ABT-773: a new ketolide antibiotic

The In Vitro Antimicrobial Susceptibility of Borrelia burgdorferi sensu lato: Shedding Light on the Known Unknowns

Human Lyme borreliosis (LB) represents a multisystem disorder that can progress in stages. The causative agents are transmitted by hard ticks of the Ixodes ricinus complex that have been infected with the spirochete Borrelia burgdorferi sensu lato. Today, LB is considered the most important human tick-borne illness in the Northern Hemisphere. The causative agent was identified and successfully isolated in 1982 and, shortly thereafter, antibiotic treatment was found to be safe and efficacious. Since then, various in vitro studies have been conducted in order to improve our knowledge of the activity of antimicrobial agents against B. burgdorferi s. l. The full spectrum of in vitro antibiotic susceptibility has still not been defined for some of the more recently developed compounds. Moreover, our current understanding of the in vitro interactions between B. burgdorferi s. l. and antimicrobial agents, and their possible mechanisms of resistance remains very limited and is largely based on in vitro susceptibility experiments on only a few isolates of Borrelia. Even less is known about the possible mechanisms of the in vitro persistence of spirochetes exposed to antimicrobial agents in the presence of human and animal cell lines. Only a relatively small number of laboratory studies and cell culture experiments have been conducted. This review summarizes what is and what is not known about the in vitro susceptibility of B. burgdorferi s. l. It aims to shed light on the known unknowns that continue to fuel current debates on possible treatment resistance and mechanisms of persistence of Lyme disease spirochetes in the presence of antimicrobial agents.

Microorganisms as Shapers of Human Civilization, from Pandemics to Even Our Genomes: Villains or Friends? A Historical Approach

Universal history is characterized by continuous evolution, in which civilizations are born and die. This evolution is associated with multiple factors, among which the role of microorganisms is often overlooked. Viruses and bacteria have written or decisively contributed to terrible episodes of history, such as the Black Death in 14th century Europe, the annihilation of pre-Columbian American civilizations, and pandemics such as the 1918 Spanish flu or the current COVID-19 pandemic caused by the coronavirus SARS-CoV-2. Nevertheless, it is clear that we could not live in a world without these tiny beings. Endogenous retroviruses have been key to our evolution and for the regulation of gene expression, and the gut microbiota helps us digest compounds that we could not otherwise process. In addition, we have used microorganisms to preserve or prepare food for millennia and more recently to obtain drugs such as antibiotics or to develop recombinant DNA technologies. Due to the enormous importance of microorganisms for our survival, they have significantly influenced the population genetics of different human groups. This paper will review the role of microorganisms as "villains" who have been responsible for tremendous mortality throughout history but also as "friends" who help us survive and evolve.

Antibiotics: natural products essential to human health

For more than 50 years, natural products have served us well in combating infectious bacteria and fungi. Microbial and plant secondary metabolites helped to double our life span during the 20th century, reduced pain and suffering, and revolutionized medicine. Most antibiotics are either (i) natural products of microorganisms, (ii) semi-synthetically produced from natural products, or (iii) chemically synthesized based on the structure of the natural products. Production of antibiotics began with penicillin in the late 1940s and proceeded with great success until the 1970-1980s when it became harder and harder to discover new and useful products. Furthermore, resistance development in pathogens became a major problem, which is still with us today. In addition, new pathogens are continually emerging and there are still bacteria that are not eliminated by any antibiotic, e.g., Pseudomonas aeruginosa. In addition to these problems, many of the major pharmaceutical companies have abandoned the antibiotic field, leaving much of the discovery efforts to small companies, new companies, and the biotechnology industries. Despite these problems, development of new antibiotics has continued, albeit at a much lower pace than in the last century. We have seen the (i) appearance of newly discovered antibiotics (e.g., candins), (ii) development of old but unutilized antibiotics (e.g., daptomycin), (iii) production of new semi-synthetic versions of old antibiotics (e.g., glycylcyclines, streptogrammins), as well as the (iv) very useful application of old but underutilized antibiotics (e.g., teicoplanin).

