Antibiofilm activity of sodium bicarbonate, sodium metaperiodate and SDS combination against dental unit waterline-associated bacteria and yeast.

AIM: To determine the effect of sodium bicarbonate (SB), sodium metaperiodate (SMP) and sodium dodecyl sulfate (SDS) combination on biofilm formation and dispersal in dental unit waterline (DUWL)-associated bacteria and yeast. METHODS AND RESULTS: The in vitro effect of SB, SMP and SDS alone and in combination on biofilm formation and dispersal in Pseudomonas aeruginosa, Klebsiella pneumoniae, Actinomyces naeslundii, and Candida albicans was investigated using a 96-well microtitre plate biofilm assay. The combination showed a broad-spectrum inhibitory effect on growth as well as biofilm formation of both gram-negative and gram-positive bacteria, and yeast. In addition, the SB + SMP + SDS combination was significantly more effective in dispersing biofilm than the individual compounds. The combination dispersed more than 90% of P. aeruginosa biofilm whereas the commercial products, Oxygenal 6, Sterilex Ultra, and PeraSafe showed no biofilm dispersal activity. CONCLUSION: The composition comprising SB, SMP, and SDS was effective in inhibiting as well as dispersing biofilms in DUWL-associated bacteria and yeast. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that a composition comprising environmentally friendly and biologically safe compounds such as SB, SMP, and SDS has a potential application in reducing DUWL-associated acquired infections in dental clinics.

Effect of ovotransferrin, protamine sulfate and EDTA combination on biofilm formation by catheter-associated bacteria.

AIMS: To determine the effect of a composition comprising ovotransferrin (OT), protamine sulfate (PS) and ethylenediaminetetraacetic acid (EDTA) on biofilm formation by catheter-associated bacteria. METHODS AND RESULTS: The in vitro activity of OT, PS and EDTA alone and in combinations against biofilm formation by Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Enterococcus faecalis and Staphylococcus epidermidis was investigated. All the three compounds either alone or in combinations failed to inhibit the growth completely at the concentrations tested. However, the subinhibitory concentrations of three compounds in a composition showed synergistic inhibitory effect on biofilm formation by K. pneumoniae, Ps. aeruginosa and S. epidermidis. Furthermore, 79-95% reduction in Ps. aeruginosa and S. epidermidis biofilm formation was observed in a clear vinyl urinary catheter treated with the composition. CONCLUSION: The subinhibitory concentrations of OT, PS and EDTA in a composition were effective in reducing biofilm formation by catheter-associated bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that a synergistic composition-comprising non-antibiotic generally regarded as safe (GRAS) compounds such as OT, PS and EDTA may be used in the prevention of catheter-related infections.

Protective effects of cold temperature and surface-contact on acid tolerance of Salmonella spp.

AIMS: To determine the effect of cold-storage temperature and surface contact on the survival of Salmonella spp. during acid challenge. To determine the contribution of sigma transcriptional factor (encoded by rpoS) in surface contact-mediated acid tolerance. METHODS AND RESULTS: Salmonella serovar Typhimurium cells in exponential and stationary growth phase were subjected to acid challenge in planktonic and surface-associated states. Low temperatures offered protection against acid challenge to cells which were in stationary growth phase (but not to those in exponential growth phase). The cells from stationary, as well as logarithmic growth phase, acquired increased acid tolerance upon surface contact with various surfaces, such as fresh-cut apples, agar and polyethersulphone membranes. The alternative sigma transcription factor was not required to acquire surface contact-mediated acid tolerance. CONCLUSIONS: Salmonella spp. take advantage of low temperature and surface association to overcome acid challenge. Some of the acid tolerance mechanisms are independent of the sigma transcription factor regulon. SIGNIFICANCE AND IMPACT OF THE STUDY: Effective control measures during produce processing must take into account the different susceptibilities of planktonic vs surface-associated food-borne pathogens.

Production of Aspergillus xylanase by lignocellulosic waste fermentation and its application.

Strains of Aspergillus terreus and A. niger, known to produce xylanase with undetectable amounts of cellulase, were studied for xylanase (EC 3.2.1.8) production on various lignocellulosic substrates using solid state fermentation. Of the lignocellulosic substrates used, wheat bran was the best for xylanase production. The effects of various parameters, such as moistening agent, level of initial moisture content, temperature of incubation, inoculum size and incubation time, on xylanase production were studied. The best medium for A. terreus was wheat bran moistened with 1:5 Mandels and Strenberg mineral solution containing 0.1% tryptone, at 35 degrees C, and at inoculum concentration 2x107-2x108 spores 5 g-1 substrate; for A. niger, the best medium was wheat bran moistened with 1:5 Mandels and Strenberg mineral solution containing 0.1% yeast extract, at 35 degrees C, and at an inoculum concentration of 2x107-2x108 spores 5 g-1 substrate. Under these conditions, A. terreus produced 68.9 IU ml-1 of xylanase, and A. niger, 74.5 IU ml-1, after 4 d of incubation. A crude culture filtrate of the two Aspergillus strains was used for the hydrolysis of various lignocellulosic materials. Xylanase preparations from the two strains selectively removed the hemicellulose fraction from all lignocellulosic materials tested.

Preparation, characterization and application of Aspergillus sp. xylanase immobilized on Eudragit S-100.

Aspergillus sp. 5 (strain 5) and Aspergillus sp. 44 (strain 44) produced xylanase (34.3 and 32.7 IU ml-1, respectively) with very low levels of cellulases when grown on 1% wheat bran medium. Xylanase was non-covalently immobilized on Eudragit S-100 for saccharification. The system retained 70 and 80% of strain 5 and strain 44 xylanase activity, respectively. On immobilization, optimum temperature of activity broadened between 50 and 60 degrees C as compared to 50 degrees C in the case of the free enzymes. No significant shift in the pH optima was observed on immobilization. However, immobilization increased enzyme stability mainly by decreasing the temperature sensitivity to the inactivation reaction. The K(m) values increased from 5.6 to 8.3 mg ml-1 for strain 5 xylanase and 7.0 to 9.0 mg ml-1 for strain 44 xylanase. Enzymatic saccharification of xylan and wheat bran was improved on xylanase immobilization. Immobilized xylanase from both the strains produced three times more sugar as compared to free xylanase. In repeated batch saccharification studies immobilized xylanase was recycled three times without loss of enzyme activity.