Streptococcus Flashcards
What are the methods to classify strep?
Lancefield Groups
Site of origin, type of infection
Hemolysis
Biochemical characteristics
What are the general characteristics of streptococcus?
Gram positive cocci that divide linearly Catalase negative Aerotolerant anaerobes Small colonies Grow well on BAP, some need CO2 Several pathogens Several commensals
What are the types of lancefield groups?
A, B, C
Based on C-carbohydrate
What strep does not have the C-carbohydrate?
S. viridans
What are the types of hemolysis does strep have?
Alpha
Alpha prime
Beta
What is hemolysis?
Clearing of blood around colony due to the presence of hemolysins in the bacteria
What is alpha prime hemolysis?
Colonies are surrounded by a zone of non-hemolysis & an outer zone of beta hemolysis
What is BAP composed of?
5% sheep’s blood in tryptic soy agar
Enriched - helps bacteria grow
Differential - types of hemolysis we see
What are the groups of beta hemolytic strep?
Group A
Group B
Group C,F,G
What strep is Group A?
Strep pyogenes
What strep is group B?
Strep agalatactiae
What are the virulence factors of S. pyogenes used for?
Helping in adhesion & eluding the immune system
What are the virulence factors for S. pyogenes?
Fibronectin
Capsules
Enzymes
What is fibronectin & what are some types?
Binding protein Lipoteichoic acid Hyaluronic acid capsule Toxins Enzymes
What do capsules do?
Mask bacterial antigens
Eluding immune recognition
What do enzymes do for S. pyogenes & what are some types?
Produced Streptolysin O Streptolysin S DNAse Streptokinase hyaluronidase Eyrthrogenic exotoxins
What are Streptolysin O & Streptolysin S?
Hemolysins produced by the bacteria
What is streptolysin O?
Antigenic
We produce antibodies against it
ASO test collects blood from the patient to determine ASO antibodies indicating a recent strep infection
What are the air requirements for streptolysin O?
Oxygen labile - sensitive & destroyed by
Can be seen anaerobically either by an anaerobic plate by stabbing the agar
Enhanced hemolysis is seen in stab
What do strep O & S lyse?
WBC & platelets
What are the air requirements for strep S?
Oxygen stable
Accounts for the hemolysis we see on routine BAP plates
Diseases associated with S. pyogenes?
Bacterial pharyngitis Pyodermal infections Necrotizing fascitis Streptococcal toxic shock syndrome Poststreptococcal squelae
Group A strep are what type of strep?
A type of pyogenic strep
What is the C-carbohydrate for strep pyogenes?
A
What protein is in strep pyogenes & what does it do?
M protein - more than 80 serotypes of these Produced by the emm genes Is attached to the cell wall Essential for virulence Makes organism resistant to phagocytosis
S. pyogenes colonizes what?
Throat & skin
What does pharyngitis mean?
Strep throat
What are the characteristics of pharyngitis & tonsillitis?
Most bacterial pharyngitis is S. pyogenes
Ages 5-15
Brief incubation, sore throat, malaise, fever, headache, nausea, vomiting
Spread by droplet
Cervical lymph nodes are enlarged - neck
Symptoms subside within 3-5 days unless sequelae occur
What do pyodermal infections cause?
Eyrsipelas Impetigo Cellulitis Arthritis Wound infection
What is impetigo?
Found more in small children
Associated with bug bites or abrasions
What are erysipelas?
Infects skin & subcutaneous tissue
Very red with definite border
What is cellulitis?
Caused by deeper invasion & can lead to sepsis
Cellulitis in patients with vascular disease or diabetes can lead to gangrene
Scarlet fever occurs if what?
If the bacteria has the pyrogenic exotoxin
Within 1-2 days of the infection
Causes a diffuse red rash on the upper chest that spreads
As it disappears, the skin desquamates - peels
What is necrotizing faciitis?
Flesh eating strep
What are characteristics of necrotizing nasciitis?
Caused by different bacteria
Type 2 NF is caused by S. pyogenes
Invasive, rapid inflammation & necrosis of skin, subcutaneous fat are fscia
Follows trauma, burn, lacerations
Patient who is immunocompromised is at risk
Healthy patients without a portal have also been identified
What is a portal?
Way to get in
Lesion where bacteria is introduced
What are characteristics of streptococcal toxic shock syndrome?
