Hygiene Control

Enumerate vs. enrich+detect — how do you decide which to use?

Depends on expected concentration, not danger level.

High expected numbers (spoilage flora) → dilute and count.
example answer:
Lactic acid bacteria are the spoilage flora of packed cooked ham and are expected in high numbers (up to 10⁶–10⁷ CFU/g). After dilution, a plate will contain a countable number of colonies (30–300), so the concentration can be calculated and reported in log CFU/g.

Very low/absent expected numbers (most pathogens) → enrich, detect, confirm.
example answer:
Use enrichment, detection and confirmation. A 25 g sample is incubated in enrichment broth, so that the few Salmonella cells present can multiply to detectable numbers. A small volume is then plated on a selective agar, and suspect colonies are confirmed as Salmonella. The result is qualitative: Salmonella detected or not detected in 25 g. It does not give a count

Enumeration gives log CFU/g; enrichment gives presence/absence or Most Probable Number.

Why is direct microscopy rarely used for bacteria in food?

No amplification step — need >10⁶ cells/ml already present just to see any under the scope, so low (but still unsafe) counts look empty.

Food debris (fat droplets, particles) looks like bacteria → false counts either way.
Can't tell dead from alive (bacteria killed in pasturisation would still be counted for).

Better suited to fungi (bigger, ID'd by shape).

Elevated total plate count vs. elevated Enterobacteriaceae on a heated product — what does each mean?

Total count = general indicator (low-quality ingredients, storage, poor hygiene).

Enterobacteriaceae on a heated product = process failure specifically: inadequate heating or post-process contamination.

Enterobacteriaceae= heat-sensitive: proper pasteurisation kills them all.

final answer

a. An elevated total plate count is a general indicator of reduced microbial quality. It can be caused by low-quality ingredients, poor hygiene during production, or storage for too long or at too high a temperature.

b. Enterobacteriaceae in a heated product indicate a process failure. They are heat-sensitive and are killed by adequate pasteurisation, so they should be absent after heating. Their presence means either the heating was inadequate, or the product was recontaminated after the heating step.

What does each indicate: faecal coliforms, S. aureus, yeasts/fungi, LAB?

Faecal coliforms = faecal contamination. (through hands or raw vagatables aswell as they can carry fecal contanination through manure)

S. aureus = manual handling.

Yeasts/fungi = fruit/veg spoilage.

LAB = fruit/veg/MAP meat spoilage.

Pathogen–food associations: Salmonella, S. aureus, Listeria, B. cereus, V. vulnificus.

Salmonella–animal products.

S. aureus–manual work.

Listeria–RTE refrigerated products.

B. cereus–cooked foods.

V. vulnificus–seafood.

Volume plated: pour plate / spread plate / spiral plate?

Pour plate = 1 ml. Spread plate = 100 µl. Spiral plate = 50 µl.

Concentration formula + result format?

C = n × (1/d) × (1/V), V in ml. Convert to log₁₀, report as x.x log CFU/g or /ml (one decimal).

200 CFU counted, 100 µl of the 10⁻² dilution plated. C = ?

C = 200 × (1/10⁻²) × (1/0.1) = 200,000 CFU/g = 2.0×10⁵. log₁₀ = 5.3 log CFU/g.

50 colonies on -3 plate → expected count on -4 plate?

~5 colonies. One more dilution step = ÷10. Going back down a dilution step = ×10.

Preferred countable colony range, and why?

30–300.
Below 30 = high counting error.
Above 300 = colonies merge/uncountable so we undercount as they compete for space and nutrients

All plates show 0 colonies, even the least diluted — how do you report it?

Report as "<" the detection limit of your least-diluted plate. Use that plate's d and V in the formula with an inequality.

All plates overgrown, even the most dilute — how do you report it?

Report as ">" using 300 (top of countable range) on your most dilute plate, same formula with an inequality.

Multiple countable plates across dilutions — which one do you calculate from?

The one whose count falls in the 30–300 range. Don't average or default to least/most dilute.

Selective vs. non-selective vs. chromogenic media?

Non-selective = rich, supports wide range (PCA, BHI).

Selective = inhibits non-target, favours target (VRBG, ALOA).

