BLM Food Microbiology

The main microorganism in yoghurt is __________.

• Streptococcus thermophilus

• Lactobacillus acidophilus

• Leuconostoc citrovorum

• Streptococcus lactis

What is the purpose of enrichment broth in microbiological examination of food?

• provide nutrients necessary for development of wide range of microorganisms

• provide as a diluent to the procedure

• enhance mixture of food for analysis

• none of the above

Which of the following is an enrichment medium?

• Alkaline peptone water

• Loeffler serum slope

• Deoxycholate citrate agar

• Mac Conkey's agar

What is the purpose of serial dilution?

• To increase the concentration of a sample

• To decrease the concentration of a sample

• To measure the pH of a sample

• To measure the temperature of a sample

How is serial dilution performed?

• By adding a known volume of original sample to an equal volume of diluent

• By heating the sample

• By freezing the sample

• By centrifuging the sample

What are the advantages of using serial dilution?

• allows for precise measurement of concentration of a sample

• allows isolation of pure cultures of microorganisms from mixed populations

• allows for preparation of solutions with a known concentration

• All of the above

What are the limitations of using serial dilution?

• It can be time-consuming

• Errors can occur if volumes and concentrations are not measured accurately

• It may not be suitable for certain types of samples

• All of the above

How is the number of bacteria or other microorganisms calculated using serial dilution?

• plating aliquots of dilutedsamples on nutrient agar/suitable media&counting

• centrifuging aliquotsofdilutedsamples onnutrient agar/suitable media&count

• freezing aliquots of dilutedsamples on nutrient agar/other suitable media

• heating aliquots of dilutedsamples on nutrient agar/other suitable media

The purpose of providing durham tubes in each dilution tubes?

• to observe level of broth

• to detect pH of the broth

• to detect gas produced by micro organisms.

• none of the above

The volume of sample used to do spread plating on agar after serial dilution?

• 1 ml

• 0.5 ml

• 0.2 ml

• 0.1 ml