Staphylococcus-Streptococcus-Enterococcus

Gr + cocci ~ 21 genera

Common features Spherical shape Gram stain reaction Absence of endospores Catalase activity subdividing

Catalase positive genera StaphylococcusMicrococcus

StomatococcusAlloiococcus

Catalase negative genera StreptococcusEnterococcus

Staphylococcus Gram positive Grow pattern cluster of grapes

single cells, pairs, short chains

Nonmotile Aerobic or facultatively anaerobic Catalase-positive Grow in 10 % NaCl medium @ 18-40 o C

Most common Staph. causing diseases S. aureus

S. epidermidis S. saprophyticus S. capitis S. haemolyticus

Produce coagulase

Coagulase negative staphylococcus

Micrococcus

Can be confused with CN staphs Differ in that, they grow only aerobically Resistant to lizostafin and furazolidone Isolation of micrococcus in clinical samples

Contamination ?

Stomatococcus Alloiococcus Stomatococcus

mucilaginosus Only species in this

genus Infection in the

immunocompromised host

Alloiococcus otitidis Only species in this

genus Aerobic Gr + Disease??

Staphylococcus and their diseases S. aureus

Toxin-mediated Food poisoning Toxic shock syndrome, scalded skin

syndrome Cutaneous

Impetigo Folliculitis Furuncles Carbuncles, wound infections

Staphylococcus and their diseases S. aureus

Others Bacteremia Endocarditis, Pneumoniae Empyema Osteomyelitis Septic arthritis

Staphylococcus and their diseases S. epidermidis

Bacteremia Endocarditis, Surgical wounds Urinary tract infections Opportunistic infections of catheters,

shunts, prostetic devices and peritoneal dialysates

Staphylococcus and their diseases S. saprophyticus

Urinary tract infections Opportunistic infections Resistant to novobiocin

Staphylococcus/physiology & structure Capsule Peptidoglycan Teichoic acids Protein A Coagulase and other sutface proteins Cytoplasmic membrane

Staphylococcus/capsule Loose-fitting Polysaccharide layer (slime layer) In vitro rare

Staphylococcus/peptidoglycan Half of the cell wall More rigide compared to Gr negatives Endotoxin-like activity

Endogenous pyrogenes Activation of complement Production of int-1 from monocytes Aggregation of polymorphonuclears

Staphylococcus/teichoic acids Teichoic & lipoteichoic acid

Polysaccharide A in S. aureus Polysaccharide B in S. epidermidis

Mediate the attachment of staphs to mucosal surfaces

Poor immunogens (except when bound to

peptidoglycan)

Staphylococcus/protein A The surface of most S. aureus is coated with

protein A (not CNS) Affinity to bind Fc receptor of IgG1, IgG2 &

IgG4 prevents the antibody-mediated immune clearence of the bacteria

Staphylococcus/coagulase & other surface proteins S. aureus clumping factor (bound

coagulase)

Collagen-binding protein adherence to

Elastin-binding protein host tissues Fibronectin-binding protein

Staphylococcus/pathogenesis & immunity Toxins

&

Enzymes

Staphylococcus/toxins Alpha toxin Beta toxin Delta toxin Gamma toxin & Panton-Valentine Leukocidin Exfoliative toxins Enterotoxins Toxic shock syndrome toxin-1

Staphylococcus/toxins

Toxin important mediator of tissue damage in staphylococcal diseasestoxic for many cells (erythrocytes, leukocytes, hepatocytes,..)

produced by most strains of S. aureus

Staphylococcus/toxins

Toxin sphingomyelinase C

toxic for many cellsrole in tissue destruction & abscess formation produced by most strains of S. aureus

Staphylococcus/toxins

Toxin wide spectrum of cytolytic activitydetergent-like activityproduced by most strains of S. aureus

Staphylococcus/toxins

Toxin & Panton-Valentine Leukocidincomposed of two polypeptide chains toxic for many cells

Staphylococcus/toxins

Exfoliative toxins staphylococcal scalded skin syndrome (SSSS)exfoliative dermatitistwo types: ETA & ETBproduced by 5 to 10 % of all S. aureus strains

