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Expression of Cholera Toxin under Non-AKI Conditions in Vibrio cholerae El Tor Induced by Increasing the Exposed Surface of Cultures. Joaquín Sánchez, 2004.The regulatory systems controlling expression of the ctxAB genes encoding cholera toxin [CT] in the classical and El Tor biotypes of pathogenic Vibrio cholerae have been characterized and found to be almost identical . Notwithstanding this, special in vitro conditions, called AKI conditions, are required for El Tor bacteria to produce CT . The AKI conditions involve biphasic cultures.In phase 1 the organism is grown in a still tube for 4 h . Inphase 2 the medium is poured into a flask to continue growthwith shaking . Virtually no expression of CT occurs if this protocolis not followed . Here we demonstrated that CT expression takesplace in single-phase still cultures if the volume-to-surface-arearatio is decreased, both under air and under an inert atmosphere.The expression of key genes involved in the regulation of CTproduction was analyzed, and we found that the expression patternclosely resembles the in vivo expression pattern. Identification of a Broadly Active Phage Lytic Enzyme with Lethal Activity against Antibiotic-Resistant Enterococcus faecalis and Enterococcus faecium. Pauline Yoong, 2004.Enterococcus faecalis and Enterococcus faecium infections are increasingly difficult to treat due to high levels of resistance to antibiotics . PlyV12, a bacteriophage lytic enzyme, was isolated and shown to effectively kill both E . faecalis and E . faecium (including vancomycin-resistant strains), as well as other human pathogens . We propose its development and use as an alternative therapeutic tool . Transformation of Leuconostoc carnosum 4010 and Evidence for Natural Competence of the Organism. Søren Helmark, 2004.Plasmid transformation in Leuconostoc carnosum 4010 was analyzed . A successful transformation protocol for L . carnosum was established by modifying an existing protocol for Lactococcus lactis . Several parameters, including the number of generations that the cells had grown at the time of harvest, glycine concentration, the time of incubation for phenotypic expression, and the electrical field strength, were investigated and proved to have influence on the transformation frequency . Electrocompetence was found to be transient and to peak in the early exponential growth phase . Optimized conditions resulted in transformation frequencies of up to 6.7 x 105 transformants per microgram of plasmid DNA . A total of five plasmids in L . carnosum were successfully introduced and maintained . Interestingly, we discovered that DNA uptake was of a frequency of 3 x 10–6 to 19 x 10–6 transformants per CFU in the absence of an applied electrical field . We concluded that L . carnosum is naturally competent .
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