Staphylococcus aureus

Summary

Staphylococcus aureus, often found on human skin and in the nose, is a Gram-positive bacterium that can cause various infections, from skin conditions like pimples and boils to severe systemic infections like pneumonia and sepsis. It can form biofilms on medical implants and produce toxins leading to diseases like toxic shock syndrome. The bacterium has developed resistance to several antibiotics, leading to the emergence of MRSA strains, which are a significant concern in healthcare settings and the community.

Takeaways

• 🌟 Staphylococcus aureus, often referred to as staph, is a Gram-positive, round-shaped bacterium that grows in grape-like clusters and is commonly found on human skin.
• 🔬 It is named for its appearance under a microscope, where it forms sticky, purple-staining clusters due to its peptidoglycan cell wall, and its colonies exhibit a golden-yellow hue on blood agar plates.
• 🌱 Staphylococcus aureus is a facultative anaerobe, meaning it can survive in both aerobic and anaerobic conditions, and it does not move or form spores.
• 🧪 Catalase production allows S. aureus to break down hydrogen peroxide into water and oxygen, a feature that can be used to differentiate it from other cocci, which are catalase-negative.
• 🔍 Coagulase production is a key distinguishing factor for S. aureus, as it converts fibrinogen into fibrin, causing a visible clotting reaction in the presence of plasma.
• 🌐 It is a common part of the human skin flora, colonizing about 25% of the population, usually without causing harm.
• 🚨 Overgrowth or skin damage can lead to infections ranging from localized skin infections like pimples and boils to more serious conditions like abscesses, cellulitis, and even systemic infections.
• 🏥 MRSA (Methicillin-resistant S. aureus) strains have developed resistance to many antibiotics, including methicillin, and are categorized into HA-MRSA found in healthcare settings and CA-MRSA found in the community.
• 💊 Treatment of S. aureus infections involves antibiotic susceptibility testing to select the most effective antibiotic, with options including clindamycin, vancomycin, and others for MRSA.
• 🔬 S. aureus can produce toxins such as TSST-1, PVL, hemolysin, exfoliatin, and enterotoxins, which can cause a range of symptoms from skin conditions to food poisoning and toxic shock syndrome.

Q & A

What does the name 'Staphylococcus aureus' suggest about its appearance?

The name 'Staphylococcus aureus' suggests a 'golden cluster of grapes', reflecting its tendency to grow in round, sticky clusters that resemble grapes and appear golden-yellow on blood agar plates.

How does the Gram stain reaction of Staphylococcus aureus contribute to its identification?

Staphylococcus aureus is Gram positive, meaning it stains purple due to its peptidoglycan cell wall, which helps in its identification under a microscope.

What is the significance of Staphylococcus aureus being a facultative anaerobe?

Being a facultative anaerobe means Staphylococcus aureus can survive in both aerobic and anaerobic environments, which contributes to its resilience and ability to cause infections in various conditions.

How can you differentiate Staphylococcus aureus from other catalase-negative cocci using hydrogen peroxide?

Staphylococcus aureus is catalase positive, so when a few drops of hydrogen peroxide are added, it will foam up, unlike catalase-negative bacteria which show no reaction.

What enzyme produced by Staphylococcus aureus helps in distinguishing it from other staphylococci species?

Staphylococcus aureus produces coagulase, an enzyme that converts fibrinogen into fibrin, which helps in clumping when mixed with plasma, distinguishing it from coagulase-negative staphylococci species.

Where is Staphylococcus aureus commonly found on the human body?

Staphylococcus aureus is commonly found in the nostrils, groin, armpits, and other parts of the skin, often as a normal part of the skin flora.

What factors can lead to Staphylococcus aureus causing infections rather than just colonization?

Factors such as pH, humidity, sweat levels, and the presence of other bacteria on the skin can affect the amount of Staphylococcus aureus present, leading to infections if there are high levels and breaks in the skin.

What are some of the localized skin infections that Staphylococcus aureus can cause?

Localized skin infections caused by Staphylococcus aureus include pimples, furuncles, boils, carbuncles, impetigo, cellulitis, and subcutaneous abscesses.

