Microbiology of fruits and vegetables

MICROBIOLOGY OF

Fruits and
Vegetables



MICROBIOLOGY OF

Fruits and
Vegetables
Edited by

Gerald M. Sapers
James R. Gorny
Ahmed E. Yousef

Boca Raton London New York

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Microbiology of fruits and vegetables / edited by Gerald M. Sapers, James R. Gorny, Ahmed E. Yousef.
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Includes bibliographical references and index.
ISBN 0-8493-2261-8
1. Fruit--Microbiology. 2. Vegetables--Microbiology. I. Sapers, Gerald M. II. Gorny, James R. III.
Yousef, Ahmed Elmeleigy.
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Preface
Fruits and vegetables represent an important part of the human diet, providing
essential vitamins, minerals, and fiber, and adding variety to the diet. In their
Food Guide Pyramid, the U.S. Department of Agriculture encourages consumption of 3–5 servings of vegetable items, and 2–4 servings of fruit items per
day. In today’s global economy, fresh fruits and vegetables are available year
round.
In the U.S. and other technologically advanced countries, high-quality fresh
and processed fruits and vegetables are widely available. Fresh-cut fruits
and vegetables represent a large and rapidly growing segment of the fresh
produce industry. These commodities have an excellent safety record with
respect to incidence of foodborne illness. Nevertheless, surveillance statistics
compiled by the U.S. Centers for Disease Control and Prevention indicate that
significant and increasing numbers of outbreaks have been associated with
fresh fruits and vegetables, or their products. The presence of human pathogens in fresh produce is borne out by U.S. Food and Drug Administration
product recall data, and by microbiological surveys of domestically produced
and imported commodities. Increased recognition of a food safety problem
with produce may reflect greater consumption of fruits and vegetables,
more frequent eating out, greater reliance on imports of out-of-season fruits

and vegetables from ‘‘third world’’ producers, and improved surveillance and
reporting methods by public health agencies.
In addition to safety concerns, microbial spoilage of fresh produce represents a source of waste for consumers, and an economic loss to growers,
packers, and retailers. Post-harvest decay, bacterial soft rot, and microbial
spoilage of fresh-cuts and processed juices are continuing problems.
In recent years, extensive research has been conducted on microbiological
problems relating to the safety and spoilage of fruits and vegetables. Active
areas of research include incidence of human pathogen contamination, sources
of microbial contamination, microbial attachment to produce surfaces, intractable spoilage problems, efficacy of sanitizing treatments for fresh produce,
novel interventions for produce disinfection, and methodologies for microbiological evaluation of fruits and vegetables.
In this book, we have attempted a comprehensive examination of these
topics, focusing on issues, rather than attempting an encyclopedic compilation
of information about all commodities, classes of microorganisms, or categories
of spoilage. We have not included certain topics, such as preharvest diseases of
produce or production of fermented vegetables, which are adequately covered


Preface

elsewhere. We have selected chapter authors who are active researchers in their
respective fields, and thus bring a working knowledge of current issues,
industry practices, and advances in technology.
The book is divided into five sections: (I) Contamination and State of
Microflora on Fruits and Vegetables; (II) Microbial Spoilage of Fruits and
Vegetables; (III) Food Safety Issues; (IV) Interventions to Reduce Spoilage
and Risk of Foodborne Illness; and (V) Microbiological Evaluation of Fruits
and Vegetables. Within each section we have grouped chapters that cover
specific issues related to the overall topic. For example, Section I contains
chapters on sources of microbial contamination, attachment of microorganisms to fresh produce, internalization and infiltration of microorganisms in
produce, and stress adaptation by microorganisms and safety of produce.

