selection-Systemic_Bacteriology_and_Mycology.pdf

Chapter.1. Characters of the genus {":ttt}[*ix{-" + 1. Gram-positive spherical cocci arranged in grape-like clusters. 2. Catalase positive. 3, Opaque pigmented colonies are usually produced on agar..1. The rhility to pr...

Chapter.1. Characters of the genus {":ttt}[*ix{-" + 1. Gram-positive spherical cocci arranged in grape-like clusters. 2. Catalase positive. 3, Opaque pigmented colonies are usually produced on agar..1. The rhility to produ*e staphylocoagukce dividss the genus into two groups: A" Coagulase-positive staphylococci: S" aurCI$o lras the greatest pathogenic potential and is the most medically important species" B. Coagutase-xegative staphylococci: e.g., S. epidermidis and S. saprophyticus which are lrr lcss plthogcnic. + I a + S. aurcus is a facultative anaerobe. rBf It usualiv produces golden yello*' enelopigment. s 1) Nutrient agflr. 2\ Blood agar: producing complete (B-) haemr:lysis due to production _3) Mannitol salt agar (selective indicator merliurn) producing yellorv colonies due to rnannitol fermentation : e fftis mediurnfucilitates isol,ati.on af S. aareus (salt talerant) frorn specimens contaminated by other bacteria. -4- ,* Virulence factors and pathogenerisl 1 i Entsrotoxin B* Coagulase b ( /TSST-r Os-toxin Pratein A J Collagen bind,ing protein Fibronectin hinding iIJ protein II 1. $trphylocorgulsse:. Coagulase is an extracellutar protein that has the ability to convert plasma frhrinogen to fibrin. c Afibrin bawier isformed leading to: S Protection fiomphagocytic and immune defences. S Localization of infection e.g.firnncles. 2. Adhecln: The clumping factor (fibrinogen-binding protein);: r Leading to attashment of tho organism to traumatized tissue and blood clots. 3. Protein A: r trt is prescnt on nurface of S. au.reus.. It Inhibits op$onization by non-specific binding to the Fc'portion of IgG - 4. Ilaemolyrins B.g. Alphr toxin: o These are pore-forming toxins that lyse host cell membranes.. They cause haemolysis on blood agar. 5. Invasinr:. Promote bacterial spread in tissues e.g. I-eucocidin, staphylokinase and hyaluronidase. 6. Erotoxinr having euperantfien mechanism : a) Enterotoxim responsible for staphylococcal food poisoning h) Toxic chock syndrome torin-l ([SST-1). c) Epidermolytir (exfoliatin) toxins rosponsible for staphylococcal scalded skin syndrome (SSSS). + ' contact r'l'ith j !. Shcdding human lcsions, fcrmitcs contaminatcii fiom rcspiratory- tractf \ '.rt ,r-.-..1.:* '-l\vF:/. especially the ----.-^ ^*l nose and skin. r Contaminated hands of tl"re healthcare r'l'orkers' Aureus A. Fyogenic dissases: 1. Locdized skin infections, the most common: a. Folliculitis, furuncles, carbu*cles, or abscesses b. Surgical site infections. c. Traurnatic wound infe*tions fotrlowing skin injury and burns. 2. 3. r lead to deep Iuvasion of bloodstream {bafieraemia) and spread to numerous body sites infections e.g. osteornyelitis, endocarditis and meningitis. { /,g,t. A resulting septicaemir may be rapidly fatal. B. Toxin mediated disersee; 1, Staphylococcal food Poisoning: S Incidence: r It is the commonest type of bacterinl food poisoning' & Stanhvlococcal food poisonins is due to ; a Incubation period is short: 1-6 hours after ingestion sf foods corrtaining preformed toxin" s# i. The source of food contamination mey be: I A carrier such as food handlers harhsuring S. aureus on their hands or in the noEe' a A person with pyogenic staphyls0occal infection e.g., furuncle. t Incriminated foods inelude protein rich food like mayonnaise, milk and its products e.g. ice cream sr enrhohydrate rich food e'g. pasta, cake and koskosi' Toxins produced hy the organism use & superantigen mechanism: produced There are at least six antigenic types of enterotoxins (A, B, C, D, E and G) by 50% of S. aureus skains. Staphytrococcal enterotoxins do not change the chsracters of the food regarding its taste,co1guorodour,in*ddition,@ofboi1ingmayki1lthe organism but does gg! destroy the toxin since it is heat stable" S The disesse is characterized bv r Violent vomiting and diarhea, usually without f,ever & usually self'limited. -6- 2. Toxic shock syndrome (TSS): I Incidence: 'H* recoclrtrd rllt t First described in young rnenstruating females who use H tu*p!; nu{ vaginal tampons that are !e& in place for extended periad. agiral colorizatio; Any individual suffering from TSST-1 producing ly S-aurcas S. aureus inftctions anprhere in the hody. T$S ic due to infcction or colonization by T$STl-producing S. aureus, LEJ The disease is characterized bv: t Sudden ouset of high fever, diarrhoea, vomiting and red rash. I Hypotension with cardiac and renal failure may occur due to the superantigen action ofTSST-1. a The rnortality rate rnay reach 10-15%. 