Question

Unfortunately, within a few hours of her ruptured appendix diagnosis, Tara started to experience tachypnea, tachycardia, altered mental status, and hypotension. Her earlier blood-test results showed elevated white blood cells and other inflammatory markers, as well as an electrolyte imbalance. She also had mild pyuria, or pus in the urine.

Tara's new signs all suggested she had developed sepsis, but the blood cultures wouldn't be back for a few more days and, in most cases of sepsis, those tests are negative or inconclusive anyway. So she was given more IV fluids with electrolytes, and her broad-spectrum antibiotics were increased.

Despite increased fluids, Tara's blood pressure remained low. This drastically impacted her lung function and her circulation, so oxygen was not being effectively delivered to her body. As this progressed, her lips turned blue, a condition called cyanosis. Now more confused and unable to catch her breath, Tara had progressed into septic shock!

She was placed on life support, including hemodialysis and mechanical ventilation, and moved to the intensive care unit. Despite every possible intervention, Tara experienced multiple organ failure due to the sepsis, and, sadly, she passed away the next morning.

Tara's parents were devastated and could not help wondering what would have happened if they had brought their daughter to the hospital sooner.

The microbiology lab was able to isolate one of the organisms from Tara’s blood. Using a Kirby-Bauer test (disk diffusion assay), they assessed the organism for antibiotic resistance. The first column of numbers shows the size of the zone of inhibition (ZOI) in millimeters (mm). The remaining columns show the values needed to define the organism as “resistant,” “intermediate,” or “susceptible” to that antibiotic. Based on these data, which antibiotic(s) would not be an appropriate choice for treatment? Select all that apply. (NCLEX-HESI-TEAS style)

HINT: “Resistant” indicates that the organism is not sufficiently affected by the antibiotic.

Kirby-Bauer Assay
	Measured
	ZOI (mm)	R	I	S
Amoxicillin	25	≤28	-	≥29
Ciprofloxacin	25	≤15	16-20	≥21
Erythromycin	23	≤13	14-22	≥23
Gentamicin	16	≤12	13-14	≥15
Rifampin	26	≤16	17-19	≥20
Tetracycline	18	≤14	15-18	≥19

Rifampin

Tetracycline

Erythromycin

Ciprofloxacin

Amoxicillin

Gentamicin

PREVIOUS ANSWERS THAT WERE WRONG:

1,3,4,5

1,2,3,4,5

1,4,5

3,4,5

Answer 1

#. Zone of inhibition

The area around the disc where there is a lack of bacterial growth.

#. The two things that determine the size of the zone of inhibition

1) Sensitivity of the organisms to the antibiotic

2) Rate of diffusion of the antibiotic

#. The larger the zone of inhibition, the susceptible the bacterium is to the antibiotic.

In this case the antibiotics which would not be appropriate for treatment are :-

Tetracycline

Gentamicin

Because their zone of inhibition is less and also the susceptibility is also low .