Which cephalosporin has activity against gram-negative anaerobic pathogens like Bacteroides fragilis?

Cefoxitin is the correct choice as it is a second-generation cephalosporin specifically known for its effectiveness against gram-negative anaerobic organisms, including Bacteroides fragilis. This is significant because many first-generation cephalosporins, such as cefazolin, primarily target gram-positive bacteria and have limited activity against anaerobic Gram-negatives.

Cefoxitin’s side chain allows it to penetrate the bacterial cell wall more effectively and enables it to inhibit the growth of anaerobes, making it a preferred choice for intra-abdominal infections where Bacteroides fragilis is commonly implicated. This characteristic distinguishes it from later-generation cephalosporins like cefepime and ceftriaxone, which focus more on broader-spectrum activity against aerobic gram-negative bacteria but do not have the same level of efficacy against anaerobes.

Cefazolin, as a first-generation cephalosporin, lacks significant activity against the noted anaerobic pathogens, and thus would not be appropriate for treating infections where Bacteroides fragilis is a concern.