PHD - Staphylococci, Streptococci, and Enterococci (Steed) Flashcards
What is an advantage of having colonies of staph epidermidis on the skin?
Protection from staph aureus and staph pyogenes cutaneous infections
Keratinocytes that are infected with staph epidermidis produce anti-microbial peptides in response to infection. This prevents other staph from infecting the skin in that area.
What is rheumatic fever and how is it related to streptococcal infection?
Rheumatic Fever is characterized by immune-mediated damage to the heart muscle.
Streptococcal cell walls and myocardial cell surface antigens have similar proteins. Antibodies against Strep will cross-react with myocardial cells, causing heart damage.
This is a form of molecular mimicry
Which bacterium is always responsible for bullous impetigo?
Staph aureus
Bullous impetigo is a less contagious version of impetigo that tends to affect the face, axillae, trunk and perianal region. It may also involve mucous membranes.
Which patient population is recommended to get vaccinated with Prevnar?
Prevnar is recommended for infants as young as 2 months and for patients over 65.
This vaccine is also recommended for immunocompromised patients, patients with organ damage, and those who go to daycare.
What are the 4 major virulence factors of streptococcus pyogenes?
- M protein
- Streptolysins O and S
- Superantigenic exotoxins
- Hyaluronic capsule
Your patient is a 3-month-old infant who presents with a red rash and desquamation of the skin of the gluteal region, legs, and upper back. What is the mechanism that caused this disease process?
A. Biofilm formation
B. Enterotoxin-mediated superantigen activity
C. Exotoxin-mediated destruction of the stratum granulosum cell-cell cohesion
D. Leukocidin activity in combination with protein A activation of TNF
E. Superantigen-mediated cytokine production
C. Exotoxin-mediated destruction of the stratum granulosum cell-cell cohesion
This child has staphylococcal scalded skin syndrome (SSSS), which is caused by release of exfoliatins A and B. These exfoliatins interfere with cell-cell cohesion molecules in the upper layers of skin, causing desquamation and redness.
B would cause non-mentrual toxic shock syndrome and food poisoning
D is a virulence factor of Staph aureus
E would cause toxic-shock syndrome
What are the main stages of biofilm formation in Staph infections?
- Attachment of planktonic cells
- Multiplication and exodus - mediated by autolysin A
- Accumulation and formation of exopolysaccharide
- Formation of mature biofilm
What is vancomycin-intermediate staph aureus (VISA) and how is this form more difficult to treat?
VISA are staph bacteria that have an intermediate resistance to vancomycin.
Chromosomal mutations –> thicker cell wall –> traps vancomycin in cell wall and prevents it from reaching its target
What are the 4 requirements for the expression of Toxic Shock Syndrome Toxin-1 (TSST-1) that are provided by the use of highly absorbent tampons?
- Elevated protein
- Relatively neutral pH (6.5 to 8)
- Elevated pCO2
- Elevated pO2
1-3 are provided by the menstrual blood. 4 is caused by the tampon itself.
Which two Lancefield System groups contain beta-hemolytic streptococci?
A and B
A (S. pyogenes) and B (S. agalactiae) are both highly pathogenic and pyogenic.
What is the morphological difference between Staph and Strep on culture?
Staph grows in clusters
Strep grows in chains
Staphylo means cluster
Strepto means chain
What are the 3 types of carriers of staph aureus and how can this make it difficult to determine carrier status?
- Persistent carrier (~20%) - carry the same strain over time
- At increased risk of infection
- Intermittent carriers (~30%) - carry different strains over time
- Difficult to determine because there are times when this individual does not have staph present
- Non-carriers (50%)
True or False: Staphylococci are able to colonize on virtually all animals.
True
Which drugs are used to treat Staphylococcus agalactiae?
- High-dose parenteral penicillin
- Ampicillin
- Ceftriaxone
What type of hemolysis does Strep pneumoniae cause and how would this colony appear on a blood agar plate?
Alpha hemolysis
Remember that alpha hemolysis is characterized by oxidation of hemoglobin to form methemoglobin. Methemoglobin appears as green on the blood agar plate.
How is the SCCmec gene different between healthcare-associated vs. community-acquired MRSA?
- Healthcare-associated has a large SCCmec gene - means it is multi-antibiotic resistant bacteria
- Community-acquired has a small SCCmec gene - means it is resistant to only methicillin and erythromycin
What is the standard drug of choice to treat streptococcus pneumoniae? What about if the bacteria are tolerant to this drug of choice?
Penicillin
If the bacteria are tolerant or moderately resistant to Penicillin, a third-generation cephalosporin (eg ceftriaxone), should be given.
