Further research is required to explore the detailed mechanisms. “
“l-Asparaginase-producing microbes are conventionally screened on phenol red l-asparagine-containing plates. However, sometimes the contrast of the zone obtained (between yellow and pink) is not very sharp and distinct. In the present investigation, an improved method for screening of the microorganisms producing extracellular l-asparaginase is reported wherein bromothymol blue (BTB) is incorporated as pH indicator in l-asparagine-containing medium instead of phenol red. Plates containing BTB at acidic pH are yellow and turn dark blue at alkaline Selleck RG 7204 pH. Thus, a dense dark blue zone is formed around microbial colonies producing l-asparaginase, differentiating between enzyme
producers and non-producers. The present method is more sensitive and accurate than the conventional method for screening of both fungi and bacteria producing extracellular l-asparaginase. Furthermore, BTB gives a transient green colour at neutral pH (7.0) and dark blue colour at higher pH 8.0–9.0, indicating the potency of the microorganism for l-asparaginase production. P450 inhibitor “
“Studies of enterohemorrhagic Escherichia
coli (EHEC) infection mechanisms using mammals require large numbers of animals and are both costly and associated with ethical problems. Here, we evaluated the pathogenic mechanisms of EHEC in the silkworm model. Injection of a clinically isolated EHEC O157:H7 Sakai into either the silkworm hemolymph or intraperitoneal fluid of mice killed the host animals. EHEC O157:H7 Sakai deletion mutants of the rfbE gene, which encodes perosamine synthetase, a monosaccharide
component synthetase of the O-antigen, or deletion mutants of the waaL gene, which encodes O-antigen ligase against the lipid A-core region of lipopolysaccharide (LPS), had attenuated killing ability in both silkworms and mice. Introduction of the rfbE gene or the waaL gene into the respective mutants Carnitine palmitoyltransferase II restored the killing ability in silkworms. Growth of both mutants was inhibited by a major antimicrobial peptide in the silkworm hemolymph, moricin. The viability of both mutants was decreased in swine serum. The bactericidal effect of swine serum against both mutants was inactivated by heat treatment. These findings suggest that the LPS O-antigen of EHEC O157:H7 plays an important defensive role against antimicrobial factors in the host body fluid and is thus essential to the lethal effects of EHEC in animals. Infectious diseases caused by enterohemorrhagic Escherichia coli (EHEC) O157:H7 are a serious clinical problem and are associated with encephalopathy and nephropathy (Tarr, 1995; Law, 2000). An understanding of the molecular mechanisms of EHEC O157:H7 virulence is important for establishing effective therapeutic strategies. Unlike other E. coli strains, EHEC produces Shiga toxins and hemolysins. Shiga toxins are encoded by the stx1 and stx2 genes on the phage DNA that is integrated into the EHEC genome (Sato et al.