ABSTRACT
The objective of this study was to evaluate the in vitro and in vivo efficacy of clavulanic acid (C/A) in combination with tazobactam against clinical strains of carbapenem-resistant Acinetobacter baumannii. The MIC of 24 clinical strains of A. baumannii was determined, and a checkerboard assay and time-kill curve analysis were performed in selected strains to determine the synergy between C/A and tazobactam. The efficacy of C/A in monotherapy and in combination with tazobactam was evaluated in vitro in cell culture experiments and in a murine peritoneal sepsis model. The C/A and C/A plus tazobactam MIC50 were 128 and <1 mg/L, respectively. The checkerboard assay showed that tazobactam (4 and 8 mg/L) demonstrated synergy with C/A against A. baumannii Ab40, an OXA-24 producer strain, and Ab293, a lacking OXA ß-lactamase strain. The time-kill curve assay showed both bactericidal and synergistic effects against Ab40 and Ab293, with C/A 1xMIC and tazobactam (4 and 8 mg/L) at 24 h. In the murine peritoneal sepsis model with Ab293 strain, the combination of C/A and tazobactam reduced bacterial loads in tissues and blood by 2 and 4 log10 CFU/g or mL compared with C/A alone. Combining C/A with tazobactam could be considered as a potential alternative strategy to treat A. baumannii in some cases, and future work with more strains is needed to confirm this possibility.
ABSTRACT
In 2019, the biggest listeriosis outbreak by Listeria monocytogenes (Lm) in the South of Spain was reported, resulting in the death of three patients from 207 confirmed cases. One strain, belonging to clonal complex 388 (Lm CC388), has been isolated. We aimed to determine the Lm CC388 virulence in comparison with other highly virulent clones such as Lm CC1 and Lm CC4, in vitro and in vivo. Four L. monocytogenes strains (Lm CC388, Lm CC1, Lm CC4 and ATCC 19115) were used. Attachment to human lung epithelial cells (A549 cells) by these strains was characterized by adherence and invasion assays. Their cytotoxicities to A549 cells were evaluated by determining the cells viability. Their hemolysis activity was determined also. A murine intravenous infection model using these was performed to determine the concentration of bacteria in tissues and blood. Lm CC388 interaction with A549 cells is non-significantly higher than that of ATCC 19115 and Lm CC1, and lower than that of Lm CC4. Lm CC388 cytotoxicity is higher than that of ATCC 19115 and Lm CC1, and lower than that of Lm CC4. Moreover, Lm CC388 hemolysis activity is lower than that of the Lm CC4 strain, and higher than that of Lm CC1. Finally, in the murine intravenous infection model by Lm CC388, higher bacterial loads in tissues and at similar levels of Lm CC4 were observed. Although a lower rate of mortality of patients during the listeriosis outbreak in Spain in 2019 has been reported, the Lm CC388 strain has shown a greater or similar pathogenicity level in vitro and in an animal model, like Lm CC1 and Lm CC4.
