BACTE PART 1

• Bile esculin agar is a culture medium used for the differential isolation and presumptive identification of group D streptococci and enterococci.
• Blood Agar components:

  Trypticase soy agar

  Brucella agar, or

  beef heart infusion with 5% sheep blood
• Blood Agar's primary purpose is the cultivation of fastidious

  microorganisms, determination of hemolytic reactions.
• Columbia colistin-nalidixic acid (CNA) agar is composed of Columbia agar base with 10 mg colistin per liter, 15 mg nalidixic acid per liter, and 5% sheep blood. It is for the selective isolation of gram-positive cocci.
• MacConkey agar is a selective medium containing lactose, bile salts, crystal violet, neutral red, and agar. It is used to differentiate between Gram-negative and Gram-positive bacteria based on their ability to ferment lactose.
• Cystine-tellurite blood agar Infusion agar base with 5% sheep

  blood. Reduction of potassium tellurite by Corynebacterium diphtheriae produces black colonies. Isolation of C. diphtheriae
• Bile esculin agar - nutrient agar base with ferric citrate. Hydrolysis of esculin by group D streptococci imparts a

  brown color to medium; sodium desoxycholate inhibits many

  bacteria. Differential isolation and presumptive identification of

  group D streptococci and enterococci
• Gastrointestinal pathogen Campylobacter jejuni can grow at 42°C. Other bacteria, such as Listeria monocytogenes and Yersinia enterocolitica, can grow at 4° C to 43° C but grow best at temperatures between 20° and 40°C. Cold enrichment has been used to enhance the recovery of these organisms in the laboratory.
• Acid-fast stains are used to stain bacteria that have a high lipid and wax content in their cell walls and do not stain well with traditional bacterial stains. Carbolfuchsin (a red dye) is used as the primary stain. The cell wall is treated to allow penetration of the dye either by heat (Ziehl-Neelsen method) or by a detergent (Kinyoun method). Acidified alcohol is used as a decolorizer, and methylene blue is the counterstain. Acid-fast bacteria retain the primary stain and are red. Bacteria that are not acid-fast are blue.
• Partially Acid Fast – species that are partially acid fast resist decolorization with a weak (1%) sulfuric acid solution, but lose the carbolfuchsin dye when treated with acid-alcohol. e.g. Nocardia spp.
• Culture in Modified Thayer Martin, New York City, and Martin–Lewis agar should be held a minimum of 48 hours before being considered negative.
• MTM, New York City, and Martin–Lewis agars contain blood factors needed to support the growth of N. gonorrhoeae as well as antibiotics that prevent growth of normal genital flora
• Trimethoprim is the component of the Modified Thayer Matin that is used to inhibit the swarming of Proteus
• Media - Component - Function

  Thayer-Martin Agar

  Vancomycin - Gram + inhibitor

  Colistin Gram - inhibitor

  Nystatin - Fungi inhibitor

  Martin Lewis - Anisomycin - Fungi inhibitor

  NYC Media - Trimethoprim - Swarming inhibitor

  Amphotericin B - Fungi inhibitor
• The aminoglycoside antibiotics are bactericidal agents that

  act by inhibiting Protein Synthesis
• Cell wall Synthesis - penicillin, cephalosporins, bacitracin and vancomycin.

  Protein Synthesis – Aminoglycosides, macrolides, lincosamides, streptogramins, chloramphenicol, tetracyclines

  Nucleic acid Synthesis - quinolones, metronidazole, and rifampin.
• 1.2% gelatin may be added to prevent SPS from inhibiting Neisseria and Peptostreptococcus
• All of these genera of bacteria will produce positive result to

  catalase test EXCEPT:

  A. Planococcus

  B. Micrococcus

  C. Staphylococcus

  D. Streptococcus

  D
• Result of Staphylococci and Micrococci in lysostaphin

  susceptibility test.

  Staphylococci are susceptible, while Micrococci are not inhibited.
• Bacitracin - Furazolidone - Lysostaphin

  Staphylococcus R S S

  Micrococcus S R R
• Hyaluronidase is one of the virulence factors of Staphylococcus aureus that damages the intercellular matrix (basement membrane) of tissues.
• Which detects the presence of the “clumping factor” present

  on the surface of the cell wall of S. aureus, which reacts with the fibrinogen in the plasma.

  A. Tube coagulase test

  B. Slide coagulase test

  C. Latex Agglutination test

  D. All of the above

  B
• Which describes S. saprophyticus?

  A. It is coagulase positive and susceptible to 5 μg of novobiocin

  B. It is coagulase positive and resistant to 5 μg of novobiocin

  C. It is coagulase negative and susceptible to 5 μg of novobiocin

  D. It is coagulase negative and resistant to 5 μg of novobiocin

  It is coagulase negative and resistant to 5 μg of novobiocin
• Acetoin production is detected by the addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation
• The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive. This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.
• Staphylococcus spp. utilize glucose

  A. Oxidatively

  B. Anaerobically

  C. Neither

  D. Both

  D
• What is the color of the positive result of modified oxidase test?

  A. Purple

  B. Red

  C. Pink

  D. Orange

  A
• The antistreptolysin O (ASO) titer is used to indicate

  a recent infection with

  A. Group A Streptococci

  B. Group B Streptococci

  C. Group C Streptococci

  D. Group D Streptococci

  A
• SXT is inhibitory to most streptococci except:

  A. S. pyogenes

  B. S. pneumoniae

  C. S. agalactiae

  D. S. pyogenes and S. pneumoniae

  E. S. pyogenes and S. agalactiae

  E
• The bile esculin test differentiates those bacteria that can hydrolyze esculin and also grow in the presence of

  A. 4% bile salts or 40% bile

  B. 40% bile salts or 4% bile

  C. 4% bile salts or 10% bile

  D. 10% bile salts or 4% bile

  A
• Optochin at a concentration in excess of 5 μg/mL inhibits

  A. S. pneumoniae

  B. Viridans streptococci

  C. Both

  D. Neither

  C
• Bile Esculin Test Principle

  Gram-positive bacteria other than some streptococci and

  enterococci are inhibited by the bile salts in this medium.

  Organisms capable of growth in the presence of 4% bile and

  able to hydrolyze esculin to esculetin will demonstrate growth. In addition, esculetin reacts with ferric ions (Fe3+) and forms a dark brown to black precipitate.
• Optochin test - A zone of inhibition of 14 mm or more around the 6-mm disk is considered a presumptive identification of S. pneumoniae.
• Gram positive cocci, in short chains, but also in pairs

  and singly. Long chains are formed in fluid cultures;

  Catalase negative; PYR positive

  A. S. pneumoniae

  B. S. pyogenes

  C. Both

  D. Neither

  B
• Group B streptococci are resistant to bacitracin, resistant to SXT and negative respectively for PYR.
• With some exceptions, group B streptococci will grow in 6.5% salt broth.
• In Modified Thayer Martin Medium for the growth of Neisseria spp., which is added to prevent the growth of yeasts and molds from vaginal specimens?

  A. Colistin

  B. Nystatin

  C. Trimethoprim

  D. Both A and C

  B
• Which test may be used to confirm the identification of N. meningitidis or N. gonorrhoeae?

  A. Carbohydrate utilization test

  B. DNA test

  C. Rapid Latex Slide Agglutination Test

  D. All of the above

  D
• Which Neisseria spp. is lactose positive?

  A. N. gonorrhoeae

  B. N. meningitidis

  C. N. lactamica

  D. Both A and C

  C
• N. lactamica utilizes lactose by producing the enzyme β-galactosidase. All other Neisseria spp. that grow on MTM media are lactose negative.