Gram+ Cocci Flashcards
what are the 3 major genera of Gram+ Cocci?
- staphylococci
- streptococci
- enterococci
in what formation (clusters or chains) do staphylococci and streptococci grow in, respectively, and why is this?
staphylococci: clusters, because they divide in random planes
streptococci: chains, because they divide in a single plane (same direction)
both appear blue/purple, because they are Gram+
what kind of bacteria family does this describe?
- Gram+ cocci
- grow in clusters
- resistant to heat and drying, persist on fomites
- normal skin or nasal flora
- common wound and nosocomial infections
staphylocci
*note that fomites are simply objects or materials that can carry infection
which of these is Catalase positive, streptococci or staphylococci?
(remember that these are both families of Gram+ cocci)
all pathogenic STAPHylococci are CATALASE POSITIVE
how are staphylococci divided?
(2 categories, hint - a major and then sort of everything else)
- coagulase positive: Staph. aureus
- coagulase negative (CoNS/CNS): all other pathogenic strains (S. epidermidis, S. saprophyticus)
*note that coagulase clots plasma
what species of bacteria does this describe?
- appear as golden colonies on agar
- coagulase positive
- normal flora of anterior nares (1/3 people)
- considered most common bacterial human pathogen
staphylococcus aureus !
describe the function of the following virulence factors of Staph. aureus:
a. Protein A
b. invasins (staphylokinase, collagenase, lipase)
c. cytotoxins (hemolysins, PVL/Leukocidin)
d. superantigen exotoxins (TSST-1, enterotoxin, exfoliatin)
a. Protein A: binds Fc portion of antibodies, escapes immune response (Fc receptors on phagocytes cannot bind)
b. invasins: for invading deep tissue
c. cytotoxins: lyse human cells
d. superantigen exotoxins: cause polyclonal T cell activation (lots of cytokines released, inflammation)
this surface protein of Staph. aureus binds the Fc portion of antibodies to evade the immune system. what is?
Protein A: anti-opsonization effect
*remember that Fc receptors are present on phagocytes, and thus their action will be blocked by Protein A
what are 4 important invasins that may be present in Staph. aureus? (Gram+ cocci)
invasins: for invading deep tissue
- staphylokinase
- collagenase
- lipase
- hyaluronidase
what are 2 important cytotoxins that may be present in Staph. aureus? (Gram+ cocci)
cytotoxins: lyse human cells
- hemolysins: lyse erythrocytes (example: alpha-toxin)
- PVL (Panton-Valentine Leukocidin): lyse PMNs, produced predominantly by CA-MRSA
*CA-MRSA = community-acquired MRSA
what are 3 important cell surface virulence factors of Staph. aureus? (Gram+ cocci)
- Protein A: anti-opsonin effect by binding Fc portion of antibodies
- capsule: antiphagocytic polysaccharide
- adhesins: facilitate attachment to host cells/tissue
what are 3 important superantigen toxins that may be present in Staph. aureus? (Gram+ cocci)
superantigen exotoxins: cause non-specific polyclonal T cell activation via cross-linking MHC to TCR
- TSST-1 (toxic shock syndrome toxin)
- enterotoxins (food poisoning)
- exfoliatin (“scalded skin syndrome”)
what are the SSTI clinical manifestations of Staph. aureus infection (4)? (Gram+ cocci)
SSTIs: Skin and Soft Tissue Infections; usually require surgical debridement with antibiotics, most common presentation of staphylococcal infections
- furuncles: small pus-filled local infections
- carbuncles: larger skin abscesses
- impetigo: spreading, crusted skin infection
- cellulitis: deep skin infection
FUR and CARs for UNCLES is IMPEritive to buy with your CELL
most common cause of bone infections in children (osteomyelitis)
staph. aureus infection (Gram+ cocci)
S. aureus metastasis of superficial infections may cause:
- osteomyelitis
- septic joint/ septic arthritis (esp. children)
- pneumonia (often follows viral influenza, esp. hospitalized patients)
- endocarditis (associated with IV drug use, rapid onset of vegetation on valve - usually tricsupid)
- bacteremia and septicemia
what are the 3 most common toxinoses of staph. aureus infection (Gram+ cocci)?
