Surface-adherent Bacteria Research Articles

Effect of Drinking Water Salt Content on the Interaction between Surfactants and Bacteria.

Sodium dodecyl sulfate (SDS) is a common surfactant used in various hygienic products. Its interactions with bacteria were studied previously, but the three-way interaction between surfactants, bacteria, and dissolved salts in the context of bacterial adhesion has not been studied. Here, we examined the combined effects of SDS (at concentrations typical of everyday hygienic activities) and salts, sodium chloride, and calcium chloride (at concentrations typically found in tap water) on the adhesion behavior of the common opportunistic pathogen Pseudomonas aeruginosa. We found that bacterial adhesion in the absence of SDS was dependent on the cation concentration rather than the total ionic strength and that combined treatment with several millimolar NaCl and SDS can increase bacterial adhesion. The addition of low concentrations of SDS (2 mM) to tens to hundreds millimolar concentrations of NaCl, typical of systems that suffer seawater incursion, reduced bacterial adhesion dramatically. Combined treatment with Ca+2 (in concentrations typical of those found in hard water) and SDS produced a small increase in total adhesion but a dramatic increase in the strength of adhesion. We conclude that the type and concentration of salts in water can have a considerable effect on the efficacy of soap in reducing bacterial adhesion and should be taken under consideration in critical applications. IMPORTANCE Surface-adhering bacteria are a reoccurring problem in many settings, including households, municipal water systems, food production facilities, and hospitals. Surfactants, and specifically sodium dodecyl sulfate (also known as SDS/SLS), are commonly used to remove bacterial contamination, but data regarding the interaction of SDS with bacteria and especially the effects of water-dissolved salts on this interaction are lacking. Here, we show that calcium and sodium ions can dramatically affect the efficacy of SDS on bacterial adhesion behavior and conclude that salt concentrations and ion species in the water supply should be considered in SDS applications.

Levofloxacin impregnation and extended release: Concentration model for insulin catheters

Increasing the lifetime of percutaneous insulin delivery catheters to minimize painful needle sticks increases the risk of infection. To combat surface-adherent bacteria and potential biofilm formation, we developed a method to impregnate levofloxacin antibiotic into the outer polymer of the catheter so that it can leach into the external medium. Complementarily, we developed a method to quantify the concentration of antibiotic to ensure the minimum inhibitory concentration (MIC) is maintained throughout the duration of catheter use. Additionally, we have investigated the extent of antibiotic resistance after a zwitterionic nonfouling coating treatment to ensure suitable release after further surface modification. Levofloxacin was incorporated into the catheter through the swelling of the outer polyurethane of the bilayer catheter and subsequent solvent evaporation. The zone of inhibition was measured over time with S. epidermidis on LB agar plates. The release of levofloxacin was measured using optical absorbance spectroscopy in water and quantified against a linear standard curve at 292 nm. We developed a model using Fick's second law of diffusion to calculate the concentration around the catheter. Visible inhibition of bacterial growth and biofilm formation was shown for up to 38 days. A total of 8–45 µg of antibiotic was released over 26 days and a concentration of 820,000 µg/mL in the 0.17 µL control volume was reached at day 26 for the minimally-loaded samples, an amount many orders of magnitude greater than the MIC. After the nonfouling treatment, the lowest concentration reached was 16 µg/mL after 26 days. In conclusion, we have demonstrated a suitable method to induce antibacterial activity for insulin catheters, maintain the MIC, and sustain antibacterial character following further surface coatings.

Antimicrobial peptides (AMP) in biofilm induced orthopaedic device-related infections

Orthopaedic device-related infection (ODRI) represent is one of the most challenging complications to manage in orthopaedic and trauma surgery. Biofilm formation is one of the crucial steps in the development of implant related orthopaedic infections due to the surface-adherent bacteria. Bacterial biofilms have several innate antimicrobial resistance mechanisms and hence difficult to eliminate with conventional antibiotics. Chronic, indolent, unresponsive infection can lead to clinical disability affecting quality of life with socio-economic consequences and compromised patient related health care outcomes. Although there is a basic understanding of the mechanism of biofilm associated antimicrobial resistance, enhanced knowledge, innovative treatment strategies and new therapeutic modalities is the need of the hour to manage biofilm associated Orthopaedic device-related infection (ODRI). Antimicrobial peptides (AMPs) represent an exciting opportunity to treat biofilm infections due to their diverse mechanisms of action. This article highlights the current role and mechanism of Antimicrobial peptides (AMPs) in preventing and eradicating Orthopaedic device-related infection (ODRI).

