Bacterial Growth Inhibition Test Research Articles

Isolation and characterization of α-amylase from thermophilic Geobacillus stearothermophilus

Metabolite formation from radical-based oxidation of the environmental pollutant triclosan (TCS) was compared using an ascomycete (Phoma sp. UHH 5-1-03) and a basidiomycete (Trametes versicolor) laccase, laccase-redox mediator systems, and electrochemical oxidation (EC). Laccase oxidation predominantly yielded TCS di- and trimers, but notably also caused TCS ether bond cleavage. The latter was more prominent during EC-catalysed TCS oxidation, which generally resulted in a broader and more divergent product spectrum. By contrast, only quantitative but not qualitative differences in TCS metabolite formation were observed for the two laccases. Application of the presumable natural laccase redox mediator syringaldehyde (SYD) shifted the TCS-transforming reactions of laccase systems from oligomerization more towards ether bond cleavage. However, the observed rapid removal of SYD from reaction systems caused by predominant adduct formation from SYD and TCS, and concomitant conversion of SYD into 2,6-dimethoxy-1,4-benzoquinone (DMBQ) clearly demonstrates that SYD does not function as a “true” laccase redox mediator in the sense of being recycled during TCS oxidation. Laccase treatment of TCS without SYD decreased the anti-bacterial TCS activity more than treatment employing SYD in addition, indicating that SYD and/or its transformation products contribute to bacterial toxicity. DMBQ was found to be about 80% more active in a bacterial growth inhibition test than its parent compound SYD in terms of IC20 values. These observations establish DMBQ as a potential cause of toxicity effects of SYD-laccase systems. They further illustrate that a natural origin of a redox mediator does not automatically qualify its use as environmentally benign or non-hazardous.

Biodegradability and ecotoxicitiy of tramadol, ranitidine, and their photoderivatives in the aquatic environment

This study was designed to assess the fate and the overall potential impacts of the widely prescribed drugs ranitidine and tramadol after their introduction into the aquatic environment. The probability to detect these two drugs in the aquatic environment was studied by analyzing their abiotic and biotic degradation properties. For this purpose, samples were irradiated with different light sources, and three widely used biodegradability tests from the OECD series, the closed bottle test (OECD 301 D), the manometric respirometry test (OECD 301 F) and the Zahn-Wellens test (OECD 302 B), were conducted. The ecotoxicity of the photolytically formed transformation products was assessed by performing the bacterial growth inhibition test (EN ISO 10712). Furthermore, quantitative structure-activity relationship analysis and a risk analysis based on the calculation of the predicted environmental concentrations have also been conducted to assess the environmental risk potential of the transformation products. The possible formation of stable products by microbial or photolytical transformation has been investigated with DOC and LC-MS analytics. In the present study, neither ranitidine, nor tramadol, nor their photoderivatives were found to be readily or inherently biodegradable according to test guidelines. The photolytic transformation was faster under a UV lamp compared to the reaction under an Xe lamp with a spectrum that mimics sunlight. No chronic toxicity against bacteria was found for ranitidine or its photolytic decomposition products, but a low toxicity was detected for the resulting mixture of the photolytic transformation products of tramadol. The study demonstrates that transformation products may have a higher environmental risk potential than the respective parent compounds.

Toxicity Study for Halogenated Aromatics to Mixed Bacteria in River Water

The bacterial growth inhibition test was used to determine toxicity of the halogenated aromatics on the mixed bacteria from the Yangtze River. The concentration values causing 50% reduction of bacteria growth for 24 hr (IC50) and the maximum tolerance concentration for 7 d (MATC) were gained according to the concentration-response curves. An obvious linear relationship was found between the two toxicity descriptors. The following quantitative structure- activity relationships were developed by using the valence molecular connectivity index method: -lgIC50=0.8266Xpcv- 0.2363Xpv+3.811 (R2=0.833) and -lgMATC=1.2016Xpcv-0.3783Xpv+4.614 (R2=0.900). The two equations were found to fit well. It suggested that the models derived from the molecular connectivity index could be used successfully to predict the toxicity of halogenated aromatic compounds.

