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35 Cards in this Set

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*STREPTOCOCCUS PYOGENES CHARACTERISTICS

What are the characteristics of STREP?

A) Morphology?

B) How do the different classes of STREP differ?
A) MORPHOLOGY: gram + cocci, often found in a chain, anaerobes but are aerotolerant

B) Some important streptococci are classed as GROUP A BETA HEMOLYTIC (strep pyogenes)- - each with a variety of invasive systemic infections and local infection followed by sequelae
C) What do development and identification of STREP emphasize?
C)
1) Microscopic observatoin
2) Description of zone HEMOLYSIS
3) Detecton of cell wall carbohydrate antigens (C- carbohydrate)
4) Detection of cell wall protein antigens further subdivided by immunological analysis of their M proteins (M proteins= fimbrae)
What are the three different types of hemolysis?
1) GAMMA HEMOLYSIS: no hemolysis

2) ALPHA HEMOLYSIS: cloudy green zone, that contains intact red cells with an altered green heme pigment

3) BETA HEMOLYSIS: clear one in which all red cells are lysed
* See diagram for classificaiton of STREP PYOGENES
*
*What are the (8) different types of ACUTE DISEASES CAUSED BY GROUP A BETA HEMOLYTIC STREPTOCOCCI?
1) PUERPERAL FEVER

2) ACUTE PHARYNGITIS AND TONSILITIS

3) SCARLET FEVER

4) IMPETIGO

5) ERYSIPELIS

6) STREPTOCOCCAL TOXIC SHOCK SYNDROME

7) NECROTIZING FASCITIS

8) OTHERS: sinusitis, mastoiditis, otitis media, pneumonia etc...
1) PUERPERAL FEVER
an infection of the uterus immediately after childbirth

often common and frequently fatal

now uncommon in developed countries
2) ACUTE PHARYNGITIS AND TONSILITIS
mild form called "strep- throat"

other symptoms incude fever, chills, malaise, elevated white cell count etc

adequate treatment is essential to prevent rheumatic fever
3) SCARLET FEVER
some pharyngitis caused by strep pyogenes is accompanied by a CUTANEOUS RASH of scarlet fever caused by exotixin.

the three types of toxin are speA, speB, speC

immunity to the toxin does not mean immunity to infection
4) IMPETIGO
minor superficial skin lesion underlying tissue
5) ERYSIPELIS
a severe cellulitis of the dermis and underlying tissues
6) STREPTOCOCCAL TOXIC SHOCK SYNDROME
a life threatening syndrome characterized by severe hypotension (systolic below 90mmhg)

the principal cause of symptoms is streptococcal pyrogenic exotoxins A, B, C and act as SUPERANTIGENS that cause over production of lymphokines
7) NECROTIZING FASCITIS
aka dissecting fascitis

a highly invasive strain of s. pyogenes that produces rapidly progressing highly destructive muscle infections that are life- threatening

surgery may be needed to supplement ab treatment
8) OTHERS: sinusitis, mastoiditis, otitis media, pneumonia etc...
*
*PATHOGENESIS OF INFECTIONS CAUSED BY STREP PYOGENES

What are 4 things that contribute to the INVASIVENESS of STREP PYOGENES?
1) STREPTOLYSINS: it's a hemolytic enzyme that also lyses or injures other cells- - cause BETA hemolysis on blood agar

STREPTOLYSIN O: oxygen-labile and functions only in reductin atmosphere

STREPTOLYSIN S: poorly antigenic and stable in oxygen

2) STREPTOKINASE: triggers the proteolytic system of the blood that destroys fibrin clots

3) DNase

4) and 15 other extracellular products
What two factors play role because of their ANTIPHAGOCYTIC activity?
1) HYALURONIC ACID CAPSULE: because capsuleless bacteria are not pathogenic

2) M- PROTEINS: extend from the bacterial membrane through the capsule and into the extracellular medium

EVIDENCE: strains that make large amounts of M- protein result in immunity to streptococci of that particular M-type
What three factors have conclusively played roles in the clinical presentation of the disease?
1) speA, speB, speC, which cause rash in scarlet fever
EVIDENCE: ab against one particular exotoxin prevents scarlet fever caused by that exotoxin

2) speA, speB, speC which causes strep toxic shock syndrome
EVIDENCE: ab against one particular exotoxin will prevent toxic shock in infections with s. pyogenes producing that toxin
What are two examples of SEQUELAE OF S. PYOGENES IN GROUP A BETA HEMOLYTIC INFECTIONS? (1)

When does it occur?