I wish to thank the individual chapter authors for the authoritative
and comprehensive coverage of their respective topics, and my co-editors,
Dr. James R. Gorny and Dr. Ahmed E. Yousef, for their assistance in
developing the concept and organizational structure of the book, identifying
suitable chapter authors, reviewing the completed chapters, and helping me
assemble the manuscripts into a form suitable for publication. I also thank
Susan Lee, Food Science Editor at Dekker/CRC Press and her editorial staff
for their guidance, invaluable help, and patience in working with us on this
project. I thank my employer, the USDA Agricultural Research Service’s
Eastern Regional Research Center, for allowing me the time, and providing
the resources, that enabled me to participate in this project. Finally, I must
thank my wife for her unlimited patience and understanding during the
many long hours when I was attached to the computer and unavailable to meet
her needs.
Gerald M. Sapers


Editors
Gerald M. Sapers received his Ph.D. in food technology from MIT in 1961. He
joined the USDA’s Eastern Regional Research Center (ERRC) in 1968, after 2
years at the U.S. Army Natick Laboratories, and 6 years in private industry.
He has conducted research on dehydrated potato stability, apple volatiles,
safety of home canned tomatoes, utilization of natural pigments, pigmentation
of small fruits, cherry dyeing, control of enzymatic browning in minimally
processed fruits and vegetables, mushroom washing, and microbiological
safety of fresh produce, which is his current area of research. He has been a
Lead Scientist at ERRC since 1991. Dr. Sapers has published 110 scientific
papers, 3 book chapters and 5 patents. He is an active member of the Institute
of Food Technologists’ Fruit and Vegetable Products Division, and the
International Fresh-cut Produce Association.

James R. Gorny received his Ph.D. in plant biology from the University of
California, Davis, and his M.S. and B.S. degrees in food science from
Louisiana State University in Baton Rouge. He is currently vice president of
Technology and Regulatory Affairs for the International Fresh-cut Produce
Association, and has been the author and editor of numerous scientific
publications including: Editor-In-Chief of the IFPA Food Safety Guidelines
for the Fresh-cut Produce Industry and a contributor to the chapter on
‘‘Produce Food Safety’’ in the recently revised U.S. Department of Agriculture
Handbook 66. His research has focused on the effects of modified atmospheres on the quality and safety of whole and fresh-cut fruit produce. He
has been actively involved in the fresh-cut produce industry since 1986, and
has worked extensively as a consultant on food safety, packaging, quality
assurance, operations, and general management issues, both nationally and
internationally.
Ahmed E. Yousef received his Ph.D. in food science from the University
of Wisconsin (UW)-Madison in 1984. Subsequently, he served as a postdoctoral researcher at the Department of Food Science and the Department
of Food Microbiology and Toxicology, UW. Dr. Yousef joined The Ohio
State University (OSU) as an assistant professor in 1991. At OSU, Dr. Yousef
investigated food biopreservation using bacteriocins, explored new applications of ozone in food processing, and addressed the safety of foods processed
by novel technologies such as pulsed electric field, high pressure processing
and ohmic heating. He is currently a professor at the Department of Food


Editors

Science and Technology and the Department of Microbiology, teaching
the main food microbiology course at OSU. Dr. Yousef has published
2 books, 10 book chapters, and 70 scientific papers and review articles, and a
patent. He is an active member of the Institute of Food Technologists, the
American Society for Microbiology, and the International Association of Food
Protection.

Contributors
Bassam A. Annous
Eastern Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Wyndmoor, Pennsylvania
Jerry A. Bartz
Department of Plant Pathology
University of Florida
Gainesville, Florida
Robert B. Beelman
Department of Food Science
Pennsylvania State University
University Park, Pennsylvania
Larry R. Beuchat
Center for Food Safety
Department of Food Science and
Technology
University of Georgia
Griffin, Georgia
Maria T. Brandl
Western Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Albany, California
F. Breidt, Jr.
Agricultural Research Service
U.S. Department of Agriculture

and Department of Food Science
North Carolina State University
Raleigh, North Carolina

