Video Chapter 3 part 2

Video Chapter 3 part 2


>>So we’re back for Chapter 3, Part 2. The cell wall is where we left off,
so just to rehash really quickly. The two main functions of the cell wall
are to maintain the shape of the organism. This is true for pretty much
all cells that have cell walls. And provide structural support. So that if water flows into the cell
the cell, itself, does not burst. So it prevents the cell from
rupturing during osmosis. Now when it comes to bacterial
cell walls the main structure of the cell wall is something
called peptidoglycan. Remember this, we will talk about it repeatedly,
peptidoglycan will come up over and over. It’s a carbohydrate made up of two repeating
sugar molecules, N-acetyl glucosamine, we shorten this as NAG, and
N-acetyl muramic acid, NAM. So if you’re ever asked like on a
test what the two main components of peptidoglycan are the
answers are NAG and NAM. You do not have to write out N-acetyl
glucosamine or N-acetyl muramic acid, NAG and NAM are completely suitable. Now the NAG and NAM make a crosslinked meshwork
that is held together with short peptide chains. So basically what we’re seeing is
these are usually tetra peptides and we see four amino acids actually
linking the NAGs and NAMs to one another. So this will look something like
this if you can see it here, these represent those tetra peptides. So we’re linking the NAGs and NAMs to one
another to make this sort of chain-link fence. Now the goal here is to actually wrap
multiple pieces of this around one another, giving the cells structural stability. So giving that cell wall a lot of rigid
support because of the crosslinking and that chain-link fence structure of the
NAG and NAM joined together as peptidoglycan. Now another reason why this is very important
is because bacteria are very often divided into categories based upon how much
peptidoglycan we find in their cell walls. Gram positive cell walls
are rich in peptidoglycan. They’re going to have a lot of
peptidoglycan so you can see this here, this would be an example of
a gram positive cell wall. This being the cell membrane. If you look the bulk of the
cell wall is peptidoglycan. Now the gram negative cells actually contain
much less peptidoglycan, it’s usually somewhere around 20%, the cell wall is not
necessarily smaller, do not think that, okay? That’s a very common mistake that people
think this is less of a cell wall. It’s not less cell wall, it’s just that
the main component here isn’t going to be the peptidoglycan. 20% peptidoglycan and about
80% other components. Because there are additional
components to the cell wall, gram negative bacteria are often considered
more complex than the gram positives because they’ve got a whole different set
of additional components, meanwhile the bulk of this gram positive cell is peptidoglycan. So let’s look a little bit more closely. So here we see a gram positive cell. Again, this large sheet of peptidoglycan. It’s going to be somewhere between 60 and 90% of
the cell wall, so this is most of the cell wall. There will be some additional components. Teichoic acid or lipoteichoic acid, sometimes teichoic acid is
referred to as wall teichoic acid. These serve as ion passageways to actually
help get ions down to the cell membrane so that the cell membrane can regulate
what comes into and out of the cell. Remember the cell wall’s job is not regulation,
it does not determine what comes into and out of a cell, that’s
the cell membrane’s job. This is here for support and protection. Now notice that these are also
cells that have a single membrane. The only membrane available in a gram
positive cell is that cell membrane. Well, I mention this because if we flip over to the gram negative cells you’ll
see here this thin layer of peptidoglycan and it’s usually somewhere around 20%
of the makeup of the entire cell wall. That thinness helps to give the gram
negative cells a little bit more flexibility and a little bit more sensitivity to
lysis so they’re slightly easier to lysis. Note that this is a two-membrane system. These will contain your basic cell
membrane and as part of that other 80% that is not peptidoglycan their cell membrane
will also be forged of an outer membrane, and we actually call it the outer membrane. It’s sometimes referred to as the
lipopolysaccharide layer or the LPS. So this is a two-membrane system. The gram positives will only have one membrane. You’ll notice that in these
membranes you’ll see lots of pores, these are known as porin proteins there
to, again, help move things in to the cell. Now this is not again regulation, they’re just
there so that things that would normally need to cross the membrane actually
have access to the cell membrane. So how do we differentiate between
