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Micro Quiz 2
Staphylococcus and Streptococcus
| Question | Answer |
|---|---|
| General characteristics of staphylococcus and micrococcus | Gram positive cocci, catalase positive and clinically significant organisms within this group are primarily Staphylococcus |
| Staphylococcus- Epidemiology | organisms that cause infection (skin/mucous) colonizers that gain entry through some form of trauma or invasive procedure into a normally sterile site, may live as normal flora prior to infection, problem in hospital-many organisms have acquired antimicro |
| Staphylococcus aureus virulence | only able to invade via broken skin or mucous membranes, have various ways to avoid host defenses |
| ways S. aureus avoid host defenses | -hide their antigens to avoid immune response -kill infection-fighting cells (phagocytes) -survive within host infection-fighting cells develop resistance to antibiotics -release toxins |
| virulence of S. aureus | produce many enzymes that increase virulence: Hyaluronidase, Beta lactamase, Coagulase, DNase and protein A |
| Hyaluronidase | enzyme that S. aureus produces, "spreading factor"=breaks down connective tissue |
| beta lactamase | enzyme that S. aureus produces, disrupts the Beta lactam ring of certain antibiotics, rendering them useless |
| Coagulase | enzyme that S. aureus produces. clot formation around the bacteria protecting it from recognition from phagocytes |
| DNase | enzyme that S. aureus produces, ability to break down DNA |
| Protein A | S. aureus produces protein A that increases virulence, found in the cell wall can bind to IgG blocking phagocytosis |
| toxins produced by S. aureus | S. aureus produces: exotoxins, cytolytic toxins, enterotoxins |
| exotoxins-S. aureus | a toxic protein produced by a bacterium and released into its environment |
| cytolytic toxins-S. aureus | 4 hemolysins- alpha, beta, gamma and delta, hemolysins destroy RBCs, WBCs, neutrophils, macrophages and platelets, leukocidins-destroys leukocytes |
| enterotoxins-S. aureus | exotoxins that cause food poisoning, reulting in vomiting and diarrhea |
| diseases caused by Staphylococcus aureus | skin and wound infections-folliculitis, furuncles, carbuncles, impetigo, toxin mediated syndromes-toxic shock syndrome, scalded skin syndrome food poisoning other infections |
| folliculitis | inflammation of one or more hair follicles, can occur anywhere on the skin starts when hair follicles are damage by friction from clohing, blockage of follicle or shaving damaged follicles are infected with staphylococcus |
| furuncles | extension of folliculitis are large painful raised nodules with underlying collection of dead and necrotic issue (Boils) |
| carbuncles | furuncles and extend to deeper subcutaneous tissue (fever and chill) |
| impetigo | superficial infections (occur on face/limbs), "school sores"-affects children and contagious, caught from someone else with it or appear out of the blue, starts at site of minor skin injury, insect bite or scratched eczema |
| toxic shock syndrome | infection is localized but S. aureus produces toxins that have systemic effects-fever hypotension and maybe death, most commonly associated with post-surgical infections, Toxin TSST- 1 is the reason for the systemic symptoms |
| scalded skin syndrome (Ritter's disease) | extensive exfoliative dermatitis effects primarily neonates, produces a toxin that causes epidermis of skin to slough off and produce a burn-like appearance-caused by Staphylococcal exfoliative toxin-produced and excreted in kidneys |
| food poisoning | resulting from ingestion of pre-formed toxin, source of contamination is generally a contaminated food worker, sandwich fillings, meat products ect. foods at room temperature are susceptible to high levels of toxin production-S. aureus |
| food poisoning symptoms | nausea, cramping, diarrhea, vomiting 2-8 hours after ingestion and continue for 24-48 hours death is rare |
| other infections | staphylococcus pneumonia (following influenza virus), staphylococcal bacteremia (leading to endocarditis in IV drug users), septic arthritis, S. aureus is a common post-operative infection and important nosocomial agent |
| Staphylococci- coagulase negative | abbreviations-CONS-Coag. Negative Staph STCN- Staph. Coag. Negative |
| Staphylococcus epidermidis | most common Coagulase neg Staphylococcus, very common normal flora on skin, less virulent-strictly an opportunistic pathogen, infections occur as nosocomial infections related to medical procedures and practices (catheter insertion) |
