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What is the primary purpose of the Triple Sugar Iron agar (TSIA) test?

To identify gram-positive bacteria

To measure pH levels in bacterial cultures

To detect lactose fermentation in anaerobic conditions

To differentiate among Enterobacteriaceae and intestinal bacilli (correct)

Which indicator is used in the TSIA medium to detect hydrogen sulfide production?

Bromothymol blue

Methyl red

Phenol red

Ferrous sulfate (correct)

In a TSIA test, what does a result of K/A with black precipitate indicate?

Lactose fermentation with hydrogen sulfide production

Glucose fermentation only, hydrogen sulfide produced (correct)

Glucose fermentation only, no gas produced

Fermentation of all sugars with gas production

Which of the following combinations represents a result indicating gas production in the TSIA test?

A/A,G,H2S Signup and view all the answers

What does the term 'K' in K/A and K/K signify in the TSIA test results?

Alkaline reaction with peptone utilization Signup and view all the answers

Which of the following best describes a result of A/A,G from a TSIA test?

Fermentation of glucose and lactose or sucrose with gas Signup and view all the answers

What type of bacteria does the TSIA test primarily differentiate?

Gram-negative bacilli within Enterobacteriaceae Signup and view all the answers

In the context of the TSIA test, what does the production of hydrogen sulfide (H2S) indicate?

Reduction of sulfur compounds by certain bacteria Signup and view all the answers

Which feature differentiates E. coli O157:H7 from other strains of E. coli regarding sorbitol fermentation?

It does not ferment sorbitol within 48 hours. Signup and view all the answers

Which of the following O serotypes is primarily associated with the pathogenicity of uropathogenic E. coli strains responsible for urinary tract infections?

O antigen types that produce hemolysin. Signup and view all the answers

What role does the K antigen play in strains of E. coli that cause pyelonephritis?

It acts as a virulence factor that inhibits phagocytosis. Signup and view all the answers

Shigella is differentiated into groups based primarily on which factor?

O antigen serotyping. Signup and view all the answers

In the context of bacterial agglutination tests, which characteristic is significant for confirming E. coli O157:H7?

Production of shiga-like toxin. Signup and view all the answers

What color indicates the presence of phenylpyruvic acid in the phenylalanine test?

Green Signup and view all the answers

In lysine iron agar (LIA), what is the result if an organism produces lysine decarboxylase after glucose fermentation?

The butt reverts to purple. Signup and view all the answers

Which process occurs in the aerobic environment of the LIA slant?

Lysine deamination Signup and view all the answers

What happens to the LIA butt when glucose is fermented but lysine decarboxylase is not produced?

It turns yellow. Signup and view all the answers

What is the significance of the ferric chloride in the phenylalanine test?

It chelates phenylpyruvic acid to form a colored complex. Signup and view all the answers

Which of the following states refers to the presence of lysine deaminase in the LIA test?

Burgundy slant and yellow butt Signup and view all the answers

At what pH does bromocresol purple change from yellow to purple?

At or above pH 6.8 Signup and view all the answers

What outcome indicates that a bacterial species lacks phenylalanine deaminase production?

The medium remains straw colored. Signup and view all the answers

What does the acidic yellow butt in an LIA medium signify?

Glucose fermentation has occurred. Signup and view all the answers

In the context of lysine iron agar, what role does cadaverine play?

It neutralizes acids and raises pH. Signup and view all the answers

What role do peritrichous flagella play in motile enteric bacteria?

They facilitate movement. Signup and view all the answers

Which statement is true regarding antigenic structure in enteric bacteria?

They assist in differentiating organisms within a genus or species. Signup and view all the answers

What is the primary characteristic used to differentiate lactose-fermenting from non-lactose-fermenting colonies on selective media?

Color produced by fermentation. Signup and view all the answers

Which selective medium is commonly used for identifying potential enteric pathogens in stool cultures?

Triple Sugar Iron agar. Signup and view all the answers

Which statement about Enterobacteriaceae is false?

They only grow on nonselective media. Signup and view all the answers

What type of reactions are primarily used to differentiate bacteria in the Enterobacteriaceae family?

Biochemical reactions. Signup and view all the answers

How does the incorporation of bile salts in selective media affect nonpathogenic Enterobacteriaceae?

Suppresses their growth. Signup and view all the answers

What is a common characteristic of colonies of Enterobacteriaceae on Chocolate Blood Agar?

Dull gray and relatively large. Signup and view all the answers

What is the significance of H2S production in enteric bacteria?