gram positive and gram negative cells? Well, this is done with something
called a gram stain. If you want to go along with me
in your book – hold on one second, I’ll tell you what page this is on [pause]. Page 73 in the textbook is this
gram staining image that I’m using. So what’s going on in the gram stain? Well, it’s actually a relatively simple
four-step process that’s used to sort of distinguish between the gram
positives and the gram negatives. It’s what we call a differential stain
because at the end of it you will be able to differentiate or tell the difference
between gram positive and gram negative cells. So the first step in staining,
the addition of crystal violet. Crystal violet actually holds
pretty tightly on to peptidoglycan, so the crystal violet colors the peptidoglycan. To be honest, it’s the first step so
it imparts color to all of the cells. At this point gram positive and gram
negative cells will both be purple because crystal violet is
a very dark purple color. Excess crystal violet is rinsed away and then
in the second stain we will use gram iodine. Now iodine is what’s called a mordant. It actually stabilizes the bond between
the crystal violet and the peptidoglycan, so it causes the crystal violet to hold
on to the peptidoglycan slightly more. I always tell people this marries the
crystal violet to the peptidoglycan. Now at this point in time we haven’t done
anything different to either of the cells and there aren’t any huge differences here, both cells will remain sort
of a darkened purple color. Now the most important step in this, this
is what’s called the differential step, because the alcohol, the fourth step, is
actually what’s going to help differentiate between the gram positives
and the gram negatives. So as the alcohol is applied
it actually dissolves some of the lipids on the outer membrane. So, if you remember, this outer membrane
is only found in what type of cell? Hopefully you remember, the
answer is gram negative. And that alcohol dissolves away that
outer membrane in the gram negative cell and removes the dye from
the peptidoglycan layer. So at this point what we see is that there
is a difference between the gram positive and gram negative cell, that is
why this is the differential step. Now you can’t leave it at this and just
have purple cells as gram positive, those that have held on to the
crystal violet, being gram positive, and then these non-colored
cells as being gram negative because you cannot see clear
cells under the microscope. So what we do in the fourth step is what
we call counterstain and we counterstain with a dye called saffron in red. Saffron in red is red, as indicated. Because those gram negative
bacteria have sort of been divorced from their peptidoglycan they’re nice and
clear, that saffron in red actually then adheres to the gram negative cells and it will
adhere to the gram positive cells, as well, but the saffron is not dark enough to
actually overcome that purple staining that the gram positives have acquired. So at the end of this your gram positives
stay purple and your gram negatives are red. It helps you remember lots of times if you’re
doing your checking account or you look online at your banking statement, debits, so
anything that is negative ends up in red. By the same token I always think it’s
helpful to think of using individual colors, I like to remember that all of the P’s go
together, the positive bacteria are purple because they have lots of peptidoglycan. So the positives are purple because
they have a lot of peptidoglycan. I’m going to show you this
again on another slide. It’s got a little bit more
simplified than this one. So crystal violet, application
again, everything is purple, so we’re trying to get this
to adhere to the cells. The iodine is added to actually help marry and adhere the crystal violet
to those gram positive cells. The decolorizing, alcohol step, what
happens here those gram negative cells have that outer membrane dissolved and
the crystal violet washed away, so at this point this differential step. Since this is our differential step
the gram negatives are colorless, while the gram positives remain purple. And then in order to counterstain and add color
to the gram negatives we apply saffron in red. The saffron in red colors those clear
gram negative cells and they end up – we’re not going to use this word,
we’re going to say that they are red and the gram positive cells stay purple. Gram positives, purple, because
they have lots of peptidoglycan. More on this in lab, we’ll do a lot of gram
staining in lab, so you’ll see this firsthand. Now aside from your typical gram positives
and gram negatives, we do see organisms that have what we call non-typical cell walls. And probably the most common example of these
