Martin Wiedmann

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Microbial food safety issues real world
problems that get undergrads excited about
microbiology

• Martin Wiedmann
• Department of Food Science
• 412 Stocking Hall
• Cornell University
• Phone [phone]
• E-mail mw16_at_cornell.edu

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Foodborne diseases

• Latest CDC estimates indicate the following
  annual burdens due to foodborne diseases in the
  US per year
• 325,000 serious illnesses resulting in
  hospitalizations
• 76 million cases of gastrointestinal illnesses
• 5,000 deaths

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Transmission of foodborne diseases
Animal feed/environment/protozoans
Manure
Food animals
Plant derived raw products
Animal derived food products
Food Processing Plants
RTE Foods
Humans
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Salmonella

• About 1.4 million cases annually in the US
  resulting in approx. 550 deaths
• Mostly gastrointestinal syndrome, but also
  invasive disease
• Bioterrorism agent
• Many different subtypes, e.g., Salmonella Typhi,
  Salmonella Dublin, Salmonella Typhimurium
• While cases caused by many foodborne pathogens
  (Listeria, Campylobacter, E. coli O157H7) have
  decreased over the years, Salmonella case numbers
  have not
• Apparent increase in Salmonella resistant to one
  or more antibiotics has been observed

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Antibiotic resistant Salmonella

• In 2002, 22 of Salmonella Newport, 27 of
  Salmonella Typhimurium isolates, and 8 of
  Salmonella Heidelberg displayed multi-drug
  resistance (MDR)
• MDR Salmonella Typhimurium isolates commonly
  shows two resistance type (i) resistance to
  ampicillin, kanamycin, streptomycin,
  sulfamethoxazole, and tetracycline or (ii)
  resistance to ampicillin, chloramphenicol,
  streptomycin, sulfamethoxazole, and tetracycline

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Salmonella as bioterrorism agent
Torok TJ, Tauxe RV, Wise RP, Livengood JR,
Sokolow R, Mauvais S, Birkness KA, Skeels MR,
Horan JM, Foster LR. A large community outbreak
of salmonellosis caused by intentional
contamination of restaurant salad bars.JAMA.
1997 Aug 6278(5)389-95.
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Listeria monocytogenes

• Causes septicemia, abortion and encephalitis in
  humans and in animals
• Incubation period 7 - 60 days
• Human listeriosis occurs in both epidemic and
  sporadic cases
• Affects predominantly elderly and
  immuno-compromised people, pregnant women and
  newborns.
• Approx. 2,500 human cases/year in the U.S.,
  resulting in 350 - 450 deaths/year
• Responsible for majority of microbial food recalls

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E. coli O157H7/Enterohemorhagic E. coli (EHEC)

• Severe human disease transmitted through many
  foods, including undercooked meat, raw milk,
  apple cider, raw vegetables, etc.
• Also transmitted by other means including
  drinking water, direct animal - human
  transmission
• Approx. 60,000 human cases and 50 deaths annually
  in US
• Symptoms include bloody diarrhea, hemolytic
  uremic syndrome (kidney damage)
• Children are particularly at risk

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Noroviruses

• Noroviruses are most common cause of acute
  gastroenteritis in the United States and are
  believed to be the most common cause of food
  borne illnesses (23 million total cases annually,
  9.2 million foodborne)
• Often associated with infections/outbreaks in
  crowding situations (cruise ships, homes for
  elderly etc.)
• Noroviruses cannot be grown in the laboratory
• Studies on heat resistance and disinfection
  strategies are difficult to perform
• Detection in foods and infected humans requires
  electron microscopy or molecular biology
  approaches
• Sources are most likely humans with infection
  that prepare or handle foods
• Virus appears to be able to survive on surfaces
  for days

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Norwalk-like viruses When the runs can slow you
down

• In January 1999, an outbreak of viral
  gastroenteritis affected more than 300 people who
  attended a metropolitan concert hall over a 5-day
  period.
• The first case was a concert attendee who vomited
  in the auditorium and adjacent male toilet
• Gastrointestinal illness occurred among members
  of 8/15 school parties who attended the following
  day.
• Children who sat on the same level of the
  auditorium as the first case were much more
  likely to be ill than those seated elsewhere
• Transmission most likely occurred through direct
  contact with contaminated fomites (any inanimate
  object or substance capable of absorbing,
  retaining, and transporting contagious or
  infectious organisms from one individual to
  another).

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Case study human listeriosis outbreak
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Human listeriosis cases in NYS 1/97-10/98
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Ribotyping results - November 8, 9 pm
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Ribotyping results - November 8, 12 pm
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Epidemic curve for 1/97 - 2/99 in NYS
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Follow-Up investigations by NYSDOH, Cornell
University, CDC and other state health departments
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Subtyping of human isolates - summary

• More than 100 human listeriosis cases and 21
  deaths in more than 15 states all caused by the
  identical DNA subtype

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The outbreak source?

