Identifying Bacteria

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NCLEX-PN › Identifying Bacteria

Questions 1 - 10
1

Which agar would be the best choice option to identify_Escherichia coli_?

EMB (eosin methylene blue), because it is selective and differential

Nutrient agar

Selenium enriched media

Phenethyl alcohol

Explanation

The question requires the knowledge that Escherichia coli is a facultative, Gram negative, lactose fermenting bacteria. EMB (eosin methylene blue), or Mac (MacConkey) media is superior for isolating Escherichia coli because it is both selective and differential. Nutrient agar is neither selective nor differential. Selenium enriched media would not help identify this bacteria because Escherichia coli does not require this supplemented media to grow. Phenethyl alcohol can be used to select for anaerobic bacteria, which is of no utility in this situation.

2

What is the most common infection preceding the development of Guillain-Barré syndrome?

Campylobacter jejuni

Salmonella

E. coli

S_taphylococcus aureus_

Explanation

30% of cases of Guillain-Barré are preceded by infection by C_ampylobacter jejuni._ There is no known association between S_taphylococcus aureus, Salmonella,_ or E.coli and Guillain-Barré syndrome.

3

All of the following are frequently implicated in epiglottitis except __________.

Campylobacter jejuni

H. influenzae type B

Staphylococcus aureus

Streptococcus spp

Explanation

The most commonly implicated bacteria in epiglottiits are H. influenzae type B, Streptococcus spp, and Staphylococcus aureus. _Campylobacter jejuni is a common cause of food poisoning.

4

Which of the following sexually transmitted infections is mismatched with its causative agent?

Genital warts - herpes simplex virus 2

Gonorrhea - Neisseria gonorrhea

Syphillis - Treponema pallidum

Toxic shock syndrome - Staphylococcus aureus

Explanation

Genital warts is caused by human papillomavirus. All other sexually transmitted infection is correctly matched with its causative agent.

5

E. coli (Esherichia coli) are primarily found in the colon of humans, but can also cause cystitis. Which of the following best explains why this occurs?

E coli are facultative anaerobes

E. coli are microaerophiles

E. coli are obligate aerobes

E. coli are obligate anaerobes

Explanation

The colon is anaerobic and the bladder is aerobic. This fact explains why E. coli normally lives in an anaerobic environment, but can also survive aerobically. Facultative anaerobes normally live in anaerobic conditions but can adapt to aerobic conditions. Microaerophiles describes bacteria that are obligate aerobes, but are poisoned by high levels of oxygen and thus require specific oxygen levels to grow.

6

What organism causes Rocky Mountain spotted fever?

Rickettsia rickettsii

Borrelia burgdorferi

Rickettsia helvetica

Ehrlichia chaffeensis

Explanation

Rickettsia rickettsii causes Rocky Mountain Spotted Fever, and is spread by dermacentor ticks. It causes fever, headache, muscle pain, and a rash. Borrelia burgdorferi is associated with Lyme disease, e_hrlichia chaffeensis_ is associated with human monocytotropic ehrlichiosis, andr_ickettsia helvetica_ is associated (very rarely) with meningitis.

7

What is the primary effect of botulism toxin?

Flaccid paralysis

Nausea and vomiting

Tonic paralysis

Ascending paralysis

Explanation

Botulism toxin inhibits acetylcholine release from the presynaptic nerve terminal, causing flaccid paralysis. Death in botulism exposure is generally due to respiratry failure. Tonic paralysis is the cause of respiratory arrest in other toxicity exposures, such as exposure to tetanus toxin.

8

Which of the following organisms causes fever, headache, fatigue, myalgia, and buboes?

Yersinia pestis

Staphylococcus aureus

Bacillus anthracis

Borrelia burgdorferi

Explanation

The question stem describes bubonic plague which is caused by Yersinia pestis. Staphylococcus aureus causes skin infections, toxic shock, and food poisoning. _Bacillus anthraci_s causes anthrax, which is similar to plague, but does not cause buboes. Borrelia burgdorferi causes lyme disease., which presents as rash and arthralgia.

9

90% of all P roteus infections in human are caused by what organism?

Proteus mirabilis

Proteus vulgaris

Proteus penneri

Proteus myxofaciens

Explanation

While Proteus penneri and Proteus vulgaris do cause opportunistic infections in a small percentage of people, 90% of Proteus infections in humans are caused by Proteus mirabilis.

_Proteus myxofaciens is only found in insect hosts and does not infect humans.

10

Proteus mirabilis is classified as which of the following?

Gram-negative, anaerobic, rod-shaped

Gram-positive, anaerobic, rod-shaped

Gram-positive, aerobic, coccus

Gram-negative, anaerobic, coccus

Explanation

Proteus mirabilis is a Gram-negative, facultatively anaerobic, rod-shaped (bacillus) bacteria. It produces large amounts of the enzyme urease, which is able to hydrolyze urea to ammonia, causing the distinctively high pH seen in the urine of individuals with a P. mirabilis infection.

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