Anaerobic beta-lactamase-producing-bacteria in mixed infections

Aerobic and anaerobic beta-lactamase-producing bacteria (BLPB) can play an important role in polymicrobial infections. They can have a direct pathogenic impact in causing the infection as well as an indirect effect through their ability to produce the enzyme beta-lactamase. BLPB may not only survive penicillins therapy but can also, as was demonstrated in in vitro and in vivo studies, protect other penicillin-susceptible bacteria from penicillins by releasing the free enzyme into their environment ( see figure ). This phenomenon occurs in upper respiratory tract, skin, soft tissue, abdominal, surgical and other infections.

Many Gram negative anaerobic bacteria can produce the enzyme beta-lactamse (BL). Bacteroides fragilis group has been known as a BL producer. However recent studies illustrated that other anaerobes have also become BL producers. These include up to 50% of pigmented Prevotella and Porphyromonas and Fusobacterium spp. that predominate in respiratory and head and neck infections, and Prevotella bivia, and Prevotella disiens important in female pelvic infections).

The presence of free BL in clinical specimens was reported in abscesses and mixed infections. These include abdominal infections, empyema, cerebrospinal specimens, abscesses, ear aspirates of acute and chronic ear infections, and aspirates of acutely and chronically inflamed sinuses. Many of these infections had failed beta-lactam therapies and required surgical drainage to enhance cure.

The isolation of penicillin-susceptible bacteria mixed with BLPB in patients who have failed to respond to beta-actam therapy suggests the ability of BLPB to protect a susceptible organism from the activity of those drugs.

Aerobic and anaerobic BLPB may play a role in penicillin failure to eradicate Group A beta hemolytic streptococci tonsillitis (GABHS). BLPB were recovered in over 2/3 of tonsils removed from those who failed penicillin therapy.

The presence of BLPB in mixed infection warrants administration of drugs that will be effective in eradication of BLPB as well as the other pathogens. Antimicrobials active against aerobic and anaerobic BLPB as well as GABHS were more effective in the eradication of this infection and even prevented elective tonsillectomy compared to penicillin. These include lincomycin, clindamycin , and amoxicillin/clavulanate.

Other infections where this approach was superior to penicillins therapy were acute and chronic otitis media and sinusitis, aspiration and tracheostomy-associated pneumonia, and lung abscesses.

The management of polymicrobial infections is enhanced by directing antimicrobial therapy at the eradication of both aerobic and anaerobic BLPB. Although beta lactam antibiotics are still the mainstay in treatment of numerous infections, agents effective against BLPB should be considered in the treatment of those who failed these agents.