Modeling bacterial growth in drinking water : effect of nutrients

This article presents a model of growth of naturally occurring heterotrophic bacteria in the bulk water phase in the absence of disinfectant. The model considers growth with carbon, phosphorus, and nitrogen balance, death and lysis of bacteria, and conversion of less biodegradable organic carbon to assimilable organic carbon. Experimental data from two raw and two treated waters were used to test the model. The model describes the increase of live and dead bacterial cells in the water phase, and its output closely matches the experimental data. Such a model has the ability to characterize water nutrient status as well as to predict behavior of indigenous heterotrophic bacteria. The ability to predict bacterial population dynamics with respect to nutrients is beneficial for water treatment optimization. The model, based on microbiological measurements, helps to characterize treated water quality and project performance in terms of water quality into a distribution system.

Modelling biofilm growth and disinfectant decay in drinking water

A simple biofilm model was developed to describe the growth of bacteria in drinking water biofilms and the subsequent interactions with disinfectant residuals incorporating the important processes, such as attachment of free bacteria to the biofilm on a wall surface, detachment of bacteria from the biofilm, growth of biofilm bacteria with chloramine inhibition, chloramine decay in the bulk water phase, and chloramine decay due to biofilm bacteria and wall surfaces. The model is useful in evaluating the biological stability of different waters, as it can predict concentration of organic substances in water. In addition, the model can be used to predict the bacterial growth and biofilm decay in distribution systems. A model of this kind is a useful tool in developing system management strategies to ultimately improve drinking water quality.

Effect of a commercial alcohol ethoxylate surfactant (C11–15E7) on biodegradation of phenanthrene in a saline water medium by Neptunomonas naphthovorans

Biodegradation of poorly soluble polycyclic aromatic hydrocarbons (PAHs) has been a challenge in bioremediation. In recent years, surfactant-enhanced bioremediation of PAH contaminants has attracted great attention in research. In this study, biodegradation of phenanthrene as a model PAHs solubilized in saline micellar solutions of a biodegradable commercial alcohol ethoxylate nonionic surfactant was investigated. The critical micelle concentration (CMC) of the surfactant and its solubilization capacity for phenanthrene were examined in an artificial saline water medium, and a type of marine bacteria, Neptunomonas naphthovorans, was studied for the biodegradation of phenanthrene solubilized in the surfactant micellar solutions of the saline medium. It is found that the solubility of phenanthrene in the surfactant micellar solutions increased linearly with the surfactant concentrations, but, at a fixed phenanthrene concentration, the biodegradability of phenanthrene in the micellar solutions decreased with the increase of the surfactant concentrations. This was attributed to the reduced bioavailability of phenanthrene, due to its increased solubilization extent in the micellar phase and possibly lowered mass transfer rate from the micellar phase into the aqueous phase or into the bacterial cells. In addition, an inhibitory effect of the surfactant on the bacterial growth at high surfactant concentrations may also play a role. It is concluded that the surfactant largely enhanced the solubilization of phenanthrene in the saline water medium, but excess existence of the surfactant in the medium should be minimized or avoided for the biodegradation of phenanthrene by Neptunomonas naphthovorans.

Antibacterial activity of capsaicin-coated wool fabric

Fabrics made from natural fibers, such as wool and cotton, are susceptible to attacks from micro-organisms, which may damage the fabrics and harm the human body. Antimicrobial finishing of natural textile products may involve harmful and non-environmentally friendly chemicals. In this study, a natural antibacterial agent, capsaicin, was coated on the surface of wool fabrics by a sol-gel process. The antibacterial properties of coated fabrics were evaluated against test bacteria Escherichia coli according to the American Association of Textile Chemists and Colorists (AATCC) method and standard American Society for Testing and Materials (ASTM) E2149-01. Compared with the control group (sol-gel coated fabric without capsaicin), the capsaicin-coated fabric inhibited bacterial growth markedly after 24 hours incubation at 37°C. The antibacterial efficiency after laundry washes was also investigated. Good durability to washing of capsaicin on fabric was achieved by the sol-gel coating technique.

