Fig. 1. Bacterial pathogens proliferate more rapidly in the setting of a metabolic acidosis. All bacterial strains tested, except for a methicillin-sensitive Staphylococcus aureus  (S. aureus ), had a marked growth advantage at moderately acidic pH levels (7.2–7.6) relevant to the clinical setting. Gram-negative bacteria are represented by solid bars , whereas gram-positive bacteria are represented by hatched bars . Reproduced with permission from Am J Resp Cell Mol Biol 2008; 38:362–70. E. coli =Eschericia coli ; P. mirabilis =Proteus mirabilis ; K. pneumoniae =Klebsiella pneumoniae ; K. oxytoca =Klebsiella oxytoca ; P. aeruginosa =Pseudomonas aeruginosa , S. rubidaea =Serratia rubidaea ; E. aerogenes =Enterobacter aerogenes ; E. feacalis =Enterococcus feacalis ; B. subtilis =Bacillus subtilis .