Observations on thein vitrosensitivity and resistance of Gram positive intestinal bacteria of farm animals to growth promoting antimicrobial agents

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Abstract
Results of qualitative in vitro sensitivity tests made with growth promoting antimicrobial agents on clostridia, lactobacilli and enteric streptococci, isolated from ceca of pigs, cattle and poultry, are summarized. The compounds were active in vitro against most of the 19 bacterial species studied. However, their activity spectra differed markedly. Only 4 bacterial species were naturally sensitive to all agents. The natural resistances, typical for many species and compounds, could be differentiated from the acquired resistances found with all growth promoters except avoparcin. High resistance and complex patterns of cross-resistance involving .gtoreq. 1 of the macrolide, lincosamide and streptogramin antibiotics were detected.