The Genus staphylococcus.

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The Genus staphylococcus.

The Genus staphylococcus.

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  • 1. THE GENUSSTAPHYLOCOCCUS Dr.T.V.Rao MD Dr.T.V.Rao MD 1
  • 2. What are Staphylococcus• Sir Alexander Ogston, a Scottish surgeon, first showed in 1880 that a number of human pyogenic diseases were associated with a cluster-forming micro-organism. He introduced the name staphylococcus (Greek: staphyle = bunch of grapes; kokkos = grain or berry), now used as the genus name for a group of facultatively anaerobic, catalase-positive, Gram- positive cocci. Dr.T.V.Rao MD 2
  • 3. Staphylococci: Gram positive cocci ( from Greek staphyle,means bunch of grapes ) thatoccur singly and in pairs, shortchains and irregular grape-like clusters. Dr.T.V.Rao MD 3
  • 4. Morphology of Staphylococcus Dr.T.V.Rao MD 4
  • 5. S. aureus morphology 5 Dr.T.V.Rao MD
  • 6. Classification• Family Micrococcaceae• Genus Micrococcus and Staphylococcus• Species S. aureus S. saprophyticus S. epidermidis more M. luteus than 20 species Dr.T.V.Rao MD 6
  • 7. The genus Staphylococcus contains about forty species and subspecies today.• Only some of them are important as human pathogens: –Staphylococcus aureus –Staphylococcus epidermidis –Staphylococcus hominis –Staphylococcus haemolyticus –Staphylococcus saprophyticus –others Dr.T.V.Rao MD 7
  • 8. Structure and Physiology• Gram-positive cocci, nonmotile, facultative anaerobes• Cells occur in grapelike clusters because cells division occurs along different planes and the daughter cells remain attached to one another• Salt-tolerant: allows them to tolerate the salt present on human skin• Tolerant of desiccation: allows survival on environmental surfaces (fomites) Dr.T.V.Rao MD 8
  • 9. The species Staphylococcus aureus• Morphology – Gram-positive, spherical cells, mostly arranged in irregular grape like clusters. – Polysaccharide capsule is only rarely found on cells. – The peptidoglycan layer is the major structural component of the cell wall. It is important in the pathogenesis of staphylococcal infections. Other important component of cell wall is teichoic acid. – Protein A is the major protein component of the cell wall. It is located on the cell surface but is also released into the culture medium during the cell growth. A unique property of protein A is its ability to bind to the Fc part of all IgG molecules except IgG3. It is not an antigen-antibody specific reaction. Dr.T.V.Rao MD 9
  • 10. S aureus A Unique Organism PVLAdapted from: Lowy. N Engl J Med. 1998;339:520-532. Dr.T.V.Rao MD 10
  • 11. Virulence Factors in Staphylococcus Dr.T.V.Rao MD 11
  • 12. The genus Staphylococcus can be divided into two subgroups (on the basis of its ability to clot blood plasma by enzyme coagulase): • coagulase-positive, • coagulase-negative. Dr.T.V.Rao MD 12
  • 13. Physiology and structure• Capsule or polysaccharide slime layer• Peptidoglycan layer• Teichoic acid• Protein A• Cytoplasmatic membrane• Clumping factor• Cytoplasma Dr.T.V.Rao MD 13
  • 14. Capsule or polysaccharide slime layer• A loose-fitting, polysaccharide layer (slime layer) is only occasionally found in staphylococci cultured in vitro, but is believed to be more commonly present in vivo.• Eleven capsular serotypes have been identified in S. aureus, with serotypes 5 and 7 associated with majority of infections. Dr.T.V.Rao MD 14
  • 15. Capsule helps Staphylococcus• The capsule protects the bacteria by inhibiting the chemotaxis and phagocytosis of staphylococci by polymorph nuclear leukocytes, as well as by inhibiting the proliferation of mononuclear cells.• It is also facilitates the adherence of bacteria to catheters and other synthetic material. Dr.T.V.Rao MD 15