How can Staphylococcus aureus infections become systemic and affect other organs?

If Staphylococcus aureus enters the bloodstream, it can cause bacteremia, leading to systemic infections such as septic thrombophlebitis, endocarditis, osteomyelitis, and septic arthritis, and can even reach the central nervous system or cause pneumonia.

What is the role of biofilms in Staphylococcus aureus infections on medical implants?

Biofilms are layers of 'slime' where Staphylococcus aureus can live on medical implants, making infections harder to treat as they protect the bacteria and hinder antibiotic penetration.

What are some of the toxins produced by Staphylococcus aureus that can cause severe reactions?

Staphylococcus aureus can produce toxins such as TSST-1, PVL, hemolysin, exfoliatin, and enterotoxin, which can cause toxic shock syndrome, tissue necrosis, hemolysis, staphylococcal scalded skin syndrome, and food poisoning.

How has Staphylococcus aureus developed resistance to commonly used antibiotics?

Staphylococcus aureus has developed resistance to antibiotics like penicillins through the production of beta lactamases and the evolution of the mecA gene, leading to MRSA strains that are resistant to methicillin and related antibiotics.

What alternative antibiotics are used to treat MRSA infections?

Alternative antibiotics used to treat MRSA infections include glycopeptides like vancomycin, clindamycin, tetracyclines, trimethoprim/sulfamethoxazole, linezolid, tigecycline, daptomycin, and quinupristin-dalfopristin.

Outlines

00:00

🌟 Understanding Staphylococcus Aureus

Staphylococcus aureus, often referred to as 'staph aureus', is a Gram-positive, round-shaped bacterium that grows in grape-like clusters. It is named for its golden-yellow color when grown on blood agar plates. Staph aureus is a facultative anaerobe, meaning it can survive in both aerobic and anaerobic conditions. It is non-motile and does not form spores. The bacteria are catalase-positive, which allows them to break down hydrogen peroxide into water and oxygen, a trait that can be used to differentiate them from other cocci. Staph aureus can be identified by its coagulase enzyme, which converts fibrinogen into fibrin, causing a visible clumping reaction. It is common in human skin flora, usually found in the nostrils, groin, armpits, and other skin areas. Under normal circumstances, it does not cause harm, but it can become dominant under certain conditions and lead to infections if the skin is compromised. Staph aureus can cause a range of skin infections from pimples to abscesses and can even lead to more serious conditions if it penetrates deeper into the body, affecting organs, muscles, bones, and joints.

05:00

🏥 Invasive Potential of Staph Aureus

Staphylococcus aureus can cause serious health complications when it enters the body through breaks in the skin or directly into the bloodstream during medical procedures like surgery or dental work. It can form biofilms on medical implants, which are difficult to treat due to their protective 'slime' layer. Staph aureus can also produce toxins, including TSST-1, which can lead to toxic shock syndrome, and PVL, which can cause tissue necrosis and organ failure. Other toxins like hemolysin, exfoliatin, and enterotoxin can cause a range of symptoms from skin syndromes to food poisoning. The bacterium's ability to adapt and develop antibiotic resistance, particularly methicillin-resistant strains (MRSA), poses a significant challenge to treatment. MRSA is further classified into HA-MRSA, found in healthcare settings, and CA-MRSA, found in the community.

10:05

💊 Combating Staph Aureus Infections

The treatment of Staph aureus infections has evolved due to its resistance to traditional antibiotics like penicillins. Beta lactamase inhibitors and newer beta lactam antibiotics were developed to combat resistant strains, but some strains have evolved to express a gene called mecA, which produces penicillin-binding proteins (PBPs) that are unaffected by these antibiotics, leading to the emergence of MRSA. Two types of MRSA, HA-MRSA and CA-MRSA, are particularly problematic as they cannot be treated with beta lactam antibiotics. Alternative antibiotics like vancomycin are used, but resistance to vancomycin has also emerged in strains known as VISA and VRSA. The development of new antibiotics and vaccines is ongoing to address the challenges posed by Staph aureus infections. Treatment often involves testing the bacteria against various antibiotics to select the most effective one, and hospitals may use antibiograms to guide treatment decisions.

