Twenty patients with carbapenem-resistant Enterobacteriaceae infections were treated with meropenem-vaborbactam. Thirty-day clinical success and survival rates were 65% (13/20) and 90% (18/20), respectively. Thirty-five percent of patients had microbiologic failures within 90 days. One patient developed a recurrent infection due to meropenem-vaborbactam–nonsusceptible, ompK36 porin mutant Klebsiella pneumoniae.

Meropenem-vaborbactam is a new agent with the potential to treat carbapenem-resistant Enterobacteriaceae (CRE) infections. We describe the in vitro activity of meropenem-vaborbactam against representative CRE genotypes and laboratory-engineered Escherichia coli isolates harboring mutant blaKPC genes associated with ceftazidime-avibactam resistance. We also compared disk diffusion and gradient strip testing methods to standard broth microdilution methods. Against 120 CRE isolates, median ceftazidime-avibactam and meropenem-vaborbactam MICs were 1 and 0.03 µg/ml, respectively. Ninety-eight percent (117/120) of isolates were susceptible to meropenem-vaborbactam (MICs ≤ 4 µg/ml). Against Klebsiella pneumoniae isolates harboring mutant blaKPC, the addition of vaborbactam lowered the meropenem MICs in 78% of isolates (14/18); 100% were susceptible to meropenem-vaborbactam. Median meropenem-vaborbactam MICs were higher against K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae isolates with mutant ompK36 porin genes (n = 26) than against those with wild-type ompK36 porin genes (n = 54) (0.25 versus 0.03 µg/ml; P < 0.0001). Against E. coli TOP10 isolates with plasmid constructs containing wild-type blaKPC or mutant blaKPC, the addition of vaborbactam at 8 µg/ml lowered the meropenem MICs 2- to 512-fold, resulting in meropenem-vaborbactam MICs of 0.03 µg/ml. The rates of categorical agreement with broth microdilution for disk diffusion or gradient strips ranged from 90 to 95%. Essential agreement rates were higher for research-use-only (RUO) gradient strips manufactured by bioMérieux (82%) than for those manufactured by Liofilchem (48%) (P < 0.0001). Taken together, our data highlight the potent in vitro activity of meropenem-vaborbactam against CRE, including isolates resistant to ceftazidime-avibactam. Vaborbactam inhibited both wild-type and variant KPC enzymes. On the other hand, KPC-producing K. pneumoniae isolates with ompK36 mutations displayed higher meropenem-vaborbactam MICs than isolates with wild-type ompK36. The results of susceptibility testing with RUO bioMérieux gradient strips most closely aligned with those of broth microdilution methods.

We report 2 independent patients from whom carbapenem and ceftazidime-avibactam–resistant Enterobacter cloacae complex strains were identified. The ceftazidime-avibactam resistance was attributed to a 2–amino acid deletion in the R2 loop of AmpC β-lactamase, which concurrently caused resistance to cefepime and reduced susceptibility to cefiderocol, a novel siderophore cephalosporin.

We hypothesize that the beneficial effects estradiol on cognitive performance may be mediated through GPR30, a putative membrane target of estrogens. Recently we showed that administration of a selective GPR30 agonist (G-1) to ovariectomized rats enhanced acquisition of a delayed matching-to-position (DMP) T-maze task and increased potassium-stimulated acetylcholine release in the hippocampus, similar to estradiol (E2) (Hammond et al., 2009). The present study tested whether treating with a selective GPR30 antagonist (G-15) would impair spatial learning in gonadally intact rats and in ovariectomized (OVX) rats treated with E2. As predicted, G-15 dose-dependently impaired DMP acquisition both in gonadally intact rats and in OVX rats treated with E2. G-15 specifically reduced the rate of acquisition, and this effect was associated with an increased predisposition to adopt a persistent turn. In contrast, G-15 alone at the highest dose had no significant effect on DMP acquisition in OVX controls. The effects were task dependent, as similar effects of G-15 were not observed in gonadally intact rats tested on an operant discrimination/reversal learning task motivated by the same food reward. This suggests that the effects on DMP acquisition were not due to effects on motivation for food. Effects of G-15 on DMP acquisition were similar to previously published work showing significant impairment produced by selective cholinergic denervation of the hippocampus. These data suggest that GPR30 can play an important role in mediating the effects of estradiol on spatial learning, possibly by mediating estradiol effects on basal forebrain cholinergic function.

Ceftazidime-avibactam and cefiderocol are two of the latest generation β-lactam agents that possess expanded activity against highly drug-resistant bacteria, including carbapenem-resistant Enterobacterales. Here, we show that structural changes in AmpC β-lactamases can confer reduced susceptibility to both agents. A multidrug-resistant Enterobacter cloacae clinical strain (Ent385) was found to be resistant to ceftazidime-avibactam and cefiderocol without prior exposure to either agent. The AmpC β-lactamase of Ent385 (AmpCEnt385) contained an alanine-proline deletion at positions 294 and 295 (A294_P295del) in the R2 loop. AmpCEnt385 conferred reduced susceptibility to ceftazidime-avibactam and cefiderocol when cloned into Escherichia coli TOP10. Purified AmpCEnt385 showed increased hydrolysis of ceftazidime and cefiderocol compared to AmpCEnt385Rev, in which the deletion was reverted. Comparisons of crystal structures of AmpCEnt385 and AmpCP99, the canonical AmpC of E. cloacae complex, revealed that the two-residue deletion in AmpCEnt385 induced drastic structural changes of the H-9 and H-10 helices and the R2 loop, which accounted for the increased hydrolysis of ceftazidime and cefiderocol. The potential for a single mutation in ampC to confer reduced susceptibility to both ceftazidime-avibactam and cefiderocol requires close monitoring.