Antimicrobial Activity of Nano-Magnesium Hydroxide Against Oral Bacteria and Application in Root Canal Sealer.

BackgroundThe goal of the present work was to assess the antibacterial activity of nano-magnesium hydroxide (NMH) against Streptococcus mutans (S. mutans) and to explore the antimicrobial function of AH Plus™ sealer incorporating NMH.Material/MethodsThe antimicrobial behavior of NMH against S. mutans was evaluated with bactericidal tests. A modified direct contact test was used to assess the antimicrobial activity of unset AH Plus containing NMH after 5 minutes, 20 minutes, and 60 minutes of contact with bacteria. The antimicrobial effects and the amount of surface-adhering bacteria of the solidified materials were explored by SEM and confocal laser scanning microscopy, respectively.ResultsNMH powder presented excellent antimicrobial activity against S. mutans. Mg2+ and OH− were not the main factors resulting in bacterial death. Approximately 93.1% and 98% of the S. mutans were killed in the AH Plus+7% NMH group after incubation for 5 minutes and 20 minutes, respectively. AH Plus with 5% or 7% NMH were more potent against S. mutans compared with AH Plus alone (P<0.05). Moreover, the antibacterial function of AH Plus was lost after setting. NMH enabled the solidified AH Plus to still have antibacterial properties on the seventh day.ConclusionsNMH can be used to modify AH Plus sealer to eradicate residual bacteria and prevent reinfection.

Effects of Neem Extracts on Formed Biofilm of Pseudomonas aeruginosa

Over time, bacteria have been developing increasing resistance to commonly used antibiotics in medicine. To compound this issue, certain surface adherent bacteria can undergo a community response to form biofilms, a protective layer consisting of extracellular polymeric matrix that enhances resistance to antibiotics and host defenses. Biofilm association can confer bacteria with up to 1,000 times more antibiotic‐resistance. According to the NIH, up to 65% of all human infections and 80% of chronic infections are biofilm‐associated. P. aeruginosa, a common nosocomial pathogen exhibiting antibiotic resistance, is a known biofilm producer. Due to the prevalence of biofilms and their role in the antibiotic resistance of common nosocomial pathogens, it is important to look for antibiofilm agents. One understudied source of antibiofilm agents is plant derived compounds (phytochemicals). Of note, neem leaf extracts have been shown to inhibit biofilm formation in scientific literature. The purpose of my project was to identify the effect of neem extracts (bark, fresh leaf, dried leaf) on eradicating pre‐formed biofilm of P. aeruginosa (ATCC 27853) via a microplate biofilm quantitative assay. Bacteria were first inoculated into tryptic soy broth (TSB) and incubated (37°C, overnight). Afterwards, bacteria were density standardized (A590=0.2), transferred to microplates (polystyrene U‐bottom 24‐well), and incubated (37°C, overnight) to form biofilm. To isolate and treat the pre‐formed biofilm, microplates were washed (3 times, TSB), TSB was replaced, neem extracts were placed in the appropriate wells (a final concentration of 10% for each neem extract), and plates were incubated (37°C, 5 days). Afterwards, biofilm associated bacteria were killed with glutaraldehyde (10%) and microplates were washed again (3 times, dH2O). Subsequently, crystal violet (0.1% aqueous) was added to stain the biofilm. Excess dye was removed by washing (3 times, dH2O) and stained biofilm was solubilized (8% acetic acid). Solubilized biofilm was quantitated by A590 readings. Results indicated that all the neem extracts had no significant (p&lt;0.05) effect on biofilm eradication for P. aeruginosa 27853. This suggests that neem extracts may be more effective on developing biofilm rather than formed biofilm. Further strains will be tested for neem effect on biofilm eradication.Support or Funding InformationFinancial support for VK was received from the DeNardo Education and Research Foundation.

Comparative in vitro activity of bacteriophage endolysin HY-133 against Staphylococcus aureus attached to vascular graft surface.

Novel strategies are needed for combating Staphylococcus aureus biofilm in vascular graft infections. We investigated the in vitro activity of bacteriophage endolysin HY-133, daptomycin and rifampin against S. aureus attached to vascular graft surface. Daptomycin showed rapid bactericidal effect on surface-associated S. aureus, while the activity of HY-133 on graft surface-adherent cells was moderate and rifampin did not achieve bactericidal effect. Even in the highest concentrations, all antimicrobials used failed in a complete eradication of the surface-adherent bacteria.