What kinds of symptoms do patients experience?

What is the function of M- ANTIGEN?

Why is it important to treat one with penecillin?
1) RHEUMATIC FEVER: two or three weeks from a strep sore throat some patients may experience heart and skin lesions that do no result form bacterial growth from these sites

because M- protein antigens elicit ab that cross- react with ags present in the heat and with ags in the joint

not all group a beta hemolytic streptococci cause rheumatic fever, but some cause fevers more severe than others

it is a rare disease today

this is why it's important to treat strep sore throats with PENICILLIN

all manifestations of acute rheumatic fever are short term except for cardiac damage particularly to the mitral and aortic valves

protected from reinfection with prophylactic penicillin
(2) SECOND EXAMPLE OF SEQUELAE

When does it occur?

What kinds of symptoms might a patient experience?
2) ACUTE GLOMERULONEPHRITIS: it occurs 1 week after infection of skin or throat with one of a few M- protein types of group A beta hemolytic strep

some patients experience hematuria, edema, and other symptoms of glomerulonephritis

mechanism is deposition of immune complexes that contain bacterial ags
*What are steps in LABORATORY DIAGNOSIS? (4)
1) elaborate antigenic typing is NOT routinely done

2) labs look for:
a) beta hemolysis on agar plates
b) gram +ve streptococci
c) sensitive to bacitracin, a property that correlates well with assignment to group A, the other beta- hemolytic streoptococci

3) Physicians use tiny plastic beads coated with anti- group A ab, and when incubated briefly with exudate, they will link bacteria and yield a colored product

4) A high titer of ab to STREPTOLYSIN O suggests a recent infection
EPIDEMIOLOGY:

*A) What is the mode of TRANSMISSION?

B) What % of people are carriers?
A) Respiratory droplets are the usual mode of transmission of strep pharyngitis- - but need a large inoculum to get infected

B) Approximately 5-10% of normal individuals carry group A hemolytic streptococci in the pharynx or nose

NASAL CARRIERS are MORE INFECTIOUS

Chronically carried strains are often less pathogenic, as the bacteria producing lots of M- protein are usually opsonized
How do you TREAT S. PYOGENES?
PENICILLIN
*DIFFERENT TYPES OF STREPTOCOCCUS PYOGENES

What are they?
1) GROUP B STREPTOCOCCI

2) ENTEROCOCCI (GROUP D STREPTOCOCCI)

3) OTHER

4) VIRIDANS STREPTOCOCCI (ALPHA HEMOLYTIC)

5) STREPTOCOCCUS PNEUMONIAE

6) LITERIA MONOCYTOGENES

7) LITERIA MONOCYTOGENES AS A FACULTATIVE INTRACELLULAR BACTERIUM

8) ANTHRAX
1) GROUP B STREPTOCOCCI

A) Who is affected by this?

B) What are 2 epidemiologic patterns seen?

C) What is it correlated with?

D) What other population does it affect?
A) was a minor cause of disease up until 40 years ago, and is now it is a major cause of neonatal infections: meningitis, pneumonia, and death

B)
1) EARLY ONSET: occurs within the first week and is correlated with infection from vaginal bacteria during birth

may be fulminating and rapidly fatal despite prompt ab therapy

identified pregnant women are treated with penicillin

2) LATE ONSET: correlated with infant to infant spread within a nursery with less fulminant course and lower mortality

C) Neonatal illness is correlated with lack of maternal ab at the time of delivery- - so vaginal infections acquired shortly before delivery put the newborn at risk

D) Also highly incident in people >65 years old
2) ENTEROCOCCI (GROUP D STREPTOCOCCI) (4)

A) Most imp spp

B) Common inhabitant of?

