Effects of the order of exposure to antimicrobials on the incidence of multidrug-resistant Pseudomonas aeruginosa

Multidrug-resistant Pseudomonas aeruginosa (MDRP) is one of the most important pathogens in clinical practice. To clarify the mechanisms contributing to its emergence, we isolated MDRPs using the P. aeruginosa PAO1, the whole genome sequence of which has already been elucidated. Mutant strains resistant to carbapenems, aminoglycosides, and new quinolones, which are used to treat P. aeruginosa infections, were isolated; however, none met the criteria for MDRPs. Then, PAO1 strains were exposed to these antimicrobial agents in various orders and the appearance rate of MDRP varied depending on the order of exposure; MDRPs more frequently appeared when gentamicin was applied before ciprofloxacin, but were rarely isolated when ciprofloxacin was applied first. Exposure to ciprofloxacin followed by gentamicin increased the expression of MexCD-OprJ, an RND-type multidrug efflux pump, due to the NfxB mutation. In contrast, exposure to gentamicin followed by ciprofloxacin resulted in more mutations in DNA gyrase. These results suggest that the type of quinolone resistance mechanism is related to the frequency of MDRP and that the risk of MDRP incidence is highly dependent on the order of exposure to gentamicin and ciprofloxacin.

In vitro antibacterial activities of cefiderocol against Gram-negative clinical strains isolated from China in 2020

OBJECTIVES

Cefiderocol (CFDC) is a parenteral siderophore cephalosporin that is active against Gram-negative bacteria, including carbapenem-resistant isolates. We report the in vitro activity of CFDC and other antibiotics against 1738 clinical isolates of Gram-negative bacilli (GNB) provided by five medical centres in five provinces of China in 2020 METHODS: Antibiotic susceptibility testing was performed using the Clinical and Laboratory Standards Institute broth microdilution method.

RESULTS

Against Pseudomonas aeruginosa and Acinetobacter Spp., the CFDC concentration inhibiting the growth of 90% of the isolates (MIC₉₀) (0.5 μg/mL) was identical and did not change by the carbapenem resistance phenotype. The susceptibility rate of P. aeruginosa and Acinetobacter Spp. to CFDC was high (> 98%) and was similar against isolates with and without meropenem resistance. The MIC of CFDC for all Stenotrophomonas maltophilia isolates (20 isolates) was ≤1 μg/mL and the MIC₉₀ was 0.12 μg/mL. Considerable differences were noted in the susceptibility to CFDC between all tested Enterobacterales isolates and meropenem-non-susceptible Enterobacterales isolates. The MIC₉₀ of CFDC was 1 μg/mL for all tested Enterobacterales isolates and 8 μg/mL for meropenem-non-susceptible Enterobacterales isolates.

CONCLUSIONS

CFDC demonstrated potent in vitro activity against a recent collection of clinical isolates, including meropenem-non-susceptible isolates, obtained from medical centres in mainland China.

1106. Evaluation of Penetration of Cefiderocol into Cerebrospinal Fluid Using a Rat Meningitis Model

Background

Central nervous system (CNS) infections caused by Gram-negative bacteria (GNB) are sometimes hard to treat due to antibiotic resistance and difficulty with penetration into cerebrospinal fluid (CSF). Cefiderocol (CFDC) which was approved by the FDA and the EMA in 2019 to 2020 is a siderophore cephalosporin with potent activity against various GNB including carbapenem-resistant strains. In this study, we evaluated the penetration of CFDC into CSF using a rat meningitis model.

Methods

To induce meningitis, the anesthetized immunocompetent rats were infected by intracisternal inoculation of a bacterial suspension of 8.7×10¹ CFU of E. coli SR200138. 200 mg/kg or 50 mg/kg of CFDC was administered via tail vein bolus injection to uninfected rats (n=4/sampling point) and rats with meningitis (n=4/sampling point) 24 hours after infection. CSF was collected by cisternal puncture and blood was collected from heart. The samplings were performed 0.25, 0.5, 1, 3, and 5 hours after dosing. The concentrations of CFDC in plasma and CSF for individuals were determined by LC/MS/MS. PK parameters for the average values in plasma and CSF were calculated.

