Medical Microbiology

Li Mei Department of Microbiology

November, 2006

Chapter 7 Cocci

Outline

• 5 pathogenic cocci/ Pyogenic cocci – G + : Staphylococcus

S.aureus Streptococcus

S.pyogenes, S.pneumoniae – G ­ : Neisseria

N.meningitidis, N.gonorrhea

þ Biological characteristics; þ Pathogenicity;

Section 1 Staphylococcus

Staphylococcus

• Primary reservoir human carriers nasopharynx, throat, skin

• >30 species ­main bacteria in the nosocomial infection ­S.aureus: the most virulent species. ­S.epidermidis: opportunistic pathogen. ­S.saprophyticus: rarely cause human diseases.

Biological characteristics

• Shape and structure

Biological characteristics

• Cultivation • Requirement: Low

grow on basic media facultative anaerobes 37 (28­38) pH: 7.4 7­10% NaCl

Growth properties liposoluble pigments complete/clear hemolysis (β­hemolysis) (S.aureus)

Biological characteristics S.aureus

• Biochemical reactions

Biological characteristics

Catalase test “+” Staphylococci: “+” Streptococci: “­”

Mannitol Fermentation “+” S. aureus: “+”; S.epidermidis & S.saprophyticus: “­”;

– Carbohydrate antigens: capsules & teichoic acid

– Protein antigens:

• Antigenic composition

Biological characteristics

• Staphylococcal protein A (SPA) • Characteristics:

nonspecifically bind to the Fc fragment of IgG

S. aureus

• Function: F a. anti­phagocytosis; F b. damage platelet; F c. induce hypersensitivity and inflammation;

Biological characteristics

SPA(staphylococcal protein A)

Bacteria Bacteria

Fc Fc receptor receptor

Phagocyte Phagocyte

IgG IgG

Fab Fc

SPA SPA

• Function: F a. anti­phagocytosis; F b. damage platelet; F c. induce hypersensitivity and inflammation; F d. SPA­coated S.aureus is used as reagent

(Ab carriers) of coagglutination test to identify species and types of bacteria.

Biological characteristics

SPA (staphylococcal protein A )

S. aureus Ab

Classification

• Based on the pigments and chemical reactions

Properties S. aureus S. epidermidis S. sarprophyticus

Pigment Golden yellow White Citrine Coagulase + － － Mannitol + － －

Thermostable nuclease + － －

α­hemolysin + － － SPA + － －

Pathogenicity strong Weak ­

Classification

• Based on coagulase § Coagulase” +”: S. aureus § Coagulase” ­”: e.g., S. epidermidis & S. saprophyticus

• Phage typing ­­­­is of epidemiological value S. aureus: 3 phage groups, 26 phage types. § group 1: TSST­1­producing strains § group 2: exfoliative toxin­producing strains § group 3: enterotoxin­producing strains

Resistance to environment

• Resistance: • Drying

• Heat (survive at 80 30 min); • high concentration of salt (10­15% NaCl)

• Sensitivity: • basic dyes (e.g., crystal violet)

• several antibiotics (penicillin, vancomycin) MRSA (methicillin resistant S.aureus)

Pathogenicity (S.aureus)

• Virulence factors ØInvasiveness • Surface structure

SPA, capsule/slime layer • Invasive Enzymes

ØToxin­­­exotoxins • Hemolysins • Leukocidin • Staphylococcal enterotoxin • TSST­1 • Exfoliative toxin Coagulase

Enzyme

• Coagulase: • An enzyme that converts fibrinogen in citrated human or rabbit

plasma into fibrin causing the coagulation of blood. • Roles:

inhibit the phagocytosis and function of bactericidal substances in human body by coating bacteria with fibrin

• Classification: Free coagulase ­­ plasma clotting ­­ tube coagulase test Bound coagulase ­­ agglutination of bacteria ­­ slide

coagulase test

Free coagulase

+ ­

tube coagulase test

clot

Bound coagulase

slide coagulase test

Pathogenicity (S.aureus)

• Virulence factors Ø Invasiveness • Surface structure

SPA, capsules, slime layer

• Invasive Enzyme

ØToxin­­­exotoxin • Hemolysins/Staphylolysin • Leukocidin • Staphylococcal enterotoxin • TSST­1 • Exfoliative toxin/

Epidermolytic toxin

Coagulase

Hemolysins/Staphylolysins Five kinds: α­Lysin (main pathogenic substance)

β­Lysin γ­Lysin δ­Lysin ε­Lysin

Roles: • damage host cell membrane → permeability↑; • Have cytotoxic effects on phagocytes and tissue cells;

Pathogenicity (S.aureus)

• Virulence factors Ø Invasiveness • Surface structure

SPA, capsules, slime layer

• Invasive Enzyme

ØToxin­­­exotoxin • Hemolysins/Staphylolysin • Leukocidin • Staphylococcal enterotoxin • TSST­1 • Exfoliative toxin/

Epidermolytic toxin

Coagulase

Staphylococcal enterotoxin

• ~1/2 strains of S.aureus • Heat stable protein (100, 30 min) • Resistant to proteolytic enzymes of GI tract

• Role: stimulate vomiting­control center of CNS and cause a food poisoning characterized by projectile vomiting.

