[In vitro effect of new fluoroquinolones and betalactamines combinations against enterococci]

Combinations of one of the new fluoroquinolones (ciprofloxacin, temafloxacin or tosufloxacin) with a betalactam (amoxicillin, piperacillin, or imipenem) were tested in vitro using the checkboard method against 28 strains of Streptococcus faecalis recovered in 1990 from a variety of specimens. No instance of antagonism (FIC greater than 2) was recorded. Effects of the two agents were usually additive (0.5 less than FIC less than or equal to 1). An indifferent effect (1 less than FIC less than or equal to 2) was seen in 32.1% of cases (9 strains) with the amoxicillin-tosufloxacin combination. Synergy (FIC less than or equal to 0.5) was uncommon with combinations including imipenem: effects were synergistic for only three strains with imipenem and either ciprofloxacin or tosufloxacin and for six strains with the imipenem-temafloxacin combination. Synergy was more common with combinations including ciprofloxacin and either piperacillin (10 strains, 35.7%) or amoxicillin (13 strains, 46.4%).