CIN Agar 50 FAQs and 30 MCQs
Master Cefsulodin-Irgasan-Novobiocin (CIN) Agar with this definitive guide for clinical microbiologists and lab technicians. Our resource combines 50 expert-curated FAQs and 30 challenging MCQs to sharpen your skills in isolating Yersinia enterocolitica and other fastidious enterics.
📌 What’s Covered?
✅ 50 In-Depth FAQs:
- Selective agents: How cefsulodin, irgasan, and novobiocin work
- Colony morphology: “Bull’s-eye” colonies vs. competing flora
- Protocol optimization: Inoculation, incubation (32°C/48h), and interpretation
- Clinical relevance: Diarrhea outbreaks, transfusion-related Yersinia
- Troubleshooting: Overgrowth, atypical colonies, QC failures
✅ 30 Practice MCQs:
◼️ Differentiating Yersinia from Proteus/Citrobacter
◼️ Decoding “red centers with transparent rims”
◼️ CLSI M35 guidelines for stool cultures
◼️ Comparison to MacConkey/XLD agar
🎯 Perfect For:
- Medical lab scientists (MLS/MLT)
- Public health outbreak investigators
- Microbiology students (USMLE, ASCP prep)
CIN Agar 50 FAQs
1. What is CIN Agar?
A selective and differential medium for isolating Yersinia enterocolitica.
2. What does “CIN” stand for?
Cefsulodin-Irgasan-Novobiocin.
3. Who developed CIN Agar?
Schiemann D.A. in 1979.
4. What is the primary purpose of CIN Agar?
To selectively isolate Yersinia enterocolitica from fecal/food samples.
5. Is CIN Agar selective or differential?
Both—it selects for Yersinia and differentiates via mannitol fermentation.
6. What are the key selective agents in CIN Agar?
Cefsulodin, Irgasan, Novobiocin, Crystal Violet, and bile salts.
7. Why is mannitol included?
As a fermentable carbohydrate; Yersinia ferments it, producing acidic byproducts.
8. What pH indicator is used in CIN Agar?
Neutral Red (turns red/pink at acidic pH).
9. Why is sodium pyruvate added?
To stimulate Yersinia growth.
10. How is CIN Agar prepared commercially?
As a base (Yersinia Agar Base) + CTN Selective Supplement (added post-autoclaving).
11. Why are antibiotics added after autoclaving?
Heat degrades cefsulodin, irgasan, and novobiocin.
12. What is the final pH of CIN Agar?
7.4 ± 0.2.
13. How does CIN Agar inhibit Gram-positive bacteria?
Via crystal violet, bile salts, and irgasan.
14. How does it inhibit Gram-negative competitors?
Cefsulodin and novobiocin target enteric flora.
15. What causes “bull’s-eye” colonies?
Mannitol fermentation → acid production → neutral red turns colonies dark red with translucent borders.
16. Why is Yersinia resistant to CIN’s antibiotics?
Natural resistance to cefsulodin, irgasan, and novobiocin.
17. What specimens is CIN Agar used for?
Fecal samples (clinical) and food samples.
18. Can CIN Agar isolate Aeromonas?
Yes, if cefsulodin concentration is reduced.
19. Which organisms are suppressed on CIN Agar?
E. coli, Salmonella, Proteus, Pseudomonas, Enterococcus, Staphylococcus.
20. Is CIN Agar used for viral isolation?
No—only for bacterial Yersinia spp.
21. How do Y. enterocolitica colonies appear?
Bull’s-eye”: Dark red center + translucent periphery.
22. What incubation conditions are optimal?
22–32°C for 24–48 hours.
23. Can other Yersinia species grow on CIN Agar?
Yes (e.g., Y. pseudotuberculosis, Y. intermedia), but colonies may resemble Y. enterocolitica.
24. Which non-Yersinia bacteria can grow on CIN Agar?
Aeromonas, Citrobacter freundii, Serratia liquefaciens.
25. What is a major limitation of CIN Agar?
Cannot definitively ID Y. enterocolitica—requires biochemical/genetic confirmation.
