Bacteriology: 7.1 Specimen Collection, Media, and Methods Flashcards
The ASEPTIC collection of BLOOD CULTURE requires that the skin be cleansed with
70% alcohol and then 2% iodine or an iodophor
When cleansing the skin with alcohol and then iodine for the collection of a blood culture, the IODINE (or iodophor) SHOULD REMAIN INTACT on the skin for at least
60 seconds
What is the purpose of adding 0.025%-0.050% sodium polyanetholsulfonate (SPS) to nutrient broth media for the collection of blood cultures?
Inhibits phagocytosis and complement
is used in most commercial blood culture products because it functions as an ANTICOAGULANT and PREVENTS PHAGOCYTOSIS and COMPLEMENT ACTIVATION
0.025%-0.050% sodium polyanetholsulfonate (SPS)
neutralizes aminoglycoside antibiotics
0.025%-0.050% sodium polyanetholsulfonate (SPS)
Addition of SPS may inhibit some Neisseria and Peptostreptococcus, but this can be reversed with
1.2% gelatin
Addition of – may inhibit some Neisseria and Peptostreptococcus, but this can be reversed with 1.2% gelatin.
0.025%-0.050% sodium polyanetholsulfonate (SPS)
A flexible calcium alginate nasopharyngeal swab is the collection device of choice for recovery of which organism from the nasopharynx?
Corynebacterium diptheriae
must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area.
Corynebacterium diptheriae
– nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.
flexible calcium alginate
Semisolid transport media such as Amies, Stuart, or Cary-Blair are suitable for the transport of swabs for culture of most pathogens except:
Neisseria gonorrhoeae
Specimens for culture of – are best if plated immediately or transported in a medium containing activated charcoal to absorb inhibitory substances that hinder their recovery.
N. gonorrhoeae
Specimens for culture of N. gonorrhoeae are best if plated immediately or transported in a medium containing – to absorb inhibitory substances that hinder their recovery.
activated charcoal
Select the method of choice for recovery of anaerobic bacteria from a deep abscess.
Needle aspirate after surface decontamination
Select the primary and differential media of choice for recovery of most fecal pathogens.
Hektoen, MacConkey, Campy, colistin-nalidixic acid (CNA) agars
– selectively isolates pathogenic coliforms, especially Salmonella and Shigella.
Hektoen agar
– differentiates lactose fermenters from nonfermenters
MacConkey agar
– contains antibiotics that prohibit growth of gram-negative coliforms but not gram-positive cocci
CNA agar
– contains the antibiotics cephalothin, trimethoprim, vancomycin, polymyxin B, and amphotericin B to prevent growth of Enterobacteriaceae, Pseudomonas spp., and fungi
Campy agar
Campy agar contains the antibiotics (5) to prevent growth of Enterobacteriaceae, Pseudomonas spp., and fungi
cephalothin, trimethoprim, vancomycin, polymyxin B, and amphotericin B
Campy agar contains the antibiotics cephalothin, trimethoprim, vancomycin, polymyxin B, and amphotericin B to prevent growth of (3)
Enterobacteriaceae, Pseudomonas spp., and fungi
Select the media of choice for recovery of Vibro cholerae from a stool specimen.
Thiosulfate-cittate-bile-sucrose (TCBS) agar and alkaline peptone water (APW) broth.
is used to grow Vibrio cholerae, which appear as yellow colonies as a result of the use of both citrate and sucrose.
Thiosulfate-cittate-bile-sucrose (TCBS) agar
used as an enrichment broth and should be subcultured to TCBS agar for further evaluation of Vibrio colonies.
alkaline peptone water (APW) broth.
Colistin-nalidixic acid agar (CNA) is usually primarily for the recovery of:
Staphylococcus aureus
inhibits the growth of gram-negative bacteria and is used to isolate gram-positive cocci from specimens.
CNA agar
This medium is especially useful for stool and wound cultures because these may contain large numbers of gram-negative rods.
CNA agar
In the United States, most blood agar plates are prepared with 5% or 10% red blood cells (RBCs) obtained from:
Sheep
are used in blood agar plates because they are readily available and less inhibitory than cells of other species.
