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2 Coatings for Medical Applications
Published in Peerawatt Nunthavarawong, Sanjay Mavinkere Rangappa, Suchart Siengchin, Mathew Thoppil-Mathew, Antimicrobial and Antiviral Materials, 2022
Many studies show that gram-positive bacteria were more resistant to photocatalytic disinfection on TiO2 than gram-negative bacteria due to differences in the cell wall structure. Gram-positive bacteria have a thicker peptidoglycan layer and no outer membrane, whereas gram-negative bacteria have three layers of the cell wall; an inner membrane, a thin peptidoglycan layer, and an outer membrane [16, 22, 33-38]. There are some examples of gram-positive bacteria killed by photocatalytic disinfection on TiO2. For example, TiO2 suspension was studied to kill gram-positive bacteria as follows; Lactobacillus acidophilus [39-43], Listeria monocytogenes [22], Bacillus cereus [44], MRSA and Staphylococcus saprophyticus [45]. For TiO2 thin film application, there were some examples of studies as follows; Clostridium perfringens spores NCIMB 6125 [9], Staphylococcus aureus [46], Lactococcus lactis 411 [38], and Bacillus thuringiensis [47]. In addition, there were few TiO2 coating applications for killing organisms, for example, Actinobacillus actinomycetemcomitans [48] and Streptococcus iniae [49]. Nagame and colleagues [50] studied in killed Streptococcus cricetus by Kobe Steel TiO2 99.98% anatase. Tsuang and colleagues [29] studied the effect of TiO2 on orthopedic implants, and they found that TiO2 was the ability to kill Enterococcus hirae. TiO2 can kill gram-positive bacteria by photocatalytic disinfection [2].
Nanoparticles of Marine Origin and Their Potential Applications
Published in Se-Kwon Kim, Marine Biochemistry, 2023
Fatemeh Sedaghat, Morteza Yousefzadi, Reza Sheikhakbari-Mehr
AgNPs exhibit potential antimicrobial properties against infectious microbes such as Escherichia coli, Bacillus subtilis, Vibrio cholerae, Pseudomonas aeruginosa, and Staphylococcus aureus. The application of nanomaterials as new antimicrobials provides novel modes of action on different cellular targets in comparison with existing antibiotics. Multiple drug resistance to traditional antibiotics has created a great requirement for the development of new antimicrobial agents. Bacteria are classified as gram-negative or gram-positive. The peptidoglycan is the key component of the bacterial cell wall. Gram-negative bacteria have only a thin peptidoglycan layer (~2–3 nm) between their two membranes, while Gram-positive bacteria lack the outer membrane (substituted by a thick peptidoglycan layer). Smaller sized NPs disrupt the function of the membrane (such as permeability or respiration) by attaching to its surface and subsequently, penetrating the cell and cause further damage by interacting with the DNA. The antimicrobial properties of Ag encourage its use in biomedical applications, animal husbandry, food packaging, water purification, cosmetics, clothing, and numerous household products. Now, Ag is the engineered nanomaterial most commonly used in consumer products. Clothing, respirators, household water filters, contraceptives, antibacterial sprays, cosmetics, detergent, dietary supplements, cutting boards, socks, shoes, cell phones laptop keyboards, and toys are among the retail products that purportedly exploit the antimicrobial properties of Ag nanomaterials. Several researchers investigated the antimicrobial efficacy against different bacterial and fungal pathogens [Ramkumara et al., 2016; Franci et al., 2015; Prabhu and Poulose, 2012].
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Gram staining is a technique to distinguish between two major bacterial groups, based on stain retention by their cell walls. Gram-positive bacteria are stained bright purple, while Gram-negative bacteria are decolorized.
A Review on Bioflotation of Coal and Minerals: Classification, Mechanisms, Challenges, and Future Perspectives
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Kaveh Asgari, Qingqing Huang, Hamid Khoshdast, Ahmad Hassanzadeh
Gram-negative bacteria refer to a group that cannot absorb violet crystals during Gram staining due to their wall type and outer membrane. In the second stage of Gram staining, when safranin is added, they show a red and pink color. The cell membrane of Gram-negative bacteria has a multi-layered and very complex structure. The inner membrane of Gram-negative bacteria, called the cytoplasmic membrane, is covered with a flat wall of Peptidoglycan (a huge polymer including sugar derivatives and amino acids), to which the outer membrane is attached. Among the Gram-negative bacteria are the fourth group of BV4 bacteria such as Chlamydia, Acidobacteria and Spirochetes and the three main branches of Proteobacteria. Gram-positive bacteria, meanwhile, refers to a group of bacteria that respond positively to Gram staining. The gram-positive bacteria absorb violet crystals by the Peptidoglycan in its wall and appear dark blue or purple. Gram-positive bacteria usually do not have an outer membrane in their cell wall and have a relatively simple cell wall consisting of two to three layers. Staphylococcus is one of the most important Gram-positive bacteria (Gram 1884; Sharma 2001).
Human and livestock pathogens and their control during composting
Published in Critical Reviews in Environmental Science and Technology, 2022
Modes of action vary according to the structure of the bacteria cell wall (Cetin-Karaca, 2011; Davidson & Zivanovic, 2003; Raybaudi-Massilia et al., 2009; Ricke, 2003). Gram negative bacteria such as E. coli and Salmonella are more sensitive to short chain acids than gram positive bacteria (Raybaudi-Massilia et al., 2009). Once in the cell, the acid R-COOH dissociates, reducing the intracellular pH and leading the ATPase pumps to work excessively to transport the excess protons out of the cell instead of providing energy to the cell. The dissociated form R-COO– also damages the bacterial DNA (Cetin-Karaca, 2011). Conversely, gram positive bacteria such as Bacillus spp., Clostridium spp. and Listeria spp. are more sensitive than gram negative bacteria to lipophilic acids. These acids disrupt the cell wall and inhibit the transport of substrate molecules into the cell, leading to its starvation (Raybaudi-Massilia et al., 2009).
Biofilms formed on metallic materials by E. coli and S. epidermidis and their evaluation by crystal violet staining and its reflection
Published in Transactions of the IMF, 2022
M. Takayanagi, H. Kanematsu, H. Miura, T. Kogo, R. Kawai, A. Ogawa, N. Hirai, T. Kato, M. Yoshitake, T. Tanaka, D. M. Barry
The first step is the staining with crystal violet. All bacteria are stained a violet colour by this process. In the next step, a Gram’s iodine solution (composed of iodine and potassium iodide) is added to form a complex between the crystal violet and iodine. Through this process, the complex staining bacteria become insoluble in water. Then ethyl alcohol is added to the sample. The complex of crystal violet and iodine is trapped in the cell of gram-positive bacteria. On the other hand, the cell of gram-negative bacteria cannot retain the complex due to their thin peptidoglycan layer, and as a result, the colour is lost. Finally, they are stained with safranine. At this final stage, gram-positive bacteria do not change their violet colour, while gram-negative bacteria show a red colour. The colour difference is derived from the difference in a cell’s outer structure. Gram-positive bacteria have thick peptidoglycan layers, and these layers are the main reason for stained gram-positive bacteria showing a violet colour. However, the authors have also used crystal violet and their staining behaviours to evaluate biofilms, as described below. The crystal violet stains not only EPS, but also bacteria, and the staining extents are different between the two categories – gram-negative bacteria and gram-positive ones, as described above. The amount of stained parts for gram-positive bacteria is generally larger than that for gram-negative bacteria since the former has thick peptide glycan layers more susceptive to staining. Therefore, in this experiment, the authors chose E. coli and S. epidermidis, as representative models .