It helps differentiate specific genera in stool cultures. Signup and view all the answers

What is the primary purpose of using differential media in the lab for enteric bacteria?

To allow rapid presumptive identification of bacteria. Signup and view all the answers

Which antigen is primarily involved in the heat and alcohol resistance of bacterial cell walls?

O antigens Signup and view all the answers

What is the effect of boiling K antigens for 15 minutes?

It destroys them and unmasks O antigens Signup and view all the answers

Which type of antigen is predominantly found in agglutination tests related to O antigens?

IgM Signup and view all the answers

In which region do enteric bacteria generally cause infections when they become pathogenic?

Urinary tract Signup and view all the answers

What characteristic of E. coli makes it a significant cause of urinary tract infections?

Capsule formation Signup and view all the answers

Which antigen is specifically referred to as the virulence antigen in Salmonella species?

K antigen Signup and view all the answers

What makes H antigens unique compared to other classes of antigens?

They are heat-labile and located on flagella Signup and view all the answers

Which of the following best describes the primary role of enteric bacteria in the human body?

They contribute to normal function and nutrition Signup and view all the answers

What role do specific antisera play in identifying K antigens?

They are used in capsular swelling tests Signup and view all the answers

How many different heat-stable somatic O antigens are known to exist among Enterobacteriaceae?

Nearly 150 Signup and view all the answers

Study Notes

Enterobacteriaceae: General Introduction

Enterobacteriaceae are a large, heterogeneous group of Gram-negative rods.
Their natural habitat is the intestinal tract of humans and animals.
They are facultative anaerobes.
Motility, if present, is peritrichous flagella (except Shigella and Klebsiella).
Classified by biochemistry (lactose fermenters/non-fermenters), motility, and antigenic structure.

Enterobacteriaceae: Escherichia coli

Normal inhabitant of the GI tract.
Some strains cause gastroenteritis.
A major cause of urinary tract infection and neonatal meningitis and septicemia.
May have a capsule.
Lactose fermenting.
Most are motile.
Selective agar - ENDO.

E. coli-associated diarrheal diseases

E. coli causing diarrhea are extremely common worldwide.
Classified by virulence properties; each group causes disease via different mechanisms.
At least six groups have been characterized.
Adherence properties encoded by genes on plasmids.
Toxins often plasmid or phage-mediated.
K1 has a strong association with virulence, particularly neonatal meningitis.

E. coli toxins

Two types of enterotoxins:
- LT (heat-labile): binds to (monosialotetrahexosylganglioside) gangliosides on small intestine epithelial cells, ADP-ribosylates Gs, increasing cAMP production, leading to fluid transport into the bowel.
- ST (heat-stable): binds to specific receptors that stimulate production of cGMP, similar results LT
Both composed of 5 beta subunits (binding) and 1 alpha subunit (enzymatic activity).

E. coli Adhesions

Also called colonization factors.
Include both pili (fimbriae) and non-fimbrial factors.
At least 21 different types of adhesions.
Antibodies to these may protect from colonization.

E. coli Infections

Neonatal meningitis (leading cause): usually caused by strains with the K1 capsular antigen.
Several distinct types involved in gastroenteritis:
- ETEC (enterotoxigenic): watery diarrhea
- EIEC (enteroinvasive): similar to shigellosis
- EPEC (enteropathogenic): watery diarrhea
- EAEC (enteroaggregative): persistent diarrhea
- EHEC (enterohemorrhagic): bloody diarrhea; potentially hemolytic uremic syndrome.

E. coli: EPEC Gastroenteritis

Involved in attachment to intestinal mucosa.
Leads to microvillus effacement and intimate attachment.
Pathogenicity requires bundle-forming pilus and EPEC adherence factor.
Loss of microvilli, actin pedestal formation.

E. coli: EIEC Gastroenteritis

Attaches to intestinal mucosa via pili and outer membrane proteins.
Invasion of intestinal cells; lateral movement between cells.
Symptoms similar to shigellosis.

E. coli: EAEC Gastroenteritis

Mucous biofilm formation via autoagglutinins.
Causes diarrhea (acute and chronic).
Associated with foodborne illnesses, traveler's diarrhea, and HIV patients.
Some produce ST-like toxins, others hemolysins.

E. coli: EHEC Gastroenteritis

Attached via pili to intestinal mucosa and produces shiga-like toxins.
Symptoms begin with watery diarrhea and progress to bloody diarrhea.
Associated with hemolytic uremic syndrome (HUS).
Can be differentiated from other strains by sorbitol fermentation on sorbitol MacConkey (SMAC).

