Gram-positive cocci Flashcards
What test do we use to differentiate Staphylococci from Streptococci and Enterococci?
Which result indicates which bacteria?
Catalase Test
Catalse (+) = Staphylococci
Catalse (-) = Streptococci or Enterococci
What are some important catalase-positive organisms?
- Staphylococci
- Nocardia
- Pseudomonas
- Listeria
- E. coli
- Candida
- Aspergillus
- Serratia
- B cepacia
- H pylori
Once a bacteria is determined to be catalase (+), what is the next test you run to determine the bacteria species?
Coagulase Test
What test results would indicate that the bacteria is Staphylococcus aureus?
Catalase (+)
Coagulase (+)
Staphylococcus aureus also ferments mannitol (this test is not used often)
Hemolytic Activity Test
- Alpha (a) shows: ?
- Indicates bacteria: ?
- Beta (B) shows: ?
- Indicates bacteria: ?
- Gammma (y) shows: ?
- Indicates bacteria: ?
Hemolytic Activity Test
- Alpha (a) shows: partial hemolysis. Green-ish color around colony due to release of peroxide
- Indicates bacteria: Strep pneumoniae and Viridans Strep
- Beta (B) shows: Total lysis of RBCs
- Indicates bacteria: Strep pyogenes (Group A Strep) and Strep agalactiae (Group B Strep)
- Gammma (y) shows: Zero hemolytic activity
- Indicates bacteria: Enterococcus and Sterp bovis
Staphylococcus
Shape: ?
____ anaerobes
Color: ?
Species associated with disease: ?
Staphylococcus
Shape: groups of circles (looks like bunches of grapes)
Facultative anaerobes
Color: yellow
Species associated with disease:
- S. aureus (Cat + and Coag +)
- S. epidermidis (Cat +, Coag -, Novobiocin sensitive)
- S. saprophyticus (Cat +. Coag -. Novobiocin resistant)
S. aureus virulence factors that inhibit phagocytosis (2 examples)
S. aureus virulence factors that inhibit phagocytosis
- Coagulase = clumping factor: binds fibrinogen, converts to fibrin, hides bacteria from host
- Protein A binds to Fc region of IgG, protects S. aureus from opsonization and phagocytosis
S. aureus exotoxin virulence factors (4 examples):
S. aureus exotoxin virulence factors:
- Exfoliative toxins A and B: causes Staphylococcal Scalded Skin Syndrome (SSSS). Found in 5-10% of S. aureus strains
- Enterotoxins: 8 distinct heat stable toxins that cause food poisoning with vomiting and diarrhea (rapid: 4 hours after ingestion)
- Toxic Shock Syndrome toxin (TSST-1): heat and protease resistant toxin responsible for menstruation-associated toxic shock. Able to cross mucosal barriers.
- Superantigens: binds to MHC II and T Cell Receptor –> Polyclonal T Cell activation –> Release of cytokines, leakage of endothelia
Where is S. aureus commonly found?
In the nose (30% of people are persistent carriers of S. aureus)
Staphylococcus aureus
Diseases caused by exotoxin release (3 examples)
Diseases caused by direct organ invasion (8 examples/general idea)
Staphylococcus aureus
Diseases caused by exotoxin release:
- Gastroenteritis (food poisoning) caused by enterotoxins
- Toxic Shock syndrome caused by TSST-1
- Scalded skin syndrome caused by Exfoliative toxins A and B
Diseases caused by direct organ invasion:
- Pneumonia
- Meningitis
- Osteomyelitis
- Septic arthritis
- Acute bacterial endocarditis
- Skin infections
- Bacteremia/sepsis
- UTI
S. aureus food poisoning
Caused by ?
Symptoms ?