- Toxic Shock Syndrome: TSST-1 exotoxin —> high fever, hypotension, rash, multi-organ failure, desquamation (palms, soles)
- food poisoning (Gastroenteritis): heat stable enterotoxins on food —> acute onset of GI distress
- Scalded Skin Syndrome (neonates, children): exfoliatin —> red flush, bullae (blisters), bulbous impetigo, desquamation
note that toxinoses may be associated with “negative cultures” because it is released exotoxin causing symptoms
what type of bacteria have endotoxins?
Gram- (typically LPS)
[Gram+ have exotoxins]
generally speaking, what are the 3 categories of clinical manifestations of Staph. aureus? (Gram+ cocci)
- SSTIs: skin and soft tissue infections
- infections of other tissues (osteomyelitis, septic joint, endocarditis, pneumonia, septicemia)
- toxinoses (superantigens): toxic shock, food poisoning, scalded skin syndrome
what kind of drugs are methicillin, oxacillin, and nafcillin?
methicillin, oxacillin, and nafcillin are “anti-staphylococcal penicillins”
contain bulky side groups that prevent binding of penicillinase/ beta-lactamase by staphylococcus
[of course remember that there is now MRSA - methicillin resistant S. aureus]
what are the 3 important penicillinase-resistant penicillins, which were developed after almost all clinical strains of staphylococcus developed penicillin resistance (via penicillinase/ beta-lactamase)?
nom nom nom bacteria yum
- nafcillin
- oxacillin
- methicillin (watch out for MRSA!)
[note that MRSA resistance protein PBP2a is encoded by the mec A gene]
what confers methicillin resistance in MRSA?
MRSA = methicillin resistant Staph. aureus
PBP2a (penicillin binding protein), encoded by mec A gene
HA-MRSA vs CA-MRSA
hospital-acquired MRSA: tend to be resistant to additional antibiotics (tetracycline and clindamycin), but less virulent
community acquired MRSA: susceptible to broader range of antibiotics, but more virulent (PVL/Panton-Valentine Leukocidin gene present)
how are we treating Staph. aureus infections these days?
if MSSA (methicillin-sensitive SA) —> treat with oxacillin or nafcillin (methicillin not used clinically anymore)
but… most clinical isolates are MRSA
so…
vancomycin is first line of treatment for MRSA
[note that VISA and VRSA are on the rise]
vancomycin is the first line of treatment for _____ infections
MRSA
where are the 2 important coagulase negative staphylococci found? (must be able to name them first!)
- Staph. epidermidis: normal skin flora
- Staph. saprophyticus: normal vaginal flora
which bacteria does this describe?
- produces cell surface polysaccharide “slime” that adheres to bioprosthetics
- frequently involved in nosocomial and opportunistic infections (catheters, medical devices, IV lines)
- most are highly resistant to penicillins and methicillins
staph. epidermis (Gram+ cocci, coagulase negative): major component of normal skin flora, causes wound infections through broken skin, relatively less virulent
which bacteria does this describe?
- causes UTI and cystitis in females
- natural resistance to novobiocin
- sensitive to penicillin/oxacillin
Staph. saprophyticus (Gram+ cocci, coagulase negative): normal vaginal flora
what kind of infections does Staph. saprophyticus cause, and what distinguishes it from other coagulase negative staphylocci and staph. aureus?
Staph. saprophyticus (Gram+ cocci, coagulase negative): normal vaginal flora
causes UTI and cystitis in females
has natural resistance to novobiocin
(but sensitive to penicillin/oxacillin)
how would you treat Staph. epidermidis?
Staph. epidermidis: Gram+ cocci, coagulase negative, normal skin flora
highly resistant to antibiotics —> treat with vancomycin
You are culturing 2 unknown bacterias. One one plate, you note golden colonies, which contain cocci in clusters. Further testing reveals they are Gram+, catalase positive, and coagulase positive. (plate 1)
On the other plate, you note cocci in clusters. Further testing reveals they are Gram+, catalase positive, coagulase negative, and novobiocin resistant. (plate 2)
What is the identity of these cultures?
plate 1: Staph. aureus
plate 2: Staph. saprophyticus
(why is it not Staph. epidermidis? because the culture is novobiocin resistant, a unique feature of S. saprophyticus)
what family of bacteria does this describe?
