Food Food (soil) (soil) Water Water Time Time Microbial Growth Requirements organism temperature
FoodFood(soil)(soil)
WaterWater TimeTime
Microbial Growth Requirements
organism temperature
FoodFood(soil)(soil)
WaterWater TimeTime
Microbial Growth Microbial Growth RequirementsRequirements
Sleuthing Microbial Growth NichesSleuthing Microbial Growth Niches
• Observe operating practices (if possible), including sanitation
• Maintenance and repair practices
• Equipment design (including modifications)
The Slicer DilemmaThe Slicer DilemmaSausage slicer
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Problem: Daily post-operational swabs of the slicer blade are consistently positive for the presence of Listeria. However,
pre-op swabs and finished product testing always yield negative results. The product is fermented sausage with a pH below
4.0. What is going on, and where should I begin my investigation?
Slicer Investigation BeginsSlicer Investigation Begins
• Observe the process (including sanitation) -Beware of gloves! See if workers and
supervisors understand how to use gloves -Blade sharpening and handling of machine
controls and product -Stoppages and start-ups -Handling of bins and pallets by hand-truckers -Any other actions that may cause
contamination (hand wash stations, aerosols, condensation, hygiene, outerwear, etc.)
More slicer investigationMore slicer investigation
• Observe maintenance practices
-After adjustments, repairs, replacing parts, etc., is the area (including non-product contact surfaces) sanitized efficiently?
-Take operational samples
Check out the Slicer DesignCheck out the Slicer Design
• Maintenance personnel are historians
-Is the machine being used as it should?
-How old is the equipment?
-Has the design been altered? If so, how?
-The most common red flag is neglect
-Old habits die hard
-A new set of eyes
Sleuthing the Slicer ProblemSleuthing the Slicer Problem
• Operating/maintenance procedures and process
-No environmental issues were observed
-Operators switched machines almost on a daily basis
-Sanitation was effective
-Other slicers were OK
-Maintenance practices appeared sound
More SleuthingMore Sleuthing
• Investigating the machine’s design
-Blade housing
Chat With PersonnelChat With Personnel
• QA manager, sanitation engineer and maintenance supervisor agreed that although blade housing is hollow, it is air-tight.
• Experienced maintenance man (the “historian”) reveals that the 30 year old slicer was modified.
• Visual inspection confirms radical changes
Digging InDigging In
• Several new bolts were observed
• Blade was removed showing discolored liquid marks (now dry) on surface of housing
• When bolts were removed brown liquid began to leak from inside housing
• Brown liquid tested positive for presence of Listeria
What Happened?What Happened?
• Over the years, sanitizer, rinse water and food residue entered the hollow blade housing through tiny openings around added bolts
• Conditions inside did not reach kill temperature• Rotation of the blade caused a vacuum and
drew the contaminated liquid out • Original design was altered and system was out
of control
Suggestions: Eliminating the SourceSuggestions: Eliminating the Source
• Options for regaining microbial control
-Purchase new equipment
-Have maintenance department alter bolt holes with filler to prevent leaks
-Drill new drainage holes
-Have machine overhauled
-Alternative heat treatments (need validation)
Summary: Finding The SourceSummary: Finding The Source
• Growth niches are dependent upon nutrients, moisture and time
• Investigations should include observing the operation, maintenance and design
• Paradigms of plant personnel can be very telling (neglect raises red flags, new set of eyes, etc.)
• Veteran maintenance personnel are historians• Use the proper sampling device for the job (food
contact and non-contact surfaces and air)