are what we term the acid-fast bacteria. Most commonly in two species, the
mycobacterium and the nocardia. Instead of that normal cell wall as gram
positive or gram negative that we see, their cell walls actually contain
something called mycolic acid. Now for the most part this is a
modified gram positive structure. These cells actually do have a lot of
peptidoglycan, but they are extremely difficult to stain with traditional gram
staining mechanisms, right? That mycolic acid is actually a wax
that’s coating the outside of the cell, and if you think about waxes on things
like fruits or leaves or feathers, okay, the goal of a wax is waterproofing because those
stains we’re using are aqueous stains they sort of roll off of these bacteria. We had a really hard time
staining them so they’re sort of acid etched first to get
the stain to hold on. The mycolic acid, itself, actually acts
as vero [Assumed Spelling] inspector. In other words, it contributes to
the five requirements of infection because the mycolic acid is resistant
to certain types of chemicals and dyes, it is also extremely difficult
to digest through, so it helps these organisms not be phagocytized. They can be engulfed as part of phagocytosis,
but it’s very difficult to break them down once they’re inside of the phagocyte. In fact, several of these types of
organisms will actually live inside of cells that have phagocytized them. They’re actually able to reproduce in a
phagocytic cell without being broken down. The two most common disease causing versions
of these, tuberculosis, known to live in things like alveoli or macrophages and leprosy,
both of these are species of mycobacterium. Mycobacterium tuberculosis and
mycobacterium lepre for the leprosy, okay? Now a little bit more about that outer
membrane before we start moving on. Remember, this is only seen
in gram negative bacteria, there are two clinically relevant
parts to that lipopolysaccharide layer. Remember this is another
word for the outer membrane. Probably the most relevant is
something called Lipid A, okay? Lipid A’s job is to anchor
that lipopolysaccharide layer to the outer membrane to the peptidoglycan. The reason Lipid A is clinically relevant is
that Lipid A is what’s known as an endotoxin. This is a toxin that’s actually a part of
the bacteria, so it’s an internal toxin. It’s part of the makeup of the organisms. The danger with Lipid A is that if gram
negative cells end up breaking down, so in other words they’re
dying, and releasing Lipid A out into the host’s body the
Lipid A will ax the toxin, usually causing some rather mild symptoms. We see lots of GI issues. You might see a slight fever. It depends upon the amount of the
endotoxin that is released into the body. In extreme cases where we see massive
endotoxin releases you can see toxic shock, but that is relatively rare. The other clinically relevant part
of that outer membrane, again, only in the gram negative organisms,
are what we call O polysaccharides. Now these are called the hydrate chains
that you can usually find on the outside of the outer membrane and the reason
they’re clinically relevant is because they are different from
one species of bacteria to another. They’re also recognized by
your adaptive immune response. In other words, antigens, these will act as
antigens to help your body build antibodies. They are commonly used as diagnostic markers. For example, E.coli 0157H7, and we
often see designations like this with no one telling you what they mean. The 0157 is because this is
the 157th O polysaccharide that has been identified in E.coli. If you do not know, E.coli 0157H7
is enterohemorrhagic E.coli. Most people get it from eating
contaminated and then undercooked raw meat. So this is a good identification marker. Now the Lipid A is actually going
to have an affect on the body. This is for identification and then
antigen accumulation when it comes to that adaptive immune response. So moving a little bit further into
the cell, the cytoplasmic membrane, remember this is the same thing as a
cell membrane or the plasma membrane, these are all terms for the exact same thing. Do not get confused if you see
one or the other on a test. Now this is a pretty typical cell membrane. It’s a lipid bilayer, follows
the fluid mosaic model with proteins embedded within
the phospholipid bilayer. Its major action is regulation. Now this is the majority of what will be done
with the cell membrane, regulating comes into and out of the cell, so good things, keep
them coming in, bad things keep them moving out or keep them out all together. But one thing that’s a little different
about cell membranes and bacteria is that they are also a site for reactions, specifically what we call