- Gram+ cocci arranged in chains or pairs
- catalase negative
- mostly fastidious (require enriched media)
- sensitive to drying and heat
- classified based on hemolysis pattern on blood agar and cell wall antigen
Streptococcus
*note that because they are fastidious, they will not grow well outside the human body (not found on fomites)
One way to classify streptococcus is by hemolysis pattern on blood agar. Describe this system of categorization.
beta-hemolysis: complete hemolysis, yellow zone around colony
alpha-hemolysis: partial hemolysis, green/brown zone around colony
gamma-hemolysis: no hemolysis
describe how Streptococcus are classified by cell wall antigen
Streptococcus Lancefield Groups: based on antigen cell wall polysaccharide called C-carbohydrate
groups A-U: reaction with specific antisera in slide agglutination assay
Groups A, B, D, and “none” are common human pathogens
*note that Group A is not a group but in fact a strain that has Group A on its surface (and this strain is in fact Strep. pyogenes fyi)
what are the important streptococci species to know in the following categories:
a. beta hemolytic (2)
b. alpha hemolytic (2)
c. gamma hemolytic (1)
beta hemolytic:
- Strep. pyogenes / Group A (bacitracin sensitive)
- Strep. agalactiae / Group B (bacitracin resistant)
alpha hemolytic (non-Lancefield):
- Strep. pneumoniae (optochin sensitive)
- Viridins group (optochin resistant)
gamma hemolytic:
- Strep. bovis / Group D
which bacteria has the following?
- M protein (virulence factor)
- Streptolysin O and S
- Streptokinase
- pyrogenic exotoxins A, B, C
GAS (Group A Streptococci): aka Strep. pyogenes (Gram+ cocci)
- M protein: highly variable antigenic, essential for infection
- Streptolysin O and S: lyse RBCs (causes beta hemolysis) - measure with ASO titers
- Streptococcal pyrogenic exotoxins (SPE): superantigen toxins
what are ASO titers used for?
ASO titers measure antibodies against streptolysin O or S, which cause beta hemolysis (lyse RBC)
released by GAS (Group A Strep), aka Strep. pyogenes (Gram+ cocci)
positive titers indicate recent infection
this virulence factor is highly variable antigenic and essential for infection by GAS (Strep. pyogenes, Gram+ cocci). what is?
M protein: fimbrae, antiphagocytic, inhibits complement
what are 4 important clinical manifestations of GAS/Strep. pyogenes infection?
- Streptococcal pharyngitis: “strep throat” - purulent pharynx inflammation, can be associated with scarlet fever
- Streptococcal skin infections: lymphangitis, erysipelas and cellulitis, necrotizing fasciitis
- Streptococcal toxic shock syndrome: via SPE superantigens
- post-infection sequelae of GAS infection: antibody mediated (Rheumatic fever, acute glomerulonephritis)
what are possible streptococcal skin infections caused by GAS (Strep. pyogenes)?
(hint - 3, with possible severe 4th)
- lymphangitis: red streaks stretching from infected area
- erysipelas and (3.) cellulitis —> can lead to (4.) necrotizing fasciitis
what toxin mediates streptococcal toxic shock syndrome caused by GAS (Strep. pyogenes) infection?
SPE: streptococcal pyrogenic exotoxin, acts as superantigen
what are the 2 major post-infection sequelae of GAS (Strep. pyogenes) infection?
antibody mediated
- Acute Rheumatic Fever (ARF): via molecular mimicry to antibodies against M protein —> myocarditis, arthritis, fever, chorea, progression to chronic rheumatic heart disease
- Acute Poststreptococcal Glomerulonephritis (APSGN): Type III hypersensitivity (immune complexes cause kidney damage) —> hematouria, proteinuria, oliguria, hypervolemia
Pt is a 45yo M presenting to the ED with fever and symptoms of myocarditis, arthritis, and chorea. PMH is significant for pharyngitis 3 weeks ago.
What is going on? What are your concerns?
Patient had pharyngitis from GAS (Strep. pyogenes) infection, and body produced antibodies against M protein (virulent factor, essential for GAS infection).
These cross reacted with body’s own cells (molecular mimicry), causing acute rheumatic fever (ARF).
Can progress to chronic rheumatic heart disease if left untreated.
