Staphylococcus

Staphylococcus Colony Morphology

Gram Positive
Cocci in clusters, singles, or pairs

What other bacteria are included in the Staphylococcus family?

Microccus, Kocuria, Arthrobacter, Stomatococcus, Planococcus

Describe the overall behavior of Staph in the human body.

Some species are true pathogens, but many are normal inhabitants that are found on the skin and mucous membranes. Some can also be opportunistic pathogens.

How can you distinguish Micrococcus (M.luteus) from Staphylococcus, especially when Gram staining or growing cultures on a plate?

Micrococcus are GP cocci too, but they are found in tetrads instead of just clusters, but GS alone won't distinguish from CoNS.On a BA plate, they will appear yellow and they are susceptible to bacitracin and oxidase positive. In addition, they are usually contaminants because they are ubiquitous to the environment and rarely cause infection.

Describe the Oxidase Test.

Micrococcus possess the cytochrome enzyme, which Coag negative staph do not. On a special disc, there is substrate embedded that the cytochrome will metabolize and cause a blue pigment to appear, making it oxidase positive.

Basic features of all staphylococcus

Gram positive cocci, catalase positive, will grow on BA, CHOC, but not on MAC
White, gray, or yellow creamy colonies, can be beta hemolytic (S.aureus) or nonhemolytic (MRSA, S.epidermidis)

Origins of Staph and S.aureus

1880-Ogston named staph (bunch of grapes) and coccus (berry)
1884-Rosenbach named S.aureus (gold) and S.albus (white)

How common is S.aureus as resident flora?

25-30% of the population have S.aureus as normal flora

Can MRSA be normal flora?

Yes, but it is rare. This is why before surgery, patients are nasally swabbed to see if they have MRSA because surgical sites can be targets.

Why are surgical sites considered sterile even though the skin is not?

Surgery is done in a sterile environment, and the incision site and tools should all be sterile before it is done.

Who is most at risk for MRSA or S.aureus infections?

People with chronic conditions, elderly and newborns, hospital patients, sports teams

What is the most common method of S.aureus transmission?

direct skin-skin contact, or indirectly by sharing items such as towels, as well as touching fomites 

What is the main resevoir of S.aureus in the body?

Nares, but they can also be found in damp, warm areas such as the groin, axilla, and other folds and creases of the skin as well as the pharynx

What is the main type of infection S.aureus causes?

Skin and soft tissue infections

What factors can predispose a person to contracting S.aureus?

Presence in skin and nares, hot and humid climates, anatomical features/abnormalities

Enterotoxins produced by S.aureus

Exotoxins that are heat stable and cause diarrhea and vomiting
Most commonly seen with ETs A and D (sometimes B) because of improperly stored meat and dairy

Describe superantigens and how they cause harm to the body.

Superantigens cause a highly aggressive, overactive immune response by overactivating T cells and causing cytokine storms, which can lead to organ failure and death. TSST-1 and enterotoxins produced by S.aureus are both superantigens.

What differentiates S.aureus food poisoning from salmonella or E.coli food poisoning?

S.aureus food poisioning is caused by toxins whereas E.coli or salmonella are caused by the bacteria multiplying in the GI tract and their intrinsic virulence factors

Why did superabsorbent tampons lead to cases of toxic shock syndrome?

The vagina is typically an anaerobic environment, but the insertion of the tampon + the pockets in which blood is absorbed introduced oxygen to the vagina, which allowed for the aerobic S.aureus bacteria to grow. Since they were superabsorbent, people were also likely to leave them in for longer and the bacteria would produce the TSST-1 toxin.

Describe toxic shock syndrome

A rare, but fast progressing disease caused by TSSToxins, and can lead to amputation, organ failure and death. Along with being associated with highly absorbent tampon use, is also seen with skin wounds and surgical sites.

Describe the intrinsic virulence factors of S.aureus.

Enzymes such as coagulase, protease, hyaluronidase, lipase that can act to break down connective tissues and kill WBCs to spread their infection further
Protein A-found in the cell wall of S.aureus and other GP bacteria, binds to the Fc region of IgG to block phagocytosis

Describe the exfoliative toxin of S.aureus and its effects

Produced by phage group II, causes sloughing of the epidermis and bullous impetigo
Mainly associated with Scalded Skin Syndrome/Ritter's disease, which is mainly seen in children under 5

Why can diseases such as SSS that mainly affect children be much more concerning if adults contract it?

Children recover from SSS on their own typically, but adults who contract it are typically immunocompromised, so it leads to higher mortality

Describe how cytolytic toxins cause damage to the body.

Damage to WBCs and RBCs

Describe the harm the 3 types of hemolysins (cytolytic toxins) cause to the body

alpha-damage to RBCs, platelets, macrophage, tissue damage
beta-acts on the sphingomyelin (sphingolipid) in RBCs, known as the hot-cold lysin because it has enhanced activity (seen on BA) when incubated at 37C then 4C
gamma-Panton-Valentine Leukocidin, an exotoxin that kills neutrophils and suppresses phagocytosis and is seen in cutaneous infections and pneumonia

Compare and contrast abcesses and cellulitis/folliculitis.

Abcesses are painful, raised, red, swollen bumps filled with pus and surrounded by necrotic tissue
Cellulitis indicates infection of layers below the epidermis, and will have redness, swelling, and pain but no pus or raised bumps
Folliculitis is mild inflammation of the hair follicle or an oil gland, and manifests as raised, red dots.

