Question 1

A 21-year-old male college student who had complained of headache and feeling feverish the night before is brought this morning to the emergency department (ED) when his roommate was unable to rouse him. He had been well until yesterday. Vital signs include fever (39.8°C/103.1°F), tachycardia, and hypotension (BP 70/55). Remarkable on physical examination is petechial rash (purpuric in areas) and nuchal rigidity with positive Kernig and Brudzinski signs. CSF is cloudy with high protein and low glucose. Intracellular, red diplococci are seen on Gram stain. What is the most likely genus?

A) Staphylococcus
B) Streptococcus
C) Chlamydia
D) Mycobacterium
E) Neisseria

Neisseria

Accepted Answer

Gram-negative bacteria should be described as red or pink, so the description fits a Gram-negative diplococcus which is most likely Neisseria. Staph and Strep would be purple, and neither Chlamydophila nor Mycobacterium will show up on Gram stain.

Question 2

A 24-year-old female presents with dysuria, as well as urinary urgency and frequency. A urine dipstick test is positive for both leukocyte esterase and nitrites. What genus or family is noted for the production of nitrites?

A) Escherichia
B) Staphylococcus
C) Streptococcus
D) Vibrio

Escherichia

Accepted Answer

Since all choices are in italics, all are genus names and you do not need to look for a family name. Since all Enterobacteriaceae generally produce nitrate reductase, they all eventually produce a positive dipstick nitrite test. Escherichia is the only choice belonging to this family. Other members of Enterobacteriaceae that cause urinary tract infections include Proteus and Klebsiella. Staph and Strep are Gram-positive and Vibrio is a genus of Gram-negative, comma-shaped bacteria. A positive nitrite test rules out Staph. saprophyticus as the cause of a urinary tract infection.

Question 3

What rapid test commonly used on Gramnegative rods rules out Enterobacteriaceae if positive?&#10;A) Catalase&#10;B) Coagulase&#10;C) Oxidase&#10;D) Chitinase&#10;E) Urease

Accepted Answer

Most common Gram-negative rods are oxidase-positive. The major exceptions are members of the Enterobacteriaceae. A catalase test (utilizing hydrogen peroxide) is most commonly used to distinguish Staphylococci (+) from Streptococci (-). (Most aerobes will be catalase-positive and many obligate anaerobes are catalase-negative.) Coagulase is used to distinguish Staph. aureus (+) from other medical isolates (coagulase-negative Staph). No medically important bacteria have chitinase. There are several medically important urease-positive bacteria, most importantly Helicobacter pylori, Proteus sp., and Ureaplasma urealyticum.

Question 4

A patient presents with rapid onset severe respiratory symptoms. Chest radiographs show a hemorrhagic lymphadenitis. The isolation of chains of fairly large, aerobic Gram-positive rods, some of which have started to sporulate from a patient with this resentation, should raise a major concern of which organism? (You should be able to answer this question from the genus alone, although a question might also mention that it was nonmotile.)

A) Actinomyces israelii
B) Bacillus anthracis
C) Campylobacter jejuni
D) Clostridium perfringens
E) Haemophilus influenzae

Accepted Answer

Bacillus is the correct genus. There are two Gram-positive spore-forming rods. Bacillus is aerobic with one species (Bacillus anthracis), causing hemorrhagic lymphadenitis and pulmonary edema. The other genus with bacterial endospores, the Clostridia, do not grow aerobically. The other Gram-positive organism listed, Actinomyces, often described as a branching bacterium, is also anaerobic. Campylobacter and Haemophilus are both Gram-negative.

Question 5

A patient undergoing chemotherapy develops a cough. Acid-fast stain of his sputum shows rods and slightly longer forms, with some branching; they vary in their acidfast reaction from one area of the slide to the next. The acid-fast stain was performed by n experienced medical technologist and, when redone, showed the same variation. The growth was done aerobically. What is the most likely agent?

A) Actinomyces
B) Chlamydophila
C) Mycobacterium avian-intracellulare (MAI or MAC)
D) Nocardia

Accepted Answer

Either Nocardia or MAI is possible from the clinical scenario, but the most likely agent from the acid-fast stain description, the focus of the question, is Nocardia. Also, MAI would not grow in 2 days (so some mention of time would be made) and Actinomyces would only grow anaerobically, which would also be stated. Chlamydophila would not grow except in tissue culture.

Question 6

A female patient with a new genital lesion presents to your sexually transmitted disease clinic. She is homeless, has no health insurance, and is an intravenous drug user. You suspect syphilis. Which of these techniques would be most appropriate to emonstrate treponemes?

A) Immunological test such as the VDRL
B) Dark-field microscopy
C) Acid-fast stain
D) Gram stain
E) Electrophoresis

Accepted Answer

First, notice that the question specifically asks about demonstrating the presence of treponemes and not making the diagnosis of syphilis. (Also, note that the lesions are still present, which suggests that it is too early for serological methods to be reliable.) Then, remember that Treponema pallidum is still only cultured by research labs. Because treponemes are so thin in cross-section, they do not reliably show up on a Gram stain; thus, dark-field or FA (not mentioned as a choice) staining would be necessary.

