Denise - Streptococcus Flashcards
How is streptococcus classified
(5)
Based on the haemolytic propertied of the organism e.g. Alpha haemolytic strep
Based on the presence of surface antigens determined by immunological assays
Based on biochemical reactions
Based on protein analysis
Based on genetic analysis
Classify step based on haemolysis
Alpha haemolytic strep
Beta haemolytic strep
Gamma/no haemolytic strep
How do we classify strep based on their serological groups, how is this done
Based on the Lancefield groups of streps
How do we group streps based on Lancefield groups?
(6)
C-substance polysaccharide in their cell walls
Antigenic differences
Easily extractable
Classified primarily Beta Haemolytic strep
GAS (Group A strep) and GBS (Group B strep) are the most clinically significant
S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups
Which streps cannot be identified using lancefield groupings and why
S. pneumoniae and S. viridans (the alpha haemolytic streps) have no group specific antigen i.e. cannot be grouped based on lancefield groups
Write about S. pneumoniae
One of the 12 priority pathogens according to WHO
High burden of disease and rising rates of penicillin resistance
What type of resistance is seen in S. pneumoniae
Penicillin resistance
Why is S. pneumoniae listed as one of the 12 priority pathogens
High carriage rates
Genetic adaptability
Ability to shift from commensal to pathogenic interaction in its host
Write about the pathogenesis of S. Pneumonia
(3)
Colonisation is the prerequisite for both transmission to other individuals and invasive disease in the carrier
Carriers can shed S. pneumoniae in nasal secretions and thereby transmit the bacterium
Dissemination beyond its niche along the nasal epithelium, either by aspiration, bacteraemia or local spread
How does S. pneumonia spread from a carrier to another individual
Nasal secretions
How does S. pneumonia spread from the nasal epithelium to cause infection
Aspiration (bacteria into respiratory system)
Bacteraemia (bacteria in circulation)
Local spread (spread into tissues)
What infection is caused if there is aspiration of S. pneumonia
This will cause pneumonia in the lung
What infection is caused if there if S. pneumonia colonisation leads to bacteraemia
This will cause meningitis
This can occur directly from colonisation or can lead on from pneumonia
What does local spread of S. pneumonia from nasal epithelium lead to
Otitis media
What factors affect S. pneumonia shedding from nasal epithelium of carriers
(5)
Pneumolysin increases shedding
Capsule type and amount increases shedding
Viral co-infection increases shedding
Anticapsule IgG decreases shedding
Anticapsule IgA1 has no effect
How does pneumolysin increase shedding of S. pneumoniae?
(3)
Inflammation promotes secretion production by nasal epithelium
Bacteria present in mucus lining epithelium
Runny nose -> sneezing -> facilitates spread
How does capsule type and amount increase shedding?
(2)
Capsulated strains of S. pneumonia inhibit entrapment by mucin
S. pneumonia can escape the mucous produced by the S. pneumoniae
How can anticapsule IgG decrease Shedding?
IgG binds to bacteria
Agglutination blocks release
Bacteria can’t escape in mucous
Why does anticapsule IgA1 have no effect on S. pneumoniae
Bacterial protease relieves agglutination
Why does viral co-infection increase shedding of S. pneumoniae
Increases bacterial load and increases mucous production
Nasal epithelium infected with virus -> increases production of mucous
More bacteria present in mucous
Spread by runny nose etc
What are the two types of infections caused by S. pnuemonia
Non invasive
Invasive soft tissue infections
List the most common S. pneumonia non invasive infections
Acute bacterial pneumoniae
Otitis media
Write about acute bacterial pneumoniae caused by S. pneumoniae
(5)
Lower respiratory tract infection
Preceeded by viral infection
Community acquired infection Pneumonia CAP
Older adults
Seasonality - increased in winter months
Write about otitis media caused by S. pneumonia
Most common cause of middle ear infection in children
What indicates an S. pneumonia invasive infection
Isolation of S. pneumoniae from a normally sterile site e.g. blood or CSF
What are the main invasive infections caused by S. pneumoniae
Blood stream infection (SEPSIS)
Meningitis
What percentage of S. pneumoniae pneumonia infections will lead to BSIs i.e. SEPSIS
15-30% of people with pneumoniae will lead to invasive disease
Write about S. pneumonia caused meningitis
(2)
Majority of invasive pneumococcal disease (IPD) infections are caused by a subset of predominant streptococcus pneumoniae serotypes
Approximately 8-10 of 90 different serotypes cause meningitis
Write about S. pneumoniae epidemiology
Young children
Older adults
Immunocompromised
Mortality rate is now much greater in adults >65 years of age than in children <2
Comment on the recent trends in invasive S. pneumonia
IPD is a notifiable disease in Ireland
Ever increasing number
What does IPD include
Meningitis
BSI
Sterile site infection
Comment on incidence rate of IPD versus age of patients
(3)
Less common in children under 2
Increasingly common in those over 65
Very low amounts in teenagers (near zero infections)
What are the virulence factors of S. pneumoniae?