  • 16. Staphylococcal enzymes–Coagulase–Catalase–Hyaluronidase–Fibrinolysin–Lipases–Nuclease–Penicillinase Dr.T.V.Rao MD 16
  • 17. Enzymes1. Coagulase – Triggers blood clotting2. Hyaluronidase – Breaks down hyaluronic acid, enabling the bacteria to spread between cells3. Staphylokinase – Dissolves fibrin threads in blood clots, allowing Staphylococcus aureus to free itself from clots Dr.T.V.Rao MD 17
  • 18. Enzymes (cont.)4. Lipases – Digest lipids, allowing staphylococcus to grow on the skin’s surface and in cutaneous oil glands5. -lactamase – Breaks down penicillin – Allows the bacteria to survive treatment with -lactam antimicrobial drugs Dr.T.V.Rao MD 18
  • 19. Protein A• The surface of most S. aureus strains (but not the coagulase-negative staphylococci) is uniformly coated with protein A.• This protein is covalently linked to the peptidoglycan layer and has a unique affinity for binding to the Fc receptor of immunoglobulin IgG.• The presence of protein A has been exploited in some serological tests, in which protein A-coated S. aureus is used as a nonspecific carrier of antibodies directed against other antigens.• Additionally, detection of protein A can be used as a specific identification test for S. aureus. Dr.T.V.Rao MD 19
  • 20. Peptidoglycan• Half of the cell wall by weight is peptidoglycan, a feature common to gram-positive bacteria.• The subunits of peptidoglycan are N-acetylmuramic acid and N-acetylglucosoamine.• Unlike gram-negative bacteria, the peptidoglycan layer in gram-positive bacteria consists of many cross-linked layers, which makes the cell wall more rigid. Dr.T.V.Rao MD 20
  • 21. Teichoic acid• Teichoic acid is species-specific, phosphate- containing polymers that are bound covalently to the peptidoglycan layer or through lipophilic linkage to the cytoplasmic membrane (lipoteichoic acid).• Teichoic acid mediates the atachment of staphylococci to mucosal surfaces through its specific binding to fibronectin. Dr.T.V.Rao MD 21
  • 22. Coagulase and other surface proteins• The outer surface of most strains of S. aureus contains clumping factor (also called bound coagulase).• This protein binds fibrinogen, converts it to insoluble fibrin, causing the staphylococci to clump or aggregate.• Detection of this protein is the primary test for identifying S. aureus. Dr.T.V.Rao MD 22
  • 23. • Other surface proteins that appear to be important for adherence to host tissues include:• collagen-binding protein• elastin-binding protein• fibronectin-binding protein Dr.T.V.Rao MD 23
  • 24. Cytoplasmic membrane•The cytoplasmic membrane is made up of a complex of proteins, lipids, and small amount of carbohydrates.•It serve as an osmotic barrier for the cell and provides an anchorage for the cellular biosynthetic and respiratory enzymes. Dr.T.V.Rao MD 24
  • 25. Staphylococcal toxins• S. aureus produces many virulence factors, including at least five cytolytic or membrane-damaging toxins: – alpha toxin – beta toxin – delta toxin – gamma toxin – Panton-Valentin toxin – two exfoliative toxins – eigth enterotoxins (A-E, G-I) – Toxic Shock Syndrome Toxin 1 (TSST-1) Dr.T.V.Rao MD 25
  • 26. Toxin-mediated• Toxic shock syndrome toxin (TSST-1) is a super-antigen capable of activating large number of T cells• Was associated with use of tampons but is also known to be associated with postoperative wound or soft tissue infections Dr.T.V.Rao MD 26
  • 27. TSST and other Toxins• The enterotoxins and TSST-1 belong to a class of polypeptide known as super antigens.• Staphylococcus aureus strains produce several other extracellular, biologically active substances, including proteases, phosphatases, lipases, lysozyme etc. Dr.T.V.Rao MD 27
  • 28. Dr.T.V.Rao MD 28
