Non-Acid-Fast Gram-Positive Rods in Throat Culture: Clinical Significance

Isolation of non-acid-fast, Gram-positive, catalase-positive rods from a throat swab does not necessarily indicate disease.

Common Commensals (Normal Flora)

• Corynebacterium spp. (diphtheroids) – ubiquitous, usually contaminants
• Lactobacillus spp. – part of oral/pharyngeal microbiome
• Propionibacterium (Cutibacterium) spp. – skin/oral commensals
• Actinomyces spp. – oral anaerobes; can cause actinomycosis if mucosal breach
• Rothia spp., Micrococcus spp.

Potential Pathogens (Same Morphology)

• Staphylococcus aureus (catalase +, coagulase +)
• Streptococcus pyogenes (Group A Strep – catalase –, but can appear similar on Gram stain)
• Bacillus spp. (spore-forming; usually contaminants)
• Listeria spp. (rare pharyngeal colonization)

Clinical Decision-Making

• Asymptomatic carrier → no treatment.
• Symptomatic (pharyngitis, fever, exudate) → correlate with rapid strep/PCR for GAS; consider Arcanobacterium haemolyticum, Neisseria gonorrhoeae.
• Immunocompromised host → lower threshold for significance.
• Pure heavy growth of single organism → more suggestive.

Always interpret culture in clinical context. Colonization ≠ infection.