Queseria Chipilo’s recall last August of Oaxaca String, Queso Fresco, and Queso Fresco Hoja De Plátano cheeses due to Listeria contamination was only the tip of the pathogen iceberg.

The Passaic, NJ-based company opted to temporarily close, placed an embargo on all its cheese products and ultimately destroyed all its production. No illnesses were connected to the crisis.

But now the cheese-maker is back in operation, and in receipt of a March 3 warning letter from the U.S. Food and Drug Administration (FDA) that says a series of inspections point to conditions being ripe for contamination of both the company’s processing plant and its cheese products.

Queseria’s ready-to-eat Oaxaca string cheese and seven specific locations inside its facility were contaminated with Listeria monocytogenes, according to the FDA, based on environmental samples collected for laboratory analysis.

FDA inspected the Queseria Chipilo facility from Aug. 9 to 18, 2010, and again from Aug. 26 through Sept. 23, and from Oct. 25 to Nov. 8.  It first took product samples and said lab-test results showed the string cheese was contaminated.

Agency inspectors then took 69 environmental samples from inside the plant.  When the results were in, FDA said it had identified seven sites inside the plant that were harboring Listeria. They included:

— The food contract surface at the base of the bin where the string cheese was placed.

— The food contact surface at the top of the measuring scale.

— The cracked and depressed area of floor near a drain.

— The interior edge in the production floor drain.

— The front left wheel of a salt bin adjacent to the commercial strip curtain.

— The floor of the production area adjacent to two round metal kettles.

“Pulsed Field Gel Electrophoresis (PFGE) testing results showed that seven L. monocytogenes isolates obtained from the environmental swabs collected from your facility in August 2010 had an identical PFGE pattern with an isolate obtained from your finished product Que Sabroso Oaxaca String Cheese,” FDA said in the warning letter.

“This is significant because the seven swabs were collected from multiple different locations in your production area, from food contact and non-food contact surfaces; indicating that L. monocytogenes was transported throughout your facility and was reasonably likely to contaminate food.”

FDA said that during the inspection it found “significant violations” at the cheese-making facility.

Those included knives being used to open packages of curd mozzarella without first being cleaned or sanitized, dirty exhaust fans, use of dirt-covered extension cords above cheese products, and a filth accumulation on the ceiling and electric cheese mixer.

FDA said the company’s food contact surfaces were not corrosion-resistant and plumbing problems included clogged drains in the men’s room and in a cheese production area.

Employees’ hygienic practices also concerned the inspectors. Aprons were said to be stored in the women’s rest room unprotected from contamination, an employee was observed cutting ready-to-eat cheese against his cut-through apron, and employees were coming and going from the production area without cleaning and sanitizing hands, gloves, and aprons.

In the warning letter, made public this week, FDA acknowledged the company has corrected its plumbing and drainage problems.  It said other violations continue to exist.

In its most recent inspection, FDA said it was concerned about cheese being stored in a hallway for five hours without refrigeration.  It also said the cheese maker was not able to provide documentation for employee training, and was not doing any environmental sampling on its own.