Antimicrobial susceptibility of Borrelia burgdorferi sensu lato: what we know, what we don't know, and what we need to know

Human Lyme borreliosis is a multisystem disorder that can progress in stages and is transmitted by ticks of the Ixodes ricinus complex infected with the spirochete Borrelia burgdorferi sensu lato. Today, Lyme borreliosis is regarded as the most important human tickborne illness in the northern hemisphere. Soon after the causative agent was correctly identified and successfully isolated in 1982, antibiotic treatment was shown to be effective and since then a variety of in vitro and in vivo studies have been performed to further characterize the activity of antimicrobial agents against B. burgdorferi s.l. Although many antimicrobial agents have been tested for their in vitro activity against borreliae, the full spectrum of antibiotic susceptibility in B. burgdorferi s.l. has not been defined for many compounds. Moreover, our current understanding of possible antimicrobial resistance mechanisms in B. burgdorferi s.l. is limited and is largely founded on in vitro experiments on relatively few borrelial isolates. This review will summarize what is and what is not known about antimicrobial resistance in B. burgdorferi s.l. and will discuss open questions that continue to fuel the current debate on treatment-resistant Lyme borreliosis.

A novel ketolide class: Synthesis and antibacterial activity of a lead compound

Synthesis and antibacterial activity of a new class of ketolide antibiotics, exemplified by the prototype GW680788X (1), are described. The structure of (1) has been elucidated by spectroscopic analysis. The good antibacterial activity shown by (1) in comparison with clarithromycin prompted us to consider this compound as a lead molecule for further exploration.

Synthesis and antibacterial activity of 6-O-heteroarylcarbamoyl-11,12-lactoketolides

A new series of erythromycin A derivatives, the 6-O-heteroarylcarbamoyl-11,12-lactoketolides, with activity against macrolide-resistant streptococci, are described. Structurally, these macrolide antibiotics are characterized by a heteroaryl side chain attached to the macrolactone core through a carbamate linkage at the C6 position, as well as 11,12-gamma-lactone and 3-keto functionalities. The synthesis and antibacterial activity of this new series of ketolides are discussed.

Synthesis and antibacterial activity of C2-fluoro, C6-carbamate ketolides, and their C9-oximes

Novel C6-carbamate ketolides with C2-fluorination and C9-oximation have been synthesized. The best compounds in this series displayed MIC values of 0.03-0.12 microg/mL against streptococci containing erm and mef resistance determinants and 2-4 microg/mL against Haemophilus influenzae. Several compounds also showed measurable activity against erm(B)-containing enterococci with MIC values of 2-8 microg/mL. In vivo activity was adversely affected by fluorination, possibly as a result of increased serum protein binding.

Interaction of the new ketolide ABT-773 (cethromycin) with human polymorphonuclear neutrophils and the phagocytic cell line PLB-985 in vitro

A classical velocity centrifugation technique was used to study the in vitro uptake of the new ketolide ABT-773 by human polymorphonuclear neutrophils (PMNs) and a myelomonoblastic cell line, PLB-985, which can be differentiated into PMNs under certain culture conditions, compared to that of HMR 3004. ABT-773 was rapidly taken up by PMNs (cellular concentration to extracellular concentration ratio [C/E], about 34 at 30 s and up to 207 at 5 min), and uptake plateaued from 30 to 180 min (C/E, about 300). ABT-773 was accumulated significantly better than HMR 3004 from 5 to 180 min. Nondifferentiated PLB-985 cells (ND-PLB) accumulated significantly less ABT-773 and HMR 3004 than PMNs and PLB-985 cells differentiated into PMNs (D-PLB). Whatever the cell type and in contrast to the results obtained with HMR 3004, ABT-773 was mainly located in the cytosol (about 75%) and was rapidly released from loaded cells (about 40% at 5 min), followed by a plateau, likely owing to avid reuptake. Verapamil and H89, an inhibitor of protein kinase A, increased drug efflux. Uptake was sensitive to external pH, and the activation energy was moderate (about 50 kJ/mol). The existence of an active transport system on the PMN membrane was suggested by the following findings: concentration-dependent and saturable uptake (V(max), about 10,000 ng/2.5 x 10(6) PMNs/5 min; K(m), about 60 microg/ml) the inhibitory effects of PMN activators or inhibitors (phorbol myristate acetate, verapamil, Ni(2+)) and the significantly decreased levels of accumulation by killed cells and cells treated at low temperatures. In addition, various macrolides impaired ABT-773 uptake, contrary to the findings for the quinolone levofloxacin. ND- and D-PLB also presented saturation kinetics that defined an active transport system (V(max) and K(m) values were similar to those obtained with PMNs), but the activation pathway of the carrier system did not seem to be fully functional in ND-PLB. As has been observed with other erythromycin A derivatives, ABT-773 impaired oxidant production by phagocytes in a time- and concentration-dependent manner. These data extend our previous results on the existence of an active transport system common to all macrolides and ketolides, at least in PMNs.

