Nov. 19 (UPI) -- Tom's of Maine, which markets its products as being made with "safe and hardworking natural ingredients," has received a warning from the Food and Drug Administration about a "black mold-like substance" found in a factory where its toothpaste is made.

The FDA warned in a letter dated Nov. 5, that Tom's of Maine -- which is owned by Colgate-Palmolive -- "failed to maintain buildings used in the manufacture, processing, packing or holding of drug products in a good state of repair," after finding a "black mold-like substance" near a batch of Tom's Silly Strawberry Anti-cavity toothpaste.

The FDA's inspection took place in May at Tom's of Maine's manufacturing plant in Sanford, Maine.

In the letter, the FDA also noted Tom's Simply White Clean Mint toothpaste was produced with water containing the bacteria Pseudomonas aeruginosa, a germ that can cause drug-resistant infections in the blood and lungs. The FDA also noted Ralstonia insidiosa bacteria in the water.

"Water is a major ingredient in many of your OTC drug products. It is essential that you employ a water system that is robustly designed, and that you effectively control, maintain and monitor the system to ensure it consistently produces water suitable for pharmaceutical use," the FDA wrote.

Another type of bacteria, Paracoccus yeei, was found in Tom's of Maine Wicked Cool! Anticavity Toothpaste, according to the FDA. Paracoccus yeei has been linked to infections, such as peritonitis and conjunctivitis, while none have been linked to Tom's of Maine products.

Tom's of Maine blamed the Paracoccus yeei bacteria on a "laboratory error," as the FDA called the company's response "inadequate."

"It does not include additional supporting evidence or testing results for the finished products," the FDA countered. "It is essential that your facility is in a good state of repair and sanitary conditions are maintained to protect drug products from potential routes of contamination."

Tom's of Maine issued a statement, saying it is working with the FDA to fix all of the problems.

"We have always tested finished goods before they leave our control, and we remain fully confident in the safety and quality of the toothpaste we make," Tom's of Maine said in a statement.

"In addition, we have engaged water specialists to evaluate our systems at Sanford, have implemented additional safeguards to ensure compliance with FDA standards and our water testing shows no issues," the company added, while promising to upgrade the plant's water system.

"Tom's is committed to making safe and effective natural products for our customers, and to maintaining the trust in our brand."