3. Staphylococcal scaldcd skin ryndrome (S$SS): E' Incidence: in neonates and children under 5 years afage. k!, $$S fo[ows infectioils caused by S. fl]ueu$ that produces exfoliafin toxins. t!, The disease is characterized bv: a Large bullae are farmed under the epidermis, which rupture leaving rnoist, red, scalded dermis. Full recovery without scar formation is the ruie 1. Specimens may include pus, sputum, urifle, CSF, blood in cases of bacteraemia, septicaemia and endocarditis. 2. Ilirect detection iu Gram-stained smear$: r ffram-Fositive socci ars seen in clusters in assosiation with pus cells^ e lu{icroscopy cannot discrirninate staphylococcal species. 3. Cultivaticn: r Specimens other than the blood should be plated directly onto blood agar and mannitol salt agar and incutated at 37oC. r Blood samples should be cultivated hy the blood culture technique" r Subcultures are plated on blood agar and incubated as above. 4. Identilication: S After 24h incubation, the growth should be examined for colony rnerphology, Gram stain and catalase production" S. aureus is identified a* follows: r On blotd ngflrt golden yellow colonies surrounded by cornplete haernolysis. * {}n mannitol salt agar: yellow colonies.. Gram-stained film: Ciram positive cocci in clusters. r Coagulase test & Catalase test: positivc. o ClumFing factor test: positivc. w Coagulase and clumpingfaclar *re the mast important rnarkers f*r identifufng,$. *ureus in the laborntory.  5, In cass of food potroning: r Specimens: food remna$ts, vomitus and faeces shsuld be tested for the causative S. arueus and its enterotoxin r Isolation: on selective media such as mauaitol salt agar as the specimens are usually contaminated with other bactsria. o Iletcdion of enterotoxin production by the isolated stains or directly in the sample is done by ELISA. 5. In cese oftodc ehock ryndroue: o Cllnical fiudings. - r fsolation of the organism from suspected sites e.g. urounds, vagina or from tampons by I culture on mannitol salt agar, - = 74 o Detec$on of T$ST-1 in the btood by HLISA. {' N'8.: Strein typing is required in the epidemiologic studies of outbrea}c of S. aureus I diseases such as food poisoning and surgical site irfections. - * Strain tyPW can be done hy colony morphalogt, biotype profiles, phage = typ6, plasmid - analysis, ribatyping, chromosomal analysis and pCR. * {.Prevention and control: ? o Improved hygiene especially hand hygiene and proper infection contol practices techniques in hospitals are the most effertive methods of preveation..& Treatment and Antibiotic SuscepffbiHtiee: & aseptic - r fiay require surgical drainage and antibiotic therapy to prevent dissemination. Abscesses - o Systemic infectionr reguire vigorous antibiotic fieafineut. * '3' Therapy is seriously frced with the following antibiotic-resist3nce petterus of S. cureuc: L Penicillin rccistsut S. rureus: -r o 9lYoof S. aureus strains are resistant to penicillin due to E Feollmdno P ,/ il fiactamase (penicillinace) production /- 4 r Resistant strains remain susceptible to the semi-synthetic penicillin,"(,ffU (e.g. oxacillin and methicillin) andio cephalosporins. ''.fY t& f 2. Methicilfiu resietant Fenrcrl1rn 4 o S, aureus (MRSA); It is a more serious type of resistance, r There is a ehange in the penicillin binding protein (pBp) - which is the binding site for the antibiotic on the organism's cell wa11. l,lr':'t,t:{l:,ri::r;r, !t o This type of resistance is due to the presence of mec-A gelre on the chromosome of MRSA. * l ,'rq4g:: ;[. { ; Infections caused by MRSA strains canaot be treated with any of the beta- lactarn *o,Iffi I} Also, MRSA isolates are often multiresistant to sther a*tibiotics. t vancomycin is used as the drug of choice far tueatrnent of MRSA infections. - 3. Vancomycin resislant S. aureus: ,l a Some strains of MRSA displayed interrnediate (VISA) or fuIIresistance (VRSA) to vancomycin. - The new antibiotics linezolid and streptogrnmins are used for frBatment of infections not - responding to vancomycin ) a -B- tr Morphology flnd Culturrl Ch*racterirficsi tr S. epider*tirlis i-s similur to S. uu except in the 2) It gives *4rite x*cax't hacmolvtic colonics on biood agar. + Virul*nce fattors: s Glycocalyx (or sHme): l; It is an extrace[lular polysaccharide which enables the organism to colonize prosthetic devices and facilitates formationof,a protective hiolilm on the device surface. c Bialilm: aIa &-.w 5r;-RFACE It is an aggregate of microorganisms