Lippincott chapter 9 Flashcards
Short describe Streptococci:
- gram-positive
- nonmotile
- catalase negative
What is the shape of the Streptococcus and Enterococcus?
- ovoid to spherical in shape
- occur as pairs or chains
- most are aerotolerant anaerobes (they grow even in the presence of oxygen)
What medium is used for the isolation of Streptococcus and Enterococcus?
blood enriched medium
What are the diseases caused by the group A Streptococci (streptococcus pyogenes)?
acute infection of the throat and skin
What is caused by group B streptococci (Streptocccus agalactiae)?
- female genital tract colonization, resulting in neonatal sepsis
What is caused by Streptocccus pneumoniae?
- pneumonia
- otitis media
- meningitis
What is caused by the viridans group of streptococci?
- endocarditis
How are the Streptoccci classified?
for example by the:
- hemolytic properties of the organisms
- the presence of surface antigens determined by immunologic assays
What does the α- Hemolytic streptococci cause on the blood agar?
α- Hemolytic streptococci cause a chemical change in the hemoglobin red cells in blood agar, resulting in the appearance of a green pigment that forms a ring around the colony
γ- Hemolytic:
γ- Hemolytic streptococci is a term applied to streptococci that cause no color change or lysis or red blood cells
C-substances:
many species of streptococci have polysaccharide in their cell walls known as C-substance, which is an antigeninc, and easily extractable with dilute acid.
Lancefield scheme:
The Lancefield scheme classifies primarily β-hemolytic streptococci into groups A through U on the basis of their C-substances
β-Hemolytic streptococci:
cause gross lysis of RBCs, resulting in a clear ring around the colony.
What are the most important groups β-Hemolytic streptococci?
Type A and B
what can some strains of S. pyogenes cause?
- postinfectious sequelae
- rheumatic fever
- acute glomerulonephritis
What is the most clinically important member of group A β-Hemolytic streptococci?
S. pyogenes
How is S. pyogenes spread from person to person?
by skin contact and via the respiratory tract
Capsule (S. pyogenes):
- nonimmunogenic (because the body does not recongize it as a foreign body)
- antiphagocytic
What does the cell wall of S. pyogenes contain?
- M protein
- Group A-specific C-substance
- Protein F (fibronectin-binding protein)
- Extracellular products
When is S. pyogenes not infectious?
in the absence of M protein
Where is the M protein located?
M protein extend from an anchor in the cell membrane, through the cell wall and then the capsule, with the N-terminal end of the protein exposed on the surface of the bacterium
M protein properties:
- antiphagocytic
- form a coat that interferes with complementbinding
Group A-specific C-substance:
this component is composed of rhamnose and N-acetylglucosamine. (Note: all group A streptococci, by defenition, contain this antigen)
Protein F (fibronectin-binding protein):
- mediates attachment to fibronectin in the pharyngeal epithelium.
- M proteins and lipoteichoic acids also bind to fibronectin.
Extracellular products:
Like staphylococcus aureus, S. pyogenes secretes a wide range of exotoxins that often vary from one strain to another and that play roles in the pathogenesis of disease caused by these organisms.
Where is the reservior for S. pyogenes in nature?
skin and mucus membranes o human host
How is group A streptococcal infection spread from person to person?
- through respiratory droplets or skin contact
- happens especially in crowded enviroments such as classrooms and children´s play areas.
Myonecrosis =
Death of muscle cell
Fasciitis =
Inflammation of the tissue under the skin that covers a surface of underlying tissue
Cellulitis =
Acute inflammation of subcutaneous tissue
What can streptococcal pharyngitis cause after spreading in the blood?
- Cellulitis
- Myonecrosis
- Fasciitis
What is a major cause of cellulitis?
S. pyogenes
S. pyogenes pharyngitis =
Strep throat
What is S. pyogenes pharyngitis (“strep throat”) associated with?
Severe, purulent inflammation of posterior oropharynx and tonsillar areas
Scarlet fever:
If a sunburn like rash develops in the neck, trunk, and extremities in response to the release of pyrogenic exotoxin to which the patient does not have antibodies, the syndrome is designated as scarlet fever.
What is impetigo?
It is a bacterial infection that involves the superficial skin.
What is a classical cause of impetigo?
S. aureus
How is the impetigo treated?
Impetigo is treated with a topical agent such as mupiocin, or systemically pencillin or a first-generation cephalosporin such as cephalexin, which are effective against both S. aureus and S. pyogenes.
Erysipelas:
Affecting all age groups, patients with erysipelas experience a fiery red, advancing erythema, especially on the face or lower limbs.
How is puerperal sepsis initiated?
This infection is initiated druing, or following soon after, the delivery of a newborn
What is puerperal sepsis caused by?
Exogenous transmission or endogenously, from the mother´s vaginal flora. This is a disease of the uterine endometrium in which patients experience a purulent vaginal discharge and are systematically ill
GAS disease =
group A streptococcal disease
What happens with patients with group A streptococcal (GAS) disease?
