Staphylococcus-Streptococcus-Enterococcus

Gr + cocci ~ 21 genera Common features Spherical shape Gram stain reaction Absence of endospores Catalase activity subdividing Catalase positive genera Staphylococcus Micrococcus Stomatococcus Alloiococcus Catalase negative genera Streptococcus Enterococcus

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 a Toxin important mediator of tissue damage in staphylococcal diseases toxic for many cells (erythrocytes, leukocytes, hepatocytes,..) produced by most strains of S. aureus

Staphylococcus/toxins b Toxin sphingomyelinase C toxic for many cells role in tissue destruction & abscess formation produced by most strains of S. aureus

Staphylococcus/toxins d Toxin wide spectrum of cytolytic activity detergent-like activity produced by most strains of S. aureus

Staphylococcus/toxins g Toxin & Panton-Valentine Leukocidin composed of two polypeptide chains toxic for many cells

Staphylococcus/toxins Exfoliative toxins staphylococcal scalded skin syndrome (SSSS) exfoliative dermatitis two types: ETA & ETB produced 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 resistant all S. aureus responsible for menstruation-associated TSS produce TSST-1 50 % of the strains responsible for other forms of TSS produce TSST-1 superantigens

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 (b-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 Lancefield groupings according to serologic properties (A-H, K-M, O-V) Hemolytic patterns: b, a & g hemolysis 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 b-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 chains Highly conserved among all ggroup A streptococci 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 b-hem. Streptolysine O lyse erythrocytes 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 b-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 b-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 a-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 a-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 Meningitis Sinusitis Otitis media Bacteremia

Streptococcus pneumoniae/Pathogenesis&Immunity The 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 a or b-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 PYR pyrolidonyl-b-naphthylamide