Bactericidal effects of various concentrations of enrofloxacin, florfenicol, tilmicosin phosphate, and tulathromycin on clinical isolates of Mannheimia haemolytica.

Objective: To determine bactericidal effects of enrofloxacin, florfenicol, tilmicosin, and tulathromycin on clinical isolates of Mannheimia haemolytica at various bacterial densities and drug concentrations.

Sample: 4 unique isolates of M haemolytica recovered from clinically infected cattle.

Procedures: Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) were determined for each drug and isolate.

Killing of Streptococcus pneumoniae by azithromycin, clarithromycin, erythromycin, telithromycin and gemifloxacin using drug minimum inhibitory concentrations and mutant prevention concentrations.

Streptococcus pneumoniae continues to be a significant respiratory pathogen, and increasing antimicrobial resistance compromises the use of β-lactam and macrolide antibiotics. Bacterial eradication impacts clinical outcome, and bacterial loads at the site of infection may fluctuate. Killing of two macrolide- and quinolone-susceptible clinical S.

Mutant prevention concentration of tigecycline for clinical isolates of Streptococcus pneumoniae and Staphylococcus aureus.

Background: The mutant prevention concentration (MPC) reflects the antimicrobial susceptibility of the resistant mutant subpopulations present in large bacterial populations. In principle, combining the MPC with pharmacokinetic measurements can guide treatment to restrict the enrichment of resistant subpopulations, just as the MIC is used with pharmacokinetics to restrict the growth of bulk, susceptible populations. Little is known about the MPC of tigecycline, one of the more recently approved antimicrobials.

Contribution of the R8 substituent to the in vitro antibacterial potency of besifloxacin and comparator ophthalmic fluoroquinolones.

Introduction: Previous work has shown that besifloxacin, an 8-chloro-fluoroquinolone, has more potent activity against gram-positive pathogens than moxifloxacin and gatifloxacin, which carry an 8-methoxy group. This study was conducted to determine the contribution of the R7 and R8 substituent to fluoroquinolone antibacterial activity.

Materials And Methods: Besifloxacin, moxifloxacin, gatifloxacin, their R8 structural analogs, and ciprofloxacin were tested against representative isolates of various gram-positive and gram-negative species and previously characterized fluoroquinolone-resistant mutants of Staphylococcus aureus.

Comparative minimum inhibitory and mutant prevention drug concentrations of enrofloxacin, ceftiofur, florfenicol, tilmicosin and tulathromycin against bovine clinical isolates of Mannheimia haemolytica.

Mannheimia haemolytica is the most prevalent cause of bovine respiratory disease (BRD) and this disease accounts for 75% of morbidity, 50-70% of feedlot deaths and is estimated to cost up to $1 billion dollars annually in the USA. Antimicrobial therapy is essential for reducing morbidity, mortality and impacting on the financial burden of this disease. Due to the concern of increasing antimicrobial resistance, investigation of antibacterial agents for their potential for selecting for resistance is of paramount importance.