S. aureus food poisoning
Caused by S. aureus enterotoxins (heat stable, thus even if bacteria is killed by being cooked the toxin remains)
Symptoms: vomiting, diarrhea, and stomach cramping; no fever
S. aureus toxic shock syndrome
Caused by:
Symptoms:
Labs:
S. aureus toxic shock syndrome
Caused by:
- Localized growth of S. aureus releases TSST-1 into the blood
- Classic presentation: patients with superabsorbent tampons or nasal packing
Symptoms:
- Macular erthematous rash - entire skin layer can desquamate
- Vomiting
- Hypotension
- Fever
Labs:
- Increased liver function tests (LFTs)
S. aureus Scalded Skin Syndrome
Also called ________ in newborns
Causes:
Symptoms:
S. aureus Scalded Skin Syndrome
Also called Ritter’s Disease in newborns
Causes:
- S. aureus releases exfoliative toxins A and B
Symptoms:
- Peri-oral erythema that expands to the entier body
- Large bullea forms (no bacteria within bullae)
or
- Bullous Impetigo: localized SSSS; fluid-filled blisters; S. aureus within blisters; erythema does not extend beyond blister
Note: A bulla is a fluid-filled sac or lesion that appears when fluid is trapped under a thin layer of your skin
Define the following:
Folliculitis:
Furuncles:
Carbuncles:
Define the following:
Folliculitis: infection around hair follicle; pus-filled lesions form around follicle. If occurs at base of eye it is called a stye
Furuncles: (aka boils); extension of folliculitis. Large, painful, underlying collection of necrotic tissue. Erythemitous, raised, swollen.
Carbuncles: Collection of furuncles; estend to deeper tissues; can lead to spread to other sites of body and bacteremia. Often include chills and fever which indicates systemic spread
Staph aureus is a common cause of bacteremia. Half of S. aureus bacteremia cases follow ________ or ________
Staph aureus is a common cause of bacteremia. Half of S. aureus bacteremia cases follow surgical procedures or prolonged catheter use
Staph aureus in blood can adhere to ____ tissues; can be sudden onset of high fever (103 to 105 F). High mortalitiy (50%). ____ destruction and embolisms to brain or lung can occur
Staph aureus in blood can adhere to heart tissues; can be sudden onset of high fever (103 to 105 F). High mortalitiy (50%). Valvular destruction and embolisms to brain or lung can occur
Endocarditis caused by Streptococcus viridans vs Staphylococcus aureus
Streptococcus viridans endocarditis often accumulates slowly overtime
Staphylococcus aureus endocarditis often has a rapid progression
Staphylococcus epidermidis
Tests:
Location in body:
Site of infection/symptoms:
Staphylococcus epidermidis
Tests:
- Catalase (+)
- Coagulase (-)
- Novobiocin sensitive
Location in body:
- Found on the skin; does not usually cause infection
Site of infection/symptoms:
- Produces slime layer/biofilms (inhibits phagocytosis/increases Abx resistance) on foreign material, thus causes:
- Endocarditis in artificial valves
- Infection related to catheters, shunts, IVs, etc.
- Artificial joint infections
Note: Since S. epidermidis is on the skin, it is a frequent contaminant in blood cultures
Staphylococcus saprophyticus
Tests:
Site of infection/symptoms:
Staphylococcus saprophyticus
Tests:
- Catalase (+)
- Coagulase (-)
- Novobiocin resistant
Site of infection/symptoms:
- UTI (2nd most common cause of UTI in young, sexually active women)
Staphylococcus aereus treatment
Staphylococcus aereus treatment
- < 10% of Staph is sensitive to penicillin
-
MRSA (~60-70% of clinical isolates)
- Vancomycin is 1st line of defence against MRSA
- VRSA: Vancomycin resistance emerging
- VISA: Vancomycin intermediate resistance SA (low level of resistance)
- Community-acquired: more susceptible to sulfa sdrugs, tetracyclline, tigecycline
- Hospital-acquired: requires linezolid, rifampin, clindamycin
What does a negative catalase test indicate?