membrane dependent reactions. Now a membrane dependent
reaction is exactly what it says, it’s a reaction that you have got
to have a membrane to complete. In other words, a reaction will not go
through without the presence of a membrane. There are several of these that cells depend on. Probably the most common example is
going to be the electron transport chain. The electron transport chain is
a membrane dependent reaction, you’ve got to have a membrane to complete it. Well, that’s easy for eukaryotic
organisms because they have things like mitochondria, it’s a
membrane bound organelle. In fact, if you remember, lots of
times mitochondria are described as a membrane bound sac with another
membrane bound sac folded up inside of it. That’s because these membranes
are needed to run the reactions. So in order to complete cellular respiration and do the electron transport chain
you’ve got to have a membrane. Well, think back about the
bacteria and membranes, they don’t have membrane bound organelles. Bacteria, prokaryotes are never
going to have mitochondria. There are no mitochondria in a prokaryotic cell, so the only membrane available
is going to be cell membranes. So the electron transport chain and
any other membrane dependent reaction, so look for that as a buzz word when it
comes to the test, look for that term, membrane dependent reaction,
they’re all going to happen on the cell membrane, when it comes to bacteria. So the cell wall to the two S’s that shape
and support stability, either one of those. The cell membrane does the two R’s, regulation
and is a site for membrane dependent reaction. Now a little bit more on differences
in cell envelope structure. The outer membrane of gram negative bacteria
actually is contributing a little bit of an extra barrier. That outer membrane actually impervious
to certain antimicrobial chemicals. This word means they cannot cross
through, a good word for you, impervious to certain antimicrobial
chemicals, so certain drugs and certain disinfectants will not
cross the gram negative outer membrane. So what that means is that it’s slightly more
difficult to inhibit the gram negative bacteria. The gram positives are a
little bit easier to kill. The nice thing, though, is that alcohol based
compounds will dissolve the outer membrane, so anything that has alcohol in it
is actually meant to kill bacteria by weakening the cell membrane, itself. Think about alcohol swabs that we use to clean
skin before they do things like take blood or give shots, a lot of that
has to do with getting rid of the gram negative bacteria
that you can find on the skin. Anytime you’re going to treat an infection
caused by a gram negative organism that drug has got to be able
to cross that outer membrane. It’s a major sort of obstacle
to destroying these organisms. It’s not something that we absolutely
cannot do, it’s done all the time. We have plenty of drugs that work on gram
negatives and plenty of disinfectants. Think anything that’s alcohol based. It’s just slightly more difficult
than destroying the gram positives. So moving into the cell, right, yay, we made it. The cytoplasm, 70% to 80% water. Honestly, this is going to be the major
component of the cell, just like any cell. Most cells are somewhere between 70% and
80% water, so that’s the bulk of the cell. Dissolved in the water are soluble
proteins, salts, sugars or carbohydrates. These are there as nutrients,
they’re basically building blocks for synthesis or some type of energy source. The carbohydrates would be your energy sources. The proteins are usually
building blocks for synthesis, things we’re going to use
to make other components. This is where nearly all
chemical reactions will happen. The exception are those membrane
dependent reactions. All other chemical reactions are
going to happen within the cytoplasm, and within the cytoplasm we will see
the DNA actually coiled and sitting in the cytoplasm, not in a separate area. So the DNA is sitting in the cytoplasm
in a region called the nucleoid, often it’s also referred to as the
nucleoid region, either one is appropriate. So let’s take a little bit
closer look at that DNA. For most bacteria it is going to
exist as a single circular chromosome. There are a few exceptions to this,
Vibrio cholerae is an example. Now the exception is that Vibrio cholerae
actually has two circular chromosomes, one large and one small. Now the thing to remember about chromosomes is
that chromosomes contain necessary information. It’s DNA and instructions that the
cell has to have in order to survive, and new cells that get made will also
have to have bacterial chromosomes. If it’s one they need to make one
copy and put it into a new cell. If it’s something like Vibrio cholerae that
