Aim:The objective of this study was to assess if avibactam, a new β-lactamase inhibitor, can restore the potency of carbapenems, a sub-class of β-lactams, against Mycobacterium abscessus clinical isolates. Materials & methods: 28 M. abscessus clinical isolates that are resistant to multiple drugs currently used to treat its infection were included. MIC of carbapenems alone and in combination with avibactam against these strains were determined. Results: Tebipenem, an oral carbapenem, and ertapenem and panipenem exhibited the greatest shift in MIC when supplemented with avibactam. Conclusion: Avibactam restores MICs of tebipenem, ertapenem and panipenem against M. abscessus to therapeutically achievable concentrations and raises the possibility of usefulness of these carbapenems to treat drug-resistant M. abscessus infections. Mycobacterium abscessus is a rapidly growing nontuberculous mycobacterium found widely in soil and water and can cause a spectrum of infections [1]. Prevalence of M. abscessus infections in the lungs of people with chronic conditions, such as cystic fibrosis is significant and can often lead to serious morbidity [2]. A survey revealed that M. abscessus is present in the sputum of approximately 13% of cystic fibrosis patients in the USA [3]. Among nontuberculous mycobacterium lung infections, M. abscessus is one of the prevalent species and often leads to a chronic and incurable disease [4][5][6]. Drug resistance in M. abscessus is steadily rising globally, making it increasingly difficult to manage infections with these strains [7]. Therefore, new drugs and novel regimens are acutely needed to treat infections with M. abscessus. An ideal new drug would inhibit a novel target so that it can be effective against M. abscessus strains that are resistant to currently used drugs.The peptidoglycan is an Achilles' heel of bacteria as agents that inhibit its biosynthesis, namely β-lactams and glycopeptides, comprise some of the most widely used class of antibacterials in modern medicine. β-lactams derive their activity by preventing formation of linkage between peptide side chains by inhibiting the transpeptidases that catalyze this reaction [8]. Recently it was demon strated that majority of the linkages in the peptidoglycan layer of M. abscessus are generated by LD-transpeptidases [9] and that this class of enzyme is selectively more susceptible to the carbapenem class of β-lactams [10][11][12]. Imipenem, a carbapenem, has superior activity compared with For reprint orders, please contact: reprints@futuremedicine.com

Mycobacterium abscessusis a nontuberculous mycobacterium that causes invasive pulmonary infections in patients with structural lung disease.M. abscessusis intrinsically resistant to several classes of antibiotics, and an increasing number of strains isolated from patients exhibit resistance to most antibiotics considered for treatment of infections by this mycobacterium. Therefore, there is an unmet need for new regimens with improved efficacy to treat this disease. Synthesis of the essential cell wall peptidoglycan inM. abscessusis achieved via two enzyme classes,l,d- andd,d-transpeptidases, with each class preferentially inhibited by different subclasses of β-lactam antibiotics. We hypothesized that a combination of two β-lactams that comprehensively inhibit the two enzyme classes will exhibit synergy in killingM. abscessus. Paired combinations of antibiotics tested forin vitrosynergy againstM. abscessusincluded dual β-lactams, a β-lactam and a β-lactamase inhibitor, and a β-lactam and a rifamycin. Of the initial 206 combinations screened, 24 pairs exhibited synergy. A total of 13/24 pairs were combinations of two β-lactams, and 12/24 pairs brought the MICs of both drugs to within the therapeutic range. Additionally, synergistic drug pairs significantly reduced the frequency of selection of spontaneous resistant mutants. These novel combinations of currently available antibiotics may offer viable immediate treatment options against highly-resistantM. abscessusinfections.

there is no preclinical mouse model to investigate pulmonary Mycobacteroides abscessus (formerly Mycobacterium abscessus) infection in an immunocompetent mouse strain, especially in the context of antibiotic testing and regimen development. We developed a mouse model of pulmonary M. abscessus infection using the aerosolized route of infection that leads to an increase in bacterial burden postimplantation and develops pathology as a result. in this mouse model, treatment with corticosteroid allows for initial proliferation and sustained M. abscessus pulmonary infection and permits evaluation of efficacies of antibiotics. Administration of corticosteroids that permitted higher levels of bacterial burden in the lungs were more likely to have pathology. treatment of mice with antibiotics administered intranasally or subcutaneously significantly reduced lung M. abscessus burden. in addition to the reference strain, independent clinical isolates of M. abscessus also readily establish infection and proliferate in the lungs of mice in this model. In the setting of structural lung conditions such as cystic fibrosis, bronchiectasis, and COPD, Mycobacteroides abscessus (formerly Mycobacterium abscessus) can cause chronic pulmonary infection 1,2 that is often incurable and associated with rapid lung function decline 3-5. There is a current interest in developing new drugs and regimens to treat M. abscessus infection, as the cure rate with existing antibiotics is only 30-50% 6. While there have been many exciting demonstrations of in vitro potencies of antibiotics against M. abscessus 7-13 , it has also been established that potency observed in vitro for M. abscessus often does not translate to an equivalent clinical efficacy in the case of pulmonary infections 3. This highlights the need for a preclinical animal model to evaluate experimental antibiotics. A mammalian model that recapitulates aerosol infection leading to progressive M. abscessus burden and development of lung pathology as observed in human disease would facilitate preclinical studies of antibiotic efficacy and M. abscessus genetic determinants for virulence. In investigations of Mycobacterium tuberculosis (M. tuberculosis), several studies have demonstrated that aerosol infected C3HeB/FeJ mice closely mimic human pulmonary pathology 14-17. However, when infected with M. abscessus, these mice are able to clear the infection 18. Other immunocompetent mouse strains also clear the infection over time, although certain genetically manipulated immunocompromised strains were able to maintain bacterial burden 19-22. This is a compromise in favor of perpetuating the infection, but at a loss of immune cells and inflammatory markers normally observed in response to infection. Therefore, as mice are unable to mount an immune response, this precludes evaluation of critical aspects of host-pathogen interactions and pathology development that may impact efficacy of antibiotic treatments. We hypothesized that transient pharmacologically-induced immune suppression of immunoco...