Keywords

💡Staphylococcus aureus

Staphylococcus aureus, often abbreviated as staph aureus, is a type of bacteria that can be both a normal part of the skin flora and a cause of various infections. It is characterized by its round shape and tendency to grow in clusters, which is why it is sometimes called a 'golden cluster of grapes'. The video discusses how it can cause infections when skin is compromised and its resistance to various antibiotics.

💡Gram-positive

Gram-positive is a classification used in microbiology to describe bacteria that retain the crystal violet dye during the Gram staining process. Staphylococcus aureus is Gram-positive, which means it has a thick peptidoglycan layer in its cell wall that gives it a purple color when stained, as mentioned in the video.

💡Catalase

Catalase is an enzyme produced by some bacteria, including Staphylococcus aureus, which converts hydrogen peroxide into water and oxygen. The video explains that catalase-positive bacteria, like staph aureus, will produce foam when hydrogen peroxide is added, which is a test used to differentiate it from catalase-negative bacteria.

💡Coagulase

Coagulase is an enzyme produced by Staphylococcus aureus that converts fibrinogen into fibrin, leading to blood clotting. The video describes a test where adding plasma containing fibrinogen to a mixture with staph aureus will result in visible clumping if the bacteria are coagulase positive, helping to identify the presence of staph aureus.

💡Biofilm

Biofilm refers to a slimy layer that certain bacteria, including Staphylococcus aureus, can form on surfaces. In the video, it is explained that staph aureus can create biofilms on medical implants, which makes it difficult for antibiotics to penetrate and the bacteria to eliminate.

💡Methicillin-resistant S. aureus (MRSA)

MRSA refers to strains of Staphylococcus aureus that are resistant to methicillin, a type of antibiotic. The video discusses how MRSA strains have become a significant problem worldwide due to their resistance to many antibiotics, and how they are classified into health-care associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA).

💡Vancomycin

Vancomycin is a glycopeptide antibiotic that is often used to treat MRSA infections since MRSA is resistant to many other antibiotics. However, the video mentions that some strains of Staphylococcus aureus have developed resistance even to vancomycin, leading to the emergence of VISA and VRSA strains.

💡Superantigens

Superantigens are toxins produced by Staphylococcus aureus that can trigger a massive immune response. The video explains that superantigens like TSST-1 can cause a 'cytokine storm' leading to toxic shock syndrome, which is a severe and potentially life-threatening condition.

💡Enterotoxin

Enterotoxin is a type of toxin that can cause food poisoning. Staphylococcus aureus can produce enterotoxin when it contaminates food, as discussed in the video. This toxin can survive cooking processes and cause symptoms such as vomiting and diarrhea if ingested.

💡Antibiotic resistance

Antibiotic resistance refers to the ability of bacteria to withstand the effects of antibiotics. The video highlights how Staphylococcus aureus has developed resistance to various antibiotics, making it harder to treat infections caused by this bacterium.

💡Septicemia

Septicemia, also known as bacteremia, is a condition where bacteria are present in the bloodstream. The video mentions that if Staphylococcus aureus enters the bloodstream, it can lead to septicemia, which can cause a widespread immune reaction and potentially severe health complications.

Highlights

Staphylococcus aureus, often called staph, is a round-shaped bacterium that grows in clusters resembling grapes.

Staph aureus is Gram positive and facultative anaerobes, capable of surviving in both aerobic and anaerobic environments.

Staph aureus colonies have a distinctive golden-yellow color when grown on blood agar plates.

Catalase enzyme produced by Staph aureus helps differentiate it from other cocci like streptococci and enterococci.

Coagulase enzyme produced by Staph aureus converts fibrinogen into fibrin, aiding in its identification.

Staph aureus is commonly found in the nostrils, groin, armpits, and other parts of human skin.

Staph aureus can cause localized skin infections like pimples, furuncles, boils, and carbuncles.

Infections can spread to deeper tissues causing cellulitis, abscesses, and other severe conditions.

Staph aureus can cause systemic infections such as septic thrombophlebitis, bacteremia, and sepsis.