Sheep RBCs
The type of hemolysis is determined by the source of RBCs.
are chosen because of the characteristically clear hemolysis produced by β-hemolytic streptococci, Staphylococcus, and other pathogens producing β-hemolysins
Sheep RBCs
does not support the growth of Haemophilus haemolyticus, eliminating the possibility of confusing it with β-hemolytic streptococci in throat cultures.
Sheep blood
Sheep blood does not support the growth of – eliminating the possibility of confusing it with β-hemolytic streptococci in throat cultures.
Haemophilus haemolyticus
All of the following are appropriate when attempting to isolate N. gonorrhoeae from a genital specimen except:
Culture specimens in ambient oxygen at 37°C
(3) agars contain blood factors needed to support the growth of N. gonorrhoeae as well as antibiotics that prevent growth of normal genital flora.
MTM, New York City, and Martin-Lewis
MTM, New York City, and Martin-Lewis agars contain blood factors needed to support the growth of – as well as antibiotics that prevent growth of normal genital flora
N. gonorrhoeae
MTM, New York City, and Martin-Lewis agars
Cultures must be incubated in – cultures should be held a minimum of 48 hours before being considered negative.
3%-7% CO2 at 35°C
Chocolate agar and modified Thayer-Martin agar are used for the recovery of:
Haemophilus spp. and N. gonorrhoeae, respectively
Chocolate agar are used for the recovery of:
Haemophilus spp.
Thayer-Martin agar are used for the recovery of:
N. gonorrhoeae
Thayer-Martin agar are used for the recovery of:
N. gonorrhoeae
provides X factor (hemin) and
V factor (NAD) required for the growth of Haemophilus spp
Chocolate agar
X factor from chocolate agar also known as
hemin
V factor from chocolate agar also known as
NAD
is a chocolate agar containing the antibiotics that permit isolation of N. gonorrhoeae in specimens containing large numbers of gram-negative bacteria, including commensal Neisseria spp.
Thayer-Martin medium
Cycloserine-cefoxitin-fructose agar (CCFA) is used for the recovery of:
Clostridium difficile
is used for recovery of C. difficile from stool cultures.
Cycloserine-cefoxitin-fructose agar (CCFA)
inhibit growth of gram-negative coliforms in the stool specimen.
Cycloserine and cefoxitin
ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.
C. difficile
Deoxycholate agar (DCA) is useful for the isolation of
Enterobacteriaceae
inhibits gram-positive organisms.
Deoxycholate agar (DCA)
are too fastidious to grow on DCA.
N. gonorrhoeae and Neisseria meningitidis
The media contain lactose and neutral red, allowing differentiation of lactose fermenters (pink colonies) from nonfermenters (colorless).
Deoxycholate agar (DCA)
Deoxycholate agar (DCA)
he media contain lactose and neutral red, allowing differentiation of lactose fermenters (– colonies) from nonfermenters (colorless).
pink
Deoxycholate agar (DCA)
he media contain lactose and neutral red, allowing differentiation of lactose fermenters (pink colonies) from nonfermenters (–).
colorless
Xylose lysine deoxycholate (XLD) agar is a highly selective medium used for recovery of which bacteria?
Enterobacteriaceae from gastrointestinal specimens
is selective for gram-negative coliforms because of a high concentration (0.25%) of deoxycholate, which inhibits gram-positive bacteria.
XLD agar
is differential for Shigella and Salmonella spp. The medium contains xylose, lactose, and sucrose, which are fermented by most normal intestinal coliforms producing yellow colonies.
XLD agar
XLD agar
does not ferment the sugars and produces red (or clear) colonies.
Shigella
XLD agar
ferment xylose; however, they also decarboxylate lysine in the medium, causing production of ammonia.first appear yellow but become red.
Salmonella
produce hydrogen sulfide (H2S) from sodium thiosulfate and therefore appear as red colonies with black centers
Salmonella
A sheep blood agar plate is used as a primary isolation medium when all of the following organisms are to be recovered from a wound specimen except:
Haemophilus influenzae and Haemophilus parainfluenzae
Both gram-positive cocci and gram-negative bacilli will grow on blood agar plates, but the medium is used in conjunction with a selective medium such as –agar for gram-positive cocci and MacConkey agar for gram-negative bacilli.
