Anti-pseudomonad Activity of Manuka Honey and Antibiotics in a Specialized ex vivo Model Simulating Cystic Fibrosis Lung Infection

Abstract

Pseudomonas aeruginosa causes problematic chronic lung infections in those suffering from cystic fibrosis. This is due to its antimicrobial resistance mechanisms and its ability to form robust biofilm communities with increased antimicrobial tolerances. Using novel antimicrobials or repurposing current ones is required in order to overcome these problems. Manuka honey is a natural antimicrobial agent that has been used for many decades in the treatment of chronic surface wounds with great success, particularly those infected with P. aeruginosa . Here we aim to determine whether the antimicrobial activity of manuka honey could potentially be repurposed to inhibit pulmonary P. aeruginosa infections using two ex vivo models. P. aeruginosa isolates ( n = 28) from an international panel were tested for their susceptibility to manuka honey and clinically relevant antibiotics (ciprofloxacin, ceftazidime, and tobramycin), alone and in combination, using conventional antimicrobial susceptibility testing (AST). To increase clinical applicability, two ex vivo porcine lung (EVPL) models (using alveolar and bronchiolar tissue) were used to determine the anti-biofilm effects of manuka honey alone and in combination with antibiotics. All P. aeruginosa isolates were susceptible to manuka honey, however, varying incidences of resistance were seen against antibiotics. The combination of sub-inhibitory manuka honey and antibiotics using conventional AST had no effect on activity against the majority of isolates tested. Using the two ex vivo models, 64% (w/v) manuka honey inhibited many of the isolates where abnormally high concentrations of antibiotics could not. Typically, combinations of both manuka honey and antibiotics had increased antimicrobial activity. These results highlight the potential of manuka honey as a future antimicrobial for the treatment of pulmonary P. aeruginosa isolates, clearing potential infection reservoirs within the upper airway.

Antibacterial activity of varying UMF-graded Manuka honeys

“…Our data corroborate the measurable antimicrobial activity of Manuka honey against a spectrum of clinical isolates from skin and soft tissue sources, including those with multi-drug resistance such as MRSA, ESBL producers, CRE, and MDR P . aeruginosa [6, 27–30]. Lower MIC values were achieved against Staphylococcus species than with gram-negative pathogens, consistent with the overall trends of prior studies [3].…”

Antibiofilm Activity of Heather and Manuka Honeys and Antivirulence Potential of Some of Their Constituents on the DsbA1 Enzyme of Pseudomonas aeruginosa

“…The decrease in S. aureus , A. baumanii , E. coli , S. Enteriditis and P. aeruginosa biofilm formation observed for Heather honey is reported here for the first time. Manuka honey decreased biofilm formation in P. aeruginosa , E. faecalis , A. baumanii , and E. coli , in agreement with previous studies [ 45 , 46 , 47 , 48 , 49 ]. Its effect on K. pneumoniae and S. Enteriditis biofilms has not been previously reported.…”

“…This prompted us to test its activity against a range of Gram-positive and Gram-negative single-species biofilms. This was done using a crystal violet assay, a commonly-used indirect method of biofilm quantification [ 50 ], and in comparison with Manuka honey, already known for its ability to decrease bacterial biofilm formation [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. The decrease in S. aureus , A. baumanii , E. coli , S. Enteriditis and P. aeruginosa biofilm formation observed for Heather honey is reported here for the first time.…”

“…Both honeys have demonstrated antibacterial activity [ 36 , 38 , 39 ] and an inhibitory effect on polymicrobial biofilms [ 40 ]. Manuka honey can disrupt biofilm formation in several pathogens [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. To the best of our knowledge, the effect of Heather honey on monobacterial biofilms has never been reported, and neither has the potential affinity of Manuka nor Heather honey constituents for DsbA been predicted.…”

Exposure to a Manuka Honey Wound Gel Is Associated With Changes in Bacterial Virulence and Antimicrobial Susceptibility

“…The effect of sub-lethal exposure to manuka honey has received relatively little research attention although stepwise training experiments using planktonic cultures of Escherichia coli, P. aeruginosa, S. aureus and S. epidermidis suggest only transient reductions in sensitivity to honey ( Blair et al, 2009 ; Cooper et al, 2010 ). The anti-biofilm potential of manuka honey has been described ( Maddocks et al, 2012 ; Lu et al, 2019 ; Roberts et al, 2019 ), although elevations in imipenem MIC of up to 4-fold and increased biofilm forming potential have been observed in cultures derived from honey exposed sessile communities ( Camplin and Maddocks, 2014 ). Passaging experiments using other antimicrobials have demonstrated that adaptation can manifest in ways other than through changes in drug sensitivity ( Latimer et al, 2012 ; Lu et al, 2014 ; Henly et al, 2019 ).…”