Food Microbiology Lecture Final Pres

7/28/2019 Food Microbiology Lecture Final Pres

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Foodborne disease

Caused by consuming contaminated foods orbeverages.

Poisonous chemicals, or other harmfulsubstances can cause foodborne diseases ifthey are present in food.

Our focus is on those caused by organisms.


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Foodborne disease

More than 250 different foodborne diseaseshave been described.

Most of these diseases are infections, causedby a variety of bacteria, viruses, and parasitesthat can be foodborne.

Other diseases are poisonings, caused byharmful toxins or chemicals


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Campylobacter

causes fever, diarrhea, and abdominal cramps.

The most commonly identified bacterial cause ofdiarrheal illness in the world.

Live in the intestines of healthy birds Most raw poultry meat has Campylobacter on it.

Eating undercookedchicken, or other food thathas been contaminated with juices dripping from

raw chicken is the most frequent source of thisinfection.

Guillain-Barre syndrome can be caused byCampylobacter infection


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Salmonella

is widespread in the intestines of birds, reptilesand mammals.

can spread to humans via a variety of different

foods of animal origin. Salmonellosis, typically includes fever, diarrhea

and abdominal cramps.

In persons with poor underlying health orweakened immune systems, it can invade thebloodstream and cause life-threateninginfections.


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E.Coli O157: H7

has a reservoir in cattle and other similaranimals.

Human illness typically follows consumptionof food or water that has been contaminatedwith microscopic amounts of cow feces.

The illness it causes is often a severe andbloody diarrhea and painful abdominalcramps, without much fever.


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E.Coli O157: H7

In 3% to 5% of cases, a complication calledhemolytic uremic syndrome (HUS) can occurseveral weeks after the initial symptoms.

This severe complication includes temporaryanemia, profuse bleeding, and kidney failure.


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Calicivirus

is an extremely common cause of foodborneillness, though it is rarely diagnosed, becausethe laboratory test is not widely available.

It causes an acute gastrointestinal illness,usually with more vomiting than diarrhea,that resolves within two days.

Unlike many foodborne pathogens that haveanimal reservoirs, it is believed that Norwalk-like viruses spread primarily from oneinfected person to another.


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Calicivirus

Infected kitchen workers can contaminate asalad or sandwich as they prepare it, if theyhave the virus on their hands.

Infected fishermen have contaminatedoysters as they harvested them.


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But facilities available

locally for bacteria. So lets talk more of bacteria that cause

foodborne illness


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Foodborne by direct infectionFoodborne through toxin

Foodborne diseases


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Foodborne through toxin

some foodborne diseases are caused by thepresence of a toxin in the food that wasproduced by a microbe in the food.

For example, the bacterium Staphylococcusaureus

a toxin that causes intense vomiting.


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Foodborne through toxin

The rare but deadly disease botulism occurswhen the bacterium Clostridium botulinumgrows and produces apowerful paralytictoxin in foods.

These toxins can produce illness even if themicrobes that produced them are no longer

there.


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What happens in the body after

the microbes that produceillness are swallowed? After they are swallowed, there is a delay, called

the incubation period, before the symptoms of

illness begin. may range from hours to days, depending on the

organism, and on how many of them wereswallowed.

During the incubation period, the microbes passthrough the stomach into the intestine, attach tothe cells lining the intestinal walls, and begin tomultiply there.


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What happens in the body after

the microbes that produceillness are swallowed?

Some types of microbes stay in the intestine,

some produce a toxin that is absorbed intothe bloodstream, and

some can directly invade the deeper bodytissues.

The symptoms produced depend greatly onthe type of microbe.


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What are foodborne disease

outbreaks and why do they

occur? Occurs when

a group of people consume the samecontaminated food and

two or more of them come down with the sameillness.

It may be a group that ate a meal together somewhere, or

who do not know each other at all, but who allhappened to buy and eat the same contaminateditem from a grocery store or restaurant.


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What are foodborne disease

outbreaks and why do they

occur? For it to occur, something must have

happened to contaminate a batch of food

Often, a combination of events A contaminated food may be left out a room

temperature for many hours, allowing thebacteria to multiply to high numbers, and then be

insufficiently cooked to kill the bacteria.


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How is a foodborne disease

outbreak investigated?

