This document summarizes information about emerging foodborne pathogens and the complex modern food system. It discusses factors that allow microbes to adapt and become emerging pathogens, such as genetic mutations, stress responses, and antibiotic resistance. Specific emerging pathogens that pose food safety risks are described in detail, including enterohemorrhagic E. coli, Campylobacter jejuni, Vibrio species, Clostridium difficile, Yersinia enterocolitica, Bacillus cereus, Listeria monocytogenes, Salmonella species, and Enterobacter sakazakii. The document contrasts the modern global and industrialized food system with past local systems and reviews foodborne disease surveillance data.

1. Emerging Pathogens Relevant to
Food Safety
Dr. Sally Yoder
March 31, 2009

2. What do microbes need to survive?
• Nutrients
• Water
• Temperature
• Time

3. Sources of microorganisms
• Environment
– Soil
– Bodies of water
– Wildlife
• Food production
– Pre-harvest (animals and plants)
– Post-harvest processing
– Post-process contamination

4. Food borne disease incidence
• 76 million cases of food borne disease
each year
• 325,000 hospitalizations
• 5,000 deaths
• FoodNet Surveillance
– 1997: 14.3 million people (5%) in 5 states
– 2007: 45.5 millions people (15%) in 10 states

5. Our food system is complex!
• Past
– Foods were produced and consumed locally
– Little variety in foods
– Little need for extended shelf life
– Most meals prepared and eaten at home
– Fewer people in high-risk groups
– Food safety and security were not a concern

6. Our food system is complex!
• Present
– Global food distribution
– Demand for a wide variety of foods (fresh,
minimally processed, canned)
– Extended shelf life
– Prepared foods
– Outbreaks can be reported immediately in the
U.S. and throughout the world
– More people in high risk groups
– Increased potential for food terrorism

7. Microbes can adapt quickly
• Mutations and other genetic changes
– New virulence factors
– Increased resistance to antibiotics
• Bacteriophage
– Incorporation of new virulence factors/survival
mechanisms
• Stress adaptation response
– Improved survival in harsh environments
– Tolerance to heat, cold, osmotic stress, starvation,
pH changes, etc. may make organisms harder to
control

8. VBNC
• Viable but non culturable
– Campylobacter
– Listeria monocytogenes
– Mycobacterium tuberculosis
– Helicobacter pylori
– Vibrio cholerae
– Some serovars of Salmonella

9. What is an emerging pathogen?
• Natural genetic drift
• Previously unrecognized
• Newly established link to food
• Improve methods of isolation and detection
• Improved surveillance
• Changing preferences of consumers
• Transglobal movement of goods
• Adaptation to selective pressure
– Antimicrobial resistance
– Changes in production practices

10. Enterohemorrhagic E. coli
• Intimin produces A/E lesions (eae gene), affect
large intestine and produce Shiga-like toxins
• Formerly, called Shiga-like toxin (SLT-I and
SLT-II) because of similarity to toxin produced
by Shigella dysenteriae
– Now called Shiga-toxin (Stx1 and Stx2)
– Susceptible cells (in large intestine) have Stx receptor,
globotriaosylceramide (Gb3)
– Cattle lack Gb3 receptor
• O157:H7, non-O157 STEC (O26:H11,
O111, O103, O121, O45, O145)

11. Campylobacter jejuni
• Campylobacteriosis
– Fairly common cause of food borne illness
• Surpassed Salmonella as most common cause of food
borne illness in 1997 (CDC)
– Easily isolated from stools but is difficult to isolate
from foods (low CFU/g and VBNC)
– Symptoms are usually flu-like and pass quickly
– Serious illness may also occur
• Reiter’s syndrome
– Joint pain and arthritis for 1 yr after infection
• Guillain-Barré syndrome
– Neuromuscular paralysis, long-term disability, death
• Hemolytic uremic syndrome

12. Vibrio spp.
• V. parahaemolyticus
– Most common cause of vibriosis
• Everyone is susceptible
• Major symptom is watery diarrhea
• Large infectious dose (million or more cells)
• V. vulnificus
– Most severe illness
– Leading cause of death in US due to seafood
consumption
• Usually associated with Gulf Coast oysters
– High mortality rate in middle-aged males with
cirrhosis or hepatitis

13. Clostridium difficile
• Major cause of nosocomial diarrhea
• Toxin A (enterotoxin) and toxin B (cytotoxin)
• Infection ranges from:
– Asymptomatic colonization (2-3% general population, up to
40% of hospital workers)
– Severe diarrhea (C. difficile-associated diarrhea, CDAD)
– Pseudomembranosus colitis
• Therapeutic use of clindamycin, cephalosporins
increases risk of CDAD
• Spores can survive for up to 5 mos. in hospital setting
• Common cause of illness and death in neonatal pigs
• Zoonotic transmission to food?

14. Yersinia enterocolitica
• Unique
– “Pathogen that came in from the cold”
• 0-1°C observed for pork, chicken, beef
• 0-4°C observed in milk → psychrotroph
• If present, likely to find other enteric pathogens
(Shigella, Salmonella, Campylobacter, etc.)
• Animal reservoirs
– Swine (common vector of human infection)
• Chitterlings consumed by young children in GA
– Rodents, ruminants, birds, cats, dogs
– Fish, oysters, crabs
– Humans are not natural carriers

15. Bacillus cereus
• Aerobic, spore-forming rod
– Soil, dust, water
– Found at low levels (102 – 104) in many foods
• Fresh and processed meat products
• Raw milk
• Two major kinds of enterotoxin
– Diarrheal
• Infectious dose ranges from 105 to 108 CFU/g
• Cereal dishes, meats, milk, vegetables, fish
– Emetic
• Infectious dose about 109 CFU/g
• Rice, potato, pasta, cheese

16. Listeria monocytogenes
• Ubiquitous!
– Soil, streams, natural environment
– Mammals, birds, fish, shellfish
• Has uncanny ability to survive lethal processes and
nonsporeforming
• Listeriosis (~25% mortality rate)
– Infectious dose ~1,000 cells
– Manifestations
• Often, flu-like symptoms
• Septicemia, meningitis, encephalitis
• In pregnant women
– Septicemia → may pass to fetus
– May cause spontaneous abortion in 2nd/3rd trimester
– May cause stillbirth
• Infections have declined 42% since 1996-98 baseline (CDC, 2007)
• Deli meats, hispanic cheeses, hummus

17. Salmonella spp.
• S. Typhimurium DT 104
– Increase in human disease in UK since 1990s
– Livestock → meats
– Resistant to ampicillin, chloramphenicol,
streptomycin, tetracyclines, sulfonamides, and
more
• Other drug-resistant strains
– Enteriditis, Cholerasuis, other non-typhoidal

18. Enterobacter sakazakii
• Gram-negative rods with unusual thermal
resistance
• Powdered infant formula
– Formula may contain 1 CFU/100 g
– 4-log reduction desired in infant formula
• May cause meningitis, sepsis, neonatal
necrotizing enterocolitis (NEC)
– Mortality rate 40-60%
– Enterotoxin causes gangrene in infant GIT (NEC)
– Preterm infants are more susceptible than full-term

19. Food borne diseases
of former importance
• Why aren’t we worried about these
diseases?
– Cholera
– Tuberculosis
– Typhoid fever
– Trichinosis

20. Good article to read
Tauxe, R. V. 1997. Emerging foodborne
diseases: an evolving public health
challenge. Emerging Infectious Diseases.
3:425-434.