Gram-positive Cocci Notes PDF

Gram-positive cocci of medical importance 1  Gram-positive cocci of medical importance Staphylococcus Streptococcus Enterococcus 2  Staphylococcus 1881 Sir Alexander Ogston Greek :...

Gram-positive cocci of medical importance 1  Gram-positive cocci of medical importance Staphylococcus Streptococcus Enterococcus 2  Staphylococcus 1881 Sir Alexander Ogston Greek : staphyle = bunch of grapes kokkos = grain or berry Microscopic appearance – Gram stain shows gram-positive cocci in grape-like clusters 3 Gram-positive cocci in grape-like clusters 4 Time line of the discovery of the species belonging to the genus Staphylococcus. Karsten Becker et al. Clin. Microbiol. Rev. 2014; doi:10.1128/CMR.00109-13 5  Staphylococcus Coagulase-positive : Staphylococcus aureus Coagulase-negative : Staphylococcus epidermidis Staphylococcus saprophyticus other species 6  List of coagulase-positive staphylococci: Staphylococcus aureus S. delphini* S. hyicus* S. intermedius* S. lutrae* Staphylococcus schleiferi subsp. coagulans* *Involved in human disease, although primarily animal pathogens 7  Coagulase-negative staphylococci (CoNS) Staphylococcus epidermidis Staphylococcus saprophyticus Staphylococcus lugdunensis Staphylococcus schleiferi Staphylococcus haemolyticus Staphylococcus hominis 8 Staphylococcus aureus - description Gram-positive cocci Characteristically in irregular clusters Diameter: 0.7 -1.5 m 9  S. aureus - cultural characteristics Culture media of choice is blood agar. Grows well aerobically, less well anaerobically. (facultative anaerobes) Optimal temperature: 37C 10  S. aureus - cultural characteristics Colonial morphology – sharply defined, round, convex, smooth, 1-4 mm diameter – pale yellow to dark orange carotenoid pigment (staphyloxanthin) – white Complete haemolysis 11 12  S. aureus on blood agar Colonies typically appear golden-coloured with a clear zone on blood agar 13  S. aureus - cultural characteristics Selective media is mannitol salt agar – tolerate high salt concentration – ferment mannitol to produce acid – yellow colonies *Will be covered in practical demonstration 14  S. aureus on mannitol salt agar 15  Staphylococcus aureus Virulent. Causes vast range of diseases even in healthy hosts. Produces large number of virulence factors – cell surface proteins – enzymes – toxins 16 S. aureus - virulence factors 17  I. cell surface proteins Protein A – binds Fc region of IgG and prevents IgG acting as opsonins – prevents phagocytosis Clumping factor (bound coagulase) – bind to fibrinogen – clumping when mixed with plasma Coagulase slide test add undiluted plasma to saline suspension on microscope slide → rapid clumping 18  Protein A binds with Fc portion of IgG antibodies at the complement-binding site, preventing complement activation. This results in decreased production of C3b, leading to impaired opsonization and phagocytosis. 19 Coagulase slide test 20  I. cell surface proteins Extracellular matrix binding proteins – Fibrinogen-binding proteins – Fibronectin-binding proteins – Collagen-binding proteins – Laminin-binding proteins 21  II. enzymes Coagulase – convert fibrinogen to fibrin – wall of fibrin protects against phagocytosis Coagulase tube test tube with diluted plasma add 2 or 3 colonies and incubate for 3-6 hours at 37C → distinct clot 22 Fibrin clot 23  Enzymes Catalase: converts H2O2 to water and oxygen Hyaluronidase: hydrolyses hyaluronic acid in a cellular matrix of connective tissue Staphylokinase: degrade fibrin Deoxyribonuclease: degrades DNA Lipase: degrades lipase Protease: proteolysis 24 Catalase test Catalase: converts H2O2 to water and oxygen 25  III. toxins 1. Haemolysins 2. Panton Valentine (P-V) leucocidin 3. Enterotoxin → food poisoning 4. Epidermolytic toxin (exfoliatin) → Staphylococcal scalded skin syndrome 5. Toxic shock syndrome toxin (TSST-1) → toxic shock syndrome 26  S. aureus - colonisation Colonise anterior nares – skin, nasopharynx, vagina 10% to 35% of adults are carriers. Higher carriage rates among patients with type 1 diabetes, IVDU, on haemodialysis, various skin diseases and health-care workers. Carriers at increased risks for infections by the colonising strain. 