CNA agar
Both gram-positive cocci and gram-negative bacilli will grow on blood agar plates, but the medium is used in conjunction with a selective medium such as –agar for gram-negative bacilli.
MacConkey agar
– requires X and V factors, and H. parainfluenzae requires V factor; the primary isolation medium for Haemophilus is chocolate agar.
H. influenzae
H. influenzae requires X and V factors, and – requires V factor; the primary isolation medium for Haemophilus is chocolate agar.
H. parainfluenzae
H. influenzae requires X and V factors, and H. parainfluenzae requires V factor; the primary isolation medium for Haemophilus is –
chocolate agar.
Prereduced and vitamin K1-supplemented blood agar plates are recommended isolation media for:
Bacteroides, Peptostreptococcus, and Clostridium
Anaerobic culture media
The final oxidation reduction potential (Eh) of the medium should be approximately —mV to minimize the effects of exposure of organisms to oxygen during inoculation.
150 mV
can be prereduced before sterilization by boiling, saturation with oxygen-free gas, and addition of cysteine or other thiol compounds.
Anaerobic culture media
Which procedure is appropriate for culture of genital specimens in order to recover Chlamydia spp.?
Inoculate cycloheximide-treated McCoy cells
are strict intracellular organisms and must be cultured using living cells. Direct smears can also be made at the time of culture.
Chlamydiae
Staining cells with – may reveal the characteristic reddish-brown inclusions sometimes seen in Chlamydia infections.
iodine
– monoclonal antibodies may be used to identify the organisms in infected cells of chalmydia infections
Fluorescein-conjugated
Specimens for virus cultures should be transported in media containing
Antibiotics and nutrient
Media for transporting specimens for virus culture include (3)
Hanks balanced salt solution with bovine albumin
Stuart transport media
Leibovitz-Emory media.
Media used for transporting specimens for viral culture are similar to those for bacteria with the addition of a nutrient such as–
Specimens should be refrigerated after being placed in the transport
media until the culture media can be inoculated.
fetal calf serum or albumin and antibiotics.
Cerebrospinal fluid (CSF) should be cultured immediately, but if delayed the specimen should be
Incubated at 37C and cultured as soon as possible
Fastidious organisms such as Neisseria and Haemophilus frequently isolated from the CSF of patients with bacterial meningitis are preserved by placing the fluid in – CO2 at –°C (or at room temperature for no longer than 30 min), if the specimen cannot be cultured immediately.
3%-7% CO2 at 35°C-37°C
The most sensitive method for the detection of β-lactamase in bacteria is by the use of:
Chromogenic cephalosporin
β-Lactamase production by bacteria is detected using one of these drugs as a substrate.
penicillin and cephalosporin
– is hydrolyzed by β-lactamase into acidic products that can be detected as a color change by a pH indicator.
Penicillin
In the iodometric method, a disk containing a penicillin-starch substrate turns –when a drop of iodine is added
blue
The most sensitive method of detection is based upon the ability of the organism to hydrolyze the β-lactam ring of a –
chromogenic cephalosporin.
The breakpoint of an antimicrobial drug refers to?
the level of drug that is achievable in serum
refers to an antimicrobial concentration in the serum associated with optimal therapy using the customary dosing schedule
breakpoint
An organism is – if the MIC is at or below the breakpoint.
susceptible
Which of the following variables may change the result of an MIC?
Inoculum size, incubation time, and growth rate of the bacteria
In vitro testing of drugs is reliable if the method is standardized. In addition to the first three variables, the – affect the results of MIC testing and must be carefully controlled.
type of media and the stability of antibiotics
According to the Kirby-Bauer standard antimicrobial susceptibility testing method, what should be done when interpreting the zone size of a motile, swarming organism such as a Proteus species
The swarming area should be ignored
Which class of antibiotics is used for the treatment of serious gram-negative infections as well as infections with Mycobacterium tuberculosis?
