Gram Negative and Gram Positive - I need help: In simple or complex terms, what is the difference between Gram neg (Nov/11/2005 )
I am lost..... can anyone explain what Gram negative and positive is? In simple terms, or more complicated, I just need to know what they are and what the difference is! Thanks! -- crossbow1313@hotmail.com
Prokaryotic life can be divided into two groups, Gram positive or Gram negative (this is not always the case but it is for the most part). This is based on a staining procedure, Gram positive bacteria stain purple whereas Gram negative bacteria will stain pink. This has to do with the presence and thickness of cell wall on the cell. In Gram positive bacteria, there is one membrane which is surrounded by a thick cell wall made of peptidoglycan. In Gram negative bacteria, there is an inner membrane followed by a much thinner peptidoglycan layer and an outer membrane. This difference in peptidoglycan thickness results in the difference in clolour when the cells are Gram stained. The Gram positive cells, because of their thicker cell wall, are able to keep the stain in the cell and hence stain purple. Check out this link for the Gram stain procedure:
http://medic.med.uth.tmc.edu/path/grampro.htm
This link has an image of Gram stained bacteria:
http://www.uphs.upenn.edu/bugdrug/antibiot...ocframeset1.htm
http://medic.med.uth.tmc.edu/path/grampro.htm
This link has an image of Gram stained bacteria:
http://www.uphs.upenn.edu/bugdrug/antibiot...ocframeset1.htm
Alright, I understand it much better now, but I need to predict what will happen for my hypothesis. Which bacteria, Gram negative or Positive, do you think would be more resistant to antibacterials or disinfectants?
There is no way to reliably tell, unless you test the chemical in question (or if it has already been tested).
Some antimicrobial compounds are more effective against Gram positive organisms, some are more effective against Gram negative organisms, and some broad spectrum antimicrobials are effective against both. It really depends on the mechanism of action of the compound (how it kills the cell or how it renders it unable to grow).
Also, realize that knowing whether an antimicrobial is effective or not against a particular bacteria in advance is not enough -- many strains of bacteria have aquired resistance to (protection against) many antimicrobials and are thus not affected by them. For example, penicillin was at one time a very effective antibiotic which works by interfering with bacterial cell wall synthesis. But, many bacteria have aquired the ability to produce an enzyme (beta-lactamase) that destroys the penicillin, rendering it useless against them.
So, members of this class of antibiotics (the beta-lactams, named for a part of their molecular structure) are effective against Gram positive bugs (e.g. penicillin) and against Gram negative bugs (e.g. ampicillin and amoxycillin), but only if the particular isolate (strain) of the target bacteria hasn't acquired resistance to the drug.
Some antimicrobial compounds are more effective against Gram positive organisms, some are more effective against Gram negative organisms, and some broad spectrum antimicrobials are effective against both. It really depends on the mechanism of action of the compound (how it kills the cell or how it renders it unable to grow).
Also, realize that knowing whether an antimicrobial is effective or not against a particular bacteria in advance is not enough -- many strains of bacteria have aquired resistance to (protection against) many antimicrobials and are thus not affected by them. For example, penicillin was at one time a very effective antibiotic which works by interfering with bacterial cell wall synthesis. But, many bacteria have aquired the ability to produce an enzyme (beta-lactamase) that destroys the penicillin, rendering it useless against them.
So, members of this class of antibiotics (the beta-lactams, named for a part of their molecular structure) are effective against Gram positive bugs (e.g. penicillin) and against Gram negative bugs (e.g. ampicillin and amoxycillin), but only if the particular isolate (strain) of the target bacteria hasn't acquired resistance to the drug.
Alright....... so if there is really no way to tell, then what should I say for my hypothesis, perhaps something simple such as "The bleach will be the most effective on the Bacillus subtilus and the E. coli"? That sounds just a little too simple, do you have any suggestions for a more complex, better-sounding hypothesis on my overall experiment? Anyone? Thanks
"The bleach will be the most effective on the Bacillus subtilus and the E. coli" is more of a conclusion than a hypothesis...
Your hypothesis should be more general, and state what you expect to see, something like "I expect that, due to genetic differences between E. coli and B. subtilis, some chemicals will be effective against only one of the test organisims, and some will be effective against both. Some chemicals may have no effect against either organisim."
If you're going to test the chemicals at various dilutions, you can also say "I expect the size of the zones of clearing (if present) to be dependant upon the concentration of the chemical tested, and that of those chemicals that are effective against both organisms, some will be effective against one at a lower concentration than is necessary for effectiveness against the other".
If you're going to sample the cleared zones for viability, you can also say "I also expect that some of the effective chemicals will be bacteriostatic (stop the organism from growing, but not kill it), and others will be bacteriolytic (kill the organism)".
In the first hypothesis statement, you want to use a generic statement like "due to genetic differences" because you can't conclude on the basis of your experiments that the presence or absence of a zone of clearing was entirely or even partially due to the Gram status of the organism -- the particular strain you're using might be susceptible or resistant to the chemical by other means.
Have you been given the two organisms to test as representative organisms for this hypothesis? Or have you decided on these two yourself?
The only reason I ask is that Bacillus subtilis apart from being Gram positive are also noted for the resistance of their endospores to chemical and physical agents, as such you are not demonstrating that a substance containing Sodium hypochlorite has different effectiveness on only the cell wall. If you are just looking at Gram positive against Gram negative, would it not be better to go for something like Staphylococcus aureus instead? Also speaking from experience its not the difference in Gram negative or Gram positive bacteria that causes the problems, it’s the spore formers.
You should also look at different contact times as well as concentrations, by that I mean leave the bleach on the test area for 15 minutes then rinse. The contact time being the time the disinfectant has on the surface that is being sanitized.
A few other points of note, what concentrations are you starting with have you thought about how you are going to get the same concentrations of both organisms in your starting culture?.
Don’t use a hypothesis that you cant prove or is too vague, I’d go for something such as ‘Due to Gram-positive bacteria having a thick layer of peptidoglycan external to the cytoplasmic membrane this will resist the intrusion of chemicals such as Sodium hypochlorite. In contrast, the structure of the Gram-negative bacterium wall only having a thin layer of peptidoglycan located in the periplasimic space between the inner cytoplasmic membrane and a second outer cytoplasmic membrane, will be more susceptible to chemicals.’