Results

CFDC concentration and the PK parameters are shown in Figure and Table, respectively. The penetration of CFDC from plasma to CSF was observed in both uninfected and meningitis groups, and the penetration rates increased in the rats withs meningitis (AUC_CSF/AUC_plasma: 0.149-0.183) compared with the uninfected rats (AUC_CSF/AUC_plasma: 0.0508-0.0588). The penetration rates of CFDC in the meningitis were comparable to those of piperacillin, cefepime, and meropenem in human (0.32, 0.103, and 0.39 in strongly inflamed meninges, respectively) [1]. In both groups, elimination of CFDC from CSF was slower compared with that from plasma as seen with other β-lactam antibiotics such as meropenem, suggesting that T_{> MIC}, an indicator that correlates with the efficacy of β-lactams, may be higher in CSF [2].

Table. PK Parameters of Cefiderocol after Intravenous Bolus Administration in Uninfected Rats and Rats with Meningitis

Figure. Concentrations of Cefiderocol after Intravenous Bolus Administration in Uninfected Rats and Rats with Meningitis

Conclusion

It was confirmed that CFDC penetrates into CSF from plasma in a rat model and the penetration rate was increased 3-fold in meningitis.

References

1. Nau, R. et al. Clin Microbiol Rev. 2010 Oct;23(4):858–883.

2. Nau, R. et al. Antimicrob Agents Chemother. 1998 Aug;42(8):2012–2016.

Disclosures

Miki Takemura, MS, SHIONOGI & CO., LTD. (Employee) Sachi Kanazawa, PhD, Shionogi & Co., Ltd. (Employee) Naoki Kohira, PhD, Shionogi & Co., Ltd. (Employee) Yuki Aoe, BS, Shionogi TechnoAdvance Research Co., Ltd. (Employee) Atsushi Morimoto, n/a, Shionogi TechnoAdvance Research Co., Ltd. (Employee) Kana Horiuchi, MPharm, Shionogi & Co., Ltd. (Employee) Yuji Inoue, MPharm, Shionogi & Co., Ltd. (Employee) Yoshinori Yamano, PhD, Shionogi (Employee)

Discovery of 2-Sulfinyl-Diazabicyclooctane Derivatives, Potential Oral β-Lactamase Inhibitors for Infections Caused by Serine β-Lactamase-Producing Enterobacterales

Coadministration of β-lactam and β-lactamase inhibitor (BLI) is one of the well-established therapeutic measures for bacterial infections caused by β-lactam-resistant Gram-negative bacteria, whereas we have only two options for orally active BLI, clavulanic acid and sulbactam. Furthermore, these BLIs are losing their clinical usefulness because of the spread of new β-lactamases, including extended-spectrum β-lactamases (ESBLs) belonging to class A β-lactamases, class C and D β-lactamases, and carbapenemases, which are hardly or not inhibited by these classical BLIs. From the viewpoints of medical cost and burden of healthcare personnel, oral therapy offers many advantages. In our search for novel diazabicyclooctane (DBO) BLIs possessing a thio-functional group at the C2 position, we discovered a 2-sulfinyl-DBO derivative (2), which restores the antibacterial activities of an orally available third-generation cephalosporin, ceftibuten (CTB), against various serine β-lactamase-producing strains including carbapenem-resistant Enterobacteriaceae (CRE). It can be orally absorbed via the ester prodrug modification and exhibits in vivo efficacy in a combination with CTB.

