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Microbiological Considerations in the Selection and Validation of Filter Sterilization
Published in Maik W. Jornitz, Filtration and Purification in the Biopharmaceutical Industry, 2019
Given levels of variability inherent in microbial analysis and considering also that microorganisms are not homogeneously distributed in most environments or materials it is not appropriate to, for example, set a target level of X cfu/mL and reject the material at a level of Xþ1 cfu/mL. The cfu is not a direct measure or count of microorganisms present. The cfu is exactly what its name implies: it is a “unit” of microorganisms capable of growing into a single visible colony on solid medium. Said unit may consist of 10 viable cells or it may contain 30 viable cells. It is quite possible that a large unit of cells could break into two or more smaller groups and manifest as two or three cfu rather than one. Therefore, some latitude should always be given regarding microbiological limits. The recently implemented harmonized compendial microbial limit tests (USP <61>, <62>, and <1111> 2017a–c) state that in the case of an established level of 10 cfu the maximum acceptable count should be 20 cfu. Similarly, if the established target level is 103 cfu the maximum acceptable count should be 2000 cfu. In general, a membrane filtration approach to bioburden testing will be easier for most users to implement and with the majority of products more suitable than direct plating methods in the evaluation of prefiltration bioburden.
Microbial ecology of biofiltration
Published in Joseph S. Devinny, Marc A. Deshusses, Todd S. Webster, Biofiltration for Air Pollution Control, 2017
Joseph S. Devinny, Marc A. Deshusses, Todd S. Webster
The viable heterotrophic plate count is a convenient and inexpensive microbial enumeration technique (Alexander, 1977; Brock and Madigan, 1991). When a sufficiently dilute suspension is added to a nutrient agar plate, individual cells grow to become distinct colonies on the surface of the agar. Different species produce colonies of different colors and shapes. Fungal colonies may have a fuzzy appearance. It is presumed that each colony on the plate arises from a single cell in the original suspension. The colonies can be seen and counted with the naked eye, so determining the number of cells in the sample of suspension is simple. The number of colony forming units (CFUs) can be counted and expressed as the number of microbes per gram of wet or oven-dry medium.
Indoor Issues and Health Implications (and Ventilation Requirements)
Published in Rodger Edwards, Handbook of Domestic Ventilation, 2006
The amounts and levels of mould spores within dwellings vary considerably. A common representation of the number of microbes present in a given sample, as used by microbiologists, is the actual number of pieces of matter containing microbes and are which in turn capable of breeding and spreading. The actual term used is the colony forming unit, often denoted as the cfu. When examining a Petri dish for evidence of microbial growth, the microbiologist is often seeking to determine the number of cfu present. For example, in a case where contamination of food was suspected, the inference would be the higher the number of cfu, the higher the level of contamination. When airborne levels of microbes need to be quantified, air samples of a predetermined volume are passed through a collecting medium (possibly a sterile filter pad). Microbial cultures are then incubated in a medium supportive of the microbes of interest. The numbers of cfu are then counted. Airborne levels of microbial contamination are expressed as the number of cfu per cubic metre (cfu/m3) of air. The words “level” and “concentration” are used interchangeably within the literature, and this practice is followed within this book.
Nitric acid oxidation and urea modification of carbon fibres as biofilm carriers
Published in Environmental Technology, 2023
Qijie Liu, Ling Shao, Zhenzhong Liu, Yingwei Chen, Guangze Dai, Jialei Ying
The CF supports (0.02 g) were immersed in the bacterial suspension (10 mL) to immobilise the bacterial cells, and the bacterial suspension was shaken at 200 rpm using a universal shaker. The OD600 of the suspension was measured at each time point using a visible-light spectrophotometer (UV2000, UNICO). To eliminate the influence of organisms released by broken cells and ensure the accuracy of the experiments, a colony-forming unit (CFU) formation assay was performed to evaluate the residual amount of bacteria. An aliquot (1 mL) of the suspension was collected after 2 h of adsorption for the CFU formation assay. The diluted samples (20 μL each in triplicate) were evenly dispersed by gradient dilution onto nutrient agar culture medium plates and incubated at 37 °C for 24 h, after which the colonies were counted.
Bioethanol production from sugarcane molasses with supplemented nutrients by industrial yeast
Published in Biofuels, 2023
Hasan Shahriar Raby, Md Anowar Saadat, Ahmed Nazmus Sakib, Fatema Moni Chowdhury, Abu Yousuf
The colony-forming unit (CFU) represents the number of viable cells in the growth medium. The number of growth supplements was varied to observe the effect of supplements on cell viability. A significant difference was observed in the CFU result with the feeding of supplements. Figure 1 shows four distinct phases- lag, log, stationary, and death phase, however, the lag phase was shorter in the absence of supplementation. However, the duration of the log phase was extended upon the introduction of supplementation, resulting in the maximum viable cell count observed during this phase compared to non-supplemented conditions. Figure 1 also illustrates that the dosing of supplements has a substantial impact on yeast growth. The growth rate of yeast exhibited variability with different dosages of supplements. Quadruple supplementation resulted in the highest growth rate compared to initial and doubled supplementation. However, the effectiveness of supplement addition was found to be higher during the early stages in terms of cell viability
Effect of silica nano-spheres on adhesion of oral bacteria and human fibroblasts
Published in Biomaterial Investigations in Dentistry, 2020
Pawel Kallas, Hua Kang, Håkon Valen, Håvard Jostein Haugen, Martin Andersson, Mats Hulander
Both S. aureus (Newman strain) and S. mitis (NCTC 12261) were grown in tryptic soy broth (TSB) medium overnight at 37 °C and 5% CO2 atmosphere in centrifuge tubes. The overnight culture was diluted 10 times and left to grow again in the same conditions for 2 h. After that, samples were centrifuged at 5000 rpm (2912 rcf) at 21 °C to obtain a pellet (Thermo Scientific™ Heraeus Multifuge X3FR Centrifuge, Waltham, MA). The supernatant was discarded, and the pellet was resuspended in PBS (OD600 = 0.6, Thermo Scientific™ Spectronic 200E, Waltham, MA) before use in the experiments. The average colony-forming unit (CFU) was measured by culturing bacteria overnight on agar plates.