The normal flora of the pharynx includes a large number of species that should be neither fully identified nor reported when observed in throat cultures:
• viridans (alpha-haemolytic) streptococci and pneumococci
• nonpathogenic Neisseria spp
• Branhamella (formerly Neisseria) catarrhalis (this can also be a respiratory pathogen)
• staphylococci (S. aureus, S. epidermidis)
• Haemophilus spp
• yeasts (Candida spp) in limited quantity
• various strictly anaerobic Gram-positive cocci and Gram-negative rods, spirochaetes and filamentous forms.
The throats of elderly, immunodeficient, or malnourished patients, particularly when they have received antibiotics, may be colonized by Enterobacteriaceae (Escherichia coli, Klebsiella spp, etc.) and by the nonfermentative Gram-negative groups (Acinetobacter spp and Pseudomonas spp). Such patients may also have in their pharynx a proliferation of S. aureus or of Candida spp, or other yeast-like fungi. Although these microorganisms do not cause pharyngitis, except in association with granulocytopenia, it is advisable to report such isolates to the clinician, as they occasionally indicate the existence of (or may sometimes give rise to) a lower respiratory tract infection (e.g., pneumonia) or bacteraemia. However, an antibiogram should not be performed routinely on these colonizing microorganisms.