Toxic shock syndrome toxin­1(TSST­1)

• Role: • Induce fever, shock, hypotension, multi­organs failure; • enhance the host susceptibility to endotoxin • Cause TSS (Toxic shock syndrome)

Exfoliative toxin

Epidermolytic toxin

• Role: blister of skin SSSS

SSSS: staphylococcal scalded skin syndrome

Pathogenicity

• Disease Ø Invasive infection/pyogenic infection • local infection: folliculitis; boil; carbuncle; impetigo, etc.

(Lesion is limited in local area) • organ infection: pneumonia; meningitis, etc.

• Systemic infection: Septicemia; pyemia

Boil/furuncle

folliculitis

Impetigo­ staph skin infection, multiple pustules (small skin abscesses) Carbuncle

Pathogenicity

ØToxin­associated diseases • Food poisoning (enterotoxin) • TSS (TSST­1)

– Sudden high fever, shock, kidney failure, and red skin rash, etc. • SSSS (Exfoliative toxin) (staphylococcal scalded skin

syndrome) • Staphylococcal enterocolitis ­ dysbacteriosis

­­ most often occurs in infants and young children.

­­ low mortality rate.

skin blister →denudation (like scald)

Staphylococcal scalded skin syndrome (SSSS)

Diseases caused by coagulase ­ staphylococci

• Diseases: – S.epidermidis

• urinary tract infection (UTI) • Bacterial endocarditis • Septicemia • Wound infection

– S.saprophyticus • community­acquired UTI

pathogenic cocci

– G + cocci: Staphylococcus S. aureus

Streptococcus S. pyogenes S. pneumoniae

– G ­ cocci: Neisseria N. meningitidis N. gonorrhea

Section 2 Streptococcus

­­ widely exist:

water, air, feces, human nasopharynx.

­­ diseases:

①pyogenic infection;

②scarlet fever;

③streptococcal hypersensitive disease;

④rheumatic fever;

Biological characteristics

• Morphology & cultivation properties • G + , arranged in chains,

no special structure • Nutrient requirement: high

Fastidious (“flesh­eating bacteria”)

• Facultative/obligate anaerobe • On blood agar:

different hemolysis

Biological characteristics

• Morphology & cultivation properties • G + , arranged in chains,

no special structure • Nutrient requirement: high

Fastidious (“flesh­eating bacteria”)

• facultative/obligate anaerobe • On blood agar:

different hemolysis

Biological characteristics • Classification ØHemolytic activity • α­hemolytic strep.

Incomplete hemolysis (α) Opportunistic pathogens e.g., S.pneumoniae, S.viridans

• β­hemolytic strep. Complete hemolysis (β) Main human pathogens e.g., S. pyogenes

• γ­streptococcus No hemolysis, No pathogenicity e.g., enterococci.

a

b

c

Biological characteristics

ØAntigenic structure • Carbohydrate antigens

– group­specific antigen – 20 groups (A~H, K~V) – Group A­ main human pathogens

• Protein antigens – type­specific antigen – M, R, T protein – Group A >60 serotypes

Cell wall

Streptococcus

Capsule Protein

Polysaccharide

Peptidoglycan

Biological characteristics • Resistance • Heat labile: killed at 60, 30 min

• Antibiotics sensitivity: penicillin, erythromycin, tetracycline, etc.

Pathogenicity (Strep. Group A)

• Virulence factors

– Surface structures LTA: adhere to host cells M­protein:

a.Anti­phagocytosis b.Be associated with rheumatic heart disease &

glomerulonephritis c.Adhere to epithelial cells

d.Clump platelet and leukocyte

Pathogenicity (Strep. Group A)

– Invasive enzymes Hyaluronidase (spreading factor) Streptokinase (SK)

Streptodornase (SD)

< Toxins­­­exotoxins • Streptolysin (hemolysin) • Erythrogenic toxin

Streptolysins

Polypeptide (28aa) Protein (MW60,000) Chemical

destroy WBC virulence of many tissues

destroy WBC, platelet virulence of MΦ, N.C

Biological activity

Weak Strong (ASO test) Antigenicity

oxygen­stable oxygen­labile O 2

Streptolysin S (SLS) Streptolysin O (SLO) Properties

ASO: Antistreptolysin­O, antibody

Anti­SLO Test (ASO test) • Definition: a neutralization test between the toxin (SLO) and its specific anti­toxin (ASO) which is used to diagnose or monitor rheumatic fever caused by Group A strep..

