T21: Gram-negative bacilli

salmonella - diseases

• typhoid fever

• salmonella gastroenteritis

• asymptomatic carrier

typhoid fever - causative agents

Salmonella typhi, Salmonella paratyphi

typhoid fever - infection location

terminal small intestine of human host

typhoid fever - pathogenesis

adhere to microvilli → transcytosis (transported across membrane in vesicle) → enter M cells (specialized epithelial cells in gut) → release into basolateral side → engulfed by macrophages but escape killling - no phagolysosome fusion → enter bloodstream → bacteremia — spread

typhoid fever - symptoms and complications

• hepatosplenomegaly

• rose spots

• step-ladder fever

• peyer’s patch ulceration → bowel perforation

• cholecystitis (gall bladder inflam)

salmonella gastroenteritis - causative agents

Salmonella typhimurium, Salmonella enteritidis

salmonella gastroenteritis - host

animal - poultry, pig, rate, cattle, turtle

salmonella gastroenteritis - presentations

• diarrhea

• no hepatosplenomegaly

• uncommon bacteremia and invasion (immunocompromised)

• rare invasion: osteomyelitis (painful bone infection) → sickle cell anemia

salmonella asymptomatic carrier - risk factor

gallstones

Salmonella - agar and tests

• XLD agar: H2S production (black colony)

• produce gas from glucose

typhoid fever - test

punch biopsy

→ remove a cylindrical piece of skin using sharp instrument called punch → examination & diagnosis

Shigella - disease

shigellosis (bacillary dysentery)

shigellosis (bacillary dysentery) - symptoms

• mucus bloody diarrhea

• mucosal ulcerations

• tenesmus (persistent painful sensation that you need poo or pee even tho empty bowel)

• uncommon bacteremia

shigellosis (bacillary dysentery) - most severe causative agent

Shigella dysenteriae because also produce shiga toxin → HUS (hemolytic uremic syndrome) (like EHEC)

shigellosis (bacillary dysentery) - spread

spread by actin polymerization (like EIEC)

Shigella - virulence factor

survive low pH

Shigella - agar and tests

• XLD agar: no H2S (not black)

• produce acid (not gas) from glucose

• WBC, RBC present in stool

lactose-fermenting aerobic gram-negative bacilli - common traits

• all oxidase negative

• pink on MacConkey agar

Escherichia coli - normal flora

GI

Escherichia coli - groups

• commensal: detect feces contamination

• extra-intestinal pathogenic (ExPEC)

• intestinal pathogenic

extra-intestinal pathogenic E. coli - diseases

cystitis (inflam of urinary bladder), peritonitis (peritoneum infam)

cystitis

*urgency, frequent, dysuria

peritonitis

ascites (ท้องโต), esophageal varices (swollen enlarged veins in esophagus)

enterotoxigenic (ETEC) - diarrhea

watery secretory diarrhea

enterotoxigenic (ETEC) - disease

traveler’s diarrhea

enterotoxigenic (ETEC) - transmission

contaminated food and water

enterotoxigenic (ETEC) - toxins and effect

• heat-labile (AB5): A subunit increases adenylate cyclase → increases cAMP 

• heat-stable toxin: small peptide increases guanylate cyclase → increases cGMP

• both opens CFTR channels = chloride, sodium, water into lumen

• → water follows into lumen via osmosis → excess water in lumen → secretory diarrhea

enteropathogenic (EPEC) - diarrhea

watery osmotic diarrhea

enteropathogenic (EPEC) - symptoms

attaching and effacing lesions

enteropathogenic (EPEC) - pathogenesis

bundle-forming pilus (Type III secretion system) inject Tir (translocated intimin receptor) into host → binds to intimin → polymerize actin → decreases size of microvilli → attaching & effacing lesions (bacteria stick to the intestine and erase the tiny villi) → decreased absorption, increased lumen osmotic pressure = water is pulled into lumen → watery osmotic diarrhea

enteroinvasive (EIEC) - diarrhea

mucus bloody diarrhea

enteroinvasive (EIEC) - disease

dysentery (ปวดบิด)

enteroinvasive (EIEC) - pathogenesis

EIEC directly invades colon epithelium (host cell) → contained in phagosome & replicates itself → WBC try to kill → EIEC lyse and escape phagosome → move to adjacent cell → cell death → ulcer

enteroinvasive (EIEC) - symptoms

colonic ulceration, fever, tenesmus (feel like need to poo)

enterohemorrhagic (EHEC) - diarrhea

bloody diarrhea

enterohemorrhagic (EHEC) - spread from

undercooked beef, veggies (sprouts), unpasteurized milk

enterohemorrhagic (EHEC) - test

sorbital MacConkey agar (SMAC) - colourless

enterohemorrhagic (EHEC) - toxin

shiga toxin (Stx)

