Question 1

A 68-year-old man with a history of diabetes and hypertension develops fever, chills, and confusion after three weeks in the ICU with an indwelling urinary catheter and central venous line. His WBC count is elevated with a left shift, and urinalysis shows cloudy urine with trace leukocyte esterase and nitrites. What is the most likely general type of infectious disease he is experiencing?

Accepted Answer

Urinary tract infection with possible septicemia

Question 2

Which of the following predisposing factors most significantly increased this patient's risk for developing a nosocomial infection?

Accepted Answer

Indwelling urinary catheter and central venous line

Question 3

The Gram stain image provided shows many pink, rod-shaped bacteria. What is the correct interpretation of this Gram stain?

Accepted Answer

Gram-negative bacilli, single rods

Question 4

Why is the oxidase test result important in narrowing down the identity of a Gram-negative rod isolated from a clinical specimen?

Accepted Answer

A negative oxidase test excludes Pseudomonas and supports Enterobacteriaceae.

Question 5

A MacConkey agar plate inoculated with the unknown organism shows growth but no color change. What does this result indicate?

Accepted Answer

The organism is Gram-negative and does not ferment lactose.

Question 6

Why was Cetrimide agar not used in the identification of the unknown organism in this case?

Accepted Answer

The organism tested negative for oxidase, making Pseudomonas unlikely.

Question 7

Which of the following best explains the significance of a left shift in the WBC count in this patient?

Accepted Answer

It suggests an increased number of immature neutrophils, consistent with acute bacterial infection.

Question 8

Given the EnteroPluri-Test results (glucose +, gas +, lysine +, ornithine +, VP +, citrate +, all others -), which organism is most likely identified?

Accepted Answer

Serratia marcescens

Question 9

Which of the following best describes the role of MacConkey agar in the identification of Gram-negative bacteria?

Accepted Answer

It is selective for Gram-negative bacteria and differentiates lactose fermenters from non-fermenters.

Question 10

A patient with a central venous catheter develops erythema and tenderness at the catheter site, fever, and hypotension. Which of the following best explains the pathogenesis of his condition?

Accepted Answer

Direct inoculation of skin flora into the bloodstream via the catheter, leading to bacteremia and sepsis.

Question 11

Which of the following laboratory findings is most consistent with a diagnosis of sepsis in this patient?

Accepted Answer

WBC count: 16,500/µL with left shift, hypotension, and fever

Question 12

Which of the following best describes the clinical significance of a positive nitrite test in urinalysis?

Accepted Answer

It suggests the presence of Gram-negative bacteria capable of reducing nitrate to nitrite.

Question 13

Which of the following is the most likely final diagnosis for this patient, based on the clinical and laboratory findings?

Accepted Answer

Sepsis and urinary tract infection caused by Serratia marcescens

Question 14

Which of the following best explains why Serratia marcescens is a significant pathogen in hospital-acquired infections?

Accepted Answer

It is an opportunistic Gram-negative rod that can colonize medical devices and is often resistant to multiple antibiotics.

Question 15

Which of the following equations correctly represents the calculation of the white blood cell (WBC) count from a hemocytometer, if $$N is $$the number of cells counted, $$V is $$the volume of fluid counted in mL, and $$D is $$the dilution factor?

Accepted Answer

$$WBC = \frac{N}{V} 	imes D$$

Question 16

A patient’s urinalysis shows trace leukocyte esterase and nitrites. Which of the following best explains the underlying microbiological process?

Accepted Answer

Gram-negative bacteria reduce urinary nitrate to nitrite, and leukocyte esterase indicates white blood cell activity.

Question 17

Which of the following best describes the clinical importance of using selective and differential media in the identification of pathogens from clinical specimens?

Accepted Answer

Selective media favor the growth of certain bacteria, while differential media distinguish between bacteria based on metabolic properties.

Question 18

Which of the following best explains why the EnteroPluri-Test is useful in the identification of Enterobacteriaceae?

Accepted Answer

It allows for simultaneous testing of multiple biochemical reactions, generating a code for species identification.

Question 19

A patient with sepsis has a blood pressure of 90/58 mmHg, heart rate of 118 bpm, and respiratory rate of 26 per minute. Which of the following equations best represents the calculation of mean arterial pressure (MAP)?

Accepted Answer

$$MAP = \frac{2 	imes Diastolic + Systolic}{3}$$

Case Study Lab Report: Identifying an Infectious Disease and Pathogen in a Hospitalized Patient

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