Week 2 -Strep Flashcards
what are Streptococcus and Enterococcus
-members of the Streptococcaceae family
-catalase negative , can give weak positive if media is from blood
-pairs and chains - nicer chains in broth
-facultative anaerobes but cant use oxygen for respiration can be aerotolerant aerobes
-BH strains produce exotoxins that damage RNCs
-use fermentative processes for metabolism with lactic acid end product
-can be capnophilic
-need more nutrition than Staph, have poor growth on plain TSA media but enhanced growth media with lysed blood like chocolate
what is the cellular morph of Strep
-GPC in pairs and chains
-GPDC only if Streptococcus pneumoniae and growing colonies on plate
-elongated vs spherical cells
what is the cell wall structure of strep
-just like all other GP with peptidoglycan/teichoic acid
-common c polysaccaride - used for Lancefield grouping and for extracting cell wall AG (C carb) to react with AB causing agglutination
Viridans and S pneiumo dont have the C carb so other tests are done.
There is a NH strep group with the same Lancefield grouping so you need more tests for that category.
What occurs in Alpha hemolysis
hemoglobin is reduced to methemoglobin which is why the area surrounding the colonies will look green
what are variations that can occur in hemolysis slide 15
-S anginosus - is A, N, and BH
-Enterococci are NH but can be BH or AH
-Group B Strep have a very small BH while some are NH
what are Group A streptococcus and where are they found
Streptococcus pyogenes
-most virulent
-fastidious
-humans are ONLY known reservoir - UPT, skin
-Transient flora is in the vaginal tract
-can be asymptomatic but must always be treated
what are the Structural virulence factors associated with GAS
Capsule - has hyaluronic acid the same as humans and therefore doesnt recognize the foreign response
M protein - promotes attachment to membrane surfaces - skin. The protein is attached to peptidoglycan which extends to the cell surface interfering with phagocytosis
Protein F- fibronectin binding protein works with lipoteichoic acid to attach to host epithelial cells . Fibronectin responsible for cell adhesion, growth and wound healing
Lipoteichoic acid+M protein+Protein F = secure attachment of Streptococcus to oral mucosal cells
what are the extracellular products responsible for virulence factors for GAS
Streptolysin O - oxygen labile only active in ANO conditions
-causing BH in ana
-lyses PLTs, RNC, leuks,
-immunogenic - formation of AB by host - test with Anti-streptolysin O test (ASOT)
Streptokinase - lyses fibrin clots used as a clot buster
Streptolysin S (oxygen stable)
-lyses lueks, RBC
-non immunogenic
-causes the BH around GAS in BA in o2
Pyrogenic Exotoxins
-super AG, erythrogenic toxin
-interacts with class II MHC to produce IL-1 tumor necrotizing factor
-scarlet fever
-DNAses
Hyaluronidase
-separates connective tissues and spreads the infection
What is the clinical significance of GAS
- pharyngitis/tonsillitis - Strep throat
-droplet or close contact
-throat culture - gold standard
what are some other infections caused by GAS other than strep throat
Pyodermal Infections - skin disease that has pus
Impetigo - vesicular and pustular facial infections
-highly contagious
-especially in warm weather
-may be cause by S pyogenes or S aureus
Cellulitis -deeper
-Erysipelas - older people
-Spreading skin lesions very erythematous
Scarlet fever
-rash that spreads on chest to trunk and extremities after the throat infection so it is secondary
what is necrotizing fasciitis, symptoms and risk factors
soft tissue infection
Type 1 - polymicrobial
Type 2 - GAS AH, BH or MRSA
-flesh eating disease, necrosis of skin, fat and fascia.
