Microbio CHPT 33 - FINAL EXAM

Agents + Source of Waterborne Disease

Common source of waterborne disease transmission:

• potable water used for drinking + cooking

  • undergoes extensive treatment → including filtration + chlorination

  • filtration removes turbidity + many microorganisms, chlorination makes drinking water safe

• recreational water from public ponds, lakes, swimming pools, etc

Public Health + Water Quality

perfectly transparent water MAY STILL be contaminated

• routine test for indicator organisms:

  • presence of indicator organism signals potential for disease

    • EX: coliforms (NOT ALL coliforms are fecal)

  • coliforms testing is NOT a good indicator for viral pathogens

  • fecal coliforms are used in water safety testing

  • E. Coli → key fecal coliform

Testing for Coliforms + E. Coli

• Membrane filter (MF) procedure

  • at least 100mL of freshly collected water is passed thru a sterile membrane filter, trapping any bacteria on filter surface

  • filter placed on plate EMB medium → selective for G(-), lactose utilizing bacteria + differential for strongly fermentative species

• Define Substrate Test

  • detects total coliforms + specifically identify E. Coli

In US water quality is reported to EPA monthly via Safe Drinking Water Act

• this served to reduce # of waterborne diseases in US

• countries w/o chlorination + filtration methods → waterborne + diarrheal diseases = major cause of death in children

Vibrio Cholerae + Cholera

Cholera

• severe gastrointestinal diarrheal disease caused by vibrio cholerae

  • transmitted via ingestion of contaminated water

  • controlled by application of water treatment

• Pathogenesis

  • attaches to epithelial cells in small intestine where it grows + release cholera toxin

    • cholera toxin causes fluid loss, causing dehydration

    • mortality rate = 25-50%

• Diagnosis + Treatment + Prevention of Cholera

  • presence of this bacilli in the “rice water” stools of pts is key diagnostic test

  • Treatment → oral rehydration + electrolyte replacement therapy

  • Prevention → attention to personal hygiene + avoidance of untreated water or ice, + raw, undercooked, and contaminated foods

Legionellosis

caused by Legionella Pneumophila

• are G(-) bacterium known to be major waterborne pathogen in residential water systems, existing as biofilm

  • this protects bacteria from chlorine present in potable waters n biofilms + infected parasites are reservoirs for transmitting legionellosis by waterborne route

• identified via fluorescence microscopy

Epidemiology

• often found in large # in improperly sanitized colling towers + evaporative condensers of large AC systems

  • NOT SPREAD person to person

• L. Pneumophila → detected in hot water tanks + spas; also causes outbreaks in pools (Esp. if chlorine or other sanitizer) lvls are not maintained

• Detection → cultured from bronchial washing, pleural fluids, or other body fluids or tissues (urine, blood)

  • can be treated w. antibiotics (Erythromycin + rifampin)

Typhoid Fever + Norovirus illness

Typhoid Fever

• along w/ vibrio cholera, the most important water waterborne pathogenic bacteria includes Salmonella Enterica (typhi)

  • G(-) flagellated bacterium

  • causes Typhoid Fever

  • transmitted in feces-contaminated water

Norovirus

• common viral cause of gastrointestinal illness

  • symptoms → vomiting, diarrhea, + malaise (rarely fatal)

  • virus attacks tuft cells

• EASILY TRANSMITTED person-to-person OR food by fecal-oral route

  • most common outbreaks are well water or recreational waters contaminated w/ sewage

Food Spoilage + Food Preservation

any change in appearance, small, or taste of a food product that makes it unpalatable to the consumer

• food may still be safe to eat but is regarded as unacceptable

  • perishable food typ. have higher moisture content + must be stored in conditions to limit microbial growth

  • semi-perishable food include foods like fresh fruits + vegetables that also must be stored w. care to limit microbial growth

  • nonperishable foods have low moisture content + have much longer shelf life

Fresh food → spoiled by both bacteria + fungi

• each food is typ. spoiled by specific grp of microorganisms

Food Preservation

• goal is to slow the growth of microorganisms that spoil food or that can cause foodborne disease

  • major methods include altering temps, acidity, or moisture lvl of food, or treating it w/ radiation or chemicals that prevent microbial growth

Refrigeration

• slows microbial growth rate + delays spoilage

• freezing allows for longer storage BUT isn’t suitable for all foods

Heating

• used to reduce the bacterial load (EX: pasteurization) of a product or to actually sterilize it (EX: canning)

• if viable microorganism remains, they can prod gas, causing the can or glass jar to bulge or even explode

• endospore-forming clostridium → anaerobic bacteria that can grow in canned food causing botulism

Drying + Dehydration

• sugar + salt reduce the availability of water for microbial growth

• many foods are preserved by addition of small amounts of antimicrobial chemicals