(5)
Surface structure (capsule)
Pili
Choline Binding protein A
Autolysins LytA
Pneumolysin
How does a capsule affect virulence of S. pneumoniae?
(6)
Capsule is antiphagocytic
Capsule is antigenic
Polysaccharide
Essential for colonisation -> non capsulated strains are usually avirulent
Target for Pneumococcal Conjugate Vaccines
>90 strains recognised based on capsular carbohydrates
How do pili affect virulence of S. pneumoniae
Not all pneumococci express pili
Attachment to the epithelial cells in the nasopharynx and upper respiratory tract
How does choline binding protein A affect?
(6)
Polypeptides
Number varies from 13 to 16
Anchors the protein to the choline residues present in the cell wall
Responsible for remodelling the cell wall
Responsible for adhesion
Promotes invasion
What are the two main enzymes responsible for virulence of S. pneumonia
Autolysins LytA
Pneumolysin
What does autolysins LytA do in S. pneumoniae
Cell wall degrading protease
Responsible for the release of virulence factors
What does pneumolysin do?
(6)
Cytolytic protein
Released by autolysin
Attacks cell membranes
Proinflammatory
Inhibits PMN
Activates complement
Describe the process behind autolysins LytA and pneumolysin in S. pneumoniae.
(5)
S. pneumoniae infection
Autolysin is responsible for lysis of S. pneumoniae
Lysis releases the virulence factors out of S. pneumoniae
Pneumolysin released
Pneumolysin damages mammalian cell membranes
What is done with S. pneumoniae on day 1 of laboratory investigation?
(2)
Direct gram stain
Inoculation on blood agar
What specimens are seen in S. pneumoniae infections
(6)
Sputum
Pleural fluid or lung aspirate
Pus
Aspirates
CSF
Blood
What investigation is done on CSF and blood for S. pneumoniae
Direct Molecular detection
Film array ME
What investigation is done on CSF?
(4)
White cells increased
Bacteria
Glucose decreased
protein increased
What investigation is carried out on day 1 for S. pneumoniae?
(2)
Direct microscopy gram stain
Only done on blood cultures which have flagged positive
How does S. pneumoniae appear on gram stain
Gram positive diplococci lancet shaped
Write about the growth requirements for S. pneumonia
(6)
Fastidious
Blood agar
37 degrees celsius
5% CO2
O2
Anaerobically
Write about the colonial morphology of S. pneumoniae
Alpha haemolysis
Draughtsman colonies or mucoid colonies
What are the basic characteristic results of S. pneumonia
Gram positive diplococci
KOH negative
Catalase negative
Oxidase negative
Lanceolate shaped
What confirmatory identification tests are done for S. pneumonia on day 2
(3)
Optochin susceptibility
Bile susceptible
Vitek or Maldi TOF identification
Why might the Vitek be used instead of Maldi for S. pneumoniae ID
Maldi lack of discrimination between s. pneumoniae and other closely related alpha-haemolytic streptococci
How is S. pneumonia treated
B lactams -> penicillin (if not resistant)
Macrolide -> Erythromycin
Cephalosporin -> Cefotaxime
Write about S. pneumoniae resistance
(3)
PNSP -> penicillin non-susceptible pneumococci increased gradually with age
11% isolate in younger patients but 29% in older patients over 75
Reduced susceptibility to cefotaxime and erythromycin is also observed in older patients
What is done with S. pneumonia which is confirmed
(3)
CSF sent to IMSRL (Irish Meningitis and sepsis Reference Laboratory) on Temple street
Real time PCR directly on specimen
Serogroup Capsule-PCR
What Pneumococcal vaccines are there currently
(3)
PCV7 - infants
PCV13 - infants
PPV23 - for adults over 65 and immunocompromised
What is the PPV23 vaccine
(5)
Pneumococcal polysaccharide vaccine
Purified capsular polysaccharide from 23 capsular types of S. pneumoniae
Accounts for up to 90% of IPD
Only for those >2 years old
Uptake is poor - only 30%
Why is the PPV23 vaccine only suitable for those over 2?