-lots of cases without breaks in skin
-invasive - can kill in 12 hours
Type 3- gas, gangrene due to clostridium
if on genitals it is called Fournier gangrene
Risk factors high if
-weak immune system, health issues
-cuts in skin
-if you had chicken pox or viral infections that cause a rash
-steroid use that suppress immune function
Symptoms
-starts suddenly after injury
-pain get better after 24 hours and then worse
-skin in red, swollen and hot
-fever,chiils, nausea and vomiting
Streptococcal Toxic Shock Syndrome - GAS
-invasive
-shuts down entire organ system
-unknown portal of entry can be injury
-Lympadenitis –infection of lymph gland
-Lymphangitis –infection/inflammation of the lymph channels
-Puerperal sepsis (infection of uterine lining) usually during or after delivery
what are GAS Post infection Disorders
-complications because of immune response
Rheumatic Fever
-happens a month after pharyngitis
-fever, inflammation of the heart, joints and blood vessels
-if you get repeated infections youll have valve damage
-sequelae: rhematic heart disease
Acute Glomerulonephritis (AGN)
-after cutaneous or pharyngeal infection
-AG-AB complex deposits in the glomeruli causing damage
What is the theory behind why GAS post infection disorders occur
-Cross reactivity between strep antigens and heart tissue
-toxicity from bacterial exotoxins and invasion of heart tissues
how do we identify GAS
- small /medium with large BH - due to streptolysin O which is oxygen labile
-GP cocci in chains
-catalase negative
-hippurate hydrolysis negative
-NG in 6.5% NaCl
-bacitracin sensitive
-PYR positive
-fastidious - needs blood or other enrichment
-test with PathoDx for BHS
-Lancefield grouping for A
Do we do AST on GAS,GBS, GCS and GGS
-S pyogenes (GAS) and S agalactiae (GBS) is susceptible to penicillin
-D test is peni alternative or if pt on erythromycin or clindamycin on MG with 5% SB
-Etest or M.I.C. Evaluator :not at TMI for sterile sites
What is the D zone test
-erythromycin and clindamycin are popular for pt allergic to peni need to test for both
-test for msr gene which is an efflux pump and doesnt impact clinda
-test for erm gene which codes for 23S rRNA methylation causing erythromycin resistance and clindamycin resistance which can be constitutive or inducible
-presence of the methylase enzyme confers resistance to clindamycin
-seen as decreased zone size (antagonism) to clindamycin where the two ABtics interact = D formation on the agar because theyll be side by side 12mm apart -MH with blood
-you can do this test with Staph but the discs will be 15mm apart with reg MH
-So if erythromycin is testing as resistant, you need to test it to see if it is resistant due to the erm gene since if it is, you can’t use clindamycin as well.
-we don’t do BHS AST on the Vitek, you need to perform this manually
what is the E test/M.I.C.E
-not a diffusion method
-plastic strip with antimicrobial concentration with MIC reading scale
-full dilutions on white side and half dilutions on black side
-forms a ZOI
How do we treat GAS
- no vaccine since hyaluronic acid in Strep capsule is also found in humans
-peni, eryt, clinda, cephalo are used
-treat pharyngitis aggressively so you dont get Rheumatic Fever ,and AGN
-Skin infections - drainage, debridement (remove pus and infective tissues) and abtic therapy
-Prophylactic penicillin therapy- prevents Rheumatic Fever, endocarditis . This is done before dental surgery can be given to those with STT or NF infections
Streptococcus agalactiae –Group B streptococcus (GBS)
What do type is it and characteristics, virulence factors
- Acid stable polysaccharide in the cell wall so C -AG is used to ID
Virulence Factors
***Capsule- sialic acid - prevents phagocytosis and inhibits activation of complement system. but is ineffective after opsonization. This process allows molecules to have stronger binding to cell surface receptors on phagocytes and NK cells . If the AG is coated with opsonins it can bind to immune cells
Extracellular products
hemolysin
CAMP factor
Enzymes (neuraminidase, DNAse, and protease)
where does GBS live and how is it identified on a plate
- naturally found in female genital tract and male urethra
-pharynx and gastrointestinal tract
