Select β-lactam combinations exhibit synergy against Mycobacterium abscessus in vitro

Abstract

18Mycobacterium abscessus (Mab) is a nontuberculous mycobacterium that causes 19 invasive pulmonary infections in patients with structural lung disease. Mab is intrinsically 20 resistant to several classes of antibiotics and an increasing number of strains isolated 21 from patients exhibit resistance to most antibiotics considered for treatment of Mab 22 infections. Therefore, there is an unmet need for new regimens with improved efficacy 23 to treat this disease. Synthesis of the essential cell wall peptidoglycan in Mab is 24 achieved via two enzyme classes, L,D-and D-D-transpeptidases, with each class 25 preferentially inhibited by different subclasses of β-lactam antibiotics. We hypothesized 26 that a combination of two β-lactams that comprehensively inhibit the two enzyme 27 classes will exhibit synergy in killing Mab. Paired combinations of antibiotics tested for in 28 vitro synergy against Mab included dual β-lactams, a β-lactam and a β-lactamase 29 inhibitor, and a β-lactam and a rifamycin. Of the initial 206 combinations screened, 24 30 pairs exhibited synergy. 13/24 pairs were combinations of two β-lactams. 12/24 pairs 31 brought the minimum inhibitory concentrations of both drugs to within the therapeutic 32 range. Additionally, synergistic drug pairs significantly reduced the frequency of 33 selection of spontaneous resistant mutants. These novel combinations of currently-34 available antibiotics may offer viable immediate treatment options against highly-35 resistant Mab infections.36Mycobacterium abscessus (Mab) is considered to be among the most virulent of the 38 rapidly-growing nontuberculous mycobacteria (NTM). It may be environmentally or 39 nosocomially acquired (1) and can lead to severe and invasive pulmonary infections in 40 immunocompromised patients or those with structural lung diseases, such as 41 bronchiectasis or cystic fibrosis (CF). In the CF population, invasive Mab infections are 42 associated with rapid lung function decline (2-4), so adequate treatment of these 43 infections is paramount. Mab is intrinsically resistant to several classes of antibiotics 44 and the percentage of clinical isolates exhibiting resistance to the few drugs currently 45 available to treat this infection is steadily increasing (5-8). Sputum culture conversion 46 rates as low as 25% have been described with antibiotic treatment alone (9) and the 47 52 based on empirical evidence, as few systematic clinical trials have been performed to 53 elucidate the optimal therapeutic regimen against Mab. It is also frequently necessary in 54 clinical practice to tailor treatment regimens based on the resistance profiles of 55 individual Mab isolates, as the high degree of variability in antibiotic resistance observed 56 among Mab strains often precludes use of a standardized regimen (10). 58Macrolide antibiotics have historically been considered the backbone of treatment 59 against many NTMs, including Mab (2, 12). However, two of the three Mab subspecies, 60 abscessus and bolletii, harbor a functional erm(41) g...

Effect of Amoxicillin in combination with Imipenem-Relebactam against Mycobacterium abscessus

“…This is of note, since relebactam is a derivative of avibactam, the difference in inhibition efficacy is unusual 29 . This is possibly due to the additive effect between amoxicillin and imipenem alongside relebactam aiding in reducing the overall inhibitory concentrations, whereas www.nature.com/scientificreports www.nature.com/scientificreports/ the combination of ceftazidime-avibactam is less potent since M. abscessus is more resistant to ceftazidime than imipenem, reducing this additive effect 22 .…”

“…This was repeated using a varying concentration of nitrocefin (1-500 µM) with a shorter range of relebactam concentrations (0, 0.5, 0.75, 1 and 2.5 µM) and initial velocities (v i ) were plotted against substrate concentration. Data analysis was performed as previously described 22,26 . Data analysis was conducted using Graphpad Prism 7.…”

Development of a penem antibiotic against Mycobacteroides abscessus

“…This enzyme hydrolyzes many β-lactam antibiotics currently used to treat bacterial infections and, therefore, contributes to its inherent resistance to many antibiotics in the class 18 . Co-administration of the β-lactamase inhibitor avibactam inhibits Bla Mab and can reduce the MIC of β-lactam antibiotics with initially high MICs 15,[19][20][21] . To assess if avibactam potentiates the activity of T405 against M. abscessus, we determined the MIC of T405 in combination with avibactam against reference strain ATCC 19977 and 10 clinical isolates.…”

“…The M. abscessus reference strain ATCC 19977 (ATCC, Manassas, VA) as well as 20 deidentified clinical strains obtained from patients at the Johns Hopkins Hospital 15,16 were used for this study. The clinical isolates have been identified to the sub-species level 26 and the MICs of many other β-lactams against these strains have been published 15,21 . The strains were grown in Middlebrook 7H9 broth (Difco) supplemented with 0.5% glycerol, 10% albumin-dextrose-NaCl enrichment, and 0.05% Tween-80, at 37°C with constant shaking at 220 RPM in an orbital shaker.…”

Alternative and Experimental Therapies of Mycobacterium abscessus Infections

“…Avibactam may also directly inhibit L,D-transpeptidases [ 57 ], which may explain why its addition to imipenem is more effective then imipenem alone. Several dual-β-lactam combinations have indeed shown synergy against clinical isolates in vitro, i.e., imipenem with cefoxitin or cefdinir, as well as with avibactam [ 22 ]. Similar synergy was shown in a murine chronic pulmonary infection model [ 23 ].…”