Staphylococcus/toxins

Enterotoxins 8 serologically distinct enterotoxins exist (A-E, G-I)

stable to heating

resistant to gastric & jejunal

enzymes produced by 30 to 50 % of all S. aureus strains are superantigens

Staphylococcus/toxins

Toxic shock syndrome toxin-1

heat & proteolysis resistantall S. aureus responsible for

menstruation-associated TSS produce TSST-150 % of the strains responsible for other forms of TSS produce TSST-1superantigens

Staphylococcus/enzymes Coagulase Catalase Hyaluronidase Fibrinolysin Lipases Nuclease Penicillinase

Staphylococcus/enzymes Coagulase

S. aureus 2 forms

Bound free

Staphylococcus/enzymes Catalase

“All staphylococci produce catalase” H2O2 (toxic) H2O

O2

Staphylococcus/enzymes Hyaluronidase

Hydrolyzes hyaluronic acids facilitates the spread of S. aureus in tissues

> 90 % of S. aureus produce hyaluronidase

Staphylococcus/enzymes Fibrinolysine

Staphylokinase All S. aureus Dissolve fibrine clots

Staphylococcus/enzymes Lipases

All S. aureus & 30 % of the CNS produce several different lipases

Nuclease A marker for S. aureus

Penicillinase (-lactamase)

Staphylococcus/IDENTIFICATION Microscopy Culture:

Nutritionally enriched agar media with sheep blood Selective agar media for S. aureus with 7.5 % NaCl +

mannitol Aerobic and anaerobic Large, smooth colonies

Identification Positive coagulase, heat-stable nuclease, alkaline

phosphatase, mannitol ferment. S. aureus

Streptococcus Gram positive Grow pattern pairs, chains Most species are facultatively anaerobes Some grow only in atmosphere enhanced

with CO2

Nutritional requirements are complex Blood, serum

“Catalase-negative”

Streptococcus Classification is complicated

3 different schemes are used

1. Lancefield groupings according to serologic properties (A-H, K-M, O-V)

2. Hemolytic patterns: & hemolysis

3. Biochemical properties

Streptococci and their diseases S. pyogenes (group

A) Pharyngitis, scarlet fever, pyoderma, erysipelas, cellulitis,

necrotizing fasciitis,

streptococcal toxic shock syndrome,

bacteremia, rheumatic fever, glomerulonephritis

Streptococci and their diseases S. agalactiae

(group B) Neonatal

infections (meningitis, pneumoniae, bacteremia)

Urinary tract infections

Amnionitis, Endometritis Wound infections

Streptococcus pyogenes/physiology & structure Spherical cocci Form short (clinical specimen) or long chains

(liquid media) Grow on enriched blood agar media White colonies 1-2 mm with large zones of

-hemolysis Encapsulated strains mucoid Basic structure in the cell wall is

peptidoglycan as Staphs group spec. Ag

Streptococcus pyogenes/physiology & structure Group specific carbohydrate

Within the cell wall 10 % of the dry weight Is used to classify group A streptococci and

distinguish them from others

Streptococcus pyogenes/physiology & structure Type specific proteins

M protein major type-specific protein associated with virulent streptococci

2 polypeptide chains1. Highly conserved among all ggroup A streptococci

2. Responsible for the antigenic variability >80 serotypes

T protein (trypsin-resistant) secondary Usefull when bacteria fail to express the M protein

Streptococcus pyogenes/physiology & structure Other cell surface components

M-like proteins Lipoteichoic acid F protein

Capsule (hyaluronic acid)

Streptococcus pyogenes/Pathogenesis&Immunity Virulence of S. pyogenes

The ability of the bacteria to adhere to the surface of the host cells Invade into the epithelial cells Avoid opsonization & phagocytosis Produce a variety of toxins & enzymes

Streptococcus pyogenes/Pathogenesis&Immunity Pyrogenic exotoxins(Streptococcal pyrogenic exotoxin, Spes)

Produced by lysogenic strains Superantigens Responsible for the streptococcal toxic

shock syndrome

Streptococcus pyogenes/Pathogenesis&Immunity Streptolysin S & O

Streptolysine S lyse erythrocytes

leukocytes

platelets

responsible for -hem.

