MOFFITT MORNING REPORT PEARLS 3/21/17: Our Anaerobic Friend Bacteroides!

Good morning everyone! Thanks to Dan for presenting the case of a young woman with alcohol withdrawal who was found to have colitis and bacteremia with possible colonic perforation. Pearls below on our old anaerobic friend, Bacteroides!


Top Pearls:

  1. Bacteroides is the major anaerobic pathogen causing intraabdominal infection and bacteremia.
  2. Metronidazole is the narrowest drug of choice against Bacteroides.
  3. Clindamycin and fluoroquinolones do not have reliable activity against Bacteroides.


For those who want more info:

The “B. fragilis group” (which includes various Bacteroides strains as well as Parabacteroides) are the major anaerobic pathogens causing intraabdominal/pelvic sepsis and bacteremia. Bacteroides do not typically cause anaerobic infections above the diaphragm, where the major anaerobic pathogens are Fusobacterium, Prevotella, and peptostreptococci. These orodental and pulmonary infections usually have mixed flora which are often resistant to metronidazole.

Resistance rates among anaerobic bacteria are increasing. A significant number of Bacteroides strains are now resistant to clindamycin (44%), moxifloxacin (38%), and cefoxitin (10%).

Antibiotics predictably active against Bacteroides (resistance rate): Metronidazole (<1%), Zosyn (0.5%), Unasyn (3%), tigecycline (4%), carbapenems (<1%, up to 5% in one study).

Two cases of MDR B. fragilis have been reported in the U.S. Eek!!

The conclusion here is that metronidazole, carbapenems, and zosyn/unasyn are predictably active against Bacteroides. Clindamycin and fluoroquinolones do not have reliable activity.

*Pearl: Use Clinda above the diaphragm and Flagyl below the diaphragm.

In one study (Redondo MC Clin Infect Dis 1995), patients with B. fragilis group bacteremia had 28% mortality, and 20% increased mortality compared to matched control patients with the same principal diagnosis but without bacteremia.

*Pearl: “Diarrhea” is derived from the Greek “to flow through.” Eww.






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