| Staphylococcus epidermidis infections | occurs because: organisms are capable of producing a slime layer that allows them easily attach to medical devices, have ability to acquire resistance to antibiotics commonly used in hospital environments |
| Staphylococcus saprophyticus | coagulase neg staphylococci, "community acquired", most commonly associated with urinary tract infections in young sexually active females- |
| micrococcus species | catalase positive coagulase negative, no known virulence factors, rarely associated with infection, contaminant-found in environment and indigenous skin flora, M. luteus |
| steps in isolation and identification of staphylococcus | 1. direct smear from specimen, 2. streaking culture plates-size, texture, color, hemolysis, 3. colonies Gram stained , 4. isolated bacteria are speciated-generally using physiological/biochemical tests, 5. antibiotic susceptibility testing |
| gram stain | Staphylococcus and Micrococcus appear as Gram positive cocci in pairs tetrads and or clusters |
| Media | growth on 5% sheep blood and chocolate bu not MacConkey plates, |
| incubation | 35 degrees C in CO2 or ambient air-Growth on BAP in 24 hours not fastidious and grow in the presence of room oxygen |
| approach to identification | Gram stain-GPC(gram pos cocci) in clusters, catalase -positive, coagulase-positive=presumptive S. aureus negative=STCN, micrococcus, |
| presumptive ID | preliminary results-need additional testing to confirm the identification |
| which test differentiates Staphylococcus from Micrococcus? | catalase doesn't differentiate them, coagulase differentiate S. aureus from STCN and Micrococcus, oxidase and bacitracin differentiate STCN from Micrococcus |
| gas generation: catalase test | some bacteria and macrophages can reduce oxygen to hydrogen peroxide-can be toxic to bacteria, some bacteria possess defense mechanism can mon, harm done by hydrogen peroxide, resistant bacteria use 2 enzymes to catalyze the conversion of hydrogen peroxid |
| Catalase test | adding colony from culture to hydrogen peroxide on glass slide, if bacteria in question produce catalase, will convert the hydrogen peroxide and oxygen gas will be evolved-bubbles to form=positive |
| catalase test significance | catalase test used on many types of bacteria, most significant when used to identify Gram positive cocci, is pivotal test divides Gram positive cocci into staphylococci (catalase+) and streptococci(catalase-) |
| coagulase test | if catalase test is pos. organism is possibly staphylococcus, then perform slide coagulase test-distinguishes S. aureus from other types of Staphylococci |
| cell-bound coagulase | "clumping factor" causes agglutination in human rabbit or pig plasma |
| on surface of bacterial cell | coagulase on bacterial cell directly converts fibrinogen to fibrin which precipitates onto the cell surface causing agglutination |
| coagulase test | neg slide result can be confirmed with tube method detects free coagulase or staphylocoagulase-extracellular molecule clot to form when bacterial cells are incubated with serum |
| coagulase test | free coagulase binds with other factors to make a complex that resembles thrombin and indirectly converts fibrinogen to fibrin, tube is checked for presence of clot at 4 hours incubation and 18 hours |
| colonies look S. aureus | beta hemolytic yellow/tan creamy colonies and slide coag is neg can perform tube coagulase test -free coagulase made by the organism but not bound to the cell wall |
| approach to identification STCN and micrococcus | coagulase neg-modified oxidase test=STCN=neg micrococcus=pos bacitracin susceptibility- STCN-resistance micrococcus-s novobiocin disc- identification of S. saprophyticus in urine cultures-S. saprophyicus-r other STCN=S |
| oxidase test | cytochrome oxidase test is used for Gram negative rods organisms with this enzyme can use oxygen for energy production |
| cytochrome oxidase | an enzyme found in some bacteria that transfer electrons to oxygen the final electron acceptor in some electron transport chains-enzyme oxidizes reduced cytochrome to make this transfer of energy |
| oxidase test | presence of cytochrome oxidase can be detected when colonies are exposed to methyl phenylenediamine-electron donor to cytochrome oxidase-bacteria oxidizes disk/reagent disk will turn purple=positive test no color change=neg |
| oxidase test | modified oxidase test-6% solution of tetramethyl-phenylene-diamine in dimethyl sulphoxide is used to differentiate micrococci from staphylococci- blue purple=pos |
| bacitracin (A) disc | "A" disc contains 0.04 units of bacitracin-diffuses into agar bacitracin is antibiotic isolated from the bacillus species organism-inhibit bacterial cell wall synthesis |