Naveen Chikthimmah
Department of Food Science
Pennsylvania State University
University Park, Pennsylvania
Pascal Delaquis
Food Safety and Quality
Agriculture and Agri-Food Canada
Summerland, British Columbia,
Canada
Mary Ann Dombrink-Kurtzman
National Center for Agricultural
Utilization Research
Agricultural Research Service
U.S. Department of Agriculture
Peoria, Illinois
Elazar Fallik
Department of Postharvest Sciences
of Fresh Produce
ARO-The Volcani Center
Bet-Dagan, Israel
William F. Fett
Eastern Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Wyndmoor, Pennsylvania
Daniel Y.C. Fung

Department of Animal Sciences and
Industry
Kansas State University
Manhattan, Kansas


Contributors

Jim Gorny
International Fresh-cut Produce
Association
Davis, California
Lisa Gorski
Western Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Albany, California
Dongsheng Guan
Department of Animal and Food
Sciences
University of Delaware
Newark, Delaware
Yingchan Han
Department of Food Sciences
Purdue University
West Lafayette, Indiana
Dallas G. Hoover
Department of Animal and Food
Sciences
University of Delaware

Newark, Delaware
J.H. Hotchkiss
Department of Food Sciences
Cornell University
Ithaca, New York
William C. Hurst
Department of Food Science and
Technology
University of Georgia
Athens, Georgia
Lauren Jackson
Center for Food Safety and
Applied Nutrition
U.S. Food and Drug Administration
Bedford, Illinois

Susanne E. Keller
National Center for Food Safety
and Technology
U.S. Food and Drug
Administration
Summit Argo, Illinois
Michael F. Kozempel
Eastern Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Wyndmoor, Pennsylvania
Ching-Hsing Liao
Eastern Regional Research Center
Agricultural Research Service

U.S. Department of Agriculture
Wyndmoor, Pennsylvania
Richard H. Linton
Center for Food Safety Engineering
Purdue University
West Lafayette, Indiana
Robert E. Mandrell
Western Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Albany, California
Pamela G. Marrone
AgraQuest, Inc.
Davis, California
Julien Mercier
AgraQuest, Inc.
Davis, California
Arthur J. Miller
U.S. Food and Drug
Administration
Center for Food Safety and
Applied Nutrition
College Park, Maryland


Contributors

J.-M. Monier
Laboratoire d’Ecologie Microbienne
Universite´ Claude Bernard Lyon 1

Villeurbanne, France

Travis L. Selby
Department of Food Sciences
Purdue University
West Lafayette, Indiana

Philip E. Nelson
Department of Food Sciences
Purdue University
West Lafayette, Indiana

Charles R. Sterling
Department of Veterinary Science
and Microbiology
University of Arizona
Tucson, Arizona

Ynes R. Ortega
Center for Food Safety
Department of Food Science and
Technology
University of Georgia
Griffin, Georgia
Mickey E. Parish
Citrus Research and Education
Center
University of Florida
Lake Alfred, Florida
Luis A. Rodriguez-Romo

Department of Food Science and
Technology
The Ohio State University
Columbus, Ohio
Gerald M. Sapers
Eastern Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Wyndmoor, Pennsylvania

Dike O. Ukuku
Eastern Regional Research Center
Agricultural Research Service
U.S. Department of Agriculture
Wyndmoor, Pennsylvania
B.G. Werner
Department of Food Sciences
Cornell University
Ithaca, New York
Ahmed E. Yousef
Department of Food Science and
Technology
The Ohio State University
Columbus, Ohio



Contents

SECTION I

Contamination and State of Microflora
on Fruits and Vegetables

Chapter 1
Microbial Contamination of Fresh Fruits and Vegetables ..........................
Jim Gorny
Chapter 2
Attachment of Microorganisms to Fresh Produce ....................................
Robert E. Mandrell, Lisa Gorski, and
Maria T. Brandl

3

33

Chapter 3
Internalization and Infiltration ..................................................................
Jerry A. Bartz

75

Chapter 4
Microbial Stress Adaptation and Safety of Produce .................................
Luis A. Rodriguez-Romo and Ahmed E. Yousef