• B subunit bind to Gb3 on endothelial, glomerulus → *hemorrhagic colitis

• A subunit disrupt protein synthesis of endothelia → blood vessel broken → clotting → RBC squish → hemolysis

enterohemorrhagic (EHEC) - disease

hemolytic uremic syndrome (HUS) *thrombocytopenia → hemolytic anemia → AKI (acute kidney injury) 

Enterobacterales - common characteristics

• facultative anaerobes that ferment glucose except Campylobacter and Helicobacter

• oxidase-negative - except Campylobacter, Helicobacter, Plesiomonas

• catalase +

Enterobacterales - common virulence factors

• somatic O polysaccharides

• capsular K antigen

• flagella H protein

Klebsiella pneumoniae - normal flora

intestine

Klebsiella pneumoniae - drugs

multidrug resistance

Klebsiella pneumoniae - diseases

• pneumonia in alcoholic/diabetic, from aspiration *lobar consolidation

• UTI

• intraabdominal infections

• liver abscess

Campylobacter jejuni & Helicobacter pylori - common characteristic

microaerophilic (thrives in low O2 environments)

Campylobacter jejuni - characteristics & morphology

• curved spiral rod (seagull wing)

• motile

• oxidase +

Campylobacter jejuni - reservoir

environment

Campylobacter jejuni - diseases

• gastroenteritis: *profuse watery diarrhea → dysentery (mucus bloody diarrhea)

• guillain-barre syndrome: acute inflammatory demyelinating polyneuropathy (damage/disease of many peripheral nerves)

C. jejuni gastroenteritis - pathogenesis

• release IL-18 to attract neutrophil

• cytolethal distending toxin (CDT) → provides strong inflam response

C. jejuni Guillain-Barre syndrome - pathogenesis

cross-reacting lipooligosaccharide on C. jejuni with epitopes on myelin sheath

C. jejuni Guillain-Barre syndrome - symptoms

symmetrical muscle weakness starting from lower body

Helicobacter pylori - characteristics & morphology

• spiral bacilli with polar flagella

• most common bacteria

• carcinogen

Helicobacter pylori - diseases

peptic ulcer, gastric adenocarcinoma

Helicobacter pylori - virulence factors

• urease

• mucinase

urease

urea → NH3 → increase pH → can survive in acidic stomach

Helicobacter pylori - diagnosis

• stool antigen test

• carbon urea breath test

• biopsy → rapid urease test positive (red, pink)

gastric adenocarcinoma from Helicobacter pylori - pathogenesis

host cell mutate from free radical → progress from chronic atrophic gastritis

Vibrionaceae - common characteristics

• curved rod/comma

• polar flagella

• oxidase +

• non-lactose fermenting

• halophile

• TCBS agar

• water-borne (seafood)

Vibrio cholerae - differentiating method

• only vibrio that can grow without salt

• TCBS agar: yellow

Vibrio cholerae - virulence factors

• toxin-coregulated Pili A (TcpA)

• cholera toxin (AB5)

toxin-coregulated Pili A (TcpA)

attach to enterocyte

cholera toxin (AB5)

increase adenylate cyclase → increase cAMP → increase CFTR

Vibrio cholerae - disease

cholera

cholera

• watery secretory diarrhea (rice water)

• dehydration

• electrolyte imbalance

• hypovolemic shock

cholera - treatment

rehydrate (oral rehydration salt), oral antibiotic

Vibrio parahaemolyticus - characteristics

• halophile

• TCBS agar: green

Vibrio parahaemolyticus - disease

watery diarrhea, mucus-bloody stool

Vibrio vulnificus - characteristics

TCBS agar: green

Vibrio vulnificus - infects what group

liver disease because decreased iron binding protein = increased free iron

Vibrio vulnificus - virulence factors

siderophore: acquire host iron

Vibrio vulnificus - diseases

• skin, wound infection: hemorrhagic bleb

• no diarrhea

difference between watery secretory & watery osmotic diarrhea

• Secretory diarrhea = ion channel–mediated secretion → watery stool that continues during fasting (low osmotic gap).

• Osmotic diarrhea = unabsorbed solutes → watery stool that stops with fasting (high osmotic gap).