Performance evaluation of a low conductive growth medium (LCGM) for growth of healthy and stressed Listeria monocytogenes and other common bacterial species

• Published in: International journal of food microbiology 2006-08, Vol.111 (1), p.12-20
• Main Authors: Banada, Padmapriya P., Liu, Yi-Shao, Yang, Liju, Bashir, Rashid, Bhunia, Arun K.
• Format: Article
• Language: English
• Subjects: absorbance; acid treatment; ActA; actin; Bacteria; bacterial contamination; bacterial proteins; bioelectrical impedance; Biological and medical sciences; Colony Count, Microbial; Conductivity; Culture Media - chemistry; Electric Conductivity; electrical conductivity; Food industries; Food Microbiology; food pathogens; Fundamental and applied biological sciences. Psychology; genes; Hydrogen-Ion Concentration; Internalin B; Kinetics; Listeria monocytogenes; Listeria monocytogenes - growth & development; Listeria monocytogenes - isolation & purification; Low conductive growth medium; microbial detection; microbial growth; Osmosis; osmotic treatment; salt stress; selective media; sodium chloride; Spectrophotometry; Temperature; Time Factors; viability; virulence; Virulence Factors - analysis
• ISSN: 0168-1605; 1879-3460
• DOI: 10.1016/j.ijfoodmicro.2006.04.040

The performance of a low conductive growth medium (LCGM) (conductivity of < 1300 μS) was evaluated for its ability to support growth of food borne bacterial pathogens including Listeria monocytogenes and to determine the expression of the two key virulence proteins in L. monocytogenes for possible applications in an impedance-based microfluidic biochip detection platform. Growth of Listeria was monitored spectrophotometrically and the lag phase, generation time, growth rate and maximum population density were determined using the Gompertz equation. LCGM had a lag phase of 2.3 h and showed a higher cell density compared to Luria Bertini (LB) broth. Length of lag phase was highly dependent on initial inoculum concentrations. The changes in conductivity with respect to growth in the low conductive medium were monitored using a conductivity probe. L. monocytogenes growth could be detected within 2 h (0.1 mS) in LCGM and within 6 h in LB. The performance of the media was also evaluated for the recovery of Listeria cells exposed to various stresses as 42 °C for 1, 2 or 6 h, an osmotic stress in 10.5% NaCl, an acidic stress at pH 2, 3 or 5 and a combined stress of 10.5% NaCl, pH 5 and 1 h exposure at 42 °C. The recovery rate was comparable with that of Tryptic soy broth containing yeast extract (TSBYE). L. monocytogenes in LCGM supported the expression of two key virulence markers, actin polymerization protein (ActA) and internalin B (InlB), which could be detected using specific antibodies. In general LCGM also supported the growth of several other bacterial species suggesting its implication in microbial quality monitoring of products. In conclusion, LCGM is a sensitive low conductive medium that supports the growth as well as the expression of virulence markers for potential applications in sensitive detection of L. monocytogenes or other food borne pathogens in impedance-based sensor platform.