Lipodisqs for eukaryote lipidomics with retention of viability: Sensitivity and resistance to Leucobacter infection linked to C.elegans cuticle composition.

Lipodisq™ nanoparticles have been used to extract surface lipids from the cuticle of two strains (wild type, N2 and the bacteria-resistant strain, agmo-1) of the C. elegans nematode without loss of viability. The extracted lipids were characterized by thin layer chromatography and MALDI-TOF-MS. The lipid profiles differed between the two strains. The extracted lipids from the bacteria-resistant strain, agmo-1, contained ether-linked (O-alkyl chain) lipids, in contrast to the wild-type strain which contained exclusively ester- linked (O-acyl) lipids. This observation is consistent with the loss of a functional alkylglycerol monooxygenase (AGMO) in the bacterial resistant strain agmo-1. The presence and abundance of other lipid species also differs between the wild-type N2 and agmo-1 nematodes, suggesting that the agmo-1 mutant strain attempts to compensate for the increase in ether-linked lipids by modulating other lipid-synthesis pathways. Together these differences not only affect the fragility of the cuticle and the buoyancy of the worm in aqueous buffer, but also interactions with surface-adhering bacteria. The much greater chemical stability of O-alkyl, non-hydrolysable linked lipids compared with hydrolysable O-acyl linked lipids, may be the origin of the resistance of the agmo-1 strain to bacterial infection, providing a more resilient cuticle for the nematode. Additionally, we show that lipid extraction with a polymer of styrene and maleic acid (SMA) provides a viable route to lipidomics studies with minimal perturbation of the organism.

Effect of the quantities of food residues on the desiccation resistance of spoilage lactic acid bacteria adhered to a stainless steel surface

Although lactic acid bacteria (LAB) are regarded as beneficial, these Gram-positive bacteria are considered spoilage microorganisms in various processed foods. In order to study the effect of food residues on the survival of spoilage LAB, Lactobacillus sakei and Leuconostoc mesenteroides were subjected to drying conditions in the presence of small amounts of meat gravy, dairy milk, soy milk, or egg. Bacterial suspensions (100 μL) were placed on a steel surface (50 mm diameter dish) and dried for 2 h at room temperature in the absence of food residue. Drying reduced bacterial cell counts from about 7 to 8 log CFU/dish to 3–4 log CFU/dish. As little as 10 μL of meat gravy, dairy milk or soy milk, or 1 μL of egg yolk per mL of LAB suspension was sufficient to demonstrate a protective effect on the adhered spoilage LAB, as confirmed by scanning electron microscopy. The results of this study suggest that small sediments of food, where they are protein or carbohydrate rich, can increase the resistance of surface-adherent bacteria to desiccation. Therefore, small amounts of food residue can render sanitization processes ineffective and encourage cross contamination.

Antibacterial activity of microstructured Ag/Au sacrificial anode thin films.

Ten different Ag dot arrays (16 to 625 microstructured dots per square mm) were fabricated on a continuous Au thin film and for comparison also on Ti film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Escherichia coli and Staphylococcus aureus were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards both bacterial strains was induced by Ag dot arrays on fabricated Au thin film (sacrificial anode system for Ag), due to the release of Ag ions from dissolution of Ag dots in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag) which remained intact to the original dot shape. The required number of Ag dots on gold film to achieve complete bactericidal effects for both bacterial strains was seven times lower than that observed with Ag dot arrays on Ti film.

Effect of quantity of food residues on resistance to desiccation of food-related pathogens adhered to a stainless steel surface

In order to study the effect of food residues on the survival of food-borne pathogens, Salmonella Typhimurium, Staphylococcus aureus, and Listeria monocytogenes were subjected to drying conditions in the presence of small amounts of food such as carrot juice, aqueous solution of nori, milk, and soy-milk. After drying for 2 h at room temperature in the absence of food residue, cell counts of S. Typhimurium, S. aureus, and L. monocytogenes decreased from 8 to 3, 6, and 5 log cfu/dish, respectively. Five milligrams of fresh carrot, 0.05 mg dried nori, and 100 nL milk or soy milk per 10 mm φ surface were sufficient to demonstrate a protective effect on the adhered pathogens, as confirmed by atomic force microscopy. Results from this study suggest that small sediments of food, not only protein rich but also carbohydrate rich, increase the resistance of surface-adherent bacteria to desiccation, rendering sanitization processes ineffective and encouraging cross contamination.

