title: Postantibiotic effect and postantibiotic sub-minimum inhibitory concentration effect of valnemulin against Staphylococcus aureus isolates from swine and chickens.
abstract: The postantibiotic effect (PAE) and postantibiotic sub-minimum inhibitory concentration (MIC) effect (PA-SME) of valnemulin against Staphylococcus aureus were investigated in vitro using a spectrophotometric technique and classic viable count method. A standard curve was constructed by regression analysis of the number of colonies and the corresponding optical density (OD) at 630 nm of the inoculum. After exposure to valnemulin at different concentrations for an hour, the antibiotic was removed by centrifuging and washing. The PA-SMEs were measured after initial exposure to valnemulin at 4 × the MIC, and then, valnemulin was added to reach corresponding desired concentrations in the resuspended culture. Samples were collected hourly until the culture became turbid. The results were calculated by converting the OD values into the counts of bacteria in accordance with the curve. The MIC of valnemulin against eight strains was identically 0.125 μg ml(-1) . The mean PAEs were 2.12 h (1 × MIC) and 5.06 h (4 × MIC), and the mean PA-SMEs were 6.85 h (0.1 × MIC), 9.12 h (0.2 × MIC) and 10.8 h (0.3 × MIC). The results showed that the strains with identical MICs exhibited different PAEs and PA-SMEs. Valnemulin produced prolonged PAE and PA-SME periods for Staph. aureus, supporting a longer dosing interval while formulating a daily administration dosage.
  
  
  CONCLUSIONS
  In this study, valnemulin demonstrated prolonged postantibiotic effects and postantibiotic sub-MIC effects on strains of Staphylococcus aureus. The strains with identical MICs of valnemulin exhibited different PAEs and PA-SMEs. Staphylococcus aureus isolated from different species has little impact on the postantibiotic effect of valnemulin. The result suggests a longer dosing interval while formulating a daily administration dosage, and it may play a valuable role of valnemulin in treating Staph. aureus infections in animals.
authors.affiliation: National Reference Laboratory of Veterinary Drug Residues (SCAU), College of Veterinary Medicine, South China Agricultural University, Guangzhou, China.
authors.forename: D H
authors.initials: DH
authors.lastname: Zhao
authors.forename: Y
authors.initials: Y
authors.lastname: Yu
authors.forename: Y F
authors.initials: YF
authors.lastname: Zhou
authors.forename: W
authors.initials: W
authors.lastname: Shi
authors.forename: H
authors.initials: H
authors.lastname: Deng
authors.forename: Y H
authors.initials: YH
authors.lastname: Liu
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D058491:Bacterial Load; D002645:Chickens / Q000382:microbiology; D004224:Diterpenes / Q000008:administration & dosage / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D011201:Poultry Diseases / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D013552:Swine / Q000382:microbiology; D013553:Swine Diseases / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D004224:Diterpenes; C117845:valnemulin
keywords: Staphylococcus aureus; postantibiotic effect; postantibiotic sub-MIC effect; valnemulin