Antibiotic resistance and protease production by Photorhabdus luminescens and Xenorhabdus poinarii bacteria symbiotic with entomopathogenic nematodes: variation among species and strains

Bacteria in the genera Photorhabdus and Xenorhabdus are highly pathogenic to insects and are symbiotically associated with nematodes in the genera Heterorhabditis and Steinernema, respectively. We compared extracellular protease production and resistance to antibiotics (chloramphenicol, erythromycin, neomycin and tetracycline) for 32 isolates of P. luminescens and 11 isolates of X. poinarii taken from nematodes isolated from soil in southern New Jersey. P. luminescens produced greater amounts of protease, and was more resistant to erythromycin and less resistant to neomycin than X. poinarii. No interspecific differences in resistance to chloramphenicol or tetracycline were detected. Variability within species was not related to the site, habitat or soil core from which the isolates were obtained, and was not associated with variation in the color of the host cadaver for P. luminescens. Resistance to erythromycin was positively correlated with resistance to both neomycin and tetracycline for P. luminescens, but was negatively correlated with resistance to neomycin for X. poinarii. Antibiotic resistance profiles and extracellular protease production might be useful characteristics for distinguishing among species and strains of these bacteria, probably have ecological significance with respect to intra- and interspecific competition within host cadavers, and could have implications for the utility of these organisms for biological control.