Harr

• What is used to attain asepsis of the skin for blood cultures?


  70% alcohol followed by 2% iodine
• Why should iodine remain on the skin for 1 minute during blood culture preparation?

  Instant antisepsis does not occur when cleansing the skin
• What is the function of SPS in blood culture products?

  SPS functions as an anticoagulant and prevents phagocytosis
• What effect does SPS have on Neisseria and Peptostreptococcus?

  Addition of SPS may inhibit them, but this can be reversed with 1.2% gelatin
• From where must C. diphtheriae be recovered?


  From the deep layers of the pseudomembrane in the nasopharynx
• What is the best choice for collecting a specimen from the posterior nares and pharynx?

  A flexible calcium alginate nasopharyngeal swab
• How should specimens for culture of N. gonorrhoeae be handled?


  They should be plated immediately or transported in activated charcoal medium
• What is the correct order for cleansing the skin for blood culture?


  70% alcohol and then 2% iodine or an iodophor
• How long should iodine remain on the skin during blood culture preparation?


  At least 60 seconds
• What is the purpose of adding sodium polyanetholsulfonate (SPS) to nutrient broth media?


  It inhibits phagocytosis and complement
• What is the collection device of choice for recovering Corynebacterium diphtheriae?


  A flexible calcium alginate nasopharyngeal swab
• What is the best transport method for Neisseria gonorrhoeae specimens?


  Transport in a medium containing activated charcoal
• Which transport media are suitable for most pathogens except Neisseria gonorrhoeae?


  Amies, Stuart, or Cary–Blair media
• What is the method of choice for recovering anaerobic bacteria from a deep abscess?


  Needle aspirate after surface decontamination
• What are the primary and differential media of choice for recovery of most fecal pathogens?

  Hektoen, MacConkey, Campy, colistin–nalidixic acid (CNA) agars
• What media is used for recovery of Vibrio cholerae from stool specimens?


  Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth
• What is the primary use of colistin–nalidixic acid agar (CNA)?


  For the recovery of gram-positive cocci
• What type of red blood cells are used in most blood agar plates in the United States?

  5% or 10% red blood cells from sheep
• Why are sheep RBCs preferred in blood agar plates?


  They are less inhibitory than cells from other species
• What is the appropriate transport method for isolating N. gonorrhoeae from genital specimens?


  Culture specimens in ambient oxygen at 37°C
• What is the purpose of chocolate agar and modified Thayer–Martin agar?


  For the recovery of Haemophilus spp. and N. gonorrhoeae, respectively
• What is CCFA used for?


  For the recovery of Clostridium difficile
• What does deoxycholate agar (DCA) isolate?


  It isolates Enterobacteriaceae
• What is Xylose lysine deoxycholate (XLD) agar selective for?


  For the recovery of Enterobacteriaceae from gastrointestinal specimens
• What is the primary isolation medium for Haemophilus species?


  Chocolate agar
• What is the appropriate procedure for culturing genital specimens to recover Chlamydia spp.?


  Inoculate cycloheximide-treated McCoy cells
• How should cerebrospinal fluid (CSF) be handled if delayed for culture?


  It should be incubated at 37°C and cultured as soon as possible
• Why is it important to culture CSF immediately?


  Fastidious organisms like Neisseria and Haemophilus are frequently isolated
• What is the significance of using prereduced and vitamin K1-supplemented blood agar plates?

  They are recommended isolation media for anaerobic bacteria
• What is the role of antibiotics in media for transporting specimens for viral culture?


  They prevent the growth of contaminating bacteria
• What is the importance of using living cells for culturing Chlamydia spp.?


  Chlamydia are strict intracellular organisms
• What is the effect of exposure to oxygen on anaerobic culture media?

  It can contaminate the specimens
• What is the significance of the oxidation reduction potential (Eh) in anaerobic culture media?


  It should be approximately –150 mV to minimize exposure to oxygen
• What is the role of neutral red in deoxycholate agar?


  It allows differentiation of lactose fermenters from nonfermenters
• How does XLD agar differentiate between Shigella and Salmonella?


  Shigella does not ferment sugars and produces red colonies, while Salmonella ferments xylose but produces ammonia, turning red colonies with black centers
• Why is it important to hold cultures for a minimum of 48 hours before considering them negative?


  To ensure that fastidious organisms are not missed
• What is the role of antibiotics in modified Thayer–Martin agar?


  They prevent the growth of normal genital flora
• What is the significance of using prereduced and vitamin K1-supplemented blood agar plates?


  They are recommended for the isolation of anaerobic bacteria
• What is the approximate potential needed to minimize the effects of exposure of organisms to oxygen during inoculation?


  –150 mV
• What staining method may reveal characteristic reddish-brown inclusions in Chlamydia infections?


  Iodine staining