CLINICAL MICROBIOLOGY QUIZZES Flashcards
How do Gram negative cells differ from gram positive cells?
They have a thinner peptidoglycan layer
Of the following indicators, which will be yellow at pH 6.0?
Phenol red
Which group of disinfectants does Iodine belong to?
Halogens
What type of media is MAC agar?
Selective and differential
What are the standard autoclaving conditions?
15 lbs/sq inch at 121ºC for 15 min
What is the optimal storage temperature and length of time for storing planted specimens?
4°C – 1 week
What is the bacterial concentration in a 0.5 McFarland standard?
1.5 x 10 8 CFU/mL
What feature of fungi causes the fluorescent appearance in Calcoflour White stain?
The cell wall binds the stain
What is the purpose of vancomycin in Thayer-Martin agar?
To inhibit growth of gram positive bacteria
Why would throat specimens be incubated anaerobically?
Streptolysin O may be inactivated by oxygen
What size particles does a biological safety cabinet’s HEPA filter remove?
0.3 µm in diameter
Which of the following statements pertains to Haemophilus influenzae?
Most infections caused by capsular serotype b
What is a suggested quality control organism that would demonstrate a positive reaction on Simmons citrate agar slants?
Enterobacter aerogenes
What media enhances the recovery of Brucella from blood cultures?
Biphasic media
The Gram stain of a positive blood culture from a patient with infective endocarditis shows Gram positive cocci in chains. Which site is the most likely organism group an inhabitant of?
Oral cavity
Which organism is the novobiocin susceptibility test used to identify?
Staphylococcus saprophyticus
Which species of Streptococci is most commonly responsible for neonatal sepsis in newborn children?
Streptococcus agalactiae
When isolated from one of multiple blood cultures, which of the following would be deemed a probable contaminant?
Propionibacterium species
Which statement relates to blood cultures that are incubated in a continuous monitoring system?
Require blind subculturing in certain circumstances
What is pyocyanin characteristically produced by?
Pseudomonas aeruginosa
What is Beta lactamase?
an enzyme which inactivates penicillin
What is the name of a superficial skin infection in children which gives erythematous lesions due to rupturing vesicles?
Impetigo
In the nitrate reduction test, what does a red colour indicate after the addition of zinc dust?
nitrate not reduced
What is a furuncle?
abscess involving hair shaft
How is Viridans Streptococcus (normal skin flora) differentiated from Streptococcus pneumoniae?
lysis by surface active agents
Which organism is known to cause necrotizing fasciitis?
Streptococcus pyogenes
Which organism is grouped by its carbohydrate cell wall antigens?
Streptococcus pyogenes
What is the colonial and microscopic morphology of Corynebacterium species?
Fine dry grey on blood agar; gram positive bacilli
Which of the following provides a factor required by the etiologic agent of “pink eye”?
Staphylococcus aureus
What condition would cause a gram positive organism to stain gram negative?
The culture plate is very old
What is the principle of the bile esculin test?
Detects an organism’s ability to hydrolyse esculin in the presence of 40% bile
What may cause false negative coagulase tests with staphylococci as a result of lysis of the coagulase – induced clot?
fibrinolysin
Which organism commonly causes the formation of bullae in soft tissue infections caused by brackish sea water?
Vibrio vulnificus
What do all members of the family Enterobacteriaceae ferment?
Glucose
Which organism causes an ulcer progressing to a black eschar and also is known as “wool-sorter’s disease”?
Bacillus anthracis
Which test may give a false positive reaction if the organism is growing on blood agar?
Catalase
Purpose of DNase
used to determine the production of deoxyribonuclease by organisms, particularly Staphylococcus aureus and Serratia
positive=zone of clearing negative=opacity surrounding inoculum
What does PEA inhibit?
Gram neg bacilli
What is CIN agar specific for?
bullseye pink colonies –Yersina
What is AT80 agar specific for?
Aermonas, has halo colonies (typically show up within 48hrs)
What characteristics does E. coli 0157:H7 have?
lactose fermenter, non-sorbitol fermenter
What is the purpose of incubating a Campylobacter isolation plate at 42° C?
to inhibit other normal stool flora and allow the growth of thermophilic Campylobacters
Which transport medium is recommended for culture of stool samples?
Cary-Blair
What is the appropriate gas mixture for growing Campylobacter jejuni?
5% oxygen, 10% carbon dioxide, 85% nitrogen
What is the identification of Neisseria gonorrhoeae based on?
Positive oxidase test, ability to ferment glucose, but not maltose, sucrose, lactose
How can a diagnosis of Chlamydia trachomatis, be confirmed?
Submitting a specimen for nucleic acid probe testing
Which antigens are significant in the typing of Salmonella typhi?
K and O antigens
What are two disease conditions that may be seen with E. coli 0157: H7?
HUS and hemmorgenic collitis
How much can the sensitivity of a CSF Gram stain be increased by using a cytospin?
Up to 1,000 fold
Which of the following describes the colonial morphology of Actinomyces israelii?
A molar tooth
Which is the correct statement concerning Clostridium difficile?
