|RASMUSSEN, MARK - Iowa State University|
Submitted to: Journal of Antibiotics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2013
Publication Date: 2/11/2014
Citation: Kraatz, M., Whitehead, T.R., Cotta, M.A., Berhow, M.A., Rasmussen, M.A. 2014. Effects of chlorophyll-derived efflux pump inhibitor pheophorbide a and pyropheophorbide a on growth and macrolide antibiotic resistance of indicator and anaerobic swine manure bacteria. International Journal of Antibiotics. Available: http://dx.doi.org/10.1155/2014/185068.
Interpretive Summary: Antimicrobial compounds have been commonly used as feed additives for domestic animals to reduce infection and promote growth. Recent reports have suggested such feeding practices may result in increased microbial resistance to antibiotics, which can have an impact on human health. While many investigations have centered on antibiotic resistance in coliforms and other aerobic bacteria, less attention has been directed towards investigating antibiotic resistance in the anaerobic microflora found in the feces and stored manure of domestic animals which may serve as reservoirs of antibiotic resistance genes. As part of our project determining the antibiotic resistances of bacterial populations present in swine feces and manure storage pits, we investigated potential reduction of resistance using breakdown products of chlorophyll. Results of this study suggest that these compounds may naturally decrease bacterial resistance to the antibiotics erythromycin and tylosin.
Technical Abstract: Natural plant compounds, such as the chlorophyll a catabolites pheophorbide a (php) and pyropheophorbide a (pyp), are potentially active in the gastrointestinal tracts and wastes of livestock as antimicrobial resistance-modifying agents through inhibition of bacterial efflux pumps. To investigate whether php, a known efflux pump inhibitor, and pyp influences bacterial resistance, we determined their long-term effects on the aerobic and anaerobic MICs of erythromycin for erythromycin-naïve and highly resistant reference strains of clinically relevant indicator bacteria with macrolide or multidrug resistance efflux pumps. Pyp (0.5 and 50 µg ml^-1^) reduced the final MIC endpoint for Staphylococcus (S.) aureus ATCC 29213 and Escherichia (E.) coli P475.10.99.C3 by up to 1536 and 1024 µg erythromycin ml^-1^ or 1.4- and 1.2-fold, respectively. Estimation of growth parameters of S. aureus using spectrophotometry revealed that pyp exerted an intrinsic inhibitory effect under anaerobic conditions and was synergistically active, thereby potentiating the growth-retarding effect of erythromycin and partially reversing high-level erythromycin resistance. Anaerobe colony counts of total and erythromycin-resistant bacteria from stored swine manure samples on habitat-simulating media tended to be lower in the presence of 10 µg pyp ml^-1^. Tylosin, php and pyp were not detectable by HPLC in the manure or medium (php, pyp), whereas the background concentration in the medium of tylosin or a compound with the same retention time was 56.3±2.2 µg g^-1^ wet weight. This is the first study showing that pyp affects growth and the level of sensitivity to erythromycin of S. aureus, E. coli and anaerobic manure bacteria.