Human oral defenses against gram-negative rods

Area of Science:

• Microbiology
• Oral Biology
• Immunology

Background:

• Gram-negative rods are rarely found in the pharynx of healthy individuals, suggesting robust oral defense mechanisms.
• Understanding these protective mechanisms is crucial for comprehending oral health and infection prevention.

Purpose of the Study:

• To investigate the elimination dynamics of gram-negative rods from the oral cavity following a gargle challenge.
• To elucidate the roles of physical clearance and local bactericidal activity in oral defense against these bacteria.

Main Methods:

• Normal volunteers gargled with suspensions of Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis.
• Serial quantitative pharyngeal cultures were performed over 3 hours to assess bacterial elimination.
• Radiolabeled E. coli (technetium-99m) was used to quantify physical clearance from the oral cavity.
• In vitro adherence of piliated and nonpiliated E. coli to buccal epithelial cells was evaluated.

Main Results:

• Bacterial counts decreased rapidly, with less than 1% of the initial inoculum remaining after 3 hours.
• Buccal mucosa showed the fastest bacterial clearance, while the tongue exhibited the slowest.
• Physical clearance was rapid, with external counts decreasing significantly over 180 minutes.
• While piliated E. coli showed better in vitro adherence, no difference in in vivo clearance was observed between piliated and nonpiliated strains.

Conclusions:

• The oral cavity possesses highly effective defense mechanisms against gram-negative rods.
• Both physical clearance and local bactericidal activity contribute significantly to the elimination of these bacteria.
• These findings underscore the importance of intact oral defenses in preventing pharyngeal colonization by gram-negative pathogens.