May follow a severe strep infection & symptoms mimic Staph toxic shock
Patients can have necrotizing fasciitis, organ failure, & death
Group A strep in this condition produce & exotoxin - SpeA
SpeA acts as a super antigen, over-activating the immune system
Young children, especially with chicken pox & elderly are most at risk
What are some post streptococcal infection squelae?
Rheumatic fever
Glomerulonephritis
Psoriasis
What are the characteristics of rheumatic fever?
Fever & inflammation of heart, joints, blood vessels, & subcutaneous tissues
Begins about 1 month after the infection
No longer common in the US
Cross reactivity of antibodies to heart tissue -> heart damage
What are characteristics of glomerulonephritis?
Group A strep
Periorbital edema
More common in children
Follows sore throat or skin infection
Circulating immune complexes may deposit in the glomeruli, leading to inflammation & glomerulonephritis
Usually self limiting
RBC casts seen in urine - blood & protein
What are types of ways group A strep is diagnosed by laboratory?
Rapid strep test for pharyngitis
Growth on BAP in ambient air & subsequent testing
How does the rapid strep test for pharyngitis work?
Direct sample is chemically extracted & tested with immunoassay
Negatives should follow up with culture
If there is growth of group A on a BAP in ambient air, what subsequent testing should occur?
Microbiologist suspicion of GAS leads to serotyping
GAS is PYR+ & sensitive to bacitracin
How is group A strep treated?
Susceptible to penicillin
Erythromycin for patients allergic to penicillin
What is group B strep?
Streptococcus agalactiae
What are the two syndromes that group B strep causes?
Early onset <7 days
Late onset 7 days - 3 months
What does early onset of group B strep cause?
The majority of cases
Due to vertical transmission from a colonized mother
What is the percentage of women that are colonized with group B strep vaginally/rectally?
10-30%
What are the characteristics of early onset GBS?
Associated with prolonged ruptured membranes & obstetric complications & premature birth
Baby has pneumonia &/or sepsis
High mortality rate
Mother colonized with GBS
What are the characteristics of late onset GBS in the newborn?
Meningitis & sepsis
Lower mortality rate
Mother not colonized with GBS
What are the steps to screen pregnant women for GBS?
Do urine culture & look for GBS
At 35-37 weeks gestation, vaginal & rectal swabs are collected, & inoculated into todd-hewitt, trans-vag, or lim broth
Broths contain colistin & nalidixic acid, or gentamicin & nalidixic acid; they are selective
Incubate 18-24 hours & subculture to BAP or chromagar in CO2 incubator - differential
Read plates 24 hours later
What does selective media do?
Inhibits growth of some bacteria while promoting others
What does colistin do?
Kills gram negative bacteria
What are the characteristics of GBS infection in adults?
May follow pregnancy or abortion, causing endometritis or wound infections, & endocarditis
Elderly that are immunocompromised are more at risk
Treatment of choice is penicillin, or penicillin & an aminoglycoside
How is GBS confirmed in adults?
Types of cultures: CSF, blood vag, rectal
Grown to pure culture, on blood - will be beta hemolytic in most cases
Lancefield typing can be done - type B
Bacteria are positive for hippurate hydrolysis & for CAMP factor
What are characteristics of group C & G strep?
Divided into large & small colony forms
Large colony forming units of beta hemolysis with C or G carbohydrates belong to Streptococcus dysgalactiae subspecies equisimilis - infections are uncommon, but similar to group A strep
Small colony forming units of beta hemolysis with C & G antigens belong to the S. anginosis
What are the characteristics of the PYR test?
Detects activity of the pyrrolidonyl aminopeptidase
PYR impregnated disks are moistened & 1-2 colonies are rubbed on the paper
Incubated at room temp for 2 minutes & add color developer
Read within 5 minutes
Red - positive = group A strep
What are the characteristics of hippurate hydrolysis?
Detects the presences of hippuricase
Hippuricase hydrolyzes the substrate sodium hippurate to sodium benzoate & glycine
Bacteria is added to liquid substrate & incubated for 2 hours at 35C
Glycine is detected by the addition of ninhydrin making a purple color
What are the characteristics of the SXT plate?
Selective with antibiotics suflamethoxazole & trimethoprim used to set up throat cultures
Group A strep will grow, but group C & G are sensitive & won’t grow
What is childbed fever associated with?
Group A strep
What does childbed fever cause?
Death or infection of a woman who just had a baby
What did Semmelweis do?
Drastically cut childbed fever (peurperal fever) in half by washing hands with bleach