  • 29. Exfoliative toxins• Staphylococcal scalded skin syndrome (SSSS), a spectrum of diseases characterized by exfoliative dermatitis, is mediated by exfoliative toxins.• The prevalence of toxin production in S. aureus strains varies geographically but is generally less than 5% to 10%. Dr.T.V.Rao MD 29
  • 30. • Preformed, heat-resistant enterotoxin mediates staphylococcal food poisoning (symptoms in 2-6 hours; usually self-limiting)• Exfoliative toxins A and B results in staphylococcal scalded skin syndrome; usually in infants and neonates Dr.T.V.Rao MD 30
  • 31. Enterotoxins• Eigth serologically distinct staphylococcal enterotoxins (A-E, G-I) and three subtypes of enterotoxin C have been identified.• The enterotoxin are stable to heating at 100 C for 30 minutes and are resistant to hydrolysis by gastric and jejunal enzymes. Dr.T.V.Rao MD 31
  • 32. Enterotoxins• Thus, once a food product has been contaminated with enterotoxin-producing staphylococci and the toxin have been produced, neither reheating the food nor the digestive process will be protective.• These toxins are produced by 30% to 50% of all S. aureus strains.• Enterotoxin A is most commonly associated with disease. Enterotoxins C and D are found in contamined milk products, and enterotoxin B causes staphylococcal pseudomembranous enterocolitis. Dr.T.V.Rao MD 32
  • 33. Toxic Shock Syndrome Toxin - 1• TSST-1, formerly called pyrogenic exotoxin C and enterotoxin F, is a heat and proteolysis resistant, chromozomally mediated exotoxin.• The ability of TSST-1 to penetrate mucosal barriers, even though the infection remains localized in the vagina or at the site of a wound, is responsible for the systemic effects of TSS.• Death in patients with TSS is due to hypovolemic shock leading to multiorgan failure. Dr.T.V.Rao MD 33
  • 34. Catalase•All staphylococci produce catalase, which catalyzes the conversion of toxic hydrogen peroxide to water and oxygen.•Hydrogen peroxide can accumulate during bacterial metabolism or after phagycytosis. Dr.T.V.Rao MD 34
  • 35. Coagulase• S. aureus strains possess two forms of coagulase: – bound, – free.• Coagulase bound to the staphylococcal cell wall can directly convert fibrinogen to insoluble fibrin and cause the staphylococci to clump.• The cell-free coagulase accomplishes the same result by reacting with a globulin plasma factor. Dr.T.V.Rao MD 35
  • 36. Coagulase Normal coagulation of plasma Thrombin Fibrinogen Fibrin (soluble ) (insoluble) 36 Staphylococcus aureus coagulation of plasma* “Free” staphylocoagulase Fibrinogen + CRF Fibrin*EDTA Rabbit plasma is preferred for the “free” or tube coagulasetest because it contains a large amount of CRF Dr.T.V.Rao MD
  • 37. What is the role of Coagulase• The role of coagulase in the pathogenesis of disease is speculative, but coagulase may cause the formation of fibrin layer around a staphylococcal abscess, thus localizing the infection and protecting the organisms from phagocytosis. Dr.T.V.Rao MD 37
  • 38. Hyaluronidase•Hyaluronidase hydrolyzes hyaluronic acid, the acidic mucopolysaccharides present in the acellular matrix of connective tissue.•This enzyme facilitates the spread of S. aureus in tissues.•More than 90% of S. aureus strains produce this enzyme. Dr.T.V.Rao MD 38
  • 39. Fibrinolysin•Fibrinolysin, also called staphylokinase, is produced by virtually all S. aureus strains and can dissolve fibrin clots.•Staphylokinase is distinct from the fibrinolytic enzymes produced by streptococci. Dr.T.V.Rao MD 39
  • 40. The genus Staphylococcus can be divided into two subgroups (on the basis of its ability to clot blood plasma by enzyme coagulase): • coagulase-positive, • coagulase-negative. Dr.T.V.Rao MD 40
  • 41. Subgroup of coagulase-negative species contains from human staphylococci: – Staphylococcus epidermidis, – Staphylococcus hominis, – Staphylococcus haemolyticus, – Staphylococcus saprophyticus, – Staphylococcus simulans, – Staphylococcus warneri and other. Dr.T.V.Rao MD 41