| bacitracin disc | antibiotic originally isolated from the bacillus species organism belongs to a class of antibiotics that inhibit bacterial cell wall synthesis |
| procedure of 'A' disc | well isolated colony is streaked heavily in one quadrant of BAP and then streaked for isolation, 'A' disc placed on heavily streaked first quadrant-incubate overnight 35-37 degrees C, clear zone around disc=susceptibilty to bacitracin |
| novobiocin disc | presence of coagulase neg staphylococci in urine specimen, 5ug novobiocin disc zone size of less than 16mm is resistant=staphylococcus saprophyticus is resistant to novobiocin all other STCN are susceptible |
| approach to identification of S. aureus | GPC, catalase +, coagulase +,=Presumptive S.aureus need to 2 confirm tests-mannitol salt plate (MSA), DNAse enzyme test, VP test and rapid kit testing (Staphyloslide |
| Mannitol Salt Agar | is a selective and differential media, high concentration of salt (7.5%) selects for halophilic organisms=Staphylococci, contains sugar mannitol and pH indicator phenol red |
| fermentation of mannitol | if organism can ferment mannitol=cause the phenol red in agar to turn yellow=positive result. S. aureus will result positive, so ferment mannitol most STCN will not |
| DNAse agar (Deoxyribonuclease) | has DNA in it, exoenzyme excreted from the bacterial cell will break the DNA down into smaller molecules, HCL (hydrochloride) reagent is used to precipitate out the undestroyed DNA |
| DNAse Agar #2 | around area of growth the bacterium has made DNAse and destroyed DNA=clear zones rest of plate will turn an opaque white (still has dna) methyl green added to see result better |
| VP-Voges-Prosakuer test | different bacteria convert dextrose and glucose to pyruvate-different metabolic pathways-produce unstable acidic products converts to neutral compounds,butylene glycol pathway produce actoin |
| vp test slide 2 | VP test detects organisms utilize the butylene glycol pathway=end product acetoin, reagents used for VP test are Barritt's A (alpha-napthol) Barritt's B (potassium hydroxide KOH) end product(+ test) is red color |
| columbia CNA with sheep blood | selective media=contains the antibiotics Colistin and Nalidixic acid, suppresses growth of Gram neg organisms and support growth of Gram pos organisms-differentiates hemolytic reaction |
| PEA phenylethyl alcohol agar | selective-with or without sheep blood, contains phenylethyl alcohol to inhibit Gram neg organisms and allow for isolation of Gram pos, |
| tests to determine bacterial resistance | detection of Methicillin Resistant S. aureus detection- cefoxitin disk screen test, oxacilin/ methicillin agar screen chromogenic agars, PB2 latex agglutination test |
| tests to determine bacterial resistance | beta-lactamase detect enzyme penicillinase confers resistance to beta-lactam antibiotics, molecular testing-gene probes detect resistant genes |
| general characteristics-streptococcus. enterococcus | catalase neg, Gram pos cocci in pairs and chains, facultative anaerobes, some species are capnophilic (increase CO2), weak false pos catalase test-isolate is taken from plate with blood |
| rgeneral charateristics 2 | streptococci are elongated than spherical, lancefield classifications-grouping of cell wall carbohydrates to classify streptocci-group A-S. pyogenes, group B-S. agalactiae, group C- S. equi, group D- S. Bovis /enteroccus-S. gallolyticus |
| Beta hemolytic | S. pyogenes and S. agalactiae |
| alpha hemolytic | S. pneumoniae and viridans streptococci |
| gamma hemolytic | E. faecalis-can show as alpha or beta hemolytic and E. faecium |
| strep epidemiology | organisms within this group are found as part of the normal flora, gain access to normally sterile sites can cause life threatening infection |
| streptococcus pyogenes | carried in upper respiratory tract-should be considered virulent whenever encountered, |
| M protein | causes Streptococcal cell to resist phagocytosis and plays role in adhence to mucosal cells |
| capsule | hyaluronic acid capsule allow bacteria to mask its antigens and become unrecognized to the host |
| streptolysin O | oxygen labile (inactivated by oxygen) found in anaerobic conditions |
| streptolysin S | oxygen stable-found in aerobic conditions |
| exotoxins-SPE | streptococcal pyogenic exotoxins can cause scarlet fever |
| localized infections with S. pyogenes | pharyngitis-strep throat, tonsilitis, impetigo-localized skin disease, small vesicles/progresses to weeping lesions, erysipelas-infection of skin/subcutaneous tissue, cellulitis-deeper invasion of streptococci |