95

SECTION II

Microbial Spoilage of Fruits
and Vegetables

Chapter 5
Bacterial Soft Rot ...................................................................................... 117
Ching-Hsing Liao


Contents

Chapter 6
Microbial Spoilage of Fresh Mushrooms .................................................. 135
Naveen Chikthimmah and Robert B. Beelman
Chapter 7
Spoilage of Juices and Beverages by Alicyclobacillus spp.......................... 159
Mickey E. Parish

SECTION III

Food Safety Issues

Chapter 8
Interventions to Ensure the Microbial Safety of Sprouts .......................... 187
William F. Fett
Chapter 9
Microbiological Safety of Fresh Citrus and Apple Juices ......................... 211
Susanne E. Keller and Arthur J. Miller
Chapter 10
Microbiological Safety Issues of Fresh Melons ......................................... 231
Dike O. Ukuku and Gerald M. Sapers

Chapter 11
Fresh-Cut Vegetables ................................................................................. 253
Pascal Delaquis
Chapter 12
Outbreaks Associated with Cyclospora and Cryptosporidium.................... 267
Ynes R. Ortega and Charles R. Sterling
Chapter 13
Patulin ........................................................................................................ 281
Lauren Jackson and
Mary Ann Dombrink-Kurtzman
Chapter 14
Safety of Minimally Processed, Acidified, and Fermented
Vegetable Products..................................................................................... 313
F. Breidt, Jr.


Contents

SECTION IV

Interventions to Reduce Spoilage and
Risk of Foodborne Illness

Chapter 15
HACCP: A Process Control Approach for Fruit and Vegetable Safety ... 339
William C. Hurst
Chapter 16
Effect of Quality Sorting and Culling on the Microbiological
Quality of Fresh Produce........................................................................... 365
Susanne E. Keller

Chapter 17
Washing and Sanitizing Treatments for Fruits and Vegetables ................ 375
Gerald M. Sapers
Chapter 18
Gas-/Vapor-Phase Sanitation (Decontamination) Treatments .................. 401
Richard H. Linton, Yingchang Han, Travis L. Selby, and
Philip E. Nelson
Chapter 19
Modified Atmosphere Packaging............................................................... 437
B.G. Werner and J.H. Hotchkiss
Chapter 20
Hot Water Treatments for Control of Fungal Decay on
Fresh Produce ............................................................................................ 461
Elazar Fallik
Chapter 21
Surface Pasteurization with Hot Water and Steam ................................... 479
Bassam A. Annous and Michael F. Kozempel
Chapter 22
Novel Nonthermal Treatments .................................................................. 497
Dongsheng Guan and Dallas G. Hoover
Chapter 23
Biological Control of Microbial Spoilage of Fresh Produce ..................... 523
Julien Mercier and Pamela G. Marrone


Contents

SECTION V Microbiological Evaluation of Fruits
and Vegetables
Chapter 24

Sampling, Detection, and Enumeration of Pathogenic and
Spoilage Microorganisms ........................................................................... 543
Larry R. Beuchat
Chapter 25
Rapid Detection of Microbial Contaminants ............................................ 565
Daniel Y.C. Fung
Chapter 26
Methods in Microscopy for the Visualization of Bacteria and
Their Behavior on Plants ........................................................................... 595
Maria T. Brandl and J.-M. Monier
Index........................................................................................................... 621


