1、lecture 10biol 5331staphylococci and streptococcibiol 533lecture 10medical microbiologylecture 10biol 5332staphylococci 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 relative

2、ly heat-resistant; temperature range of 18 - 40 clecture 10biol 5333staphylococci 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% nacll

3、ecture 10biol 5334staphylococci relationship to disease (only 3 important)s. aureuscauses a number of diseasess. epidermidispresent in normal flora (normally benign, except when introduced via catheters, etc.)s. saprophyticuscauses uninary tract infectionslecture 10biol 5335staphylococci microbial p

4、hysiology and structure capsule may not be found growing on media, but it is usually present in vivo teichoic acids are phosphate containing polysaccharides bound to both peptidoglycan and cytoplasmic membrane species specific poor immunogens, but when bound to peptidoglycan, get an antibody respons

5、electure 10biol 5336pathogenesis of s. aureus features typical of staphylococci infections: initial lesion is normally mild and localized results in a boilnormally, it is self-limiting can result in systemic infectionlecture 10biol 5337pathogenesis of s. aureus stage i: encounterhumans are major res

6、ervoir for s. aureus colonize nose and are found in about 30% of individuals transiently found on skin, oropharynx, and feces transmitted via: hand contact aerosols from pneumonia patientslecture 10biol 5338pathogenesis of s. aureus stage i, continued certain occupations are more prone to colonizati

7、on physicians, nurses, hospital workers certain classes of patients are more prone to colonization diabetics, hemodialysis patients, and drug abuserslecture 10biol 5339pathogenesis of s. aureus stage ii: entrynot normally through unbroken skin can enter if large numbers have accumulated through poor

8、 hygienelecture 10biol 53310pathogenesis of s. aureus stage iii: spread and multiplication survival depends 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 norma

9、lly defeatedlecture 10biol 53311pathogenesis of s. aureus stage iv: damage local infection leads to formation of abscess (collection of pus) in skin, boils or furuncles interconnected abscesses are called carbuncles may also spread in subcutaneous or submucosal tissuescellulitislecture 10biol 53312p

10、athogenesis of s. aureus stage iv, continued developmentinvolves both host and bacterial factors acute inflammatory reaction proportion of bacteria survive and are capable of lysing neutrophils that engulfed them outpouring of lysosomal enzymes that damage surrounding tissues inflammatory area surro

11、unded by fibrin clotlecture 10biol 53313virulence factors of s. aureus stage iv, continued virulence factorsmost designed to avoid phagocytosis or survive once ingested wall components surrounded by capsule: not as effective as pneumococcus or meningococcus cell wall murein activates complement by a

12、lternative pathway teichoic acid also activates and involved in adherence protein a interferes with opsonization by binding with fc region of abcomplement activated primary pathwaylecture 10biol 53314virulence factors of s. aureus stage iv, continued secretion of enzymes catalasehydrogen peroxide to

13、 water and oxygen (all staphylococci produce) coagulasemakes fibrin clot (wbc penetrate badly; only s. aureus) hylauronidasedegrades connective tissues (facilitates spread; 90% of s. aureus strains) fibrinolysin (staphylokinase)dissolve fibrin clots (virtually all s. aureus)lecture 10biol 53315virul

14、ence factors of s. aureus stage iv, continued secretion of enzymes lipasesrequired for invasion into cutaneous and subcutaneous tissues (found in all s. aureus and 30% of others) nucleaseheat stable (role is uncertain; s. aureus) penicillinaselecture 10biol 53316virulence factors of s. aureus stage

15、iv, continued secretion of toxins cytolytic (membrane-damaging by pores) alpha, beta, (sphingomyelinase c), delta, gamma, leukocidin (cannot lyse red blood cells) others lyse rbc and leukocytes (referred to previously as hemolysins) cause lysis of neutrophils leading to massive lysosomal enzyme secr

16、etionlecture 10biol 53317virulence factors of s. aureus stage iv, continued secretion of toxins exfoliative toxin (scalded skin syndrome) extrachromosomal toxic shock syndrome toxin-1 (enterotoxin f)exotoxin secreted during growth some produce enterotoxin b instead (role not clear)lecture 10biol 533

17、18virulence factors of s. aureus stage iv, continued secretion of toxins enterotoxins (a-e)found in both s. aureus and s. epidermidis resistant to hydrolysis by gastric and jejunal enzymes stable to heating at 100c for 30 minutes mechanism of toxin activity not understood; no satisfactory animal mod

18、el stimulate intestinal peristalsis and have cns effect; intense vomitinglecture 10biol 53319pathogenesis of s. aureus treatment antibiotics types: methicillin, oxacillin, nafcillin, and dicloxacillin (semisynthetic penicillins resistant to -lactam hydrolysis) majority of patients can be treated, bu