The incidence of nontuberculous mycobacterial diseases in the US is rising and has surpassed tuberculosis. Most notable among the nontuberculous mycobacteria is Mycobacteroides abscessus , an emerging environmental opportunistic pathogen capable of causing chronic infections. M. abscessus disease is difficult to treat and the current treatment recommendations include repurposed antibiotics, several of which are associated with undesirable side effects. In this study, we have evaluated the activity of omadacycline, a new tetracycline derivative, against M. abscessus using in vitro and in vivo approaches. Omadacycline exhibited an MIC 90 of 0.5 μg/ml against a panel of 32 contemporary M. abscessus clinical isolates several of which were resistant to antibiotics that are commonly used for treatment of M. abscessus disease. Omadacycline when combined with clarithromycin, azithromycin, cefdinir, rifabutin or linezolid also exhibited synergism against several M. abscessus strains and did not exhibit antagonism when combined with an additional nine antibiotics also commonly considered to treat M. abscessus disease. Concentration-dependent activity of omadacycline was observed in time-kill assessments. Efficacy of omadacycline was evaluated in a mouse model of lung infection against four M. abscessus strains. A dose equivalent to the 300 mg standard oral human dose was used. Compared to the untreated control group, within four weeks of treatment, 1 to 3 log 10 fewer M. abscessus colony forming units were observed in the lungs of mice treated with omadacycline. Treatment outcome was biphasic, with bactericidal activity observed after the first two weeks of treatment against all four M. abscessus strains.

Mycobacterium abscessus is an emerging pathogen capable of causing invasive pulmonary infections in patients with chronic lung diseases. These infections are difficult to treat, necessitating prolonged multidrug therapy, which is further complicated by extensive intrinsic and acquired resistance exhibited by clinical M. abscessus isolates. Therefore, development of novel treatment regimens effective against drug-resistant strains is crucial. Prior studies have demonstrated synergistic efficacy of several ␤-lactams against M. abscessus in vitro; however, these combinations have never been tested in an animal model of M. abscessus pulmonary disease. We utilized a recently developed murine system of sustained M. abscessus lung infection delivered via an aerosol route to test the bactericidal efficacy of four novel dual ␤-lactam combinations and one ␤-lactam/␤-lactamase inhibitor combination. All five of the novel combinations exhibited synergy and resulted in at least 6-log 10 reductions in bacterial burden in the lungs of mice at 4 weeks compared to untreated controls (P ϭ 0.038).

β-lactams are the most widely used antibiotics and are effective against a spectrum of pathogenic bacteria. Here, we focus on the state-of-the-art understanding of the molecular underpinnings that determine the overall efficacy of β-lactams against TB and include historical perspectives of this antibiotic class against this ancient disease. We summarize literature that describes why earlier generations of β-lactams are ineffective and the potential promise of newer β-lactams that exhibit improved efficacy against TB. Emerging evidence warrants renewed consideration of newer β-lactams in regimens for treatment of drug-resistant TB. © 2018 IUBMB Life, 70(9):881-888, 2018.

β-lactams, the most widely used class of antibiotics, are well-tolerated, and their molecular mechanisms of action against many bacteria are well-documented. Mycobacterium abscessus (Mab) is a highly drug-resistant rapidly-growing nontuberculous mycobacteria (NTM). Only in recent years have we started to gain insight into the unique relationship between β-lactams and their targets in Mab. In this mini-review, we summarize recent findings that have begun to unravel the molecular basis for overall efficacy of β-lactams against Mab and discuss emerging evidence that indicates that we have yet to harness the full potential of this antibiotic class to treat Mab infections.

Abstractβ-lactams are the most widely used antibiotic class to treat bacterial infections in humans. Mycobacteroides abscessus is an emerging pulmonary pathogen resistant to most antibiotics, including penicillins and cephalosporins. With no current FDA-approved treatment and cure rates <50%, there is a pressing need for effective therapies. Here we report T405, a new β-lactam of the penem subclass that exhibits potent activity against M. abscessus and a panel of drug-resistant strains isolated from cystic fibrosis patients. Additionally, in combination with the β-lactamase inhibitor avibactam, the rate of spontaneous resistance of M. abscessus to T405 approached the limit of detection. Lastly, we show the favorable pharmacokinetic profile of T405 in mice and the absence of toxicity at elevated dosage, which support the clinical potential of this compound.