Food Microbiology
Usmle Step 1: Microbiology
Compiled By Simon Mwangi
Edition: 2024/25
, Hospitality & Food & Beverages | Food Microbiology I of LXIII pages
1. Function and chemical composition of bacterial structure: Peptidoglycan
Function:
1. Rigid support
2. Protects against osmotic pressure
Chemical composition:
Sugar backbone with crosslinked peptide side chains
2. Function and chemical composition of bacterial structure: Cell wall/cell membrane
Gram positives only
Function: Major surface antigen
Chemical composition: Teichoic acid, which induces TNF and IL1
3. Function and chemical composition of bacterial structure: Outer membrane
Gram negatives only
Function: Site of endotoxin (lipopolysaccharide) and major surface antigen
Chemical composition: Lipid A induces TNF and IL1, and polysaccharide is the antigen
4. Function and chemical composition of bacterial structure: Plasma membrane
Function: Site of oxidative and transport enzymes
Chemical composition: Lipoprotein bilayer
5. Function and chemical composition of bacterial structure: Ribosome
Function: Protein synthesis
Chemical composition: 50S and 30S subunits
6. Function and chemical composition of bacterial structure: Periplasm
Function: Space between the cytoplasmic membrane and outer membrane in gramnegative bacteria
Chemical composition: Contains many hydrolytic enzymes, including betalactamases
7. Function and chemical composition of bacterial structure: Capsule
Function: Protects against phagocytosis
Chemical composition: Polysaccharide (except Bacillus anthracis which contains Dglutamate)
8. Function and chemical composition of bacterial structure: Pilus/fimbria
Function: Mediates adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during
Chemical composition: Glycoprotein
9. Function and chemical composition of bacterial structure: Flagellum
Function: Motility
Chemical composition: Protein
10. Function and chemical composition of bacterial structure: Spore
Function: Provides resistance to dehydration, heat, and chemicals
Chemical composition: Keratinlike coat and dipicolinic acid
Food Microbiology 2024/25 Edition
, Hospitality & Food & Beverages | Food Microbiology II of LXIII pages
11. Function and chemical composition of bacterial structure: Plasmid
Function: Contains a variety of genes for antibiotic resistance, enzymes, and toxins
Chemical composition: DNA
12. Function and chemical composition of bacterial structure: Glycocalyx
Function: Mediates adherence to surfaces, especially foreign surfaces (eg indwelling catheters)
Chemical composition: Polysaccharide
13. Function of this structure: IgA proteases
Function: Allow some organisms to colonize mucosal surfaces
14. Which bacteria have IgA proteases?
1. Streptococcus pneumoniae
2. Neisseria meningitidis
3. Neisseria gonorrheae
4. Hemophilus influenzae
15. Which bacterial substances induce cytokines, and which are they?
Cytokines induced:
1. IL1
2. TNF
Gram positive inducer: Teichoic acid
Gram negative inducer: Lipopolysaccharide (Endoxtoxin)
16. What does the capsule of Bacillus anthracis consist of?
Dglutamate
17. What bacterial structure contains Dglutamate?
Capsule of Bacillus anthracis
18. What are the main differences between gram negative and gram positive organisms?
Peptidoglycan cell wall: Gram positive has thick. Gram negative has thin.
Flagellar basal body rings: Gram positive has two. Gram negative has four.
Outer antigen: Gram positive: Teichoic acid. Gram negative: Lipidpolysaccharide
Periplasmic space: Gram positive does not have. Gram negative has.
Porin channel: Gram positive does not have. Gram negative has.
Lysozyme and penicillin attack: Gram positive are sensitive. Gram negative are resistant.