27  Clinical manifestations A major cause of skin, soft-tissue, respiratory, bone, joint and endovascular infections. 1. Invasive infections 2. Toxigenic infections 28  1. Invasive infections Direct infection – superficial (SSTI) : folliculitis, furunculosis (boils), carbuncle, impetigo, wound infection, cellulitis, abscess – deep infection : osteomyelitis, septic arthritis, pneumonia Blood stream infection – bacteraemia – metastatic infection : endocarditis, meningitis, pneumonia, osteomyelitis, arthritis 29 Folliculitis 30 Folliculitis is infection of the hair follicle. 31 Boil (furuncle) 32 Furuncle is a deep-seated infection in and around the hair follicle progressing from a folliculitis. surrounding 33 Carbuncle 34 Impetigo 35  2. Toxigenic infections Staphylococcal food poisoning Staphylococcal scalded skin syndrome Toxic shock syndrome 36  Staphylococcal food poisoning S. aureus inoculated into food (cold meat, custard and creams) by colonised or infected food handler. Organisms multiply and produce enterotoxin. Symptomatic 1-6 hours following ingestion. Nausea, vomiting, abdominal pain and diarrhoea. Lasts 24 hours. 37 Staphylococcal scalded skin syndrome Most common in neonates and children < 8 years. Erythema with generalised flaccid bullae formation. Spontaneous bullae rupture with skin denudation. Diffuse dermal involvement. Cleavage of epidermis at level of stratum granulosum. Complications include secondary infections and bacteraemia. 38 Staphylococcal scalded skin syndrome 39  Toxic shock syndrome Came to prominence in 1980-1981 – numerous cases associated with super-absorbent tampons for use during menstruation (menstrual TSS) Characterised by fulminant onset, high fever, erythematous rash with subsequent desquamation, hypotension and multiorgan damage. Now, non-menstrual cases associated with localised infections and surgery. Mortality 3 to 6%. 40  Sunburn-like rash due to toxic shock syndrome erythroderma 41 Skin desquamation related to toxic shock syndrome 42  Superantigens Enterotoxins, epidermolytic toxins and TSST-1 – stimulate T cells non-specifically without normal antigenic recognition – binds with high affinity to MHC Class II receptors of monocytes and macrophages at sites distinct from classic antigen binding groove – complex recognised by variable portion Vb of T- cell receptor. Any T cell with appropriate Vb element can be stimulated – up to 20% T cells may be stimulated leading to dramatic cytokine liberation 43  S. aureus - laboratory investigations Specimens pus sputum faeces / vomit or remains of food blood cultures anterior nasal/ perineal swabs - carriers Gram stain direct film of pus, swab or sputum Culture blood agar examine colonies next day test presence of coagulase Antibiotic sensitivity test 44  Commercially produced agglutination kits for identification of S. aureus Fastaph Slidex Staphaurex Staphaurex Plus Staphyloslide *Will be covered in practical demonstration Microgen® Staph Latex Agglutination Kit 45  Staphylococcus epidermidis Description – coagulase-negative – Gram stain features similar to S. aureus – white colonies on blood agar no complete haemolysis Habitat – most prevalent and persistent species on human skin and mucous membrane (normal flora) 46 Staphylococcus epidermidis on blood agar 47  S. epidermidis - epidemiology A major cause of infection particularly in hospitalised patients with indwelling foreign bodies and in immunocompromised patients. Most infections are nosocomial and resistant to multiple antibiotics – 80%-90% produce beta-lactamases – 75% to 90% methicillin-resistant 48  S. epidermidis - pathogenicity Adherence to biomaterials by polysaccharides and surface proteins. Production of extracellular slime. Most important factor in pathogenesis of polymer- associated infections is formation of biofilm – multilayer cell clusters embedded in an amorphous extracellular material – protect against host defence mechanisms and antibiotics 49 Schematic model of phases involved in S. epidermidis biofilm formation and bacterial factors involved. 