Researchers have evaluated a range of studies focussed on Salmonella in insects to gather data for assessing the safety of insect-based foods.

The systematic review looked at 36 studies investigating Salmonella in insects.

“Data on the persistence of Salmonella can be useful for further analysis by risk assessors and decision-makers involved in the safety of insect-based food, contributing to defining the sanitary requirements and risk mitigation measures along the supply chain,” said researchers in the journal npj Science of Food.

In Europe, insect-based foods are classed as novel foods, while in the United States, insects can be used as food if they have been produced for that specific purpose following relevant rules.

Few studies were conducted on insect species currently relevant for food production, such as the house cricket or migratory locust.

Traditional consumption of insects has highlighted potential allergic reactions, but the scaling up of insect farms and processing plants calls for data on the behavior of foodborne pathogens in these conditions, said scientists.

In insect farming, the possibility of contamination by pathogenic bacteria can occur along the production chain, especially if basic good hygiene practices are not followed.

“Contaminated substrate, insufficient hygienic measures, or lack of measures for preventing the entrance of undesired pests can all cause the introduction of Salmonella into insect production facilities,” according to the study.

Findings of Salmonella in Insects
Absence of Salmonella in insects before artificial contamination was found in 24 papers. only one study adopted farming methods similar to industrial ones.

Seventeen studies were carried out on complete metamorphosis insects, which include beetles, bees, and ants, in North America, with nine in Europe and one in South America. Some studies found Salmonella persisted during the metamorphosis from larva to adult.

The longest Salmonella persistence was reported in the black blow fly, in which the pathogen survived for 29 days at 5 degrees C (41 degrees F). This decreased to five days at 26 degrees C (78.8 degrees F). Using a high level of contamination, Salmonella was also found in the feces of a type of beetle for 28 days.

For incomplete metamorphosis insects, such as grasshoppers and cockroaches, a dozen studies were carried out in North America, with one each in South Asia and the Middle East.

The insect showing the longest Salmonella persistence was the German cockroach. The American cockroach excreted Salmonella via feces for 44 days until all insects died.

Some insect species have been observed to reduce or even eliminate some pathogens in the substrate they feed on. Other studies have shown mild treatments, such as solar-drying and oven-drying, were not effective for Salmonella elimination in contaminated raw insects.

Scientists said future research should focus on insect species with potential as food or feed.

“To guarantee data uniformity and allow comparison of Salmonella persistence in insects, we recommend defining species-specific reference study protocols.”

Another systematic review investigated the occurrence of Salmonella in crickets and mealworms.

Ten studies on crickets and nine on mealworms were included. Salmonella Wandsworth and Salmonella Stanley were isolated only in one sample of ready-to-eat crickets.

The Italian Ministry of Health funded the research and published in the International Journal of Food Microbiology.

Researchers said that few studies were found, and those included had limitations in study design as sampling was mostly based on convenience and not on a sound statistical basis. 

“The present systematic review underlines the need to obtain reliable data about Salmonella presence in insects considering the growing market and the scaling up of existing farms.”