Question 7

The CSF from a 2-week-old infant with meningitis shows rods with tumbling motility. These bacteria are found to be Gram-positive and do not form spores. What is the most likely agent?&#10;A) Actinomyces&#10;B) Bacillus&#10;C) Clostridium&#10;D) Corynebacterium&#10;E) Listeria

Accepted Answer

Listeria is the correct answer. Both Bacillus and Clostridium can be eliminated because they are spore-formers. Actinomyces and corynebacteria are both Gram-positive and nonmotile and are not common causative agents of neonatal meningitis. Listeria has a tumbling motility when grown in broth, in this case CSF.

Question 8

Both a 53-year-old farmer and his 21-yearold son present in August with fever, myalgia, and malaise, which they came down with within a few hours of each other. The son had been home in southern Minnesota for only 3 weeks to help field train two new hunting dogs. You ask about potential tick bites, and the son did have one on him, which was quite engorged. Platelets and granulocytes are low in each man's blood. You ask one of your experienced techs to do a Giemsa stain on a thick blood smear. He calls, reporting clusters of cells resembling raspberries in granulocytes, even though nothing grows in any of the blood cultures. You realize that the blood cultures you set up will not grow and that you have two patients who have infections with a tick-borne obligate intracellular parasite of granulocytes. What genus does the organism belong to?

A) Anaplasma (formerly Ehrlichia)
B) Borrelia
C) Chlamydia
D) Haemophilus
E) Mycoplasma

Accepted Answer

Obligate intracellular bacteria transmitted through arthropods would most likely be the genera: Rickettsia, Orientia, Anaplasma, and Ehrlichia, with the latter two infecting white cells and Anaplasma causing the described disease (Human granulocytic anaplasmosis).

Question 9

A full-term 6-day-old neonate is brought in with a purulent conjunctivitis which the parents noticed earlier today. On Gram stain of the purulent exudate, no bacteria are seen. Which of the following bacteria is most likely the cause of the conjunctivitis?

A) Chlamydia trachomatis
B) Escherichia coli
C) Listeria monocytogenes
D) Neisseria gonorrhoeae
E) Streptococcus pneumoniae

Accepted Answer

Neonatal eye infections are most likely to be Chlamydia trachomatis, which does not show up on Gram stain. All of the remaining organisms stain well with Gram stain.

Question 10

An 83-year-old who still lives in her own home has developed pneumonia following influenza. The Gram stain of her sputa is shown. What is the most likely agent?  &#10;A) Chlamydophila pneumoniae&#10;B) Influenza virus&#10;C) Klebsiella pneumoniae&#10;D) Mycoplasma pneumoniae&#10;E) Staphylococcus aureus&#10;F) Streptococcus pneumoniae

Accepted Answer

The most common cause of pneumonia in people over 65 years of age has generally been S. pneumoniae. Although the other agents also cause pneumonia, S. pneumoniae is the only organism that fits the descriptions of Gram-positive cocci in chains. It is also quite common following influenza. If the woman had not been vaccinated for influenza, then she also may not have been vaccinated for pneumococcus.

Question 11

The reagent used to distinguish staphylococci from streptococci is&#10;A) Hydrogen peroxide&#10;B) Fibronectin&#10;C) Fibrinogen&#10;D) Oxidase

Accepted Answer

The answer of The reagent used to distinguish staphylococci from...

Question 12

A 14-month-old boy is brought in by his parents with fever, fussiness and lethargy, and apparent headache. On examination, the neck is stiff. His parents have not allowed his routine childhood vaccines. Very short Gramnegative rods are seen in the CSF, so antibiotics are immediately started. The organism grows on chocolate agar but not blood agar. No one else in the family is ill. What is the most likely causative agent?

A) Escherichia coli
B) Haemophilus influenzae type b
C) Klebsiella pneumoniae
D) Neisseria meningitidis
E) Streptococcus pneumoniae

Accepted Answer

The answer of A 14-month-old boy is brought in by...

Question 13

A healthy 7-year-old boy who has not traveled outside the United States is brought in by his parents in June with signs of meningitis. No bacteria are seen in the Gram stain of the CSF, and no bacterial capsule material is present as determined by a series of latex particle agglutination tests standard to the diagnosis of meningitis. The CSF glucose level is slightly low, protein is near normal, and white cell count is less than 500 cells/microL, mainly lymphocytes. What is the most likely causative agent?

A) Chlamydophila pneumoniae
B) Enterovirus
C) Mycoplasma pneumoniae
D) Mycobacterium tuberculosis
E) Treponema pallidum

Accepted Answer

The answer of A healthy 7-year-old boy who has not...

Question 14

In any case, a clue indicating that the causative organism is an obligate intracellular pathogen transmitted by an arthropod bite should lead you to which of the following groups of organisms?&#10;A) Chlamydiae&#10;B) Enterobacteriaceae&#10;C) Rickettsias including Anaplasma and Ehrlichia&#10;D) Spirochetes including Borrelia burgdorferi

Accepted Answer

The answer of In any case, a clue indicating that...

Question 15

What is the main difference between fluorochrome staining (e.g., auraminerhodamine screening for Mycobacterium tuberculosis) and indirect fluorescent antibody (IFA) staining?&#10;A) Fluorochromes are more specific and used just for Mycobacterium tuberculosis.&#10;B) IFAs are less specific since they use antibody to a different species' antibody (i.e., rabbit antibody to human antibody).&#10;C) Fluorochrome staining is less sensitive than comparable staining with light microscopy.&#10;D) IFA's specificity is dependent on the primary antibody used; fluorochromes lack the antibody specificity.

Accepted Answer

The answer of What is the main difference between fluorochrome...

Deck 3: Important Bacterial Genera