Chromogenic = elective subtype, target colonies get a distinct colour.

A non-selective medium such as PCA is rich and contains no inhibitors, so a wide range of micro-organisms can grow. It is used to determine the total plate count of the chicken.

A selective medium such as VRBG contains compounds that inhibit non-target organisms, so mainly the target group grows. It is used to enumerate Enterobacteriaceae.

A chromogenic medium is also elective: it contains a substrate that is converted by an enzyme of the target organism into a coloured product. Target colonies therefore have a distinct colour and can be distinguished from other organisms that still grow on the plate.

Selectivity vs. specificity vs. electivity?

Selectivity = inhibits competitors, grows target.

Specificity = discriminates target from look-alikes.

Electivity = gives target distinct/recognisable colonies (e.g. colour).

Enrichment → detection → confirmation sequence?

Sample → enrich in selective broth → plate small volume for detection → isolate suspect colonies → confirm ID.

Result: detected/not detected, not a count.

MPN technique — what's a code like "3-2-1"?

3 tubes each at 1g/0.1g/0.01g, scored +/−. "3-2-1" = 3/3, 2/3, 1/3 positive. Look up in MPN table for a concentration estimate.

90 colonies on VRBG, only 4/5 tested confirm as true positives — adjust how?

Multiply raw count by confirmed fraction: 90 × 4/5 = 72. Then apply C = n×(1/d)×(1/V).

Surface sampling methods, and what does swab+ATP measure?

Dipslides, Rodac plates, swabs → CFU/cm².

ATP test = substrate+luciferase+ATP→light; measures general organic residue (microbial + food/somatic cells), not specifically microbes.

a. ATP on the swab reacts with luciferase and gives light. The light measures the amount of ATP. This comes from all organic residue (microbes and food), so it isn’t specific for micro-organisms.

b. ATP is high because food residue is left, so cleaning was poor. Rodac is low because few living microbes are left, so disinfection worked. They measure different things.

c. ATP: result within a minute. Rodac: counts living micro-organisms specifically.

Other environmental samples, and how is air sampled?

Dust, first product after C&D, rinsing line parts. Air: suck air over a plate/strip → CFU/m³. Early-warning tool along the process line.

Why doesn't end-product testing alone guarantee safety?

Small samples miss contamination (e.g. n=5 → 33% chance of accepting a contaminated lot). Takes days, expensive, and gives no info on the process itself.

Alternative to end-testing — name it and its synonyms.

Controlling critical steps throughout the process.

Synonyms: GMP/GHP, control measures, preventive measures, hygiene, PRP/OPRP.

Testing becomes a verification tool, not the safety mechanism.

Three main routes of pathogen contamination (milk example)?

(1) In raw materials — parasites, zoonoses.

(2) Survival of heating — sporeformers (B. cereus).

(3) Recontamination after heating — viruses, Listeria, Salmonella. Route 3 = most controllable via hygiene.

Transient vs. resident skin flora?

Transient = temporary, from illness/raw food/dirt contact, washed off fairly easily. Resident = permanent part of skin (e.g. S. aureus), hard to remove by washing.

Why don't gloves replace hand hygiene?

Hands must be clean before gloving. Gloves get contaminated during use too. Long gloves are for high-care areas only, not a routine default.

Practical hand-washing factors beyond just washing?

Timing, compliance (protocol ≠ followed), hand drying (wet hands transfer more), often followed by disinfection in high-care areas.

Define cleaning + typical log reduction.

Physical/chemical removal of dirt/soil. <1 log reduction, ~50–90% removed. Does not reliably kill microbes.

Cleaning vs. disinfection — full comparison?

Cleaning: <1 log, 50–90% removed, removes dirt/nutrients, prevents growth.

Disinfection: 5 log, 99.999% killed, kills to desired level, not sterile.

Why does leftover soil defeat disinfection? (3 mechanisms)

Nutrient source for regrowth.

Physical shield blocking disinfectant contact.

Chemically reacts with/consumes disinfectant. → Cleaning must precede disinfection.

Manager skips cleaning, doubles disinfectant on a meat slicer — predict outcome.

Soil left → bacteria grow, and soil blocks/inactivates disinfectant (esp. chlorinated).