[can occur 2-3 weeks after pharyngitis, usually only when initial infection is untreated]
Pt is a 17yo F presenting to the ED with hematuria, proteinuria, oliguria, and hypervolemia. PMH is significant for pharyngitis 1 week ago.
What is going on? What type of reaction is this?
Patient had GAS (Strep. pyogenes) infection, which caused Type III hypersensitivity - immune complexes deposited in kidney.
This caused Acute Poststreptococcal Glomerulonephritis (APSGN) —> dark urine, protein in urine, lower urine production, fluid retention
[can occur 1-2 weeks after pharyngitis OR skin infection by GAS]
how are we treating GAS (Strep. pyogenes) infection these days?
what if a patient had a skin infection, but you don’t know if it’s strep. or staph.?
GAS are uniformly penicillin sensitive
*note that if a patient has skin infection and you don’t know if it’s staph. or strep., you’d probably start with something anti-staph. since those are penicillin resistance, and this would work on strep. as well. If you know it’s a strep. infection you could go to penicillin right away.
describe the epidemiology for Strep. pyogenes (GAS) infection - where it’s found, how it’s transmitted, portal of entry, predominant group affected?
Strep. pyogenes (GAS):
- inhabits throat, nasopharynx, occasionally skin
- transmitted via contact, droplets, food (spreads easily in crowds)
- enters via skin or pharynx
- children are predominant group affected for cutaneous and throat infections (1/3 of all bacterial pharyngitis in children due to GAS)
*note systemic and progressive sequelae possible if untreated
which bacteria does this describe?
- normal flora of female reproductive tract
- colonization can be intermittent, transient, or persistent
- leading cause of neonatal sepsis, meningitis, or pneumonia (pregnant women are screened for colonization)
- bacitracin resistant
Group B Streptococci: Strep. agalactiae
beta hemolytic, Gram+ cocci
[note if pregnant woman has positive screen, treat with antibiotic intrapartum]
what is the leading cause of neonatal sepsis, meningitis, and pneumonia?
Group B Streptococci (Strep. agalactiae) infection from colonization in mother
remember that Strep. agalactiae is a normal flora of female reproductive tract (Gram+ cocci, beta hemolytic, bacitracin resistant)
what are the names of GAS and GBS bacteria and how can you distinguish between them in culture?
GAS (Group A streptococci) = Strep. pyogenes —> bacitracin sensitive
GBS (Group B streptococci) = Strep. agalactiae —> bacitracin resistant
This large complex group of bacteria includes S. mitis, S. mutans, S. oralis, S. salivarus, S. sanguis, and S. milleri.
As their names may suggest, they are widespread oral inhabitants (gums and teeth). They are not very invasive but may enter during dental or oral surgery.
Therefore, they may cause dental caries or subacute infective endocarditis.
What is?
Viridans Group Streptococci: basically all alpha hemolytic Streptococci other than S. pneumoniae
“non-Lancefield” group, Gram+ cocci
optochin resistant
(S. pneumoniae is sensitive)
contrast endocarditis called by Viridans Group (alpha hemolytic Streptococci) vs Strep. aureus (beta hemolytic Streptococci)
Viridans - causes subacute ineffective endocarditis: slower progression, low virulence, originates in mouth, higher risk for patients with history of heart transplant or prosthetic valve
S. aureus - causes acute endocarditis: large and rapidly growing vegetation, high virulence, originates in skin/nares, can affect healthy or damaged valves
how would you categorize Streptococci pneumoniae, and how does it appear under the microscope?
alpha hemolytic Gram+ Streptococci, optochin sensitive, “non-Lancefield” group
appear as Lancet (church window) shaped cells arranged in pairs (diplococci)
what is the important virulence factor of streptococci pneuomniae (alpha hemolytic, Gram+ diplococci)?
polysaccharide capsule: antiphagocytic and antigenic, appears glossy on plate culture
heavily encapsulated forms are associated with more severe disease
85+ capsule serotypes
where does streptococci pneumoniae infection come from? (alpha hemolytic, Gram+ diplococci)
normal flora in nasopharynx of carriers, infections often endogenous (from yourself)
delicate organism, doesn’t survive well outside of habitat
among susceptible patients includes those who have had splenectomy or with sickle cell disease (functionally asplenic) —> leading cause of Overwhelming Post-Splenectomy Infections (OPSI)
what are 4 important clinical manifestations of streptococci pneumoniae infection? (Gram+ diplococci, alpha hemolytic, optochin sensitive)
- lobar pneumonia (esp. community acquired bacterial pneumonia)
- otitis media (most frequent ear infection in children)
- meningitis
- bacteremia and sepsis (esp. asplenic patients)
a bacterial colony shows alpha hemolysis and sensitivity to optochin
what is it
streptococci pneumoniae: Gram+ diplococci
intermediate level resistance to penicillin is emerging in strep. pneumoniae
how is this mediated and what are we now using to treat?
