Microbiology Course Objectives – Flashcards
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| Components of gram negative cell walls |
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| Outer membrane, peptidoglycan, periplasmic space, cytoplasmic membrane, cellular appendages |
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| Components of gram positive cell walls |
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| peptidoglycan, cytoplasmic membrane, cellular appendages |
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| Aerobic |
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| a organism that can grow in ambient air |
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| facultative anaerobe |
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| a organism that can grow in ambient air or anaerobic conditions |
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| microaerophilic |
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| an organism that can grow in environments where the partial pressure of oxygen is less than atmospheric partial pressure of oxygen |
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| capnophilic |
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| an organism that prefers to grow in an atmosphere of concentrated carbon dioxide |
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| Blood Agar |
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| infused with 5% sheep’s blood, used for cultivation of fastidious microorganisms, and determination of hemolytic reactions |
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| Chocolate Agar |
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| enriched with 2% hemoglobin or IsoVitaleX, used for cultivation of Haemophilus spp. and pathogenic Neisseria spp. |
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| MacConkey Agar |
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| infused with lactose, gram positive organisms inhibited by crystal violet and bile salts, neutral red as indicator, used for isolation and determination of lactose fermenting and non-lactose-fermenting enteric bacilli |
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| MacConkey Sorbitol Agar |
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| modification of MacConkey agar in which lactose has been replaced by d-sorbitol, used for selection and differentiation of E.coli in stool specimens |
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| XLD (xylose lysine desoxycholate) Agar |
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| Sodium desoxycholate inhbitis gram-positive organisms, used for isolation and differentiation of Salmonella and Shigella spp. from other gram-negative enteric bacilli |
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| Thayer- Martin Agar |
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| Blood agar base enriched with hemoglobin and supplement B, used to select for N.gonorrhoea and N.meningitidis |
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| Bordet-Gengou Agar |
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| contains blood, potato extract, and glycerol with antibiotics, used to isolate for Bordetella pertussis |
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| Buffered charcoal yeast extract (BCYE) Agar |
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| yeast extract, agar, charcoal and salts, enrichment for Legionella spp. |
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| Campy blood Agar |
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| Brucella agar base with sheeps blood and antibiotics (vancomycin), selective for Campylobacter spp. |
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| Cefsulodin-irgasan-novobiocin (CIN) Agar |
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| yeast extract, mannitol and bile salt, selective for Yersinia spp.; may be useful for isolation of Aeromonas spp. |
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| Columbia colistin malidixic (CNA) Agar |
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| derivative of sheep’s blood agar, selective isolation of gram-positive cocci |
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| Cysteine-tellurite blood Agar |
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| infusion agar base with sheeps blood, isolation of C.diphtheriae due to reduction of potassium tellurite which shows as black colonies |
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| Mannitol salts Agar |
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| High salt concentration, selective isolation of staphylococci |
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| Regan Lowe Agar |
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| charcoal agar supplemented with horse blood, enrichment and selective medium for isolation of Bordetalla pertussis |
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| Thiosulfate citrate bile salts (TCBS) Agar |
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| peptone base with yeast extract, selective and differential for vibrios |
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| Chromagar MRSA |
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| isolation and differentiation of methicillin resistant Staphylococcus aureus |
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| Chromagar O157 |
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| detection of E.coli O157 |
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| LIM Broth |
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| selective enrichment broth for determination of group B streptococci |
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| Mueller-Hinton Agar |
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| used for antibiotic susceptibility testing, isolates Neisseria spp. and Moraxella spp. |
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| four important criteria for collection of specimens for bacterial culture |
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| (1) Timing (2) Appropriate collection techniques (3) specimen transport (4) specimen labeling |
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| Characteristics that differentiate Staphylococi from Streptococci |
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| Catalse test (staph is positive, strep is negative) and gram stain (staph has grape like clusters, strep in chains) |
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| Beta Hemolytic Strep |
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| S.agalactiae and S.pyogenes |