An adequate antibody response does not develop in those under 2 years of age
What are the PCV vaccines
(6)
Pneumococcal Conjugated Vaccines
PCV7 and PCV13
Conjugated to a protein for enhanced immunogenicity
Immunogenic from 6 weeks of age
Active against 75-90% of IPD serotypes
Uptake great with >90%
Comment on the outcome of S. pneumoniae vaccination
(4)
Clear evidence that the vaccines have reduced the burden of IPD in children
However, number of non vaccine type infections has increased
Evidence of herd protection seen
Vaccine uptake for PPV23 needs to be improved
Write about S. viridans
(6)
Commensals in the GIT, Respiratory and female genital tracts and are most prevalent in the oral cavity
Considered to be of low pathogenicity
Many species but not usually differentiated
May gain access to bloodstream through minor trauma to gums
Propensity to adhere to cardiac valves
In those with damaged heart valves can cause sub acute bacterial endocarditis
How can S. viridans gain access to blood stream?
Through minor trauma to gums
What can S. viridans cause to those with damaged heart valves
Sub acute bacterial endocarditis
What is Streptococcal endocarditis
(4)
Patients with abnormal or damaged heart valves
Bacteria infects valves during a bacteraemia
Prophylactic penicillin may be given prior to dental treatment
Caused by oral streptococci e.g. S. mitis or S. oralis
What species might cause streptococcal endocarditis
Oral streptococci e.g. S. mitis, S. oralis
Where is S. mutans often found
Found in mouth/on teeth
Produces biofilm which can be involved in plaque formation and tooth decay
What infections can S. mutans cause
Tooth decay
What are the basic characteristics of S. viridans
Gram positive cocci in chains
Catalase negative
Oxidase negative
Fastidious
Facultative anaerobes
Alpha haemolysis
What is done to S. viridans on day 1
Isolation on blood agar
What is done to S. viridans on day 2
Gram stain
Investigate haemolysis
Biochemical speciation
Identification on Vitek or MALDI
What is done on day 3 for S. viridans
Optochin susceptibility testing
How does S. viridans react to optochin
S. viridans is resistant to optochin
What is meant by Lancefield grouping?
(3)
Lancefield Groups based on differences in cell wall polysaccharides
13 Lancefield Groups
Groups A, B, C, D, F and G most commonly implicated in human infections
What is Lancefield group A
Streptococcus pyogenes
What is Lancefield group B
Streptococcus agalactiae
What is Lancefield group C
Found in pharynx: can cause pharyngitis, sinusitis, impetigo, endocarditis
What is Lancefield group D
Enterococci
Can cause wound lesions, urinary tract infections and some cases of SBE
What is Lancefield group F
Streptococcus anginosus; grow better anaerobically
What is Lancefield group G
Resemble group A strains
What are the three types of infections caused by S. pyogenes
Non invasive
Invasive soft tissue
Non-suppurative sequelae
List the main non invasive infections caused by S. pyogenes
Pharyngitis
Scarlet fever
Skin infections
What is pharyngitis
(5)
Common infection
Abrupt onset
Difficult to differentiate from viral infection
5-30% of cases in children
5-10% of cases in adults
What are the four symptoms of pharyngitis
Headache
Fever
Reddening
Pus
Write about scarlet fever caused by S. pyogenes
(5)
Scarletina
Erythematous rash of skin and mucous membranes
Rash looks like sunburn and feels like sandpaper
Strawberry tongue
Erythrogenic toxin
What non invasive skin infections does S. pyogenes cause
Impetigo
Erysipelsia
What is impetigo
Honey crust lesions
Pus filled blisters
What is erysipelsia?
