In-vitro antibacterial activity of levofloxacin against hospital isolates: a multicentre study

Abstract

The objective of this study was to evaluate the activity of the fluoroquinolone, levofloxacin, against hospital isolates of bacteria. MICs of levofloxacin were determined for 2154 strains by agar dilution. Breakpoints for susceptibility testing were calculated using the agar diffusion technique with 5 micrograms discs. The activity of levofloxacin against nalidixic acid- and pefloxacin-susceptible Enterobacteriaceae (n = 668) was higher (MIC50/90 0.06-0.12 mg/L) than previously reported for ofloxacin. As seen with other fluoroquinolones, this activity was reduced against nalidixic acid-resistant and pefloxacin-intermediate and -resistant strains (MIC 1-8 mg/L). MICs for Pseudomonas aeruginosa (n = 104) were between 0.12 and 128 mg/L. Levofloxacin had good activity against nalidixic acid- and pefloxacin-susceptible Acinetobacter baumannii (n = 12; MIC 0.06-0.25 mg/L), but the activity was reduced against nalidixic acid- and pefloxacin-resistant strains (n = 80; MIC 1-32 mg/L). Haemophilus influenzae (n = 70), Haemophilus parainfluenzae (n = 47) and Moraxella catarrhalis (n = 64) were inhibited by low concentrations of levofloxacin (MICs 0.016-0.03 mg/L, 0.03-0.12 mg/L) and 0.03-0.12 mg/L, respectively). Clostridium perfringens (n = 23; MIC 0.25-1 mg/L) was more susceptible than Bacteroides fragilis (n = 60; MIC 0.5-4 mg/L). Levofloxacin showed superior activity compared with ofloxacin against methicillin-susceptible staphylococci (n = 107; MIC 0.03-0.5 mg/L); the resistant strains (MICs 2-32 mg/L) were usually also resistant to methicillin. Levofloxacin was less effective against enterococci (n = 105; MIC 1-32 mg/L), but streptococci (n = 192) and pneumococci (n = 129), including 58 penicillin-non-susceptible strains, were inhibited by low concentrations (MICs 0.5-2 mg/L). According to the regression curve, zone diameters were usually 20-22 mm, 17-19 mm and 15-16 mm for MICs of 1, 2 and 4 mg/L, respectively. In conclusion, this study, performed on a large number of strains, confirms the superior anti-bacterial activity of levofloxacin compared with ofloxacin, especially against pathogens isolated from respiratory tract infections.

Invasive Streptococcus pneumoniae in France: Antimicrobial Resistance, Serotype, and Molecular Epidemiology Findings from a Monthly National Study in 2000 to 2002

“…As previously reported, erythromycin resistance is due to the erm(B) methylase gene (5,9). Our results also confirm the low occurrence of fluoroquinolone resistance among French pneumococci (4,5,28), but the method used could not detect any first-stage mutants (16,25). Vancomycin tolerance in S. pneumoniae has been involved in clinical failure (11,18).…”

Relevance of Soft-Tissue Penetration by Levofloxacin for Target Site Bacterial Killing in Patients with Sepsis

“…All S. aureus and P. aeruginosa strains used were clinical isolates obtained at the General Hospital of Vienna. For in vivo PK-in vitro PD simulations, one S. aureus strain and one P. aeruginosa strain for which the MICs corresponded to the MIC at which 90% of isolates are inhibited (MIC 90 ) for S. aureus (MIC 90 ϭ 0.5 g/ml) and P. aeruginosa (MIC 90 ϭ 2 g/ml) found in the literature were chosen (17,31,32). All bacteria were stored frozen in liquid nitrogen at Ϫ196°C until they were used.…”

Determination of levofloxacin in plasma, bronchoalveolar lavage and bone tissues by high-performance liquid chromatography with ultraviolet detection using a fully automated extraction method

“…Its antibacterial action appears to be twice as active as the racemate ofloxacin in vitro [1]. Levofloxacin exerts antibacterial activity via antagonism of the interaction between bacterial DNA gyrase and DNA.…”