Introduction of a Thio Functional Group to Diazabicyclooctane: An Effective Modification to Potentiate the Activity of β-Lactams against Gram-Negative Bacteria Producing Class A, C, and D Serine β-Lactamases

By the emergence and worldwide spread of multi-drug-resistant Gram-negative bacteria, there have been growing demands for efficacious drugs to cure these resistant infections. The key mechanism for resistance to β-lactam antibiotics is the production of β-lactamases, which hydrolyze and deactivate β-lactams. Diazabicyclooctane (DBO) analogs play an important role as one of the new classes of β-lactamase inhibitors (BLIs), and several compounds such as avibactam (AVI) have been approved by the FDA, along with many derivatives under clinical or preclinical development. Although these compounds have a similar amide substituent at the C2 position, we have recently reported the synthesis of novel DBO analogs which possess a thio functional group. This structural modification enhances the ability to restore the antimicrobial activities of cefixime (CMF) against pathogens producing classes A, C, and D serine β-lactamases compared with AVI and expands the structural tolerance at the six position. Furthermore, some of these analogs showed intrinsic microbial activities based on multipenicillin binding protein (PBP) inhibition. This is the unique feature which has never been observed in DBOs. One of our DBOs had a pharmacokinetic profile comparable to that of other DBOs. These results indicate that the introduction of a thio functional group into DBO is a novel and effective modification to discover a clinically useful new BLI.

Reduced susceptibility mechanism to cefiderocol, a siderophore cephalosporin, among clinical isolates from a global surveillance programme (SIDERO-WT-2014)

OBJECTIVE

To investigate possible mechanistic factors to explain cefiderocol (CFDC) non-susceptibility, we characterized 38 clinical isolates with a CFDC minimum inhibitory concentration (MIC) of >4μg/mL from a multi-national surveillance study.

METHODS

The MIC measurement in the presence of β-lactamase inhibitors and whole genome sequencing were performed.

RESULTS

The MIC decrease of CFDC by β-lactamase inhibitors was observed against all of the test isolates. Among the 38 isolates, NDM and PER genes were observed in 5 and 25 isolates, respectively. No other β-lactamases responsible for high MIC were identified in the other eight isolates. The MIC of CDFC against Escherichia coli isogenic strains introduced with NDM and PER β-lactamase increased by ≥16-fold, suggesting the contribution of NDM and PER to the non-susceptibility to CFDC. Against NDM producers, a ≥8-fold MIC increase was observed only when both serine- and metallo-type β-lactamase inhibitors were added. In addition, many of the PER or NDM producers remained susceptible to CFDC. These results suggested that the presence of only NDM or PER would not lead to non-susceptibility to CFDC and that multiple factors would be related to CFDC resistance.

CONCLUSION

Multiple factors including NDM and PER could be related to reduced susceptibility to CFDC.

In Vitro Antibacterial Properties of Cefiderocol, a Novel Siderophore Cephalosporin, against Gram-Negative Bacteria

Cefiderocol (CFDC; S-649266), a novel parenteral siderophore cephalosporin conjugated with a catechol moiety, has a characteristic antibacterial spectrum with a potent activity against a broad range of aerobic Gram-negative bacterial species, including carbapenem-resistant strains of Enterobacteriaceae and nonfermenting bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii Cefiderocol has affinity mainly for penicillin-binding protein 3 (PBP3) of Enterobacteriaceae and nonfermenting bacteria similar to that of ceftazidime. A deficiency of the iron transporter PiuA in P. aeruginosa or both CirA and Fiu in Escherichia coli caused 16-fold increases in cefiderocol MICs, suggesting that these iron transporters contribute to the permeation of cefiderocol across the outer membrane. The deficiency of OmpK35/36 in Klebsiella pneumoniae and the overproduction of efflux pump MexA-MexB-OprM in P. aeruginosa showed no significant impact on the activity of cefiderocol.

