Gram positive: may develop resistance to staphylococci and therefore not reliable, Bacillus anthracis

Gram negative: Pseudomonas, Enterobacteriaceae, Neisseria, Haemophilus, Moraxella, Pasteurella

Anaerobes: not reliable

Other: atypicals including mycoplasma, chlamydophila, Legionella

Does not cover: most gram positives including Streptococci, Enterococci (except in urine); Stenotrophomonas, anaerobes