| systemic infections with s. pyogenes | progression of infection with involvement of deeper tissue and organs-necrotising fasciitis, scarlet fever, streptococcal toxic shock syndrome, rheumatic fever acute glomerulonephritis |
| necrotizing fasciites | flesh eating bacteria, invasive infection characterized by rapidly progressing inflammation and necrosis of tissue, subcutaneousfat and fascia, life treatening condition 70%, mostly occurs in pts with underlying illness experience trauma to skin |
| scarlet fever | upper trunk red spreading rash, SPE- streptococcal pyogenic exotoxins, strawberry tongue-bumps are larger |
| streptococcal toxic shock syndrome | causes by virulent strains of exotoxin producing streptococcus, always group-A organisms such as s. pyogenes, described in setting of surgical wounds burns childbirth diabetics elderly neonates and immunocompromised |
| STSS-rapidly progressive | soft tissue infections generally constitute cellulitis/necrotizing process including necrotizing fasciitis from an infectious organism, renal/respiratory failure |
| rheumatic fever | complication that typically follows s. pyogenes pharyngitis, antibodies produced to help fight streptococcal infection cross react and begin attacking heart tissue, inflammation of heart joints blood vessels and subcutaneous tissues, damage to heart valve |
| acute glomerulonephritis | poststreptococcal glomerulonephritis, antibody-antigen complexes form within the host and deposited in glomerulus of kidney inflammatory response causes damage to glomerulus=impairment of kidney function |
| streptococcus agalactiae | seen as cause of mastitis in cattle, associated with neonates in humans, before/during birthing process, colonization of vagina and rectal area with group B strep 10-30% all pregnant women-all women be screened 35-37 weeks gestation |
| s. agalactiae | infection manifests itself as pnemonia or meningitis with bacteremia in neonates, high mortality rate if not detected and treated early, drug of choice for treatment is Penicillin |
| strepococcus pneumoniae | can be normal flora of upper respiratory tract, pathogenic when a ccess to lungs by aspiration and causes bacterial pneumonia, access to blood/meninges=bacterial meningitis, otitis media and sinusitis, virulence=polysaccharide capsule |
| viridans streptococci | viridans=green, large group of alpha hemolytic streptococci-normal inhabitant of upper respiratory and GI tract, s. intermedius, s.sanguis, s.mitis, s. mutans, group d/bovis group |
| viridans strep organisms | low virulence organisms-cause disease if host defenses are compromised, common cause of bacterial endocarditis, heart valves are damaged by Rheumatic fever=most susceptible , can cause localized skin infections |
| Group D strep | S. gallolyticus-found in endocarditis association with colon cancer, s. infantarius-neonatal meningitis, used to be classified as bovis group-now two separate species with new names, |
| enterococci | non=hemolytic/alpha hemolytic, colonizers of GI tract, virulence=able to grow in extreme conditions-presence of bile/high concentration of salt, presence of enzymes-help adhere to heart valves/renal epithelial cells, resistant to commonly used antibiotics |
| enterococcal infections | causes of nosocomial infections commonly identified species are E. faecalis and E.faecium, UTI's are most common infections and associated with catheterization, bacteremia in dialysis and post surgical pts, endocarditis, wound infections-burn pts |
| rare streptococcal like organisms | gemella and pediococcus species- alpha/gamma hemolytic, easily decolorize-may appear as gram neg cocci, normal flora but have been isolated from cases of endocarditis wound and abscesses |
| leuconostoc | gram pos, alpha hemolytic, irregular cocciod morphology, cross react with Lancefield group D antisera, intrinsically resistant to Vanco, seen as opportunistic pathogen in pts who have been treated with vanco for another infection, cause meningitis, |
| s. pneumoniae | is typically lancet shaped gram pos cocci in singles, pairs or short chains |
| cultivation of strept/enterococcus | grow on 5% sheep blood/chocolate agars, no growth on MAC, growth selective media CNA and PEA, incubation5-10% CO2, colony appearance=various types of hemolysis begin in identification process |
| Lim broth (Todd-Hewitt broth) | selective enrichment of group B strep, most common used to supoort growth of s. agalactiae and dimish growth of normal vaginal flora using Colistin and Naldixic acid |
| Carrot broth | selective for Group B strept, selective and differential broth for isolation and identification of s. agalactiae |
| bacitracin susceptibility |
Created by:
lkolb10