The in vitro antimicrobial susceptibility of organisms isolated from bacteraemic versus non-bacteraemic patients was evaluated using
data (1997–2001) from the Meropenem Yearly Susceptibility Test Information Collection (MYSTIC) Programme. Minimum inhibitory
concentration values and susceptibility breakpoints of meropenem and other broad-spectrum antimicrobials were determined using standard
methodology. Three thousand one hundred and thirty-six blood culture (BC) isolates and 17,261 non-BC isolates were obtained from 51
European MYSTIC centres. Gram-positive bacteria appeared to be more prevalent in BC isolates compared with other sources. Escherichia
coli, methicillin-susceptible Staphylococcus aureus and Pseudomonas aeruginosa were isolated most frequently. Antimicrobial susceptibility
of isolates from bacteraemic versus non-bacteraemic patients was similar. Meropenem and imipenem were the most active agents against
the majority of the Gram-positive and Gram-negative organisms. Ceftazidime, gentamicin and ciprofloxacin generally exhibited the lowest
activities against the most commonly isolated organisms. Meropenem was most active against P. aeruginosa and showed the highest potency
and activity against all extended-spectrum and AmpC B-lactamase producers. These results are relevant to the choice of initial, empirical
therapy for patients with suspected bacteraemia.

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