C) Ab?
A) Enterococcus faecalis

B) Common inhabitant of GI tract

C) Resistant to most ab including VANCOMYCIN

* NOTE: also cause of UTI's
3) OTHER
Groups G C D cause various infections in children and adults
4) VIRIDANS STREPTOCOCCI (ALPHA HEMOLYTIC)

A) What parts of the body do they inhabit?

B) What is it the most frequent cause of?
A) Inhabit the MOUTH, NOSE, and PHARYNX

B) alpha- hemolytic streptococci are the most frequent cause of INFECTIVE ENDOCARDITIS

can produce transient bacteremia through minor oral trauma, even during chewing tough meat

bacteria set up a focus infection on a pre-existing minor lesion on the endocardium- - and multiply and yield a mass of fibrin and platelets

VEGETATION: mass attached to valves detected by ultrasound

if left untreated, it may be fatal
5) STREPTOCOCCUS PNEUMONIAE

A) What are a few characteristics (3)

What is the QUELLING REACTION?
1) Gram + diplococci, and are slightly lancet shaped, with the points facing outwards

2) Alpha hemolytic and may be hard to distinguish from VIRIDANS strep

the most used test to make this distinction is OPTOCHIN SENSITIVITY of the pneumococcus

3) Biochemically and genetically related to other streptococci

An IMPORTANT feature of pneumococci is the presence of a large polysaccharide capsule

Different pneumococcal types can be identified via QUELLING REACTION when specific ab reacts with a pneumococcal capsule, the capsule swells enough to allow the differce to be seen microscopically
B) What is the PATHOGENSIS of pneumococcus?

1) Typical disease caused?

2) Common inhabitant of?

3) Why does it not infect the LOWER RESPIRATORY TRACT often?

4) Where do they grow?

5) What happens if actions of #3 fail?
1) Most typical pneumococcal disease is pneumonia

2) pneumoccoci are common inhabitants of the throat and are a usual source of pulmonary infection

the resident bacteria are not transient, for the same type can be recovered after a long period from the same individual

the bacterial pop us generally small and ab to capsule polysaccharide is generally not stimulated

3)
a) aspiration of mucus is rare
b) cilia is alwaus driving mucus UP the respiratory tract
c) alveolar macs can phagocytize limited number of bacteria

4) Pneumococci grow only extracellularly, and once they are phagocytosed, they are killed. The CAPSULE does hinder phagocytosis, and capsuleless mutants are NONPATHOGENIC

** the presence of anti-capsulat ab greatly promotes phagocytosis- - called SURFACE PHAGOCYTOSIS and works well in a dry
alveolus and poorly in the presence of alveolar edema

5) If you get failure in mechanisms mentioned #3, they escape surface pahgocytosis and multiply, serious fluid enters the alveoili- - and provides a good source of medium and hinders surface phagocytosis (see notes!!!)
C) What is PNEUMOCOCCAL PNEUMONIA?
1) it is the most frequent form of bacterial pneumonia

2) can be preceded by nonspecific prodromal symptoms, followed by chills and high fever

3) untreated cases progress to LOBAR DISTRIBUTION- - but doesn't happen if treat with antibiotics

4) high leukocytosis is common

5) bacteremia in 20% of cases

6) fatal in 5- 20% of cases even with appropriate antibiotic treatment

7) untreated cases often produce a dramatic drop in fever and sense of well- being

8) immuno- deficient ind are at much higher risk at getting disease
D) Laboratory Diagnosis
1) Microscopic examination

2) Multiple antibiotic resistance is frequent- - and sensitivity testing is required
E) Other Pneumococcal infections?
* see notes!
F) What are a few steps in PREVENTION?
* see notes!
6) LITERIA MONOCYTOGENES
*
7) LITERIA MONOCYTOGENES AS A FACULTATIVE INTRACELLULAR BACTERIUM
*
8) ANTHRAX
*