More bacteria, spoils sooner, possibly more pathogens. Doubling conc. doesn't fix it — risks residues instead.

How can cleaning equipment itself cause contamination?

Unwashed brushes/sponges/cloths become reservoirs and spread contamination.

Cleaning also generates aerosols and can splash from drains.

Dry vs. wet cleaning — when used, can dry stand alone?

Dry (sweep/vacuum) used where water is risky (e.g. powder factories).

Usually precedes wet cleaning, not a standalone replacement in wet processes.

Foam/gel cleaning — key properties?

Increases contact time, is chemical cleaning, uses little water/energy, NOT necessarily labour-intensive.

Caution: condensation/safety hazard.

Main aim of a detergent?

Decrease surface tension, dissolve dirt.

Not a disinfectant — dissolving dirt ≠ killing microbes.

Why alternate normal cleaning with acid cleaning?

Removes calcification/scale, not a microbial-kill step.

Disinfection standard + precondition?

5 log reduction (99.999%), not sterile.

Must clean first — soil blocks disinfectant action.

Heat vs. UV disinfection?

Heat: denatures proteins; wet heat/steam > dry heat.

UV: damages RNA/DNA; only for clear liquids/filtered water

(can't penetrate turbid liquids or solids).

Oxidizers (halogens, H2O2, peracetic acid, ozone) — mechanism + weakness each?

Mechanism: oxidation of proteins/enzymes.

Halogens: soil-sensitive.

H2O2: degraded by catalase.

Peracetic acid: unstable/corrosive.

Ozone: very unstable/corrosive.

Alcohols — mechanism + concentration quirk?

Cause membrane leakage.

Higher conc. → bacteriostatic not bactericidal (dehydration instead of lysis). ~70% is the sweet spot.

Aldehydes, phenols, quats — mechanism + downside each?

Aldehydes: cell wall disturbance; unstable in alkaline, toxic.

Phenols: disturb enzymes; smell, highly toxic.

Quats: change membrane permeability; Gram-negatives can develop resistance.

Why alternate quats with a chlorinated disinfectant weekly?

Continuous use selects for resistance (esp. Gram-negatives to quats).

Alternating (different mechanism) prevents that resistance building up.

Factors that determine disinfectant choice?

Rinsability, water hardness, contact time available, solubility, cost vs. concentration, type/amount of soil.

Growth phase and disinfectant susceptibility?

Exponential-phase cells are much more susceptible than stationary-phase cells (shown with BAC data).

Steps of biofilm formation?

Needs time+surface+nutrients (unwashed, wet surface).

Attachment → multiplication → extracellular matrix formation (now resistant to C&D).

Why does biofilm resist disinfection?

Disinfectant can't penetrate deep layers. Reacts with matrix instead of cells. Chronic sub-lethal exposure can select for resistance within the biofilm.

Hygienic equipment definition + Class I vs. II?

Equipment cleanable and freed of relevant microbes.

Class I = cleaned in-place, no dismantling (CIP).
Class II = must be dismantled to clean.

Aseptic equipment, and why does hygienic design matter overall?

Sterilizable + impermeable to microbes, maintains sterility.

Core point: cleaning/disinfection fails if equipment can't be cleaned — design is a prerequisite.

4 hygienic design features and why?

No gaps/elastomer seals (trap residue).
Full drainage (no pooling).
Rounded edges >3mm (no residue traps).
No dead ends (no stagnant contamination).

Spell out GMP, GHP, OPRP, HACCP, TQM.

GMP=Good Manufacturing Practices. GHP=Good Hygienic Practices. OPRP=Operational Pre-Requisites Programme. HACCP=Hazard Analysis (and) Critical Control Points. TQM=Total Quality Management.

Food safety systems pyramid, bottom to top?

General food hygiene principles → food-related hygienic requirements → HACCP → ISO/TQM. Run together, not as alternatives.

GMP's "impossible vs. unlikely" design philosophy?

Impossible (strongest): structural blocks, e.g. sealed doors, barriers.

Unlikely: training, colour-coding, easy access to right equipment.

Structural fix > behavioural fix.

The 7 HACCP principles, in order?