Staph aureus can enter the central nervous system causing meningitis or spinal epidural abscesses.

The bacterium can also cause infective endocarditis by damaging heart valves.

Staph aureus can form biofilms on medical implants, making it difficult to treat.

Staph aureus releases superantigens and toxins causing a range of diseases from skin infections to food poisoning.

Treatment of Staph aureus infections involves the use of antibiotics, but resistance is a growing problem.

Methicillin resistant Staph aureus (MRSA) strains are resistant to many antibiotics, including penicillins.

Vancomycin is used to treat MRSA, but some strains have developed resistance, known as VISA and VRSA.

The development of new antibiotics and vaccines is crucial to combat Staph aureus infections.

Antibiotic resistance in Staph aureus is a significant challenge due to overuse of antibiotics.

Transcripts

Staphylococcus aureus, sometimes called staph aureus, is coccal, or round-shaped, and grows

in clusters.

In fact, its name, broken down, means “golden cluster of grapes”.

It sorta starts making sense if you look at it under a microscope - it tends to grow in

sticky clusters, and it stains purple when Gram-stained due to its peptidoglycan cell

wall, so it’s Gram positive and it resembles grapes.

As for its “golden” color, when it’s grown on blood agar plates, the colonies have

a distinctive golden-yellow color.

Staphylococcus aureus are Gram positive and facultative anaerobes, meaning that they can

survive in aerobic and anaerobic environments.

They’re non-motile and don’t form spores.

Staphylococci produce an enzyme called catalase which converts hydrogen peroxide to water

and oxygen.

Other common cocci, such as streptococci and enterococci, are catalase negative so they

don’t have this ability and we can use a few drops of hydrogen peroxide to differentiate

them.

Catalase positive bacteria will foam up, while in catalase negative bacteria, nothing happens.

Now, a couple of other staphylococci species, like Staph epidermidis and Staph saprophyticus

are also catalase positive, so to distinguish between them we can look for another enzyme

that’s made by Staph aureus, called coagulase.

Coagulase converts fibrinogen into fibrin.

So let’s say that we stir up some Staph aureus bacteria in a liquid “emulsion”,

and then add a few drops of plasma which contains fibrinogen.

The coagulase positive staph aureus will convert the soluble fibrinogen to sticky fibrin, which

then visibly clumps up, whereas coagulase negative bacteria won’t.

Staph aureus is extremely common and about a quarter of the population is colonized by

it, usually in their nostrils, groin, armpits, and other parts of their skin.

But, most of the time it’s a normal part of our skin flora, and doesn’t cause trouble.

The skin flora is a complex ecosystem of different bacterial species and occasionally, Staph

aureus can begin to dominate that ecosystem.

In individuals that have staph aureus colonization, a number of factors like the pH, humidity,

sweat levels of the skin, as well as presence of other bacteria on our skin, all affect

the amount of staph aureus that’s present.

If more and more Staph aureus is around on the skin, it begins to penetrate through tiny

microfissures in the skin, like you get with eczema, as well as larger breaks in the skin

like you might get after shaving.

In fact, it’s particularly troublesome in terms of causing wound infections where there

is a large break in the skin either from trauma or after a surgery.

So low levels of staph aureus with intact skin leads to colonization, whereas high levels

of Staph aureus with breaks in the skin lead to infections.

When staph aureus invades into the skin it can lead to localized skin infections like

a pimple which can evolve into a furuncle, or a boil.

A bunch of furuncles clustered together make a carbuncle.

There can also be diffuse skin infections, like superficial impetigo which is an infection

of the epidermis, or deeper-reaching cellulitis, which is an infection of the dermis and can

spread over larger surfaces rapidly.

If the infection goes deeper, it can develop into a subcutaneous abscess - a collection

of pus that’s walled off and sometimes develops thin walls within it - called septations.

These abscesses can occur all over the body including in the mouth where they’re called

dental abscesses, and they can develop within various organs like the liver, kidney, spleen,

and brain.

Now if the infection is overlying a muscle, it can spread into the muscle causing a pyomyositis.

