Infections caused by anaerobic bacteria are common, and may be serious and life-threatening. Anaerobes predominant in the bacterial flora of normal human skin and mucous membranes, and are a common cause of bacterial infections of endogenous origin. Infections due to anaerobes can evolve all body systems and sites. The predominate ones include: abdominal, pelvic, respiratory, and skin and soft tissues infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. Failure to direct therapy against these organisms often leads to clinical failures. Their isolation requires appropriate methods of collection, transportation and cultivation of specimens. Treatment of anaerobic bacterial infection is complicated by the slow growth of these organisms, which makes diagnosis in the laboratory only possible after several days, by their often polymicrobial nature and by the growing resistance of anaerobic bacteria to antimicrobial agents.

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Friday, December 31, 2010

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.

Bacterial Interference by anaerobes in ear, sinus, and tonsillar infections

Interactions between bacteria that include antagonism (interference) and synergism maintain balance between members of the normal endogenous flora and play a role in preventing colonization by potential pathogens.  Bacterial interference can assist in the recovery from infections, in promotion of health and prevention of upper respiratory tract infection. Bacteria capable of interfering with the growth of potential respiratory pathogens include alpha- hemolytic streptococci, non-hemolytic streptococci, and the anaerobic bacteria Prevotella and Peptostreptococcus spp.

Bacterial Interference in colonization by pathogens

Bacterial interference plays a role in the emergence of upper respiratory tract infections and their eradication. These infections include recurrent pharyngo-tonsillitis, otitis media , and sinusitis. The tonsils, and nasopharyngeal flora of patients with these infections harbor less interfering bacteria than those without that history. The presence of interfering bacteria may therefore play a role in preventing pharyngo-tonsillitis, otitis media, and sinusitis.
Treatment with antimicrobials and smoking can affect the balance between the interfering organisms and potential pathogens.  Antimicrobials that spare the normal flora, can assist in preserving the interfering flora.

Balance between interfering bacteria and pathogens

Introduction into the indigenous microflora of low virulence bacteria that are capable of interfering with colonization and infection with virulent organisms has been used as a means of preventing the failure of antimicrobials in the treatment of pharyngo-tonsillitis and otitis media.