Once an outbreak is strongly suspected, aninvestigation begins.

A search is made for more cases among persons

who may have been exposed. Determined:

The symptoms and time of onset, and location of possible cases is determined, and a "case definition" is developed that describes these

typical cases.

The outbreak is systematically described bytime, place, and person.


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How is a foodborne disease

outbreak investigated?

A graph is drawn of the number of peoplewho fell ill

A map of where the ill people live, work, or

eat. Calculating the distribution of cases by age

and sex shows who is affected.

If the causative microbe is not known,samples of stool or blood are collected fromill people and sent to the public healthlaboratory to make the diagnosis.


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To identify the food or other

source of the outbreak

The investigators first interview a fewpersons with the most typical cases aboutexposures In this way, certain potential exposures may be

excluded while others that are mentionedrepeatedly emerge as possibilities.

Combined with other information, such as

the likely sources for the specific microbeinvolved, these hypotheses are then tested ina formal epidemiologic investigation.


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The investigators conduct systematicinterviews about a list of possible exposureswith the ill persons, and with a comparable

group people who are not ill. By comparing how often an exposure is

reported by ill people and by well people,investigators can measure the association ofthe exposure with illness.

Using probability statistics, the probability ofno association is directly calculated.


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Once a food item is statistically implicated inthis manner, further investigation

into its ingredients and

preparation, and

microbiologic culture of leftover ingredients or thefood itself (if available) may provide additional

information about the nature of contamination.


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Some might think

that the best investigation method would be justto culture all the leftover foods in the kitchen,

and conclude that the one that is positive is theone that caused the outbreak.

can be misleading, because it happens after

the fact.


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Remember

Laboratory testing without epidemiologicinvestigation can lead to the wrongconclusion.


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Even without isolatingmicrobes from food, a well-

conducted epidemiologic

investigation can guide

immediate efforts to control

the outbreak.


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How does food become

contaminated?

Many foodborne microbes are present in healthyanimals (usually in their intestines) raised forfood.

Meat and poultry carcasses can becomecontaminated during slaughter by contact with small amounts of

intestinal contents.

Similarly, fresh fruits and vegetables can becontaminated if they are washed or irrigated with water that is

contaminated with animal manure or human sewage.


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contaminated?

Some types of Salmonella can infect a hen's

ovary so that the internal contents of a normal

looking egg can be contaminated with

Salmonella even before the shell in formed.

Oysters and other filter feeding shellfish can

concentrate

Vibrio bacteria that are naturally present in sea water, or other microbes that are present in human sewage

dumped into the sea.


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contaminated?

Later in food processing, other foodbornemicrobes can be introduced

from infected humans who handle the food, or

by cross contamination from some other rawagricultural product.

For example, Shigella bacteria, hepatitis A virus and

Norwalk virus can be introduced by the unwashedhands of food handlers who are themselvesinfected.


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contaminated?

In the kitchen, microbes can be transferredfrom one food to another food by

using the same knife, cutting board or otherutensil to prepare both without washing thesurface or utensil in between.

A food that is fully cooked can become

recontaminated if it touches other raw foodsor drippings from raw foods that containpathogens.


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contaminated?

The way that food is handled after it iscontaminated can also make a difference inwhether or not an outbreak occurs.

Many bacterial microbes need to multiply to alarger number before enough are present infood to cause disease.


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contaminated?

Given warm moist conditions and an amplesupply of nutrients, one bacterium thatreproduces by dividing itself every half hourcan produce 17 million progeny in 12 hours.

As a result, lightly contaminated food left outovernight can be highly infectious by the next day.


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Refrigeration or freezing

In general, refrigeration or freezing preventsvirtually all bacteria from growing butgenerally preserves them in a state ofsuspended animation.

This general rule has a few surprisingexceptions.

Two foodborne bacteria, Listeria monocytogenesand Yersinia enterocolitica can actually grow atrefrigerator temperatures.


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High salt, high sugar or high

acid

High salt, high sugar or high acid levels keepbacteria from growing,

which is why salted meats, jam, and pickledvegetables are traditional preserved foods.


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Heat

Microbes are killed by heat.

If food is heated to an internal temperatureabove 160oF, or 78oC, for even a few seconds

sufficient to kill parasites, viruses or bacteria, exceptfor the Clostridium bacteria, which produce a heat-resistant form called a spore.

