Bacterial Metabolism and Genetics

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Questions and Answers

What is generated by the Entner-Doudoroff pathway per molecule of glucose?

Two NADPH and one ATP

One NADPH and one ATP (correct)

One NADH and two ATP

Two NADH and no ATP

Which type of fermentation exclusively produces ethanol as a major end product?

Alcoholic fermentation (correct)

Heterolactic fermentation

Homolactic fermentation

Acetic fermentation

What type of DNA do plasmids consist of?

Double-stranded circular DNA (correct)

Single-stranded linear DNA

Double-stranded linear DNA

Single-stranded circular DNA

Which fermentation pathway produces lactic acid as its primary product?

Homolactic fermentation Signup and view all the answers

What is the characteristic structure of a bacterial chromosome?

Single, closed circular strand Signup and view all the answers

Which of the following is not a product of heterolactic fermentation?

Ethanol Signup and view all the answers

In what manner are plasmids typically characterized within bacteria?

Self-replicating circular pieces Signup and view all the answers

Which fermentation process uses pyruvate to produce mixed end products?

Heterolactic fermentation Signup and view all the answers

What is the role of β-galactosidase in the fermentation process of lactose?

It degrades lactose into glucose and galactose. Signup and view all the answers

Which method of genetic transfer involves the direct contact between two bacteria?

Conjugation Signup and view all the answers

What determines whether a plasmid can replicate in the bacterial cytoplasm?

Compatibility of the plasmid Signup and view all the answers

In microscopy, what does resolving power refer to?

The ability to distinguish between two closely spaced points. Signup and view all the answers

Which fluorescent dye specifically binds to mycolic acid in mycobacterial cell walls?

Auramine Rhodamine Signup and view all the answers

What is the primary function of lactose permease in bacteria?

To facilitate the entry of lactose into the cell. Signup and view all the answers

What is a characteristic feature of wall-deficient bacteria?

They do not have a cell wall. Signup and view all the answers

Which of the following best describes the structure of lactose?

A disaccharide formed by glucose and galactose linked by a galactoside bond. Signup and view all the answers

What type of specimen should be aspirated rather than swabbed?

Wound specimen Signup and view all the answers

Which organism is primarily responsible for strep throat?

Streptococcus pyogenes Signup and view all the answers

What is an essential requirement when processing stool samples?

They must be processed immediately Signup and view all the answers

What component in oxgall is selective for the growth of certain bacteria in stool samples?

Bile salts Signup and view all the answers

What is the differential component of the medium used for stool samples that indicates the presence of certain bacteria?

Esculin Signup and view all the answers

What specific type of medium is used for isolating Salmonella species?

Bismuth Sulfite Agar Signup and view all the answers

Which of the following intestinal parasites can be identified through stool examination?

Ascaris lumbricoides Signup and view all the answers

What outcome is indicated by the hydrolysis of esculin in stool sample processing?

Iron salts production resulting in color change Signup and view all the answers

What is the primary purpose of Phenylalanine Deaminase Agar?

To detect an organism’s ability to deaminate phenylalanine Signup and view all the answers

Which of the following indicates a positive reaction in Phenylalanine Deaminase Agar?

A dark green slant upon the addition of ferric chloride Signup and view all the answers

What parameter is NOT useful in identifying species of Enterobacteriaceae?

Lactose fermentation Signup and view all the answers

What does Salmonella-Shigella Agar primarily select for?

Salmonella and some strains of Shigella Signup and view all the answers

Which component in Salmonella-Shigella Agar inhibits the growth of gram-positive organisms?

Bile salts Signup and view all the answers

What pH indicator is used in MacConkey Agar?

Neutral red Signup and view all the answers

Which statement about MacConkey Agar is true?

It uses lactose as the only carbohydrate source. Signup and view all the answers

What component of the media serves as a sulfur source and hydrogen sulfide indicator in Phenylalanine Deaminase Agar?

Sodium thiosulfate Signup and view all the answers

Which hemolysin is characterized by being O2 stable and causing surface hemolysis on SBA aerobically?

Streptolysin S Signup and view all the answers

What type of coagulase test directly causes a clot to form when bacterial cells are incubated with plasma?

TUBE coagulase test Signup and view all the answers

Which of the following is the most common pathogen associated with bacterial pharyngitis?

Streptococcus pyogenes Signup and view all the answers

Which clinical infection is characterized as a flesh-eating disease?

Necrotizing fasciitis Signup and view all the answers

What laboratory test is indicated as positive for confirming group D Streptococci?

Bile esculin test Signup and view all the answers

In laboratory diagnosis of beta-hemolytic streptococci, which test differentiates S.pyogenes from other beta-hemolytic strains?