(5)
Acute skin infection
Cellulitis
Diffuse redness
Pain
Potential spread to the bloodstream
What invasive soft tissue infections does S. pyogenes cause
Necrotising facitis
Streptococcal Toxic Shock Syndrome
Write about necrotising facitis
(7)
Rare infection
Tissues under the skin and muscles
Pain Redness Swelling
Fluid filled blisters/swollen tissues
Associated with wounds/breaks in the skin
Predisposition includes: cancer, diabetes, dialysis and steroids
Infected tissue has to be cut off
What predisposes someone to necrotising facitis?
(4)
Cancer
Diabetes
Dialysis
Steroids
What is streptococcal Toxic Shock Syndrome
Caused by superantigen
1-2 weeks after the onset of acute illness
What are the main symptoms of toxic shock syndrome
(5)
High fever
Rash
Hypotension
Multiorgan failure
Desquamation typically of the palms and soles
What are the two non suppurative sequelae infections caused by S. pyogenes
Rheumatic fever
Glomerular nephritis
What is a non suppurative sequelae
Immune reactions 1-5 weeks after infection
What causes rheumatic fever
Its seen post pharyngitis
What causes glomerular nephritis
Its seen post skin infection
What are cutaneous infections
Infections of upper respiratory tract and of skin and soft tissue
What are the three main cutaneous infections caused by S. pyogenes
Pharyngitis
Cellulitis
Impetigo
What is the main destructive soft tissue infection caused by S. pyogenes?
Necrotising faciitis
What are the two toxin mediated infections caused by S. pyogenes
Scarlet fever
Toxic Shock Syndrome
What are the non-suppurative sequelae caused by S. pyogenes?
Acute glomerulonephritis
Rheumatic fever
Write about S. pyogenes epidemiology
Only invasive infections are notifiable iGAS (invasive group A streptococci)
Streptococcal Toxic Shock/ Necrotising Faciitis/ BSI
Increase in notified iGAS infections since october 2022
Write about S. pyogenes virulence
(4)
Wide range of virulence factors
Enable bacteria to attach to host cells
Spread by penetrating host tissues
Evade the immune response
What are the S. pyogenes virulence factors
(8)
Capsule
M protein
Streptolysins
Anti C5a peptidase
Streptokinase
Hyaluronidase
Exotoxins SPE A and C
DNase
Write about M protein
(8)
Surface adhesin
Inhibits phagocytosis
Binds Fc portion of IgG
M types 1, 3, 12 and 28 are the most common isolates found in patients with shock and multiorgan failure
Strains lacking M protein are less virulent
Rheumatic heart disease
T-protein surface antigen
R-protein on some strains
List the S. pyogenes Toxins and ExoEnzymes
(6)
Pyrogenic exotoxins
Streptolysin O and S
Streptokinase
C5a peptidase
Streptodornases
Hyaluronidase
What does pyrogenic exotoxins do
Cause various effects, including the rashes seen in scarlet fever and streptococcal toxic shock disease
What does Streptolysin O and S do
Damages mammalian cells, resulting in cell lysis and release of lysosomal enzymes
Lysis of RBCs, PMNs and platelets
What does streptokinase do
Catalyses conversion of plasminogen to plasmin, causing lysis of clots, facilitating the rapid spread of organisms
What does C5a peptidase do
(2)
Inactivates complement component C5a
Cleaves the chemoattractant C5a
What does streptodornases do
DNAses degrade the viscous DNA in necrotising tissue or exudates, aiding the spread of infection
What does hyaluronidase do
Disrupts the organisation of ground substance, facilitating the spread of infection
Breaks down tissue hyaluronic acid
What does streptolysin S do
Oxygen stable
Not antigenic
Leucocidal action
What does Streptolysin O do
(3)
Oxygen labile
Cytotoxic for red blood cells, neutrophils, platelets, cardiac tissue
Responsible for haemolysis that we see on blood agar
What are the streptococcal exotoxins
(3)
SPE-A
SPE-B
SPE-C
What does SPE stand for
Streptococcal pyrogenic exotoxins
What are SPE-A and SPE-C
(3)
Erythrogenic toxins
Similar to staph enterotoxins
Associated with invasive infections and toxic shock syndrome
What is SpeB
Cysteine protease
Associated with tissue destruction
What are the exotoxins SPE A and C also called
Superantigens
What does DNase do
Degrades extracellula
What specimens is S. pyogenes found in
Throat swabs
Pus
Skin
What are the growth requirements of S. pyogenes
Fastidious
Blood agar
Haemolysis enhanced anaerobically
37 degrees Celsius
5% CO2, O2, Anaerobically
What confirmatory tests are done on S, pyogenes
Rapid latex agglutination on patient samples
What is the colonial morphology of S. pyogenes
(5)
Beta haemolysis
Gram positive cocci in chains
KoH negative
Catalase negative
Oxidase negative
What confirmatory test is done on day 2 for S. pyogenes
(4)
Lancefield Grouping
MacConkey
Susceptible to bacitracin
PYR
How does S. pyogenes grow on MacConkey?
