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Streptococcus pneumoniaeStreptococcus pneumoniae StaphylococciStaphylococci

(Gram positive cocci)(Gram positive cocci)Lecture 38Lecture 38

Faculty: Dr. Alvin Fox

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• S. pneumoniaeS. pneumoniae

− diplococcidiplococci

− PneumococcusPneumococcus

− autolysinautolysin

− bile solubility testbile solubility test

− optochin susceptibilityoptochin susceptibility

− capsulecapsule

− Quellung reactionQuellung reaction

− Polyvalent vaccine Polyvalent vaccine

• Staphylococcus aureusStaphylococcus aureus- coagulase (+)- coagulase (+)- MRSA (methicillin resistant - MRSA (methicillin resistant S. aureusS. aureus))- opportunistic diseases- opportunistic diseases- food poisoning/enterotoxins- food poisoning/enterotoxins- toxic shock syndrome/toxic shock toxin- toxic shock syndrome/toxic shock toxin- exfoliative toxin/scalded skin syndrome- exfoliative toxin/scalded skin syndrome- α, β, γ and δ cytotoxinscytotoxins- leucocidin- leucocidin- lipase- lipase- hyaluronidase- hyaluronidase- protein A- protein A- coagulase (–)- coagulase (–)- Staphylococcus epidermidis- Staphylococcus epidermidis- Staphylococcus saprophyticus- Staphylococcus saprophyticus

KEYWORDS

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S. pneumoniaeS. pneumoniae

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S. pneumoniae • leading cause of pneumonialeading cause of pneumonia

– particularly young and oldparticularly young and old

– member normal flora, nasopharynxmember normal flora, nasopharynx

– replication and spread after damage to upper replication and spread after damage to upper respiratory tract (e.g. after the flu) respiratory tract (e.g. after the flu)

• bacteremiabacteremia• meningitismeningitis• middle ear infections (otitis media) - childrenmiddle ear infections (otitis media) - children

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S. pneumoniae

• α hemolytic hemolytic• pneumolysin pneumolysin

– degrades red blood cells under aerobic conditions degrades red blood cells under aerobic conditions

• grows well on sheep blood agargrows well on sheep blood agar• no group antigen no group antigen

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Diagnosis - spinal fluidDiagnosis - spinal fluid

• direct Gram stainingdirect Gram staining• detection of capsular antigendetection of capsular antigen

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Autolysis – identification after Autolysis – identification after growthgrowth

BileBile

peptidoglycanpeptidoglycan

lipoteichoic acidlipoteichoic acid

teichoic acidteichoic acid-choline-choline

autolysinautolysin

autolysinautolysin

Cell membraneCell membrane

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C polysaccharide

• Teichoic acid (C polysaccharide)– precipitates in serum– binds C-reactive protein

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optochin resistant

optochin sensitive

IdentificationIdentification

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CapsuleCapsule

• prominent prominent – virulent strains virulent strains

• anti-phagocyticanti-phagocytic• carbohydrate antigens carbohydrate antigens

– highly variable among strainshighly variable among strains

– numerous serotypesnumerous serotypes

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Capsular vaccineCapsular vaccine• ImmunityImmunity

– serotype specificserotype specific

– to eradicate the organism in normal flora to eradicate the organism in normal flora

• VaccineVaccine– a few major serotypes (polyvalent)a few major serotypes (polyvalent)

• Vaccination or the susceptible populationVaccination or the susceptible population– young children young children

– elderlyelderly

• ImmunizationImmunization– major serotypes susceptible to change major serotypes susceptible to change

– population monitoring essentialpopulation monitoring essential

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Quellung reactionQuellung reaction

• using antisera using antisera

• capsule "fixed" capsule "fixed"

• visible microscopicallyvisible microscopically

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PathogenesisPathogenesis

• Teichoic acidTeichoic acid– complement activation complement activation – large numbers of inflammatory cells at large numbers of inflammatory cells at

infection siteinfection site

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TherapyTherapy

• S. pneumoniaeS. pneumoniae – most strains susceptible to penicillin most strains susceptible to penicillin

– resistance is commonresistance is common

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STAPHYLOCOCCISTAPHYLOCOCCI

• Gram positiveGram positive• Facultative anaerobesFacultative anaerobes• Grape like-clustersGrape like-clusters• Catalase positiveCatalase positive• Major components Major components

of normal flora of normal flora - skinskin

- nares nares

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Staphylococcus aureusStaphylococcus aureus