Single particle tracking reveals spatial and dynamic organization of the Escherichia coli biofilm matrix

Biofilms are communities of surface-adherent bacteria surrounded by secreted polymers known as the extracellular polymeric substance. Biofilms are harmful in many industries, and thus it is of great interest to understand their mechanical properties and structure to determine ways to destabilize them. By performing single particle tracking with beads of varying surface functionalization it was found that charge interactions play a key role in mediating mobility within biofilms. With a combination of single particle tracking and microrheological concepts, it was found that Escherichia coli biofilms display height dependent charge density that evolves over time. Statistical analyses of bead trajectories and confocal microscopy showed inter-connecting micron scale channels that penetrate throughout the biofilm, which may be important for nutrient transfer through the system. This methodology provides significant insight into a particular biofilm system and can be applied to many others to provide comparisons of biofilm structure. The elucidation of structure provides evidence for the permeability of biofilms to microscale objects, and the ability of a biofilm to mature and change properties over time.

Synergetic inactivation of Staphylococcus epidermidis and Streptococcus mutansin a TiO2/H2O2/UV system.

TiO 2 photocatalysis can be used to kill surface adherent bacteria on biomaterials, and is particularly interesting for use with percutaneous implants and devices. Its efficiency and safety, however, depend on the activation energy required. This in vitro study investigates synergetic effects against the clinically relevant strains S. epidermidis and S. mutans when combining photocatalytic surfaces with H2O2. After 20 min exposure to 0.1 wt% H2O2 and UV light on TiO2 surfaces, viabilities of S. epidermidis and S. mutans were reduced by 99.7% and 98.9%, respectively. Without H2O2 the corresponding viability reduction was 86% for S. epidermidis and 65% for S. mutans. This study indicates that low concentrations of H2O2 can enhance the efficiency of photocatalytic TiO2 surfaces, which could potentially improve current techniques used for decontamination and debridement of TiO2 coated biomedical implants and devices.

Pathogenesis and treatment concepts of orthopaedic biofilm infections

Implant-associated infection is caused by surface-adhering bacteria persisting as biofilm. Periprosthetic joint infection is difficult to diagnose and treat. The high susceptibility of implanted devices to infection is because of a locally acquired host defense defect, and persistence is mainly because of the rapid formation of a biofilm resistant to host defense and antimicrobial agents. Successful treatment of periprosthetic joint infection requires the optimal surgical procedure combined with long-term antimicrobial therapy directed against surface-adhering microorganisms. Surgical treatment according to an algorithm has been validated in several observational studies. The role of rifampin against device-associated staphylococcal infection has been evaluated in an animal model, in observational studies and in a controlled trial. Given the limited efficacy of traditional antibiotics in implant-associated infections, novel strategies such as coating of the device, vaccination against biofilms, and quorum-sensing inhibitors are promising future options for prevention and treatment.

Automated time-resolved analysis of bacteria–substrate interactions using functionalized microparticles and flow cytometry

Surface biofouling poses an increasing problem in industrial and health care applications, driving research for surface coatings to prevent anti-microbial colonization and characterization of the efficacy of the same. The diversity and increasing sophistication of such coatings, which postulate different types of anti-microbial action on planktonic and surface adhering bacteria, challenge the suitability of current approaches to evaluate and compare the different approaches as well as the speed and accuracy at which screening can be made. We describe and provide proof of principle for a method to use microparticles functionalized with molecular coatings through self-assembly together with flow cytometry readout to evaluate Escherichia coli bacteria surface adhesion and killing efficiency. Advantages of the method are the automation of the method that allows recording an immense number of interactions and the possibility to simultaneously record effects on both surface adhering and planktonic bacteria. We demonstrate and discuss design criteria to obtain this information on two coatings, poly( L-lysine)- graft-C 3H 6N +(CH 3) 2C 12H 25 (PLL- g-QAC) and poly( L-lysine)- graft-poly(ethylene glycol)-C 3H 6N +(CH 3) 2C 12H 25 (PLL- g-PEG-QAC), which exemplify two different approaches to creating anti-microbial interfaces. Despite an apparent higher killing efficiency of the PLL- g-QAC during brief exposures, the rapid fouling of that surface quickly reduces its efficiency, whereas the PLL- g-PEG-QAC coating showed greater promise in reducing the growth and interfacial colonization of bacteria over longer time scales.