A 29-year-old male presents to the emergency department complaining of back pain. Upon physical examination, you notice facial edema and a BP of 150/95. He tells you that his urine has been a dark color recently ever since he got over a strep infection. What is this condition called and would you expect to see on a histologic section of the kidney?
Acute Glomerulonephritis
Histologic section would show immune complexes within the glomeruli. These immune complexes consist of anti-strep antibodies that cross-react with self-antigen or strep-antigen.
What are the invasive infections caused by Streptococcus agalactiae in adults?
- Pneumonia
- UTIs
- Skin/soft tissue infections (w/ or w/o osteomyelitis)
- Bacteremia (w/ or w/o endocarditis)
- Meningitis
What is one way to get around the action of bacterial beta-lactamases?
Clavulanic acid
Clavulanic acid is a beta-lactamase inhibitor. Using this with penicillin or amoxicillin will help to prevent breakdown of the drug before it has a chance to work on the bacteria.
Augmentin = amoxicillin + clavulanic acid
Which specific part of the body do Staph aureus bacteria prefer to reside?
Anterior Nares
These bacteria also colonize the axillae and perineum
What are the 4 types of Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs)?
- Protein A - binds Fc portion of IgG/IgM to inhibit opsonization and complement activation
- Clumping factor - binds fibrinogen and platelets
- Fibronectin-binding proteins
- Collagen-binding proteins
A 26-year-old female presents to you clinic complaining of pain with swallowing, a cough, and a runny nose. Upon examination, you notice that the tonsils are swollen and that there are red patches on the pharynx and uvula (seen below). What bacteria has infected your patient and what do you prescribe?
Streptococcus pyogenes
Treat with penicillin
Remember that strep. pyogenes presents as pharyngitis, skin infection, toxic shock syndrome, or necrotizing fasciitis.
What are staphylokinases and how do they contribute to staph infections?
Staphylokinases are enzymes used to break off staph cells from a cluster via fibrin lysis.
This allows single staph bacterial cells to travel and infect other parts of the body.
Based on the image below, which type of hemolysis is occurring in the sample labeled B?
Beta hemolysis
Notice the yellow colony growing with a clear space surrounding it. This clear space is where hemolysis of RBCs in the blood agar has occurred.
True or False: Strep viridans grows in 6.5% NaCl.
False.
Enterococcus sp. grow on 6.5% NaCl agar plates, but streptococci do not. This is a good way to differentiate between Strep and Enterococci.
What is erysipelas and which type of streptococcus causes it?
Erysipelas is a strep. pyogenes infection of the upper layers of the epidermis.
Patients will typically present with a bright red rash that has clearly demarcated lines.
How and when does late onset Strep. agalactiae present?
Within 7-90 days
Presents as meningitis and bacteremia
50% of meningitis survivors will have permanent neurologic sequelae.
You are working as a pathologist and receive a urine sample from a patient suspected of having a UTI. You begin to make bacterial cultures. You decide that you should do a blood agar and a 7.5% NaCl plate. What other type of agar should you use if you suspect that this bacteria is Staph?
Mannitol Salt Agar
Only few types of bacteria (staph and micrococcus) are able to grow in high concentrations of salt.
Mannitol and phenol red are also added to the agar. Mannitol-fermenting bacteria will produce acid upon fermentation of the sugar. Phenol Red dye change color from red to yellow in the presence of acid.
What drug is typically used to treat penicillin-resistant Staph aureus?
Vancomycin
Vancomycin generally works on all Staph. strains. However, resistance to vancomycin is becoming evident.
What are the 6 main types of invasice Staph aureus infection?
- Bacteremia/septic shock
- Endocarditis
- Osteomyelitis
- Septic arthritis
- Pneumona (often with abscess)
- Deep organ abscess
What is the basis of the Lancefield System of identification in Streptococci and Enterococci?
C-substance
The C-substance is the cell wall carbohydrate antigen
On what type of culture medium do Staphylococci typically grow best?
Blood agar with 7.5% NaCl
This type of bacteria grow best with blood agar, and will typically show up on the agar as “white streaks” because they break down blood (beta hemolytic). Some are gamma hemolytic, meaning they grow on blood agar, but don’t break down the blood.
How and when does early onset strep. agalactiae infection present?
Early onset presents within 6 days of birth
Typically presents as bacteremia and pneumonia
During vaginal delivery, Strep. agalactiae gets into the nasal, vaginal, and oral openings of the newborn.
What are superantigens and what are the two main types of superantigens involved with Staph?