That the bacteria is either Streptococci or Enterococci
What are the main catalase negative bacteria?
What kind of hemolytic activity do they have?
- Streptococcus pyogenes (GAS) - B hemolytic activity
- Streptococcus agalactiae (GBS) - B hemolytic activity
- Streptococcus pneumoniae - a hemolytic activity
- Enterococcus faecalis - y hemolytic activity
- Enterococcus faecium - y hemolytic activity
- Viridans Streptococci - a hemolytic activity
What are the 3 schemes used to classify Streptococci species?
- Lancefield antigen: C-polysaccharide; groups A through S
- Hemolytic patterns: a, B, or y hemolysis
- Biochemical properties
Side note:
- B hemolytic streps are classified through Lancefield groupings
- a and y hemolytic streps are classified by biochemical testing
What is the main example of Group A Strep (GAS)?
What tests would confirm this bacteria?
- Streptococcus pyogenes
- B-hymolytic and Bacitracin sensitive
What is the main example of Group B Strep (GBS)?
What test would confirm this bacteria?
- Streptococcus agalactiae
- B-hemolytic
What are the main Group D bacteria?
- Enterococcus (technically not a Streptococcus but its own Genus)
- S. bovis (non-Enterococcal Group D Strep)
S. pneumoniae
Does it have the Lancefield antigen?
__-hemolytic
S. pneumoniae
No Lancefield antigen
a-hemolytic
Streptococcus viridans
Does it have lancefield antigens?
What is the most important species?
Streptococcus viridans
Yes it has variuos lancefield antigens
The most important species is Streptococcus mutans (dental caries)
Note: Streptococcus viridans is a diverse group of many species
S. pyogenes (GAS) cloaking virulence factors
S. pyogenes (GAS) virulence factors
Cloaking Devices:
-
M-Proteins and M-like proteins:
- Antiphagocytic factor
- 2 types: Class I and Class II; only Class I is associated with rheumatic fever
-
Hyaluronic acid capsue (present in some)
- Interferes with phagocytosis
- Non-immunogenic (looks like host connective tissue)
- Associated with invasive infections
How does S. pyogenes M protein lead to the development of rheumatic fever?
Antibodies against M protein cross react with heart cells
S. pyogenes (GAS) cell destruction virulence factors
S. pyogenes (GAS) cell destruction virulence factors
- Hemolysins: Makes pores in host membranes - Cell destruction
- Streptolysin S: Major factor leading to B-hemolysis on blood agar
-
Streptolysin O:
- Oxygen-sensitive hyemolysin, doesn’t contribute to B-hemolysis on blood agar plates grown aerobically
- Immunogenic - can be used to diagnose rheumatic fever and glomerulonephritis (anti-streptolysin O antibody test = ASO test = indicates Strep pyogenes infection)
S. pyogenes (GAS) toxic virulence factors
S. pyogenes (GAS) toxic virulence factors
-
Pyrogenic exotoxins:
- Phage-encoded superantigens
- Cross-link MHC II to TCR
- Induce T-cell activation and massive cytokine production
- Results in non-productive and non-specific immune response
List of diseases that S. pyogenes (GAS) can cause
- Pharyngitis “strep throat”
- Scarlet fever
- Acute Rheumatic Fever/Rheumatic Fever
- Acute Glomerulonephritis
- Non-Suppurative Sequelae
- Skin infections including:
- Impetigo
- Erysipelas
- Cellulitis
- Necrotizing fasciitis “flesh-eating disease” (often with STSS)
Pharyngitis “strep throat” caused by S. pyogenes (GAS)
Symptoms:
Pharyngitis “strep throat” caused by S. pyogenes (GAS)
Symptoms:
- Fever > 102, chills, headache
- Painful to swallow
Notes:
- Common in 5-15 year-olds (but possible in alll ages)
- Highest incidence in winter and spring
- Self-limiting, but treatment advisable to avoid sequelae
Scarlet Fever caused by S. pyogenes (GAS)