  • Nitrites, sulfites, propionate, + benzoate

• Irradiation → ionizing radiation deactivation of key macromolecules

Many common foods are preserved, produced, or enhanced by the actions of microbes

• fermentation → anaerobic catabolism of organic compounds

Foodborne Diseases + Food Epidemiology

Food poisoning / Food Intoxication

• diseases that results from ingestion of foods containing preformed microbial toxins

• microorganisms don’t have to grow in the host ; ingestion of toxin causes the illness

Food Infection

• often results from ingestion of pathogen-contaminated food followed by growth of pathogen in the host

• 8 microorganisms account for the great majority of foodborne illness, hospitalizations, + deaths in the US:

  • Salmonella species

  • Clostridum perfringens

  • Campylobacter jejuni

  • S. Aureus

  • Listeria

  • E. Coli

  • Norovirus → MOST common culprit (60% of cases)

  • Toxoplasma (protist)

Food Disease Epidemiology

• 1 standard is isolation of pathogen from food:

  • req. treatment of food to suspend microorganism in homogenous solution (EX: paddle blender, stomacher)

• need to isolate from diseased pt to establish relationship between pathogen and illness

Widespread disease outbreaks:

• clusters of case caused by microorganisms in single source of food

• caused by contamination at processing plant or food distribution center

  • US 2006 → spinach + E. Coli

Staphylococcal Food Poisoning

Food poisoning often caused by toxins produced by S. Aureus

• can grow on common foods, and some strains produce heat-stable enterotoxins

• gastroenteritis occurs within a few hrs of consumption

Enterotoxins of S. Aureus classified as superantigens produce large T cell response + inflammatory response

• can lead to potentially lethal toxic shock syndrome

Clostridial Food Poisoning

C. Perfringens + C. Botulinum causes serious food poisoning

• prods endospores that may not be killed during cooking/canning process

C. Perfringens is 4th most often cause of foodborne disease in US behind norovirus ; Campylobacter infections + Salmonella infections

Botulism

• is severe + potentially fatal food poisoning

  • caused by exotoxin prod by C. Botulinum

• Botulinum toxin = neurotoxin

  • will affect autonomic nerves that control key body functions likes respiration + heartbeat

• improperly processed home-canned foods = common source of illness

Salmonellosis + Pathogenic E. Coli

Salmonellosis

gastrointestinal illness caused by foodborne salmonella infection

• caused by eating food contaminated w/ Salmonella or salmonella-infected animals

Salmonella ingested in food or water invades phagocytes + grows as intracellular pathogen

Pathogenic E. Coli

• few strains are foodborne pathogens that prod POTENT enterotoxins

  • EX: Shiga toxin- E. Coli (STEC) , E. Coli O157;H7 prod verotoxin (causes bloody diarrhea + kidney failure)

• other E. Coli are enterotoxigenic (ETEC), enteroinvasive (EIEC), + enteropathogenic (EPEC)

Campylobacter + Listeriosis

Campylobacter

• common cause of bacterial foodborne infections in US

• transmitted to human via contaminated food

  • raw poultry, pork, raw shellfish, or in surface waters

• infections in infants often traced to infected puppies + kittens

Listeriosis

• caused by Listeria monocytogenes; is intracellular pathogen

  • leads to bacteremia + meningitis

  • Acid, salt + cold-tolerant + facultatively aerobic

• mortality rate → 16% ; mostly seen in elderly, pregnant women, newborns, + adults w/ weakened immune system

Other Foodborne Infectious Diseases

Yersinia Enterocolitica

• Causes foodborne infections from contaminated meats + dairy products

Bacillus Cereus

• grows in food that is cooked and left to cool slowly

• Causes diarrhea and vomiting

Enteric Bacterium Shigella

• causes food infection, shigellosis and species of vibrio can also cause food poisoning, primarily from consumption of contaminated shellfish

Viruses

• enteroviruses like Poliovirus, norovirus, Hep A are shed into food or water from feces

  • 70% annual foodborne infections in US caused by norovirus

  • Remaining is from Rotavirus, Hep A, and astrovirus

Protists

• Foodborne diseases from → Giardia intestinalis, cryptosporidium parvum, cyclospora cayetanensis, Toxoplasma gondii

  • Spread in foods contaminated by fecal matter in water

• Toxoplasma Gondii → spread via raw or undercooked

Prions

• foodborne disease agent that is neither cellular or viral ; ARE PROTEINS

  • Causes degeneration of neural tissues and inhibits normal protein function

• Variant Creutzfeldt-Jacob disease (vCJD)

  • Is linked to consumption of meat from cattle suffering with BSE (prion disease)