26. Why is autoclaving supplements avoided?
Antibiotics (cefsulodin/novobiocin) are heat-labile.
27. What happens if CTN supplement is added at >50°C?
Antibiotics may degrade, reducing selectivity.
28. How long can prepared CIN Agar be stored?
3–8 weeks at 2–8°C.
29. What QC organisms are used for CIN Agar?
Y. enterocolitica ATCC 27729 (growth + bull’s-eye).
E. coli ATCC 25922 (no growth).30. What color is unprepared CIN Agar powder?
Yellow to pink.
31. What color is solidified CIN Agar?
Orange-red/pink.
32. How should used CIN Agar be disposed of?
Autoclave or incinerate.
33. Is CIN Agar hazardous?
No, but clinical specimens are biohazardous.
34. Why is magnesium sulfate included?
Stimulates Yersinia growth.
35. What role does sodium deoxycholate play?
Inhibits Gram-positive and some Gram-negative bacteria.
36. How does irgasan (triclosan) work?
Broad-spectrum antimicrobial against Gram-positive/negative bacteria and fungi.
37. What is the function of neutral red?
pH indicator (red at pH ≤6.8, yellow at ≥8.0).
38. What if no colonies appear after incubation?
Incorrect storage of supplements.
Over-autoclaving.
Sample lacked Yersinia.39. What if non-Yersinia organisms grow?
CTN supplement was expired/underdosed.
Contamination during preparation.40. What if the medium appears cloudy?
Contaminated during preparation.
41. Can CIN Agar be used for water testing?
Yes, but may require filtration/concentration.
42. What is an alternative to CIN Agar?
MacConkey Agar (less selective for Yersinia).
43. How is CIN Agar modified for Aeromonas?
Reduce cefsulodin concentration.
44. Why is Y. enterocolitica significant?
Causes gastroenteritis, pseudoappendicitis, and systemic infections.
45. What foods are associated with Yersinia outbreaks?
Undercooked pork, dairy, contaminated water.
46. How was CIN Agar optimized since 1979?
Adjusted antibiotic concentrations for better selectivity.
47. What are newer alternatives to CIN Agar?
Chromogenic media (e.g., YECA for Yersinia).
48. How does CIN Agar compare to XLD Agar?
XLD targets Salmonella/Shigella; CIN targets Yersinia.
49. Is CIN Agar equivalent to YSA (Yersinia Selective Agar)?
Yes—YSA is a commercial variant.
50. Can CIN Agar replace PCR for Yersinia detection?
No—it’s a presumptive test; PCR confirms.
CIN Agar 30 MCQs
1. What is the primary purpose of CIN Agar?
A) Isolate Salmonella spp.