  • 42. The species Staphylococcus aureus• Morphology – Gram-positive, spherical cells, mostly arranged in irregular grape like clusters. – Polysaccharide capsule is only rarely found on cells. – The peptidoglycan layer is the major structural component of the cell wall. It is important in the pathogenesis of staphylococcal infections. Other important component of cell wall is teichoic acid. – Protein A is the major protein component of the cell wall. It is located on the cell surface but is also released into the culture medium during the cell growth. A unique property of protein A is its ability to bind to the Fc part of all IgG molecules except IgG3. It is not an antigen-antibody specific reaction. Dr.T.V.Rao MD 42
  • 43. The species Staphylococcus aureus culture characteristics• Colonies on solid media are round, regular, smooth, slightly convex and 2 to 3 mm in diameter after 24h incubation.• Most strains show a -hemolysis surrounding the colonies on blood agar.• S. aureus cells produce cream, yellow or orange pigment. Dr.T.V.Rao MD 43
  • 44. Blood agar plate, S. aureus 44 Dr.T.V.Rao MD
  • 45. The species Staphylococcus aureus resistance• Like most of medical important non- sporeforming bacteria, S. aureus is rapidly killed by temperature above 60 C• S. aureus is susceptible to disinfectants and antiseptics commonly used.• S. aureus can survive and remain virulent long periods of drying especially in an environment with pus. Dr.T.V.Rao MD 45
  • 46. The species Staphylococcus aureus pathogenicity• S. aureus is pathogenic for human as well as for all domestic and free- living warm-blooded animals.• S. aureus causes disease through the production of toxin or through direct invasion and destruction of tissue. Dr.T.V.Rao MD 46
  • 47. Clinical Manifestations• The clinical manifestations of some staphylococcal diseases are almost exclusively the result of toxin activity (e.g. staphylococcal food poisoning and TSS), whereas other diseases result from the proliferation of the staphylococci, leading to abscess formation and tissue destruction (e.g. cutaneous infection, endocarditis, pneumonia, empyema, osteomyelitis, septic arthritis). Dr.T.V.Rao MD 47
  • 48. Staphylococcal Diseases– Systemic Disease • Toxic shock syndrome-TSS toxin is absorbed into the blood and causes shock • Bacteremia-presence of bacteria in the blood • Endocarditis-occurs when bacteria attack the lining of the heart • Pneumonia-inflammation of the lungs in which the alveoli and bronchioles become filled with fluid • Osteomyelitis-inflammation of the bone marrow and the surrounding bone Dr.T.V.Rao MD 48
  • 49. Factors predisposing to S. aureus infections • Host factors • Pathogen Factors– Breach in skin – Catalase (counteracts– Chemotaxis defects host defenses)– Opsinization defects – Coagulase– Neutrophil functional – Hyaluronidase defects – Lipases (Imp. in– Diabetes mellitus disseminating infection)– Presence of foreign bodies – B lactamase(ass. With antibiotic resistance) Dr.T.V.Rao MD 49
  • 50. Clinical diseases• Staphylococcal pyogenic infections: – folliculitis, – furuncle, – carbuncle, – bullous impetigo, – panaritia and paronychia, – wound infections, – mastitis, – osteomyelitis, – staphylococcal pneumonia and other. Dr.T.V.Rao MD 50
  • 51. Defining Staphylococcal Diseases Range from localized to systemic• Localized cutaneous infections – invade skin through wounds, follicles, or glands 51 – Folliculitis – superficial inflammation of hair follicle; usually resolved with no complications but can progress – Furuncle – boil; inflammation of hair follicle or sebaceous gland progresses into abscess or pustule – Carbuncle – larger and deeper lesion created by aggregation and interconnection of a cluster of furuncles – Impetigo – bubble-like swellings that can break and peel away; most common in newborns Dr.T.V.Rao MD