19. What bacteria do not gram stain well?
Mnemonic: These Rascals May Microscopically Lack Color
1. Treponema
2. Rickettsia
3. Mycobacteria
4. Mycoplasma
5. Legionella pneumophila
6. Chlamydia
Food Microbiology 2024/25 Edition
, Hospitality & Food & Beverages | Food Microbiology III of LXIII pages
20. Why does the following bug not gram stain well?: Treponema
Too thin to be visualized
21. Why does the following bug not gram stain well?: Rickettsia
Intracellular parasite
22. Why does the following bug not gram stain well?: Mycobacteria
highlipidcontent cell wall
23. Why does the following bug not gram stain well?: Mycoplasma
No cell wall
24. Why does the following bug not gram stain well?: Legionella pneumophila
Primarily intracellular
25. Why does the following bug not gram stain well?: Chlamydia
Intracellular parasite which lacks muramic acid in cell wall
26. How is the following bug visualized?: Treponema
1. Darkfield microscopy
2. Fluorescent antibody staining
3. silver stain
27. Why does the following bug not gram stain well?: Mycobacteria
Acid fast for high lipid content cell wall
28. What are the stages of bacterial growth and what are their relative lengths?
1. Lag phase: x
2. Log phase: 1.5x
3. Stationary phase: 2.5x
4. Death phase: 4x
29. What happens in the following phase of bacterial growth, and where does it fall in the order?: Lag
1st phase: Metabolic activity without division
30. What happens in the following phase of bacterial growth, and where does it fall in the order?: Log
2nd phase: Rapid cell division
31. What happens in the following phase of bacterial growth, and where does it fall in the order?: Stationary
3rd phase: Nutrient depletion slows growth
32. What happens in the following phase of bacterial growth, and where does it fall in the order?: Death
4th phase: Prolonged nutrient depletion and buildup of waste products leads to death
33. Bacterial endotoxins and exotoxins: Source?
Exotoxin: Certain species of gram positive and gram negative bacteria
Endotoxin: Cell wall of most gramnegative bacteria
34. Bacterial endotoxins and exotoxins: Secreted from cell?
Exotoxin: Yes
Endotoxin: No
35. Bacterial endotoxins and exotoxins: Chemistry
Exotoxin: Polypeptide
Endotoxin: Lipopolysaccharide
36. Bacterial endotoxins and exotoxins: Location of genes
Exotoxin: Plasmid or bacteriophage
Endotoxin: Bacterial chromosome
Food Microbiology 2024/25 Edition
Usmle Step 1: Microbiology
Compiled By Simon Mwangi
Edition: 2024/25
, Hospitality & Food & Beverages | Food Microbiology I of LXIII pages
1. Function and chemical composition of bacterial structure: Peptidoglycan
Function:
1. Rigid support
2. Protects against osmotic pressure
Chemical composition:
Sugar backbone with crosslinked peptide side chains
2. Function and chemical composition of bacterial structure: Cell wall/cell membrane
Gram positives only
Function: Major surface antigen
Chemical composition: Teichoic acid, which induces TNF and IL1
3. Function and chemical composition of bacterial structure: Outer membrane
Gram negatives only
Function: Site of endotoxin (lipopolysaccharide) and major surface antigen
Chemical composition: Lipid A induces TNF and IL1, and polysaccharide is the antigen
4. Function and chemical composition of bacterial structure: Plasma membrane
Function: Site of oxidative and transport enzymes
Chemical composition: Lipoprotein bilayer
5. Function and chemical composition of bacterial structure: Ribosome
Function: Protein synthesis
Chemical composition: 50S and 30S subunits
6. Function and chemical composition of bacterial structure: Periplasm
Function: Space between the cytoplasmic membrane and outer membrane in gramnegative bacteria
Chemical composition: Contains many hydrolytic enzymes, including betalactamases
7. Function and chemical composition of bacterial structure: Capsule
Function: Protects against phagocytosis
Chemical composition: Polysaccharide (except Bacillus anthracis which contains Dglutamate)
8. Function and chemical composition of bacterial structure: Pilus/fimbria
Function: Mediates adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during
Chemical composition: Glycoprotein
9. Function and chemical composition of bacterial structure: Flagellum
Function: Motility
Chemical composition: Protein
10. Function and chemical composition of bacterial structure: Spore
Function: Provides resistance to dehydration, heat, and chemicals
Chemical composition: Keratinlike coat and dipicolinic acid
Food Microbiology 2024/25 Edition
, Hospitality & Food & Beverages | Food Microbiology II of LXIII pages
11. Function and chemical composition of bacterial structure: Plasmid
Function: Contains a variety of genes for antibiotic resistance, enzymes, and toxins
Chemical composition: DNA
12. Function and chemical composition of bacterial structure: Glycocalyx
Function: Mediates adherence to surfaces, especially foreign surfaces (eg indwelling catheters)
