Streptococcus Flashcards
What type of bacteria (including catalase test) is Streptococcus?
Gram (+) cocci organized in chains and are catalase (-).
What characteristics are used to further classify Streptococci?
Hemolytic reactions on blood agar plates, serological specificity and biochemical reactions.
Define Hemolysis and the 3 types of hemolysis.
The lysis of red blood cells caused by specific bacterial enzymes.
- Alpha: Partial lysis of RBCs (green discoloration round colonies
- Beta: Complete lysis of RBCs (clearing of agar around colonies)
- Gamma: No lysis of RBCs (No change in agar around colonies)
What serological specificities are used to classify Streptococcus?
A) Lancefield Grouping: Beta-hemolytic streptococcus groups based on carbohydrates present in cell wall (group A-U). Groups A,B,D are important human pathogens.
B) Polysaccharide Capsules: Used to type Strep. pheumoniae
How are Biochemical reactions used to classify Streptococcus?
Sugar fermentation, tests for presence of particular enzymes and susceptibility of organisms to chemicals/physical conditions.
List the order of tests to differentiate specific Streptococcus groups.
Gram (+) –> Catalase ( - ) –> Hemolytic (Alpha, Beta, Gamma) –> Lancefield Grouping
Streptococcus pyogenes is ____ -hemolytic, Lancefield group ___
Beta; Group A
What antibiotic is S. pyogenes sensitive to?
Bacitracin – does not grow when this antibiotic is placed near it
Where is S. pyogenes normally carried and what percent of carriers are asymptomatic?
Nasopharynx; 15-20% asymptomatic
How is S. pyogenes transmitted?
Respiratory droplets or direct contact.
What are the virulence factors of S. pyogenes?
Capsule. M protein. Extracellular Enzymes. Exotoxins.
What does the organism’s capsule contain and what is its function?
Hyaluronic acid, which prevents phagocytosis.
What is the function of M protein?
Helps organism attach to cell surface and is extremely anti-phagocytotic.
List the specific enzymes that S. pyogenes makes.
Streptolysin O & S. Hyaluronidase. Streptokinase.
What does hyalurodinase do?
Breaks down hyaluronic acid in connective tissue.
Name the exotoxins produced by S. pyogenes and what they cause. What is the type of disease that these 3 toxins cause?
Erythrogenic toxin: Scarlet Fever
Exotoxin A: Toxic Shock
Exotoxin B: Necrotizing fascilitis
All “Toxin-Mediated” Diseases.
What are the clinical manifestations of Group A Streptococcus infections?
Pyogenic infections, toxin-mediated diseases and immunologically-mediated diseases.
What are pyogenic infections? Give 2 examples.
Pus producing infections.
- Pharygitis
- Skin infections
Why do immunologically-mediated diseases occur?
From complications of pyogenic infections.
What are suppurative (pus forming) complications of pharyngitis?
Peritonsillar abcess, sinusitis and otitis (ear).
What are non-suppurative complications of pharyngitis?
Rheumatic Fever
What are suppurative complications of skin infections?
Necrotizing fasciitis, and Toxic Shock Syndrome
What are non-suppurative complications of skin/throat infections?
Acute Glomerulonephritis – inflammation of renal glomerulus
What symptoms present during rheumatic fever and how long after pharyngeal infections with Group A streptococcus?
Fever, carditis and polyarthritis present 2-3 weeks after infection.
Is Rheumatic fever caused by the pharyngeal infections with Group A streptococcus?
No, its caused by antibodies to self antigens (M protein cross reacting with tissue).
What is the proper prevention and treatment for Rheumatic fever?
Prevent with prompt treatment of Streptococcus pharyngitis and treatment for RHD with penicillin prophylactic treatment.
What can Rheumatic Heart Disease lead to?
Inflammation may lead to myocardial/endocardial damage. Damaged heart valves predisposes to bacterial endocarditis.
What type of treatment needs to be given to patients with a history of RHD before dental/surgical procedures?
Prophylactic antibiotic treatment.
What symptoms present in Acute Glomerulonephritis and how long after throat/skin infections do they occur?
Hypertension, edema and hematuria begin after 10-20 days of throat/skin infection.
What is the proper prevention and treatment for Acute Glomerulonephritis?
No prevention available, no prophylactic treatment as recurrences are rare.
Streptococcus agalactiae is ___-hemolytic, Lancefield group ___
Beta; Group B
Which antibiotic is this organism resistant to?
Bacitracin
What does this organism hydrolyze?
Hippurate
Where is Streptococcus agalactiae found?
In the normal flora of the GI and GU tracts.
What diseases does this organism cause?
Neonatal meningitis and sepsis.
What percent of women of child bearing age carry Group B strep?
25%
What percent of those women give vertical transmission to their babies? What percent of babies develop an invasive disease?
50%; 1-2%
If the mother is not a carrier, what is another form of transmission of this organism?
Nosocomial – infected while in hospital
What is done to prevent high risk mothers from transmitting?
Prophylactic antimicrobials that are are cultured at 25 weeks.
Streptococcus pneumoniae is __-hemolytic, ___cocci
Alpha, diplococci
It is sensitive to what chemical?
Optochin
How many antigenically distinct types of capsular polysaccharides are there in S. pneumoniae?
More than 85 (meaning lots of forms for this organism to inhibit phagocytosis).
Where is the organism normally found and in what population?
Normal flora of oropharynx, normally found in elderly
What type of infection does this organism cause?
Respiratory tract infection (pneumonia, sinusitis, otitis) and meningitis.
What is the treatment and prevention for this infection?
Penicillin (though 25% of strain is resistant now) and preventable through 2 vaccines by Capsular polysaccharides.
Viridians Group Streptococcus is either ___ or ___ hemolytic.
Alpha; gamma
Viridians Group Streptococcus is resistant to what chemical?
Optochin
Is Viridians Group Streptococcus soluble or non-soluble in bile?
Non-soluble
Can Viridians Group Streptococcus be grouped in Lancefield typing?
No
What are the clinical manifestations of Viridians Group Streptococcus?
Endocarditis and dental caries
Group D Streptococci is also called?
Enterococci
Where is Enterococci located
In the normal enteric (gut) flora
It is bile-esculin (+) or (-)? How can it be grown?
Bile-esculin (+); Growth in 6.5% NaCl
What are the clinical manifestations of Group D Streptococci (Enterococci)?
Urinary tract infections. Wound infections. Endocarditis.
How do you treat Enterococci?
Resistant to Penicillin, so must use Vancomycin (last resort) but can also be resistant to this drug
