A sputum sample was brought to the laboratory for analysis. Gram stain revealed the following: rare epithelial cells, 8 to 10 polymorphonuclear leukocytes per high-power field, and pleomorphic Gram-negative rods. As the laboratory consultant, which of the following interpretations should you make?
**Core Concept**
The presence of pleomorphic Gram-negative rods in a sputum sample, along with a moderate number of polymorphonuclear leukocytes (PMNs), suggests a bacterial infection. The Gram stain findings are indicative of a respiratory tract infection, possibly caused by a gram-negative bacterium such as *Klebsiella pneumoniae* or *Pseudomonas aeruginosa*.
**Why the Correct Answer is Right**
The presence of pleomorphic Gram-negative rods in a sputum sample, along with a moderate number of PMNs, is consistent with a bacterial infection of the respiratory tract. The polymorphonuclear leukocytes are indicative of an inflammatory response to the infection. The pleomorphic rods may be seen in various gram-negative bacteria, including *Klebsiella pneumoniae*, which is known to cause respiratory tract infections, particularly in hospitalized patients or those with underlying lung disease.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is too broad, as many types of infections can cause a similar Gram stain pattern. It does not provide a specific diagnosis or interpretation of the laboratory findings.
**Option B:** This option is incorrect because it does not take into account the type of bacteria or the clinical context. The presence of pleomorphic Gram-negative rods and a moderate number of PMNs suggests a specific type of bacterial infection, rather than a viral or fungal infection.
**Option C:** This option is incorrect because it does not provide a clear interpretation of the laboratory findings. While the presence of epithelial cells and PMNs is consistent with a respiratory tract infection, it does not provide a specific diagnosis or type of bacteria.
**Clinical Pearl / High-Yield Fact**
In the context of a respiratory tract infection, the presence of pleomorphic Gram-negative rods and a moderate number of PMNs is highly suggestive of *Klebsiella pneumoniae* or *Pseudomonas aeruginosa*. These bacteria are common causes of respiratory tract infections in hospitalized patients or those with underlying lung disease.
**Correct Answer: C. Infection with a gram-negative rod such as Klebsiella pneumoniae.**