Comparison of in vitro activities of ketolides, macrolides, and an azalide against the spirochete Borrelia burgdorferi

Two ketolides, three macrolides, and one azalide were tested in vitro against 17 isolates of the B. burgdorferi s.l. complex. As measured in micrograms per milliliter, activity was highest for cethromycin (MIC at which 90% of the tested isolates were inhibited [MIC(90)], 0.0019 micro g/ml) and telithromycin (MIC(90), 0.0078 micro g/ml). Electron-microscope analysis and time-kill studies also supported enhanced effectiveness of both ketolides.

Activities of ABT-773 against microaerophilic and fastidious organisms

ABT-773 was tested against 317 fastidious isolates; it inhibited 99% of organisms at a concentration of 4.0 microg/ml. With ampicillin-sulbactam and levofloxacin, only 2 and 6% of these strains, respectively, were resistant at the breakpoint. With clindamycin, penicillin G, and metronidazole, 22, 26, and 58% of the strains, respectively, were resistant.

Antibiotics in the treatment of acute exacerbations of chronic bronchitis

The benefit of antimicrobial therapy for patients with an acute exacerbation of chronic bronchitis (AECB) remains controversial for two main reasons. First, the distal airways of patients with chronic bronchitis are persistently colonised, even during clinically stable periods, with the same bacteria that have been associated with AECB. Second, bacterial infection is only one of several causes of AECB. These factors have led to conflicting analyses on the role of bacterial agents and the response to antimicrobial therapy of patients with AECB. An episode of AECB is said to be present when a patient with chronic obstructive pulmonary disease (COPD) experiences some combination of increased dyspnoea, increased sputum volume, increased sputum purulence and worsening lung function. While the average COPD patient experiences 2 - 4 episodes of AECB per year, some patients, particularly those with more severe airway obstruction, are more susceptible to these attacks than others. Bacterial agents appear to be particularly associated with AECB in patients with low lung function and those with frequent episodes accompanied by purulent sputum. Non-typeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis account for up to 50% of episodes of AECB. Gram-negative bacilli are more likely to occur in patients with more severe lung disease. Antibiotics have been used to ameliorate AECB, to prevent AECB and to prevent the long-term loss of lung function that characterises COPD. Numerous prevention trials have been conducted with fairly consistent results; antibiotics do not lessen the number of episodes of AECB but do reduce the number of days lost from work. Most antibiotic trials have studied the impact of treatment on episodes of AECB and results have been inconsistent, largely due to patient selection and end point definition. In patients with severe airway obstruction, especially in the presence of purulent sputum, antibiotic therapy significantly shortens the duration of symptoms and can be cost-effective. Over the past 50 years, virtually all classes of antimicrobial agents have been studied in AECB. Important considerations include penetration into respiratory secretions, spectrum of activity and antimicrobial resistance. These factors limit the usefulness of drugs such as amoxicillin, erythromycin and trimethoprim-sulfamethoxazole. Extended-spectrum oral cephalosporins, newer macrolides and doxycycline have demonstrated efficacy in clinical trials. Amoxicillin-clavulanate and flouoroquinolones should generally be reserved for patients with more severe disease. A number of investigational agents, including ketolides and newer quinolones, hold promise for treatment of AECB.