Clindamycin has activity against a broad range of bacteria. Against which organism is clindamycin notably INEFFECTIVE?

Clindamycin is a lincosamide antibiotic that inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit. It is effective against most gram-positive organisms (Staphylococcus aureus, Streptococci) and anaerobes (Bacteroides, Fusobacterium, Peptostreptococcus). In dentistry, clindamycin is used as an alternative to amoxicillin for infective endocarditis prophylaxis in penicillin-allergic patients. However, clindamycin has NO significant activity against gram-negative aerobic rods, especially Pseudomonas aeruginosa, which has intrinsic resistance due to its outer membrane permeability barrier and efflux pumps. Enterobacteriaceae are also typically resistant to clindamycin.