Effect of efflux pump inhibitors on the susceptibility of Mycobacterium avium complex to clarithromycin

Discovery of 2-phenylquinazolines as potent Mycobacterium avium efflux pump inhibitors able to synergize with clarithromycin against clinical isolate

Nontuberculous mycobacteria (NTM), which include the Mycobacterium avium complex, are classified as difficult-to-treat pathogens due to their ability to quickly develop drug resistance against the most common antibiotics used to treat NTM infections. The overexpression of efflux pumps (EPs) was demonstrated to be a key mechanism of clarithromycin (CLA) resistance in NTM. Therefore, in this work, 24 compounds from an in-house library, characterized by chemical diversity, were tested as potential NTM EP inhibitors (EPIs) against Mycobacterium smegmatis mc2 155 and M. avium clinical isolates. Based on the acquired results, 12 novel analogs of the best derivatives 1b and 7b were designed and synthesized to improve the NTM EP inhibition activity. Among the second set of compounds, 13b emerged as the most potent NTM EPI. At a concentration of 4 µg/mL, it reduced the CLA minimum inhibitory concentration by 16-fold against the clinical isolate M. avium 2373 overexpressing EPs as primary mechanism of CLA resistance.

Efflux pump effects on levofloxacin resistance in Mycobacterium abscessus

Mycobacterium abscessus (M. abscessus) inherently displays resistance to most antibiotics, with the underlying drug resistance mechanisms remaining largely unexplored. Efflux pump is believed to play an important role in mediating drug resistance. The current study examined the potential of efflux pump inhibitors to reverse levofloxacin (LFX) resistance in M. abscessus. The reference strain of M. abscessus (ATCC19977) and 60 clinical isolates, including 41 M. abscessus subsp. abscessus and 19 M. abscessus subsp. massilense, were investigated. The drug sensitivity of M. abscessus against LFX alone or in conjunction with efflux pump inhibitors, including verapamil (VP), reserpine (RSP), carbonyl cyanide 3-chlorophenylhydrazone (CCCP), or dicyclohexylcarbodiimide (DCC), were determined by AlarmarBlue microplate assay. Drug-resistant regions of the gyrA and gyrB genes from the drug-resistant strains were sequenced. The transcription level of the efflux pump genes was monitored using qRT-PCR. All the tested strains were resistant to LFX. The drug-resistant regions from the gyrA and gyrB genes showed no mutation associated with LFX resistance. CCCP, DCC, VP, and RSP increased the susceptibility of 93.3% (56/60), 91.7% (55/60), 85% (51/60), and 83.3% (50/60) isolates to LFX by 2 to 32-fold, respectively. Elevated transcription of seven efflux pump genes was observed in isolates with a high reduction in LFX MIC values in the presence of efflux pump inhibitors. Efflux pump inhibitors can improve the antibacterial activity of LFX against M. abscessus in vitro. The overexpression of efflux-related genes in LFX-resistant isolates suggests that efflux pumps are associated with the development of LFX resistance in M. abscessus.

Potentiation and Mechanism of Berberine as an Antibiotic Adjuvant Against Multidrug-Resistant Bacteria

The growing global apprehension towards multi-drug resistant (MDR) bacteria necessitates the development of innovative strategies to combat these infections. Berberine (BER), an isoquinoline quaternary alkaloid derived from various medicinal plants, has surfaced as a promising antibiotic adjuvant due to its ability to enhance the effectiveness of conventional antibiotics against drug-resistant bacterial strains. Here, we overview the augmenting properties and mechanisms of BER as an adjunctive antibiotic against MDR bacteria. BER has been observed to exhibit synergistic effects when co-administered with a range of antibiotics, including β-lactams, quinolones, aminoglycosides, tetracyclines, macrolides, lincosamides and fusidic acid. The adjunctive properties of BER led to an increase in antimicrobial effectiveness for these antibiotics against the corresponding bacteria, a decrease in minimal inhibitory concentrations, and even the reversal from resistance to susceptibility sometimes. The potential mechanisms responsible for these effects included the inhibition of antibiotic efflux, the disruption of biofilm formation, the modulation of host immune responses, and the restoration of gut microbiota homeostasis. In brief, BER demonstrated significant potential as an antibiotic adjuvant against MDR bacteria and is a promising candidate for combination therapy. Further research is necessary to fully elucidate its mechanism of action and address the challenges associated with its clinical application.

