Comparison of the effects of different nutrient media on production of heat-stable enterotoxin-b by Escherichia coli.
Trypticase soy broth (TSB) has been commonly used to culture Escherichia coli strains for detection or harvest of heat-stable enterotoxin-b (STb); however, in our experience, the yields have been low. In this study, we compared STb yields resulting from growth in brain heart infusion broth (BHI) supplemented with 2% casamino acids (BHI-CA) with that from TSB. Since strains may concurrently express heat-labile enterotoxin (LT) and lincomycin has been reported to cause increased expression of LT, we also compared its effects on STb production. STb(+) clones had significantly higher production of STb when grown in BHI-CA compared to TSB, based on enzyme-linked immunosorbent assay (ELISA) conducted on cell-free supernatants. The superiority of BHI-CA to TSB was further tested on 17 porcine enterotoxigenic E. coli (ETEC) isolates, all positive for the STb gene (estB) by PCR. Cell-free supernatants of 100% of the ETEC isolates were detectably positive for STb by ELISA when grown in BHI-CA, in contrast to only 10 strains positive (59%) when TSB supernatants were analyzed. For all the samples, the amounts of STb expressed in BHI-CA based on ELISA were significantly higher than those from TSB (p<or=0.03). Incorporation of lincomycin at a concentration optimal for LT production into these media caused a significant decrease in STb levels, and use of both lincomycin and polymyxin B at these concentrations abolished detectable STb production altogether. We conclude that BHI-CA is a better medium for supporting STb production than is TSB. Culture in BHI-CA followed by testing by STb-ELISA is a useful combination for detecting STb production.
Erume
J
J
School of Veterinary Medicine and Biomedical Sciences, University of Nebraska - Lincoln, Fair St & East Campus Loop, Lincoln, NE 68583 - 0905, USA.
Berberov
E M
EM
Moxley
R A
RA
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001427:Bacterial Toxins / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D004768:Enterotoxins / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D004927:Escherichia coli Infections / Q000145:classification / Q000662:veterinary; D029968:Escherichia coli Proteins / Q000032:analysis / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics; D008034:Lincomycin / Q000494:pharmacology; D009268:Nalidixic Acid / Q000494:pharmacology; D011112:Polymyxin B / Q000494:pharmacology; D013552:Swine / Q000382:microbiology; D013553:Swine Diseases / Q000382:microbiology
D000900:Anti-Bacterial Agents; D001427:Bacterial Toxins; D003470:Culture Media; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D009268:Nalidixic Acid; D008034:Lincomycin; C027538:heat-labile enterotoxin, E coli; D011112:Polymyxin B