File Name: what is gram positive and gram negative bacteria .zip
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the gram-staining method of bacterial differentiation. Gram-negative bacteria are found everywhere, in virtually all environments on Earth that support life. The gram-negative bacteria include the model organism Escherichia coli , as well as many pathogenic bacteria , such as Pseudomonas aeruginosa , Chlamydia trachomatis , and Yersinia pestis. They are an important medical challenge, as their outer membrane protects them from many antibiotics including penicillin ; detergents that would normally damage the peptidoglycans of the inner cell membrane; and lysozyme , an antimicrobial enzyme produced by animals that forms part of the innate immune system. Additionally, the outer leaflet of this membrane comprises a complex lipopolysaccharide LPS whose lipid A component can cause a toxic reaction when these bacteria are lysed by immune cells.
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Planktonic cultures of Gram negative Pseudomonas libanensis also had a higher log 10 reduction than Gram positive Staphylococcus epidermidis.
Mixed species biofilms of P. However, when grown in co-culture, Gram negative P. Emission spectra indicated OH and O, capable of structural cell wall bond breakage, were present in the plasma. This study indicates that cell wall thickness correlates with CAP inactivation times of bacteria, but cell membranes and biofilm matrix are also likely to play a role.
Plasma is ionized gas and can be generated using a range of gases, including argon, helium, nitrogen and compressed air. Plasma contains radicals, excited molecules, charged particles and UV photons. Cold atmospheric plasma CAP is active towards a broad spectrum of microorganisms. There is an active debate about which plasma species are responsible for microbial inactivation, with reactive oxygen, hydrogen peroxide H 2 O 2 and UV photons the most likely candidates 1 , 2 , 3 , 4.
Many studies have tested the antibacterial activity of CAP in vitro , but only very limited data on clinical trials have been reported to date 5 , 6. It appears that the antimicrobial efficiency of CAP depends on specific properties of the devices used, making it challenging to investigate the mode of action. It has a DC power supply and can be used with a range of rare gases. A number of studies have shown its antibacterial effectiveness 10 , Cold plasma is hypothesised to have different targets within the cell, including cell membrane and cell wall, DNA and intracellular proteins 4 , Plasma species were shown to be able to break important bonds in the cell wall peptidoglycan structure in Gram positive bacteria 13 , 14 as well as leading to membrane lipid peroxidation in Gram negative bacteria This disruption of the outer shell of the cell will lead to leakage of cellular components, including potassium, nucleic acid and proteins.
After the cell wall is broken, reactive species can penetrate into the interior of the cell and further damage DNA and intracellular protein from oxidative or nitrosative species In bacteria, the Gram stain provides an important classification system, as several cell properties can be correlated with the cell envelope.
These differences in the cell envelope confer different properties to the cell, in particular responses to external stresses, including heat, UV radiation and antibiotics. Most in vitro studies focus on investigating plasma mediated killing of laboratory-cultured single-species planktonic cells. However, this does not resemble the natural conditions of bacterial existence. The vast majority of bacteria live in aggregates attached to a surface in often multi-species biofilms.
Bacterial biofilms cause problems in several industries by colonizing factory equipment and contaminating products. They are also a major contributor to human infections and are particularly hard to eradicate with antibiotic therapy.
Biofilms promote bacterial survival in the environment, as they coordinate group behaviour, enhance metabolic interactions, enhance gene transfer, produce a protective exopolysaccharide matrix from the cells and increase antibiotic resistance 16 , 17 , 18 , 19 , Here we show that cold-plasma-induced bacterial biofilm killing is correlated with the thickness of the bacterial cell wall, but additional factors are involved in determining sensitivity to CAP inactivation.
Using a commercially-available plasma source, a much higher reduction in cell numbers is achieved for Gram negative bacteria than Gram positive bacteria, independent of planktonic or biofilm mode of growth. Moreover, clinically-relevant P. This has implications for eradicating environmental biofilms and treating clinical significant infections, in which bacteria are known to often occur as multispecies communities.
Strains had single attached cells and small microcolonies were beginning to form. Only isolated dead red cells were observed with the majority being green viable cells.
All biofilms were tested for inactivation rates using the kINPen med operated with argon gas Fig. A similarly high reduction was observed for P. For B. The error bars represent standard deviations for 3 biofilm samples. A profound difference of CFU log 10 reductions after CAP treatment was observed between Gram positive and Gram negative species biofilms, prompting us to investigate a possible correlation of CAP inactivation rates with cell wall dimensions.
Values of cell wall thickness were sourced from previous studies. For P. The cell wall thickness of E. No indication of cell wall thickness measurements or high resolution TEM images were found for P. In natural habitats, bacteria often occur in mixed-species communities instead of mono-species cultures. One example is the co-occurrence of P. To investigate whether CAP can eradicate mixed-species biofilms in a similar fashion to single species, co-cultures of P. As for single-species biofilms, P.
However, the final CFU log 10 reduction was only 2. Interestingly, S. Mixed biofilms of P. After treatment, cells were scraped from the coupon and dilutions plated onto Pseudomonas agar P.
To evaluate whether species-dependent inactivation occurs only during biofilm mode of growth, the Gram positive S. A similar response compared to biofilm treatment was observed.