Antibacterial and immunological properties of piperine evidenced by preclinical studies: a systematic review

Aim: To review in vitro, in vivo, and in silico studies examining the antibacterial and immunomodulatory properties of piperine (PPN). Methods: This systematic review followed PRISMA guidelines, and five databases were searched. Results: A total of 40 articles were included in this study. Six aspects of PPN activity were identified, including antibacterial spectrum, association with antibiotics, efflux pump inhibition, biofilm effects, protein target binding, and modulation of immune functions/virulence factors. Most studies focused on Mycobacterium spp. and Staphylococcus aureus. Cell lineages and in vivo models were employed to study PPN antibacterial effects. Conclusion: We highlight PPN as a potential adjuvant in the treatment of bacterial infections. PPN possesses several antibacterial properties that need further exploration to determine the mechanisms behind its pharmacological activity.

The potential role of drug transporters and amikacin modifying enzymes in M. avium

OBJECTIVES

Mycobacterium avium (M. avium) complex bacteria cause opportunistic infections in humans. Treatment yields cure rates of 60% and consists of a macrolide, a rifamycin, and ethambutol, and in severe cases, amikacin. Mechanisms of antibiotic tolerance remain mostly unknown. Therefore, we studied the contribution of efflux and amikacin modification to antibiotic susceptibility.

METHODS

We characterised M. avium ABC transporters and studied their expression together with other transporters following exposure to clarithromycin, amikacin, ethambutol, and rifampicin. We determined the effect of combining the efflux pump inhibitors berberine, verapamil and CCCP (carbonyl cyanide m-chlorophenyl hydrazone), to study the role of efflux on susceptibility. Finally, we studied the modification of amikacin by M. avium using metabolomic analysis.

RESULTS

Clustering shows conservation between M. avium and M. tuberculosis and transporters from most bacterial subfamilies (2-6, 7a/b, 10-12) were found. The largest number of transporter encoding genes was up-regulated after clarithromycin exposure, and the least following amikacin exposure. Only berberine increased the susceptibility to clarithromycin. Finally, because of the limited effect of amikacin on transporter expression, we studied amikacin modification and showed that M. avium, in contrast to M. abscessus, is not able to modify amikacin.

CONCLUSION

We show that M. avium carries ABC transporters from all major families important for antibiotic efflux, including homologues shown to have affinity for drugs included in treatment. Efflux inhibition in M. avium can increase susceptibility, but this effect is efflux pump inhibitor- and antibiotic-specific. Finally, the lack of amikacin modifying activity in M. avium is important for its activity.

Characterization of DNA Gyrase Activity and Elucidation of the Impact of Amino Acid Substitution in GyrA on Fluoroquinolone Resistance in Mycobacterium avium

Mycobacterium avium, a member of the M. avium complex (MAC), is the major pathogen contributing to nontuberculous mycobacteria (NTM) infections worldwide. Fluoroquinolones (FQs) are recommended for the treatment of macrolide-resistant MACs. The association of FQ resistance and mutations in the quinolone resistance-determining region (QRDR) of gyrA of M. avium is not yet clearly understood, as many FQ-resistant clinical M. avium isolates do not have such mutations. This study aimed to elucidate the role of amino acid substitution in the QRDR of M. avium GyrA in the development of FQ resistance. We found four clinical M. avium subsp. hominissuis isolates with Asp-to-Gly change at position 95 (Asp95Gly) and Asp95Tyr mutations in gyrA that were highly resistant to FQs and had 2- to 32-fold-higher MICs than the wild-type (WT) isolates. To clarify the contribution of amino acid substitutions to FQ resistance, we produced recombinant WT GyrA, GyrB, and four GyrA mutant proteins (Ala91Val, Asp95Ala, Asp95Gly, and Asp95Tyr) to elucidate their potential role in FQ resistance, using them to perform FQ-inhibited DNA supercoiling assays. While all the mutant GyrAs contributed to the higher (1.3- to 35.6-fold) FQ 50% inhibitory concentration (IC50) than the WT, Asp95Tyr was the most resistant mutant, with an IC50 15- to 35.6-higher than that of the WT, followed by the Asp95Gly mutant, with an IC50 12.5- to 17.6-fold higher than that of the WT, indicating that these amino acid substitutions significantly reduced the inhibitory activity of FQs. Our results showed that amino acid substitutions in the gyrA of M. avium contribute to FQ resistance. IMPORTANCE The emergence of fluoroquinolone (FQ) resistance has further compounded the control of emerging Mycobacterium avium-associated nontuberculous mycobacteria infections worldwide. For M. avium, the association of FQ resistance and mutations in the quinolone resistance-determining region (QRDR) of gyrA is not yet clearly understood. Here, we report that four clinical M. avium isolates with a mutation in the QRDR of gyrA were highly resistant to FQs. We further clarified the impact of mutations in the QRDR of GyrA proteins by performing in vitro FQ-inhibited DNA supercoiling assays. These results confirmed that, like in Mycobacterium tuberculosis, mutations in the QRDR of gyrA also strongly contribute to FQ resistance in M. avium. Since many FQ-resistant M. avium isolates do have these mutations, the detailed molecular mechanism of FQ resistance in M. avium needs further exploration.

