Bacteriology Flashcards
The cellular immune response plays a role in whether a person exposed to Mycobacterium tuberculosis will develop tuberculosis disease (TB). Which of the following factors will make a person most at-risk of progressing from infect to active disease
a) Amount of exposure
b) Malnutrition
c) Allergies
d) Age of patient
B - Malnutrition
TB is spread by airborne particles called droplet nuclei. After initial infection, the disease usually goes to an asymptomatic and non-infectious phase called latent TB. The risk of a patient with a positive TB screening test progressing to active disease ranges from about 3% to 15% throughout their lifetime. Malnutrition can have a significant impact on whether or not an exposed patient will progress from latent TB to active disease
All of the following organisms stain with an acid-fast stain, or one of its variants, EXCEPT
a) Mycobacterium spp.
b) Cryptosporidium spp.
c) Actinomyces spp.
d) Nocardia spp.
C - Actinomyces spp.
What is the best method for the detection of Chlamydia trachomatis in cases of sexually transmitted disease
a) Non-culture EIA methods
b) Cervical tissue culture
c) Culture of Thayer-Martin agar
d) DNA amplification techniques
D - DNA amplification techniques
DNA amplification probes for the DNA of C. trachomatis and are the most sensitive tests available. PCR is one of the most common forms of this method
Pseudomonas aeruginosa is often used as a bacterial species for the quality control of KIA (Kligler iron agar). What is the expected reaction
a) Acid slant/acid deep
b) Alkaline slant/acid deep
c) Alkaline slant/acid deep/H2S
d) Alkaline slant/alkaline deep
D - Alkaline slant/alkaline deep
P. aeruginosa is a non-fermenter, so it cannot produce acid from glucose in a fermentative medium. There is no change in the KIA tube, and both slant and deep remain alkaline (red/red)
A tech is testing a sorbitol negative isolate for possible E. coli O157:H7 from a MACSORB plate. The biochemical identification proves the organism is E. coli. Serological testing for the O157 somatic antigen is positive. Serological testing for the H7 flagellar antigen is negative. Quality control for all serological testing passed. What should the tech do next
a) Report out the organism as E. coli O157:H7
b) Repeat biochemical testing
c) Repeat O157 serological testing
d) Subculture the organism to motility medium for repeat H7 serological testing
D - Subculture the organism to motility medium for repeat H7 serological testing
The flagellar antigen (H7) can be initially negative for serotyping when taken directly off the MACSORB plate. Subculturing to a motility medium can increase the production of the flagella and allow repeat testing for the H7 antigen to show agglutination
A technologist subcultures a positive blood culture and notes the follow characteristics on the isolated colonies
* Growth of non-hemolytic colonies with ground-glass appearance, displaying a “medusa head”
* Gram stain reveals a large, gram-positive rod with central and subterminal spores that do not swell the cells
* Catalase positive
* Non-motile
What is the most likely conclusion and action
a) The organism is NOT Bacillus anthracis, continue identification per laboratory procedures
b) Cannot rule out Bacillus anthracis, refer isolate to your Laboratory Response Network (LRN) reference lab
c) The organism is likely Bacillus anthracis, continue identification per laboratory procedures
d) The organism is likely Bacillus anthracis, continue identification testing for confirmation
B - Cannot rule out Bacillus anthracis, refer isolate to your Laboratory Response Network (LRN) reference lab
Any isolate with the following features should be immediately referred to your LRN reference lab for definitive identification of the organism
* Gram stain shows large, gram positive rods with sub-terminal or central spores
* Gray colonies with ground-glass appearance
* Non-hemolytic on BAP
* Tenacious or “sticky” colonies like petroleum jelly
* Catalase positive
* Non-motile
Most commonly, an organism with these characteristics is B. anthracis; however B. cereus variant mycoides and B. megaterium may also fit this description
If septic arthritis is suspected, specimens from which of the following normally sterile sites should be collected to detect the microorganism causing the condition
a) Serous fluid
b) Synovial fluid
c) CSF
d) Blood
B - Synovial fluid
Synovial fluid is the fluid that gives lubrication to the joint and provides nourishment for articular cartilage. It would likely grow the microorganism causing the septic joint
A wound specimen was received into the laboratory and a large gram positive rod was isolated. The microbiologist suspected the isolate was a probable anthracis and had to rule in/out before reporting. All of the following tests must be performed before calling the species B. anthracis except
a) Catalase
b) Motility
c) Presence of hemolysis
d) Oxidase
D - Oxidase
Oxidase is most often performed on non-fermentative gram NEGATIVE rods
However, the bioterrorist agent Brucella can be tested with oxidase to help rule in this species. Brucella stains as tiny gram negative coccobacilli and is oxidase positive
A new tech has a presumptive Shigella species via biochemical identification on a stool culture. To confirm, serological testing is performed. The serological testing is negative and the quality control which was run simultaneously passed. What should the tech do next
a) Repeat biochemical testing or use an alternate method
b) Repeat serological testing
c) Heat a suspension of the organism and then repeat the serological testing
d) Report out the organism as E. coli
C - Heat a suspension of the organism and then repeat the serological testing
