The present study attempted to determine the influence of exogenous oxidative stress on the cell viability of Escherichia coli. In this regard, 3mM hydrogen peroxide (H 2 O 2) was added to the late log phase of E. coli culture, and afterwards the phenotype, cell morphology and the ability to form colony forming units (CFU) on agar plates were examined. As expected, a quick phenotypic suppression as well as a rapid decline in viable and culturable cell numbers was observed at the mid-stationary phase as compared to control. Interestingly, a large mass of cell aggregates was noticed upon addition of H 2 O 2. Thus the current investigation corroborated the previous findings and further added to the existing knowledge on oxidative stress events in E. coli.

Keywords: enteric diseases hepatitis B virus infections human immunodeficiency virus infection malaria tuberculosis urinary tract infections a b s t r a c tBangladesh has experienced a variety of diseases caused by natural dissemination of an array of pathogenic microorganisms into the environment. While cures for these diseases largely depend on the medication strategies of physicians, determining the reasons for disease persistence as well for the onset of reinfection is also essential. Routine diagnosis of common diseases usually means treatment with a range of appropriate medicines; however, failure of these medications because of the drug resistance of microorganisms accompanied by a lack of alertness about the etiology of diseases often leads to fatal results. The present review reports on emerging diseases in Bangladesh and focuses on associated microbiological research into ongoing diseases including enteric, urinary tract, and malarial complications. The viruses associated with acquired immunodeficiency syndrome and hepatitis are also discussed.

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BackgroundWith a preceding scrutiny of bacterial cellular responses against heat shock and oxidative stresses, current research further investigated such impact on yeast cell. Present study attempted to observe the influence of high temperature (44–46 °C) on the growth and budding pattern of Saccharomyces cerevisiae SUBSC01. Effect of elevated sugar concentrations as another stress stimulant was also observed. Cell growth was measured through the estimation of the optical density at 600 nm (OD600) and by the enumeration of colony forming units on the agar plates up to 450 min.ResultsSubsequent transformation in the yeast morphology and the cellular arrangement were noticed. A delayed and lengthy lag phase was observed when yeast strain was grown at 30, 37, and 40 °C, while at 32.5 °C, optimal growth pattern was noticed. Cells were found to lose culturability completely at 46 °C whereby cells without the cytoplasmic contents were also observed under the light microscope. Thus the critical growth temperature was recorded as 45 °C which was the highest temperature at which S. cerevisiae SUBSC01 could grow. However, a complete growth retardation was observed at 45 °C with the high concentrations of dextrose (0.36 g/l) and sucrose (0.18 g/l). Notably, yeast budding was found at 44 and 45 °C up to 270 min of incubation, which was further noticed to be suppressed at 46 °C.ConclusionsPresent study revealed that the optimal and the critical growth temperatures of S. cerevisiae SUBSC01 were 32.5 and 45 °C, respectively; and also projected on the inhibitory concentrations of sugars on yeast growth at that temperature.

Bacterial homeostasis depends on an array of physical and chemical stimulants. Current investigation assessed the impact of one of such factors, the speed of aeration, on cell viability and culturability of Escherichia coli, Pseudomonas spp. and Bacillus spp. Each of the bacterial strain was incubated at 37°C with a shaking speed of 0, 100 or 200 rotation per minute (rpm) separately up to 72 hours, with a simultaneous monitoring of morphological changes and cell culturability. All bacterial species were found to optimally grow at 100 rpm whereas at 0 rpm growths of E. coli and Pseudomonas spp. were bit slower compared to that of Bacillus spp. The capacity to form colony forming units (CFUs) of E. coli and Pseudomonas spp. on Luria Burtani (LB) agar plates were observed to be inhibited after 36 hours of growth at 200 rpm; i.e., approximately 3-log reduced CFUs than those formed by Bacillus spp. Besides, morphologically impaired cells were observed for the former two bacteria cultivated at 200 rpm. Taken together, it is assumed that the high speed shaking might evolve the oxidative stress endogenously which possibly rendered the cells lose their culturability.

In the previously studied export quality shrimp samples, presence of a range of pathogenic bacteria including Listeria spp. and Klebsiella spp. were detected. The presence of eae gene in Escherichia coli, aero specific gene in Aeromonas spp., and sodB gene in Vibrio spp. were observed which might confer the associated virulence. Present study further attempted to detect the existence of virulent genes in Listeria spp. and Klebsiella isolates from the same shrimp samples through the gene specific polymerase chain reaction (PCR). Visualization of bands of iap (457 bp) and gyrB2 (711 bp) genes after PCR amplification referred the presence of virulence strains of Listeria spp. and Klebsiella spp., respectively in the export quality shrimp samples. Together with the previous findings of virulence genes of several pathogenic bacteria, the outcomes of current study further conferred the possible detrimental impact of the export quality frozen shrimps as and when consumed.

BackgroundThe bacterial stressed state upon temperature raise has widely been observed especially in Escherichia coli cells. The current study extended such physiological investigation on Bacillus spp. SUBB01 under aeration at 100 rpm on different culture media along with the high temperature exposure at 48, 50, 52, 53 and 54 °C. Bacterial growth was determined through the enumeration of the viable and culturable cells; i.e., cells capable of producing the colony forming units on Luria–Bertani and nutrient agar plates up to 24 h. Microscopic experiments were conducted to scrutinize the successive physiological changes. Suppression of bacterial growth due to the elevated heat was further confirmed by the observation of non-viability through spot tests.ResultsAs expected, a quick drop in both cell turbidity and colony forming units (~104) along with spores were observed after 12–24 h of incubation period, when cells were grown at 54 °C in both Luria–Bertani and nutrient broth and agar. The critical temperature (the temperature above which it is no longer possible to survive) of Bacillus spp. SUBB01 was estimated to be 53 °C. Furthermore, a positive impact was observed on the inhibited E. coli SUBE01 growth at 45 and 47 °C, upon the supplementation of the extracellular fractions of Bacillus species into the growing culture.ConclusionsOverall the present analysis revealed the conversion of the culturable cells into the viable and nonculturable (VBNC) state as a result of heat shock response in Bacillus spp. SUBB01 and the cellular adaptation at extremely high temperature.