Invasive salmonellosis in paediatric patients in the Northern Territory, Australia, 2005-2015.

AIM: To describe the epidemiology of invasive Salmonella disease in children in the Northern Territory, Australia. METHODS: Design: A retrospective review of invasive salmonellosis cases identified by pathology records and the Northern Territory Notifiable Disease Surveillance System. Case definitions: Those aged 18 years or under, with Salmonella cultured from a usually sterile site, collected in the Northern Territory between 1 July 2005 and 30 June 2015. OUTCOME MEASURES: The primary outcome measure was the annual incidence rate of invasive salmonellosis, comparing rates between Indigenous and non-Indigenous children. RESULTS: There were 86 cases of invasive Salmonella infection in children over the 10-year period; an annual incidence of 14.1 per 100 000 population, in those aged less than 18 years. Gastrointestinal Salmonella notifications were similar between Indigenous and non-Indigenous children. In children aged less than 15 years, the rate of invasive salmonellosis was higher in Indigenous children compared to non-Indigenous children (23.4 per 100 000 compared with 11.6 per 100 000); rate ratio 2.0 (95% confidence interval 1.3-3.3, P = 0.002). Indigenous children with invasive salmonellosis had a median hospital stay of 8 days, which was compared to 5 days for non-Indigenous children (P = 0.015). The highest incidence rate of invasive salmonellosis occurred in Indigenous patients less than 12 months of age (138 per 100 000). CONCLUSION: The Northern Territory of Australia has high rates of invasive salmonellosis in children. Indigenous and non-Indigenous children experience similar rates of Salmonella gastroenteritis but Indigenous children experience higher rates of invasive salmonellosis.

Treatment of a methylmalonyl-CoA mutase stopcodon mutation.

There are limited treatment options for the metabolic disorder methylmalonic aciduria. The disorder can be caused by nonsense mutations within the methylmalonyl-CoA mutase gene, resulting in the production of a truncated protein with little or no catalytic activity. We used a genomic reporter assay and mouse primary cell lines which carry a stop-codon mutation in the human methylmalonyl-CoA mutase gene to test the effects of gentamicin and PTC124 for stop-codon read-through potential. Fibroblast cell lines were established from methylmalonic aciduria knockout-stop codon mice. Addition of gentamicin to the culture medium caused a 1.5- to 2-fold increase in mRNA expression of the human methylmalonyl-CoA mutase gene. Without treatment the cells contained 19% of the normal levels of methylmalonyl-CoA mutase enzyme activity which increased to 32% with treatment, suggesting a functional improvement. Treatment with PTC124 increased the amount of human methylmalonyl-CoA mutase gene mRNA by 1.6±0.3-fold and a trend suggesting increased enzyme activity. The genomic reporter assay, BAC_MMA(∗)EGFP, expresses enhanced green fluorescent protein when read-through of the stop codon occurs. Using flow cytometry, RT-real-time PCR and enzyme assay, read-through was measured. Treatment with PTC124 at 20µmol/L resulted in a significant increase in enhanced green fluorescent protein, a 2-fold increase in mRNA expression and a trend to a slight increase in enzyme activity. The clinical relevance of these effects may be tested in mouse models of MMA carrying nonsense mutations in the methylmalonyl-CoA mutase gene. Pharmacological approaches have the advantage of providing a broader effect on multiple tissues, which will benefit many different disorders with similar nonsense mutations.

Mouse models for methylmalonic aciduria.

Methylmalonic aciduria (MMA) is a disorder of organic acid metabolism resulting from a functional defect of methylmalonyl-CoA mutase (MCM). MMA is associated with significant morbidity and mortality, thus therapies are necessary to help improve quality of life and prevent renal and neurological complications. Transgenic mice carrying an intact human MCM locus have been produced. Four separate transgenic lines were established and characterised as carrying two, four, five or six copies of the transgene in a single integration site. Transgenic mice from the 2-copy line were crossed with heterozygous knockout MCM mice to generate mice hemizygous for the human transgene on a homozygous knockout background. Partial rescue of the uniform neonatal lethality seen in homozygous knockout mice was observed. These rescued mice were significantly smaller than control littermates (mice with mouse MCM gene). Biochemically, these partial rescue mice exhibited elevated methylmalonic acid levels in urine, plasma, kidney, liver and brain tissue. Acylcarnitine analysis of blood spots revealed elevated propionylcarnitine levels. Analysis of mRNA expression confirms the human transgene is expressed at higher levels than observed for the wild type, with highest expression in the kidney followed closely by brain and liver. Partial rescue mouse fibroblast cultures had only 20% of the wild type MCM enzyme activity. It is anticipated that this humanised partial rescue mouse model of MMA will enable evaluation of long-term pathophysiological effects of elevated methylmalonic acid levels and be a valuable model for the investigation of therapeutic strategies, such as cell transplantation.