Superantigens are non-antigen-specific molecules that activate T-cells and macrophages to release massive amounts of cytokines, leading to shock.
Two main types:
- Enterotoxins
- Toxic Shock Toxin-1 (TSST-1)
What is the major virulence factor of Streptococcus pneumoniae?
Polysaccharide capsule
This capsule helps to evade phagocytosis by host immune cells.
Food poisoning caused by staphylococcal enterotoxins is unique and can be distinguished from a bacterial infection of the gut by what?
It does not produce fever
Staph bacteria produce enterotoxins (SEA, SEB, SEC), which cause the malaise, nausea, vomiting, and pain.
Fever is not caused because this is not technically a bacterial infection. Only toxin is involved in causing these symptoms.
What nutritional molecule is required for optimal aerobic growth of streptococci?
CO2
What are some ways to prevent the spread of MRSA?
- Handwashing
- Contact precautions - gloves, etc.
- Sparing use of antibiotics
- Detection of MRSA positive individuals
- Decolonization of carriers via mupirocin (intranasal) or chlorhexidine bathing
Are staphylococcus sp. gram positive or gram negative?
Gram positive
During lab analysis of a staph culture, you find that the organism is catalase positive, coagulase negative, and novobicin resistant. What specific type of Staph is this?
Staphylococcus saprophyticus
S. saprophyticus typically colonizes the rectum and urogenital tract in 5-10% of women. It is the second most common form of bacteria involved in UTI of young, sexually-active females.
What is the most common bacteria involved in urinary tract infections?
E. coli
What is the most common clinical manifestation of alpha-hemolytic streptococci (mutans, mitis, salivarius, and sanguis) in normal patients?
Dental caries
These bacteria are most commonly involved in the production of tooth decay because they form a biofilm over the teeth that leads to demineralization.
What are 2 methods of prevention that can decrease the risk of acquiring menstrual-associated toxic shock syndrome?
- Do not use hyperabsorbant tampons
- Prevent/eliminate S. aureus colonization in nares/wounds with mupirocin and/or clorhexidine bathing
What is pneumolysin, when is it released, and what does it do?
Pneumolysin is a pore-forming toxin that is released when pneumococci are lysed.
Main functions:
- Disrupts respiratory cilia
- Toxic to pulmonary endothelial cells and host phagocytes
- Damages endothelial cells along blood-brain barrier
What are the 2 main virulence factors of Streptococcus pneumoniae?
- Pneumolysin
- Neuraminidase
Why are Enterococci infections so difficult to treat?
Many types are resistant to penicillin and vancomycin.
Because these bacteria live in the GI tract, they are exposed to oral antibiotics over the lifespan of the individual. This increases the risk that these bacteria will be antibacterial resistant.
What is the importance of fibronectin-binding proteins for Staph infection of a host?
Staph bacteria use fibronectin to bind to endothelial cells. This allows them to adhere and replicate to further spread throughout the host.
What is Protein A and what is its mechanism of action?
Protein A is a PVL that activates the TNF receptor to increase cytokine release and attract WBCs.
When these cells are attracted to the area of Staph infection, the PVLs will destroy the WBCs.
What is the best way to distinguish between staphylococci and streptococci in a culture medium?
Catalase Test
Staohylococci produce catalase, an enzyme that converts hydrogen peroxide into oxygen and water.
The catalase test is done by putting a few drops of 3% H2O2 onto a bacterial culture and looking to see if bubbles appear (positive test).
True or False: Streptolysins O and S are toxic compounds released by Strep pyogenes that aid in myocardial cell damage during Rheumatic Fever.
True
Your patient is a 5-year-old male who was brought in by his mother because of a red rash and blistering of the skin. You swab the affected areas and colonize the bacteria on an agar plate with a disc of erythromycin and clindamycin on each side. Below are your results. What can you deduce about this type of staph?
This test indicates that the bacteria has an efflux pump that will pump some of the antibacterial medication out of the cell, making it harder to treat.
Notice that the D zone is not present, and that the zones of inhibition of both erythromycin and clindamycin are joined.
This indicates that clindamycin will be effective to treat this type of staph.
Which type of strep bacteria is susceptible to optochin?
Strep. pneumoniae
Optochin is a drug used to treat pneumococcal infections. When present there will be a zone of inhibition around the optochin disk where no Strep. pneumoniae will grow.
What do streptococci look like under the microscope (clustered, chains, rods, spherical, etc.)?
Chains
Strepto = chain
Cocci = sphere
What is the D zone on an agar plate with straph colonies and what does it indicate about the particular strain of Staph that is being cultured?