Bacitracin susceptibility test Signup and view all the answers

Which of the following conditions is a post-streptococcal sequelae that affects the heart?

Rheumatic fever Signup and view all the answers

Which organism is most commonly associated with causing gingivitis and dental caries?

Streptococcus viridans Signup and view all the answers

Study Notes

Entner-Doudoroff Pathway

Converts glucose-6-phosphate to pyruvate
Generates one NADPH per glucose molecule
Consumes one ATP
Aerobic process

Anaerobic Utilization of Pyruvic Acid (Fermentation)

Alcohol fermentation: produces ethanol as the main end product
Homolactic fermentation: produces lactic acid as the end product
Heterolactic fermentation: Produces a mix of end products including lactic acid, carbon dioxide, alcohols, formic acid, and acetic acid

Bacterial Genetics

Bacterial genome:
Bacterial chromosome: Single, closed, circular piece of double-stranded DNA
Plasmids: Small circular pieces of extrachromosomal, double-stranded DNA
- Plasmids often carry genes associated with antibiotic resistance, toxins, and virulence factors
- Located in the cytoplasm of the cell and are self-replicating
- Can be degraded or integrated into existing bacterial genetic material
- If compatible, can replicate in the cytoplasm

Specimen Collection and Processing

Processing should occur immediately to prevent temperature decrease, which can cause pH to drop and bacterial death
Specimen Collection Procedures:
Stool:
- Collect and process immediately
- Should be used to identify intestinal parasites (Ascaris lumbricoides, Trichuris trichiura)
- Used to identify intestinal protozoa (Giardia lamblia, Entamoeba histolytica)
Throat swab:
- Used to diagnose strep throat (pharyngitis) caused by bacteria Streptococcus pyogenes
Wound specimen:
- Should be aspirated rather than swabbed
- Must record the type of wound and its anatomical location
- Should be investigated for bacteria that can cause wound infection

Selective Media for Bacterial Growth

MacConkey Agar:
- Selective and differential for gram-negative bacteria
- Bile salts and crystal violet inhibit the growth of most gram-positive bacteria
- Lactose is the sole carbohydrate source
- Neutral red acts as a pH indicator
Bismuth Sulfite Agar:
- Selective medium for the isolation of Salmonella spp. from stool specimens
- Bismuth sulfite and brilliant green inhibit the growth of most gram-positive organisms and many lactose-fermenting gram-negative rods normally found in stool
Esculin agar:
- Oxgall (bile salts) is a selective ingredient that inhibit the growth of gram-positive organisms
- Esculin is the differential component; its hydrolysis produces iron salts that darken the medium
Phenylalanine Deaminase Agar:
- Detects an organism's ability to deaminate phenylalanine
- Positive reaction can differentiate Proteus, Providencia, and Morganella spp.
- A dark green slant is observed upon addition of ferric chloride
Salmonella-Shigella Agar:
- Selects for Salmonella and some strains of Shigella from stool specimens
- Contains bile salts, sodium citrate, and brilliant green to inhibit gram-positive bacteria and several lactose-fermenting gram-negative rods

Stapylococcal Coagulase

Bound Coagulase:
- Also known as "clumping factor"
- Agglutinates human, rabbit, or pig plasma
- Directly converts fibrinogen to fibrin
Free Coagulase:
- Known as "tube coagulase"
- Causes a clot to form when bacterial cells are incubated with plasma

Streptococcal Infections

Streptococcal pharyngitis:
- S. pyogenes most common pathogen (Strep throat)
Pyodermal infections:
- Impetigo, Erysipelas, cellulitis, Scarlet fever
Necrotizing fasciitis:
- Flesh eating disease
Streptococcal Toxic Shock syndrome (STSS)
Post-Streptococcal sequelae:
- Rheumatic fever, acute glomerulonephritis

Streptococcal Laboratory Identification

On SBA:
- Small, transparent, smooth beta-hemolytic
Key tests:
- Bacitracin susceptibility: S. pyogenes (sensitive, S) vs other beta-hemolytic (resistant, R)
- PYR hydrolysis: Positive

Viridans Streptococci

Means "green"
Characterized by alpha-hemolysis
Commonly found in the mouth and oropharynx

Viridans Streptococci Clinical Infections

Most common cause of subacute bacterial endocarditis
Associated with gingivitis and dental caries

Viridans Streptococci Laboratory Identification

PYR: Negative
LAP: Positive
6.5% NaCl: Negative (Group D)
Bile esculin: Positive

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Description

Explore the fundamental processes of bacterial metabolism, including the Entner-Doudoroff pathway and various fermentation methods. Additionally, delve into the structure and function of bacterial genomes, including plasmids and their roles in antibiotic resistance. Test your knowledge on these essential microbiology topics.