Penicillin and Streptomycin Affect the Microflora of the Intestinal Tract of Pigs

Abstract

IT is generally accepted that certain antibiotics stimulate growth in swine and poultry. Furthermore, many data have been published which indicate that the mode of action of antibiotics in stimulating growth is either directly or indirectly associated with the microflora in the intestinal tract of the host. Luckey (1952) reported that germ-free chicks did not favorably respond to either streptomycin, sulfasuxidine, chloromycetin, bacitracin, terramycin or penicillin whereas conventional birds gave a positive growth response when these antibiotics were fed. From these results heimplied that antibiotics effect a growth response in conventional birds by acting upon some system connected either directly or indirectly to the microflora of the host. McGinnis (1950) stated that growth acceleration, when antibiotics are fed, might be a result of either: (1) reduction in total number of bacteria in the intestinal tract, (2) synthesis of vitamins by bacteria; (3) the inhibition of either pathogenic or toxin producing bacteria. Groschke (1950) suggested that antibiotics stinmlate growth in chicks by changing the intestinal microflora from undesirable to desirable types of bacteria.