Microbio Exam 3 Gram-Negative Microorgs

Enterobacteriaceae

• Family of gram-negative, facultative anaerobic rods

• Commonly referred to as “Enterics”

• Motile and nonmotile

  • Many have fimbriae that aid in adhesion

Coliforms

• Non-sporeformers

• Gram-negative rods

• Ferment lactose at 35-37°C

• Associated with GI tract of warm-blooded animals and ruminants •

• Not necessarily pathogenic (but some may be)

• Can be used as indicator organisms for potential fecal contamination

  • Depends on the food

  • Indicator of cleanliness

Disease characteristics

• Infections

  • Invasive/non-invasive

• Toxicoinfections

• Immune response

Non-pathogens

• Pseudomonas (opportunistic, not necessarily foodborne)

• Non-pathogenic E coli

• Animal pathogens

General E coli Characteristics

• Most are commensal and non-pathogenic

  • Reside normally in GI tract of humans and warm blodded animals (contaminates through feces)

  • Some resistant to acid stress as low as pH 4.0

  • Not heat resistant

  • Some antibiotic resistance

E coli categorization, dose, and hospitalization rates

• Categorized based on

  • Serology/antigens: O - LPS, H - Flagella, K - Capsule

  • Virulence

  • Pathogenicity

  • Clinical symptoms

    • Onset- 3-4 days

• Low infectious dose

• Higher hospitalization rates

DAEC

• Diffuse-adhearing E coli

EAEC

• Enteroaggregative E coli

EHEC (STEC)

• Enterohemorrhagic E coli

EIEC

• Enteroinvasive E coli

EPEC

• Enteropathogenic E coli

ETEC

• Enterotoxigenic E coli

Enterotoxigenic E coli (ETEC) causes and main reservoir

• Causes diarrhea in infants and traveler’s diarrhea

• Not commonly observed outside U.S.

• O6, O8, O15, O20, O25, O27, O63, O78, O85, O115, O128ac, O148, O159, O167

• Humans serve as primary reservoir

Enterotoxigenic E coli

• Colonizes in small intestine (uses fimbriae)

  – Typically not a serious disease (watery diarrhea, abdominal

  cramps, low-grade fever, nausea and malaise)

Enterotoxigenic E coli enterotoxin production

• Produces enterotoxin

  • Heat-labile and/or heat-stable toxin

  • Causes accumulation of fluid and diarrhea

  • Toxicoinfection*

Enterohemorrhagic E coli (EHEC) characterizations and importance

• Extremely important in U.S. and worldwide

• 167 O antigens, 53 H antigens 74 K antigens

• Primary serotype – O157:H7 (also the big 6)

• Low infectious dose (10-100 cells)

Enterohemorrhagic E coli (EHEC) Toxin Production

• Produces Shiga toxin (Stx) – “Shiga toxin-producing E. coli”

• Similar resemblance to the toxin produced by Shigella

• Cytotoxic to African green monkey kidney (Vero) cells

• Also referred to as VTEC (Verotoxigenic E. coli)

• Release high loads of toxin that severely damage intestinal lining

• Toxin inactivates ribosomes and causes apoptosis or other dysfunction

EHEC Big 6

• O26

• O45

• O103

• O111

• O121

• O145

O157 and non-O157 STEC Hemorrhagic Colitis (HC)

• Severe abdominal cramps, diarrhea (starts watery and progresses to grossly bloody), some vomiting, low-grade or absent fever

• Usually self-limiting (5-10 days)

• Can result in Hemolytic Uremic Syndrome (HUS) or Thrombotic thrombocytopenic purpura (TTP)

O157 and non-O157 STEC Hemolytoc Uremic Syndrom (HUS)

• Younger populations

• Shiga toxin targets glomerulus

• Renal failure and hemolytic anemia

• Kidney damage or complete loss of function

O157 and non-O157 STEC Thrombotic thrombocytopenic purpura (TTP)

• Elderly populations

• HUS symptoms + fever and neurologic symptoms

• 50% mortality rate

O157 and non O157 STEC Reservoirs and Transmission

• Animals (ruminants, dogs, horses, swine, cats, seagulls, rats)

• Cattle are highly associated but not negatively affected (up to 60% carriage in herds)

• Humans (person-to-person)

O157 and non-O157 STEC Common Sources

• Ground beef (raw or undercooked)

• Fresh produce (lettuce, sprouts, spinach, unpasteurized juice)

• Unpasteurized milk and cheese

• Water (wells and swimming)

• Petting zoos (fecal-oral)

• Childcare (fecal-oral)

E coli O157:H7 Acid resistance

• pH 4.4-9.0 growth range

  • Weeks-long survival at pH 3.8 in low temperatures

  • Unpasteurized juice outbreaks led to regulations

E coli O157:H7 Antibiotic Resistance

• Noticeably more cases

• Abx should not necessarily be prescribed

E coli O157:H7 Heat Resistance

• Not normally observed

• Susceptible to normal processing temperatures (72- 74°C/161-165°F)

E coli O157:H7 Sorbitol Formation

• Negative for sorbitol fermentation (unlike other STEC)

E coli Pathogenicity

• Noninvasive/Moderately

  • Adherence factors

    • Aggregative

    • Intimate attachment

  • Immune response to the detected attachment and toxins

    • Diarrhea

  • Toxins can result in violent cell death

    • Bloody diarrhea

Salmonella enterica Characteristics

• Causes invasive infection

• Leading cause of bacterial foodborne illness in US and worldwide

  • Est > 95 million cases worldwide each year

    • Non-typhoidal cases = 3.4 million

    • 1.35 million in US

Salmonella enterica Species and serovars

• Two species: enterica and bongori

  • Subspecies of enterica: (enterica, salamae, arizonae, diarizonae, houtenae, indica)

