1.Algicidal activity of Aeromonas hydrophila sdPS-7 isolate against toxic marine dinoflagellate Alexandrium minutum KB- 5
Shaima Abdul fattah ; Gires Usup ; Asmat Ahmad
Malaysian Journal of Microbiology 2016;12(1):24-29
Aims: Several harmful dinoflagellate species are widely found in Malaysian marine waters. These microalgae are
capable of producing a variety of toxins that can intoxicate humans through consumption of contaminated seafood.
Therefore, the present work aimed to investigate the potential of a marine bacterium sdPS-7 isolate as a biological
control agent against Alexandrium minutum KB-5.
Methodology and results: The isolate sdPS-7 was obtained from marine sediments in Malaysia and examined for its
algicidal activity toward the toxic dinoflagellate A. minutum KB-5 in laboratory culture. Based on morphological and
molecular characterization, this isolate was identified as Aeromonas hydrophila sdPS-7. Alexandrium minutum KB-5
cultures were exposed to cell free bacteria culture filtrate and the effect on dinoflagelate growth was evaluated based on
direct cell counts in the treated samples compared to non-treated control cultures. The bacterial filtrate was treated at
different temperatures, salinities and exposed to repeated freezing and thawing five times to study its algicidal activity
stability thereafter. The results showed a potent inhibition of the growth of A. minutum KB-5. The strongest effect was
observed when the bacterium culture filtrate was mixed with A. minutum KB-5 cultures that were in lag phase, resulting
in 99% or higher mortality. The cell-free filtrate proved to be heat- stable when exposed to temperatures of 2 °C to 100
°C for one hour each. There was also no substantial salinity as well as (freezing – thawing) effect on the filtrate algicidal
activity.
Conclusion, significance and impact of study: This study illustrated the potential use of the marine bacterial
Aeromonas hydrophila sdPS-7 filtrates in controlling the growth of the toxic dinoflagellate A. minutum KB-5.
Biological Control Agents
;
Aeromonas hydrophila
2.Anti-biofilm activity of the marine bacterium Pseudoalteromonas ruthenica KLPp3 against Serratia marcescens and Vibrio alginolyticus
Asmat Ahmad ; Mohd Faiq Iqbal Sulieman ; Gires Usup
Malaysian Journal of Microbiology 2016;12(1):30-34
Aims: Pseudoalteromonas ruthenica KLPp3 is the marine Gram-negative strain isolated from the surface of mud crab at
Pulau Perhentian Malaysia. In this work, the anti-biofilm activity of P. ruthenica supernatant was examined on Serratia
marcescen and Vibrio alginolyticus.
Methodology and results: The crude extract of P. ruthenica KLPp3 was obtained using ethyl acetate. The subminimum
inhibitory concentration (MIC) of the crude extract was determined using the minimum inhibitory test. The subMIC
crude extract was tested against two of the S. marcescen virulence factors, which are the swarming ability and
production of prodigiosin. The crystal violet assay was used to test the anti-biofilm activity of the sub-MIC crude extract
against S. marcescen and V. alginolyticus. The productions of prodigiosin were reduced by 72%. The swarming area
was reduced by 56.06%. It inhibits 26.9% and 48.5% of biofilm production in S. marcescens and V. alginolyticus
respectively. The crude extract was heat stable.
Conclusion, significance and impact of study: Besides combating the S. marcescens virulence factor, P. ruthenica
KLPp3 crude extract in sub-MIC reduces the formation of biofilm of S. marcescens and V. alginolyticus, which may find
applications in biofilm inhibition and prevention.
Anti-Infective Agents
3.Isolation and characterization of pigmented bacteria showing antimicrobial activity from Malaysian marine environment
Mahtab Jafarzade ; Nur Ain Yahya ; Suhaiza Mohamad ; Gires Usup ; Asmat Ahmad
Malaysian Journal of Microbiology 2013;9(2):152-160
Aims: Natural products play a prominent role in the discovery of leads for the development of drugs in the treatment of human diseases. Much of nature remains to be explored, especially marine and microbial environments.
Methodology and results: Fifty-five pigmented marine bacteria were isolated from sponges, seawater, mangrove
sediment, sea cucumber and mussel from different coastal area of Malaysia. The antimicrobial activities of these
bacteria were investigated by disk diffusion method against pathogenic bacteria. Out of 55 isolates, 18 isolates exhibited antimicrobial activity, which based on morphological characterization, 53% of them were Gram positive and 47% were Gram negative. All active isolates were able to tolerate more than 4% NaCl in the nutrient agar medium that indicated they were autochthonous to marine environment and moderate salt tolerant in nature. Molecular identification of isolates
by the strong antimicrobial activities indicates that isolates WPRA3 (JX020764) and SM11-3j belong to genus Serratia and isolate SDPM1 (JQ083392) belongs to genus Zooshikella.
Conclusion, significance and impact of study: The results of present study revealed that the active isolates are
potential producer of antimicrobial secondary metabolites and might be utilized as drug candidate