Chemical composition: Polysaccharide
13. Function of this structure: IgA proteases
Function: Allow some organisms to colonize mucosal surfaces
14. Which bacteria have IgA proteases?
1. Streptococcus pneumoniae
2. Neisseria meningitidis
3. Neisseria gonorrheae
4. Hemophilus influenzae
15. Which bacterial substances induce cytokines, and which are they?
Cytokines induced:
1. IL1
2. TNF
Gram positive inducer: Teichoic acid
Gram negative inducer: Lipopolysaccharide (Endoxtoxin)
16. What does the capsule of Bacillus anthracis consist of?
Dglutamate
17. What bacterial structure contains Dglutamate?
Capsule of Bacillus anthracis
18. What are the main differences between gram negative and gram positive organisms?
Peptidoglycan cell wall: Gram positive has thick. Gram negative has thin.
Flagellar basal body rings: Gram positive has two. Gram negative has four.
Outer antigen: Gram positive: Teichoic acid. Gram negative: Lipidpolysaccharide
Periplasmic space: Gram positive does not have. Gram negative has.
Porin channel: Gram positive does not have. Gram negative has.
Lysozyme and penicillin attack: Gram positive are sensitive. Gram negative are resistant.
19. What bacteria do not gram stain well?
Mnemonic: These Rascals May Microscopically Lack Color
1. Treponema
2. Rickettsia
3. Mycobacteria
4. Mycoplasma
5. Legionella pneumophila
6. Chlamydia
Food Microbiology 2024/25 Edition
, Hospitality & Food & Beverages | Food Microbiology III of LXIII pages
20. Why does the following bug not gram stain well?: Treponema
Too thin to be visualized
21. Why does the following bug not gram stain well?: Rickettsia
Intracellular parasite
22. Why does the following bug not gram stain well?: Mycobacteria
highlipidcontent cell wall
23. Why does the following bug not gram stain well?: Mycoplasma
No cell wall
24. Why does the following bug not gram stain well?: Legionella pneumophila
Primarily intracellular
25. Why does the following bug not gram stain well?: Chlamydia
Intracellular parasite which lacks muramic acid in cell wall
26. How is the following bug visualized?: Treponema
1. Darkfield microscopy
2. Fluorescent antibody staining
3. silver stain
27. Why does the following bug not gram stain well?: Mycobacteria
Acid fast for high lipid content cell wall
28. What are the stages of bacterial growth and what are their relative lengths?
1. Lag phase: x
2. Log phase: 1.5x
3. Stationary phase: 2.5x
4. Death phase: 4x
29. What happens in the following phase of bacterial growth, and where does it fall in the order?: Lag
1st phase: Metabolic activity without division
30. What happens in the following phase of bacterial growth, and where does it fall in the order?: Log
2nd phase: Rapid cell division
31. What happens in the following phase of bacterial growth, and where does it fall in the order?: Stationary
3rd phase: Nutrient depletion slows growth
32. What happens in the following phase of bacterial growth, and where does it fall in the order?: Death
4th phase: Prolonged nutrient depletion and buildup of waste products leads to death
33. Bacterial endotoxins and exotoxins: Source?
Exotoxin: Certain species of gram positive and gram negative bacteria
Endotoxin: Cell wall of most gramnegative bacteria
34. Bacterial endotoxins and exotoxins: Secreted from cell?
Exotoxin: Yes
Endotoxin: No
35. Bacterial endotoxins and exotoxins: Chemistry
Exotoxin: Polypeptide
Endotoxin: Lipopolysaccharide
36. Bacterial endotoxins and exotoxins: Location of genes
Exotoxin: Plasmid or bacteriophage
Endotoxin: Bacterial chromosome
Food Microbiology 2024/25 Edition
