Effect of stress on production of heat labile enterotoxin by Escherichia coli.

Enterotoxigenic Escherichia coli (ETEC) is an important pathogen responsible for secretory diarrhoea. The production of heat labile enterotoxin (LT), by ETEC, is largely responsible for the pathogenesis of diarrhoea. In the present study we investigated the effect of stress factors such as temperature, pH, osmotic stress and nutritional limitation on the production of LT by ETEC using in-house GMI-ELISA. Four strains of E. coli consisting, one standard strain MTCC 723 and three clinical isolates were used in the study. Maximum amount of LT (OD 3.285) was produced at 37 0 C followed by 40 0 C (OD 3.305). Growth of E. coli in medium with pH 8.6 resulted in maximum amount of LT production (OD 3.489). LT was not detectable when bacteria were grown in medium with pH ≤7.2 and ≥ 9.2. Sodium chloride concentration of 0.2 M stimulated maximum amount of LT production. Maximum amount of LT was produced when the bacteria were grown in medium containing 2.5g/l of glucose. All the stress factors had a significant effect on the LT production by E. coli , though quantitative differences in the various strains were observed.

Effect of exposure to hydrogen peroxide on the virulence of Escherichia coli.

PURPOSE: To eliminate pathogenic bacteria, the host presents conditions that are stressful for bacteria. Oxidative stress arises when the concentration of pro-oxidants like hydrogen peroxide (H2O2 ) and superoxide anion increases to a level over the basal defence capacity of the cell. In the present study, we studied the effect of oxidative stress on the production of certain virulence factors by Escherichia coli . METHODS: E. coli was exposed to oxidative stress by growing in the presence of different concentrations of H2O2 . The effect of oxidative stress on the expression of surface hydrophobicity, adherence, haemolysin production, serum resistance and phagocytosis was studied. RESULTS: Oxidative stress caused a significant decrease in the expression of all the virulence factors of E. coli . CONCLUSIONS: Synthesis of virulence factors can be significantly altered by oxidative stress and such changes may affect the pathogenicity of E. coli.

Malignant melanoma of nasopharynx extending to the nose with metastasis in the neck.

Malignant melanoma is a rare tumor in otorhinolaryngology. In this paper, we have reported the first case of melanoma of nasopharynx which we came across in 20 years of ENT practice. A 55 year old male patient with complaints of swelling of nose and left side of neck, nasal blockage and epistaxis was diagnosed as melanoma of nose with metastasis in the neck based on clinical and radiological examination. The tumour was excised by lateral rhinotomy with supraomohyoid block dissection on the left side. The tumour was found to originate from lateral wall of nasopharynx and middle turbinate. The surgery was followed by radiotherapy. Diagnosis of melanoma was confirmed on histopathology. During 30 months follow-up, no recurrence was noticed.