50 S. epidermidis: polymer-associated infections Foreign body Type of infection Intravascular catheters Prosthetic heart valves Pacemakers Bacteraemia Vascular prostheses Ventriculoatrial CSF shunts Chronic ambulatory peritoneal dialysis catheters Peritonitis Ventriculoperitoneal CSF shunts VA and VP CSF shunts Ventriculitis 51 52  S. epidermidis - infections of other prosthetic devices Prosthetic joint Intraocular lenses Breast implants Genitourinary prostheses 53  S. epidermidis - infections Endocarditis – native valve endocarditis uncommon (5%) – early prosthetic valve endocarditis most common cause 54 S. epidermidis - infection characteristics Markedly different from S. aureus. Long latent period between device contamination and clinical presentation. Subtle and nonspecific and clinical course more subacute. Nosocomial. Involve indwelling foreign devices. Resistant to multiple antibiotics. 55  Staphylococcus saprophyticus Urinary tract pathogen – cause upper and lower urinary tract infection (UTI) Second commonest cause of UTI in young females (15-20%) – young sexually active women 56 Streptococcus 57  Streptococcus - description Gram-positive oval or spherical cocci in pairs or chains. Catalase negative. 58 Gram-positive cocci in pairs (diplococci) 59 Gram-positive cocci in chains 60 Arrangement - Plane of division 61 61  Streptococci of importance in human infection Streptococcus pyogenes (GAS) Viridans streptococci Streptococcus pneumoniae Streptococcus agalactiae (GBS) 62  Streptococcus pyogenes (GAS) Gram-positive cocci in chains. Colonise nasopharynx and skin. Virulence i. M protein ii. Streptolysin O iii. Streptolysin S iv. Streptococcal pyrogenic exotoxin (SPE) v. “Spreading factors” hyaluronidase, deoxyribonucleases, streptokinase 63  S. pyogenes - infections Acute pharyngitis / tonsillitis Scarlet fever Impetigo, erysipelas, cellulitis, sepsis in burns, necrotising fasciitis. Toxic shock syndrome Puerpural sepsis, endocarditis, pneumonia - post viral Non-suppurative post-streptococcal sequelae: acute rheumatic fever, acute glomerulonephritis. 64 Exudative pharyngitis 65 Scarlet fever 66 Circumoral pallor 67 68 69 70  Erysipelas sharply demarcated margins 71 Erysipelas 72 Erysipelas 73  Necrotizing fasciitis: extensive oedema, erythema, bullae formation and necrosis in this patient's thigh 74 Necrotizing fasciitis Haemorrhagic bullae 75 Necrotizing fasciitis 76  Viridans streptococci Heterogenous group. Important species – S. sanguinis, S. mitis, S. mutans, S. anginosus Normal habitat is oral cavity and upper respiratory tract. 77  Viridans streptococci - infections Dental caries, plaques and periodontal diseases. Infective endocarditis. Bacteraemia. Deep seated abscesses (intracranial, hepatic, pleuropulmonary). 78  Streptococcus pneumoniae Pneumococcus. Gram-positive cocci in pairs (diplococci). Most significant virulence factor is capsule. 79 Gram-positive cocci in pairs (diplococci) 80  S. pneumoniae - infections Pneumonia (commonest bacterial cause) Acute exacerbation of COPD Acute otitis media Sinusitis Meningitis Bacteraemia (*splenectomised patients) 81  Streptococcus agalactiae (GBS) Colonise vagina and upper respiratory tract. Leading cause of neonatal sepsis and meningitis. In adults – puerperal sepsis – pneumonia – septic arthritis, osteomyelitis – cellulitis, foot ulcers, decubitus ulcers infections 82 83  Enterococci Previously included with group D streptococci. Enterococcus faecalis and Enterococcus faecium most commonly associated with human disease. Major habitat is gastrointestinal tract of man and animals. 84  Enterococci Important cause of nosocomial infection – urinary tract infections – septicaemia – infective endocarditis – wound infections – intra-abdominal infections – pelvic infections 85