-plate shows large colony with narrow zone usually BH can be NH
-GPC in chains
-Catalase Nege
-Lancefield B grouping
-PYR neg
-CAMP positive
-Bacitracin Resistant
-Hippurate hydrolysis positive
what are GBS clinically significant
- most common cause of newborn death less than 7 days old
-high mortality rate
-women become colonized at time of delivery causing the newborn to be colonized as it comes down the birth canal
-infections within first 3 days presenting as pneumonia or meningitis with bacteremia
-rare for late onset- it would an unknown infection source
-in adults - UTI, endocarditis , endometriosis
How are specimen collected and processed from pregnant women for GBS
-screened at 35-37 weeks
-vaginal-rectal perineal swab
-swab in Todd Hewitt broth (red) with gentamicin and nalidixic acid leave the swab overnight in the media
-incubate overnight and subculture onto CNA CO2 or chromogenic media Brilliance GBS
What is Brilliance GBS
-mix of chromogens, inhibins, and antibiotics
-grows GBS and inhibits the rest
- pink colonies are presumptive GBS
-confirm ID with PathoDx
What is the CAMP Factor Test
Christie, Atkins, Munch Peterson all 1st saw the reaction
-GBS release protein called CAMP factor
CAMP factor + beta-hemolysin by S aureus = enhanced beta hemolysis in shape of “arrowhead shaped” area of intense hemolysis
how to treat and prevent GBS
-Antepartum GBS detection and chemoprophylaxis
-use peni for intrapartum chemoprophylaxis
-use both peni and aminoglycoside (gentamicin) for severe infections
Group C and Group G streptococcus what are they and how are they identified
- grouped with pyogenic strep
-strains with large colony
-human pathogen
-same virulence factors as group A
-only report group A in throat swabs but Group C or G in throat cultures - confusion if they cause phargytisis or not
-medium colony BH (with large zone)
-GPC in chains
-Catalase negative
-Lancefield group C or G
ALPHA HEMOLYTIC Streptococci (AHS) examples
Viridans streptococcus group
Streptococcus pneumoniae
where is Streptococcus pneumoniae found, how is it transmitted
- naturally commensal, found in adult resp tract and it opportunistic
-normal flora
-transmitted through contaminated resp secretions person to person
-endogenous infections
What virulence factors are associated with Streptococcus pneumoniae
antigenic polysaccharide capsule
-inhibits phagocytosis by PMNs allowing the organism to multiply and produce infection
-isolates without the capsule are non pathogenic
-if the isolate has opsonized it is avirulent
-can be identified with antisera
-other toxins produced but dont have a role in disease production
-hemolysin
-IgGA
-hyaluronidase
What is the clinical significance of Streptococcus pneumoniae
- Most common cause of community-acquired bacterial pneumonia
-in ppl with depressed immune system - alcoholic, asthma, smokers its worse
-orgs will move down the resp tract
-org can cause otitis media or sinusitis it it goes into inner ear
-leading cause of bacterial meningitis
-overwhelming septicemia
-once the org gets to the alveoli it spreads to other alveoli
-lobar pneumonia occurs when the org reaches the septa separating the major lung lobes
can cause bacteremia, empyema (pus in space between lung and chest/pleural wall)
what does it take for a person to get
pneumococcal pneumonia
-org has to be in the nasopharynx
-person must lack a specific AB against that strain
-not a primary infection
-occurs due to predisposing conditions like Alcoholism, Malnutrition and URT viral infection
how do we identify S pneumoniae in the lab
- AH “checker shaped” concave (because of the autolysis) or mucoid - innie
-GPDC - ovoid or lancet shaped
-bile soluble
-optochin sensitive
what is the AST to be done on S pneumoniae
- screen for peni resistance with oxacillin disc
-if >20mm peni susceptible (treat with erythro or chloramphenicol)
-if <19 confirm by MIC
-use MH with blood incubate in CO2
-invasive isolates (like CSF) test with MICE/Etest right away
-CLSI will be breakpoint specific meningitis or not , oral vs parenteral (intravenous) - look at the breakpoints
D test
-use MH with blood in CO2 looking for inducible resistance of clinda (erm gene). report both eryth and clinda results