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| Alpha hemolytic strep |
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| s. pneumoniae, Viridans, S.bovis, S.milleri |
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| Catalase Test |
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| hydrogen peroxide allows direct analysis of bacterial colony for presence of catalase enzyme. Positive = bubbles ( Staphylococci, Corynebacteria, some GNRS). Negative = no bubbles (streptococci, clostridia) |
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| Coagulase Test |
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| EDTA plasma mixed with organism clumps on slide because of alteration of fibrinogen or in a tube due to activation of coagulase reacting facto.r. Positive = clumping (S.aureus), negative = no clumping (all other staph) |
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| Novobiocin Test |
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| antibiotic disk on miller-hinton plate, lawn growth. Positive = resistant zone < 22mm (s.saprophyticus), negative = sensitive zone > 22mm (other staph) |
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| PYR |
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| identify S. pyogenes and entercocci from other strep due to red color change on disk |
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| Bile Solubility |
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| differentiates S. pneumonia from Viridins strep. Strep pneumonia disintegrates on the agar, and viridins strep does not |
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| P disk |
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| test use to determine the effect of Optochin on an organism. Optochin lyses pneumococci, but alpha-streptococci are resistant. Positive = zone of inhibition > 14mm (Streptococcus pneumoniae), negative- no zone of inhibition ( other alpha hemolytic streptococci) |
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| Bacitracin (A disk) |
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| used to determine the effect of bacitracin on an organism, streptococcus pyogenes is inhibited by bacitracin, other beta hemolytic streoptococci are not. Positive = any zone of inhibition (group A), negative= no zone |
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| Esculin hydrolysis |
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| most gram-positive bacteria are inhibited by bile in an agar slant. If streptococci and enterococci can grow in the presence of 40% bile and hydrolyze esculin, they turn the indicator a dark brown color. This is a result of esculetin and ferric ions to form phenolic iron complex. Positive = blackening of the agar, (streptococci and entercocci), negative = no blackening |
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| NaCl Broth |
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| used to determine the ability of an organism to grow in high concentrations of salt. Used to differentiate enterococci from nonenterococci. Positive = visible turbidity in broth with/without color change ( enterococcus faecalis), negative = no turbidity, no color change (streptococcus) |
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| Staph Latex Test |
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| alternative test to coagulase testing. Latex beads are coated with clumping factor and protein A. S. aureus will clump = positive. More sensitive than coagulase test |
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| Strep Latex Test |
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| Lancefield grouping: antisera agglutination reactions. Antisera + carbohydrate from unknown beta hemolytic strep allows you to determine it's group. The latex beads contain the antisera and you extract the carbohydrate antigen from the organism by acid or enzyme. Mix the latex beads with the carbohydrate antigen and clumping determines group. |
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| Bacillus spp. |
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| found in the soil, can cause cutaneous, pulmonary infections along with food poisoning. Spores can be seen via special spore stain, They are gram positive rods in singles or chains, and on the blood plate they are large, spreading, flat colonies. They can be identified on the basis of motility, hemolysis, penicillin resistance and lecithinase. |
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| Listeria spp. |
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| found everywhere, transmitted to humans via food or through the placenta. Can cause septicemia or meningitis. On the gram stain it’s a gram-positive coccobacilli, and on the blood plate its hemolytic. It can be IDed by a positive catalase test, positive motility test, positive CAMP test, positive Esculin hydrolysis test and positive hippurate hydrolysis test. |
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| Corynebacterium spp. |
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| obligate human parasite transmitted via drop nuclei. It can cause throat inflammation, pseudomembrane; toxin and cutaneous infections. Treated by antitoxin, penicillin, erythromycin, or vaccination. On a gram stain it is pleomorphic, but some spp. needs selective media to be cultured. |
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| Erysiplothrix spp. |
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| found in animals and causes wound infections. On the gram stain it shows short rods and long filaments. On the blood plate it can be either large and rough or small and smooth. Identified by a negative motility test and H2S produced on TSI |
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| Lactobacillus spp. |
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| fond in food and nature, normal flora of the oral, GI and vaginal tracts. It is a rare pathogen and presents on the gram stain as pleomorphic, long chains, coccobacilli or spiral forms. On the plate it has multiple morphologies and is often alpha hemolytic. It can be IDed by colony and microscopic morphologies and a negative catalase test |
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| How to differentiate C. diphtheria from other Corynebacterium spp.? |
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| Elek Test and Urease Test |
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| How to differentiate pathogen Neisseria from nonpathogen Neisseria and Moraxella? |
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| N. gonorrhoeae ferments glucose only N. meningitis and M. catarrhalis ferment glucose AND maltose |
