In vitro antibacterial effect of fosfomycin combination therapy against colistin-resistant Klebsiella pneumoniae .

Objectives: Colistin is still a "last-resort" antibiotic used to manage human infections due to multidrug-resistant (MDR) Klebsiella pneumoniae . However, colistin-resistant K. pneumoniae (CR-Kp) isolates emerged a decade ago and had a worldwide distribution. The purpose of this study was to evaluate the genetic data of CR-Kp and identify the antibacterial activity of fosfomycin (FM) alone and in combination with amikacin (AMK) or colistin (COL) against CR-Kp in vitro.

Methods: Three clinical CR-Kp isolates from three patients were collected. Whole-genome sequencing and bioinformatics analysis were performed. The Pharmacokinetics Auto Simulation System 400, by simulating human pharmacokinetics in vitro, was employed to simulate FM, AMK, and COL alone and in combination. Different pharmacodynamic parameters were calculated for determining the antimicrobial effect.

Results: Whole-genome sequencing revealed that none of the three isolates contain mcr gene and that no insertion was found in pmrAB , phoPQ , or mgrB genes. We found the antibacterial activity of AMK alone was more efficient than FM or COL against CR-Kp. The area between the control growth and antibacterial killing curves of FM (8 g every 8 hours) combined with AMK (15 mg/kg once daily) was higher than 170 LogCFU/mL·h-1 . In addition, the area between the control growth and antibacterial killing curves of FM (8 g every 8 hours) combined with COL (75,000 IU/kg every12 hours) was higher than that of monotherapies (>100 LogCFU/mL·h-1 vs <80 LogCFU/mL·h-1 ).

Conclusion: FM (8 g every 8 hours) combined with AMK (15 mg/kg once daily) was effective at maximizing bacterial killing against CR-Kp.