An oxidase-positive, gram-negative rod which produces a bluish-green pigment has been grown in culture from a swab obtained from an infected burn wound. This organism is susceptible to gentamicin, ticarcillin and tobramicin, but resistant to all the other antibiotics. Which of the following organisms is it likely to be?

**Core Concept:** Oxidase-positive gram-negative rods are a diverse group of bacteria that contain cytochrome oxidase enzymes. They can be found in various clinical samples and are known for producing pigments like bluish-green pigment. Susceptibility patterns for antibiotics depend on the specific organism and its antibiotic resistance mechanisms.

**Why the Correct Answer is Right:** The correct answer, **Option C: Pseudomonas aeruginosa**, is a well-known oxidase-positive, gram-negative rod that produces a bluish-green pigment called pyocyanin. It is susceptible to gentamicin, ticarcillin, and tobramycin due to their ability to penetrate bacterial cell walls and target specific enzymes or receptors.

**Why Each Wrong Option is Incorrect:**

**A. Salmonella spp.** are gram-negative rods but are typically non-oxidase positive and cause different infections like enteric fever. They are not susceptible to the mentioned antibiotics.

**B. Escherichia coli (E. coli)** is also a non-oxidase-positive gram-negative rod causing various infections. It is susceptible to different antibiotics but not the mentioned ones.

**D. Staphylococcus aureus (S. aureus)** is a gram-positive coccus causing different infections but is not an oxidase-positive bacterium and not susceptible to the mentioned antibiotics.

**Clinical Pearl:** Susceptibility testing of bacterial isolates is essential to guide appropriate antibiotic therapy. Infections caused by P. aeruginosa can be treated effectively with the mentioned antibiotics.

**Correct Answer:** **Option C: Pseudomonas aeruginosa**

**Explanation:** Pseudomonas aeruginosa is a pathogenic bacterium that can cause infections in burn wounds. Its susceptibility to gentamicin, ticarcillin, and tobramycin is due to their ability to penetrate the bacterial cell wall and target specific enzymes or receptors. These antibiotics can be effective in treating P. aeruginosa infections, especially in burn wounds where the bacteria thrives in the warm, moist, and anaerobic environment.

✓ Correct Answer: D. Pseudomonas aeruginosa