Bacillus cereus

1
Bacillus cereus

• Food Microbiology

2
Methods

• Direct Plate
• Dilute in Phosphate Buffer
• 50 g Samples
• Gentle Blend/Shake
• MPN

3
Mannitol Egg Yolk Polymixin B

• Polymixin Selective Antibiotic
• Egg Yolk Differential
• Lecithinase or Phospholipase by B. cereus
• Mannitol
• B. cereus can NOT ferment mannitol NO pH Change

4
Solid Method

• Pre-Poured Plates
• Only Plate 0.1 ml Aliquots
• 15-150 Countalbe
• Typical
• Round, flat, dry, with or without clear zone
• ground glass appearance
• Creamy White
• PRESUMPTIVE

5
Confirmation

• Motility Test
• Positive
• Rhizoid Growth
• Put 2 loopfuls in center of nutrient agar plate
• 30 C for 24-48 h
• Rhizoid Growth (Hairlike Appendages)
• Hemolytic Activity
• Trypticase Sheep Blood Agar
• Clear Zones
• 24 hours

6
Confirmation

• Nitrate Test Positive
• Lysozyme Test
• Nutrient Broth with Lysozyme
• Breaks beta 1,4 linkages
• B. cereus will Grow
• V-P Test
• Positive

7
MPN Method

• Trypitase Soy Polymixin Broth
• 24-48 h at 35 C
• Growth is Positive
• Presumptive
• Streak onto Mannitol Egg Yolk Polymixin
• Confirmation Tests