Listeria innocua Transformed with an Antibiotic Resistance Plasmid as a Thermal-resistance Indicator for Listeria monocytogenes

Abstract

Listeria innocua PFEI is a chloramphenicol- and erythromycin-resistant organism obtained by electotransforming L. innocua ATCC 33091 with the plasmid pGK12. L. innocua ATCC 33091 and L. innocua PFEI were more heat resistant between 56 and 66°C than Listeria monocytogenes F5069 and Scott A when evaluated in sterile phosphate buffer or milk. Decimal reduction times of each L. innocua strain were 1.5 to 3 times longer in either heating menstruum than were D-values of the most heat resistant L. monocytogenes strain studied (F5069). L. innocua PFEI retained the plasmid during heating so that, of 300 survivors evaluated, 100% were resistant to chloramphenicol and 98% were resistant to erythromycin. Thus, L. innocua ATCC 33091 or PFEI would be useful indicator organisms to evaluate the lethality of thermal processes with respect to L. monocytogenes. L. innocua PFEI has the advantages that it could easily be selected and enumerated among a large, complex, background microflora, but it may not be appropriate for application in a food processing environment.

Cold Shock Induction of Thermal Sensitivity in Listeria monocytogenes

“…Further experimentation is warranted to elucidate the persistence of the increased thermal sensitivity induced by cold shock. The 27% higher D value of the L. innocua strain compared to the mean D value of the L. monocytogenes strains tested supports a previous report (14) of greater thermal resistance in L. innocua compared to that in L. monocytogenes.…”

Heat Resistance in Liquids of Enterococcus spp., Listeria spp., Escherichia coli, Yersinia enterocolitica, Salmonella spp. and Campylobacterspp

“…To function satisfactorily in this respect it is desirable that the indicator has heat resistance equal to or greater than the average heat resistance of L. monocytogenes or, more desirably, has heat resistance equal to that of the most resistant strains of this species. In the present work, heat resistance results for L. innocua were found in 5 reports [138,112,56,48,133]. The equation for the thermal destruction line constructed was log 10 D ( D in s) = 14.2559 - 0.20077 t ( r = -0.95519).…”

“…and Yersinia enterocolitica . Some of these bacteria are well-known food-associated human pathogens, others are utilized – enterococci and E. coli – or proposed – L. innocua [56,48] – as indicators. Some types of E. coli also appear as food-linked human pathogens [119,121,122,27,29,86,10,174,62,93] and enterococci have recently emerged as one of the leading causes of nosocomial, non-food-associated, infections [94].…”

Effect of Steam‐ and Hot‐Water Post‐Process Pasteurization on Microbial and Physical Property Measures of Fully Cooked Vacuum‐Packaged Chicken Breast Strips

“…innocua M1 was used in this study (Murphy and others 2001a). Listeria innocua M1 was developed as a heat resistance indicator for L. monocytogenes (Fairchild and Foegeding 1993;Foegeding and Stanley 1991). The Listeria culture was resistant to 50 ppm of rifampicin and 250 ppm of streptomycin.…”