Fails to grow on MacConkey
How does S. pyogenes grow with Bacitracin
S. pyogenes is susceptible to bacitracin
Is S. pyogenes PYR positive or negative?
Its PYR positive
What is PYR
Pyrrolidonyl arylamidase
Write about S. agalactiae
Opportunistic pathogen
Often colonisation
Capsule may contribute to virulence
Write about the colonisation of S. agalactiae
(5)
Found in the intestines of up to 30% of adults
Found in the vagina of up to 25% of women
Asymptomatic
May be intermittent
90% of adults posses no protective antibodies to Gram B Strep
Write about the pathophysiology of group B streptococcus
Prenatal onset GBS
Early-onset GBS
Late-onset GBS
Write about the prenatal-onset of group B strep
Occurs when a baby is infected with GBS during pregnancy
Write about the early-onset of group B strep
Occurs when a baby is infected with GBS within the first week of life
Write about the late-onset of group B strep
Occurs when a baby is infected with GBS after 1 week to several months of age
Write about the epidemiology of Group B strep
Infections in adults: the elderly, pregnant women, others with other disease
Most common cause of life-threatening infection in newborn babies
Write about early onset infectious GBS
Up to 80% of GBS infection in babies
0-6 days (usually <24 hours)
Usually septicaemia, also meningitis and pneumonia
11% mortality
Write about late onset infectious group B septicaemia
(5)
Up to 20% of GBS infection in babies
7+ days (rare after 3 months)
Usually meningitis with septicaemia
5% mortality
50% of GBS meningitis survivors have neurological sequelae
What specimens are Group B streps found in
Urine Sample UTI
Blood cultures BSI
CSF
What specimens come in for surveillance in carriage of Group B strep
High vaginal swab
Screening for GU carriage
Carriage preceeds infection
What are the growth requirements for Group B strep
Fastidious
Grown on blood agar -> haemolysis enhanced anaerobically
37 degrees celsius
5% CO2
What is done on day 1 for Group B streps
Isolation on blood agar
Direct detection using geneXpert -> S. agalactiae
What are the basic characterisation results for Group B strep, S. agalactiae
Lancefield group B
KOH Negative
Oxidase Negative
CAMP factor
Hydrolysis of hippurate
Does not hydrolyse aesculin
Some grow on MacConkey agar (bile)
What is the CAMP test
Detects the production of extracellular protein CAMP factor
CAMP factor acts synergistically with the beta lysin produced by S. aureus
A zone of enhanced lysis of sheep or bovine blood
CAMP positive = Group B strep
CAMP negative = Not GBS
What is the Hippurate hydrolysis test
(4)
Used to differentiate S. agalactiae from other Beta Haemolytic streps
Hippurate is hydrolysed by hippuricase into Benzoic acid and glycine
Ninhydrin reagent is used as an indicator to detect Glycine
Ninhydrin reacts with glycine to form a deep blue or purple colour
What do we done when we confirm we have a Group B strep
(3)
CSF sent to Irish Meningitis and Sepsis Reference Lab in Temple Street
Real Time PCR directly on specimen
Serogroup capsule - PCR
Write about Group C and G streptococcus
(4)
Commensal flora of the human upper airway
Asymptomatic colonisers of the skin, gastrointestinal tract and female genital tract
S. dysgalactiae subspecies S. equisimilis (SDSE)
Resembles S. pyogenes infections
Write about the non enterococcal group D
(7)
Streptococcus bovis
Faecal flora
Alpha or non haemolytic
Occasionally causes UTI and Endcarditis
Bile Aesculin Positive
PYR Negative
Does not grow in 6.5% salt
Write about beta haemolytic strep treatment
Penicillin
Clarithromycin (allergy)
Necrotizing fasciitis - surgery + clindamycin