• Patients included in this outbreak were
  significantly more likely to have eaten hot dogs
  then controls
• November matching subtypes found in opened
  packages of deli meats collected in retail
  (including deli meats produced by Sara Lee) by
  NYSAGM
• Middle of December L. monocytogenes isolated
  from opened package of hot dogs from affected
  patient subsequent tests reveal L. monocytogenes
  DUP-1044A contamination of unopened packages
• December 22, 1998 Sara Lee announces recall of
  hot dogs and other packaged meats produced at its
  Bil Mar Foods unit in Zeeland, MI

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DNA fingerprinting methods
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Molecular characterization and taxonomy
Bacterium 1
Bacterium 2
1300 kb
1200 kb
Bact 1
Bact 2
Gel Electrophoresis (separates DNA pieces by size)
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PCR-RFLP characterization of hly

• PCR amplification of complete hly ORF, followed
  by restriction enzyme digest using HhaI and Hpa
  II
• Differentiates 8 different hlyA alleles

M 1 2 3 4 5 6 7
8 9 10
Uneven lanes HhaI Even lanes HpaII
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Examples of different L. monocytogenes ribotypes
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PFGE Types
C
C
C
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DNA sequencing-based subtyping
Isolate 1 AACATGCAGACTGACGATTCGACGTAGGCTAGACGTTGAC
TG Isolate 2 AACATGCAGACTGACGATTCGTCGTAGGCTAGACGTT
GACTG Isolate 3 AACATGCAGACTGACGATTCGACGTAGGCTAGAC
GTTGACTG Isolate 4 AACATGCATACTGACGATTCGACGAAGGCTA
GACGTTGACTG
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Use of DNA fingerprinting to control Listeria
in food processing plants
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Subtyping Results seafood processing plant
Sample Ribotype Sample Source
RiboPrint Pattern
Sample Source
VISIT 1
1039C (E) Floor drain, raw materials
area 1039C (E) Floor drain, hallway to
finished area 1039C (IP) Troll Red King
Salmon, in brine, head area 1039C (IP)
Troll Red King Salmon, in brine, belly area 1039C
(IP) Brine, Troll Red King Salmon 1039C
(IP) Faroe Island Salmon, in brine, head
area 1039C (F) Smoked Sable 1039C
(F) Cold-Smoked Norwegian Salmon 1044A
(E) Floor drain, brining cold room 1 1044A
(R) Raw Troll Red King Salmon, head
area 1044A (IP) Brine, Faroe Island
Salmon 1045 (R) Raw Troll Red King
Salmon, belly area 1045 (IP) Faroe
Island Salmon, in brine, head area 1053
(IP) Norwegian Salmon, in brine 1062
(E) Floor drain 1, raw materials
preparation 1039C (E) Floor drain 1,
raw materials preparation 1039C (E)
Floor drain, brining cold room 1 1039C
(E) Floor drain 2, raw materials
preparation 1039C (E) Floor drain 2,
raw materials receiving 1039C (E) Floor
drain, finished product area 1039C (E)
Floor drain, hallway to finished area 1039C
(IP) Brine, Troll Red King Salmon 1039C
(F) Smoked Sable 1044A (IP) Sable, in
brine 1044A (IP) Brine, Faroe Island
Salmon 1062 (IP) Brine, Norwegian
Salmon









VISIT 2





VISIT 3



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Subtyping Results - cont.
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L. monocytogenes persistence in plants
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2000 US outbreak - Environmental persistence of
L. monocytogenes?

• 1988 one human listeriosis case linked to hot
  dogs produced by plant X
• 2000 29 human listeriosis cases linked to sliced
  turkey meats from plant X

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Ideas for food micro activities for undergrads

• Brainstorm about (1) what microorganisms cause
  foodborne illness (and how much), (2) what foods
  cause foodborne illness (and why), and (3) how
  can you reduce your personal risk of foodborne
  illness
• Use current examples (ProMed FSNet)
• Lab activities (stage outbreak investigation)
• Can include simple (detection with selective
  media) to fairly complex (DNA sequencing with
  bioinformatics) lab activities

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Food Micro resources

• FSNet http//www.foodsafety.ksu.edu
• ProMed http//www.promedmail.org
• The PathogenTracker game http//scicentr1.tc.cor
  nell.edu/pathogentrackergame/Intro/introduction/we
  lcome.htm
• FightBac http//www.fightbac.org/
• Encyclopedia of Food Microbiology (can be made
  available on-line through institutional
  libraries)
• Food Microbiology an Introduction (ASM Press)
• Food Microbiology Fundamentals and Frontiers
  more advanced (ASM Press)
• Modern Food Microbiology (CHIPS)
• Food Microbiology Laboratory (Taylor Francis
  Ltd)

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Summary and conclusions

• Foodborne disease affects everyone and foodborne
  disease burdens in US and internationally are not
  trivial
• Foodborne disease is a highly suitable topic for
  introducing undergrads to many/all concepts in
  microbiology
• Undergrad food micro education can be as simple
  and as complex as you wish

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