Serotyping of Shigella species is used to determine the serogroup (A, B, C, or D) and species of the organisms. This testing looks for the O (somatic) antigen that is located in the outer membrane of the cell wall. This antigen is heat-stable, so if the organism is heated, the O antigen will remain. Some species of Shigella contain the K (capsular) antigen located in the polysaccharide capsule of the organism. The K can “cover” the O since the capsule is external to the cell wall, and can be removed with heat while preserving the O antigen. After heating, repeat serological testing should provide a result for the Shigella serotype
What bacteria is responsible for the bubonic plague
a) Mycobacterium tuberculosis
b) Yersinia pestis
c) Vibrio cholerae
d) Corynebacterium diphtheriae
B - Yersinia pestis
Y. pestis causes bubonic plague and is transmitted from infected rats and other rodents to humans by the bite of rat fleas
A tech receives a request for VRE colonization testing on a patient in the hospital. Which of the following is an appropriate are of the body for culture for screening
a) Anterior nares
b) Rectal area
c) Groin
d) Urine
B - Rectal area
Stool specimens or rectal swabs are used to screen for colonization of patients with VRE. Enterococcus spp. are normal flora organisms in the gastrointestinal system and thus any VRE isolated would be carried in the gastrointestinal system. Screening helps to reduce the spread of the infection within the hospital
All of the following statements are associated with MALDI-TOF mass spectrophotometry used in clinical microbiology except
a) Bacteria is amplified using a laser
b) Molecules are measured based on a mass-to-charge ratio
c) A matrix absorbs energy from the laser and converts it into heat
d) A spectrum is created
A - Bacteria is amplified using a laser
The bacteria is not amplified
A CSF was collected from a lumbar puncture to evaluate for possible meningitis. Four tubes were collected and sent to the microbiology laboratory for analysis. Which of the four tubes is preferred for microbiology studies
a) Tube 1
b) Tube 2
c) Tube 3
d) Tube 4
B - Tube 2
This tube will be more concentrated and allow for the recovery of low numbers of bacterial organisms causing meningitis. In addition, this specimen will most often be free of bloods cells or bacteria introduced by the spinal tap procedure
A patient came into the emergency department with symptoms of meningitis. The patient was suspected of having a blocked cerebral shunt, which can cause meningitis. The shunt was drained and sent to the microbiology department for culture. All of the follow organisms are associated with shunt infections except
a) CONS
b) Klebsiella pneumoniae
c) E. coli
d) Neisseria meningitidis
D - Neisseria meningitidis
This organism is typically not seen in cerebral shunt infections even though it is a cause of meningitis. The following organisms are most often seen in shunt infections: CONS, S. aureus, Cutibacterium acnes (P. acnes), viridans group strep, P. aeruginosa, K. pneumoniae, E. coli, and Serratia marcescens
MRSA is a serious health concern in the hospital environment and also in the community for patients who have had no contact with the healthcare setting. In order to control the spread of MRSA and prevent infection with the organism, it is recommended to screen patients for MRSA prior to being admitted to a healthcare setting. Which of the follow antimicrobials is best to use when testing for methicillin resistance
a) Methicillin
b) Cefoxitin
c) Penicillin
d) Oxacillin
B - Cefoxitin
Cefoxitin is the recommended antimicrobial to use for the detection of methicillin resistance in S. aureus isolates. Since methicillin is no longer used in the United States, resistance has routinely be tested using oxacillin. However, it is now known that cefoxitin is a better inducer of resistance mediated by the mecA gene - the gene responsible for methicillin resistance in S. aureus
FOX POS and Oxacillin resistant means MRSA
What color would the agar be around a colony of Staphylococcus epidermidis growing on Mannitol Salt agar (MSA)
a) Yellow
b) Red
c) Brown
d) Clear
B - Red
Mannitol salt agar is commonly used for selective differentiation of staphylococci. It contains peptone base, mannitol, and a phenol red indicator. At a 7.5% salt concentration, it also inhibits most bacterial growth
No change in the color of the original agar (red) indicates that the mannitol was not fermented, which S. epidermidis would show
Irregular-size, gray white colonies, with irregular margins are recovered by a stool specimen in a case of antibiotic-associated colitis. The colonies are flat, gray white, and spreading with irregular margins. Some patients with this infection develop pseudomembranous colitis that can be life-threatening. Growth is enhanced when cycloserine-cefoxitin-fructose agar (CCFA) is used. Gram staining shows elongated, gram positive bacilli with distinctive subterminal and central spores that provide the presumptive identification. Additional key identifying reactions are the absence of lipase and lecithinase and a chartreuse pigment under fluorescent light. With these observations, select the presumptive identification of this isolate
a) Cutibacterium acnes (P. acnes)
b) Clostridioides difficile
c) Actinomyces israeli
d) Bacteroides fragilis
B - Clostridioides difficile
Although the flat, gray white spreading colonies with irregular outer margins growing on anaerobic blood agar may be non-specific, the enhanced growth on CCFA provides for presumptive identification of C. difficile. C. diff will produce a yellow color due to fructose fermentation. Presumptive identification is further supported by the observation of longer, slender, gram positive rods with subterminal spores
A physician suspected that a young, sexually active woman had bacterial vaginosis (BV). Which of the following specimen sources is the correct specimen of choice to support a bacterial vaginosis infection
a) Urethral
b) Endocervical
c) Vaginal
d) Cervical
C - Vaginal
BV causes vaginitis, or inflammation/infection of the vaginal mucosa. Commonly associated with Gardnerella vaginalis and is characterized by a foul smelling, gray discharge. The discharge is made up of sloughed epithelial cells that care covered with tiny, gram variable rods. These cells are referred to as Clue cells.
