Although the etiology of the inflammation associated with chronic sinusitis is uncertain, bacteria can be isolated in the sinus cavity in these patients (18,19). Bacteria are believed to play a major role in the etiology and pathogenesis of most cases of chronic sinusitis, and antimicrobials are often prescribed for the treatment of this infection.
Numerous studies have examined the bacterial pathogens associated with chronic sinusitis. However, most of these studies did not employ methods that are adequate for the recovery of anaerobic bacteria. Studies have described significant differences in the microbial pathogens present in chronic as compared with acute sinusitis. S. aureus, Staphylococcus epidermidis, and anaerobic gram-negative bacilli (AGNB) predominate in chronic sinusitis. The pathogenicity of some of the low virulence organisms, such S. epidermidis, a colonizer of the nasal cavity is questionable (4,20).
Gram-negative enteric rods were also reported in recent studies (21-23). These included P. aeruginosa, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter spp. and Escherichia coli. Since these organisms are rarely found in cultures of the middle meatus obtained from normal individuals, their isolation from these symptomatic patients suggests their pathogenic role. These organisms may have been selected out following administration of antimicrobial therapy in patients with chronic sinusitis.
The usual pathogens in acute sinusitis (e.g., S. pneumoniae, H. influenzae, M. catarrhalis) are found with lower frequency (Table 1) (7-11,24-26). Polymicrobial infection is common in chronic sinusitis, which is synergistic (6) and may be more difficult to eradicate with narrow-spectrum antimicrobial agents. Chronic sinusitis caused by anaerobes is a particular concern clinically because many of the complications associated with this condition (e.g., mucocele formation, osteomyelitis, abscess) are associated with the recovery of these organisms (27).
That anaerobes play a role in chronic sinusitis is supported by the ability to induce chronic sinusitis in a rabbit by intra sinus inoculation of Bacteroides fragilis (28) and the rapid production of serum IgG antibodies against this organism in the infected animals (29). The pathogenic role of these organisms is also supported by the detection of antibodies (IgG) in patients with chronic sinusitis to two anaerobic organisms that were recovered from their sinus aspirates (F. nucleatum and Prevotella intermedia) (30). Antibody levels to these organisms declined in those who responded to therapy and were cured, but did not decrease in those who failed therapy (Fig. 4).
non-responders (N=3) responders (N=13)
FIGURE 4 Serum antibodies of Fusobacterium nucleatum and Prevotella intermedia in 16 patients with chronic sinusitis. Source: From Ref. 30.
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