Aerosol Studies with Listeria innocua and Listeria monocytogenes

Abstract

Aerosol studies of Listeria monocytogenes in food processing plants have been limited by lack of a suitable surrogate microorganism. The objective of this study was to investigate the potential of using green fluorescent protein-labeled strains of Listeria innocua as a surrogate for L. monocytogenes for aerosol studies. These studies were conducted in a laboratory bioaerosol chamber and a pilot food-processing facility. Four strains of L. innocua and five strains of L. monocytogenes were used. In the laboratory chamber study, Listeria cells were released into the environment at two different cell numbers and under two airflow conditions. Trypticase soy agar (TSA) plates and oven-roasted breasts of chicken and turkey were placed in the chamber to monitor Listeria cell numbers deposited from aerosols. A similar experimental design was used in the pilot plant study; however, only L. innocua was used. Results showed that L. monocytogenes and L. innocua survived equally well on chicken and turkey breast meats and TSA plates. No-fan and continuous fan applications, which affected airflow, had no significant effect on settling rates of aerosolized L. monocytogenes and L. innocua in the bioaerosol chamber or L. innocua in the pilot plant study. Listeriae cell numbers in the air decreased rapidly during the first 1.5 h following release, with few to no listeriae detected in the air at 3 h. Aerosol particles with diameters of 1 and 2 microM correlated directly with the number of Listeria cells in the aerosol but not with particles that were 0.3, 0.5, and 5 microM in diameter. Results indicate that L. innocua can be used as a surrogate for L. monocytogenes in an aerosol study.

Listeria monocytogenes in ready-to-eat, sliced, cooked ham and salami products, marketed in the city of São Paulo, Brazil: Occurrence, quantification, and serotyping

“…In a study using aerosols containing strains of L. innocua and L. monocytogenes introduced in a pilot processing plant and in a bioaerosol chamber, respectively, most of the Listeria organisms were deposited during the first hour after being released into the air. The results of this study also suggest that the aerosol contamination of foods in processing plants may be induced by a contamination source 1.0e2.5 m away irrespective of whether the fans are on or off (Zhang, Ma, Oyarzabal, & Doyle, 2007).…”

Airborne Listeria spp. in the red meat processing industry

“…in the air in the tested plants in this study strongly suggests that Listerias can be airborne and consequently transmitted by single colonies, solid particles, or aerosols (Zhang et al 2007). None of the air samples taken by the air sampler within any of the 3 tested slaughterhouses and 3 meat processing plants were positive for the pathogen L. monocytogenes, however, L. seeligeri and L. innocua were isolated from 8 air samples (5.06%, n = 158) of the entire sample (237.0 m 3 of the air) taken in all 6 investigated plants (Table 1).…”

“…Nevertheless, there is still insufficient information available about the environmental conditions, routes, and sources, and on how Listeria can become airborne. Consequently, the possibilities of airborne Listeria contamination of the air in food-processing facilities have to be considered as an important prediction of the potentially anticipated route of the meat and meat products contamination (Kang & Frank 1990;Zhang et al 2007). Therefore the main objectives of this test were to examine the potential presence of Listeria spp.…”

nfluences of physicochemical stresses on injury and inactivation behaviour of Listeria innocua

“…This bacterium is often used as a thermal processing surrogate for L. monocytogenes Char, Guerrero, & Alzamora, 2009), since they share similar characteristics and environments. Besides the criticism of some researchers in assuming the parallelism of both species in a variety of foods and processing conditions, there are a considerable number of works that validate L. innocua as a primary non-pathogenic indicator of L. monocytogenes (Zhang, Ma, Oyarzabal, & Doyle, 2007;Lecompte, Kondjoyan, Sarter, Portanguen, & Collignan, 2008). The similarity of growth properties of both species in a wide range of temperatures, pH and water activity values re-enforces the choice of working with a non-pathogenic species (Begot, Lebert, & Lebert, 1997).…”