Clostridium spores are killed only at

temperatures above boiling. This is why canned foods must be cooked to a high

temperature under pressure as part of the canningprocess.


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Heat

The toxins produced by bacteria vary in theirsensitivity to heat.

The staphylococcal toxin which causes vomiting isnot inactivated even if it is boiled.

Fortunately, the potent toxin that causes botulismis completely inactivated by boiling.


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What foods are most associated

with foodborne illness?

Raw foods of animal origin are the most likely to

be contaminated;

raw meat and poultry,

raw eggs,

unpasteurized milk, and

raw shellfish.

Because filter-feeding shellfish strain microbesfrom the sea over many months, they are

particularly likely to be contaminated if there are

any pathogens in the seawater.


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Foods that mingle the products of manyindividual animals, are particularly hazardousbecause a pathogen present in any one of theanimals may contaminate the whole batch.

such as bulk raw milk,

pooled raw eggs, or

ground beef,.

A single hamburger may contain meat fromhundreds of animals.


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A single restaurant omelet may contain eggsfrom hundreds of chickens.

A glass of raw milk may contain milk fromhundreds of cows.

A broiler chicken carcass can be exposed tothe drippings and juices of many thousands

of other birds that went through the samecold water tank after slaughter.


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Fruits and vegetables consumed raw are aparticular concern.

Washing can decrease but not eliminatecontamination.

The quality of the water used for washing andchilling the produce after it is harvested is critical.

Using water that is not clean can contaminatemany boxes of produce.


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Fresh manure used to fertilize vegetables canalso contaminate them.

Unpasteurized fruit juice can also becontaminated if there are pathogens in or onthe fruit that is used to make it.

What can consumers do to


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What can consumers do to

protect themselves from

foodborne illness?

COOK

For example, ground beef should be cooked to aninternal temperature of 160o F

SEPARATE

CHILL

CLEAN

REPORT


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Bacteria causing foodborne

infections

Listeria monocytogenes

Salmonella typhi

Nontyphoidal salmonella

Shigella sp. Staphylococcus aureus

Streptococcus group A

Vibrio cholerae, O1 or O139

Vibrio cholerae other serotypes Vibrio parahemolyticus

Vibrio vulnificus

Yersinia enterocolitica


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Emerging diseases: diseases whose incidence has increasedwithin the past 2 decades or threatens to increase in the near

future

Global travel

globalization of foodsupply and centralizedprocessing of foods

population growth andincreased urbanizationand crowding

population movement

due to civil wars,famines and other man-made or naturaldisasters

Irrigation, deforestationand reforestation projectsthat alter habits ofdisease-carrying insects

Increased use ofantimicrobial agents andpesticides, hastening thedevelopment of resistance

Human habits andbehavior


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E. Coli O157:H7

Currently, there are four recognized classes ofenterovirulent E. coli(collectively referred toas the EEC group) that cause gastroenteritis

in humans.

Among these is the enterohemorrhagic(EHEC) strain designated E. coliO157:H7.


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E. Coli O157:H7

E. coliserotype O157:H7 is a rare variety ofE. colithat produces large quantities of one ormore related, potent toxins that cause severe

damage to the lining of the intestine.

These toxins [verotoxin (VT), shiga-like toxin]are closely related or identical to the toxin

produced by Shigella dysenteriae.
http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm070563.htmhttp://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm070563.htmhttp://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm070563.htmhttp://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm070563.htm


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Nature of disease

characterized by severe cramping (abdominalpain) and diarrhea which is initially watery butbecomes grossly bloody.

Occasionally vomiting occurs. Fever is either low-grade or absent.

The illness is usually self-limited and

lasts for an average of 8 days.

Some individuals exhibit watery diarrheaonly.


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Nature of disease

Infective dose -- Unknown,

but from a compilation of outbreak data,

the dose may be similar to that ofShigella spp. (asfew as 10 organisms).


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Course of disease and

Complications

Some victims, particularly the very young,have developed the hemolytic uremicsyndrome (HUS),

characterized by renal failure and hemolyticanemia.

The disease can lead to permanent loss of

kidney function.


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Course of disease and

Complications

In the elderly, thrombotic thrombocytopenicpurpura (TTP). HUS, plus two other symptoms, fever and neurologic

symptoms, constitutes This illness can have a mortality rate in the elderly as

high as 50%.