Immunogenic Potential of Enterococcus faecalis Biofilm under Simulated Growth Conditions

IntroductionThe aim of this study was to evaluate the effect of growth modes (planktonic and biofilms) of Enterococcus faecalis on the intracellular survival and ability to produce tumor necrosis factor α (TNF-α) and interleukin (IL)-6 after interacting with monocytes/in vitro–differentiated macrophages. MethodsIn vitro biofilms of three E. faecalis strains (ATCC-29212, OG1RF, and FA2-2) were grown on dentin under simulated nutrient-rich and nutrient-deprived conditions. Biofilm-derived E. faecalis cells were incubated with monocytes/in vitro–differentiated human macrophages. A fluorometric assay was used to quantify the surface adherent bacteria, whereas an antibiotic protection assay was used to quantify the internalized E. faecalis cells 6 to 48 hours after interaction with macrophages. TNF-α and IL-6 produced during this interaction were quantified by an enzyme-linked immunosorbent assay. ResultsThe surface adherence and intracellular survival of E. faecalis within macrophages was significantly higher in biofilm bacteria when compared with planktonic cells (p ≤ 0.05). E. faecalis strains survived within the macrophages for up to 48 hours and produced higher levels of IL-6 with planktonic cells when compared with biofilm cells. Except in FA2-2, the planktonic cells of other strains did not show a significant increase in TNF-α compared with the biofilm cells (p > 0.05). ConclusionBiofilm cells of E. faecalis interacting with macrophages showed higher potential for surface adherence, intracellular survival and produced lesser amounts of IL-6 and TNF-α when compared to planktonic cells. Further experiments are required to understand the clinical implication of the intracellular survival of E. faecalis biofilm.

Vancomycin Bound to Ti Rods Reduces Periprosthetic Infection

A major challenge in treating periprosthetic infection is the predilection of certain bacteria to colonize implants, form biofilms, and resist treatment. We engineered an innovative self-protective implant with covalently bound antibiotics that prevents bacterial colonization and remains stable for extended periods of time. To test this surface in vivo, we developed a rat periprosthetic infection model with an intramedullary implant in S. aureus-infected femora. Using the model, we then evaluated the effect of vancomycin-modified titanium rods on the clinical presentation of bone infection. Finally, assuming delayed and chronic periprosthetic infections originate from biofilms atop contaminated implants, the numbers of surface adherent bacteria were measured to assess the capability of the implant to prevent biofilms. S. aureus (1.5 x 10(3) colony forming units) with no known resistance were injected into the femoral canal of Wistar rats, followed by the implant. Signs of infection were assessed weekly by direct clinical observation of the animals, radiograph, and microCT, and counts of bacteria adherent to the implant. Vancomycin-modified implants showed superior inhibition of bacterial attachment and proliferation compared to control titanium surfaces.

Sorption of cadmium to bacterial extracellular polymeric sediment coatings under estuarine conditions

AbstractMcrobial extracellular polymeric substances (EPS) are ubiquitous features in aquatic environments. Produced by surface‐adherent bacteria and microalgae, EPS are often present as coatings on surfaces of sediment particles and exhibit high affinities for divalent cationic metals. Thus, EPS sediment coatings may participate in the fate of potentially toxic metals. We coated particulate silica (8–10 μm) with EPS produced by NISC1, a bacterium isolated from estuarine sediments, in order to measure the metal binding characteristics of these coatings. We used the radioisotope 109Cd to measure effects of salinity (salinity = 2.5, 7.5, and 25‰), Cd concentration([Cd] = 0.038, 5, and 50 mg/L), and pH (pH = 5, 6, 7, 8, and 9) on Cd sorption to EPS‐coated (EPS‐silica) silica and to noncoated silica (NC‐silica). Also, Cd sorption by NISC1 EPS coatings was compared to coatings of polymers formed by the bacterium Alteromonas atlantica and the alga Macrocystis porifera. Under all circumstances, EPS coatings increased the affinity of silica for Cd. Extracellular polymeric substance‐particulate aggregates rapidly sorbed up to 90% of Cd from aqueous solution. Extracellular polymeric substance sediment coatings exhibited a maximum log distribution coefficient (Kd) of 6.5 at 2.5‰. Sorption of Cd to NC‐silica was affected by salinity and metal concentration, whereas sorption of Cd to EPS‐silica was only affected by salinity under high metal concentrations. Changes in pH had a dramatic effect on Cd sorption, with the proportion of free Cd to sorbed Cd changing from approximately 90% at pH 5 to 5% at pH 9. Desorption of Cd from EPS‐silica was enhanced with increasing salinity. These experiments suggest that EPS coatings actively participate in binding dissolved overlying and pore‐water metals in estuarine sediments.

