Bacteriology 3: Gram-negative Facultative Anaerobes

There are two categories of gram negative facultative anaerobes based on type of disease caused:

1.) septicemia causing

2.) diarrhea causing

One gram negative facultative anaerobe causing septicemia

Yersinia pestis

Yersinia pestis

Gram-negative facultative anaerobic coccobacillus that causes plague

Disease caused by Yersinia pestis

Plague (Black Death)

Two major forms of plague

1.) Pneumonic plague

2.) Bubonic plague

Pneumonic plague

Severe respiratory and systemic infection affecting the lungs

Five major clinical signs of pneumonic plague

1.) Acute high fever and chills

2.) Cough

3.) Difficulty breathing

4.) Extreme weakness

5.) Bloody sputum

Bubonic plague

Form of plague characterized by painful, swollen lymph nodes following an infected flea bite

Characteristic lesion of bubonic plague

Bubo

Bubo

Extremely swollen and tender lymph node near the site of infection

Bubonic plague can progress to _______ plague because...

pneumonic; bacteria spread systemically and eventually infect the lungs

Six major virulence factors of Yersinia pestis

1.) Rapid growth and systemic spread

2.) Fraction 1 capsule

3.) Type III secretion system

4.) Facultative intracellular survival

5.) Endotoxin (LPS)

Rapid growth and systemic spread of Yersinia pestis

Yersinia multiplies rapidly in the bloodstream, causing septicemia and potentially spreading to the lungs

Fraction 1 capsule of Yersinia pestis

Antiphagocytic capsule that prevents bacterial engulfment by host immune cells

Type III secretion system of Yersinia pestis

Injects virulence proteins directly into host cells, inhibiting leukocyte antimicrobial activity and inducing apoptosis

Yersinia uses its Type III secretion system to inhibit _______ activity and induce _______ leukocyte

antimicrobial; apoptosis

Facultative intracellular survival

Ability to survive and multiply inside host cells, particularly macrophages

Yersinia survives and replicates within macrophage _______ because...

phagolysosomes; it resists lysosomal enzymes

Endotoxin (LPS) of Yersinia pestis

Gram-negative bacterial cell wall component that stimulates severe inflammation and contributes to endotoxemia

Yersinia endotoxin contributes to _______ and _______ severe

inflammation; septicemia

Characteristic microscopic appearance of Yersinia pestis

Small Gram-negative coccobacilli with bipolar staining (safety-pin appearance)

Bipolar staining of Yersinia pestis

Staining pattern in which the bacterial poles stain more intensely than the center, producing a safety-pin appearance

Stain used to identify the safety-pin appearance of Yersinia

Wright-Giemsa stain

Four sample types used to identify Yersinia pestis

1.) Blood smears

2.) Lymph node aspirates

3.) Blood cultures

4.) Sputum

Two confirmatory diagnostic tests for Yersinia pestis

1.) Fluorescent antibody testing against Fraction 1 antigen

2.) PCR

Fluorescent antibody testing confirms Yersinia pestis by detecting...

Fraction 1 capsule antigen

Natural reservoir of Yersinia pestis

Wild rodents

Primary vector of Yersinia pestis

Rodent fleas

Four major steps in flea-mediated plague transmission

1.) Fleas acquire Y. pestis while feeding on infected rodents

2.) Bacteria multiply in the flea gut and can block the flea's feeding passage

3.) During subsequent feeding, infected material is regurgitated into the bite site

4.) Bacteria enter the susceptible host, causing bubonic plague

Yersinia pestis is transmitted through flea bites when...

infected material is regurgitated into the bite site during feeding

Two major routes of plague transmission

1.) Flea bites

2.) Respiratory aerosols

Two major prevention strategies for plague

1.) Rodent control

2.) Flea control

Plague is difficult to eradicate because...

wild rodent reservoirs cannot realistically be eliminated

Zoonotic bacteria

Bacteria capable of being transmitted naturally between vertebrate animals and humans