Can also do a disc diffusion with SXT or levofloxacin
how to we prevent and treat S pneumoniae
-vaccine with capsular polysaccharide from disease causing strains for select pops -old
-if meningitis is suspected use combo of vanco, and cephalosporin spectrum
what is Viridans streptococcus, where does it live, what are its virulence factors
-AHS
-fastidious and opportunistic
-often reported as normal flora or Viri strep in sterile specimen
groups: S mitis, S mutans, S salivarius, S bovis, S anginosus
-Naturally found in oral cavity , URT, GI tract and female genital tract
-low virulence
-Polysaccharide capsule
-cytolysin
-dextran and adhesins allow attachment to heart valves and endothelium causing endocarditis
-dextran is a polysaccharide used as anti thrombotic to decrease blood viscosity - binds RBC and PLTs
-dental plaque has alot of dextrans
How to identify Viridans streptococci group
- hard to speciate
-small grey AH colonies with a rough edge crusty
-umbonate
-GPC in elongated swollen pairs and chains when from plates but normal when from broth
-catalase negative
-optochin resistant
-bile solubility -insoluble
-PYR negative
-LAP Leucine aminopeptidase - LAP
what is the Streptococcus anginosus group, how is it identified , where is it found
-pinpoint colony BHS
-Caramel smell
-found in URT and GI can be isolated from throat cultures
Can be alpha/beta/NH
3 members:
S.anginosus
S.constellatus
S.intermedius
what is the clinical significance of mitis group
-dental plaque, GIT and female genital tract microflora
- found with bacterial endocarditis in native valves but not so much in prosthetic valves
-dental surgery is the route of infection
-infection found in pts with heart conditions and prosthetic heart valves
what is part of the Streptococcus anginosus group and what is the significance also with others in the group
-bacteremia, deep abscesses- brain, peritoneal , oropharynx
S intermedius
-abscesses in liver and brain
S mutans group
-found in oral cavity associated with dental
-cavities
S salivarius
-found in neutropenic pts who get endocarditis, SARS after bacteremia
S bovis (D group strep) NH
-cultures of pt with bacteriea, septicemia, endocarditis
-correlation with gastrointestinal carcinoma
S. anginosus group– Identification how
-difficult to speciate
-can do lancefield A, C, F, G but isnt always groupable
-BH
-VP positive
-Bile esculin - positive
Capnophilic
Viridans streptococci AST/ Treatment & Prevention
AST
MIC only for peni (E test, MICE) on sterile sites
-disc diffusion for ceftriaxone and vaco
Prevent and treat
-AB taken before and after dental espcially pts with heart valves
-increase resistance to penici
-treat SBE with synergistic AB : penicillin and gentamicin
what are some non hemo Streph
Enterococcus sp
Streptococcus bovis
What is Enterococcus, found where, what are its virulence factors
- used to be classified with group D Strep but now it is on its own because GDS is suscep to peni and Enterococcus is resistant
Naturally found in soil, water, food
Normal Flora in GI tract
Virulence Factors
-Adhesions, cytolysins allow entro to proliferate
- can survive in extreme conditions - bile, high salt, pH
-multidrug resistance - intrinsic, acquire plasmids and transposons
Enterococcus – Clinical Significance
- relates to its resistance to microbials
-many infections are nosocomial - 2nd highest cause of all HAI (2nd to staph)
-occasional ocular infections
-CNS and resp infections are rare
Main types of Enterococcus (genus)
E. faecalis and E. faecium
- mostly in humans
-non motile
-most infections are caused by E. faecalis
-not on chromosome so by plasmids/transposons
E.gallinarum and E.casseliflavus
-occasional infections
-low level vanco resistance but not infection control issue - directly in the chromosome will not share on plasmid or transposons
-motile
what is Vancomycin Resistant Enterococcus (VRE), epidemiology, transmission, and risk factors
-Epidemiology
most occur because of endogenous flora
-contact precautions
Transmission
- direct pt-to-pt
-indirect via hands , contaminated equipment or pt care
Risk Factors that cause
-prior vanco use
-immunosuppression
-surgery
prolonged hospital stay
-indwelling catheters
-
what are the types of Vanco resis
