MICROBIOLOGY ASCP EXAM 2023/2024 REAL EXAM EXPERT VERIFIED ANSWERS WITH RATIONALES INCLUDED LATEST UPDATE GUARANTEED PASS The procedure that assures the most accurate detection of mecA -mediated oxacillin resistance in routine broth microdilution susceptibility testing against S aureus is: a addition of 4% NaCl b incubation at 30°C c incubation for 48 hours d use of cefoxitin for testing d use of cefoxitin for testing d Cefoxitin is used as a surrogate for mecA -mediated oxacillin resistance in S aureus. S aureus with cefoxitin MICs >4 pg/mL are considered oxacil lin resistant. The Clinical Laboratory Standards Institute (CLSI) recommends addition of 2% NaCl, incubation at 35±2°C, and incubation for 24 hours when performing susceptibility testing of S aureus against oxacillin. When performing a stool culture, a col ony type typical of an enteric pathogen is subcultured on a blood agar plate. The resulting pure culture is screened with several tests to obtain the following results: TSI: acid butt, alkaline slant, no gas, no H2S phenylalanine deaminase: negative motili ty: positive serological typing: Shigella flexneri (Shigella subgroup B) The serological typing is verified with new kit and controls. The best course of action would be to: a report the organism as Shigella flexneri without further testing b verify reacti vity of motility medium with positive and negative controls c verify reactivity of the TSI slants with positive and negative controls for H2S production d verify reactivity of phenylalanine d aminase with positive and negative controls b verify reactivity of motility medium with positive and negative controls b All of the biochemical and serological reactions listed are consistent with an identification of Shigella flexneri, with the exception of motility. All Shigella are nonmotile. Susceptibility testing performed on quality control organisms using a new media lot number yielded zone sizes that were too large for all antibiotics tested. The testing was repeated using media from a previously used lot number, and all zone sizes were acce ptable. Which of the following best explains the unacceptable zone sizes? a the antibiotic disks were not stored with the proper desiccant b the depth of the media was too thick c the depth of the media was too thin d the antibiotic disks were not properly applied to the media c the depth of the media was too thin c All Mueller -Hinton agar used for disk diffusion susceptibility testing should be poured to a depth of 4mm. If the depth of the media is <4mm, this may be associated with excessively large zones and false - positive susceptibility results. Agar that is >4mm in depth may cause excessively small zone sizes. Three sets of blood cultures were obtained from an adult patient with fever and suspected endocarditis. The aerobic bottle of one set had growth of Staphylococcus epidermidis at 5 days of incubation. This indicates that: a there was low -grade bacteremia b the organism is most likely a contaminant c the patient has a line infection d the blood culture bottles are defective b the organism is most li kely a contaminant b Coagulase -negative staphylococci are commonly associated with contaminated blood cultures; however, they are also increasing as a cause of true bacteremia. Significant bacteremia in a patient with endocarditis is usually continuous an d low grade. In most cases, all blood cultures drawn will yield positive results. The facts that only 1 bottle of 1 set was positive, and that the bottle did not become positive until day 5 of incubation, indicate that this isolate is most likely a contami nant. Proper media for culture of a urethral discharge from a man include: a sheep blood and phenylethyl alcohol agars b eosin -methylene blue and sheep blood agars c thioglycollate broth and chocolate agar d chocolate and modified Thayer -Martin agars d chocolate and modified Thayer -Martin agars d Chocolate agar and chocolate agar - based selective media should be used for recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar provides the nutrients required by N gonorrhoeae and selective media contains antimicrobial agents that inhibits other organisms and permits recovery of pathogenic Neisseria. A sheep blood agar plate inoculated with 0.001mL of urine grows 70 colonies of Staphylococcus aureus. How many colony forming units per mL of urine be reported? a 70 b 700 c 7,000 d 70,000 d 70,000 d When 0.001 mL of urine is plated, the growth of one colony is equivalent to 1000 CFU/mL. Thus 70 colonies is 70,000 CFU/mL. The lowest concentration of antibiotic that inhibits growth of a test that inhibits growth of a test organism is the: a minimum inhibitory concentration b serum inhibitory concentration c minimum bactericidal titer d maximum inhibitory titer a minimum inhibitory concentration a The MIC is a basic laboratory measurement of the activity of an antibiotic against an organism. It is the lowest concentration of antibiotic that inhibits visible growth of the organism. It does not represent the concentration of antibiotic that is lethal t o the organism. Which of the following clean catch urine culture colony counts indicates the patient likely has a urinary tract infection? a 10^1 CFU/mL b 10^3 CFU/mL c 10^5 CFU/mL d no growth b 10^3 CFU/mL b Patients with infection often have at least 10 0,000 bacteria/mL of urine in the bladder. However one third of young women with symptomatic cystitis have less than 100,000 bacteria/mL of urine. The Infectious Disease Society of America consensus definition of cystitis is greater than or equal to 1,000 CFU/mL of a uropathogen. The steam autoclave method of sterilization: a uses 15 lbs of pressure for 15 minutes b utilizes dry heat for 20 minutes c produces a maximum temperature of 100 C d requires a source of ethylene oxide a uses 15 lbs of pressure for 15 minutes a The traditional gravity displacement steam sterilization cycle is 121°C for 15 minutes at 15 pounds per square inch. Ethylene oxide is an alternative sterilization method. The expected colony count in a suprapubi c urine from a healthy individual is: a 0 CFU/mL b 100 CFU/mL c 1,000 CFU/mL d 100,000 CFU/mL a 0 CFU/mL a Urine in the bladder is normally sterile. Suprapubic aspiration removes urine directly from the bladder and yields a specimen free of urethral conta mination. An aspirate of a deep wound was plated on blood agar plates and incubated aerobically and anaerobically. At 24 hours there was growth on both plates. This indicates that the organism is a(n): a nonfermenter b obligate anaerobe c aerobe d facultat ive anaerobe d facultative anaerobe d Facultative anaerobes are organisms that can grow under both aerobic and anaerobic conditions. The proper blood -to-broth ratio for blood cultures to reduce the antibacterial effect of serum in adults is: a 1:2 b 1:3 c 1:10 d 1:30 c 1:10 c Human blood contains substances that may inhibit microbial growth. Diluting blood in culture broth reduces the concentration of these substances as well as any antibiotics that may be present. The recommended blood broth ratio is 1:5 -1:10. Dilutions less than this may cause the blood to clot trapping organisms in the clot. Greater dilutions may increase the time to detection A penicillin -resistant Neisseria gonorrhoeae produces: a alpha -hemolysin b beta -lactamase
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