilms on tracheoesophageal shunt prostheses

Two quaternary ammonium silanes (QAS) were used to coat silicone rubber tracheoesophageal shunt prostheses, yielding a positively charged surface. One QAS coating [(trimethoxysilyl)-propyldimethyloctadecylammonium chloride] was applied through chemical bonding, while the other coating, Biocidal ZF, was sprayed onto the silicone rubber surface. The sprayed coating lost its stability within an hour, while the chemically bonded coating appeared stable. Upon incubation in an artificial throat model, allowing simultaneous adhesion and growth of yeast and bacteria, all coated prostheses showed significant reductions in the numbers of viable yeast (to 12% to 16%) and bacteria (to 27% to 36%) compared with those for silicone rubber controls, as confirmed using confocal laser scanning microscopy after live/dead staining of the biofilms. In situ hybridization with fluorescently labeled oligonucleotide probes showed that yeasts expressed hyphae on the untreated and Biocidal ZF-coated prostheses but not on the QAS-coated prostheses. Whether this is a result of the positive QAS coating or is due to the reduced number of bacteria is currently unknown. In summary, this is the first report on the inhibitory effects of positively charged coatings on the viability of yeasts and bacteria in mixed biofilms. Although the study initially aimed at reducing voice prosthetic biofilms, its relevance extends to all biomedical and environmental surfaces where mixed biofilms develop and present a problem.     

Production of plasmid DNA in a simple, inexpensive and reusable fermentor

Performance data for the production of plasmid DNA in bacterial cultures have been obtained using a new concept of simplified fermentor, the Lofstrand Bactolift. The unique design of this fermentor incorporates a standard 500-ml or 1-liter centrifuge bottle as the bacterial growth vessel, thus eliminating the necessity to transfer the cultures for subsequent processing. Bacterial and plasmid yields have been shown to be equal to or greater than those obtained using conventional shake flasks. Twelve 1-liter Bactolift fermentors can be operated in a standard laboratory water bath that occupies less than two square feet of bench space, as compared to a limit of six 2.8-liter Fernbach flasks containing one liter of culture held in an incubator shaker cabinet that occupies nine square feet of laboratory floor space.     

Variations in bacterial communities in laboratory-scale and big bale silos assessed by fermentation products, colony counts and denaturing gradient gel electrophoresis profiles

Aims: To assess the variation in bacterial communities in laboratory‐scale and big bale silos. Methods and Results: Wilted Italian ryegrass (628 g dry matter kg^?1) was ensiled in vacuum‐packed plastic pouches and big bales. Silos were opened after 3 months, and the fermentation products, colony counts and denaturing gradient gel electrophoresis (DGGE) profiles were determined. Eight samples were collected separately from a big bale, while one representative sample was taken from a plastic pouch. Significant variation was found between big bales in dry matter, ethanol, lactic acid, acetic acid and ammonia‐N contents. No differences were shown between plastic pouches and big bales, except that more ethanol was produced in the former air‐tight silos. Plastic pouches could resemble a specific silo and outer sampling sites of big bales based on fermentation products and DGGE profiles respectively. Conclusions: Considerable variation in fermentation products may exist between big bale silos. Plastic pouches can serve as a model of big bale silos, although they do not provide information on the heterogeneity within and between bales. Significance and Impact of the Study: Assessment of bacterial communities associated with ensiling can differ according to the criteria of fermentation products, colony counts and DGGE profiles.     

Epithelial behaviors and threshold effects in the development and evolution of internal and external cheek pouches in rodents

The internal and external cheek pouches found in certain rodents arise early in development by an evagination of the buccal epithelium. Differences in the epithelial evaginations that produce the internal pouches of the Syrian hamster (Mesocricetus auratus) and least chipmunk (Eutamias minimus) are consistent with the view that they evolved independently. The external cheek pouches of rodents of the superfamily Geomyoidea represent a macroevolutionary phenotype when compared to the internal pouches of other rodents. Externalization of an internal pouch rudiment found in the geomyoids Dipodomys and Thomomys can be explained by a simple change early in its development, the effect of which is greatly magnified by facial growth. In this example, the traditional dichotomy between microevolutonary and macroevolutionary theories is bridged by an understunding of developmental dynamics.     