Urinary Tract Infection

E. coli is the most frequent cause (90% of cases in young women).
Symptoms include: urinary frequency, dysuria, hematuria, and pyuria (Flank pain with upper tract infections).
Potential for bacteremia with sepsis.

Diffusely Adherent E. coli (DAEC)

"Stacked-brick" adherence pattern in a diffuse pattern than EAggEC.
Causes persistent watery diarrhea, rather than acute.
Primarily causes diarrhea in developing countries.

Shigella species

Four species differ antigenically and biochemically:
- S. dysenteriae (Group A).
- S. flexneri (Group B).
- S. boydii (Group C).
- S. sonnei (Group D).
All ferment mannitol (except S. dysenteriae and S. sonnei).
Some may show delayed lactose fermentation.
O antigen serotyping often used - K antigen can affect this method

Shigella species: Antigenic Structure

Differentiated by O antigen serotyping (groups A, B, C, and D).
K antigens can interfere with serotyping but are heat-labile.
Similar O antigen structure to E. coli -important to identify Shigella first before serotyping.
Shiga toxin inhibits protein synthesis in 60S ribosomes; contributes to intestinal mucosa ulceration.

Shigella Attachment and Invasion

Migrates across tight junctions.
Lyses phagosomes; cell-to-cell spread.
Uses type III secretion system; invades epithelial cells.

Type III Secretion System

Needle-like structure in Gram-negative bacteria.
Translocates bacterial effector proteins into host cells (eukaryotic).

Shigella species: Outer membrane and secreted proteins

Outer membrane proteins expressed at body temperature.
Induce phagocytosis by M cells in intestinal mucosa
Destroy vacuoles to spread laterally through cytoplasm to epithelial cells.

Shigella: Clinical Significance

Causes shigellosis (bacillary dysentery).
Fecal-oral transmission.
Low infective dose (10-200 organisms).
Incubation (1-7 days): fever, cramping, abdominal pain, and watery diarrhea followed by frequent bloody stool.
Organisms rarely disseminate.
Disease severity depends on species (e.g., S. dysenteriae most pathogenic).

Shigella: Anti-microbial therapy

Sulfonamides, streptomycin, tetracycline, ampicillin, and chloramphenicol are common treatments.
Resistance is increasingly common, therefore sensitivity testing is required.

Salmonella species: Classification

One species, Salmonella enterica, with 7 subspecies (1, 2, 3a, 3b, 4,5, and 6).
Subgroup 1 causes most human infections.
Clinically, isolates often reported as serogroups/serotypes based on Kauffman-White scheme.
H (flagellar) and O (somatic) antigens are used for classification.
Polyvalent antisera is used for preliminary grouping; followed by group-specific antisera (A, B, C1, C2, D, E)
Salmonella typhi also has Vi antigen (capsular antigen).

Salmonella: Virulence Factors

Endotoxin: plays a role in survival and intracellular survival.
Capsule: important for S. typhi and some strains of S. paratyphi.
Adhesions: both fimbrial and non-fimbrial.

Selective media for Salmonella

SS agar, bismuth sulfite agar, Hektoen enteric medium, brilliant green agar and xylose-lisine-deoxycholate (XLD) agar.

Salmonella: Clinical significance

Causes two different diseases:
- Enteric fevers
- Gastroenteritis
Transmission is via fecal-oral route, ingestion of contaminated food or water.

Salmonella: Invasion

Endosome moves to basal side of cell.
Dissemination in enteric fevers precedes inflammatory response (low-grade fever, constipation).
Rapid spread in gastroenteritis causes strong inflammatory response (mild-moderate fever, diarrhea, cramps).

Salmonella Typhi manifestation

Bacteria spread through lymphatics and bloodstream to liver and spleen, where it multiplies and is engulfed.
Dissemination throughout the body causes fever, headaches, myalgia and Gl problems.
Rose spots (erythematous, muculopapular lesions) are often seen on the abdomen.
Complications: osteomyelitis, cystitis, and gall bladder infections may occur.

Diagnosis of Typhoid Fever

Blood cultures are positive during the first week and after the second week.
Stool cultures can sometimes be positive after the second week.
Widal test: serological test for antibodies against Salmonella typhi (4-fold rise in titer between acute and convalescent phases).

