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1、BIOL 533,1,Staphylococci and Streptococci,BIOL 533 Lecture 10,Medical Microbiology,BIOL 533,2,Staphylococci,Important human pathogen Causes both relatively minor and serious diseases One of the hardiest of the non-sporeforming bacteria Can exist on dry surfaces for a long period Relatively heat-resi
2、stant; temperature range of 18 - 40 C,BIOL 533,3,Staphylococci,Morphology Gram+ grape-like cluster, but in clinical specimens, can be a single cocci or diplococci General physiological characteristics Nonmotile Facultatively anaerobic Catalase + Grows in media containing 10% NaCl,BIOL 533,4,Staphylo
3、cocci,Relationship to disease (only 3 important) S. aureuscauses a number of diseases S. epidermidispresent in normal flora (normally benign, except when introduced via catheters, etc.) S. saprophyticuscauses uninary tract infections,BIOL 533,6,Pathogenesis of S. aureus,Features typical of staphyloc
4、occi infections: Initial lesion is normally mild and localized Results in a boilnormally, it is self-limiting Can result in systemic infection,BIOL 533,7,Pathogenesis of S. aureus,Stage I: encounterhumans are major reservoir for S. aureus Colonize nose and are found in about 30% of individuals Trans
5、iently found on skin, oropharynx, and feces Transmitted via: Hand contact Aerosols from pneumonia patients,BIOL 533,8,Pathogenesis of S. aureus,Stage I, continued Certain occupations are more prone to colonization Physicians, nurses, hospital workers Certain classes of patients are more prone to col
6、onization Diabetics, hemodialysis patients, and drug abusers,BIOL 533,9,Pathogenesis of S. aureus,Stage II: entrynot normally through unbroken skin Can enter if large numbers have accumulated through poor hygiene,BIOL 533,10,Pathogenesis of S. aureus,Stage III: spread and multiplication Survival dep
7、ends on Number of organisms Site involved Speed with which inflammatory response is mounted Immunological competence of host If inoculum is small and host immunologically competent: infection normally defeated,BIOL 533,11,Pathogenesis of S. aureus,Stage IV: damage Local infection leads to formation
8、of abscess (collection of pus) In skin, boils or furuncles Interconnected abscesses are called carbuncles May also spread in subcutaneous or submucosal tissuescellulitis,BIOL 533,12,Pathogenesis of S. aureus,Stage IV, continued Developmentinvolves both host and bacterial factors Acute inflammatory r
9、eaction Proportion of bacteria survive and are capable of lysing neutrophils that engulfed them Outpouring of lysosomal enzymes that damage surrounding tissues Inflammatory area surrounded by fibrin clot,BIOL 533,13,Virulence Factors of S. aureus,Stage IV, continued Virulence factorsmost designed to
10、 avoid phagocytosis or survive once ingested Wall components Surrounded by capsule: not as effective as pneumococcus or meningococcus Cell wall murein activates complement by alternative pathway Teichoic acid also activates and involved in adherence Protein A interferes with opsonization by binding
11、with Fc region of Abcomplement activated primary pathway,BIOL 533,14,Virulence Factors of S. aureus,Stage IV, continued Secretion of enzymes Catalasehydrogen peroxide to water and oxygen (all staphylococci produce) Coagulasemakes fibrin clot (wbc penetrate badly; only S. aureus) Hylauronidasedegrade
12、s connective tissues (facilitates spread; 90% of S. aureus strains) Fibrinolysin (staphylokinase)dissolve fibrin clots (virtually all S. aureus),BIOL 533,15,Virulence Factors of S. aureus,Stage IV, continued Secretion of enzymes Lipasesrequired for invasion into cutaneous and subcutaneous tissues (f
13、ound in all S. aureus and 30% of others) Nucleaseheat stable (role is uncertain; S. aureus) Penicillinase,BIOL 533,16,Virulence Factors of S. aureus,Stage IV, continued Secretion of toxins Cytolytic (membrane-damaging by pores) Alpha, beta, (sphingomyelinase C), delta, gamma, leukocidin (cannot lyse
14、 red blood cells) Others lyse rbc and leukocytes (referred to previously as hemolysins) Cause lysis of neutrophils leading to massive lysosomal enzyme secretion,BIOL 533,17,Virulence Factors of S. aureus,Stage IV, continued Secretion of toxins Exfoliative toxin (scalded skin syndrome) extrachromosom
15、al Toxic Shock Syndrome toxin-1 (enterotoxin F)exotoxin secreted during growth Some produce enterotoxin B instead (role not clear),BIOL 533,18,Virulence Factors of S. aureus,Stage IV, continued Secretion of toxins Enterotoxins (A-E)found in both S. aureus and S. epidermidis Resistant to hydrolysis b
16、y gastric and jejunal enzymes Stable to heating at 100C for 30 minutes Mechanism of toxin activity not understood; no satisfactory animal model Stimulate intestinal peristalsis and have CNS effect; intense vomiting,BIOL 533,19,Pathogenesis of S. aureus,Treatment Antibiotics Types: Methicillin, oxacillin, nafcillin, and dicloxacillin (semisynthetic penicillins resistant to -lactam hydrolysis) Majority of patients can be treated, but 10-15% S. aureus and 40% coagulase-negative staphylococci are