- the patient may have deep local invasion either without necrosis (cellulitis) or with it (necrotizing fasciitis/myositis)
- flesh eating bacteria
What are the symptoms that patients with group A streptococcal (GAS) disease can get?
- toxic-shock like syndrome
- fever
- hypotention
- multiorgan involvment
- a sunburnlike rash
- or a combination of the above
How can group A streptococcal (GAS) disease lead to bacteremia or sepsis?
Invasive GAS disease often spreads rapidly, even in otherwise healthy individuals, leading to bacteremia or sepsis.
What defines the streptococcal toxic shock syndrome?
This syndrome is defined as isolation of group A β- hemolytic streptococci from blood or another normally sterile body site in the presence of a shock and multiorgan failure
How is the streptococcal toxic shock syndrome mediated?
By the production of streptococcal pyrogenic exotoxins that function as superantigens causing massive, nonspecific T cell activation and cytokines released
What does the streptococcal toxic shock syndrome cause in a patient?
- flulike symptoms, followed shortly by necrotizing soft tissue infection, shock, acute respiratory distress, and renal failure.
What is the treatment of the streptococcal toxic shock syndrome?
The treatment must be promt, and includes antistreptococcal antibiotics, usually consisting of high-dose pencillin G plus clindamycin
What is acute rheumatic fever?
- autoimmune disease
When does the acute rheumatic fever occur?
2 to 3 weeks after the initiation of pharyngitis
What causes acute rheumatic fever?
- cross reactions between antigens of the heart and joint tissues
- streptococcal antigen (especially the M protein epitopes)
What characterizes acute rheumatic fever?
- fever
- rash
- carditis
- arthritis
- central nervous system manifestation and Syndeham´s chorea, symptoms of which are uncontrolled movement and loss of fine motor control
How is acute rheumatic fever preventable?
It is preventable if the patient is treated within the first 10 days following onset acute pharyngitis.
What is and when does the acute glomerulonephritis occur?
This rare, postinfectious sequela occurs as soon as 1 week after impetigo or pharyngitis ensues, due to a few nephritogenic strains of group A streptococci.
What initiates the acute glomerulonephritis?
Antigen-antibody complexes on the basement membrane of the glomerulus initiate the disease.
How is group A streptococcal infections treated?
- antibiotics
- S. pyogenes has not aquired resistance to pencillin G, which remains the antibiotics of choice for acute streptococcal disease
What is the prefered drug in a patient with pencillin allergic reaction against group A streptococcal infections?
clarithromycin or azithromycin
When are pencillin G plus clarithromycin used?
it is used to treating necrotizing fasciitis and in streptococcal toxic shock syndrome. Clarithromycin is added to pencillin to inhibit protein synthesis so that huge amount of toxin is not released abruptly from rapidly dying bacteria.
How is rheumatic fever prevented?
rheumatic fever is prevented by rapid eradication of the infecting organism.
group B β-hemolytic streptococci
p 83……
S. agalactiae
- gram-positive
- catalase-negative
Where is S. agalactiae found?
- vaginocervical tract of female carriers
- urethral mucous membrane of male carriers
- GI tract
How can S. agalactiae be transmitted?
- sexually among adults
- from an infected mother to her infant at birth
What has a high mortality rate and is the leading cause of meningitis and septicemia in neonates?
group B streptococci
Group B streptococci are also an occasional cause of……
infection in postpartum women (endometritis) and individuals with impaired immune systems, in whom the organism may cause septicemia or pneumonia.
What kind of test can we use to determine the presence of group B antigen in samples? (samples e.g.: blood, cervical swaps, sputum, or spinal fluid)
latex agglutination test
What is the difference between group B streptococci and group A streptococci?
group B streptococci are β-hemolytic, with larger colonies and less hemolysis than group A.
S. pneumoniae:
- gram-positive
- nonmotile
- encaspulated
- lancet shaped
- occur in pairs (Diplococcus S. pneumoniae)
What does the S. pneumoniae cause?
S. pneumoniae is the most common cause of community aquired pneumonia and, adult bacterial meningitis and is an important cause of otitis media, sinusitis, and mastoiditis
Who has the higher chance of getting S. pneumoniae?
- young children
- older adults
- smokers
- person with certain chronic diseases
Where can S. pneumoniae be found?
nasopharynx of many healthy indivivuals
How can the pneumococcal infections be?
endogenous or exogenous
What is the most important virulence of S. pneumoniae?
the bacterial capsule
What contributes to S. pneumoniae´s pathogenesis?
the cell-associated pneumolysin and autolysin
What are the virulence of S. pneumoniae:
- capsule
- pili
- choline-binding protein A
- autolysin
- pneumolysin
Capsule (S. pneumoniae):
- antiphagocytic
- antigenic
- 85 distinct capsular serotypes, some of which endow strains greater virulence than others, as reflected by the fact that 20 serotypes account vast majority of pneumococcal infections
Pili (S. pneumoniae):
enable the attachment of encapsulated pneumococci to the epithelial cells