has two chromosomes you have to have two copies in all cells that get made, okay? So the DNA is actually sort of aggregated
in a dense area called the nucleoid. I always tell people to think about phone cords,
like very long phone cords, eventually they end up rolled into themselves,
kind of wrapped in a big ball. The DNA is sort of wound into this large
ball and it’s sitting the nucleoid region. You can see it here, that’s what this is,
that DNA is sort of wound into itself. Many bacteria, not all of them but a lot of them
will contain other nonessential pieces of DNA. Now the appropriate term for
this is extrachromosomal pieces. Now that’s a big buzz word, extrachromosomal. What we’re saying is that this
is outside of the chromosome. It’s not necessary DNA, it’s something extra. Those extrachromosomal pieces
are referred to as plasmids. Now the thing about plasmids and the reason
why they are important and we bring them up is that plasmids will contain DNA that tells
us how to make certain extras for the cell. They can have instructions on
how to be resistant to a drug, how to produce certain types of enzymes
and digest unusual food substances. They can have information
on how to make a toxin. All of these are particularly important to us. Now that means they won’t be found
in every single one of the bacteria. If the drug resistance gene is found on
a plasmid that plasmid actually has to be within the bacteria in order to have
that organism be drug resistant. Now kind of the dangerous thing about
this is that if you remember us talking about pili [Assumed Spelling] a few slides back,
conjugation pili and the process of conjugation where we moved genetic information from one
organism to another, if you remember that, we had those pili that were
attaching bacteria to one another. The information that moves is
not chromosome, it’s plasmid. So this allows bacteria to move plasmids
or copies of plasmids from one organism to the next, meaning that they can spread drug
resistance within their bacterial population. And since we’re on the subject of DNA we
have to talk about the ribosomes, okay? We talk about these because ribosomes are where
that information stored in DNA will be made into something functional, specifically protein. If you remember, ribosomes are
sites of protein synthesis, this is where we are going to make proteins. Now the prokaryotic ribosome consists of two
cell units, just like the eukaryotic ribosome. So there will be a small ribosomal subunit and
a large ribosomal subunit, you have to have both to make a fully functioning ribosome. So prokaryotes have a small subunit,
that’s 30S, a large subunit has 50S, when you put them together
you get a full 70S ribosome. Now don’t freak out, I can absolutely do math,
the S is something known as a Svedburg unit, it’s a unit of sedimentation rate. What that means is it’s how quickly
something falls through a liquid. This is not an additive measure,
it’s not like putting 20 pounds and 10 pounds together to get 30 pounds. Just because you can throw a bowling ball
into the lake and it sinks to the bottom in two seconds and you throw a pen into
the lake and it sinks to the bottom in five minutes doesn’t mean that if you
take a pen to a bowling ball they will fall to the bottom in five minutes and two seconds. So this has to do with how quickly
things fall through a liquid. Now this is another big difference
between the prokaryotes and the eukaryotes because eukaryotes actually
have larger ribosomes, right? Their small subunit is 40S, the large is 60S, and when you put them together they
make an 80S eukaryotic ribosome. If it helps you, e in eukaryote gets all the
even numbers, 40, 60, 80, what comes before p, odd prokaryotes, so o, p, 30, 50, 70. The prokaryotes are smaller, they
get all the smaller subunits. The eukaryotes are larger, they
get all of the larger subunits. So this difference will actually
be extremely important later. We’ll talk about the differences
between the prokaryotic and the eukaryotic ribosomes frequently. This is something you definitely
want to pay attention to. It will come up in several other
chapters, so commit this one to memory and be prepared to use this information. It’s going to be particularly important when we
get to antibiotics because we’re going to try to find antibiotics that have
what we call selective toxicity. In other words, they work on
the prokaryotes, but not on us. And one of the great targets because it’s so
important is the ribosome, so if we have a drug that will work on a 50S subunit,
will it ever work on our cells? It shouldn’t, eukaryote we have 40S,
60S and 80S ribosomal units, all right? We shouldn’t be affected by something that
dismantles or disables a 50S ribosomal subunit. So if you see where I’m going here you’ll
