Formation of biofilm by Listeria monocytogenes ATCC 19112 at different incubation temperatures and concentrations of sodium chloride

Biofilm formation can lead to various consequences in the food processing line such as contamination and equipment breakdowns. Since formation of biofilm can occur in various conditions; this study was carried out using L. monocytogenes ATCC 19112 and its biofilm formation ability tested under various concentrations of sodium chloride and temperatures. Cultures of L. monocytogenes ATCC 19112 were placed in 96-well microtitre plate containing concentration of sodium chloride from 1-10% (w/v) and incubated at different temperature of 4 ºC, 30 ºC and 45 ºC for up to 60 h. Absorbance reading of crystal violet staining showed the density of biofilm formed in the 96-well microtitre plates was significantly higher when incubated in 4 ºC. The formation of biofilm also occurs at a faster rate at 4 ºC and higher optical density (OD 570 nm) was observed at 45 ºC. This shows that storage under formation of biofilm that may lead to a higher contamination along the processing line in the food industry. Formation of biofilm was found to be more dependent on temperature compared to sodium chloride stress.

Detection and molecular characterization of Vibrio vulnificus from coastal waters of Malaysia.

A total of 57 Vibrio vulnificus isolates from coastal water were characterized for their antimicrobial resistance, plasmid profiles and were typed by the PCR-based techniques: a random amplification of polymorphic DNA (RAPD) method and the enterobacterial repetitive intergenic consensus sequence (ERIC) method. All isolates were susceptible to chloramphenicol, nalidixic acid, tetracycline and trimethoprim-sulfamethoxazole. Fifty-one isolates were resistant to one or more of the other antibiotics tested. Plasmid analysis indicated that only 18 isolates carried small plasmids of 1.6 to 16 megadaltons. Analysis of the RAPD and ERIC DNA fingerprints of the V. vulnificus isolates with Gel Compare and cluster analysis software revealed significant genetic heterogeneity among these isolates. The combination of RAPD and ERIC analysis allowed us to distinguish all isolates. Thus, the combination of the two techniques is recommended for epidemiological investigation.