Original Article Bangladesh J Microbiol, Volume 32, Number 1&2, June-December 2015, pp 39-44 Introduction Bacterial survival in natural environments are usually challenged by brusque changes in the nutrient exhaustion and by an array of physicochemical stimuli including temperature, pH, sugar/ salt concentrations, the redox state, toxic compounds, etc 1-9 . In natural habitats, bacterial cells must need to meet their nutritional requirements (including the carbon sources, major elements and minor elements) for cellular biosynthesis and metabolic functions 10 . Thus, apart from the natural habitats, for the in vitro cultivation of bacteria in laboratory culture media, bacteria cells are to be provided with a suitable source of carbon in simpler form (regarding the ease of uptake) for cellular biosynthesis primarily through carbon catabolic repression 10-14 . In consistent to this concept, the earlier studies indeed reported that abrupt changes in the source of carbon stimulated metabolic potential in E. coli cell through the elicitation of specific catabolic operons 10,15-17 . Through physiological and genetic analysis on E. coli, our former studies unravelled the impact of the in vitro nutrient composition accompanied with the temperature up-shift with the generation of oxidative stress retarding the cell viability of the bacterium 6,8,18- 19 . In a separate study the influence on cell viability and culturability in response to the external and internal oxidative stresses 9,18-21 in E. coli (SUBE01), Pseudomonas spp. (SUBP01), Bacillus spp. (SUBB01) and Salmonella spp. (SUBS01) has been inquired well and apparently appended the new information on the defense strategy of these bacteria especially those belonging to Salmonella (SUBS01) 9,21 . Along these lines of phenotypic observations on the cellular behaviour against the heat shock and oxidative stress, the current investigation further emphasized (1) to distinguish among the growth patterns of E. coli (SUBE01) and Salmonella spp. (SUBS01) on culture media with variations in carbon sources (dextrose, glycerol, lactose, tween 20 and sucrose), (2) to observe the retention within the cell viability in response to the diversity within carbon sources as major nutrients for in vitro cultivation. Methods and Materials Demonstration of culturable cells upon variation in carbon sources Laboratory stock culture of Escherichia coli (SUBE01) and Salmonella spp. (SUBS01) were used in this study. Experiments demonstrating the bacterial growth in terms of cell turbidity (optical density at 600 nm; i.e., OD 600 ) and colony forming units (CFUs) were conducted as described earlier by Nur et al. 21 . Minimal media (dextrose 1.0 g/l, dipotassium phosphate 7.0 g/l, monopotassium phosphate 2.0 g/l, sodium citrate 0.5 g/l, magnesium sulfate 0.1 g/l and ammonium sulfate 1.0 g/l) for both agar (MA) and broth (MB) were used for the assay of the bacterial culturability 8 . D-Sucrose, D-lactose, glycerol and tween 20 (Sigma-Aldrich Corporation, USA) were used separately as carbon source, which were included in minimal media (both agar and broth) instead of dextrose (D-glucose) (Sigma-Aldrich Corporation, USA). After 24 hour incubation on MA plates at 37°C, one loopful of the bacterial culture was introduced into 5 ml MB followed by incubation at Impact of Different Carbon Sources on the in vitro Growth and Viability of Escherichia coli (SUBE01) and Salmonella spp. (SUBS01) Cells Ifra Tun Nur 1 , Jannatun Tahera 1 , Md. Sakil Munna 1 , M. Majibur Rahman 2 , Rashed Noor 1* 1 Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka 1217, Bangladesh, 2 Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh With a previous observation of Escherichia coli growth cessation along with temperature variation within three different bacteriological culture media (nutrient agar, Luria-Bertani agar and minimal agar), current investigation further depicted on the possible growth dynamics of Escherichia coli (SUBE01) and Salmonella (SUBS01) growth and viability upon supplementation of different carbon sources (dextrose, sucrose, lactose, glycerol and tween 20) at 37°C under the aeration of 100 rpm. Viability of the tested bacterial species was assessed through the enumeration of the colony forming unit (cfu) appeared upon prescribed incubation for 12-24 hours on different agar plates consisting of the above mentioned carbon sources. Besides, to inspect the cellular phenotypic changes, morphological observations were conducted under the light microscope. Variations in bacterial growth (either growth acceleration or cessation) were further noticed through the spot tests on the agar plates. Considerable shortfalls in the culturable cells of E. coli and Salmonella spp. were noted in the minimal media separately consisting of sucrose, lactose, glycerol or tween 20 while an opposite impact of accelerated growth was noticed in the media supplied with dextrose. The data revealed a hierarchy of consequence of carbon sources as nutrient generators whereby the favourable bacterial growth and survival order of the carbon sources was estimated as dextrose > glycerol > lactose > tween 20 > sucrose. Keywords: Carbon sources; Colony forming unit (cfu), Escherichia coli, Nutrient diversity, Salmonella spp. *Corresponding author: Rashed Noor, Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka 1217, Bangladesh. Tel: +880 (02) 8355626 E-mail: noor.rashed@yahoo.com