ICAR AIEEA-PG Microbiological Quality Assurance & Rapid Methods: practice questions

1 · Microbiological criteria and how they are set · medium

Which document sets out the internationally agreed components of a microbiological criterion for foods?

1. Codex CXG 21-1997, revised in 2013
2. The WHO Laboratory Biosafety Manual
3. ISO 7218
4. ISO/IEC 17025:2017

2 · Microbiological criteria and how they are set · medium

Under the EU regulation on microbiological criteria, a process hygiene criterion:

1. Defines whether a batch already on the market is safe and must be recalled
2. Applies only to Salmonella and Listeria in ready-to-eat foods
3. Signals whether the process is working acceptably
4. Sets limits for chemical contaminants in milk

3 · Indicator organisms: coliforms, Enterobacteriaceae, E. coli · easy

Coliforms are defined as Gram-negative non-spore-forming rods that:

1. Ferment lactose with acid and gas within 48 h at 30–37 °C
2. Ferment glucose but never lactose
3. Form heat-resistant spores that survive pasteurisation at 72 °C
4. Grow only above 55 °C

4 · Indicator organisms: coliforms, Enterobacteriaceae, E. coli · easy

Which indicator is most specific for faecal contamination?

1. Yeasts and moulds
2. Escherichia coli
3. Total coliforms
4. Total viable count

5 · Standard plate count and other enumeration methods · medium

Duplicate 1 mL plates give 232 and 244 colonies at 10^-2 and 33 and 28 at 10^-3. The ISO 7218 weighted-mean count per mL is:

1. 2.4 × 10^3
2. 2.4 × 10^5
3. 3.1 × 10^4
4. 2.4 × 10^4

6 · Standard plate count and other enumeration methods · medium

A spread plate of 0.1 mL of the 10^-3 dilution has 150 colonies. The count per mL of the original sample is:

1. 1.5 × 10^6
2. 1.5 × 10^7
3. 1.5 × 10^5
4. 1.5 × 10^4

7 · Standard plate count and other enumeration methods · medium

The most probable number method is especially useful for:

1. Very high counts in cheese
2. Low numbers in liquids
3. Identifying species
4. Counting dead cells

8 · Standard plate count and other enumeration methods · easy

Microbial counts are reported to how many significant figures?

1. Four
2. Five
3. None
4. Two

9 · Detection and isolation of pathogens · easy

The usual sequence in cultural detection of a pathogen is:

1. Direct plating only, without enrichment
2. Pre-enrichment, selective enrichment, plating, confirmation
3. Confirmation first, then enrichment
4. Selective plating, then pre-enrichment, then serological confirmation

10 · Detection and isolation of pathogens · medium

In ISO 6579-1 for Salmonella, Rappaport-Vassiliadis soya broth is incubated at:

1. 25 °C
2. 37 °C under anaerobic conditions
3. 41.5 °C
4. 30 °C