make sure that this is something that you sort of keep in mind and commit to memory. Now winding down here, inclusion bodies and
microcompartments, not the most important parts of the bacterial cells, but
you will see them in bacteria. Inclusion bodies and microcompartments,
basically we’re saying storage units. Mainly they’re there for storing nutrients. Some organisms will actually pack their
microcompartments with gases for buoyancy, so to keep them up at the top of their
liquid environment or aqueous environment, so the top of a lake, the top of an ocean. So we use this to store iron. This is particularly interesting,
iron storage for orientation, basically using the iron
like little magnets, okay? So they sort of know where they are within
the atmosphere, within their environment. Microcompartments are relatively new,
early 2000s begins their discovery. What we see in the microcompartments
are sort of shells made of proteins. They’re usually arranged geometrically,
so they sort of line up or come together in a specific shape, that has
to do with their function. The microcompartments are usually full
of enzymes designed to work together in what we term a biochemical pathway. So, for example, these are
your microcompartments, what we’ll see is that in
order to break something down or build something specific the enzymes here
will be used and then we use the enzymes here and then we use the enzymes here
and then here and then here, sort of jumping from enzyme to enzyme. So they’re arranged to be
used in a specific sort of designated order, its assembly lining, okay? As far as the cytoskeleton is concerned,
honestly, the peptidoglycan determines shape for most bacteria, kind of keeps
them in their appropriate forms. Those that are sort of lacking when it comes to
cell wall peptidoglycan can use proteins made of actin, so they’ll basically have sort of microfilaments similar
to what we see in our cells. They’re usually used to sort
of alter the shape of the cell. We don’t see these too much, they don’t come into play particularly often
within the bacterial cells. For the most part peptidoglycan is
what’s doing the shape determination. Now the endospores, believe it
or not, you have already seen. If you remember that very first slide, okay,
that we did in class, that very first slide that we did in Lab, several of you saw those
long streptobacillus [Assumed Spelling] and they ended up looking something like this. They’re linked together, but it looks like they
sort of have these small holes in the middle. Now if you remember I told you do not
be shocked, those are not nuclei, okay, so there’s not a nucleus
in the center of that cell. Remember these are bacteria, okay? They are endospores, endospores get formed
through a process called sporulation and sporulation occurs when bacteria
are exposed to environmental stress. This can be running out of
nutrients, being too hot, too acidic, coming in contact with a chemical,
it depends upon the organism. What they are is specialized
resting structures of the cell. If you remember Chapter 4 and we talked about
things like cysts that form for protozoa and how it protects them for an extended period
of time until the environment gets good again, this is that version in bacteria. So they give the cell a type of dormancy,
and we see bacteria actually surviving for extended lengths of time
in the endospore state, and by extended length I’m
talking about years to decades. So endospores make the organisms resistant to
heat, drying, freezing, radiation, chemicals, things that would kill a cell
that was actually vegetative or what we consider metabolically active. So eating, normally metabolizing cell, right? This is something that is
restricted to gram positive bacilli, its usually large gram positive
bacilli are the only ones that do this. There’s one exception to that rule and it’s
actually an exception to both parts of the rule, Coxiella burnetti is a gram negative coccus
that has been found to produce spores. So remember these dormant structures. They’re going to be really important
in protecting bacteria from things like disinfectants or possibly
antibiotics and other types of drugs. This is what makes it possible for certain
bacteria to survive extreme types of treatments. So specialized resting structure, okay,
a reason why bacteria might survive even after disinfection or drug treatment. So you can see it here, this
is a little spore formation. The vegetative cell starts losing nutrients. What they do is duplicate the chromosomes,
so they’re going to divide the cell and then separate the two
chromosomes from one another. So this is the reason why
that endospore was sort of sitting inside of another cell, all right? We see sort of early spore formation, we