19、t 10-15% s. aureus and 40% coagulase-negative staphylococci are resistant; treat with vancomycinlecture 10biol 53320pathogenesis of s. aureus treatment antibiotics resistance: plasmid-borne (hydrolysis of -lactam ring) chromosomalchange in structure of penicillin-binding proteinslecture 10biol 53321

20、streptococci fermentative (oxygen tolerant) gram+ cocci in chains sensitive to penicillins human reservoirpassed from person to personlecture 10biol 53322streptococci properties of lancefield groups (cho antigens on wallsee handout) group a: cross-reaction can lead to: rheumatic fever glomerulonephr

21、itislecture 10biol 53323streptococci recent group a streptococcus virulence factors m-like proteinsbind igm igg (protease inhibitor) and alpha2 macroglobulin f proteinadherence to epithelial cells c5a peptidasedegrades c5a pyrogenic exotoxins; previously called erythrogenic toxinslecture 10biol 5332

22、4staph and strep toxinss. aureus toxic shock tsst-1s. pyogenes toxic shock tssl-1s. pyogenes scarlet feverspe-1 (children, not adults; immunity)lecture 10biol 53325staph and strep toxinss. aureus : toxic shock syndrome fever, diffuse rash exfoliation of skin on palms and soles of feet normally doesn

23、t compete well in relatively anaerobic vaginal arealecture 10biol 53326staph and strep toxinss. aureus : toxic shock syndrome super-absorbent tampon: created aerobic pockets removed mgproducing toxin after removed tampon, cases declined; did not disappear still associated with wounds, rare nasal sur

24、gerylecture 10biol 53327staph and strep toxinss. pyogenes: toxic shock-like syndrome skin or wound infection - bloodstream death rate 30%; over 10-fold higher than tsst seen in immunocompromised people also other infections occurred: soft tissue infection with influenza symptoms high fatality rate b

25、ecause rapid development of shock and multiple organ failurelecture 10biol 53328staph and strep toxinss. pyogenes: toxic shock-like syndrome features in common with scarlet fever occur in healthy people both associated with high fatality rate produce same exotoxin: streptococcal pyrogenic exotoxin (

26、spe) similar in mechanism to tsst-1lecture 10biol 53329staph and strep toxins comparing tsls-1 and tsst-1: rash, fever, shock, multiple organ failure; resemble endotoxin septic shock both toxins superantigens same mechanisms of action limited similarity at amino acid sequence levellecture 10biol 533

27、30staph and strep toxins tsls-1 related to erythrogenic toxin (scarlet fever; spea) serotypes: spe atsls or invasive s. progenes spe b spe c some strains dont produce spe a, so spe b or spe c also has rolelecture 10biol 53331staph and strep toxins how do tsst-1 and spe cause shock and multiple organ

28、 failure? hypotheses not mutually exclusivelecture 10biol 53332shock and organ failure first hypothesis: same as lps triggering release cytokines il1,tnf consistent with role as superantigen promote association between macrophage and helper t cellsproliferation of t cells producing high il2 level se

29、condarily produce il1 tnf inject tsst-1 into rabbits; elevated levels il1 tnflecture 10biol 53333shock and organ failure second hypothesis: increase bodys sensitivity to lps; consistent with: acts synergistically with lps to amplify toxic effects in vitro and in animals conceivablelow levels leachin

30、g into blood due to lysis of resident microflora normally no effect presence of spe or tsst-1 causes an effectlecture 10biol 53334shock and organ failure evidence to support role for lps in tsst and tsls injecting tsst-1 or spe is lethal to rabbits injecting exfolatin and concanavalin a not lethal t

31、o rabbits both elicit t cell proliferation, but dont enhance sensitivity to lpslecture 10biol 53335shock and organ failure evidence to support role for lps in tsst and tsls tsst-1 not lethal to gnotobiotic animals wouldnt expect leakage, but still t cell response therefore, both suggest t cell proli

32、feration not as important as synergy of lps not conclusive; difficult to prove same level t cell stimulation, proliferation occurred in all caseslecture 10biol 53336shock and organ failure third hypothesis: tsst-1 can act directly on endothelial cells damage causes malfunction in circulatory system,

33、 which creates hypotension data: swelling associated with massive leakage of fluid from capillaries is marked symptom of both tsst and tsls could also be result of action of blood vessels by cytokines, coagulation, or complement cascadelecture 10biol 53337staph and strep toxins mortality of s. pyoge

34、nes vs. s. aureus tsls higher than tss tsls strains enter bloodstream tss, only the toxin circulatess. pyogenes known to be invasive; killed by pmns and macrophage if ingestedlecture 10biol 53338s. pyogenes invasiveness strategies for evading phagocytosis; (1): m protein binds h factor better than f

35、actor b leads to degradation of c3b therefore, prevents opsonization by c3b and formation of c3 convertaselecture 10biol 53339s. pyogenes invasiveness strategies for evading phagocytosis data supporting: m mutants yield more susceptible to phagocytosis; less virulent than wild type ab against m prot