Biodegradation of Complex Bacteria on Phenolic Derivatives in River Water

To isolate, incubate, and identify 4-chlorophenol-degrading complex bacteria, determine the tolerance of these bacteria to phenolic derivatives and study their synergetic metabolism as well as the aboriginal micrpbes and co-metabolic degradation of mixed chlorophenols in river water. Microbial community of complex bacteria was identified by plate culture observation techniques and Gram stain method. Bacterial growth inhibition test was used to determine the tolerance of complex bacteria to toxicants. Biodegradability of phenolic derivatives was determined by adding 4-chlorophenol-degrading bacteria in river water. The complex bacteria were identified as Mycopiana, Alcaligenes, Pseudomonas, and Flavobacterium. The domesticated complex bacteria were more tolerant to phenolic derivatives than the aboriginal bacteria from Qinhuai River. The biodegradability of chlorophenols, dihydroxybenzenes and nitrophenols under various aquatic conditions was determined and compared. The complex bacteria exhibited a higher metabolic efficiency on chemicals than the aboriginal microbes, and the final removal rate of phenolic derivatives was increased at least by 55% when the complex bacteria were added into river water. The metabolic relationship between dominant mixed bacteria and river bacteria was studied. The complex bacteria domesticated by 4-chlorophenol can grow and be metabolized to take other chlorophenols, dihydroxybenzenes and nitrophenols as the sole carbon and energy source. There is a synergetic metabolism of most compounds between the aboriginal microbes in river water and the domesticated complex bacteria. 4-chlorophenol-degrading bacteria can co-metabolize various chlorophenols in river water.

Inhibition of Ampicillin-resistance in Bacteria by Modified DNAzymes

Abstract To overcome ampicillin-resistance of bacteria which is believed to attribute their endogenous β-lactamase, we designed three 10-23 DNAzymes(Dz 1 , Dz 2 , Dz 3 ) targeting the coding region of β-lactamase mRNA and examined their inhibitory capabilities of the ampicillin-resistance of TEM-1 and TEM-3 bacteria. Dz 1 was a traditional 10-23 DNAzyme, Dz 2 was the mutant of Dz 1 by addition of the protected nucleotide to each arm of the enzyme, and Dz 3 was a mutant of Dz 1 at antisense arms of which phosphorothioate modifications were made. Kinetic analysis, bacterial growth, and β-lactamase activity measurement showed that all the three DNAzymes worked efficiently in vitro and in vivo. A 9 hours bacterial growth inhibition test showed that the inhibition rates of TEM-1 bacteria by Dz 1 , Dz 2 , and Dz 3 were 27%, 50%, and 29%, respectively. In addition, the inhibition rates of TEM-3 bacteria by those three DNAzymes were found to be 49%, 58%, and 45%, respectively. The current findings suggest that DNAzymes may become potential candidates of alternative inhibitors for bacteria drug-resistance.

Microbial Toxicity Tests and Chemical Analysis as Monitoring Parameters at Composting of Creosote-Contaminated Soil

