6% susceptible (MIC90 0.5 μg/ml) compared with 73.2% susceptible for ceftazidime (MIC90 >64 μg/ml). The percent susceptibility values for ceftazidime-avibactam and ceftazidime against 129 P. aeruginosa isolates were 88.4% and 72.9% (MIC90 values of 16 μg/ml and 64 μg/ml) respectively. Among ceftazidime-nonsusceptible Gram-negative isolates, ceftazidime-avibactam percent susceptibility values were 94.9% for 99 Enterobacteriaceae and 60.0% for 35 P. aeruginosa MIC90 values for linezolid and vancomycin (permitted per-protocol for Gram-positive coverage) were within their respective MIC susceptibility breakpoints against the Gram-positive pathogens isolated. This analysis demonstrates that ceftazidime-avibactam was active in vitro against the majority of Enterobacteriaceae and P. aeruginosa isolated from patients with NP, including VAP, in a phase 3 trial. Copyright © 2020 American Society for Microbiology.Treating malaria in HIV co-infected individuals should consider potential drug-drug interactions. Artemether-lumefantrine is the most widely recommended treatment for uncomplicated malaria globally. Lumefantrine is metabolized by CYP3A4, an enzyme that commonly-used antiretrovirals often induce or inhibit. A population pharmacokinetic meta-analysis was conducted using individual participant data from ten studies, with 6,100 lumefantrine concentrations from 793 non-pregnant adult participants (41% HIV-malaria co-infected, 36% malaria-infected, 20% HIV-infected, and 3% healthy volunteers). Lumefantrine exposure increased 3.4-fold with co-administration of lopinavir/ritonavir-based antiretroviral therapy (ART), while it decreased by 47% with efavirenz-based ART and by 59% in the patients with rifampicin-based anti-tuberculosis treatment. Nevirapine- or dolutegravir-based ART and malaria- or HIV-infection were not associated with significant effects. Monte Carlo simulations showed that those on concomitant efavirenz or rifampicin have 49% and 80% probability of day-7 concentrations less then 200 ng/mL respectively, a threshold associated with an increased risk of treatment failure. The risk of achieving sub-therapeutic concentrations increases with larger body weight. An extended 5-day and 6-day artemether-lumefantrine regimen is predicted to overcome these drug-drug interactions with efavirenz and rifampicin respectively. Copyright © 2020 Francis et al.We investigated dose fractionated polymyxin B (PB) on acute kidney injury (AKI). PB 12 mg/kg/day (once, twice, and thrice daily) was administered in rats over 72 hours. Thrice-daily group demonstrated the highest KIM-1 increase (p=0.018) vs. controls (p=0.99) and histopathological damage (p=0.013). A three-compartment model best described the data (bias 0.129 mg/L, imprecision 0.729 mg2/L2, R2 0.652,). AUC24h were similar (p=0.87). Thrice-daily dosing scheme resulted in the most PB-associated AKI in a rat model. Copyright © 2020 American Society for Microbiology.Cefazolin has become a prominent therapy for methicillin-susceptible Staphylococcus aureus (MSSA) infections. However, an important concern is the cefazolin-inoculum effect (CzIE), a phenomenon mediated by staphylococcal β-lactamases. Four variants of staphylococcal β-lactamases have been described based on serological methodologies and limited sequence information. Here, we sought to reassess the classification of staphylococcal β-lactamases and their correlation with the CzIE. We included a large collection of 690 contemporary bloodstream MSSA isolates recovered from Latin America, a region with high prevalence of the CzIE. We determined cefazolin MICs at standard and high-inoculum by broth-microdilution. Whole-genome-sequencing was performed to classify the β-lactamase based on the predicted full sequence of BlaZ. We used the classical schemes for β-lactamase classification and compared it to BlaZ allotypes found in unique sequences using the genomic information. Phylogenetic analyses were performed based on the BlaZ and core-genome sequences. The overall prevalence of the CzIE was 40%. Among 641 genomes, type C was the most predominant β-lactamase (37%), followed by type A (33%). We found twenty-nine allotypes and 43 different substitutions in BlaZ. A single allotype, designated BlaZ-2, showed a robust and statistically significant association with the CzIE. Two other allotypes (BlaZ-3 and BlaZ-5) were associated with the lack of the CzIE. Three amino acid substitutions (A9V, E112A and G145E) showed statistically significant association with CzIE (P = less then 0.01). CC30 was the predominant clone among isolates displaying CzIE. Thus, we provide a novel approach to the classification of the staphylococcal β-lactamases with the potential to more accurately identify MSSA strains exhibiting the CzIE. Copyright © 2020 American Society for Microbiology.Increasing number of variants of the carbapenem-hydrolyzing class D β-lactamase OXA-48 are identified in Enterobacterales worldwide. Among them, OXA-181 and OXA-232 are of particular interest, as they differ from each other by a single amino-acid (AA) substitution at position 214 (R in OXA-181, and S in OXA-232), that results in reduced carbapenem-hydrolyzing activity for OXA-232. To investigate the role of the AA214, the X-ray structure of OXA-232 was determined and the AA214 of OXA-48 and of OXA-232 was replaced by G, L, D, E, S, R, and K using site-directed mutagenesis. These mutants were phenotypically characterized, and three mutants of OXA-232 were purified to study their steady-state kinetic properties. X-ray structure of OXA-232 along with molecular modelling studies showed that the interaction via a salt bridge between R214 and D159 in OXA-48 is not possible with G214 or S214 mutations. In contrast, with K214 that is also positively charged, the interaction with D159 is maintained. With the E214 mutant an alternative binding conformation of imipenem was evidenced that is not compatible with a nucleophilic attack by S70. Thus, imipenem has very poor apparent affinity for the E214 mutant because of its non-productive binding mode. DMOG Similarly, we could explain the lack of temocillin hydrolysis by OXA-232, which is due to the unfavorable interaction between the negatively charged R1 substituent of temocillin with the S214 residue.Overall, we demonstrate that the AA214 in OXA-48-like β-lactamases is critical for the carbapenemase activity. Copyright © 2020 American Society for Microbiology.