B) Selectively grow Yersinia enterocolitica
C) Enrich Escherichia coli
D) Culture anaerobic bacteria
2. The acronym “CIN” stands for:
A) Colistin-Irgasan-Nalidixic acid
B) Cefsulodin-Irgasan-Novobiocin
C) Chloramphenicol-Isoniazid-Nitrofurantoin
D) Ciprofloxacin-Isoniazid-Novobiocin
3. Which pH indicator is used in CIN Agar?
A) Phenol red
B) Neutral red
C) Bromothymol blue
D) Methyl red
4. Which component stimulates Yersinia growth in CIN Agar?
A) Sodium chloride
B) Sodium pyruvate
C) Magnesium sulfate
D) All of the above
5. Why are cefsulodin and novobiocin added post-autoclaving?
A) To enhance color change
B) They are heat-labile antibiotics
C) To prevent agar solidification
D) To reduce toxicity
6. What is the final pH of CIN Agar?
A) 6.2 ± 0.2
B) 7.4 ± 0.2
C) 8.0 ± 0.2
D) 5.4 ± 0.2
7. Which organism is not inhibited by CIN Agar?
A) Escherichia coli
B) Staphylococcus aureus
C) Yersinia enterocolitica
D) Enterococcus faecalis
8. The “bull’s-eye” appearance of Y. enterocolitica colonies is due to:
A) Hemolysis
B) Mannitol fermentation
C) Spore formation
D) Capsule production
9. Which selective agent targets Gram-positive bacteria in CIN Agar?
A) Cefsulodin
B) Crystal violet
C) Sodium pyruvate
D) Neutral red
10. CIN Agar is primarily used for which specimen type?
A) Blood cultures
B) Fecal samples
C) CSF
D) Sputum
11. Which temperature range is optimal for incubating CIN Agar?
A) 35–37°C
B) 22–32°C
C) 42–45°C
D) 15–20°C
12. Which non-Yersinia organism may grow on CIN Agar if cefsulodin is reduced?
A) Aeromonas spp.
B) Mycobacterium tuberculosis
C) Candida albicans
D) Clostridium difficile
13. Which QC organism should show growth with “bull’s-eye” colonies?
A) E. coli ATCC 25922
B) Y. enterocolitica ATCC 27729
C) S. aureus ATCC 25923
D) P. aeruginosa ATCC 27853
14. What indicates CIN Agar preparation failure?
A) Pink color post-solidification
B) Growth of E. coli ATCC 25922
C) Cloudy medium before inoculation
D) All of the above
15. How long can prepared CIN Agar be stored at 2–8°C?
A) 1 week
B) 3–8 weeks
C) 6 months
D) 1 year
16. Which component acts as a carbon source in CIN Agar?
A) Mannitol
B) Sodium deoxycholate
C) Neutral red
D) Magnesium sulfate
17. What is the role of irgasan (triclosan)?
A) Inhibit fungi
B) Enhance Yersinia pigment
C) Suppress Gram-positive and Gram-negative bacteria
D) Stabilize pH
18. Which Yersinia species may produce false-positive results?
A) Y. pestis
B) Y. pseudotuberculosis
C) Y. ruckeri
D) All of the above
19. A key limitation of CIN Agar is:
A) It kills Yersinia
B) Requires PCR for confirmation
C) Only works for viral cultures
D) Turns black with Salmonella
20. Which test is needed to confirm Y. enterocolitica after CIN Agar?
A) Oxidase test
B) Urease test
C) Coagulase test
D) Catalase test
21. A fecal sample from a food poisoning outbreak shows bull’s-eye colonies on CIN Agar. The most likely pathogen is:
A) Salmonella
B) Yersinia enterocolitica
C) Shigella
D) Vibrio cholerae
22. If Proteus mirabilis grows on CIN Agar, what is the likely issue?
A) Incorrect incubation temperature
B) CTN supplement failure
C) Over-autoclaving
D) All of the above
23. How does CIN Agar differ from MacConkey Agar?
A) CIN selects for Yersinia; MacConkey selects for enterics
B) CIN uses blood; MacConkey uses bile salts
C) CIN is for anaerobes; MacConkey is for aerobes
D) No difference
24. Which agar is not selective for Yersinia?
A) CIN Agar
B) YSA (Yersinia Selective Agar)
C) Hektoen Enteric Agar
D) Modified CIN Agar
25. How should CTN supplement be added to CIN Agar base?
A) Before autoclaving
B) At 60°C
C) At 45°C post-autoclaving
D) After solidification
26. What color indicates proper CIN Agar preparation?
A) Blue
B) Orange-red
C) Green
D) Black
27. How should used CIN Agar plates be discarded?
A) Autoclave/incinerate
B) Direct landfill
C) Freezing
D) Ethanol washing
28. Who first developed CIN Agar?
A) Robert Koch
B) Schiemann D.A.
C) Louis Pasteur
D) Alexander Fleming
29. CIN Agar is used to test which food for Yersinia?
A) Undercooked pork
B) Pasteurized milk
C) Canned vegetables
D) All of the above
30. What modern technique complements CIN Agar for Yersinia detection?
A) Gram staining
B) MALDI-TOF MS
C) Wet mount microscopy
D) None
- “How to read CIN agar for Yersinia“
- “CIN agar colony morphology MCQs”
- “Best temperature for Yersinia culture”
- “CLSI guidelines for stool pathogen isolation”
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