Effect of marbofloxacin and cefazolin concentrations and bacterial count on lipopolysaccharide (LPS) release by Escherichia coli and Klebsiella pneumoniae isolated from bovine clinical mastitis

Abstract

The amount of lipopolysaccharide (LPS) released by Escherichia coli and Klebsiella pneumoniae isolated from bovine clinical mastitis and cultured with marbofloxacin (MBFX), cefazolin (CEZ), ceftazidime (CAZ), and imipenem was quantified. The relationships between antimicrobial type, concentration, and bacterial count in relation to the amount of LPS released were evaluated. Bacterial morphology, which is closely associated with LPS release, was also investigated. At an initial inoculum of 10⁵ CFU/mL, the amount of LPS released after 4 hr of incubation with MBFX and CEZ was significantly lower than that for the negative control (NC) group at concentrations higher than 5× the minimum inhibitory concentration (MIC) for E. coli and higher than 50× MIC for K. pneumoniae. These findings suggest that exposure to high-dose antimicrobials results in reduced LPS release associated with bacterial growth and lysis. Conversely, at an initial inoculum of 10⁸ CFU/mL, incubation with MBFX and CEZ at concentrations of 50× MIC and 250× MIC for 4 hr resulted in an amount of LPS released that was comparable to that for the NC group for both E. coli and K. pneumoniae. Both MBFX and CEZ also induced bacterial filamentation, but the morphological changes were less pronounced than those induced by CAZ and were associated with lower LPS release. These suggest that early administration of high concentrations of antimicrobials at low bacterial loads may mitigate the adverse effects associated with LPS release in cases of mastitis caused by E. coli and K. pneumoniae.