1. Hazard analysis.

2. Determine CCPs.

3. Critical limits.

4. Monitoring system.

5. Corrective actions.

6. Verification procedures.

7. Documentation.

HACCP monitoring vs. verification — difference?

Monitoring = real-time check that a limit is met at a CCP.

Verification = separate check that the whole system is working (e.g. audits).

Why can a documented HACCP/GMP system still fail?

Needs training AND compliance with that training. Paper system alone achieves nothing — human factor decides success.

Zoning principle + counter-current layout?

Zones (low/medium/high care) by product vulnerability, stricter toward finished product. Layout flows dirty→clean: raw material→prep→processing→packaging→distribution; air flows the same direction.

Sources zoning controls + classic enforcement example?

Raw materials, air/water, employees, pests, equipment. Classic control: shoe-change at zone boundary.

General rule for placing a zoning barrier in any process?

Find the kill/heat step. Barrier goes immediately after it, before next handling/exposure.

Ice cream: premix→pasteurise→mature 8h→freeze/pack. Where's the zone boundary?

At/after pasteurisation (the kill step). Before = raw milk/egg handling (low care). After = must stay protected (high care).

Two mechanisms making pests a hazard?

(1) Entry of contamination — carry/deposit pathogens.

(2) Physical damage to raw materials/products.

Quantified rodent risk facts?

3–8 log CFU Salmonella/dropping. Sheds Salmonella 3+ months. 3–5 litters/year, 5–8 young/litter.

Three pillars of pest control, in order?

1) Facility design (fencing, screens, sealed holes/drains).

2) Protect food/water/waste.

3) Monitoring/trapping (traps along walls; insect-light traps risk scattering parts).

Overall pest control / module philosophy?

"Prevention is better than curing" — structural design first, then remove attractants, then monitor. Same logic as control measures > end-te

Quats — how does residual organic soil affect them, and what pH do they prefer?

Quats ARE inactivated by organic soil (a common exam "true/false" trap — they are NOT soil-immune).

They also work best in neutral-to-alkaline conditions; efficacy drops in acidic/low pH, and

hard water or anionic detergents/soap also deactivate them.

Codex Alimentarius formal definitions — food hygiene vs. food handling?

Food hygiene = all conditions and measures necessary to ensure the safety and suitability of food at all stages of the food chain.

Food handling = any operation in growing/harvesting, preparation, processing, packaging, storage, transport, distribution and sale of food.

4 effects of leftover food residue/detritus on disinfection?

(1) nutrient source for regrowth,

(2) physical shield protecting microbes,

(3) diminishes/reacts with disinfectant,

(4) decreases equipment performance (e.g. fouls heat exchangers).

Legal food safety concentration standards — Salmonella and Listeria?

Salmonella: absence in 25g. Listeria monocytogenes: <100 CFU/g at the moment of consumption. These are the numbers behind why "absence in 25g" requires enrichment, not direct plating.

Rule-of-thumb spoilage threshold?

Food is considered microbiologically spoiled when count > 10⁷ CFU/g (log cfu/g > 7).

Full list of 5 strategies to "assure food safety"

1) Sterilise everything

2) sterile process line,

3) test everything before clearance,

4) regular cleaning,

5) control critical steps during processing

Enrichment volumes in the standard workflow?

25 g sample → enrich → 100 µl for detection step → 10 µl further isolation streak.

Which three organisations provide standards, guidelines, or certification for hygienic equipment design?

EHEDG vs. 3-A vs. NSF — what's the difference?

EHEDG, 3-A and NSF

All three certify hygienic food equipment design (drainage, no dead ends, rounded edges, etc.).

EHEDG = European, issues guidelines + lab cleanability testing.

3-A SSI = US, older, issues formal standards (started with dairy).

NSF = US certification body for food equipment/water safety generally.

Mainly a geography split (EU vs. US); they collaborate and often co-certify equipment.

The detection limit is the highest of ELISA, namely 10⁵cfu/ml. The detection limit of spiral plater is 10³cfu/ml, of PCR 10⁴cfu/ml, of chromogenic media 10²cfu/ml and of TEMPO 10 cfu/ml for coliforms and 10²cfu/ml for total plate count.