Date Full Report Received09/24/2014
Date Abstract Report Received09/24/2014
InvestigationInstitution: Food and Feed Safety Research Unit, USDA-ARS-SPA
Primary Investigator: Robin C. Anderson
Co-Investigators: Regina C.S. Mendonca, Mark Rasmussen
Funded ByNational Pork Board
Naturally occurring efflux pump inhibitors have been shown to significantly inhibit the activity of efflux pumps contributing to antimicrobial resistance by many bacteria, particularly against Gram-positive staphylococci and streptococci. For instance, the degradation of chlorophylls by anaerobic bacteria yields the degradation products pheophoride-a and pyropheophorbide-a and these are able to inhibit efflux pumps thereby counter-acting this resistance mechanism. Commercially reared pigs generally do not eat substantially amounts of feeds containing chlorophyll but it is not known if other naturally occurring efflux pump inhibitors may be present in their gut. Moreover, even if efflux pump inhibitors are absent in most pig diets it would be easy to supplement their diets with chlorophylls (water soluble extracts or pellets) if this were determined to be a practical way of increasing the sensitivity of otherwise antimicrobial resistant bacteria to important antimicrobials. This research was conducted to determine 1) if efflux pump inhibitors are already present and operative in the gut of grower pigs; 2) if naturally present or added efflux pump inhibitors can counteract resistance expressed by important Gram-negative and Gram-positive bacteria and 3) determine if efflux inhibitors can be developed into an inexpensive technology to preserve and enhance the efficacy of currently available antibiotics. Results from the present study provide evidence that as yet unidentified compounds affecting antibiotic resistance are present in gut contents of commercially reared pigs but further characterization of their activity is needed as the activity appears be highly specific to individual bacterial strains and with only certain antibiotics. Results further indicate that feeding chlorophyll as a source or precursor of some known efflux pump inhibitors may indeed promote a decrease in antibiotic resistance but again the activity by these potential affecter compounds appears to be highly strain and antibiotic dependent and even affecting an increase in resistance in some cases. Consequently, it is unlikely at the present time that the efflux pump inhibitors tested in the present study can be developed into an inexpensive technology to preserve and enhance the efficacy of currently available antibiotics. Results from the present study do show, however, that as yet undefined factors normally found within the gut of commercially reared pigs can have a marked impact on resistance thus providing evidence that it may be more relevant to evaluate resistance at a functional level, as it occurs in the gut environment, rather than looking solely at the genetic and metabolic capability of a microbe when assayed in pure culture.