Two gram negative facultative anaerobes causing diarrhea

1.) Escherichia coli

2.) Salmonella

Escherichia coli

Gram-negative facultative anaerobic rod that normally inhabits the intestine but includes pathogenic strains

Two major pathogenic E. coli strains

1.) Enterotoxigenic E. coli (ETEC)

2.) Enterohemorrhagic E. coli (EHEC)

Enterotoxigenic E. coli (ETEC)

Noninvasive E. coli strain that causes severe watery diarrhea through enterotoxin production

Three major clinical characteristics of Enterotoxigenic E. coli (ETEC) infection

1.) Watery diarrhea

2.) Dehydration

3.) Low-grade fever

Enterotoxigenic E. coli (ETEC) primarily affects which animals?

Young animals, especially piglets and calves

Enterotoxigenic E. coli (ETEC) is considered noninvasive because it remains in the _______ ___________

intestinal lumen

Two major virulence factors of Enterotoxigenic E. coli (ETEC)

1.) Pili

2.) Enterotoxins (LT and ST)

Pili of Enterotoxigenic E. coli (ETEC)

Adhesion structures that allow ETEC to bind specific receptors on intestinal epithelial cells

Enterotoxigenic E. coli (ETEC) strains are often host-species-specific because...

their pili bind receptors specific to particular animal species

Two major enterotoxins produced by Enterotoxigenic E. coli (ETEC)

1.) LT (heat-labile toxin)

2.) ST (heat-stable toxin)

LT (heat-labile toxin)

Enterotoxin that increases intracellular cAMP in intestinal epithelial cells

ST (heat-stable toxin)

Enterotoxin that increases intracellular cGMP in intestinal epithelial cells

ETEC causes _______ rather than bloody diarrhea because...

watery; its enterotoxins alter fluid transport without directly destroying intestinal epithelial cells

Enterohemorrhagic E. coli (EHEC)

Pathogenic E. coli strain that causes bloody diarrhea and may produce hemolytic uremic syndrome

Important zoonotic Enterohemorrhagic E. coli (EHEC) strain

E. coli O157:H7

Four major clinical characteristics of Enterohemorrhagic E. coli (EHEC) infection

1.) Bloody diarrhea

2.) High fever

3.) Severe intestinal inflammation

4.) Hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS)

Severe complication of Enterohemorrhagic E. coli (EHEC) involving red blood cell destruction and kidney injury

Three major virulence factors of Enterohemorrhagic E. coli (EHEC)

1.) Shiga toxin

2.) Type III secretion system

3.) Endotoxin (LPS)

Shiga toxin

toxin that inhibits protein synthesis in host cells; causes tissue damage and contributes to bloody diarrhea and HUS

Type III secretion system of Enterohemorrhagic E. coli (EHEC)

Injects virulence proteins directly into intestinal epithelial cells, contributing to attachment and tissue damage

Endotoxin (LPS) of Enterohemorrhagic E. coli (EHEC)

Stimulates inflammatory responses and contributes to tissue damage

EHEC causes _______ diarrhea rather than watery diarrhea because...

bloody; Shiga toxin causes tissue injury rather than only altering intestinal fluid secretion

Three major differences between ETEC and EHEC

1.) ETEC is noninvasive, while EHEC causes intestinal tissue damage

2.) ETEC causes watery diarrhea, while EHEC causes bloody diarrhea

3.) ETEC produces LT/ST, while EHEC produces Shiga toxin

ETEC vs EHEC — major virulence factors

ETEC: pili and LT/ST enterotoxins

EHEC: Shiga toxin, Type III secretion system, and LPS

ETEC vs EHEC — zoonotic potential

ETEC: generally host-species-specific

EHEC: zoonotic

Neonates are particularly susceptible to ETEC because...