SORPTION OF CADMIUM TO BACTERIAL EXTRACELLULAR POLYMERIC SEDIMENT COATINGS UNDER ESTUARINE CONDITIONS

Mcrobial extracellular polymeric substances (EPS) are ubiquitous features in aquatic environments. Produced by surface-adherent bacteria and microalgae, EPS are often present as coatings on surfaces of sediment particles and exhibit high affinities for divalent cationic metals. Thus, EPS sediment coatings may participate in the fate of potentially toxic metals. We coated particulate silica (8–10 μm) with EPS produced by NISC1, a bacterium isolated from estuarine sediments, in order to measure the metal binding characteristics of these coatings. We used the radioisotope 109Cd to measure effects of salinity (salinity = 2.5, 7.5, and 25‰), Cd concentration([Cd] = 0.038, 5, and 50 mg/L), and pH (pH = 5, 6, 7, 8, and 9) on Cd sorption to EPS-coated (EPS-silica) silica and to noncoated silica (NC-silica). Also, Cd sorption by NISC1 EPS coatings was compared to coatings of polymers formed by the bacterium Alteromonas atlantica and the alga Macrocystis porifera. Under all circumstances, EPS coatings increased the affinity of silica for Cd. Extracellular polymeric substance-particulate aggregates rapidly sorbed up to 90% of Cd from aqueous solution. Extracellular polymeric substance sediment coatings exhibited a maximum log distribution coefficient (Kd) of 6.5 at 2.5‰. Sorption of Cd to NC-silica was affected by salinity and metal concentration, whereas sorption of Cd to EPS-silica was only affected by salinity under high metal concentrations. Changes in pH had a dramatic effect on Cd sorption, with the proportion of free Cd to sorbed Cd changing from approximately 90% at pH 5 to 5% at pH 9. Desorption of Cd from EPS-silica was enhanced with increasing salinity. These experiments suggest that EPS coatings actively participate in binding dissolved overlying and pore-water metals in estuarine sediments.

Studies on characteristics of bacteria which cause infectious stone

Culture of stones and electrical microscopic observation were performed with stones collected from forty-eight patients who underwent surgery for urolithiasis. Thirty-six strains of bacteria in the stones obtained form stone culture were classified as nineteen strains of bacteria deriving from primary infection stones (Group A-I) and seventeen strains of bacteria deriving from metabolic stones (Group A-M). As for their ability to produce urease and glycocalyx, they were studied in comparison with forty-nine strains of stone surface-adhering bacteria (Group B). Glycocalyx producing ability was examined by the provisional quantitative toluidine blue assay and safranine straining method. As for the electrical microscopic observation, formation of biofilm bacterium was observed in all twenty cases of primary infection stones and in thirteen cases (46.4%) of twenty-eight cases of metabolic stones. Urease producing ability per stone was 6/14 (43.9%) in Group A-I, 4/13 (30.8%) in Group A-M and, 4/32 (12.5%) in Group B. There was a significant difference (p < 0.05) between Group A-I and Group B. Similarly for the glycocalyx producing ratio (toluidine blue assay), the values were 9/14 (64.3%) in Group A-I, 11/3 (84.6%) in Group A-M and 10/32 (31.3%) in Group B. As for the glycocalyx producing ration (safranine method), the values were 10/14 (71.4%) in Group A-I, 9/13 (69.2%) in Group A-M and 9/32 (28.1%) in Group B. As for the glycocalyx producing ability, Group A-I and Group A-M both showed significantly higher production ratios compared to Group B for both toluidine blue method and safranine method.(ABSTRACT TRUNCATED AT 250 WORDS)

Microbial Control of Silicate Weathering in Organic-Rich Ground Water

An in situ microcosm study of the influence of surface-adhering bacteria on silicate diagenesis in a shallow petroleum-contaminated aquifer showed that minerals were colonized by indigenous bacteria and chemically weathered at a rate faster than theoretically predicted. Feldspar and quartz fragments were placed in anoxic, organic-rich ground water, left for 14 months, recovered, and compared to unreacted controls with scanning electron microscopy. Ground-water geochemistry was characterized before and after the experiment. Localized mineral etching probably occurred in a reaction zone at the bacteria-mineral interface where high concentrations of organic acids, formed by bacteria during metabolism of hydrocarbon, selectively mobilized silica and aluminum from the mineral surface.