Antibiotic Resistance Influences Growth Rates and Cross-Tolerance to Lactic Acid in Escherichia coli O157:H7 H1730

Escherichia coli O157:H7-contaminated beef has been implicated in numerous foodborne outbreaks. Contamination occurs despite the use of antimicrobial interventions such as lactic acid (LA). In addition, resistance to antibiotics such as ampicillin and streptomycin among isolates has been frequently reported. The influence of antibiotic resistance (ABR) on growth rates and cross-tolerance of lettuce isolate E. coli O157:H7 H1730 to LA was evaluated. Antibiotic-resistant strain variants were generated by conferring resistance to either ampicillin (ampC) or streptomycin (strepC) or both ampicillin and streptomycin (ampC strepC) through incremental exposure to the antibiotics. Ampicillin resistance was also conferred by plasmid transformation to generate the ampP and ampP strepC strains. The minimum inhibitory concentration of LA on all the strains evaluated was 0.375% v/v. The lag phase duration of all strains except E. coli O157:H7 ampP strepC increased with increasing concentration of LA. The ampP strepC and ampC strains were most tolerant to 5% LA with declines in the cell population of 2.86 and 2.56 log CFU/mL, respectively (p < 0.05). The ampP strepC strain was the most tolerant when evaluated by the live/dead viability assay. The addition of the efflux pump inhibitor, carbonyl cyanide m-chlorophenylhydrazone, with 2.5% LA resulted in a significant increase in sensitivity in the no resistance (NR) wild-type and ampC strains, resulting in 6.62 and 6.65 log CFU/mL reduction, respectively, while the highly tolerant ampP strepC strain had a 2.90 log CFU/mL decrease. Tolerance to LA was significantly influenced by both the ABR profile of the strain and LA concentration. The results from this study indicate that E. coli O157:H7 strains with certain ABR profiles might be more tolerant to LA.

Environmental risk characteristics of bacterial antibiotic resistome in Antarctic krill

Antibiotic resistance genes (ARGs) are ubiquitous in nature, especially in the current era of antibiotic abuse, and their existence is a global concern. In the present study, we discovered that Antarctic krill-related culturable bacteria are resistant to β-lactam, tetracyclines, aminoglycosides, and sulphamethoxazole/trimethoprim based on the antibiotic efflux mechanism. In addition, the co-occurrence of ARGs with insertion sequence (IS) (tnpA, IS91) and Intl1 on the isolates and the phylogenetic analysis results of the whole-genome revealed low-frequency ARG transfer events, implying the transferability of these ARGs. These findings provide an early warning for the wide assessment of Antarctic microbiota in the spread of ARGs. Our work provides novel insights into understanding ARGs in culturable host-associated microorganisms, and their ecological risks and has important implications for future risk assessments of antibiotic resistance in extreme environments.

Efflux Pump Inhibitors Against Nontuberculous Mycobacteria

Over the last years, nontuberculous mycobacteria (NTM) have emerged as important human pathogens. Infections caused by NTM are often difficult to treat due to an intrinsic multidrug resistance for the presence of a lipid-rich outer membrane, thus encouraging an urgent need for the development of new drugs for the treatment of mycobacterial infections. Efflux pumps (EPs) are important elements that are involved in drug resistance by preventing intracellular accumulation of antibiotics. A promising strategy to decrease drug resistance is the inhibition of EP activity by EP inhibitors (EPIs), compounds that are able to increase the intracellular concentration of antimicrobials. Recently, attention has been focused on identifying EPIs in mycobacteria that could be used in combination with drugs. The aim of the present review is to provide an overview of the current knowledge on EPs and EPIs in NTM and also, the effect of potential EPIs as well as their combined use with antimycobacterial drugs in various NTM species are described.