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Abstract Multidrug resistant (MDR) P. aeruginosa accounts for 35% of all P. aeruginosa isolated from respiratory samples of patients with cystic fibrosis (CF). The usefulness of β-lactam antibiotics for treating CF, such as carbapenems and later generation cephalosporins, is limited by the development of antibacterial resistance. A proven treatment approach is the combination of a β-lactam antibiotic with a β-lactamase inhibitor. New β-lactam/β-lactamase inhibitor combinations are available, but data are lacking regarding the susceptibility of MDR CF-associated P. aeruginosa (CFPA) to these new combination therapies. In this study we determined MIC values for three new combinations; imipenem-relebactam (I-R), ceftazidime-avibactam (CZA), and ceftolozane-tazobactam (C/T) against MDR CFPA (n = 20). The MIC90 of I-R, CZA, and C/T was 64/4, 32/4, and 16/8 (all µg/mL), respectively. The susceptibility of isolates to imipenem was not significantly improved with the addition of relebactam (p = 0.68). However, susceptibility to ceftazidime was significantly improved with the addition of avibactam (p

Abstract Background Honey has broad spectrum antibacterial activity against clinically important organisms and may be suitable for treating superficial bacterial infections. However, very little data are available describing potential interactions between honey and other topically applied agents such as antiseptics or essential oils. Methods Interactions between pairs of antibacterial agents were investigated by performing checkerboard assays and determining the fractional inhibitory concentration indices (FICIs). Interactions between the two monofloral honeys marri (from Corymbia calophylla) and manuka, and the antiseptic agents benzalkonium chloride, chlorhexidine digluconate, silver (I) nitrate, tea tree oil, and Eucalyptus polybractea oil were investigated against Staphylococcus aureus ATCC® 43300 and Pseudomonas aeruginosa ATCC® 27853. Results Additive or indifferent interactions (FICI 0.5—2) were observed for all combinations against both organisms tested, with the exception of chlorhexidine and honey. Chlorhexidine and marri honey showed an antagonistic relationship against S. aureus (median FICI 2.00, range 1.25—4.83). Similarly, chlorhexidine and manuka honey showed antagonism against S. aureus (median FICI 2.33, range 2.00—2.67). Conclusions With the exception of chlorhexidine, these data indicate that honey does not interfere with the antimicrobial activity of the tested agents, and that honey may be suitable for combination therapy with other topically applied antibacterial agents for treating superficial bacterial infections.