Understanding the Differences Between Gram Positive and Gram Negative Bacteria

okay so the topic of this video will be the difference between gram positive and gram negative bacteria so let's get

started so here's a diagram of a typical bacteria cell and I want to note the three layers that most bacteria have

their innermost layer colored green here is the plasma membrane which directs what enters and exits the cell it's a

phospholipid bilayer with some proteins scattered in between phospholipid bilayer the middle layer in Gold this is

the cell wall which provides structural support to the cell it's made up of a polysaccharide called peptidoglycan the

cell wall is really the most important of the three layers when it comes to understanding gram negative and gr

positive bacteria the third red outer layer this is the capsule it's more of a sticky

outer layer for attachment and protection but like I said I really want you to focus on the cell wall so let's

get started so let's do a little compare and contrast gram positive versus gram

negative bacteria gram positive they have an innermost plasma membrane and there it is in my drawing and the gram

negative bacteria also have an innermost plasma membrane so there it is so there's our phospholipid by layer the

plasma membrane now the gr positive I bacteria have a thick cell wall made up of

peptidoglycan and so there it is kind of five layers thick right there in my animation the gram negative bacteria

also have a cell wall it's just thinner so there it is only two layers thick in my animation now again these are both

the cell wall of of the bacteria cells when we look at the gram negative bacteria they also have an additional

outer phos lipid bilayer an additional outer membrane and now we come to the third

layer called the capsule the sticky outer layer so there's the capsule for the gram positive bacteria and gram

negative also have an outer capsule so there's the capsule for the gram negative bacteria as

well well one thing to mention is gram positive bacteria are more easily treatable with antibiotics simply

because gr positive lack that second outer uh phospholipid by layer there therefore the gram negative bacteria are

harder to treat with antibiotics simply because it's harder for the antibiotic to gain entrance into the bacteria

cell eventually we're going to talk about a Gram stain and when we do we're going to mention that gram positive

bacteria underneath the microscope appear a violet purple color after performing what's called a grham stain

now the gram negative bacteria after performing a Gram stain appear a reddish to pinkish color underneath the

microscope and we're going to explain why this is in just a few moments so let's talk about this process

known as a Gram stain now the purpose of a grham stain is to help identify whatever infectious bacteria

that is getting us sick and so the reason we need to do this is because treatment will differ based upon the

outcome of this Gram stain and so when we look at the steps we're going to break this down into a a variety of

steps number one we're going to obtain bacteria from a culture and using an inoculation Loop

will'll transfer bacteria onto the inoculation Loop and then we're going to smear the bacteria across a glass

microscope slide so the next step we're going to do is we're going to fix the bacteria to

the slide so they don't get washed away when we do the upcoming steps in the Gram stain and we're going to do that by

taking our glass slide and we're actually going to pass it over an open flame a few times and the heat will fix

the bacteria to the slide as I said this way they don't get washed away when we start using some of the chemicals in the

ladder steps so the first chemical we're going to use is a chemical called Crystal

Violet and like the name implies it has a purplish violet color so we'll add a few drops of Crystal Violet onto the

bacteria samples and once we do let's zoom on in uh and take a closer look at the cells of the bacteria that are

trapped on this glass slide and when we do we see that we have the gram positive bacteria on the left

and the gram negative bacteria on the right now at this stage we don't know which bacteria in our sample are gram

positive and gram negative I'm just labeling them for our ease and simplicity so right now all we've done

is we added the crystal Violet those purple molecules were added and they passed through the layers of the

bacteria into the actual bacteria cell and then the next step is we're going to add iodine iodine kind of has a

brownish GL goldish bronish color and here come the iodine molecules and they actually pass through the layers and

they actually Bond and bind with the crystal Violet molecules that have previously entered and they kind of

Clump together and and make the molecule bigger so the next step is to wash the bacteria with alcohol alcohol is a

daining chemical and watch what happens to the gr positive bacteria on the left the cell wall will shrink and the

capsule kind of gets dissolved and uh and washed away now for the gram negative on the right the same thing

with the cell wall the cell wall kind of shrinks but notice how that's the capsule and the outer layer the outer

phospholipid by layer that were washed away this is because of the dehydrative nature of alcohol and now here's a big

thing that happens Watch What Happens next because of the alcohol wash because the cell wall is so thin for the G

negative bacteria the crystal Violet iodine molecules also get washed away so the gram negative lose their color

underneath the microscope right now if we were to view the bacteria samples the gram negative would look transparent and

have no color but the gram positive bacteria would appear a purple violet color because they retained the crystal

Violet diey so the next step is to apply a kind of a reddish color molecule D called

saffrin and so here's saffrin being added and what happens is the red pinkish saffrin molecules uh pass

through the cell wall and actually bind with the lipids of the lipid the phospholipid

bilayer and so now we can actually see the results of a Gram stain underneath the microscope underneath the microscope

the results appear the gram positive appear purple in color now you might be asking yourself why is that how come uh

they don't appear pink because they have saffrin in them as well the reason is simple that the saffrin the pink color

of the saffrin is just overshadowed and masked by the deepness the darkness of the purple Crystal violet

so you don't even really see the pink saffrin in the gr positive bacteria it's there you just don't see it and notice

how the gram negative bacteria because they lost their Crystal Violet Dy and they only have the pinkish saffrin the

gram negative bacteria underneath the microscope would appear pink in color so here are some actual pictures of a gram

positive bacteria notice the dark purple color and some pictures of gram negative bacteria notice the reddish pinkish

color so as I wrap up this video I just wanted to put the two side by side One Last Time pause the video if you want to

read through the text again but the reason a Gram stain is so important is knowing whether a bacteria is gram

positive or gram negative we can then begin proper treatment as the notes say gr positive are more easily treatable

with antibiotics that's because they only have the one phospholipid bilayer the gram negative bacteria are more

difficult to treat that's because of their dual phospholipid bilayer so there you go pause the video if you're still

reading and post your comments in the thought in the box below I hope you found this video helpful thanks for

watching