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