Isolation of capsulate anaerobic bacteria from orofacial abscesses

This study investigated the prevalence of capsulate (encapsulated) anaerobic bacteria in orofacial infections of children. Pus specimens from 182 children with chronic orofacial infections such as otitis media, sinusitis, and abscesses were cultured and compared with pharyngeal swabs from 26 healthy control children. Of 216 Bacteroides species and anaerobic cocci isolated from infected sites, 170 (79%) were capsulate, compared to only 34 (35%) of 96 isolates from normal pharyngeal flora. The difference was most striking for the B. melaninogenicus group, where 84% of isolates from infections were capsulate versus 23% from controls. The findings suggest that capsule production is associated with pathogenicity, as capsulate strains are significantly enriched in disease. Previous animal studies showed that non-capsulate organisms fail to form abscesses alone, but non-capsulate strains can acquire capsules during mixed infections and subsequently become pathogenic. These results support the hypothesis that capsular polysaccharides enhance virulence by inhibiting phagocytosis, and suggest that early antimicrobial therapy targeting these capsulate organisms may prevent chronic infection development.

Key findings

• Capsulate anaerobic bacteria were isolated significantly more frequently from orofacial abscesses (79%) than from normal pharyngeal flora (35%)
• B. melaninogenicus group showed the largest difference, with 84% of clinical isolates being capsulate compared to 23% from controls
• Capsule production appears to be a virulence factor, as capsular polysaccharides inhibit phagocytosis by leukocytes
• Animal studies demonstrated that non-capsulate organisms can acquire capsules during mixed infections over 10-14 days and become pathogenic
• Early antimicrobial therapy may prevent infection chronicity by targeting organisms before capsulate strains emerge