Acquired (***E. faecium or E. faecalis)
-vanA or vanB
-transmissible between bacteria
-outbreaks
-on plasmids and transposons and bacteria like to share them - can be VRE
Intrinsic (E. gallinarum, E. casseliflavus) chromosomal
-van C gene
-not transmissible
-not associated with outbreaks
Enterococcus Faecalis. Colonial Morphology
-medium grey NH- small BH most on ANA
-GPC on short chains -pointy ends- cocccobacilliary
-catalase negative
-PYR positive
-Bile esculin positive
-will not group with B antisera
entro can also grow in 6.5% NaCl or at 45 C or alkaline pH
-shares D group AG
how to differentiate Entero
-only do this when ruling out VRE
E. faecalis
Non Motile
Arabinose negative (sugar fermentation test)
MGP negative
-NH
E. faecium
Often more alpha hemolytic
Non Motile
Arabinose Positive
MGP negative
-AH
E.gallinarum and E casseliflavus
Motile
Arabinose Positive
MGP positive
Yellow pigment produced by E. cass only****
how do we do susceptibility testing for Entro
-usually more resistant to antibiotics especially to cephalosporins, and aminoglycosides - due to low affinity for PBPs
-low levels to ampicillin meaning we can treat E faecalis with it
-faecalis is sensitive to Vanco
-if org has low level resistance to amino glycosides must pair with cell wall active agent like the cillins
- can acquire and exchange genes for resistance
-first org to be resistant to vanco
Vancomycin Screen how is it done
-just like Oxa
-better detection even 1 colony is positive growth
-2 plates BHI with 6ug/ml vanco and plane
-control orgs: VRE and VSE - types of E faecalis
-incubate at 35C, O2 all 24hours
what is HLAR: High-level aminoglycoside resistance
-occurs due to enzyme inactivation - no synergy (using aminoglycosides with ampi or vanc) and the treatment fails
-resistant to HL gentamicin its resistant to amikacin, tobramycin, kanamycin but NOT strep
-no zone is high level resistance
-detects synergy between ampi and aminoglycoside using disk diffusion, agar dilution and broth dilution
what is the HLAR - Agar Dilution Bi-plate
-detects synergy between ampi and high level aminoglycoside
-half with genta and half with streptomycin
-BHI control plate
-0.5 McF
35C for 24 hours
10ul inoculum
how to treat and prevent Enterococci
-vanco unless VRE
-infection control
-ampicillin and aminoglycoside (in higher doses)
-infection control is very important
what is group D Streptococcs bovis, virulence, and clinical sign, treatment prevention
-only human pathogen from group D
- normal flora
-found in GI tract
-Virulence factor - dextran secretion allow org to attach to heart valvles and endothelium
Clinican Significance
-major cause of sub acute bacterial endocarditis SBE
-found in blood if you have colon cancer
-meningitis, UTI
AST
-sterile sites
Treatment Prevention
-susceptible penicillin
-SBE treatment synergistic AB combination
Streptococcus bovis – Laboratory Identification what to look for
small grey NH
Gram positive cocci in pairs and chains
Catalase negative
PYR negative - differentiating test
Bile esculin positive
Bile Insoluble
Optochin resistant
No Growth in 6.5% NaCl
PathoDx: may group with D
what are Nutritionally variant Streptococci- uncommon strp pathogen
- used to be grouped with Viridans but now its separated into Abiotrophia and Granulicatella)
-found in oral cavity of humans
-endocarditis
-very fastidious need pyridoxal hydrochloride (thiol) or B6
-SATELLITING growth on BA with staph streak as the nutrients have to be released by another org
-growth on chocolate agar as nutrients are already released
what are examples of Uncommon Streptococcal Pathogens
S.iniae –fish pathogen
-after handling fish people get cellulitis, bactermia, endocarditis
S. suis –swine pathogen -meningitis
S. porcinus – occasional human infection
all similar to group B
Gemella - normal in skin and oral
AH, NH
Easily decolorize on Gram staining (GNC in pairs, tetrads)
Endocarditis, wounds, abscesses
what is Leuconostoc
Lactobacillaceae family ,
-intrinsically resistant to vanco
Catalase negative,
GPC,
PYR – neg
LAP – neg
Bile esculin +, 6.5% NaCl growth
Can cross react with Group D
Opportunistic - Immunocompromised or treated for underlying disease with vancomycin
Meningitis, UTI
