deck_4139825 Flashcards by Stephen Murata

Compare and Contrast Staph vs Strep - Catalase?

Staph - catalase positive (bubble in presence of H2O2)Strep - catalase negative

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Compare and Contrast Staph vs Strep - colony structure?

Staph - cocci in clustersStrep - cocci in pairs/chains

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Compare and Contrast Staph vs Strep - medium for growth?

Staph - grows in minimal mediaStrep - requires complex media

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Compare and Contrast Staph vs Strep - optimal temperature?

For both staph and strep, they grow best between 35-37 Celsius

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Compare and Contrast Staph vs Strep - environmental conditions?

Staph = aerobic environment preferredStrep = anaerobic or CO2 atmosphere preferred

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Compare and Contrast Staph vs Strep - color/appearance on agar?

Staph = off color/whitishStrep = opaque

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Streptococcus belongs to what family and has what 3 subsets?

Family = Streptococcaceae3 groups = Pyogenic, pneumococci , viridans

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What are 3 ways to classify strep?

serologic properties - lancefield groups (letters of alphabet)2. hemolytic properties - beta/gamma/alpha3. biochem properties

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How does hemolytic classification of streptococci work?

Looks at amount hemolysis in blood agarBeta = complete hemolysisAlpha = incomplete hemolysisGamma = no hemolysis

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What are the 6 important species for strep?

Streptococcus pyogenes (Group A)2. Streptococcus agalactiae (Group B)3. Other Beta hemolytic streptococci4. Viridans group streptococci5. Nutritionally Deficient streptococci6. Streptococcus pneumoniae

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What are the clinical manifestations that can appear with Strep pyogenes infections?

Acute Pharyngitis (strep throat)2. Impetigo3. Erysipelas4. Necrotizing Fasciitis5. Toxic-Shock like Syndrome6. Pueperal Sepsis”7.” Scarlet Fever (is a complication of strep throat)

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Describe Acute pharyngitis caused by s pyogenes

strep throattransmitted by respiratory dropletsself limiting = will go away without antibiotics (but can result in sequelae)Reoccurs b/c strep has different m proteins and antibiotics have an antibody to a specific m protein

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Define Impetigo

localized skin disease that has a pustule with yellow crust that appears on face/extremitiesassociated with trauma/insect bitesseen in kids 2-5 yrs old

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Define erysipelas

Spreading erythema (superficial reddening) that’s well demarcatedget fever and lymphadenopathylesions on face/legs often accompany strep throat

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What is scarlet fever?

Complication of strep throat caused by eryrthrogenic toxintypically spares the face

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What are the clinical manifestations of scarlet fever?

Sore throatFeverBright red tongue with a “strawberry” appearance*Note: rash begins to fade 3-4 days after onset and desquamation begins

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What is necrotizing fasciitis?

Strep infection in deep subcutaneous tissues at the fascia level (spreads along fascial planes)There’s extensive destruction of muscle/fatMortality > 50%

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Erysipelas and Impetigo affect what layer (skin, subcutaneous, or muscle)?

skin

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What is the key clinical clue for necrotizing fasciitis?

Pain for necrotizing fasciitis is disproportionate to how it looks

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What is toxic shock-like syndrome?

Multisystem organ failure (heart, respiratory tract, kidney)SPE toxins are similar to Staph aureus TSST-1Cultures are usually positive for group A strep (unlike staph toxic shock)

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What is peuerperal sepsis?

After delivery/abortionOrganisms invade upper genital tract and cause a variety of symptoms

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What are the 2 post-streptococcal sequelae (can occur if you don’t treat strep throat)?

Rheumatic Fever and Acute Glomerulonephritis

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Describe Rheumatic Fever

Non-suppurative inflammatory disease that occurs 1-5 weeks after strep throatReoccurs in adulthoodHas characteristic cardiac lesions (Aschoff bodies) and valvular damageSymptoms = Fever, carditis, subcutaneous nodules, chorea, polyarthritis

Describe Acute glomerulonephritis

Edema, hypertension, hematuria, proteinuriaOccurs after skin / respiratory infection Certain M types are “nephritogenic”Antigen-antibody-complement complexes are deposited in glomeruli (seen on kidney biopsy)

What are 4 forms of virulence associated with Strep pyogenes?

1. Ability of the bacteria to adhere to the surface of the host cells2. Invade into the epithelial cells3. Avoid opsonization and phagocytosis4. Produce a variety of toxins and enzymes

What are 4 key virulence factors associated with Strep pyogenes?

Streptococcal pyrogenic exotoxins M proteinStreptolysins and Streptokinase

What are Streptococcal pyrogenic exotoxins (SPE)?

