Unit 1: Laboratory Practices and Microbial Techniques - Practice Quiz

1 What is the main purpose of sterilization in a microbiology laboratory?

2 Which instrument is commonly used for sterilizing culture media with steam under pressure?

3 What is a pure microbial culture?

4 Which technique is commonly used to obtain isolated microbial colonies on solid media?

5 What is the function of agar in many microbiological culture media?

6 Why are aseptic techniques used during microbial culture handling?

7 What does an incubator provide for growing microorganisms?

8 Which type of medium contains known and measured chemical components?

9 What is inoculation in microbial production?

10 Which microbial group is commonly used as a nitrogen-fixing biofertilizer?

11 What is the main role of a carrier material in a biofertilizer formulation?

12 Which property is desirable in a carrier used for biofertilizer production?

13 What is a biopesticide?

14 Which microorganism is widely used in the production of some fungal biopesticides?

15 What is the purpose of serial dilution in microbial laboratory work?

16 What does a colony-forming unit, or CFU, generally represent?

17 Which method is used to separate microbial cells from a liquid suspension according to density?

18 Why is pH important in microbial culture media?

19 What is the purpose of maintaining a stock culture?

20 Which practice helps confirm that a biofertilizer contains the intended microorganism?

21 A technician must prepare a pure Trichoderma inoculum from a soil sample containing several fungi. Which procedure is most appropriate?

22 During the production of a bacterial biofertilizer, microbial growth stops earlier than expected because the broth becomes strongly acidic. Which corrective action is most suitable for the next batch?

23 A culture medium must be sterilized without degrading a heat-sensitive vitamin solution. Which method should be used for the vitamin solution?

24 A laboratory needs of a dilution from a microbial suspension. Which preparation is correct?

25 Plate counts from a biofertilizer sample are 42 colonies at dilution and 5 colonies at dilution, using per plate. Which result should be used to estimate viable count?

26 A broth culture used for biofertilizer production contains . What viable count is expected after a tenfold dilution?

27 A bacterial biopesticide culture is growing slowly in a fermenter despite having adequate nutrients and optimum temperature. Dissolved oxygen is nearly zero. What adjustment is most appropriate?

28 Why is an actively growing log-phase culture generally preferred as the inoculum for large-scale fermentation?

29 After autoclaving a carrier material, a biological indicator containing resistant bacterial spores still shows growth. What should the technician conclude?

30 Several bacterial colonies with different colors and shapes appear on a quality-control plate from a product expected to contain one strain. What is the best interpretation?

31 Which laboratory setup best reduces contamination while transferring a pure microbial culture into sterile production medium?

32 A peat-based Rhizobium formulation loses viability rapidly during storage because the carrier dries out. Which modification is most appropriate?

33 A technician measures high turbidity in a bacterial fermentation broth, but plate counts show low viable numbers. Which explanation is most likely?

34 A fungal biopesticide is being produced by solid-state fermentation. Which condition is most important for obtaining uniform sporulation throughout the substrate?

35 In a dual-culture assay, Trichoderma grows toward a plant pathogen and creates a clear inhibition zone between the colonies. What does this result most directly indicate?

36 A phosphate-solubilizing bacterial isolate forms a clear halo around its colony on an insoluble phosphate medium. What is the most appropriate conclusion?

37 A nitrogen-fixing bacterial isolate grows on nitrogen-free medium, but a control plate inoculated with a known non-fixer also shows growth. What should be done first?

38 A newly produced Bacillus-based biopesticide has a high viable count but gives weak disease control. Which additional quality test is most relevant?

39 When scaling a bacterial culture from a flask to a fermenter, the technician adds a very small amount of old stationary-phase inoculum. The fermenter shows a long lag phase. Which change is most likely to improve the process?

40 A formulated microbial product passes viable-count testing immediately after production. Which study is needed to assign a scientifically supported expiry date?

41 A microbial inoculant production batch shows a normal total viable count, but repeated plating on a selective medium reveals an increasing proportion of non-target colonies. Which investigation is most appropriate before releasing the batch?

42 During serial dilution plating, the dilution gives 168 colonies from , while the dilution gives 1,420 colonies. Which result should be used to estimate the original concentration, assuming the plates were prepared correctly?

43 A nitrogen-fixing bacterial inoculant loses viability after sterilized carrier material is mixed with the culture. The carrier has a low water potential and contains residual peroxide from processing. Which corrective sequence is most defensible?

44 A fungal biopesticide culture produces abundant biomass but very few viable conidia. Dissolved oxygen is adequate, and microscopy shows extensive hyphal growth. Which process change is most likely to improve propagule production?

45 Two bacterial strains each promote plant growth when tested separately, but their mixture performs poorly because one strain suppresses the other in the carrier. Which experiment best distinguishes true incompatibility from an inoculum-ratio artifact?

46 A suspected contaminant grows slowly and is missed by routine endpoint inspection of a biofertilizer culture. Which quality-control design provides the strongest early warning without relying on a single indicator?

47 A batch of phosphate-solubilizing bacteria gives a large clear halo on agar but fails to increase available phosphorus in soil. Which interpretation is most scientifically justified?

48 A bacterial biopesticide retains high CFU counts after storage, but its insecticidal activity declines sharply. Which additional quality attribute should be prioritized?

49 A sterilization validation test shows no growth from one biological indicator placed near the steam inlet, but growth occurs in an indicator located in a densely packed carrier load. What is the correct conclusion?

50 A culture's optical density increases after a formulation preservative is added, but viable counts decrease. Which explanation best accounts for both observations?

51 A production strain is repeatedly subcultured and gradually loses its biocontrol activity while retaining its colony morphology. Which laboratory practice would best reduce this risk?

52 During scale-up, agitation is increased so that the impeller tip speed remains constant, but oxygen limitation appears in the larger vessel. Which factor most likely explains the failure?

53 A biofertilizer strain grows well in a laboratory medium but fails to establish on seed after inoculation. The inoculant has an adequate CFU count at manufacture. Which test most directly addresses the likely failure?

54 A microbial product is intended for use with a fungicidal seed treatment. The product works alone but fails in combination. Which validation strategy is most appropriate?

55 A plate count of a spore-forming biopesticide is unexpectedly low, although microscopy shows many intact spores. Which method comparison would best determine whether spores are viable but dormant or genuinely nonviable?

56 A formulation shows acceptable viability immediately after production but fails the shelf-life requirement because viability declines rapidly at high water activity. Which formulation change is most rational?

57 A plant-growth assay shows improved biomass in inoculated plants, but the uninoculated control has unusually poor growth and high variability. What is the most important next step before attributing the effect to the biofertilizer?

58 A bacterial isolate inhibits a pathogen on dual-culture plates, but inhibition disappears when the assay medium is buffered near neutral pH. Which conclusion is most defensible?

59 A microbial count is highly reproducible between technical replicates but differs substantially between independent production batches. Which quality-improvement action is most appropriate?

60 A biopesticide candidate produces a clear inhibition zone against a pathogen, but the zone is absent when the candidate is separated from the pathogen by a sealed barrier that permits only volatile compounds. What does this result indicate?