In Vitro Antimicrobial Activity of a Siderophore Cephalosporin, S-649266, against Enterobacteriaceae Clinical Isolates, Including Carbapenem-Resistant Strains

S-649266 is a novel siderophore cephalosporin antibiotic with a catechol moiety on the 3-position side chain. Two sets of clinical isolate collections were used to evaluate the antimicrobial activity of S-649266 against Enterobacteriaceae. These sets included 617 global isolates collected between 2009 and 2011 and 233 β-lactamase-identified isolates, including 47 KPC-, 49 NDM-, 12 VIM-, and 8 IMP-producers. The MIC90 values of S-649266 against the first set of Escherichia coli, Klebsiella pneumoniae, Serratia marcescens, Citrobacter freundii, Enterobacter aerogenes, and Enterobacter cloacae isolates were all ≤1 μg/ml, and there were only 8 isolates (1.3%) among these 617 clinical isolates with MIC values of ≥8 μg/ml. In the second set, the MIC values of S-649266 were ≤4 μg/ml against 109 strains among 116 KPC-producing and class B (metallo) carbapenemase-producing strains. In addition, S-649266 showed MIC values of ≤2 μg/ml against each of the 13 strains that produced other types of carbapenemases such as SME, NMC, and OXA-48. The mechanisms of the decreased susceptibility of 7 class B carbapenemase-producing strains with MIC values of ≥16 μg/ml are uncertain. This is the first report to demonstrate that S-649266, a novel siderophore cephalosporin, has significant antimicrobial activity against Enterobacteriaceae, including strains that produce carbapenemases such as KPC and NDM-1.

Screening for FtsZ Dimerization Inhibitors Using Fluorescence Cross-Correlation Spectroscopy and Surface Resonance Plasmon Analysis

FtsZ is an attractive target for antibiotic research because it is an essential bacterial cell division protein that polymerizes in a GTP-dependent manner. To find the seed chemical structure, we established a high-throughput, quantitative screening method combining fluorescence cross-correlation spectroscopy (FCCS) and surface plasmon resonance (SPR). As a new concept for the application of FCCS to polymerization-prone protein, Staphylococcus aureus FtsZ was fragmented into the N-terminal and C-terminal, which were fused with GFP and mCherry (red fluorescent protein), respectively. By this fragmentation, the GTP-dependent head-to-tail dimerization of each fluorescent labeled fragment of FtsZ could be observed, and the inhibitory processes of chemicals could be monitored by FCCS. In the first round of screening by FCCS, 28 candidates were quantitatively and statistically selected from 495 chemicals determined by in silico screening. Subsequently, in the second round of screening by FCCS, 71 candidates were also chosen from 888 chemicals selected via an in silico structural similarity search of the chemicals screened in the first round of screening. Moreover, the dissociation constants between the highest inhibitory chemicals and Staphylococcus aureus FtsZ were determined by SPR. Finally, by measuring the minimum inhibitory concentration, it was confirmed that the screened chemical had antibacterial activity against Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus (MRSA).

Gene cloning and characteristics of the RND-type multidrug efflux pump MuxABC-OpmB possessing two RND components in Pseudomonas aeruginosa

muxA-muxB-muxC-opmB (formerly PA2528-PA2527-PA2526-opmB), encoding a putative resistance nodulation cell division (RND)-type multidrug efflux pump system, was cloned from Pseudomonas aeruginosa PAO1. Introduction of muxABC-opmB into P. aeruginosa YM64, a drug-hypersusceptible strain, led to elevated MICs of aztreonam, macrolides, novobiocin and tetracycline. Since muxB and muxC, both of which encode RND components, were essential for function, MuxABC-OpmB is thought to be a drug efflux pump with four components. One novobiocin-resistant mutant, PMX725, isolated from P. aeruginosa PMX7 showed elevated resistance not only to novobiocin but also to aztreonam, macrolides and tetracycline. Increased mRNA expression of muxABC-opmB was observed in the mutant PMX725 compared with the parental strain. Sequencing analysis revealed that a single-nucleotide insertion had occurred in the deduced promoter region for muxABC-opmB in PMX725. In this study, we have characterized the last RND-type multidrug efflux pump predicted from the genome sequence in P. aeruginosa.