What is Listeria and how does it spread in rockmelons?

Listeriosis is caused by eating food contaminated with a bacterium called Listeria monocytogenes. It’s an uncommon illness but can be deadly if it causes septicaemia (blood poisoning) or meningitis (inflammation of the membranes around the brain).

The elderly are particularly susceptible to listeriosis, as are pregnant women and their foetuses, and those with weakened immune systems such as those on cancer treatment or medications that suppress the immune system. Symptoms include fever, muscle aches and gastrointestinal problems such as nausea, vomiting and diarrhoea.

Infection during pregnancy may lead to miscarriage, stillbirth and newborn infections but the early use of antibiotics can often prevent infection of the foetus or newborn.

Past outbreaks have been linked with raw milk, soft cheeses, salads, unwashed raw vegetables, cold diced chicken, pre-cut fruit and fruit salad.

How does it spread?

Listeria is found widely in soil, water and vegetation, and can be carried by pets and wild animals. A vegetable or fruit food product can become contaminated anywhere along the chain of food production: planting, harvesting, packing, distribution, preparation and serving.

Even on a farm, sources of contamination can include irrigated waters, wash waters and soil. Listeria can survive for up to 84 days in some soils. Heavy rains on a crop can splash listeria from soils onto the surface or skin of the vegetable or fruit, especially those that grow low to the ground, such as rockmelons. Their unique, rough skin can also trap and hold bacteria. Melons may be turned multiple times during their maturation to develop properly, which can mean more opportunities to spread pathogens.

How consumers can reduce their chances of infection?

  • Do not purchase melons that are bruised or damaged. If buying fresh cut produce, ensure it is refrigerated or surrounded by ice.
  • Fresh produce should be refrigerated within two hours of peeling or cutting. Leftover cut produce should be discarded if left at room temperature for more than two hours.
  • Wash all rockmelons with cool tap water immediately before eating. Don’t use soap or detergents. Scrub melons with a clean produce brush. Cut away any bruised or damaged areas before eating.
  • Hygiene is crucial. Hands should be washed with hot soapy water before and after handling fresh rockmelons. Cutting boards, dishes, utensils, and counter tops should always be washed with hot soapy water and cleaned after coming in contact with fresh produce, or raw meat, poultry and seafood.
  • Use different cutting boards and utensils when handling fresh produce to avoid cross-contamination. If possible, use one clean cutting board for fresh produce and a separate one for raw meat, poultry, and seafood.

This article is produced by the Nutrition Department: Theresa Dimitrakakis (APD), TinMiMi Maung (APD), Wendy Vaiano (APD), Katherine Adam (APD), Alex Salmon (APD), Lauren Snowden (APD), Lisa Brearley (APD)

Any comments or questions can be forwarded to the nutrition department: 9411 7550.