  • 52. Clinical diseases• Stahylococccal intoxications: – staphylococcal food poisoning (enterotoxicosis), – exfoliative intoxications (Ritter´s disease or SSSS), – staphylococcal toxic shock syndrome (TSS). Dr.T.V.Rao MD 52
  • 53. Boil (Furuncle ) Dr.T.V.Rao MD 53
  • 54. StyeDr.T.V.Rao MD 54
  • 55. Surgical wound infections:many causes including S. aureus Dr.T.V.Rao MD 55
  • 56. Toxic Shock Syndrome Toxin• Super antigen• Non-specific binding of toxin to receptors triggers excessive immune response Dr.T.V.Rao MD 56
  • 57. TSS Symptoms• 8-12 h post infection• Fever• Susceptibility to Endotoxins• Hypotension• Diarrhea• Multiple Organ System Failure• Erythroderma (rash) Dr.T.V.Rao MD 57
  • 58. Treatment• Antistaphylococcal antibiotics of the first choice: – oxacillin (methicillin) – cephalosporins of I. generation (cefazolin, cephalotin)• Antistaphylococcal antibiotics of the second choice: – lincosamides (e.g. clindamycin) – glycopeptides (vancomycin, teicoplanin) – linezolid – tigecyklin – daptomycin – and others Dr.T.V.Rao MD 58
  • 59. Antibiotic sensitivity pattern• Very variable and not predictable• Very imp. In Pt. Management• Mechanisms – 1.B lactamase production - plasmid mediated • Has made S. aureus resistant to penicillin group of antibiotics - 90% of S. aureus (Gp A) • B lactamase stable penicillins (cloxacillin, oxacillin, methicillin) used – 2. Alteration of penicillin binding proteins • (Chromosomal mediated) • Has made S. aureus resistant to B lactamase stable penicillins • 10-20% S. aureus Gp (B) GH Colombo/THP resistant to all Penicillins and Cephalosporins) • Vancomycin is the drug of choice Dr.T.V.Rao MD 59
  • 60. MRSA• Methicillin-resistant S. aureus• Resistant to all penicillins, cephalosporins, and penems• Usually multiply-resistant• Vancomycin resistance is very rare – so far• Hospital-acquired• Community-acquired cases now (CA MRSA) Dr.T.V.Rao MD 60
  • 61. Panton-Valentine Leukocidin• Panton-Valentine Leukocidin (PVL) consists of 2 components S and F, together with γ exotoxin lyses WBC resulting in massive release of inflammatory mediators responsible for necrosis and severe inflammation• PVL is an important virulence factor in MRSA infections Dr.T.V.Rao MD 61
  • 62. Diagnosis• Microscopy – smears of clinical materials are stained according to Gram stain• Cultivation on solid media (agar, usually blood agar)• Biochemical tests• Phage typing – susceptibility of S. aureus strains to various temperature phages Dr.T.V.Rao MD 62
  • 63. MRSA• Methicillin-resistant S. aureus• Resistant to all penicillins, cephalosporins, and penems• Usually multiply-resistant• Vancomycin resistance is very rare – so far• Hospital-acquired• Community-acquired cases now (CA MRSA) Dr.T.V.Rao MD 63
  • 64. Coagulase-negative staphylococcal spp (Cons)• S. epidermidis – most frequently isolated staphylococcal spp.• Colonizes moist body areas such as axilla, inguinal and perianal areas, anterior nares and toe webs• Important cause of nosocomial infection esp. S. epidermidis• Usually causes nosocomial infections in patients with predisposing factors such as immunodeficiency/ immunocompromised or presence of foreign bodies Dr.T.V.Rao MD 64
  • 65. Diagnosis• Specimen• Smear• Culture• Coagulase test• Biochemical Reactions• Antibiograms• Typing Dr.T.V.Rao MD 65
  • 66. Epidemiology• Staphylococci are ubiquitous. All persons have coagulase- negative staphylococci on their skin, and transient colonization of moist skin folds with S. aureus is common.• Colonization of the umbilical stump, skin and perineal area of neonates with S. aureus is common.• S. aureus and coagulase-negative staphylococci are also found in the oropharynx, gastrointestinal and urogenital tract.• Because staphylococci are found on the skin and in the nasopharynx, shedding of the bacteria is common and is responsible for many hospital-acquired infections. Dr.T.V.Rao MD 66