in which eells adhere to each other on a surface. These adherent cells are frequently embedded within a matrix of extracellular polysaccharide. a Biofilms protect bncteria from hsst defences (e.g., antibodies), detsrgents and *ntibiotics. a Biofilms also facilitate exchange of gtnetic mtterial between bacterial cetrls leading to spread of antihiotic resietauce arnorg thsm. Pathogenesis: t S. epidermidis is part of the nonnal skin flora and it is attached to the upper layer of the skin {epidsrnils) or rnucosa (carriage rate 100%}. Alrnost all infections ars endogenoue but pffrson to person trausrnissiorr by contact may cccur. S. epidermidis is an oppartunistic pathogen associated with device related {e.g., catheter related sepsis, prosthetie valve endocarditis, prosthetic joints aild shunt iafeations), urinary tract and surgical wsund inf,ections. Laborrtory diagnosio: a S. epiderrnidis is di*gnosed by its morphological and cultural characteristics. I It is sensitive to novohiocin. {+ Treatment: q- s. epidermidis infections nre dfficalt to treat. fkis js becaut a The organism is often multi resistsnt ts antibiotics. a The inf'ections usually occur in prosthetic devices where the bacteria can *equester themselves in a biofilm. o a a 1 a ,*ffi &r w tu q# a + Morphotory and eultural chryacteristics : 4 t S. saprophyticus is similsr to $. epiderrnidis' 'L, I )_ {-, Prthogeneris; I S. saprophyticus rnay formpart of the normat flora of human skin 1 and rnucosa ofgenitourlnary tract' vromen causing * It may spread to urinary tract in colonized young sexualiy active infection)' t C urinary tract infections (honeyrnoon cystitio) (endogenous This is due to the ability of the organism to adhere to uroepithelial cells' I * tabomtory diagnosis; 2 I S. saprophyticus is similar to S- epidermidis except in being novohistin resistant' --r--r-+-+ * {. Trea&ent: * r Quinolone; are the drugs of choice' - - - - r - - fr E- L h = * ? -10- * Characters ofthe genus Streptococcus: a *ft* gc& {._]""o.-'S 1. Gram poritive ovoid cocci arranged in chains or pairs. {'x{;tlilstt * 2, Catalase negative: Catalare test is a key test for discriminatiug stneptococci from c*talase positive staphylococci. the I 3. Growth requires onriched media containing blood or ssnrm. qStreptococcu$ pyogenes, Streptecoecus agalactiae and S*rytacacurs pneumoniae are the most irnportant species. 1.& The medically *ignificant otreptococci may be convenicnfly divtdsd on the basis of: 1. I{aemolysis on blood egar ! 1 Eeid flsr})ol!€ts fieid lisr})oiysis.UphaHa||i0irEl$ Canlrna Herulysas Herutysas I Complete haernolysis : beta" o Partial haemolysis : alpha. a No haernolysis: gaffiffia. 7 Lancelield classification; A group speeific c*rbohydrate antigen I Aecording tc which streptococci are classified into groups A to U. I Antihodies against these group antigens are used for identification of streptococcal species..i Morphology:. $. pyogenes are Gram positive cscci ir chains. * Cultural chrracters: a S. pyogenes produce beta haemolysis on blood agar. a S. pyogones grawth i$ inhihitsd by hacitrncin. -11-.1. Yirulence factors end prthogenesis: I. Fsctors that medirte adherence (colonizetion): 1. M protein: It is the most important virulencefactor. r It is a surface protein which enables the bacteria to colonize sHn and to ese*pe phagocytosir. a trt is immunogenic and divides S. pyogenes into about *0 M serorypes. 2. Fibronecfin blndlng protein (Protein F). Eriltosinl: 'rF{;\ il.i. ila \I F:filer11.,r {!nbrt}}'l 3. Lipoteichoic acids. ;a rl4!lcr,:frli{.r,' t' Lin 'i t ** !a , * -_-.* ( rr' h-a llll rt*ll F'lJ".ri',, II. Frctorr thet mediate invasion: Invastfts : * u.,,.' 1. Antiphagocytic factors: ::t,.!:ii'il': n: Lrrt r'll+!"iil''ri" 'llic \;"4; r.ri..l]ri.ri !-..rt;,,ri |.rt-l rfl: aLllrli A- M protein. B" CSa peptidfss hreaks down C5a so that it no longer attracts phagocytes. C. Eytluronic acid capsule: r It is chemically similar to that of host connective tissue; therefore, it is not immunogenic" r This allows the bacteriurn to hide its own antigens ard to go unrecognired by its host. 2. Iuvasinsl A. Streptokinase B. Streptolysins C. Streptoco*c*l pyrogenic {fibrinolysin}: (haemolysins): €xotoxin$ (SPA- A, B & C): It activates These ars ttryCI pore r These toxins ast as plasminogen of forming toxins that lyse superantigens causing toxic human plauma into hsst cell rnernhranes: shock syndrome, plasmin that digests Streptolysin 0 (oxygen septiraemia, and neerotizing librin and labile) is a highly fasciitis. {ibrinogen. immunogenic protein r In addition: It is ten times more and induce$ specifis