If it gets into the bone it can cause osteomyelitis, and if it gets into the joint space it can

cause septic arthritis.

Finally, if Staph aureus gets into the bloodstream, it can cause a septic thrombophlebitis - an

infected blood clot.

In addition, bacteria in the blood is called bacteremia, and it can lead to a number of

serious problems.

There’s typically a widespread immune reaction that causes the blood vessels to expand and

the blood pressure to fall.

The result is hypotension and poor perfusion to various organs - a process called sepsis.

Once it’s in the blood, Staph aureus can also get to various parts of the body.

It can get into the central nervous system - causing bacterial meningitis or an epidural

abscess in the spine.

It can get into the lungs causing a severe pneumonia.

It can start to grow on the heart valves in clumps called vegetations - damaging the valves

- a process called infective endocarditis.

Bits of the vegetations can then chip off and embolize further causing other local infections

around the body.

Now, in addition to invading the body through the skin, Staph aureus can also enter directly

into the bloodstream when a person is getting surgery or having dental work done.

These events occur infrequently, but when they do come up it’s important to take precautions.

For example, individuals at high risk of getting serious disease with Staph aureus - like immunocompromised

individuals or those that are at risk for infective endocarditis - should be given antibiotic

prophylaxis.

Another property of our golden staph is its ability to create biofilm on medical implants

like indwelling intravenous catheters, prosthetic heart valves, and artificial joints.

The biofilm is, essentially, a layer of “slime” within which the Staph aureus live.

It forms when a cluster of Staph aureus adheres to a surface either a natural one like the

surface of a valve or an artificial one like the surface of a catheter.

The bacteria start to produce extracellular matrix made of exopolysaccharides, or EPS,

and over time the cells get completely surrounded by it.

The cells that are surrounded by the gel-like layer of exopolysaccharides, can communicate

with one other through biochemical signals and can even swap genetic information back

and forth - including antibiotic resistance genes.

In addition, Staph aureus thrives but doesn’t divide rapidly within these biofilms, and

it’s relatively hard for antibiotics to penetrate into the biofilms.

Combined that makes it much harder to get rid of these biofilm infections, and often

requires simply removing the surface that they’re growing on, if possible.

If all of this wasn’t enough, S. aureus can also release superantigens or toxins.

In fact, there are five major toxins related to S. aureus - toxic shock syndrome toxin

1, or TSST-1, Panton-Valentine leukocidin toxin, hemolysin, exfoliatin, and enterotoxin…

toxin.

TSST-1 is produced at the site of infection, and can enter the bloodstream.

TSST-1 binds to major histocompatibility complex type II or MHC II, which is a receptor found

on immune cells called antigen presenting cells.

When TSST-1 binds to the MHC II receptors on these cells, it really stimulates them,

making them release loads of pro-inflammatory chemicals called cytokines, creating a cytokine

storm.

The cytokine storm results in a number of physiologic changes like fevers, a sunburn

like rash, low blood pressure, and poor end-organ perfusion that can result in death - and together

this is called toxic shock syndrome.

Panton-Valentine leukocidin toxin, or PVL, punches holes in leukocytes - our immune cells,

killing them, and giving the toxin its name.

Leukocytes with holes in their cell membrane, die through necrosis and that triggers inflammation.

When that happens throughout the tissue, like in a necrotizing pneumonia, large chunks of

the tissue begin to die off and the organ cannot do its job properly leading to organ

failure.

Hemolysin is another pore-forming toxin that destroys erythrocytes or red blood cells,

releasing their hemoglobin, which contain iron, into the blood.

Staph aureus uses iron in its own metabolism, so this is one way it gets access to that

coveted heavy metal.

Exfoliatin toxin causes staphylococcal scalded skin syndrome, SSSS, or Ritter’s disease.

It creates painful patches of red skin, with fluid filled blisters, but it often resolves

within a few weeks.

Finally, there’s enterotoxin.

Staph aureus might land on food and start to generate enterotoxin.

The enterotoxin is quite stable in the environment, and can remain active even after the bacteria

are killed off by cooking.

The toxin can even withstand boiling at 100 degrees Celsius for a few minutes!