their normal intestinal microbiota are not fully developed

Six major laboratory characteristics of E. coli

1.) Gram-negative rods

2.) Facultative anaerobic

3.) Bile-salt resistant

4.) Growth on MacConkey agar

5.) Oxidase-negative

6.) Lactose-positive

E. coli can grow on MacConkey agar because...

it is resistant to bile salts

E. coli produces _______ colonies on MacConkey agar because...

pink/red; lactose fermentation produces acid that changes the pH indicator

E. coli is _______-positive, distinguishing it from Salmonella

lactose

Two antigens used to identify E. coli strains

1.) O antigen

2.) H antigen

O antigen

LPS antigen used in E. coli serotyping

H antigen

Flagellar antigen used in E. coli serotyping

E. coli vaccines are difficult to develop effectively because...

there are numerous pathogenic strains and immune protection is variable

Salmonella

Gram-negative facultative anaerobic rod that causes intestinal and potentially systemic disease

Two major forms of Salmonella disease

1.) Gastroenteritis

2.) Enteric fever

Salmonella gastroenteritis

Intestinal infection characterized by bacterial invasion, inflammation, and diarrhea

Four major steps in Salmonella gastroenteritis pathogenesis

1.) Colonization of the intestine

2.) Invasion of intestinal epithelial cells

3.) Neutrophil infiltration and inflammation

4.) Increased intestinal fluid secretion

Salmonella primarily enters intestinal tissues through...

M cells

M cells

Specialized intestinal epithelial cells through which Salmonella can enter underlying tissues

Salmonella invasion stimulates infiltration of _______ into intestinal tissues

neutrophils

Salmonella causes diarrhea partly through macrophage production of _______

prostaglandins

Prostaglandins contribute to Salmonella-associated diarrhea by...

stimulating intestinal adenylate cyclase and increasing fluid secretion

Enteric fever

Severe systemic Salmonella infection characterized by dissemination through lymphatics and blood

Two major consequences of enteric fever

1.) Septicemia

2.) Endotoxemia

Enteric fever develops when Salmonella spreads through the _______ and _______

lymphatics; bloodstream

Three major virulence mechanisms of Salmonella

1.) Type III secretion system

2.) Facultative intracellular survival

3.) Endotoxin (LPS)

Type III secretion system of Salmonella

Injects virulence proteins into host cells to promote bacterial entry and intracellular survival

Two major functions of the Salmonella Type III secretion system

1.) Promotes bacterial uptake into intestinal cells and macrophages

2.) Interferes with phagosome-lysosome fusion

Salmonella survives within macrophages by preventing...

phagosome-lysosome fusion

Facultative intracellular survival of Salmonella

Ability of Salmonella to survive and replicate inside intestinal epithelial cells and macrophages

Intracellular survival contributes to systemic Salmonella infection because...

bacteria can persist within host cells and disseminate beyond the intestine

Endotoxin (LPS) of Salmonella

Stimulates severe inflammation and contributes to endotoxemia during systemic infection

Antibiotic administration may convert enteric Salmonella disease into _______ disease because...

septicemic; disruption of normal intestinal flora allows pathogenic bacteria to multiply and spread systemically

Normal intestinal microbiota help prevent Salmonella infection by...

competing with pathogenic bacteria and restricting their growth

Six major laboratory characteristics of Salmonella

1.) Gram-negative rods

2.) Facultative anaerobic

3.) Bile-salt resistant

4.) Growth on MacConkey agar

5.) Oxidase-negative

6.) Lactose-negative

Salmonella is _______negative, distinguishing it from E. coli

lactose

Salmonella produces _______ colonies on MacConkey agar because...

colorless; it does not ferment lactose

Most practical initial laboratory test for distinguishing E. coli from Salmonella

Lactose fermentation test

E. coli vs Salmonella — lactose fermentation

E. coli: positive

Salmonella: negative

Salmonella serovar

Distinct antigenic variant of Salmonella that may differ in host range and disease characteristics

Two major categories of Salmonella serovars based on host range

1.) Host-species-specific serovars

2.) Broad-host-range serovars

Host-species-specific

Salmonella serovars Serovars that primarily infect particular animal species

Broad-host-range

Salmonella serovars Serovars capable of infecting multiple animal species, including humans

Example of a zoonotic Salmonella serovar

Salmonella Typhimurium