  • 67. . Staphylococcus epidermidis• Skin commensal• Has predilection for plastic material• Ass. With infection of IV lines, prosthetic heart valves, shunts• Causes urinary tract infection in catheterized patients• Has variable ABS pattern• Treatment should be aided with ABST Dr.T.V.Rao MD 67
  • 68. Importance of S.saprophyticus• S. saprophyticus frequently isolated in rectum and genitourinary tract of young women• Can be causative agent in UTI in young healthy women• 2nd most common urinary pathogen (other than E. coli) in uncomplicated cystitis in young women• Colony counts of ≥ 105 CFU/ml usu. indicative of significant Bacteriuria Dr.T.V.Rao MD 68
  • 69. . Staphylococcus saprophyticus• Skin commensal• Imp. Cause of UTI in sexually active young women• Usually sensitive to wide range of antibiotics Dr.T.V.Rao MD 69
  • 70. Peptococcus species• Members of the genus Peptococcus are strictly anaerobic cluster-forming gram-positive cocci.• These microorganisms grow only under anaerobic conditions.• They are part of the normal microflora of the mouth, upper respiratory tract, bowel, and female genital tract.• They often participate with many other bacterial species in mixed anaerobic infections in the abdomen, pelvis, lung, or brain. Dr.T.V.Rao MD 70
  • 71. Related microorganisms• The genus Micrococcus (the genus contains two species) – Micrococcus luteus – Micrococcus lyla• Both species are found in nature and colonize humans, primarily on the surface of the skin.• Although micrococci may be found in patients with opportunistic infections, their isolation in clinical specimen usually represents clinically insignificant contamination with skin flora. Dr.T.V.Rao MD 71
  • 72. Related microorganisms• The genus Stomatococcus – Stomatococcus mucilaginosus, the only species in this genus, is a commensal microorganism that resides in the oropharynx and upper respiratory tract.• In recent years, this microorganism has been reported to be the cause of an increasing number of opportunistic infections (endocarditis, septicemia, catheter-related infections) in immunocompromised patients. Dr.T.V.Rao MD 72
  • 73. Clinical Concerns and Treatment• 95% have penicillinase and are resistant to penicillin and ampicillin• MRSA – methicillin-resistant S. aureus – carry multiple resistance 73 – Some strains have resistance to all major drug groups except vancomycin• Abscesses have to be surgically perforated• Systemic infections require intensive lengthy therapy Dr.T.V.Rao MD
  • 74. Antimicrobial susceptibility• MRSA can be due to 3 different resistance mechanisms – Production of penicillin-binding protein 2a (PBP2a) encoded by mecA gene – Production of beta-lactamase – Production of modified intrinsic PBPs• Resistance due to mecA can be detected via cefoxitin disk diffusion or dilution methods according to CLSI breakpoints (≤ 21mm – resistant, ≥ 8µg/ml – resistant, respectively)• Resistance due to beta-lactamase production can be detected via the use of beta-lactamase inhibitor such as clavulanic acid which would result in an increase in zone size (disk diffusion method) or decrease of 2 dilutions Dr.T.V.Rao MD 74
  • 75. Prevention• Prevention – Hand antisepsis is the most important measure in preventing nosocomial infections – Also important is the proper cleansing of wounds and surgical openings, aseptic use of catheters or indwelling needles, an appropriate use of antiseptics Dr.T.V.Rao MD 75
  • 76. For articles of current interest on Infectious Diseases Visit … Dr.T.V.Rao MD 76
  • 77. • Programme Created ByDr.T.V.Rao MD for Medical and Paramedical Students in the Developing World • Email • doctortvrao@gmail.com Dr.T.V.Rao MD 77