Aminoglycosides
The – are bactericidal agents that act by inhibiting protein synthesis. The group includes amikacin, gentamicin, tobramycin, kanamycin, streptomycin, and spectinomycin.
aminoglycoside antibiotics
They show a low incidence of bacterial resistance but must be monitored carefully because at high doses they can cause ototoxicity and nephrotoxicity.
aminoglycoside antibiotics
These drugs are usually administered intravenously or intramuscularly because they are poorly absorbed from the gastrointestinal tract.
aminoglycoside antibiotics
The group includes amikacin, gentamicin, tobramycin, kanamycin, streptomycin, and spectinomycin.
aminoglycoside antibiotics
Select the medium best suited for the recovery of Yersinia enterocolitica from a patient with gastroenteritis
Cefsulodin-Irgasan-Novobiocin (CIN) agar
– inhibits the growth of many other organisms from the family Enterobacteriaceae.
Cefsulodin-Irgasan-Novobiocin (CIN) agar
– are also recovered from MacConkey and Salmonella-Shigella agars
Yersinia spp.
A suspected case of plague requires which of the following procedures in order to confirm Yersinia pestis?
Collection of multiple sets of blood cultures, incubation of blood cultures at both 28°C and 35°C, and culture aspirates from bubos to MacConkey agar at room temperature
confirm yersinia pestis by incubation of blood cultures at both –,and culture aspirates from bubos to MacConkey agar at room temperature
28°C and 35°C
confirm yersinia pestis byincubation of blood cultures at both 28°C and 35°C, and culture aspirates from bubos to –agar at room temperature
MacConkey agar
– is on the list of agents of bioterrorism. Isolation and identification should be performed in a facility with a Level II or higher biosafety rating.
Yersinia pestis
Yersinia pestis: Isolation and identification should be performed in a facility with a Level – or higher biosafety rating.
Level II
Yersinia pestis: If there is a high risk of aerosolizing the specimen during processing, procedures should be performed under Level – biosafety conditions.
Level III
Recovery of Y. pestis is highest if the specimen is cultured within – hours of collection.
2
Abdominal pain, fever, vomiting, and nausea prompted an elderly male to seek medical attention. A watery stool specimen producing no fecal leukocytes or erythrocytes was cultured and grew a predominance of gram-negative fermentative bacilli. The colonies were beta-hemolytic on blood agar and cream colored on MacConkey agar. The colonies were both oxidase and catalase positive. What is the most likely identification?
Aeromonas hydrophilia
The oxidase positive test result rules out the members of the –family.
Enterobacteriaceae
Colonies of Aeromonas hydrophilia and Plesiomonas spp. might be mistaken for Vibrio spp. since all three grow as – colonies on MacConkey agar, are – hemolytic on blood agar, and are –positive.
clear, beta, oxidase +
Several attendees of a medical conference in the Gulf coast area became ill after frequenting a seafood restaurant. A presumptive identification of Vibrio cholera was made after stool specimens from several subjects grew clear colonies on MacConkey agar and yellow colonies on TCBS agar. Which key tests would help eliminate Aeromonas and Plesiomonas spp.?
Mannitol fermentation, Na+ requirement
All three organisms Aeromonas hydrophilia, Plesiomonas spp., Vibrio spp
are positive for oxidase production and are motile. – spp. do not grow on TCBS agar.
Plesiomonas
Clear colonies on MacConkey agar and yellow colonies on TCBS agar indicate Vibrio or Aeromonas spp. However, only –spp. require Na+ (1% NaCl) in the medium for growth
Vibrio
A group of elementary students became ill after eating undercooked ground beef prepared in the school cafeteria. The suspected pathogen, E. coli serotype 0157:H7, is usually recovered using which of the following media?
MacConkey agar with sorbitol
– ferments lactose, and therefore, appears as dark pink colonies on MacConkey agar.
E. coli 0157:H7
To differentiate E. coli 0157:H7 from normal fecal flora, MacConkey agar with sorbitol is used. – does not ferment sorbitol, and usually are colorless colonies.
E. coli 0157:H7
To differentiate E. coli 0157:H7 from normal fecal flora, – agar with –is used. E. coli 0157:H7 does not ferment sorbitol, and usually are colorless colonies.
MacConkey agar with sorbitol
