Abstract
Listeriosis remains among the most important bacterial illnesses, with a high associated mortality rate. Efforts to control listeriosis require detailed knowledge of the epidemiology of the disease itself, and its etiological bacterium, Listeria monocytogenes. In this study we provide an in-depth analysis of the epidemiology of 224 L. monocytogenes isolates from Australian clinical and non-clinical sources. Non-human sources included meat, dairy, seafood, fruit, and vegetables, along with animal and environmental isolates. Serotyping, Multi-Locus Sequence Typing, and analysis of inlA gene sequence were performed. Serogroups IIA, IIB, and IVB comprised 94% of all isolates, with IVB over-represented among clinical isolates. Serogroup IIA was the most common among dairy and meat isolates. Lineage I isolates were most common among clinical isolates, and 52% of clinical isolates belonged to ST1. Overall 39 STs were identified in this study, with ST1 and ST3 containing the largest numbers of L. monocytogenes isolates. These STs comprised 40% of the total isolates (n = 90), and both harbored isolates from clinical and non-clinical sources. ST204 was the third most common ST. The high prevalence of this group among L. monocytogenes populations has not been reported outside Australia. Twenty-seven percent of the STs in this study contained exclusively clinical isolates. Analysis of the virulence protein InlA among isolates in this study identified a truncated form of the protein among isolates from ST121 and ST325. The ST325 group contained a previously unreported novel mutation leading to production of a 93 amino acid protein. This study provides insights in the population structure of L. monocytogenes isolated in Australia, which will contribute to public health knowledge relating to this important human pathogen.
Highlights
The burden of foodborne disease in Australia has been estimated at an annual cost of AUD$1.2 billion, comprising approximately 5.4 million cases of disease (The OzFoodNet Working Group, 2012)
In addition to the public health burden, the associated costs to the food industry are high – Listeria monocytogenes is the main contaminant linked to food recalls in Australia due to microbial contamination, with 45% of these recalls from 2005 through to 2014 due to this organism; where ready-to-eat (RTE) meat products represented the largest group of recalled products
Serogroup IVB was the predominant group among cases of listeriosis, accounting for 56.6% of clinical isolates, and was significantly over-represented among clinical isolates (p < 0.0001; Figure 1B and Supplementary Table S2)
Summary
The burden of foodborne disease in Australia has been estimated at an annual cost of AUD$1.2 billion, comprising approximately 5.4 million cases of disease (The OzFoodNet Working Group, 2012). A similar association with high mortality rates is shared by other countries, with 20–30% of hospitalized cases of invasive listeriosis resulting in fatality (Dalton et al, 2011; Scallan et al, 2011; The OzFoodNet Working Group, 2012). In addition to the public health burden, the associated costs to the food industry are high – Listeria monocytogenes is the main contaminant linked to food recalls in Australia due to microbial contamination, with 45% of these recalls from 2005 through to 2014 due to this organism (based on FSANZ1 data); where ready-to-eat (RTE) meat products represented the largest group of recalled products
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