Compare and contrast furuncles and carbuncles.

Furuncles are boils/abcesses that are an accumulation of pus and dead tissue, but are normally in isolation
Carbuncles are larger, invasive lesions and are the combination of multiple furuncles and indicate a spread of bacteria to deeper tissues/systemic spread as they are accompanies by fever and chills. Carbuncles are usually also due to untreated furuncles.

What distinguishes impetigo from staph and impetigo from strep?

Staph impetigo is bullous, strep is nonbullous
Impetigo is the formation of yellow, crusty sores known as pustules and are common in children
Very contagious

What are some morphological and biochemical differences between CoNS and S.aureus and how can you tell?

Morphological-CoNS is usually nonhemolytic
Biochemical-the coagulase test 

What type of pathogen is S.epidermidis?

Opportunistic-exists as normal flora on skin and in mucous membranes

How are S.epidermidis infections usually acquired?

In a hospital/iatrogenic-UTIs from catheters or endocarditis from artificial heart valves

What are some other serious disease manifestations of S.aureus?

Osteomyelitis-infection of the bone marrow and bones
Pneumonia
Bacteremia-IV drug users and hospitalized patients are the most at risk
Endocarditis-infection of the heart muscle/valves
Septic arthritis-infection of the joints via the bloodstream, occurs due to extremity trauma and often seen in children
Necrotizing faciitis-death of the tissue around muscle and can lead to amputation

What are the virulence factors of S.epidermidis?

S.epidermidis virulence factors center around attachment to surfaces through slime layers and biofilms, which contain a lot of Protein A and provide protection from phagocytosis

What CoNS is more similar to S.aureus and how can you tell?

S.lugdunensis because it produces inconclusive clotting factor/coagulase test results

What differentiates S.lugdunensis from S.epidermidis and what disease presentation would lead you to suspect it as the cause?

S.lugdunensis has the mecA gene that encodes oxacillin resistance, and is seen with endocarditis cases from artificial heart valves

What are morphological and disease presentation differences of S.saprophyticus that differentiates it from S.epidermidis?

Sapro is light yellow on a BA plate and novobiocin resistant
Its most common disease presentation is in young women, esp sexually active, ages 13-25

Draw the test flowchart for Staph differentation.

Why do MLS do further biochemical testing?

Oftentimes, bacteria cannot be differentiated from culture/Gram stain alone and testing provides more selectivity

Describe the catalase test.

Detects the presence of the catalase enzyme, which breaks down H2O2 to release oxygen bubbles
Positive-staph
Negative-fermenter bacteria/streptococcus

Coagulase test/Bactistaph

Tests for the presence of the coagulase enzyme by its latex agglutination ability
Positive-S.aureus-clear background, larger clumps
Inconclusive-murky background, small clumps-further testing can reveal S.lugdunensis
Negative-murky background, little to no clumps-CoNS such as S.epidermidis

What are selective media used when determining Staphylococcus species?

MSA-mannitol salt agar, which has a high salt concentration, selective for staph, and fermentation of mannitol, differentiates S.aureus (yellow) and S.epi (pink)
ChromAGAR- selective for MRSA with high salt conc. and cefotexin abx

What susceptibility tests are used for determining Staph species?

Bacitracin-Micrococcus vs CoNS-M is resistant
Novobiocin-S.saprophyticus vs CoNS-Sapro is resistant
Methicillin-S.aureus vs MRSA-MRSA is resistant

What does resistance to an abx look like for susceptibility testing?

Resistant-little to no zone of inhibition-measured around abx disc
Susceptible-wider zone with no growth around abx disc

For non-MRSA staph infections, what class of abx are commonly used for treatment?

betalactamases such as methicillin, which halt the synthesis of peptidoglycan

What is a media that can specifically detect MRSA?

Spectra plate

What abx are used for MRSA?

Vancomycin, rifampicin/gentamycin

What is/are serious but rare forms of drug resistant S.aureus?

VRSA (vancomycin resistant) and macrolide resistant S.aureus-more serious because both these abx are very broad spectrum

What is the prevalence of MRSA in the US, and what are its implications on the healthcare system?

There are close to 100,000 infections a year of MRSA
MRSA can create a huge burden on the healthcare systems-requires more PPE and isolation for the patient, longer stays, expensive abx to treat, and long term health impacts
If hospital acquired, reflects poor infection control measures/sterilization during procedures, as well as potential iatrogenic sources

Compare and contrast HA and CA infections.

Hospital acquired or nosocomial infections-occur during a hospital stay (3 days of admission or longer), due to care received in the hospital or hcw/hospital environment
Community acquired-outside of hospital setting, defined as occuring before hospital visit, spread amongst populations in close quarters/close contact such as athletes (wrestlers), prisoners, military, children, or can occur from tattoos/piercings
Both types emphasize the importance of good hygiene and public health measures

What are the most effective ways to prevent Staph infections/transmission?

Handwashing-most important, especially for those who come into direct contact with infected people
Covering cuts and wounds
Not touching open wounds without PPE
Not sharing towels, sports equipment, toothbrushes, razors, etc.
Prevent cracks and dry skin
Shower after exercising, wipe down exercise equipment after use

What role does disease surveillance play in preventing Staph infections?

Screening surgical patients pre-op with nasal swabs, give abx if positive
Rapid real time PCR on suspected patients
Reporting of suspected MRSA cases to pbh departments