3 distinct heat labile toxins (A, B, C)Are “superantigens” that stimulate cytokine response leading to shock and organ failureStrep toxic shock-like syndromeResponsible for the rash in scarlet fever “erythrogenic exotoxin”

How do Streptolysins and Streptokinase enhance pathogenesis of S pyogenes?

allow spread of bacteria in tissues

How does M protein play a role in the virulence of S pyogenes?

binds epidermal cells and allows bacteria to survive (anti-phagocytic)Degrades complement C3b*Note: strains without M protein are AVIRULENT

How do you treat strep pyogenes?

Penicillin /ampicillin/amoxacillinDrug of choiceNo resistance worldwideCephalosporinsErythromycin (if there's penicillin allergy)

Streptococcus Agalactiae belongs to what group?

GBS...Group B Strep

What are the 2 forms of GBS infections that affect neonates? Describe each

Early Onset neonatal disease = 1st week of life --> Bacteremia, pneumonia, or meningitis Late onset neonatal disease = 1 week-3 months old --> Bacteremia with meningitis

How does neonate GBS infection occur?

Maternal colonization of vagina or rectum exposes baby at deliveryLack of protective maternal antibodySialic acid on polysaccharide capsule inhibits C’ allowing organisms to multiplyThus...vaginal/rectal swabs are collected between 35-37 weeks gestation

How is GBS treated?

Penicillin / ampicillin = drug of choiceAdd gentamicin to enhance killingFor culture positive pregnant women during labor -- penicillin / ampicillin to prevent neonatal disease (KNOW)Clindamycin if penicillin allergy

What are the limitations of Rapid Group A Detection kits (KNOW)

Good specificity but sensitivity is only 70%If it’s positive you can be sure they have group a strep = good specificityIf it’s negative, it can still be there…false negativeSo if you have a negative rapid antigen test you always do a backup culture

Isolation of S. bovis from blood is associated with ______

carcinoma of colon

The Strep Milleri group includes which 3 species of strep?

S. anginosusS. constellatusS. intermedius*Note: these pyogenic bacteria are identified by characteristic caramel (butterscotch) odor when cultured on agar plates

The nutritionally deficient streptococci include? Have what vitamin deficiency?

AbiotrophiaGranulicatella*Vitamin B6 deficient

A 7-year-old child presents with a fever, pain in his ankles, knees and wrist, and a new heart murmur. His mother said that he complained of a “sore throat” last month, but the symptoms resolved without taking him to the pediatrician. A rapid screening test for strep throat is negative. His most likely diagnosis is:

Rheumatic Fever

Are strep pneumoniae gram + or -? what about catalase?

Gram positiveCatalase negative

If you suspect strep pneumoniae, what tests do you run?

Always do both a sputum and blood culture

How do you identify strep pneumoniae in the lab?

Gram stainAgar platesOptochin testBile solubility

How do you identify strep pneumoniae from a gram stain?

Gram positive and lancet shaped diplococci (sometimes seen alone or in chains)In csf = menigitisIn sputum = pneumonia

How do you identify strep pneumoniae from an agar plate?

can be runny mucoid colony or have flat dime shaped morphology with indented centers

What are the breakpoints for treating strep pneumoniae with penicillin?

If you give penicillin for meningitis, it won't cross BBB well so a low MIC is needed (.06 or less) for it to be susceptibleIf non-meningeal target – MIC can be as high as 2 (sepsis or pneumonia)

What are alternatives to penicillin for strep pneumoniae?

If allergic…uses macrolides or fluoroquinolones

What are the 2 major species of enterococci causing infection in humans?

E. FaecalisE. Faecium*enterococcus was formally group d streptococciThey are inherently resistant to many commonly used antibiotics

Are enterococci gram + or -?

Gram positive

What is PYR?

used in testing for enterococci, which are PYR positive (get a red color)

What infections are seen with enterococci?

Urinary tract Mixed bacterial wound infections and decubitiSepsis, endocarditis, meningitis (rare)Second most common nosocomial pathogen

Where is enterococci found and how is it spread?

Originates in flora of bowelTransferred between patientsAcquired thru consumption of contaminated food/water

What is VRE?

Vancomycin Resistant Enterococci

What are the 3 VRE phenotypes?

A - plasmid mediated, highly resistantB - chromosomal, high or low resistanceC - intrinsic intermediate level in E. gallinarum and casseliflavus (casseliflavus = yellow colonies)*Treat via linezolid

How are enterococcal infections treated? (know!)

Intrinsically resistant to all cephalosporins, trimethoprim-sulfa, aminoglycosidesFaecalis is susceptible to penicillin/ampFaecium is resistant to penicillin/amp

An organism is isolated from the blood of a 65 year-old male patient with a diagnosis of probable bacterial endocarditis. The organism displays streptococcus-like morphology on gram stain and is catalase-negative. On blood agar the colonies appear gamma hemolytic and are PYR positive. Patient was being treated with vancomycin plus an aminoglycoside with no response. This isolate is likely to be ____ species

Enterococcus