- Improved Production of Live Cells of Lactobacillus rhamnosus by Continuous Cultivation using Glucose-yeast Extract Medium
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Liew Siew Ling , Rosfarizan Mohamad , Raha Abdul Rahim , Ho Yin Wan , Arbakariya Bin Ariff
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J. Microbiol. 2006;44(4):439-446.
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DOI: https://doi.org/2408 [pii]
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 Abstract
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In this study, the growth kinetics of Lactobacillus rhamnosus and lactic acid production in continuous culture were assessed at a range of dilution rates (0.05 h?1 to 0.40 h?1) using a 2 L stirred tank fermenter with a working volume of 600 ml. Unstructured models, predicated on the Monod and Luedeking-Piret equations, were employed to simulate the growth of the bacterium, glucose consumption, and lactic acid production at different dilution rates in continuous cultures. The maximum specific growth rate of L. rhamnosus, ┢max, was estimated at 0.40 h?1, and the Monod cell growth saturation constant, Ks, at approximately 0.25 g/L. Maximum cell viability (1.3 ≠ 1010 CFU/ml) was achieved in the dilution rate range of D = 0.28 h?1 to 0.35 h?1. Both maximum viable cell yield and productivity were achieved at D = 0.35 h?1. The continuous cultivation of L. rhamnosus at D = 0.35 h?1 resulted in substantial improvements in cell productivity, of 267% (viable cell count) that achieved via batch cultivation.
- Plasmid Profiling and Curing of Lactobacillus Strains Isolated from the Gastrointestinal Tract of Chicken
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Sieo Chin Chin , Norhani Abdullah , Tan Wen Siang , Ho Yin Wan
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J. Microbiol. 2005;43(3):251-256.
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DOI: https://doi.org/2217 [pii]
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Abstract
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In this study, we assessed the susceptibility of 12 Lactobacillus strains, all of which had been isolated from the gastrointestinal tracts of chicken, to three antibiotics (chloramphenicol, erythromycin and tetracycline) used commonly as selective markers in transformation studies of lactic acid bacteria. Among these strains, 17%, 58%, and 25% were found to exhibit a high degree of resistance to 200 mg/ml of tetracycline, erythromycin, and chloramphenicol, respectively. Seven of the 12 Lactobacillus strains exhibiting resistance to at least 50 mg/ml of chloramphenicol or erythromycin, and five strains exhibiting resistance to at least 50 mg/ml of tetracycline, were subsequently subjected to plasmid curing with chemical curing agents, such as novobiocin, acriflavin, SDS, and ethidium bromide. In no cases did the antibiotic resistance of these strains prove to be curable, with the exception of the erythromycin resistance exhibited by five Lactobacillus strains (L. acidophilus I16 and I26, L. fermentum I24 and C17, and L. brevis C10). Analysis of the plasmid profiles of these five cured derivatives revealed that all of the derivatives, except for L. acidophilus I16, possessed profiles similar to those of wild-type strains. The curing of L. acidophilus I16 was accompanied by the loss of 4.4 kb, 6.1 kb, and 11.5 kb plasmids.
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