Bacterial mortality and the fate of bacterial production

Knowledge of the rates of bacterial mortality, particularly predatory mortality, is important in determining the fate of bacterial production. Communities of planktonic bacteria have specific growth rates on the order of 1 d⁻¹, but there is relatively little variation in bacterial abundance, implying that growth and mortality are closely coupled. A review of the mechanisms of bacterial mortality suggests that predation and parasitism are the most likely factors balancing the rapid rates of bacterial growth on daily time-scales. Experiments done in two-stage continuous cultures partially support this notion. At bacterial growth rates of 1 d⁻¹, predatory mortality was on the order of 1.5–2 d⁻¹ and nonpredatory mortality was undetectable. On the other hand, a review of existing field studies indicates that neither predation by metazoans nor protists balances rates of bacterial growth. Improved methods for measuring bacterial growth and mortality and studies of the nonpredatory mechanisms of bacterial mortality are required to resolve this paradox.     

Bacterial Colonization and Ectoenzymatic Activity in Phytoplankton-Derived Model Particles: Cleavage of Peptides and Uptake of Amino Acids

Abstract Phytoplankton-derived model particles were created in laboratory from a mixture of autoclaved diatom cultures. These particles were colonized by a marine bacterial community and incubated in rolling tanks in order to examine the relationship between aminopeptidase activity and leucine uptake. Bacteria inhabiting particles and ambient water were characterized for abundance, biovolume, aminopeptidase activity, leucine uptake, and growth rate. Particles were a less favorable habitat than ambient water for bacterial growth since growth rates of particle-attached bacteria were similar or even lower than those of free-living bacteria. During the first ∼100 h of the particle decomposition process, there were not statistically significant differences in the aminopeptidase activity:leucine uptake ratio between attached and free-living bacteria. From ∼100 h to ∼200 h, this ratio was higher for attached bacteria than for free-living bacteria. This indicates an uncoupling of aminopeptidase activity and leucine uptake. During this period, attached and free-living bacteria showed similar hydrolytic activities on a cell-specific basis. In the free-living bacterial community, variations in aminopeptidase activity per cell were associated with variations in leucine uptake per cell and growth rates. However, in the attached bacterial community, when leucine uptake and growth rates decreased, aminopeptidase activity remained constant. Thus, after ∼100 h, particle-attached bacteria were not taking advantage of their high aminopeptidase activity; consequently the hydrolysed amino acids were released into the ambient water, supporting the growth of free-living bacteria. These results demonstrate that over the particle decomposition process, the relationship between hydrolysis and uptake of the protein fraction shows different patterns of variation for attached and free-living bacterial communities. However, in our experiments, this uncoupling was not based on a hyperproduction of enzymes by attached bacteria, but on lower uptake rates when compared to the free-living bacteria. Received: 4 February 1997; Accepted: 9 May 1997     

Changes in bacterial composition and enzymatic activity in ileostomy and ileal reservoir during intermittent occlusion: a study using dogs.

Bacterial flora, activities of 10 potential mucus- and dietary polysaccharide-degrading enzymes, blood group antigenicity of the intestinal glycoproteins, and proteolytic activity in the output from experimentally colectomized dogs with conventional ileostomies and dogs with valveless ileal reservoirs (pouches) were determined. The ileostomies of dogs with conventional surgery (group II) and with pouches (group III) were occluded intermittently during a 6-week period. The duration of occlusion was progressively increased. Group I, five dogs with conventional ileostomies, served as a control group. After occlusion of the ileal pouch for 7 h, total numbers of bacteria increased threefold, glycosidase activity increased fivefold, and blood group antigenicity of the intestinal glycoproteins, which was high in the output from the nonoccluded pouch, was no longer detectable. Proteolytic activity was not influenced by occlusion of the pouch. Significantly lower numbers of bacteria, only minor glycosidase activity, high blood group antigenicities of the intestinal glycoproteins, and higher proteolytic activity were found in ileostomy effluents from groups I and II. Histopathological examination showed chronic inflammation and changes in crypt-villus ratio in all dogs with ileal reservoirs; the ileal mucosa from the dogs with conventional ileostomies did not show any abnormalities. Consequences of the flora-related enzyme activities for the ileal mucosa are discussed.