Prevalence of gram-negative rods in the normal pharyngeal flora

Ann Intern Med. 1975 Sep;83(3):355-7. doi: 10.7326/0003-4819-83-3-355.


We obtained throat cultures from 100 randomly selected people free from any chronic upper or lower respiratory disease who did not work in a hospital and who had not experienced any acute illness or received any antibacterial therapy in the 4 weeks preceding culture. Eighteen percent harbored either a species of Enterobacteriaceae or Pseudomonas aeruginosa in their pharynx. In all cases, colony counts were low, the majority being detected in broth media selective for Gram-negative rods. There were no clear-cut age or sex distributions of Gram-negative pharyngeal carriage. These data imply that, in at least some cases, isolation of Gram-negative rods from sputum of untreated patients may be a normal finding, and that in some patients with pulmonary infection, the pretreatment, upper respiratory tract flora may serve as the source of subsequent superinfection with Gram-negative rods.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acinetobacter / isolation & purification
  • Adolescent
  • Adult
  • Aged
  • Bacteria / isolation & purification*
  • Child
  • Child, Preschool
  • Enterobacteriaceae / isolation & purification*
  • Escherichia coli / isolation & purification
  • Female
  • Humans
  • Klebsiella pneumoniae / isolation & purification
  • Male
  • Middle Aged
  • Moraxella / isolation & purification
  • Pharynx / microbiology*
  • Proteus mirabilis / isolation & purification
  • Pseudomonas aeruginosa / isolation & purification
  • Sputum / microbiology