Section I
Contamination and
State of Microflora on
Fruits and Vegetables



1

Microbial Contamination
of Fresh Fruits
and Vegetables
Jim Gorny

CONTENTS
1.1
1.2

1.3
1.4

1.5

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Produce Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Microorganisms of Concern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Incidence and Association of Human Pathogens
with Produce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.1 FDA Imported Produce Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.2 FDA Domestic Produce Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.3 USDA Microbiological Data Program (MDP) . . . . . . . . . . . . . . . 10
1.4.4 Produce-Associated Foodborne Illness Traceback
Investigation Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Potential Sources of Produce Contamination by
Human Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5.1 Food Safety Risk Factors Associated with Production
of Fresh Produce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.5.1.1 Land Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.1.2 Soil Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.1.3 Wild and Domestic Animal Control . . . . . . . . . . . . . . . . 14
1.5.1.4 Irrigation Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5.1.5 Harvest Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.5.2 Food Safety Risk Factors Associated with Postharvest
Handling of Produce. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.2.1 Employee Hygiene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.2.2 Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.5.2.3 Wash and Hydrocooling Water . . . . . . . . . . . . . . . . . . . . 17
1.5.2.4 Cold Storage Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

1.5.2.5 Packaging Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.5.2.6 Modified Atmosphere Packaging of
Fresh Produce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3


4

Microbiology of Fruits and Vegetables

1.5.2.7

Refrigerated Transport, Distribution, and
Cold Storage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.5.3 Food Safety Risk Factors Associated with
Foodservice, Restaurant, and Retail Food Stores
Handling of Produce. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.5.4 Consumer Handling of Produce from Purchase to Plate . . . . . . 21
1.6 Effective Management Strategies: Contamination Prevention
and Intervention. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.6.1 Good Agricultural Practices (GAPs) . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.6.2 Current Good Manufacturing Practices (cGMPs). . . . . . . . . . . . . 23
1.6.3 Hazard Analysis Critical Control Point (HACCP) . . . . . . . . . . . . 24
1.7 Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.7.1 Microbial Ecology of Human Pathogens in the Agricultural
Production Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.7.2 Agricultural Water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.7.3 Soil Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.7.4 Proximity Risk of Potential Contaminant Sources . . . . . . . . . . . . 27

1.7.5 Intervention Strategies to Reduce the Risk of
Human Pathogen Contamination of Fresh Produce . . . . . . . . . . 27
1.8 Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

1.1

INTRODUCTION

Fresh fruits and vegetables are perceived by consumers to be healthful and
nutritious foods because of the plethora of scientifically substantiated and
documented health benefits derived from consuming fresh fruits and vegetables
[1]. However, recent foodborne illness outbreaks in the U.S. and throughout
the world have been increasingly linked epidemiologically to consumption of
fresh fruits, vegetables, and unpasteurized juices. These incidents have caused
growers, shippers, fresh-cut produce processors, distributors, retailers, importers, and government public health officials to re-evaluate the risk of contracting foodborne illness from consumption of fresh fruits and vegetables
and to re-evaluate current production and handling practices.
While the probability of contracting a foodborne illness via consumption
of fresh fruits or vegetables is very low, a small probability does exist. Because
fresh fruits and vegetables are often consumed uncooked so that there is
no ‘‘kill’’ step, prevention of produce contamination with human pathogens
is the only practical and effective means of ensuring that these food products are wholesome and safe for human consumption. This means that a
complete supply chain approach to prevent contamination at any point in the
produce continuum is essential to ensuring public health by minimizing the
incidence of foodborne illness associated with produce consumption. Ensuring


Microbial Contamination of Fresh Fruits and Vegetables

5

the integrity of produce from field to fork is the responsibility of everyone in
the produce continuum, including growers, shippers, processors, distributors,
retailers, and consumers. It must also be remembered that the health benefits
derived from eating at least five servings of fresh fruits and vegetables daily
far outweigh the very small probability of contracting a foodborne illness.
A meaningful assessment of the risk associated with contracting a
foodborne illness from consumption of fresh fruits and vegetables involves
understanding the microbiology of fresh fruits and vegetables as well as field
production, processing, and handling practices. As such, the fresh produce
industry is extraordinarily diverse and complex in the number of products
produced, how the products are grown and handled, and the geographic
areas from which these products are sourced. A typical retail grocer in North
America will have available on a daily basis upwards of 300 different
produce items for sale. The morphological characteristics of a produce item
may also contribute to its propensity for contamination, since produce
items may be derived from the leaves, stems, stalks, roots, fruits, and flowers
of plants. Because the produce continuum represents such diversity, it is
only possible to describe broad generalities about current practices of the
produce continuum and the food safety risk associated with them, as an
in-depth analysis of this plethora of products would be encyclopedic in volume.