All people are believed to be susceptible tohemorrhagic colitis,

but young children and the elderly appear toprogress to more serious symptoms morefrequently.
http://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm074156.htm?Purpurahttp://www.fda.gov/Food/FoodSafety/FoodborneIllness/FoodborneIllnessFoodbornePathogensNaturalToxins/BadBugBook/ucm074156.htm?Purpura


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Associated food

Undercooked or raw hamburger (groundbeef)

Othersimplicated

alfalfa sprouts,

unpasteurized fruit juices,

dry-cured salami, lettuce,

game meat, and cheese curds.

Raw milk was the vehicle in a school outbreakin Canada.


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Diagnosis

Hemorrhagic colitis is diagnosed by isolationofE. coliof serotype O157:H7 or otherverotoxin-producing E. colifrom diarrheal

stools.

Alternatively, the stools can be tested directlyfor the presence of verotoxin.

Confirmation can be obtained by isolation ofE. coliof the same serotype from theincriminated food.


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Food analysis

Unlike typical E. coli, isolates of O157:H7 do not ferment sorbitol and

are negative with the MUG assay;

therefore, these criteria are commonly used forselective isolation.

Sorbitol-MacConkey agar has been usedextensively to isolate this organism from clinical

specimens. Hemorrhagic colitis agar, a selective and

differential medium, is used in a direct platingmethod to isolate O157:H7 from foods.


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Food analysis

A third procedure uses Sorbitol-MacConkeymedium containing potassium tellurite andCefixime.

It includes an enrichment step

Rapid methods using a variety oftechnologies, including recombinant DNA

methods, are being developed.


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a small rod-shaped, Gram-negative bacterium,

is often isolated from clinical specimens such aswounds, feces, sputum and mesenteric lymph

nodes. However, it is not part of the normal human

flora.

Yersiniosis is frequently characterized by such

symptoms as gastroenteritis with diarrhea and/or vomiting;

however, fever and abdominal pain are the hallmarksymptoms.


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Yersinia infections mimic appendicitis andmesenteric lymphadenitis.

Illness onset is usually between 24 and 48hours after ingestion


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Associated food

Strains ofY. enterocolitica can be found in

meats (pork, beef, lamb, etc.),

oysters,

fish, and

raw milk.

The exact cause of the food contamination is

unknown.


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Associated food

However, the prevalence of this organism inthe soil and water and in animals such asbeavers, pigs, and squirrels, offers ample

opportunities for it to enter our food supply.

Poor sanitation and improper sterilizationtechniques by food handlers, including

improper storage, cannot be overlooked.


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Diagnosis

Stool culture is the best way to confirm adiagnosis ofYersinia enterocolitica.

The culture result is usually positive within 2weeks of onset of disease.

Instruct the laboratory to plate entericspecimens onto enteric media, with

incubation at 25C for 48 hours.


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Diagnosis

IfY enterocolitica is suspected, cold enhancement techniques or

cefsulodin-irgasan-novobiocin (CIN) agar should be

used. Colonies deep red center with clear colorless zone, 1-2mm in diameter

Confirmation occurs with the isolation, as well as

biochemical and

serological identification, ofY. enterocolitica from boththe human host and the ingested foodstuff.


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Diagnosis

Presumptive biochemical ID LIA: alkaline/acid(no gas, H2S -negative) Urease -positive

Other biochemical tests: Motility test medium (semisolid)

Y. ent. are motile at 25C (2 left tubes) and non-motile at 35C ( 2 right tubes)


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Diagnosis

Other biochemical tests: Lipase test.

When grown on agar media containing egg yolksuch as Anaerobic egg yolk agar, colonies mayexhibit lipase activity.

A positive reaction is indicated by oily, iridescent,pearl-like colony surrounded by precipitation ring

and outer clearing zone.


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Diagnosis

Identification

use of API 20 E system

Determination of pathogenicity is morecomplex.

presumptive pathogenic Y.enterocolitica

: esculin and salicinnegative


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YERSINIA ENTEROCOLITICA

Pathogenicity testing Pyrazinamidase test(PYZ)*

Congo Red Magnesium Oxalate (CR-MOX)*

Crystal Violet binding Test

Autoagglutination test#

Freezing Cultures#

DNA colony hybridization


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a Gram-positive bacterium,

motile by means of flagella.

