Xenorhabdus nematophila, an entomopathogenic bacterium that symbiotically associates with the entomoparasitic nematode Steinernema carpocapsae, was studied to determine its physiological parameters of glucose utilization. X. nematophila was cultured in chemically defined media containing various concentrations of glucose under optimal conditions utilizing a two-liter fermentation system. Specific growth rates were obtained from each glucose batch. Specific growth rates and their associated glucose concentrations were used to determine physiological parameters. These parameters include the bacterium’s substrate utilization constant (Ks) and its maximum specific growth rate (μmax). The bacteria exhibited a Ks value of 2.02 mg/L suggesting that X. nematophila has a high affinity for glucose. The μmax of Xenorhabdus was determined to be 1.03 h−1. Further research is needed to determine if microbial affinities to different substrates have any influence on biological relationships (symbiosis, pathogenicity, parasitism, etc.) between prokaryotes and higher organisms.