The D zone is the flat edge of the zone of inhibition on a staph culture between erythromycin and clindamycin (see below). This flat edge produces a “D” in the colony.
D zone indicates that this species is resistant to clindamycin because it can methylate the ribosomal target of clindamycin.
What class of bacteria are staphylococci in terms of oxygen use?
Facultative Anaerobes
Staphylococci are facultative anaerobes, which means that they use both glycolysis (aerobic) and fermentation (aerobic).
On a culture medium, these microbes will be able to grow throughout the whole culture. Aerobes will only be able to grow close to the surface because they need O2. Anaerobes will only be able to grow at the bottom of the tube where no O2 is present.
How do staphylococcus bacteria avoid phagocytosis by macrophages?
Protective capsule
Staph bacteria have a capsule that covers the surface of the peptidoglycan layer. This helps to shield surface antigens from immune cells and prevents the bacteria from being ingested by phagocytes.
What are 4 types of Staph aureus skin infections?
- Folliculitis - infections of hair follicles
- Furuncle - boil
- Carbuncle - group of pus-filled bumps forming an area of connected infection under the skin
- Cellulitis - bacterial infection of skin and underlying tissues
An isolate from 2 of 2 blood cultures grows well on blood agar, is beta-hemolytic, catalase positive, and coagulase positive. The name of this isolate is?
A. Staphylococcus aureus
B. Coagulase negative Staphylococcus
C. Staphylococcus aureus coagulase negative
D. Coagulase negative staphylococcus aureus
A. Staphylococcus aureus
Remember that all staph strains are catalase positive. This distinguishes between staph (catalase positive) and strep (catalase negative).
A positive coagulase test indicates that the bacteria are Staph aureus.
What is Staphylococcal scalded-skin syndrome (SSSS) and what age group does it typically occur in?
Staph. aureus infection that produces exfoliatins A and B, which cause desquamation of the skin.
Most common in neonates and infants younger than 1 year of age.
What is the most frequent cause of life threatening disease in newborns in the US?
Streptococcus agalactiae
S. agalactiae is a group B strep that causes beta hemolysis of RBCs. This is commonly screened for in pregnant women to prevent transmission during delivery.
The most common cause of bacterial meningitis in a 2-month-old baby is:
A. Enterococcus sp.
B. Staphylococcus aureus
C. Streptococcus agalactiae
D. Streptococcus pyogenes
E. Streptococcus pneumoniae
Streptococcus agalactiae
Strep. agalactiae is a group B strep that is beta-hemolytic. In infants who are older than 6 days, the infection manifests as bacterial meningitis.
What are the 6 minor Jones criteria for diagnosing acute rheumatic fever?
- Fever
- Arthralgia
- Prolonged P-R interval
- Increased SED rate, CRP
- Previous rheumatic fever
- Coagulopathy
What are the clinical manifestations of Staph. epidermidis infections?
- Bacteremia with central and peripheral intravascular catheters/prosthetics
- Endocarditis - prosthetic valves
- Surgical implants - pacemakers, shunts, catheters
- UTI - kidney transplant, kidney stone, post UT surgery
Which 2 strains of bacteria are classified as Lancefield Antigen Group D?
Streptococcus bovis and Enterococcus
A 10-year-old boy is brought into the emergency department with a a bright red rash, a fever of 103F, and a white coating on the tongue (seen below). What is the name of the tongue condition and which bacteria causes it?
Strawberry tongue, characteristic of scarlet fever
This condition is caused by Streptococcus pyogenes
What are the 5 major Jones criteria for diagnosing acute rheumatic fever?
- Carditis
- Polyarthritis
- Chorea - irregular, involuntary movements
- Subcutaneous nodules
- Erythema marginatum - skin rash that appears like rings/targets on the skin (seen below)
Susceptibility for this blood culture isolate are shown below. What is the mechanism of this methicillin result?
A. Activity of a specific type of beta-lactamase
B. Activity of an efflux pump
C. Lower affinity of an altered penicillin binding protein (PBP2a)
D. Lower affinity of cell wall D-ala-D-lactate terminals
E. Mutations in cell wall D-ala-D-ala terminals that thicken the cell wall.
C. Lower affinity of an altered penicillin-binding protein (PBP2a)
Remember that methicillin-resistance is primarily caused by altered PBP2a via a mutation on mecA gene.
A describes penicillin-resistance
B describes clindamycin resistance
D describes vancomycin-resistant staph aureus (VRSA)
E describes vancomycin-intermediate staph aureus (VISA)
Below is an image of Staphylococcus aureus colonies. What special metabolic characteristic can be seen in this colony?
