Strawberry Bacteria: Plant Diseases and Food Safety

The term “strawberry bacteria” refers to two distinct groups. The first are bacteria that contaminate the fruit intended for consumption, posing a risk to human health. The second are bacteria responsible for diseases that affect the strawberry plant itself. Understanding both facets of this term is important for consumers and gardeners alike.

Bacterial Contamination and Foodborne Illness

Because strawberries are consumed raw, they can harbor pathogenic bacteria that cause foodborne illnesses. Primary contaminants include Escherichia coli (E. coli), Salmonella, and Listeria monocytogenes. These microbes, along with viruses like Hepatitis A, can be introduced to the fruit at any point from the field to the consumer’s table.

Contamination can originate from several sources:

• Contact with inadequately composted manure, contaminated irrigation water, or soil in the field.
• Poor hygiene from workers during or after the harvest.
• Use of contaminated equipment during processing.
• Cross-contamination during transport or at retail if strawberries contact raw meat or other contaminated products.

Ingesting contaminated strawberries can lead to symptoms within 12 to 72 hours. E. coli infections may cause severe stomach cramps, bloody diarrhea, and vomiting. Salmonella commonly results in diarrhea, fever, and abdominal cramps. Listeria monocytogenes is a serious concern because it can thrive in refrigerated temperatures, posing a higher risk to pregnant women, newborns, older adults, and those with weakened immune systems.

Bacteria like E. coli and Salmonella can survive on strawberries for extended periods, even during refrigerated storage, and have been found on both field-fresh and market-sold fruit. A strawberry’s complex, porous surface provides an ideal environment for bacteria to attach. This makes proper cleaning before consumption necessary.

Bacterial Diseases of the Strawberry Plant

Separate from bacteria that risk human health are those that cause diseases in the strawberry plant, affecting its health and yield. A primary bacterial disease is Angular Leaf Spot, caused by Xanthomonas fragariae. This pathogen is highly specific to strawberry plants and concerns growers worldwide.

The symptoms of Angular Leaf Spot are most visible on the foliage, beginning as small, water-soaked lesions on the underside of leaves that appear translucent when held to light. As the disease progresses, these lesions enlarge and merge, forming reddish-brown, angular spots bounded by leaf veins. In high humidity, a sticky bacterial ooze may appear on the lesions, which dries into a whitish film.

Severe infections can affect the calyx (the green leafy cap), causing it to turn brown and dry, a symptom called “brown cap.” A diseased calyx reduces the fruit’s marketability, even though the bacterium does not directly infect the fruit tissue. The infection can also become systemic, leading to the collapse and death of the entire plant.

Xanthomonas fragariae primarily spreads through water splash from rain or overhead irrigation. The most common source of initial infection in a new field is contaminated nursery stock or transplants. Prevention focuses on using certified disease-free plants, ensuring good air circulation to keep leaves dry, and avoiding overhead watering.

Safe Washing and Storage Methods

Proper handling, washing, and storage of strawberries can minimize the risk of foodborne illness. Because strawberries are delicate, they should not be washed until just before eating. Washing them too early adds moisture that accelerates spoilage and mold growth, even in the refrigerator.

Store unwashed strawberries in the crisper drawer of a refrigerator at 40°F (4°C) or below. Keep them in their original container or a partially opened plastic bag to maintain humidity and prevent them from drying out. Discard any bruised or moldy berries immediately to prevent spoilage from spreading.

To wash strawberries, place them in a colander and rinse under cool, running water. Gently rub each berry with your fingers to dislodge surface contaminants. Soaps, detergents, or commercial produce washes are not recommended, as the fruit can absorb their residues. After rinsing, dry the strawberries thoroughly with a clean paper towel.

An alternative method is to soak berries in a solution of three parts water to one part white vinegar for several minutes, which may help reduce bacteria. Regardless of the method, always start with clean hands and use clean surfaces and utensils to prevent cross-contamination. Cut strawberries should be refrigerated within two hours.