gram positive cocci
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Gram Positive Cocci. Dental Optometry Microbiology Ken B. Waites, M.D., F(AAM). Objectives. To review and discuss: microbiological characteristics epidemiology virulence factors associated diseases laboratory detection - PowerPoint PPT PresentationTRANSCRIPT
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Gram Positive Cocci
Dental Optometry MicrobiologyKen B. Waites, M.D., F(AAM)
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Objectives• To review and discuss:
• microbiological characteristics• epidemiology• virulence factors• associated diseases • laboratory detection
of clinically important gram-positive cocci and gram-positive bacilli.
• Organisms to be discussed include:– Staphylococcus– Streptococcus– Enterococcus– Listeria– Corynebacterium– Bacillus
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Staphylococcus
• Most important genus in Family Micrococcaceae
• Other genera
– Stomatococcus
– Micrococcus
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Habitat• S. aureus
– anterior nares 50-75% healthy people– skin & mucous membranes– hospital environment
• S. epidermidis & others– resident skin flora, gut, upper respiratory
tract• S. saprophyticus
– Urinary tract in young women
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Lab Characteristics
• Gram-positive cocci (1 m) in clusters
• Culture - Aerobic• S. aureus is
hemolytic• Coagulase • Catalase • Mannitol
fermentation
S. aureus
blood agar mannitol salt agar
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Catalase Test for Distinguishing Staphylococci from Streptococci
H2O2 catalase
O2 + H2O
Bubbles
Strep. Negative Staph. positive
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Tube Coagulase Test
• Free coagulase secreted by S. aureus but not CNS
• Clots rabbit plasma
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Cell Wall of S. aureus
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Antigenic Structures & Virulence Factors of S. aureus
• Cell wall peptidoglycan– elicits production of IL-1 and opsonic antibody– PMN chemotaxis “pyogenic”– induces sepsis– activates complement– teichoic acid binds fibronectin on host cells
• Protein A - binds Fc of IgG• Capsule (some strains) antiphagocytic
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S. aureus Soluble Virulence Factors
• Catalase - reduce phagocyte killing - remove H2O2
• Coagulase - clots plasma (free & bound)• Hyaluronidase - destroys connective tissue• Beta lactamase - destroys beta lactam drugs• Altered Penicillin binding proteins (PBP2’)• Fibrinolysin• Lipases• Nucleases
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S. aureus Soluble Virulence Factors• Cytotoxins & leukocidins
– lyse white blood cells (Panton-Valentine)– release lysosomal enzymes damage tissue
• Exfoliatin – interrupts intercellular skin junctions – “Scalded Skin Syndrome”
• Toxic Shock Toxin – stimulates T cells cytokines, – endothelial damage rash– “Toxic Shock Syndrome”
• Enterotoxins – stimulate vomiting by interaction with GI neural receptors (food
poisoning)
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S. aureus DiseasesSkin and soft tissue
infections FurunclesCarbunclesWound infectionsCellulitisImpetigoBacteremia
EndocarditisCNS Infections
Brain abscess Meningitis - rare Epidural abscess
Impetigo
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S. aureus DiseasesPulmonary Infections
embolicaspiration
Musculoskeletal osteomyelitisseptic arthritis
Genitourinary Tractrenal carbunclelower UTI
Toxin mediated diseases
• scalded skin syndrome
• food poisoning
• toxic shock disease
Toxic shock
Scalded skin
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Treatment of Staph. Infections
• Increase in oxacillin-resistant organisms that are resistant to most other antibiotics except vancomycin (MRSA)
• Nosocomial infections
• Recent emergence of virulent community-acquired MRSA in skin & soft tissue infection
• First high-level vancomycin-resistant S. aureus reported July 2002 contains vanA gene from Enterococcus
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Coagulase negative staphylococci
• Opportunistic infections– bacteremias– endocarditis– neutropenic patients– Neonates– UTIs (S. saprophyticus)
• Polysaccharide “slime” – protects bacteria– mediates attachment to catheters, etc.
Staphylococcus epidermidisStaphylococcus epidermidis on sheep blood agar on sheep blood agar
White non-hemolytic colonies
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Streptococcaceae
• Streptococcus
• Enterococcus
Gram stain of staph (clusters)and strep (chains)
Staph
Strep
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Streptococcus Classification • Hemolysis
– beta– alpha– gamma
• Lancefield Groups – (A-T- hemolytic)– group-specific cell wall
polysaccharide
• Species– phenotypic biochemical
reactions
Hemolytic Reactions
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Streptococcus Habitat• Skin, mucous membranes, respiratory tract and
Gl/GU tracts, depending on species• 20% of children may carry GAS in their pharynx
during winter months. • S. pneumoniae is commonly isolated from the
respiratory tract of asymptomatic carriers.• Enterococci in gut flora are are important
pathogens in hospitals where they are selected by high antibiotic usage.