To provide a clinical diagnosis of BV, three or more of the following must be present
1. Gray discharge
2. Clue cells should be seen wet mount
3. pH >4.5
4. Fishy odor after the addition of 10% KOH to the discharge on a slide
All of the following are Lancefield carbohydrate antigens found on Beta hemolytic Streptococcus species. Which of them is not found on Streptococcus anginosus group
a) A
b) B
c) F
d) G
B - B
Group B Lancefield antigen is found on S. agalactiae (Group B strep)
MALDI-TOF is used for the identification of aerobic bacterial isolated on a urine culture bench. Upon placing the target into the MALDI-TOF instrument, no peaks were found on any target spots, including the quality control. What caused this issue
a) Quality control organism was not added to the target wells
b) Matrix solution was not added to the target wells
c) The target was not cleaned properly
d) Quality control organism has deteriorated
B - Matrix solution was not added to the target wells
Matrix solution is required to properly identify the organisms, by extracting proteins from the organisms on the target. Once the proteins are extracted with matrix, they each generate a distinct signal (peak) and then spectrum. This spectrum is compared to known spectra in a database to identify these organisms
Since there were no peaks found on the target, this points to the fact that no proteins were extracted to make those peaks. Also, since all the target spots did not work, including the quality control, this points to a procedural error that occurred with all the target wells
All of the following are characteristics of Burkholderia pseudomallei except
a) Has been reported as the cause of laboratory-acquired infection
b) Oxidase positive
c) Non-motile
d) Catalase positive
C - Non-motile
B. pseudomallei is motile, a characteristic that differentiates it from the non-motile B. mallei
A tech receives a call from the floor regarding antimicrobial therapy. The patient culture yielded an aerobic gram negative rod and the physician would like to use an antibiotic that inhibits DNA synthesis. Which of the following antibiotics would be the best choice
a) Ciprofloxacin
b) Cefazolin
c) Tetracycline
d) Gentamycin
A - Ciprofloxacin
Cipro is part of the fluoroquinolones
These are effective against aerobic gram positive and gram negative species
The target for the antibiotic is inhibition of DNA replication in the cell, with a primary target of topoisomerase II
_______ is predominantly associated with skin and soft tissue infections, such as abscesses, cellulitis, folliculitis, and impetigo
a) Healthcare-associated MRSA
b) Community-acquired MRSA
c) E. coli
d) Neisseria meningitidis
B - Community-acquired MRSA
Community-acquired MRSA infections are predominantly skin and soft tissue infections. Outbreaks can occur that are typically seen in communities such as prisons, daycare centers, and military recruits. The incidence of infection in pediatric patients is increasing due to these outbreaks. The strain responsible for the infections is called USA300 MRSA and is now being associated with significant bacteremia as well
A patient presents to the emergency room with hemorrhagic diarrhea. A stool specimen was sent to the microbiology department for culture. The specimen was plated on BAP, MAC, and MACSORB. Gram negative, oxidase negative rods grew as lactose fermenters on MAC and clear on MACSORB. Biochemical testing revealed the organism was lysine decarboxylase positive and did not produce H2S. Which organism is suspected
a) Citrobacter freundii
b) E. coli O157:H7
c) Shigella sonnei
d) Klebsiella pneumoniae
B - E. coli O157:H7
Clear colonies on MACSORB presumptively identify E. coli serogroup O157:H7. All strains of E. coli, being lactose fermenters, will produce red colonies on conventional MAC. However, unlike most E. coli strains, E. coli O157:H7 does not produce acid from sorbitol. Therefore, colonies of E. coli O157:H7 are non-pigmented when grown on modified MAC in which sorbitol has been substituted for lactose