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One of commonest opportunistic One of commonest opportunistic infections, both hospital and community infections, both hospital and community

acquiredacquired:• pneumonia

• osteomyelitis

• septic arthritis

• bacteremia

• endocarditis

• abscesses/boils

• other skin infections

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Antibiotic therapyAntibiotic therapy• Resistance to penicillinResistance to penicillin

– penicillinasepenicillinase

• Resistance to methicillin Resistance to methicillin

‾ modified penicillin binding proteinmodified penicillin binding protein

‾ methicillin resistant S. aureus (MRSA) methicillin resistant S. aureus (MRSA)

• Vancomycin Vancomycin

• current drug of choicecurrent drug of choice

• resistance observed but uncommon at this time resistance observed but uncommon at this time

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Hospital infection controlHospital infection control

• MRSA now such a problem MRSA now such a problem – monitoring by PCR of nasal swabsmonitoring by PCR of nasal swabs– eradication eradication

• antibiotics antibiotics

• whole body antisepsiswhole body antisepsis

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Food poisoningFood poisoning

• not an infectionnot an infection

• food contaminated by humans food contaminated by humans – growth of bacteriagrowth of bacteria

– production of enterotoxinproduction of enterotoxin

• onset and recovery both occur onset and recovery both occur within few hourswithin few hours

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Food poisoningFood poisoning

• VomitingVomiting

• nauseanausea

• diarrheadiarrhea

• abdominal painabdominal pain

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Toxic shock syndrome.

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Toxic shock syndromeToxic shock syndrome

• feverfever

• rashrash

• desquamationdesquamation

• vomitingvomiting

• diarrheadiarrhea

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Toxic shock syndrome

• Toxic shock toxin Toxic shock toxin

- DisseminationDissemination

• OrganismOrganism

– no dissemination no dissemination

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S. aureusS. aureus

• babiesbabies– scalded skin syndromescalded skin syndrome

• exfoliatinexfoliatin

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Lytic exotoxins:Lytic exotoxins:

• α toxintoxin• β toxin (sphingomyelinase C)toxin (sphingomyelinase C)• γ toxintoxin• δ toxinstoxins

– detergent-likedetergent-like

• leucocidinsleucocidins

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Protein A inhibits phagocytosisProtein A inhibits phagocytosis

Protein AProtein Aimmunoglobulinimmunoglobulin

Fc receptorFc receptor

BACTERIUM BACTERIUM

PHAGOCYTEPHAGOCYTE

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SpreadSpread

• tissue-degrading enzymestissue-degrading enzymes

– lipase lipase

– hyaluronidasehyaluronidase

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IdentificationIdentification• Sheep blood agarSheep blood agar– β hemolyticβ hemolytic – yellow pigmentedyellow pigmented (aureus)(aureus)

• mannitol fermentationfermentation• coagulase-positivecoagulase-positive

• phage-typing, rarely performed phage-typing, rarely performed

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Staphylococcus epidermidisStaphylococcus epidermidis

• major member, skin floramajor member, skin flora

• opportunistic infectionopportunistic infection - less common than - less common than S.aureusS.aureus

• nosomial infections nosomial infections - shunts, cathetersshunts, catheters

• artificial heart valves/joints artificial heart valves/joints

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IdentificationIdentification• Sheep blood agarSheep blood agar

– non-hemolyticnon-hemolytic– Non-pigmentedNon-pigmented

• Does not ferment mannitolDoes not ferment mannitol• Coagulase negativeCoagulase negative

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Several other coagulase Several other coagulase negative staphylococcal species negative staphylococcal species

• common on human skincommon on human skin

• some species cause opportunistic infectionsome species cause opportunistic infection

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Staphylococcus saprophyticusStaphylococcus saprophyticus

• urinary tract infectionsurinary tract infections

• this coagulase-negative species (and others) coagulase-negative species (and others) – not usually differentiated from not usually differentiated from S. epidermidisS. epidermidis

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GRAM POSITIVE COCCI

S. aureus Beta hemolytic

mannitol yellow

+ -Staphylococcus (Clusters) Streptococcus (pairs & chains)

Catalase

BETA: Bacitracin S. pyogenes (group A)

CAMP/ Hippurate S. agalactiae (group B)

Coagulase

S. epidermidisNon-hemolyticmannitol white

ALPHA: Optochin /Bile Solubility S. pneumoniae

GAMMA OR ALPHA: Bile Esculin 6.5% NaCl Group D Enterococcus

Bile Esculin 6.5% NaCl Group D Non-Enterococcus

Note: S. viridans is ALPHA hemolytic and negative for all the tests below

+

++

++

+

+

-

-

Summary Figure (Identification Scheme)

Hemolysis/TestHemolysis/Test