Symptoms:
Scarlet Fever caused by S. pyogenes (GAS)
Symptoms:
- Diffuse erythematous rash
- Begins on chest and spreads to extremities
- Caused by S. pyogene superantigen exotoxins
- Strawberry tongue
Note: Scarlet fever may accompany pharyngitis “strep throat”
How to differentiate skin infections caused by Staphylococcus aureus vs a strep species
If purulent/pus filled skin infection = likely Staphylococcus aureus
If skin infection with no pus = likely a strep bacteria
Skin infections caused by S. pyogenes (GAS)
Empetigo (aka Pyoderma) and Erysipelas
Description and Symptoms
Skin infections caused by S. pyogenes (GAS)
-
Impetigo (aka Pyoderma)
- Superficial infection, common in children, common in warm/humid summer months
-
Erysipelas
- Infection of the dermis; sharply demarcated edge
- Localized pain, erythema, fever, and chills
- Leukocytosis
- Most common in young and elderly
Skin infections caused by S. pyogenes (GAS)
Cellulitis
Description/Signs:
Skin infections caused by S. pyogenes (GAS)
Cellulitis
Description/Signs: Deeper dermal infection. Not sharply demarcated. Invasion mediated (not toxin mediated)
Skin infections caused by S. pyogenes (GAS)
Necrotizing Fasciitis
- Necrosis of connective tissue, fat tissue, and lymphatics
- Preceded by cellulitis, bullae, and gangrene
- Extremely painful with rapid progression along fascial plane
- Typically requires debridement
- Often accompanied by Streptococcal Toxic Shock Syndrome (STSS)
- Due to pyrogenic superantigen exotoxins
Non-Supportive Sequelae caused by GAS
Autoimmune reactions post-GAS infection (immunologic)
Acute Rheumatic Fever/Rehumatic Fevere caused by GAS
- Antibodies raised against M-protein and other bacterial antigens cross-react with heart tissues and muscle/valves
- Follows pharyngeal “strep throat” infections only
- Immune reaction to joints, CNS, and skin also possible
Acute Glomerulonephritis (AGN) caused by GAS
- Follows pharyngeal and skin infections
- Antibody-antigen complexes deposit on glomerular basement membrane - leads to complement fixation and inflammation (Type III Hypersensitivity)
GAS treatment and prevention
- Highly susceptible to Penicillin G
- Mixed infections with S. aureus should include vancomycin
- Increasing frequency of tetracycline and macrolide resistance
- Aminoglycosides - high level of resistance observed
- Adequate treatment of Streptococcal pharyngitis within 10 days of onset will prevent rheumatic fever
- Serious soft tissue infections require drainage and debridement
- Patients with history of rheumatic fver may required long term antibiotic prophylaxis
S. pyogenes (GAS) tests
- Catalase (-)
- B-Hemolysis
- Bacitracin sensitive
S. agalactiae = Group B Strep (GBS)
Tests:
Properties:
Tests:
- Catalase (-)
- B-Hemolytic
- Bacitracin Resistant
- Lancefield B antigen
- Produces CAMP factor (not to be confused with cyclic AMP), which is a diffusible extracellular hemolytic heat-stable protein that is synergistic with beta-lysin produced by Staph aureus resulting in enhanced lysin of RBCs/enlarges zone of hemolysis formed by S. aureus
Properties:
- Gram-positive cocci in chains
- Polysaccharide capsule (important for virulence)
Streptococcus agalactiae (GBS) is the largest caused of neonatal ____, ____, and ____
GBS colonizes the ________ and ________. Likelihood of infant colonization increase when mother is colonized with large numbers of organisms. Risks include premature delivery, prolonged membrane rupture, intrapartum fever, and post-partum disease
Streptococcus agalactiae (GBS) is the largest caused of neonatal meningitis, sepsis, and pneumonia