1.2 PRODUCE CONTAMINATION
Contamination of fruits and vegetables by human pathogens can occur
anywhere in the farm to table continuum including contamination of seed
stocks and during production, harvesting, postharvest handling, storage,
processing, transport distribution, retail display, and/or preparation (foodservice or home). Produce contaminated with human pathogens cannot be
completely disinfected by washing or rinsing the product in an aqueous
solution, and low sporadic levels of human pathogens can be found on produce [2,3]. In 2004 the Alliance for Food and Farming [4] analyzed Centers
for Disease Control and Prevention (CDC) data sets [5,6] and summarized information regarding foodborne illness outbreaks that have been

associated with produce consumption. The study’s objective was to analyze
likely sources of produce contamination and categorize the most likely place
that the contamination occurred, that being either during production/
growing or during postproduction handling. The ‘‘postproduction’’ category
included produce-associated foodborne illnesses that were most likely due to
improper handling at the foodservice, retail, or consumer level, while the
‘‘grower’’ category included foodborne illnesses associated with produce that
were most likely attributable to the farm, packing, shipping, or other
agricultural postharvest handling. Analysis of CDC data indicated that
improper handling of fruits and vegetables at foodservice establishments or
by consumers caused 83% of produce-associated foodborne illness outbreaks,
while ‘‘grower’’-implicated cases comprised 17% of produce-associated


6

Microbiology of Fruits and Vegetables

FIGURE 1.1 Produce-associated outbreaks due to suspected farm contamination versus
postproduction handling. (Adapted from Analysis of Produce Related Foodborne Illness
Outbreaks, Alliance for Food and Farming, April 2004, www.foodandfarming.info/
documents/85876_produce_analysis_604.pdf.)

foodborne illness outbreaks. Data from this report presented in Figure 1.1
show that the percentage of ‘‘grower’’-related contamination incidents as a
percent of all produce related outbreaks has been declining since 1996, and this
trend is most likely due to implementation of good agricultural practices
(GAPs) by grower/shipper/packers.
The Alliance for Food and Farming 2004 report and the CDC [7] both
indicate that about 12% of foodborne illnesses occurring in the U.S. between

1990 and 2001 has been associated with consumption of fresh fruits and
vegetables. This figure of 12% of outbreak cases associated with produce
consumption represents a greater proportion of foodborne illness burden being
represented by fresh fruits and vegetables than was reported in the past
(Table 1.1). CDC data also indicate that produce-related outbreaks have
become larger, involving more individuals and increasing in frequency.
Foodborne illness outbreak reports related to produce consumption have
most likely increased due to:



Better detection and diagnostic methods for human pathogens which
can epidemiologically associate produce consumption with illness
(PulseNet, SODA salmonella outbreak detection algorithm, etc.).


7

Microbial Contamination of Fresh Fruits and Vegetables

TABLE 1.1
Trends in Burden: Foodborne Outbreaks Related to Fresh Produce,
1973–1997

No. outbreaks per year
Median cases per outbreak
Outbreaks of known vehicle (%)
Outbreak associated cases (%)

1970s

1990s

2
21
0.7
0.6

16
43
6
12

Adapted from Sivapalasingham, S., Friedman, C.R., Cohen, L., and Tauxe, R.V.,
J. Food Prot. 67, 10, 2004.














Increased surveillance for human pathogens by public health
agencies.
Increased per capita consumption of fresh fruits and vegetables in
North America.
Increased awareness that produce may be a potential vehicle for
human pathogens, thus leading to increased epidemiological investigations of produce as a potential vector.
Increased global sourcing of produce items to ensure year around

supply of the broad diversity of produce available in modern grocery
stores.
Longer postharvest storage and longer shipment times that may
also contribute to increased potential for illness by allowing for
proliferation of an initial low number of human pathogens to an
infectious or disease-causing dosage.