• Possibly more than 2,600 serovars

  • Typhi, Gallinarum, Typhimurium, Newport, Dublin, Mjordan, Senftenburg, Tennessee

Salmonella enterica resilient and adaptive to changes in…

• Temperature

• pH 4.5-9.5

  • Wide adaptable range, but not as acid-resistant as STEC or Shigella

  • aw (growth > 0.92, survival at low aw)

  • High-ish infectious dose around 1000 cells

Salmonella enterica implicated sources

• Meat and poultry, fish, produce

• Contamination of low-moisture foods

• Anything that flies, slithers, or crawls

Salmonella enterica Ecological niche

• Ecological niche = GI tract

• Can spread to spleen, liver, lymph nodes, bile, other tissues

Salmonella enterica Clinical diseases

• Clinical diseases

• Enteric (typhoid) fever

• Acute gastroenteritis

• Systemic infections

Salmonella Typhi and Paratyphi Characteristics

• Enteric fever (typhoidal salmonella)

• Highly invasive → can spread to spleen, liver, and blood

  • Can colonize blood vessels

Salmonella Typhi and Paratyphi Symptoms, Treatment, and Onset

• Symptoms → Diarrhea, ongoing and spiking fever, abdominal pain, headache

• Treatment → Supportive therapy (some abx)

• Incubation: 7-28 days, onset 48-72 hrs, duration 7-14 days

Non-typhoidal salmonella characteristics

• Fimbriae aid in attachment

  • Uses Type III sectretion system to inject toxins and proteins to stimulate ruffling

• Supportive therapy, no abx

Non-typhoidal Salmonella: How does it invade?

• Invade muscosal cells or M cells

• Increase cAMP level, inhibit Na+ uptake, secrete Cl- → Diarrhea

• Inflammatory response to bacteria in underlying tissues causes pain and release of prostaglandins (can enter the blood stream and cause septicemia)

• Replicates with vacuole

  • Would normally be destroyed; Sal blocks fusion with lysosomes

Salmonella Outbreaks and Regulations

• Outbreaks

  • Beef and poultry

  • LMFs (eg peanut butter)

  • Produce (peaches and onions)

• Regulations

  • Almonds (4-log reduction)

  • Potential upcoming rules related to beed and poultry

Shigella Characteristics

• Similar in relatedness to E coli (EIEC) and Salmonella

• No lactose fermentation

• 4 species: dysenteriae, flexneri, boydii, sonnei

• Low infectious dose → 10 cells

• Fecal oral route → poor hygeine/hand washing

  • Shellfish, vegetables, salads, day cares

• S dysenteriae produces enterotoxin → Shiga toxin (Stx1 and Stx2)

Shigellosis

• Bloody diarrhea

• Abdominal/rectal pain

• Cramps

• Fever

Shigella Pathogenicity

• Invasive or noninvasive

• ABX can be helpful in early Shigella invasive infection

• Invasion of basal surface

Shigella Pathogenicity: Invasive

• Involves T3SS

• Invades M cells

• Inflammatory response disrupts cell tight juctions

• Enters through basal surface

• Escapes phagosome and invades neighboring cell with actin polymerization (similar to listeria)

• Cell death = bloody diarrhea

Yersinia Characteristics

• Small gram negative rods

• Y. pseudotuberculosis (can sometimes pass to humans)

• Y. pestis – cause of Plague, closely related, but not connected to food

• Y. entercolitica – primary foodborne Y. pathogen

Y enterocolitica Characteristics

• Not competitive or resistant to thermal or acid intervention

• Inadequate heat processing, post-processing contamination

• E.g., raw milk, ice cream, pork

• Isolated from wildlife (pigs) and respective contaminated foods

Y enterocolitica Symptoms

• fever, abdominal pain, diarrhea (sometimes bloody),

  Pseudoappendicular Syndrome (appendicitis—j.k.)

Y enterocolitica relation to EHEC, Shigella, and Salmonella

• Uses invasin and Yop proteins (rather than intimin, which is used by

  T3SS of other Enterics) to avoid phagocytosis and suppress immune

  system

Campylobacter spp

• Family Campylobacteraceae

• Notable species: jejuni and coli

• Spirilli rod (spirochete), motile (essential for colonization)

• Microaerophile

– 3-5% O2 and 2-10% CO2 (rest is N2) – CAMPY GAS

• Optimum growth at 42°C (poultry body temp 40°C)

• Fastidious

• Reservoirs: animals, shellfish

• Contaminates vegetables, water, raw milk

• Seasonal outbreaks

Campylobacter onset and symptoms

• Onset time: 2-5 days, lasts for days to >1 week

• Usually self-limiting

• Zoonotic cases with livestock and household pets

• Symptoms: fever, abdominal cramps, diarrhea (sometimes bloody)

• Usually self-limiting

Campylobacter how does it infect?

• Invasive GI tract infection

• Produces enterotoxin (cholera-like)

  • Activates adenylate cyclase

  • Watery diarrhea (non-bloody), inflammatory immune esponse

• Cytotoxic enterotoxin – bloody diarrhea

• Increasing abx resistance (C. coli with fluoroquinolones)

Campylobacter secondary complications

• Secondary complications: Guillain-Barre syndrome (40% cases associated with Campylobacteriosis)

• Immune-mediated paralytic disorder (LPS induces antibodies that attach peripheral nerve tissue)