Host defense at the ocular surface

Microbial infections of the cornea frequently cause painful, blinding and debilitating disease that is often difficult to treat and may require corneal transplantation. In addition, sterile corneal infiltrates that are associated with contact lens wear cause pain, visual impairment and photophobia. In this article, we review the role of Toll-Like Receptors (TLR) in bacterial keratitis and sterile corneal infiltrates, and describe the role of MD-2 regulation in LPS responsiveness by corneal epithelial cells. We conclude that both live bacteria and bacterial products activate Toll-Like Receptors in the cornea, which leads to chemokine production and neutrophil recruitment to the corneal stroma. While neutrophils are essential for bacterial killing, they also cause tissue damage that results in loss of corneal clarity. These disparate outcomes, therefore, represent a spectrum of disease severity based on this pathway, and further indicate that targeting the TLR pathway is a feasible approach to treating inflammation caused by live bacteria and microbial products. Further, as the P. aeruginosa type III secretion system (T3SS) also plays a critical role in disease pathogenesis by inducing neutrophil apoptosis and facilitating bacterial growth in the cornea, T3SS exotoxins are additional targets for therapy for P. aeruginosa keratitis.

Bacterial modes of action for enhancing of plant growth

The greatest issue affecting the sustainability of broad acre cropping both environmentally and economically is the requirement of fertilizers. These are based on mined phosphorous or other mineral ores, ammonia produced through the Harbour-Bosch process and industrially manufactured potash. As global demand for fertilizers increases, the costs associated with the production for each of these major nutrients increases. Biofertilizers such as plant growth promoting bacteria (PGPB) are a possible biotechnology that could alleviate the need for addition of increasing amounts of fertilizers. These bacteria naturally occur in soils and aggressively colonize around plant roots and have been shown to have plant growth promoting effects. PGPB are known to influence plant growth by various direct and indirect mechanisms; while some can affect plant physiology directly by mimicking synthesis of plant hormones,others increase mineral availability and nitrogen content in soil. Here we review the previously characterized modes of action for enhancement of plant growth by PGPB such as nitrogen fixation, nutrient solubilization and production of auxins and enzymes, as well as discussing more recent proposed modes of action such as secondary metabolites.

Changes in bacterial concentration in the liver correlate with that in the hepaticojejunostomy after bile duct reconstruction: implication in the pathogenesis of postoperative cholangitis

Postoperative cholangitis is a frequent and unpredictable complication of unknown etiology following bile duct reconstruction (BDR), particularly for biliary atresia. This study was undertaken to correlate the growth of bacteria in the hepaticojejunostomy with that in the liver after BDR. Quantitative bacterial culture was done on the specimens taken from the liver and from the hepaticojejunostomy at 1 week (group 1, n = 7), 1 month (group 2, n = 7), and 2 months (group 3, n = 7) following BDR with Roux-en-Y hepaticojejunostomy in piglets after 2 weeks of common bile duct ligation. The histological examination of the liver and the hepaticojejunostomy, as well as serial monitoring of hemogram and liver function tests, were performed to correlate the findings with the bacterial concentration of the liver and the hepaticojejunostomy following BDR. The bacterial concentration of the hepaticojejunostomy, expressed as log10 colony-forming units per gram (log10 CFU/g) of the hepaticojejunostomy, showed a progressive decrease from 8.38 ± 1.36 in group 1, 7.07 ± 2.54 in group 2, to 3.56 ± 1.31 in group 3 (p = 0.001). The log10 CFU/g of the liver also showed a progressive decrease from 5.02 ± 1.59 in group 1, 3.16 ± 1.56 in group 2, to 2.19 ± 1.09 in group 3 (p = 0.006). There was a significant positive correlation of the log10 CFU/g of the liver (n = 21) with that of the hepaticojejunostomy (n = 21) following BDR (r = 0.600, p = 0.004). Most of the infectious pathogens isolated from the liver were also isolated from the hepaticojejunostomy. The changes in hemoglobin, bilirubin, albumin, and ammonia significantly correlated with the changes of the bacterial concentration of the liver. The results of the study suggests that hepatic bacterial proliferation after BDR is significantly affected by microbial overgrowth in the bilioenteric anastomosis and is associated with deteriorated liver function and hemogram.

Water quality, bacterial flora and production in shrimp farms in Sri Lanka

This study investigated the possibilities of improvement in the brackish water shrimp culture industry in Sri Lanka. Feeding rates could be further reduced without negative effect on shrimp growth while improving effluent water quality. Improvements of feed quality and pond management practices were also suggested.