Search

Cefiderocol is a novel catechol siderophore cephalosporin antibiotic developed to treat resistant gram-negative infections. We describe its successful use as rescue therapy, combined with surgical debridement, to treat a patient with osteomyelitis due to extensively drug-resistant Acinetobacter baumannii. Bacterial whole-genome sequencing identified the strain and antibiotic resistance determinants., Cefiderocol is a novel catechol siderophore cephalosporin developed to treat resistant gram-negative infections. We report its successful use in conjunction with surgical debridement to treat osteomyelitis due to extensively drug-resistant Acinetobacter baumannii. Bacterial genome sequencing revealed the determinants of resistance.

Background Mycobacterium abscessus (Mab) is a highly drug-resistant nontuberculous mycobacteria (NTM). Efforts to discover new treatments for Mab infections are accelerating with a focus on cell wall synthesis proteins (L, D-transpeptidases, LdtMab1-5, and D, D-carboxypeptidase) that are targeted by combination β-lactam antibiotics. The US Food and Drug Administration (FDA) has granted Qualified Infectious Disease Product (QIDP) to the oral and intravenous (IV) formulations of Sulopenem (SUL). Data on SUL in vitro activity against Mab is currently unavailable. Here, we evaluated activity of SUL alone and in combination with Cefuroxime salt (CEF) against representative clinical isolates belonging to the Mab complex. Both CEF and SUL are available in oral formulation and can be considered as oral step-down therapy. Methods Minimum inhibitory concentrations (MICs) of SUL and CEF alone and in combination were determined using microdilution. Approximately 5 x 105 colony-forming units (CFU) per milliliter were inoculated into Middlebrook 7H9 Broth supplemented with 10% (vol/vol) oleic albumin dextrose catalase and 0.05% (vol/vol) Tween 80. CEF was added at fixed concentration of 4 µg/ml to serial dilutions of SUL. Mab isolates were incubated with test agents at 30 °C for 48 h, and MIC was defined as lowest antibiotic concentration that prevented visible bacterial growth. Results Fifty-five clinically derived and previously characterized isolates were tested in these assays. MIC50 and MIC90 of CEF is 16 and 32 ug/ml; MIC50 and MIC90 of SUL is 2 and 4 ug/ml, the range of MICs are as follows: CEF (8 → 64 ug/ml); SUL (1→8 ug/ml); and SUL and CEF at fixed 4 ug/ml (< 0.25 → 4 ug/ml). Combination SUL and CEF lowered MIC to < 0.25 ug/ml in 52 clinical isolate (Figure). Fig. MIC distributions of cefuroxime salt, sulopenem, sulopenem with 4 μg/ml cefuroxime monohydrate against 55 Mab clinical strains Conclusion Our results support the emerging hypothesis that dual β-lactam therapy is a promising strategy in the treatment of serious Mab infections. Investigating the biochemical rationale for this combination will support the application to clinical trials. Disclosures Robert A. Bonomo, MD, Entasis, Merck, Venatorx (Research Grant or Support)

Background Stenotrophomonas maltophilia is a Gram-negative, non-fermenting opportunistic pathogen. Two β-lactamases provide intrinsic resistance to β-lactams: a class B Metallo- β-lactamase L1, and a class A serine β-lactamase (SβL) L2. Recently, we described novel variants of the L1 and L2 in a collection of clinical S. maltophilia isolates collected in the US, and showed through analyses of the amino acid sequences that L1 and L2 grouped into 4 (A-D, B, C, and E) and 2 (A and D) clades, respectively. We aimed to characterize the new L1 and L2 clinical variants biochemically. Methods Representative blaL1 and blaL2 genes from each of the identified clades were cloned into pBC-SK and pET24 vectors and transformed into E. coli DH10B and BL21 (DE3) cells, respectively. Minimal inhibitory concentrations (MICs) were determined using CLSI approved methods. Cell-based assays and biochemical characterization performed on purified enzymes, including circular dichroism (CD), thermal stability, and steady-state kinetics assays, were performed. Results Susceptibility testing results using DH10-B E. coli strains expressing the L1 and L2 variants are shown in Table 1. Remarkably, while all L1 variants confer the same level of resistance to carbapenems, L2B conferred higher MICs to 3rd gen cephalosporins and aztreonam than L2D. Kinetics assays confirmed differences in the kcat of both enzymes to ceftazidime (32s-1 for L2B vs. 7s-1 for L2D) and avibactam inhibition constant Ki (1.7 μM for L2B vs. 4.5 μM for L2D). Structurally, L2B and L2D present distinctive CD spectra and thermal stabilities (ΔTm 5°C). Table 1 Conclusion As opposed to the L2 variants, our results suggest that the L1 variants may not be functionally nor structurally different. Differences between L2B and L2D might have arisen due to the use of cephalosporins and SβL inhibitors. Further experiments are on the way to determine the structural basis of these observations and the implication of these for the design of novel β-lactamase inhibitors. Disclosures Krisztina M. Papp-Wallce, PhD, Entasis (Grant/Research Support)Merck (Grant/Research Support)Venatorx (Grant/Research Support) Robert A. Bonomo, MD, Entasis, Merck, Venatorx (Research Grant or Support)

Background Catalytic mechanisms of serine β-lactamases (SBL; classes A, C and D) and metallo-β-lactamases (MBLs) have directed divergent strategies towards inhibitor design. SBL inhibitors act as high affinity substrates that -as in BATSIs- form a reversible, dative covalent bond with the conserved active site Ser. MBL inhibitors bind the active-site Zn2+ ions and displace the nucleophilic OH-. Herein, we explore the efficacy of a series of BATSI compounds with a free-thiol group at inhibiting both SBL and MBL. Methods Exploratory compounds were synthesized using stereoselective homologation of (+) pinandiol boronates to introduce the amino group on the boron-bearing carbon atom, which was subsequently acylated with mercaptopropanoic acid. Representative SBL (KPC-2, ADC-7, PDC-3 and OXA-23) and MBL (IMP-1, NDM-1 and VIM-2) were purified and used for the kinetic characterization of the BATSIs. In vitro activity was evaluated by a modified time-kill curve assay, using SBL and MBL-producing strains. Results Kinetic assays revealed that IC50 values ranged from 1.3 µM to >100 µM for this series. The best compound, s08033, demonstrated inhibitory activity against KPC-2, VIM-2, ADC-7 and PDC-3, with IC50 in the low μM range. Reduction of at least 1.5 log10-fold of viable cell counts upon exposure to sub-lethal concentrations of antibiotics (AB) + s08033, compared to the cells exposed to AB alone, demonstrated the microbiological activity of this novel compound against SBL- and MBL-producing E. coli (Table 1). Table 1 Conclusion Addition of a free-thiol group to the BATSI scaffold increases the range of these compounds resulting in a broad-spectrum inhibitor toward clinically important carbapenemases and cephalosporinases. Disclosures Robert A. Bonomo, MD, Entasis, Merck, Venatorx (Research Grant or Support)