Salmonella: Antimicrobial therapy

Enteric fevers: usually treated with chloramphenicol.
Resistant strains have emerged; susceptibility testing essential.
Gastroenteritis: usually does not require anti-microbial therapy; lost fluids and electrolytes should be replaced.

Enterobacteriaceae: Citrobacter

Opportunistic pathogens.
Causes urinary tract or respiratory tract infections, wound infections, osteomyelitis, endocarditis, and meningitis.
Citrobacter freundii is associated with nosocomial infections (UTIs, pneumonias, intra-abdominal abscesses).
Ferments lactose, hydrolyzes urea slowly.
Methyl red positive, Simmons citrate positive.
Resembles Salmonella species.

Enterobacteriaceae: Edwardsiella tarda

Causes GI disease in tropical and subtropical countries.

Enterobacteriaceae: Klebsiella

May cause neurofibromatosis (neurocutaneous syndrome of GI tract).
Motile, has both O and K antigens.

Klebsiella: Virulence factors

Capsule, adhesions, iron-capturing ability.
Causes pneumonia (mostly in immunocompromised hosts), permanent lung damage.
Major cause of nosocomial infections (septicemia, meningitis).

Enterobacteriaceae: Enterobacter

Normal flora of the GI tract.
Clinical significance: nosocomial infections, bacteremia in burn patients.

Enterobacteriaceae: Serratia

Free-living saprophyte.
Respiratory tract and urinary tract infections.
Resistant to many antimicrobials.

Enterobacteriaceae: Proteus, Providencia, and Morganella

All part of the normal flora of the GI tract (except Providencia).
All motile.
Urease production may damage epithelial cells of urinary tract.
Clinical significance: UT infections, pneumonia, septicemia, and wound infections.

Yersinia

Three important species:
- Y. pestis (causes plague).
- Y. enterocolitica (enteropathogenic).
- Y. pseudotuberculosis (enteropathogenic).

Yersinia Species Identification

Y. pestis is non-motile at 37°C and is motile at 22°C.
Y. enterocolitica and Y. pseudotuberculosis are non-motile at 37°C and motile at 22°C.
Y. pestis is identified by its characteristics: non-motile, bipolar staining, slow growth of small colonies on ordinary culture media, and better growth at lower temperatures (25-30°C).

Yersinia pestis Wayson's stain

Uses basic fuchsin-methylene blue, ethyl alcohol-phenol procedure for microscopy.
Y. pestis shows characteristic purple, safety-pin appearance due to a central vacuole.

Yersinia species: Virulence factors

Y. pestis:
- Endotoxin: responsible for many symptoms.
- Murine toxin: causes edema and necrosis in mice and rats; not a human disease factor.
Yersinia enterocolitica:
Enterotoxin (similar to E. coli ST) - causes watery diarrhea
Adhesions: fimbrial and non-fimbrial
Antiphagocytic proteins, injected directly into host cells (interfere with signal transduction, affect PMNs).
Yersinia pseudotuberculosis:
V antigen - controls expression of many virulence genes and has another unknown function.
Iron-capturing ability (Yad A) - interferes with C3b, preventing complement membrane attack complex.
Has all other virulence factors as Y. enterocolitica except the enterotoxin.

Y. pestis - Clinical Significance

Bubonic plague: transmitted by fleas from infected rodents; bacteria travel to nearest lymph nodes; high fever and enlarged lymph nodes (buboes); bacteria proliferate and stimulate inflammation; leaks into bloodstream.
Pneumonic plague: transmitted via aerosol inhalation; bacteria ingested by lung macrophages causing pneumonia, high mortality rate.

Y. pestis Transmission

Primarily through flea bites
Can also spread via aerial transmission (pneumonic plague).

Yersinia enterocolitica and Yersinia pseudotuberculosis: Clinical Significance

Acquired by ingestion of contaminated food and water.
Y. enterocolitica: mainly a human disease.
Y. pseudotuberculosis: mainly a disease of other animals.
Both cause fever, abdominal pain, and watery diarrhea.
Bacteria invade intestinal epithelium via M cells, transcytosed to basal surface, and penetrate and multiply in underlying lymphoid tissue.

Yersinia species: Medical Significance

Bacterial multiplication produces an inflammatory response that is responsible for the extreme joint pain associated with infection.
Fever is due to LPS endotoxin activity.
Bacteria may drain into adjacent mesenteric lymph nodes causing mesenteric lymphadenitis.
Reactive arthritis may occur due to cross-reactive T cells or antibodies attacking the joints.

Yersinia: Treatment

Antimicrobial susceptibility testing is essential.

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