The role of encapsulated anaerobic bacteria in synergistic infections

Abstract

The effect of encapsulation on the virulence, survival, and protection of anaerobic bacteria from phagocytosis is reviewed. Support for the importance of encapsulated Gram-negative anaerobic rods (Bacteroides sp., Prevotella sp. and Porphyromonas sp.), anaerobic and facultative Gram-positive cocci (AFGPC) was provided by their higher recovery rate in oropharyngeal infections, abscesses and blood, compared to their number in the normal flora. The pathogenicity of Bacteroides, Fusobacterium, Clostridium, and AFGPC was studied by inoculating them into mice and observing their ability to induce subcutaneous abscesses. Encapsulated Bacteroides, Fusobacteria, and AFGPC generally induced abscesses, whereas non-encapsulated organisms did not. However, many of the strains that had only a minimal number of encapsulated organisms (< 1%) survived in the abscesses, and they became heavily encapsulated when inoculated with other viable or non-viable encapsulated bacteria. Thereafter, these strains were able to induce abscesses when injected alone. Encapsulated Gram-negative anaerobic rods and AFGPC-induced bacteraemia and translocation, and increased the mortality of the infected animals more often than did the non-encapsulated form of the same strains. As determined by using selective antimicrobial therapy and quantitative cultures of abscesses induced in mice, possession of a capsule generally made Gram-negative anaerobic rods more important than their aerobic counterparts. Synergistic potentials were seen between encapsulated Gram-negative anaerobic rods and all tested aerobic bacteria and most AFGPC, and also between most AFGPC and Pseudomonas aeruginosa or Staphylococcus aureus. These studies demonstrated the importance of encapsulated anaerobes in mixed infections.

Pyocycanin, a Contributory Factor in Haem Acquisition and Virulence Enhancement of Porphyromonas gingivalis in the Lung

“…Whilst this may be advantageous to the host in that it may contribute to elimination of infected cells, it also causes tissue destruction. Several studies also support the importance of encapsulated anaerobic bacteria in respiratory infections [ 93 ]. Moreover, when relatively non-encapsulated isolates of Porphyromonas strains were mixed with P. aeruginosa , enhanced virulence of the latter was observed.…”

Peptococcus Infection after Breast Augmentation Using Autologous Fat Injection

“…However, Peptostreptococcus is considered an important pathogen in the etiology of mixed anaerobic infections, and is usually absent or present in low numbers in the plaque of healthy individuals. We presumed that a synergistic infection was caused by a pathogenic aerobic gram-positive bacterium that is more frequently associated with post-surgical infections [5]; therefore, we continued the empiric treatment with vancomycin that targeted methicillin-resistant S. aureus after consulting with an infectious disease specialist. Because all of the signs and symptoms of infection improved within 10 days of incision and drainage along with vancomycin treatment, no additional antibiotic agent to specifically target anaerobic bacteria was administered.…”