Traditionally, chemical analyses are used in the assessment of contaminated soil and in monitoring the efficiency of soil remediation processes. We investigated if chemical analysis could be supported and even partly replaced by biological toxicity tests. In two case studies creosote-contaminated soil was composted outdoors in 5- and 100-m 3 windrows. Degradation of polyaromatic hydrocarbons (PAHs) was followed by chemical analysis and toxicity tests. Polyaromatic hydrocarbons were quantified and idenfitifed by HPLC. Because the soil was also contaminated by copper-, chromium-, and arsenic-containing fungicides, these elements were analyzed by atomic absorption spectrometry. The toxicity of soil samples was assessed by a soil-contact modification of the luminescent bacteria ( Vibrio fischeri) test and in the other case also by enzyme synthesis inhibition (Toxi-ChromoPad test, Escherichia coli). The toxicity of soil water extracts was measured by the standard luminescent bacteria ( V. fischeri) test and bacterial ( Pseudomonas putida) growth inhibition test. After the first 4 months of the composting period the total amount of PAHs was reduced in all windrows, and in particular, the loss of two- and some three-ring compounds was high, almost 90%. Toxicity decreased concurrently with the decrease in PAH concentration during composting, but after 4 months, one of the piles inoculated with mycobacteria and containing more three- and four-ring compounds was found to be more toxic than at the beginning. After the next summer, total PAH content was further reduced but some four-ring or heavier compounds were demonstrated to be poorly degraded. The toxicity was also reduced to the same level as in the control pile. The total PAH content and the toxicity were both reduced significantly during 5 months of composting

Biodegradability properties of sulfonamides in activated sludge

AbstractTwelve different sulfonamides were selected for a biodegradation study using a respirometric screening test and an activated sludge simulation test. A simple bacterial growth inhibition test was applied to show that the sulfonamides did not affect the bacteria at the concentration levels used. None of the compounds were degraded in the screening test, leading to the conclusion that sulfonamides cannot be classified as readily biodegradable. In the simulation test, primary degradation of mixtures of four compounds at concentration levels of 250 to 500 μg/L were tested and analyzed using high‐performance liquid chromatography. Biodegradation occurred after lag phases of 7 to 10 d at 20°C when nonadapted sludge was applied. Test compounds were degraded within a few days. At 6°C, degradation lag phases and degradation rates were three to four times longer. Degradation curves fit well to the logistic growth model, indicating growth of specific degraders in the test system. Sulfonamide adapted bacterial cultures were able to degrade either the same compounds as previously added or four other sulfonamides in a rapid and uniform way (t1/2 from 0.2 to 3 d). This finding shows that if capable of degrading one sulfonamide substance, these bacteria may also degrade many other sulfonamides. In practice, this implies that because the biodegradation rate is found to be identical for several sulfonamides in the sludge, the compounds may be assessed as a group by studying only a few compounds in applications such as environmental fate assessments. The mechanism for inducement of sulfonamide adaptation to the bacteria was not revealed in this study.

合成洗剤の安全性に関する研究 各種細菌，魚，ヒト皮膚に及ぼす影響

Seven different synthetic detergents, i.e., four for kitchen use and two for household use obtained from domestic market and one imported from U.S.A., were assessed for their safety to use by bacterial growth inhibition, fish toxicity and human skin irritation tests. The results are as follows:1) The imported synthetic detergent and both synthetic detergents for household use inhibited bacterial growth at lower concentrations than the synthetic detergents for kitchen use.2) When the detergents were assessed by the fish toxicity test, the two detergents for kitchen use containing straight chain of alkylbenzene sodium sulfonate, as a main ingredient were most toxic. Sequential toxic manifestations eventuating in death of fish were common with all synthetic detergents tested, being diminished power of swimming, swarming up to the surface of water, difficult to keep equilibrium and incapable of swimming.3) The intensity of skin irritation varied with chemical characteristics of synthetic detergents. The four products for kitchen use (containing straight chain of alkylbenzene sodium sulfonate, as a main ingredient) were more potent than the imported product in eliciting a irritant skin response, which might be responsible for hand eczema.

Nickel and cadmium inhibition of activated sludge at extreme substrate levels

Abstract Traditionally, mathematical models defining the inhibition of the activated sludge use modified enzyme kinetics. For experimental support, some methods such as the BOD test itself, involve very low substrate concentrations. Others, such as the bacterial growth inhibition test which measures an inhibition potential blocking activity by 50%, use very high substrate concentrations. This paper outlines a series of inhibition experiments with BOD and bacterial growth inhibition tests, using nickel and cadmium as inhibitors. The results are comparatively evaluated by means of appropriate mathematical interpretation.