If the toxin is eaten, it can cause food poisoning - with symptoms like vomiting and diarrhea

a few hours after ingestion.

And, in rare situations, if the enterotoxin somehow gets into the bloodstream, it can

cause toxic shock syndrome, much like TSST-1.

The main treatment for infections is antibiotics, but Staph aureus adapts quickly and has developed

resistance to a number of antibiotics.

Penicillins, which are beta lactam antibiotics, were tried early on.

They work by disrupting disabling the enzyme DD-transpeptidase, which is a penicillin binding

protein, or PBP.

PBP is in charge of crosslinking the long strands of amino polysaccharides that make

the peptidoglycan cell wall, running in parallel.

These are made of segments of N-acetylglucosamine, or NAG, and N-acetylmuramic acid, or NAM,

in an alternating pattern - so, NAG, NAM, NAG, NAM, and so on, like a pearl necklace.

Protruding from the tips of the NAM subunits are tetrapeptide and pentapeptide chains.

These peptide chains can link to other peptide chains from the neighboring strands through

a process known as transpeptidation.

If PBPs aren’t allowed to work, no peptidoglycan is made, and the cell wall becomes leaky.

So when the bacteria try to divide and make more cell wall - they simply can’t and they

die.

Nowadays, practically all strains of Staph aureus make beta lactamases which allow them

to simply disable beta lactam antibiotics by breaking their beta lactam ring.

Next, antibiotics called beta lactamase inhibitors, like clavulanic acid, were used to bind and

disable the beta lactamases.

In addition, new types of beta lactam antibiotics, like methicillin, were identified that couldn’t

be easily destroyed by the beta lactamases.

Unfortunately, some S. aureus strains found a way around this as well by evolving and

expressing a gene called mecA, which encodes special PBPs - that are unaffected by beta

lactam antibiotics.

Methicillin and older penicillins can’t physically fit into them, rendering them ineffective.

These methicillin resistant staph aureus strains are called MRSA for short - and have become

more common around the world.

There’s two major categories of MRSA - the health-care associated MRSA, or HA-MRSA, and

community associated MRSA, or CA-MRSA.

HA-MRSA is found in places like hospitals and nursing homes, where there are lots of

chronically ill patients and a high usage of antibiotics.

CA-MRSA is found in the community, and is thought to be due to rampant antibiotic use

on factory farms, and overprescription of antibiotics.

Both HA-MRSA and CA-MRSA pose a major problem because infections with those strains cannot

be treated with beta lactam antibiotics.

As a result, another class of antibiotics - glycopeptide antibiotics, like vancomycin,

are often used instead.

Unfortunately, it’s not as effective and comes with problematic side effects.

To make matters worse, some Staph aureus strains have developed intermediate resistance to

vancomycin, and they’re called “vancomycin intermediate S. aureus”, or VISA for short.

Not the type of VISA anyone wants to get.

And strains with complete resistance are called “vancomycin resistant S. aureus”, or VRSA.

The search is on for new antibiotics and vaccines to prevent staph aureus infections, but the

overuse of antibiotics makes rapid resistance an ongoing problem.

Ultimately, treatment of Staph aureus infections involves testing the bacteria against a handful

of antibiotics and then choosing the most appropriate antibiotic from them.

Sometimes, hospitals put together an antibiogram which shows how frequently bacteria are resistant

to a particular antibiotic.

Typically when treating MRSA, antibiotics like clindamycin or vancomycin are chosen,

but alternatives include tetracyclines, trimethoprim/sulfamethoxazole, linezolid, tigecycline, daptomycin, and quinupristin-dalfopristin.

All right, quick recap!

S. aureus is a gram positive coccus that grows in clusters.

It’s a part of the normal skin and nasal flora in about a quarter of the population,

but if it overgrows or if the skin is damaged, then it can cause disease through direct colonization,

toxin production, or both.

Staph aureus is very adaptive and it has become resistant to various antibiotics.

Methicillin resistant strains are often classified as HA-MRSA or CA-MRSA, and vancomycin intermediate

and vancomycin resistant strains are called VISA and VRSA.