Beta hemolysis
S. aureus are beta-hemolytic bacteria, meaning that they break down blood cells. The red in the image is the blood agar. The yellow/white areas are where colonies of Staph have grown and caused lysis of blood.
What is the drug of choice for Streptococcus pyogenes infections and which 3 other drugs can work in place of the drug of choice if necessary?
Penicillin is the drug of choice
If patient is allergic to penicllin, give:
- Cephalosporins
- Clindamycin
- Erythromycin
True or False: invasive staph aureus is the number one cause of endocarditis in patients who havve received a prosthetic valve.
True.
Based on the image below, which type of hemolysis is evidenced by the sample labeled A?
Gamma hemolysis
Remember that gamma hemolysins do NOT break down RBCs. This causes a white bacterial colony to grow on top of the blood agar.
Based on the image below, which type of hemolysis is occurring at the sample labeled C?
Alpha hemolysis
Alpha hemolysins partially break down RBCs. This produces a greenish colored colony on the blood agar.
The green color is caused by methemoglobin, the oxidized form of hemoglobin.
Which superantigenic exotoxin is a cysteine protease responsible for necrotizing fasciitis?
SpeB
Strep. agalactiae is in which Lancefield System Group and is distinguished from other strep sp. by a positive result of what test?
Group B
A positive CAMP test indicates Strep. agalactiae.
A CAMP test consists of a blood agar plate with a strip of Staph aureus (labeled C) and a strip of Strep. agalactiae (near label A). Strep. agalactiae produces a substance called CAMP factor, which increases the amount of beta hemolysis, making a wider light area on a blood agar (labeled A).
A 57-year-old male presents to the ED with signs of septic shock after receiving an aortic valve transplant a month prior. Lab work shows that the bacteria is alpha-hemolytic, bile esculin positive, and negative on 6.5% NaCl. Which bacteria is responsible for this patient’s symptoms?
Streptococcus bovis
Which type of staphylococcus is considered to be catalase positive and coagulase positive?
Staphylococcus aureus
What is the most common cause of pneumonia and which populations are more at risk for developing this infection?
Streptococcus pneumoniae
Patients under the age of 2 or over the age of 65 are at higher risk of developing the infection and having worse symptoms.
Patients with organ dysfunction or who are immunocompromised are at increased risk for serious disease.
What are the 4 types of alpha-hemolytic Streptococci and how do they lead to infection?
S. mitis, S. salivarius, S. sanguis, and S. mutans
These 4 bacteria are normally commensals. During times of immunosuppression, they can become pathogenic and induce infection.
What are the 4 types of hemolysins and what do each type do to blood cells?
- Alpha - incomplete hemolysis of RBCs –> greenish color on blood agar
- Beta - complete hemolysis –> clear spots on blood agar where bacteria are growing
- Delta
- Gamma - no hemolysis
Your patient is a 13-year-old male who comes into the office complaining of an itchy, scaly rash on the area between his nose and upper lip. Based on the appearance of the rash, what condition does the patient have and what is the most likely cause of the rash?
Non-bullous impetigo
Caused by staphylococcus aureus or pyogenes
Non-bullous impetigo is characterized by multiple coalescing lesions of the face, particularly between the nose and upper lip. Begins as small pustules that pop and crust over.
Self-limited, usually goes away within 2 weeks
What is the mechanism of action of exfoliatins?
Exfoliatins directly destroy cell-cell cohesion molecules in the stratum granulosum of the skin.
This produces a loss of the most suferficial epidermal layers
An isolate from a peritoneal dialysis culture has gram positive cocci in chains. The colonies grow as small, alpha-hemolycic colonies on blood agar. They are catalase negative, optochin resistant, bile esculin positive, and grow in 6.5% salt broth. What is the name of this isolate?
A. Enterococcus sp.
B. Member of streptococcus anginosis
C. Streptococcus bovis
D. An alpha-hemolytic streptococcus such as Streptococcus salivarius
E. Streptococcus pneumoniae
A. Enterococcus sp.
Not C - Strep. Bovis is 6.5% NaCl broth negative
Not D - Strep. salivarius is bile esculin negative
Not E - Strep. pneumoniae is optochin sensitive
Which type of Strep or Enterococci are susceptible to bacitracin?
Strep. pyogenes
Remember that strep. pyogenes is in group A of the Lancefield System.
Which 2 types of streptococcal bacteria are not grouped within the Lancefield System?
Strep viridans and Strep pneumoniae
What are the 6 most common areas of skin that Staph. epidermidis lives on?
- Axillae
- Groin
- Perineum
- Anterior nares
- Conjunctiva
- Toe webs
