Sara A. Burgess

Thermophilic bacilli and their importance in dairy processing.

The thermophilic bacilli, such as Anoxybacillus flavithermus and Geobacillus spp., are an important group of contaminants in the dairy industry. Although these bacilli are generally not pathogenic, their presence in dairy products is an indicator of poor hygiene and high numbers are unacceptable to customers. In addition, their growth may result in milk product defects caused by the production of acids or enzymes, potentially leading to off-flavours. Dairy thermophiles are usually selected for by the conditions during dairy manufacture. These bacteria are able to grow in sections of dairy manufacturing plants where temperatures reach 40-65°C. Furthermore, because they are spore formers, they are difficult to eliminate. In addition, they exhibit a wide temperature growth range, exhibit a fast growth rate (generation time of approximately 15-20 min) and tend to readily form biofilms. Many strategies have been tested to remove, prevent and/or delay the formation of thermophilic bacilli biofilms in dairy manufacture, but with limited success. This is, in part, because little is known about the structure and composition of thermophilic bacilli biofilms in general and, more specifically, in milk processing environments. Therefore, new cleaning regimes often do not target the problem optimally. A greater understanding of the structure of thermophilic biofilms within the context of the milk processing environment and their link with spore formation is needed to develop better control measures. This review discusses the characteristics and food spoilage potential, enumeration and identification methods for the thermophilic bacilli, as well as their importance to dairy manufacture, with an emphasis on biofilm development and spore formation.

The formation of spores in biofilms of Anoxybacillus flavithermus.

Aims:  To examine the rate and the extent of spore formation in Anoxybacillus flavithermus biofilms and to test the effect of one key variable – temperature – on spore formation.

Characterization of thermophilic bacilli from a milk powder processing plant

To determine whether strains of Geobacillus stearothermophilus isolated from a milk powder manufacturing plant were different in their ability to form biofilms and produce spores. In addition, this study evaluated whether there were other physiological characteristics that could differentiate these strains.

Insights into the Geobacillus stearothermophilus species based on phylogenomic principles

BackgroundThe genus Geobacillus comprises bacteria that are Gram positive, thermophilic spore-formers, which are found in a variety of environments from hot-springs, cool soils, to food manufacturing plants, including dairy manufacturing plants. Despite considerable interest in the use of Geobacillus spp. for biotechnological applications, the taxonomy of this genus is unclear, in part because of differences in DNA-DNA hybridization (DDH) similarity values between studies. In addition, it is also difficult to use phenotypic characteristics to define a bacterial species. For example, G. stearothermophilus was traditionally defined as a species that does not utilise lactose, but the ability of dairy strains of G. stearothermophilus to use lactose has now been well established.ResultsThis study compared the genome sequences of 63 Geobacillus isolates and showed that based on two different genomic approaches (core genome comparisons and average nucleotide identity) the Geobacillus genus could be divided into sixteen taxa for those Geobacillus strains that have genome sequences available thus far. In addition, using Geobacillus stearothermophilus as an example, we show that inclusion of the accessory genome, as well as phenotypic characteristics, is not suitable for defining this species. For example, this is the first study to provide evidence of dairy adaptation in G. stearothermophilus - a phenotypic feature not typically considered standard in this species - by identifying the presence of a putative lac operon in four dairy strains.ConclusionsThe traditional polyphasic approach of combining both genotypic and phenotypic characteristics to define a bacterial species could not be used for G. stearothermophilus where many phenotypic characteristics vary within this taxon. Further evidence of this discordant use of phenotypic traits was provided by analysis of the accessory genome, where the dairy strains contained a putative lac operon. Based on the findings from this study, we recommend that novel bacterial species should be defined using a core genome approach.

Biofilm Formation and Control

Microbial contamination of dairy products is often through the release of bacteria from biofilms developing on almost any manufacturing plant surface. The microbial composition varies depending upon the product being manufactured and the environmental conditions in different parts of the dairy manufacturing plant. Microbial contamination of dairy products limits their value. Controlling biofilms through frequent cleaning costs the dairy industry in terms of labour and materials and by limiting the amount of product that can be manufactured. Recent studies on dairy biofilms have provided information on how dairy biofilms develop and suggest some alternative control measures to prevent or delay biofilm growth and reduce product contamination.

Draft Genome Sequences of Three Strains of Geobacillus stearothermophilus Isolated from a Milk Powder Manufacturing Plant

ABSTRACT Three strains of Geobacillus stearothermophilus (designated A1, P3, and D1) were isolated from a New Zealand milk powder manufacturing plant. Here, we describe their draft genome sequences. This information provided the first genomic insights into the nature of G. stearothermophilus strains present in the milk powder manufacturing environment.

Multidrug resistant Enterobacteriaceae in New Zealand: a current perspective.

Abstract In this article we review mechanisms and potential transmission pathways of multidrug resistance in Enterobacteriaceae, with an emphasis on extended-spectrum β-lactamase (ESBL)-production. This provides background to better understand challenges presented by this important group of antimicrobial resistant bacteria, and inform measures aimed at prevention and control of antimicrobial resistance in general. Humans and animals interact at various levels; household pets cohabit with humans, and other animals interact with people through direct contact, as well as through the food chain and the environment. These interactions offer opportunity for bacteria such as ESBL-producers to be shared and transmitted between species and, in turn, increase the risk of zoonotic and reverse-zoonotic disease transmission. A key step in curtailing antimicrobial resistance is improved stewardship of antimicrobials, including surveillance of their use, better infection-control and prevention, and a better understanding of prescribing practice in both veterinary and medical professions in New Zealand. This will also require prospective observational studies to examine risk factors for antimicrobial resistance. Due to the interconnectedness of humans, animals and the environment actions to effect the changes required should be undertaken using a One Health approach.

A One Health future to meet the AMR challenge

This issue of the New Zealand Veterinary Journal focuses on antimicrobial resistance (AMR), because of its rising prevalence, its impact on morbidity and mortality, and uncertainty about our ability to continue to treat infections effectively into the future. While AMR genes are not of our making, the rise in prevalence of AMR, predicted since antibiotics were first used (Finland et al. 1946; Jawetz 1963), is undoubtedly anthropogenic. However the complexity of the relationships between antimicrobial use and resistance, and their impact on ecosystems including the humans and animals that inhabit them, makes AMR one of health’s “wicked problems” (Rittel and Webber 1973; Signal et al. 2013). In order to understand how best to respond to this problem, we need to pay attention to the complex systems that underpin it, in order to understand how best to respond.

Biofilms of Thermophilic Bacilli Isolated from Dairy Processing Plants and Efficacy of Sanitizers

In many environments, bacteria can attach to a surface and grow into multicellular structures, otherwise known as biofilms. Many systems for studying these biofilms in the laboratory are available. To study biofilms of the thermophilic bacilli in milk powder-manufacturing plants, standard laboratory biofilm techniques need to be adapted. The focus of this chapter is on techniques that can be used for growing and analyzing biofilms of thermophilic bacilli that are isolated from dairy processing plants. These techniques include laboratory methods as well as how to set up a pilot-scale experiment. The laboratory methods consist of a microtiter plate assay, which is used for strain selection, and the CDC reactor, which is used for testing sanitizers and antimicrobial surfaces. In dairy processing, if a new sanitizer or antimicrobial surface appears to be promising, it is useful to carry out pilot-scale experiments before introducing it to a manufacturing plant. We describe how to set up a pilot-scale experiment for testing the efficacy of sanitizers against the thermophilic bacilli.