Streptolysine O lyse erythrocytes

leukocytes

platelets

antibodies are formed against ASO test

Streptococcus pyogenes/Pathogenesis&Immunity Streptokinases

A & B Lyse blood clots Used in medicine

Deoxyribonucleases A to D Depolymerase free DNA in pus reduce

viscosity C5a peptidase Hyaluronidase,diphosphopyridine nucleotidase

Streptococcus pyogenes/IDENTIFICATION Microscopy Culture:

Proper collection of throat swab specimen Nutritionally enriched agar media with sheep

blood Selective media (media with “bactrim”)

Identification Table 23-4

Streptococcus agalactiae (Group B) The only species that carries the group B

antigen physiology & structure

Gr + cocci Short or long chains (indistinguishable from S. pyogenes)

Buttery colonies, narrow zone of -hem. Subdividing

The B antigen group specific Capsular polysaccharides type-specific C protein (surface protein)

Streptococcus agalactiae/IDENTIFICATION Microscopy Culture:

Readily grow on a nutritionally enriched medium Large colonies -hemolysis may be absent selective broth

medium with antibiotics

Identification Preliminary identification (+) CAMP test,

hydrolysis of hippurate

Other beta-hemolytic streptococci Group C, F and G are most commonly

associated with human disease 2 species of particular importance

S. anginosus S. dysgalactiae

Viridans Streptococci -hemolytic and nonhemolytic streptococci Produce green pigment on blood agar media Require complex media supplemented with

blood products and inc. @ 5-10 % CO2 atmsp.

Streptococcus pneumoniae Encapsulated, Gr + coccus Lancet-shaped cells, in pairs or short chains -hemolytic Can grow only on enriched media (with blood

products) Catalase (-) Capsule, classified accr. to polysaccharides

90 serotypes Capsular polysaccharides are used in vaccines

Teichoic acid C polysaccharide (CRP)

S. pneumoniae / diseases

Pneumoniae Meningitis Sinusitis Otitis media Bacteremia

Streptococcus pneumoniae/Pathogenesis&ImmunityThe disease manifestations are caused primarily

by the host response to infection

Streptococcus pneumoniae/Pathogenesis&Immunity Colonization & migration

S.pn colonizes the oropharynx Can spread to the lungs, paranasal

sinuses, middle ear, blood stream By means of: Surface protein adhesins, secretory IgA

(sIgA) protease, pneumolysin

Streptococcus pneumoniae/Pathogenesis&Immunity Tissue destruction

Mobilization of inflamatory cells characteristic of pneumococcal infections

Teichoic acid Peptidoglycan fragments Pneumolysin H2O2 production Phosphorylcholin

Phagocytic survival Capsule Pneumolysin mediated suppression of the

phagocytosis

Streptococcus pneumoniae/IDENTIFICATION Microscopy

Lancet-shaped, Gr (+) diplococci, unstained capsule (Gram stain with “quellung” reaction)

Culture: Enriched supplemented medium with blood Selective medium with gentamicin

Identification Bile solubility test Optochin

Enterococcus Most frequently isolated & most commonly

responsible for human disease with streptococcus among gram-positive cocci

“enteric cocci” Possess the group D cell wall antigen 16 species in the genus E. faecalis & E. faecium are most commonly

isolated

Enterococcus/physiology & structure They can not be differentiated from S.

pneumoniae in microscope Facultatively anaerobic Optimal growth temp.= 35 oC (10oC to 45oC) White, large colonies on blood agar (after 24h)

Nonhemolytic (or or -hemolysis) Grow in the presence of

6.5 % NaCl, tolerate 40 % bile salts, hydrolyse esculin

Enterococcus/Pathogenesis&Immunity Are commensal with

limited potential for causing disease

Do not possess toxins Cannot avoid being

engulfed & killed by phagocytic cells

BUT,

Cause

Serious

Disease

Enterococcus/Pathogenesis&Immunity Virulence factors

Adhesive factors Bacteriocins

Inherently resistant to many antibiotics

Enterococcus/Clinical Diseases Can cause life-threatening infections One of the most feared nosocomial

pathogens 10% of all nos. infct. Most commonly involved sites

Urinary tract Blood stream

A sever complication: endocarditis(following bacteremia)

Enterococcus/Laboratory diagnosis Grow readily on nonselective media Resemble S. pneum.

Differentiation resistant to optochin

don’t dissolve when exposed to bile

hydrolyze PYRpyrolidonyl--naphthylamide