Produces spores
Which statement applies to Enterococcus faecium?
Able to grow in the presence of high concentrations of salt
Which of the following is an oxygen sensitive indicator used in anaerobic jars?
Methylene blue
What is the cellular response in most patients with aseptic meningitis due to Herpes Simplex Virus?
Predominantly mononucleocytes
On examining a direct Gram stain of a cerebrospinal fluid, yeast like organisms are seen. What tests should be done?
India ink preparation and urease test
Osteomyelitis is a complication of an infection from the blood or tissue, which organism is causative?
Staphylococcus aureus
What is the most common manifestation of neonatal gonorrhoeae?
Conjunctivitis
A Gram negative coccobacillary organism that is isolated from synovial fluid on chocolate agar resembles either a Moraxella species or Neisseria gonorrhoeae.
Glucose degradation
Where would an organism described as a capnophilic thermophile grow best?
In atmosphere with increased CO2 content at temperatures between 50° and 60°C
How may Proteus vulgaris be differentiated from Proteus mirabilis?
The indole test
What is the etiologic agent of pseudomembranous colitis?
Clostridium difficile
Which statement describes Francisella tularensis?
Causes a zoonotic infection associated with rabbits, rodents, and beavers
What is the most common bacterial cause of pharyngitis?
Streptococcus pyogenes
What supplies the V factor required for growth of Haemophilus influenza?
a product of hemoglobin breakdown and other bacteria
Which of the following organisms would survive for several days in throat swabs not placed in transport media?
Streptococcus pyogenes
What does the PYR test involve?
L-pyrrolidonyl-ß-naphthylamide hydrolysis
A bronchoalveolar lavage (BAL) specimen was submitted from a patient suspected of having legionellosis. Which media such be used?
Buffered charcoal yeast extract with alpha-ketoglutarate (BCYE) agar
What site can the bacteria causing whooping cough infect?
nasopharynx
In the Kinyoun acid-fast bacilli staining procedure, which of the following reagents stain any acid-fast bacilli present?
Carbol-fuchsin
What is the antigen identified in the Lancefield grouping of streptococci?
a cell wall carbohydrate
What should a specimen labeled “Pharyngeal pseudomembrane” be inoculated onto?
Blood agar, cystine-tellurite agar and Tinsdale agar
Which capsulated gram-negative organism often causes nosocomial pneumonia?
Klebsiella pneumoniae
What are ß-lactamase producing strains of Haemophilus influenzae resistant to?
Penicillan
What is thrush caused by?
Candida
Which characteristic applies to the causative organism of scarlet fever?
Group A Strep, produces erythrogenic toxin
What are common periurethral contaminants of urinary tract specimens obtained from females?
Lactobacilli
What is the maximum time period a urine should be left at room temperature before culturing?
2 Hours
What kind of urine is collected by direct puncture into the bladder using a syringe and needle?
supra pubic bladder aspiration
What is the amount of normal bacterial contamination in midstream urine?
10’5 or less bacteria per litre
What are the most common etiologic agents of uncomplicated cases of cystitis?
Klebsiella pneumoniae and E. coli
What is the key purpose of the novobiocin test?
To differentiate Staphylococcus saprophyticus from other coagulase negative staphylococcus
Which two members of the family Enterobacteriaceae are characteristically nonmotile?
Klebsiella and Shigella
Which procedure may be used to prevent falsely elevated bacterial counts in urine?
placing the urine in boric acid preservative
Which antimicrobial is routinely used to treat gram-negative urinary tract infections?
Nitrofurantoin
What is the most common cause of urinary tract infections?
ascending fecal bacteria
Which bacteria cause over 90% of urinary infections in non-hospitalized patients?
E.coli
What is a disadvantage of using urine dip slides for urine colony counts?
difficulty in obtaining isolated colonies for further tests
What is high level enterococcal resistance to Vancomycin due to?
Altered target site
Which drug against parasitic infections, is therapeutic in infections caused by anaerobic bacteria?
Metronidazole
Which of the following classes of antimicrobial agents inhibit cell wall synthesis?
Glycopeptides
Which antibiotic disk or test is recommended to screen for penicillin susceptibility in Streptococcus pneumoniae?
Oxacillin
What term refers to the multiple reproducibility of a test?
Precision
What percentage of the original inoculum needs to be killed to establish the minimum bactericidal concentration (MBC) of an antimicrobial agent?
99.9%
Which of the following may result in a falsely resistant report being generated after a Kirby Bauer disk diffusion test has been performed?
Expired disks or too heavy an inoculum
What is the term that denotes a situation in which the effect of two antimicrobial agents together is greater than the sum of the effects of either drug alone?
Synergism
What term refers to a substance that inhibits bacterial growth?
Bacteristatic
What is the action of Beta-lactam antimicrobials?
Inhibit cell wall synthesis
Which discs may be used to detect extended spectrum Beta-lactamase production by Enterobacteriaceae?
A third generation cephalosporin alone and in combination with a Beta-lactamase inhibitor
Which statement best describes the stationary phase of bacterial growth?
Numbers of new bacteria equal numbers of dead bacteria
