The ability of five new beta-lactams to permeate the outer membrane of intact Enterobacter cloacae beta-lactamase-overproducing cells was measured by using a high-pressure liquid chromatography (HPLC)-based technique that avoided certain possible artifacts of the traditional methods. Low concentrations of antibiotics were mixed with bacterial suspensions, and at different times, the cells were ...

and Klebsiella pneumoniae ATCC 700603 were used as control strains. The results were interpreted as per the CLSI (formerly NCCLS) criteria, except for ceftriaxone/sulbactam. Because there are no published breakpoints for the latter combination, the susceptibility criterion used for this combination was .8 mm increase in zone diameter of ceftriaxone/sulbactam in comparison with that of ceftriaxo...

Organisms expressing high levels of AmpC -lactamases are a major clinical concern, since they are resistant to all -lactams except for amdinocillin, cefepime, cefpirome, and carbapenems. Plasmid-borne AmpC -lactamases are increasingly reported among gram-negative bacteria worldwide. Some species of Enterobacter, Citrobacter, Morganella, and Hafnia produce chromosomal -lactamases copiously. AmpC...

Sir, Pseudomonas stutzeri is a non-fluorescent denitrifying bacterium widely distributed in the environment and rarely isolated as an opportunistic pathogen from humans. This species accounts for 1%–2% of hospital-acquired Pseudomonas spp. infections. Pseudomonas stutzeri is susceptible to many more antibiotics than the human pathogen Pseudomonas aeruginosa, its most closely related species. Th...