resistance mediated by expression of mosaic variants of PBP proteins (target of penicillin)
resistant strains are sensitive to 3rd generation cephalosporins such as cefotaxime or ceftriaxone
what are the 2 vaccines available for Strep. pneumoniae?
- Pneumovax: 23-valent polysaccharide vaccine (PPV) - protects against 23 serotypes, recommended for older adults or high risk individuals (older vaccine)
- Prevnar 13: pneumococcal conjugate vaccine (polysaccharide conjugated to protein) - more effective because proteins are more immunogenic, protects against 13 serotypes
what bacteria does this describe?
- normal GI flora, can grow in bile
- non(gamma)hemolytic, but sometimes alpha-hemolytic
- now called S. gallolyticus
- bacteremia associated with GI malignancy and colon cancer
Streptococci bovis (Group D Streptococci)
aka “non-enterococcal Group D strep”
bacteremia caused by ____ is associated with GI malignancy and colon cancer
Streptococci bovis (Group D, gamma hemolytic): normal GI flora, can grow in bile, now called S. gallolyticus
[note it can also be alpha-hemolytic]
Enterococci are genetically distinct from Streptococci but have Group ___ antigen
what are the 2 most clinically relevant species?
Enterococci have Group D antigen
- E. faecalis
- E. faecium
common inhabitants of GI tract
gamma or alpha hemolytic, possibly beta but infrequent
where are enterococcal bacteria found? are they virulent? what kind of diseases do they cause?
enterococcal bacteria: Gram+ cocci, Group D antigen (but distinct from streptococcus)
normal GI flora, not very virulent but persist well on fomites (nosocomial pathogens - multi-drug resistance)
cause opportunistic UTI, intra-abdominal abscesses/biliary infections, can lead to endocarditis or bacteremia/sepsis
why is it clinically relevant that enterococci have acquired vancomycin resistance, considering it does not usually infect healthy individuals?
genes encoding vancomycin resistance are present on transposable element - the concern is this gene being transferred to MRSA (methicillin resistant Staph. aureus)
what 2 tests are used to identify enterococci? which of these is more specific? (Group D, Gram+ cocci)
- Bile Esculin Test: can grow in bile and hydrolyze esculin (characteristic of Group D Strep. and Enterococci)
- growth in NaCl broth: enterococci are salt-resistant (differentiates from S. bovis)
You’re trying to identify an unknown bacteria. First, you complete a Bile Esculin Test, which is positive. Then, you try growing the bacteria in a 6.5% NaCl broth, which leads to no growth.
What do you have?
Bile Esculin Test: Group D strep. and enterococci can grow in 40% bile and hydrolyze esculin
however, only enterococci are salt resistant
so what you have is Streptococci bovis
T/F: sensitivity testing is needed for treatment of enterococci
explain your answer
TRUE because enterococci is resistant to many drugs
Lab results show Gram+ cocci growing in chains, which are catalase negative, beta-hemolytic, and bacitracin sensitive.
what is it
Streptococci pyogenes (GAS - Group A Streptococci)
Lab results show catalase negative bacteria which are beta hemolytic and bacitracin resistant.
what is it
Streptococci agalactiae (Group B)
leading cause of neonatal meningitis, pneumonia, and sepsis
Lab results show Gram+ diplococci which are catalase negative, alpha hemolytic, optochin and bile sensitive, and positive for Quelling (swelling) reaction in culture
what is it
Streptococci pneumoniae
lab results show catalase negative bacteria which are alpha hemolytic and optochin resistant
what is it
viridans group streptococci
cause subacute endocarditis and dental caries
lab results show bacteria that grow in both 40% bile and 6.5% NaCl
what is it
Group D enterococci: E. faecalis or E. faecium
