Utz has issued a voluntary US recall of two potato chip brands after concerns that they could be contaminated with salmonella, a type of bacteria that can lead to food-borne illness.

Certain varieties of Zapp’s and Dirty potato chips may contain contamination linked to the seasoning used on the products, according to the US Food and Drug Administration in a recall issued on Monday. The recall applies to three flavors of Zapp’s chips sold in various bag sizes, along with three flavors of Dirty chips packaged in 2-ounce bags.

In total, nine chip varieties are affected, including flavors such as salt and vinegar and sour cream and onion, as listed on the FDA’s website.

Even though the seasoning batches involved tested negative for salmonella before being used, consumers are advised not to eat these products and to discard them right away.

The concern stems from a seasoning ingredient that includes dry milk powder, which may carry salmonella. This powder was sourced from California Dairies Inc and supplied through a third-party vendor. Utz has initiated the recall nationwide as a precautionary measure, according to the press release.

The affected products are: Zapp’s Brand Bayou Blackened Ranch Potato Chips (1.5oz), Zapp’s Brand Bayou Blackened Ranch Potato Chips (2.5oz), Zapp’s Brand Bayou Blackened Ranch Potato Chips (8oz), Dirty Brand Salt and Vinegar Potato Chips (2oz), Zapp’s Brand Salt and Vinegar Potato Chips (1.5oz), Dirty Brand Maui Onion Potato Chip (2oz), Zapp’s Brand Big Cheezy Potato Chip (2.5oz), Zapp’s Brand Big Cheezy Potato Chip (8oz), and Dirty Brand Sour Cream and Onion Potato Chips (2oz).

No other products produced by Utz are included in this recall. However, the California Dairies milk powder recall affected other companies as well, including Ghirardelli, which has recalled certain powdered drink mixes such as frappe and hot cocoa products. John B Sanfilippo & Son, a popular supplier of nuts and snacks, also issued a recall of certain snack mix items in connection with the possibly contaminated milk powder.

Salmonella is a group of bacteria responsible for food-borne illnesses and accounts for about one in four diarrheal diseases worldwide, according to the World Health Organization. Symptoms of infection typically include sudden fever, stomach pain, diarrhea, nausea and occasionally vomiting.

While most infections are mild, some can become severe or even life-threatening, especially for children and older adults.