start adding layers around the outside of that one sort of compartment
of genetic information. We see outer coatings that
continue to be deposited. Eventually if the environment gets bad
enough the vegetative cell that’s coating it, so this part of the cell, all
of this portion of the cell ends up dying away, but the endospore is released. That endospore will survive for extended
periods of time, no nutrients, no metabolism, it’s sitting there waiting for the
environment to actually get acceptable again, and the endospore eventually when the
environment goes back to being good and habitable will germinate and a new
sort of vegetative cell is released and you get right back to a normal
functioning cell, all right? Now notice that we went from one cell to one
more, this is not a reproductive process, it’s not like these endospores are eggs, we’re not making large amounts
of these and sending them out. It’s usually one cell, one endospore. Now the last part of this chapter,
I’m not going to harp on it. We don’t see these very much. The archaeons, these are your
sort of other prokaryotes. They get distinguished into sort of a third
separate kingdom, so we have the eukaryotes and the prokaryotes, and the
prokaryotes get divided into bacteria and the archaeons, that’s pretty much it. The archaea are a little bit more closely
related to eukaryotes than bacteria. We know this because they share
some ribosomal RNA sequences, so they have some genetics very similar to the
eukaryotes that you will not find in bacteria. Their protein synthesis and ribosomal
subunits are actually similar to eukaryotes, so in other words they will end up having
those 80S ribosomes that we talked about. For the most part these are what we term
extremophiles, living in extreme environments. High or low temperatures,
extremely salty, extremely acidic. Some of them live on very odd sort
of nutrients, sulfur or methane. We see a couple of these in the human body or
actually on the human body and may be capable of causing disease, but that’s a
relatively sort of rare occurrence. We don’t see a lot about
the archaeons all that much. Now there is a manual, it’s known as
Bergey’s Manual of Systemic Bacteriology. Do not worry about memorizing this. I just want you to know this information
so that you have heard it before, okay? There are four major divisions
of prokaryotes, okay? The Gracilicutes, gram negative
bacteria with thin cell walls. The Firmicutes, gram positive
organisms with strong cell walls. Tenericutes, lack a cell wall and are soft,
that’s a little bit of a rare category. And the Mendosicutes, the archaeons
fall into the Mendosicute category. If you ever hear these terms just know that
we’re referencing some type of prokaryote. Do not worry about identifying
these when it comes to test time. I’m letting you know that it is a possibility. Now one thing I do want to mention, though,
before I stop is that when we classify bacteria, and I’m really mainly showing you
this for the terminology here, members of a species can show variations. When we say things like salmonella
or ashrekiacoli [Assumed Spelling], when we talk about E.coli,
E.coli is not just one thing, there are multiple different types of E.coli. The technical term for this is a Serovar,
that is a term that you would see on a test. They can also be called subspecies or strains. So these are types of the
same species of bacteria but that have different characteristics. So when I said E.coli 01577
earlier, that is a Serovar of E.coli. Just for your reference, there are over
2,000 different Serovars of salmonella, there are a lot, a lot of
different types of microorganisms, so all E.coli is not the same thing. You might also hear the term serotype, serotypes
give a distinct pattern of antibody responses, so these are tested with an
antibody antigen style interaction. This is more of sort of a clinical
term and they’re doing things like immunology style testing,
some type of immunoassay. So Serovar is what we use a little
bit more commonly or strain. Honestly, the only one I
don’t want to here is strand, there’s no such thing as a strand of bacteria. You can have a strain, you can have
a subspecies, you can have a Serovar, but you cannot have a strand of bacteria
unless you’re talking about something like streptococcus or streptobacillus, right? That describes how they’re
shaped, not being a different type. So this is the end of Chapter 3. Chapter 11 actually comes up next, so make
sure you review this, get your terms in, go back and see if you can start identifying
and putting specific characteristics, calling them virulence factors and associating
them with particular requirements of infection.

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