GBS colonizes the lower GI tract and genitourinary tract. Likelihood of infant colonization increase when mother is colonized with large numbers of organisms. Risks include premature delivery, prolonged membrane rupture, intrapartum fever, and post-partum disease
Streptococcus agalactiae (GBS) Disease
Early onset neonatal disease:
Late onset disease:
Infections in men/non-pregnant women:
Streptococcus agalactiae (GBS) Disease
Early onset neonatal disease:
- Acquired in utero or at birth and develops during 1st week
- Bacteremia, meningitis, pneumonia
- Neonates present with non-specific signs such as fever, vomiting, poor eating, and irritability
Late onset disease:
- Acquired from exogenous source
- Develops between 1 week and 3 months of age
- Bacteremia with meningitis
Infections in men/non-pregnant women:
- Generally older or immunocompromised
- Bacteremia, pneumonia, bone/joint infections, skin/soft tissue
Note: Neurologic complications are common
Streptococcus agalactiae (GBS)
Diagnosis:
Treatment:
Streptococcus agalactiae (GBS)
Diagnosis:
- Primarily done by culture
- Catalase (-), B-heomolysis, Bacitracin resistant
Treatment:
- Organisms are sensitive to penicillin; howver, start with borad spectrum antibiotics until GBS is confirmed
- Women testing positive during pregnancy (tested 35-37 weeks) should be given IV Abxs during labor (at least 4 hours prior)
Streptococcus pneumoniae (aka Pneumococcus)
Tests:
Location:
Properties:
Diseases:
Streptococcus pneumoniae (aka Pneumococcus)
Tests:
- Catalase (-)
- a-hemolytic
- Optochin sensitive
Location:
- Upper respiratory tract
Properties:
- Virulence factor: Capsule
- Arranged in pairs or short chains
Diseases:
- Most common cause of bacterial meningitis in adults/children
- Pneumonia
- Bacteremia
- Otisis media (middle ear infections in young children)
Streptococcus pneumoniae diseases (4 main examples)
-
Pneumonia: develops as bacteria multiply in alveolar spaces.
- Patients with splenic dysfunction = high mortality
- Otisis media: middle ear infections in young children
- Meningitis: in young children and adults
- Bacteremia
- Endocarditis can also occur
Viridans Streptococci
Tests:
Location:
Diseases:
Viridans Streptococci
Tests:
- Catalase (-)
- a-hemolytic
- Optochin resistant
Location:
- Oral cavity, also GI/GU tract
Diseases:
- S. mutans and S. mitis cause dental caries
- Dental manipulations can send bacteria into the blood where they can target the heart/valves. Repeated builup of these bacteria can lead to Subacute Endocarditis
Enterococcus
Tests:
Common examples:
Location:
Virulence:
Enterococcus
Tests:
- Catalase (-)
- y-hemolysis
- Grows in bile
- Growth in 6.5% NaaCl and (+) PYR status
Common examples:
- E. faecium
- E. faecalis
Location:
- Normal flora of intestinal tract (large and small intestine)
Virulence:
- Forms biofilms on tissues
- Antibiotic resistances
What patients are most at risk of developing Enterococcus infections?
Patients hospitalized for prolonged periods and treated with broad spectrum antibiotics, particularly cephalosporins
Enterococcus common infections/diseases
- UTIs
- Wound infections
- Endocarditis
- Bacteremia and sepsis following IV catheters
Streptococcus bovis (Group D Streptococcus)
Tests:
Location:
Diseases:
Streptococcus bovis (Group D Streptococcus)
Tests:
- Catalase (-)
- y-hemolysis
- Grows in bile
- Does not grow in 6.5% NaCl and has (-) PYR status
Location:
- Colonizes gut
Diseases:
- Bacteremia and sub-acute endocarditis in colon cancer patients
What antibiotic is Enterococcus resistant to?
Vancomycin
Enterococcus has also transmitted this resistance to Staphylococcus aureus