• Organisms spread by droplets, direct contact and fomites.
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Lab Characteristics• Morphology and Gram stain
– Gram-pos. cocci 0.7 - 0.9 m– pairs or chains
• Catalase-negative• Most grow on sheep blood agar• Aerobic or anaerobic• Enhanced by CO2
• Antigenic grouping• Biochemical identification
S. pyogenes in blood
S. pneumoniae in sputum
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Antigenic Structure & Virulence
Factors of S. pyogenes
• Hyaluronic acid capsule - antiphagocytic
• Hyaluronidase - tissue penetration
• Group specific cell wall antigen distinguishes from B,C,D,F,G, etc.
• Beta hemolytic
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Antigenic Structure & Virulence Factors of S. pyogenes
• M Protein
– Virulence factor present on pilus with teichoic acid
– Organisms lacking it are readily opsonized and phagocytized
– Binds fibrinogen, fibrin & degradation products forming dense coating on the organism's surface, blocking complement
– Antibody against M protein is an important protective mechanism, but repeated infections with strains possessing one of over 80 different serotypes can occur
– Autoantibody target-Acute Rheumatic Fever
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Antigenic Structure & Virulence Factors of S. pyogenes
• Erythrogenic Toxin “Scarlet Fever”• Streptokinases
– transform plasminogen to plasmin– digest fibrin
• DNAase– depolymerizes DNA
antibody used to follow pyoderma• Hemolysins “Streptolysins”
– Important immunogens– Antibody against streptolysin O used to
follow course of pyoderma– Streptolysin S - hemolysis
Strep. cellulitis
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Antigenic Structure & Virulence Factors of S. pyogenes
• Protein F - facilitates attachment by binding fibronectin
• Protein G - binds Fc portion of antibody
• Diphosphopyridine nucleotidase (DPNase) – enzyme kills WBCs
• C5a peptidase
Erysipelas
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S. agalactiae “Group B”
• Pathogen of newborns & older debilitated adults
• Antibody against type-specific capsular antigen is protective
• CAMP Test - interaction of CAMP factor (sphingomyelinase) with hemolysin of S. aureus to potentiate hemolytic activity
• Hippurate hydrolysis
GBS
S. aureus
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Diseases Due to Hemolytic StreptococciGroup Species Disease
A S. pyogenes Pharyngitis, impetigo, cellulitis, erysipelas, scarlet fever, necrotizing faciitis, rheumatic fever, glomerulonephritis
B S. agalactiae
Neonatal sepsis, pneumonia, meningitis, OB/GYN infections, Bacteremia, UTI
C S. equi, S. dysgalactiae, & others
Bacteremia, pneumonia, endocarditis, abscesses, pharyngitis, wound infections
D
S. bovis
Endocarditis, bacteremia in cancer patients
F S .anginosus
Cervicofacial abscesses, bacteremia, osteomyelitis
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S. pneumoniae• Asymptomatic carriage• Colonization precedes disease• Most common cause of:
– community acquired pneumonia (bacteremia)– otitis media (children)– meningitis
• Species-specific C polysaccharide• No Lancefield antigen • 90 capsular serotypes• Alpha hemolytic• Bile soluble, optochin susceptible• Often require CO2 for growth
Optochin test
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S. pneumoniae Virulence Factors• Antiphagocytic capsule – immunogen• PspA: inhibits opsonization• Autolysin – release cell components• Pneumolysin
• Cytotoxic – inhibit cilia, wbcs • lyses RBCs• activates classic complement path.• stimulates cytokines tissue damage & purulent
inflammation
• Hydrogen peroxide - tissue damage• Surface protein adhesins • Neuraminidase• IgA protease• Peptidoglycan
– activate alternate complement– cytokine release
• Transformation– antibiotic resistance• Intracellular invasion
Capsule Quellung Reaction
sputum - pneumonia
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Fatal Pneumococcal Meningitis
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Pneumococcal Vaccine
• 23 valent polysaccharide vaccine - adults
• 7 valent conjugate vaccine - children
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Viridans streptococci• Most human strains are commensals of the
oral cavity & upper respiratory tract • Alpha hemolysis• Do not have Lancefield group antigens• Differentiate species biochemically• Usually of low pathogenicity• Important causes of endocarditis• Dental caries (S. mutans) dextran from
glucose
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Enterococcus• At least 12 species• Usually non-hemolytic• E. faecalis most common• Distinguish from streptococci by:
– esculin hydrolysis– growth in 6.5% NaCl– PYR hydrolysis (Group A strep. are +)
• Enteric flora• Opportunist - nosocomial pathogen• Intrinsic antimicrobial resistance• E. faecium - vancomycin-resistance• Abscesses, urinary tract, endocarditis, abdominal/pelvic,
bacteremia, wound infections