Systematic Assessment of Nonproteolytic Clostridium botulinum Spores for Heat Resistance

Abstract

Heat treatment is an important controlling factor that, in combination with other hurdles (e.g., pH, a w ), is used to reduce numbers and prevent the growth of and associated neurotoxin formation by nonproteolytic C. botulinum in chilled foods. It is generally agreed that a heating process that reduces the spore concentration by a factor of 10 6 is an acceptable barrier in relation to this hazard. The purposes of the present study were to review the available data relating to heat resistance properties of nonproteolytic C. botulinum spores and to obtain an appropriate representation of parameter values suitable for use in quantitative microbial risk assessment. In total, 753 D values and 436 z values were extracted from the literature and reveal significant differences in spore heat resistance properties, particularly those corresponding to recovery in the presence or absence of lysozyme. A total of 503 D and 338 z values collected for heating temperatures at or below 83°C were used to obtain a probability distribution representing variability in spore heat resistance for strains recovered in media that did not contain lysozyme. IMPORTANCEIn total, 753 D values and 436 z values extracted from literature sources reveal significant differences in spore heat resistance properties. On the basis of collected data, two z values have been identified, z ‫؍‬ 7°C and z ‫؍‬ 9°C, for spores recovered without and with lysozyme, respectively. The findings support the use of heat treatment at 90°C for 10 min to reduce the spore concentration by a factor of 10 6 , providing that lysozyme is not present during recovery. This study indicates that greater heat treatment is required for food products containing lysozyme, and this might require consideration of alternative recommendation/guidance. In addition, the data set has been used to test hypotheses regarding the dependence of spore heat resistance on the toxin type and strain, on the heating technique used, and on the method of D value determination used. Over the last few decades, there has been an increasing demand from consumers in many countries for innovative, ready-toeat, minimally processed chilled foods such as complete meals, prepared salads and vegetables, pizza, sandwiches, sliced cooked meat, soups, and cakes (1, 2). These products have many desirable properties, such as improved taste, high nutritional value, convenience, and minimal use of additives and preservatives, but simultaneously, they also present challenges with regard to food safety. In the United Kingdom, for example, the microbiological safety of many products relies on a combination of moderate heat treatment (generally in the range of 70 to 90°C), chilled storage (at 8°C or below), a restricted shelf life (typically, a maximum of 42 days), good-quality raw materials, and hygienic manufacturing in the absence of added preservatives (1-3).Strains of Clostridium botulinum form the highly potent botulinum neurotoxin, and consumption of food containing as little as 30 ng of preformed toxin can c...

Selection and Development of Nontoxic Nonproteolytic Clostridium botulinum Surrogate Strains for Food Challenge Testing

“…Superdormant fractions comprised up to 99% of the spore population in some strains (KI2, ZBS17, RO132). The D 75 values, calculated from the log-linear part of the inactivation curves, showed a broad variation, ranging from 1.8 to 21.4 min ( Figure 3 ), but the average D 75 (7.4 min) corresponded well to the value reported in a meta-analysis of literature data for toxic group II strains (5.1 min) [ 49 ]. Furthermore, the four strains of the type E cluster included in our experiment (ZBS3, DSM1985, NCTC8266 Δbont::ermB and NCTC11219 Δbont::ermB) had the lowest spore heat resistance of all the strains in the absence of lysozyme (D 75 < 3 min), confirming a similar finding from the same meta-analysis.…”

“…Reprinted/adapted with permission from Ref. [ 49 ]. Copyright 2016, copyright Wachnicka et al D-values were calculated from the log-linear part of the reduction curve.…”

Impact of Clostridium botulinum genomic diversity on food safety

“…Additionally, Wachnicka et al . [72] has reported on a relationship between lineage (and toxin type) and spore heat resistance. A systems level approach, both data mining and systems biology modelling, can provide a framework to understand complexity and hence to discover genetic determinants of features such as minimum growth temperature, neurotoxin formation and spore heat resistance [73, 74].…”

Pan-Genomic Analysis of Clostridium botulinum Group II (Non-Proteolytic C. botulinum) Associated with Foodborne Botulism and Isolated from the Environment

“…Further details about individual sequences and strains are given in Tables S1 and S3, where they appear in the same order as in this figure. A comparison of the physiological response of strains within these two lineages has revealed a relationship between lineage (and toxin serotype) and carbohydrate utilisation pattern, but not growth response at chill temperature or at high NaCl concentrations [45]. However, a systematic assessment of literature data has established a relationship between lineage (and toxin serotype) and spore heat resistance, despite methodological differences amongst the many studies reviewed [65]. A detailed analysis of the difference in physiological response of strains in these lineages, as well as a genome-wide association study to identify the genetic mechanisms behind each physiological response, is merited.…”