1.3 MICROORGANISMS OF CONCERN
Harris et al. [8] extensively reviewed outbreaks associated with fresh produce
and reported that the most common human pathogens associated with produce
foodborne illness outbreaks are: E. coli O157:H7, Salmonella spp., Shigella
spp., Listeria monocytogenes, Crytosporidium spp. [9], Cyclospora spp.,
Clostridium botulinum, hepatitis A virus, Norwalk virus, and Norwalk-like
viruses. These microorganisms can be categorized as follows:









Soil-associated pathogenic bacteria (Clostridium botulinum, Listeria
monocytogenes).
Feces-associated pathogenic bacteria (Salmonella spp., Shigella spp.,
E. coli O157:H7, and others).
Pathogenic parasites (Cryptosporidium, Cyclospora).
Pathogenic viruses (hepatitis A, enterovirus, Norwalk-like viruses).

Many of these pathogens are spread via a human (or domestic animal)
to food to human transmission route. Handling of fruits and vegetables by

8

Microbiology of Fruits and Vegetables

infected field-workers or consumers, cross contamination, use of contaminated water, use of inadequately composted manure, or contact with contaminated soil are just a few of the ways that transmission of human pathogens
to food can occur.
Data from the CDC foodborne outbreak surveillance system show that
from 1988 to 1998 the two most commonly reported microorganisms
associated with fresh produce foodborne illness outbreaks were Salmonella
spp. and E. coli O157:H7 with 45% and 38% of the fruit and vegetable linked
outbreaks, respectively, being attributed to these two microorganisms. However, recent foodborne illness outbreaks associated with produce consumption
have been caused by viruses (hepatitis A) and parasites (Cyclospora spp.). CDC
data demonstrate that the majority of reported foodborne illnesses in the
U.S. are of unknown etiology and are most likely caused by viruses such as
Norwalk-like viruses [10,11]. Unfortunately, diagnostic tools for detection
and enumeration of viruses that may cause foodborne illnesses are severely
lacking.

1.4
1.4.1

INCIDENCE AND ASSOCIATION OF HUMAN
PATHOGENS WITH PRODUCE
FDA IMPORTED PRODUCE SURVEY

In March 1999 the U.S. Food and Drug Administration (FDA) initiated
a 1000-sample survey of imported fresh produce raw agricultural commodities from 21 countries and included: broccoli, loose-leaf lettuce (radicchio,
escarole, endive, chicory leaf, mesclun, and others), cantaloupe, celery, strawberries, scallions/green onions, tomatoes, parsley, culantro (a herb), and
cilantro [12]. Loose-leaf lettuce products included radicchio, escarole, endive,
chicory and others. These high-volume imported fresh produce raw

agricultural commodities were selected by the FDA for the imported
produce sampling assignment based on the following risk factor criteria:
epidemiological outbreak data, structural characteristics of the produce item,
growing conditions, processing and consumption rates. Raw agricultural
commodities are defined in the Federal Food, Drug, and Cosmetic Act as ‘‘any
food in its raw or natural state, including all fruits that are washed, colored, or
otherwise treated in the unpeeled natural form prior to marketing.’’ These raw
agricultural commodities were analyzed for the presence of Salmonella
spp. and E. coli O157:H7. All commodities except for cilantro, culantro, and
strawberries also were analyzed for Shigella spp. Produce imported from
Mexico, Canada, Costa Rica, Guatemala, the Netherlands, Honduras,
Belgium, Italy, Israel, Chile, Peru, Colombia, Trinidad and Tobago, New
Zealand, Nicaragua, the Dominican Republic, France, Argentina, Ecuador,
Haiti, and Korea were sampled. Six countries provided 25 or more samples for
analysis: Mexico, Canada, Costa Rica, Guatemala, the Netherlands, and
Honduras.