Some studies suggest that 1-10% of humans

may be intestinal carriers ofL. monocytogenes.

It has been found in at least

37 mammalian species, both domestic and feral,

17 species of birds and possibly some species of fish and shellfish.


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some reports suggest that normal, healthypeople are at risk,

although antacids or cimetidine may predispose.

Its ability to grow at temperatures as low as3C permits multiplication in refrigeratedfoods.


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has been associated with such foods as raw milk,

supposedly pasteurized fluid milk, cheeses

(particularly soft-ripened varieties), ice cream,

raw vegetables,

fermented raw-meat sausages,

raw and cooked poultry, raw meats (all types), and raw and

smoked fish.


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The manifestations of listeriosis include

septicemia,

meningitis (or meningoencephalitis),

encephalitis, and

intrauterine or cervical infections in pregnantwomen,

which may result in spontaneous abortion (2nd/3rdtrimester) or stillbirth.


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The infective dose ofL. monocytogenes isunknown but is believed to vary with thestrain and susceptibility of the victim.

From cases contracted through raw orsupposedly pasteurized milk, it is safe toassume that in susceptible persons, fewer

than 1,000 total organisms may causedisease.


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Food analysis complex and time consuming Identification based on: Gram stain, gray colonies with halo on PALCAM Hemolysis on BAP, narrow zone of beta hemolysis, Motility-

tumbling motility, end to end with characteristic invertedtest tube brush on semi solid agar

Catalase positive Absence of hydrogen sulfide

Hemolysis by CAMP test using test organisms Blue colonies by Henrys illumination API Listeria Serotyping: 1/2a, 1/2b and 4b commonly reported in

outbreaks


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PALCAM agar

Go to video of tumblingmotility


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Campylobacter jejuni

a Gram-negative slender, curved, and motile rod.

It is a microaerophilic organism, it has a requirement for reduced levels of oxygen.

It is relatively fragile, and sensitive toenvironmental stresses (e.g., 21% oxygen,drying, heating, disinfectants, acidic conditions).

Because of its microaerophilic characteristics theorganism requires 3 to 5% oxygen and 2 to 10% carbon dioxide for optimal growth

conditions.


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leading cause of bacterial diarrheal illness inthe United States.

It causes more disease than Shigella spp. and

Salmonella spp. combined.

causes diarrhea, which may be watery orsticky and can contain blood (usually occult)

and fecal leukocytes (white cells).


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Other symptoms often present are fever,abdominal pain, nausea, headache andmuscle pain.

The illness usually occurs 2-5 days afteringestion of the contaminated food or water.


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The infective dose ofC. jejuniis considered tobe small.

about 400-500 bacteria

in others, greater numbers are required.

The pathogenic mechanisms still notcompletely understood,

but it does produce a heat-labile toxin thatmay cause diarrhea.

may also be an invasive organism.


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Associated foods

frequently contaminates raw chicken. 20 to 100% of retail chickens are contaminated. This is not overly surprising since many healthy

chickens carry these bacteria in their intestinal tracts.

Raw milk is also a source of infections. The bacteria are often carried by healthy cattle

and by flies on farms.

Non-chlorinated water may also be a source of

infections. However, properly cooking chicken, pasteurizing

milk, and chlorinating drinking water will kill thebacteria.


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Recovery from food

Isolation from food is difficult

because the bacteria are usually present in verylow numbers (unlike the case of diarrheal stools).

The methods require an enrichment broth containing antibiotics,

special antibiotic-containing plates and a

microaerophilic atmosphere with 5% oxygen and

an elevated concentration of carbon dioxide (10%).


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Other procedures for cheese products available in Bacteriological Analytical Manual (FDA)

l i d


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Isolation procedures

is usually present in high numbers in the

diarrheal stools of individuals,

Cultured on Skirrows medium with vancomycin,

trimethoprim, cephalothin, polymixin andamphoteracin B

Failure to grow at 25C, oxidase positive and

sensitivity to nalidixic acid The optimal temperature for growth is 42C for

C jejuni, and 37C for many of the other entericCampylobacters.


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Food Microbiology Lecture Final Pres

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