36、ective 80 serotypes of m; possibly evades host antibodies by changing serotype; however, no data to support this hypothesislecture 10biol 53340s. pyogenes invasiveness strategies for evading phagocytosis; (2): protease cleaves c5a chemoattractant stimulates oxidative burst some activation of complem

37、ent could occur in spite of m protein because lysis releases wall components that activate complement streptococci could protect themselves- c5a peptidase data supporting: c5a mutants less virulent that wild type in animalslecture 10biol 53341s. pyogenes invasiveness strategies for evading phagocyto

38、sis; (3): m like proteins sequence and structural similarity to m cooh embedded; nh2 exposed most similar to m and each other at carboxy end these proteins bind fc portion of igg and igalecture 10biol 53342s. pyogenes invasiveness strategies for evading phagocytosis m like proteins; possible roles c

39、oat with host proteinless likely detected as invader by complement and immune system adherence for body cells that contain ab on surface also can bind host protease inhibitor such as 2 macroglogulin host uses protease inhibitor to protect against proteases released by phagocyteslecture 10biol 53343s

40、. pyogenes invasiveness strategies for evading phagocytosis; (4): f proteinbinds fibronectin adherence of bacteria to tissues evasion of immune system summary of invasiveness no direct evidence m-like proteins involved in virulence found in impetigo strains, not always in severe invasive strains nee

41、d mutant studies to answer questionslecture 10biol 53344s. pyogenes virulence regulation of s. pyogenes virulence genes expression m, c5a peptidase, and some m-like proteins; regulated at transcriptional level responds to co2 levels increased co2 causes increased productionlecture 10biol 53345s. pyo

42、genes virulence regulation of s. pyogenes virulence genes regulatory gene mry transcriptional activator; sequence analysis shows it is part of two-component system sensornot found activator also known that spea gene on temperate phagelecture 10biol 53346s. pyogenes pathogenesis treatment and prevent

43、ion tsst, tsls are medical emergencies surgical debridement of wounds prevents further production of toxin antibiotics; penicillin toxic effects tsst-1 countered by intravenous rehydration; counter hypotensionlecture 10biol 53347streptococcal treatment prevention vaccine possible target against m po

44、ssible problems # serotypes, but severe invasive disease caused by few ab against m cross-reacts with heartlecture 10biol 53348streptococcal sequellae hypotheses first: autoimmune theory epitopes that cross react with epitopes on cardiac myosin and sarcolemmal membrane proteins thus, t cells or anti

45、bodies could attack tissue inflammatory response damages heart valveslecture 10biol 53349streptococcal sequellae hypotheses glomerulonephritis high levels ab to streptococcal ag circulating in blood stream causes agab complexes to accumulate in kidney inflammatory response attacks kidney interfering

46、 with kidney functionlecture 10biol 53350streptococcal sequellae hypotheses data supporting ag-ab complexes visible in people with glomerulonepheritisglomeruli decrease in c3 and other complement components also seen; supports hypothesis that inflammatory response is occurring second: toxins cause s

47、equellaelecture 10biol 53351streptococcal sequellae hypotheses main argument against time lag between initial infection and development of rheumatic fever (rf; several weeks) or glomerulonephritis (10 days) normally, if due to toxin, within a week candidates for toxin most likely to cause glomerulon

48、ephritis: streptococcal o, streptokinase, or spelecture 10biol 53352glomerulonephritis hypotheses streptococcal o cytotoxin mechanism and aa sequence similarity to pneumolysin pore-forming toxin injected into lab animals; damages heart therefore, may have role in rf also, very immunogenic; maybe ab

49、damagelecture 10biol 53353glomerulonephritis hypotheses streptokinase plasminogenplasmin therefore causes symptoms similar to glomerulonephritis in animals interesting, but not provenlecture 10biol 53354rheumatic fever hypotheses spe rf strains produce spe; others dont enhances cardiotoxicity caused

50、 by streptococcal o in animals havent explained long time laglecture 10biol 53355rheumatic fever hypotheses mysterious feature of rf unexplained treated with antibiotics for as late as 9 days after symptoms, still protected against rf after 9 days, toxic products should be circulating and immune res

51、ponse underway recurrence of disease normally, infection results from different strain some result from same strain rf symptoms take as long to develop as in originallecture 10biol 53356rheumatic fever hypotheses mysterious feature of rf unexplained if caused by autoimmune response, would expect fas

52、ter response possible explanation: previously exposed produces primed immune systemlecture 10biol 53357streptococcal sequellae treatment and prevention strep throat self-limiting treat with antibiotics and prevent rf and glomerulonephritis only s. pyogenes strains cause rf or g not all people colonized actually contract rf or g because of the seriousness, treat any strain with antibioticslecture 10biol 53358streptococcal sequ