Erythrogenic toxin

pyrogenic toxin /scarlet fever toxin • protein • Serotype A,B,C • Scarlet fever

Pathogenicity (Strep. Group A)

• Diseases – Transmission:

Respiratory tract, trauma, gastrointestinal tract

< 3 types of infections <Pyogenic infection <Toxin­associated diseases <Hypersensitive disease

Pyogenic infection

–Local purulent infections: pharyngitis, tonsillitis; cellulitis, puerperal fever, erysipelas, impetigo; otitis, pneumonia, meningitis

<Systemic infection: septicemia

Abscess with surrounding cellulitis

• Acute Tonsillitis There is a risk of developing Rheumatic

Fever.

Erysipelas

Erysipelas on

the cheek

• scarlet fever: – Pharyngitis → scarlet fever

Strawberry tongue

red rash paly around mouth

Toxin­associated diseases

Acute glomerulonephritis ­edema, hypertension, hematuria and proteinuria

Rheumatic fever ­involve: heart, joints, subcutaneous tissue, and CNS; ­fever, migratory polyarthritis, carditis

Hypersensitive disease

Diseases caused by other streptococci – Group B strep.

neonatal infection adult infections: endometritis, pneumonia, meningitis,

endocarditis – Group C strep.

epidemic sore throat, acute glomerulonephritis – Group G strep.­­sore throat, cellulitis, erysipelas – Group D strep. and enterococci

nosocomial infection urinary infection, biliary tract infection, peritonitis

Prevention and treatment

• Treat the pharyngitis and tonsillitis in time • Antibiotics: penicillin for the first choice

Section 3 Pneumococcus

General properties • G + , arranged in pairs, bullet shape

• Capsule: polysaccharide • Blood agar or chocolate blood agar, fastidious

• α­hemolysis • Autolysis • Bile solubility test: “+”

­­distinguish from other α ­hemolytic streptococci.

• Ferment inulin

Pathogenicity

• Virulence factor: • Capsule • Pneumolysin & Neuraminidase

• Main disease: • Pneumonia

Laboratory diagnosis

• Differentiate S.pneumoniae from other α­hemolytic streptococcus

R Bile solubility test R Optochin sensitivity test

Positive Negative

R Capsule swollen reaction R Animal test

Treatment & prevention

(S.pneumoniae) • sensitive to a wide range of antimicrobial agents: Penicillin, erythromycin, chloramphenicol, Sulphonamides, clindamycin, vancomycin.

• Prevention: polysaccharide vaccine

Section 4 Neisseria

N. Meningitidis ­­meningitis ­­low prevalence but high mortality

N. Gonorrhoeae ­­ human gonorrhea ­­ high prevalence but low mortality

Genus Neisseria: >10 species

Common biological characteristics

• G ­ , coffee bean­shaped or kidney­shaped, in pairs

• capsules and pili • fastidious • Resistance: very low

polymorphonuclear cells

N. Meningitidis / meningococcus

• Pathogenesis ØVirulence factor: • Pili ­­ attach to nasopharyngeal mucosa • Capsule • Endotoxin ­­ damage capillary blood vessel Ø transmission: respiratory droplets ØDisease: epidemic cerebrospinal meningitis

N. Gonorrhoeae /gonococcus

• Virulence factors • Pili • IgA 1 protease • Outer membrane protein

(OMP) • LPS (endotoxin)

• Transmission: sexual contact; indirect contact; (basin, towel, etc)

• Diseases: Gonorrhea

Gonorrhea

Adults ØTransmission: STD (sexually transmitted disease) ØClinical disease: Genitourinary tract infection

Urethritis, prostatitis; epididymitis (male); cervix inflammation (female); infertility

Newborns ØOphthalmia neonatorum

Prevention and treatment • Penicillin • 1%Silver nitrate­­ ophthalmia neonatorum

• Concepts: Pathogenic/Pyogenic cocci SPA ASO test

• Pathogenicity of 5 pathogenic cocci (S.aureus, S.pyogenes, S.pneumoniae,

N.meningitidis, N.gonorrhea)

Summary of this chapter