Overnight cultures of P. After treatment, cells were scraped from the coupon and dilutions plated onto nutrient agar. The error bars represent standard deviations for 3 samples.
Emission spectra were measured to examine any qualitative changes in plasma characteristics during the treatment time. A slight decrease of intensity of metastable Ar emission was observed Fig.
We have observed a marked difference in sensitivity to CAP treatment between Gram positive and Gram negative bacterial biofilms. The visible biofilm biomass appears similar among the six different species, with all showing a layer of single cells and small microcolonies before treatment Fig.
The similar thickness and structure of the biofilms suggests that factors other than biofilm architecture are responsible for the observed variation in CAP sensitivity. The major difference between the two groups of bacteria is the thickness of the cell wall and the presence of an outer membrane in Gram negative bacteria only.
The main component of the cell wall is peptidoglycan, which is found in almost all bacteria and is responsible for preserving the integrity of the cell. Destruction of peptidoglycan either through mutations or external stresses e.
The organism with the thickest cell wall, B. However, a correlation within the Gram groups could not be seen. For example, the Gram negative E. The bacterial cytoplasmic membrane consists of phospholipids and the Gram negative outer membrane consists of phospholipids and lipopolysaccharides Peroxidation of lipids is a well-known mechanism of CAP inactivation 4 , Membrane lipids have been suggested to be the macromolecules of the cell that are most vulnerable to physical stresses due to their position at the outside of the cell envelope and their sensitivity to ROS In addition, due to the presence of pore-forming proteins porins , the outer membrane is leakier than the cytoplasmic membrane and the cell wall and thus potentially easier to penetrate by CAP, possibly leading to a higher sensitivity of Gram negative bacteria to plasma treatment.
In agreement with our observation of higher sensitivity of Gram negative cells to CAP, Laroussi et al. The study suggested that the observed cell lysis of E. Lysis may occur when the outer membrane has acquired a sufficient electrostatic charge that the outward electrostatic stress exceeds its tensile strength 34 , Moreover, a higher surface roughness or irregularity due to the presence of an outer membrane could render Gram negative cells more sensitive to electrostatic disruption This suggests that additional factors to cell wall thickness play a role in CAP sensitivity.
A study by Montie et al. However, the diffusion across a thick Gram positive cell wall would presumably still be slower than across a thin Gram negative cell wall, leading to a difference in CAP sensitivity.
In contrast, a study by Mozetic et al. Interestingly, by being operated in an open-air environment, the emission intensity of atomic oxygen and hydroxyl radicals increased without external supply of oxygen.
In contrast, a slight decrease in intensity of metastable Ar emission was observed. Argon was used as the feeding gas for the plasma equipment. Oxygen and water vapour can originate from the surrounding air or from the sample being treated. The increase in atomic oxygen and hydroxyl radical density may be due to evaporation from the samples being treated.
The decrease in emission intensity is likely a consequence of the efficient quenching of argon metastables by oxygen molecules and atoms Yusupov et al. It was shown that plasma species can break structurally-important bonds of peptidoglycan, ultimately leading to cell death In some bacteria the cell wall has additional structural elements that could also influence CAP sensitivity.
For example, B. In addition to the structural envelope of single cells, the extracellular matrix ECM in which biofilm cells are embedded is likely to affect CAP sensitivity. The ECM gives cells added protection to external stress. The ECM composition varies between species, but it consists mainly of extracellular polymeric substance, including polysaccharides, lipids, proteins and nucleic acids It has been suggested that the ECM composition plays an important role in susceptibility to reactive species, such as found in CAP 40 ,
Gram-positive bacteria are classified by the color they turn after a chemical called Gram stain is applied to them. Gram-positive bacteria stain blue when this stain is applied to them. Other bacteria stain red. They are called gram-negative. Gram-positive and gram-negative bacteria stain differently because their cell walls are different. They also cause different types of infections, and different types of antibiotics are effective against them. All bacteria may be classified as one of three basic shapes: spheres cocci , rods bacilli , and spirals or helixes spirochetes.
Gram-negative bacteria are a significant cause of infections acquired in both hospital and community settings, resulting in a high mortality rate worldwide. Currently, a Gram-negative infection is diagnosed by symptom evaluation and is treated with empiric antibiotics which target both Gram-negative and Gram-positive bacteria. A rapid and simple diagnostic method would enable immediate and targeted treatment, while dramatically reducing antibiotic overuse. Herein, we introduce a method utilizing a fluorescent derivative of colistin COL-FL , that can directly label the Gram-negative cell wall of live bacteria and universally detect the targets within 10 min.
In bacteriology , gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. Gram-positive bacteria take up the crystal violet stain used in the test, and then appear to be purple-coloured when seen through an optical microscope. This is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test.
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grampositivebacteriacontainathickpeptidoglycancellwallalongwithteichoicacid,allowingthe stain in purple during gram staining whereas gram negative bacteria contain a thin peptidoglycan cell wall. withnoteichoicacid,allowingthecellwalltostaininpinkduringcounterstaining.Arienne C. 21.05.2021 at 19:45
Gram Positive Bacteria which retain the crystal violet stain during gram staining, giving the positive color for tests, are called gram positive bacteria. They appear.