Salmonella in Eggs: Salmonella in Eggs: Issues and ResearchIssues and Research

Richard K. Gast

Egg Safety and Quality Research UnitEgg Safety and Quality Research UnitUnited States Department of AgricultureUnited States Department of Agriculture

Agricultural Research ServiceAgricultural Research ServiceRussell Research CenterRussell Research Center

Athens, GeorgiaAthens, Georgia

85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

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2020

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8080Number of outbreaksNumber of outbreaks

S. enteritidis Outbreaks in the USAS. enteritidis Outbreaks in the USA

The association of eggs with The association of eggs with human human Salmonella enteritidisSalmonella enteritidis and and

S. heidelbergS. heidelberg infections:infections:

80% of human 80% of human S. enteritidisS. enteritidis outbreaks in the outbreaks in the USA (1985USA (1985--1999) for which a food source could 1999) for which a food source could be identified were attributed to eggs or eggbe identified were attributed to eggs or egg--containing foods. containing foods.

23% of 23% of S. heidelbergS. heidelberg outbreaks in the USA outbreaks in the USA (1973(1973--2001) were attributed to eggs or egg2001) were attributed to eggs or egg--containing foods.containing foods.

The deposition of The deposition of SalmonellaSalmonella in in eggs is a consequence of the eggs is a consequence of the

colonization of reproductive organs, colonization of reproductive organs, particularly the ovary and upper particularly the ovary and upper oviduct, in systemically infected oviduct, in systemically infected

hens.hens.

OvariesOvaries OviductsOviducts EggsEggs0055

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% positive% positive

SSalmonella Recovery from Reproductivealmonella Recovery from ReproductiveTissues and Egg ContentsTissues and Egg Contents

SH 1SH 1 SH 4SH 4 SH 5SH 5 SH 11SH 11 SE 6SE 6

What is the incidence of What is the incidence of S. enteritidisS. enteritidis infection in infection in

laying flocks?laying flocks?

7% of commercial laying houses in the 7% of commercial laying houses in the USA were environmentally positive for USA were environmentally positive for

S. enteritidisS. enteritidis in a 2000 survey in a 2000 survey conducted by the USDA National conducted by the USDA National

Animal Health Monitoring System.Animal Health Monitoring System.

What is the incidence of What is the incidence of S. enteritidisS. enteritidis contamination of contamination of

eggs?eggs?In field studies of environmentally positive In field studies of environmentally positive flocks in Pennsylvania and California, the flocks in Pennsylvania and California, the prevalence of egg contamination with prevalence of egg contamination with S. enteritidisS. enteritidis was approximately 5 in 20,000 was approximately 5 in 20,000 (0.025%).(0.025%).The 1998 USDA The 1998 USDA S. enteritidisS. enteritidis Risk Risk Assessment Report estimated the overall Assessment Report estimated the overall national egg contamination prevalence to be national egg contamination prevalence to be 1 in 20,000 (0.005%).1 in 20,000 (0.005%).

Recent Events in S. enteritidis Recent Events in S. enteritidis Epidemiology and ControlEpidemiology and Control

January, 2005: The Risk Assessment Division of January, 2005: The Risk Assessment Division of USDAUSDA--FSIS estimates that 182,060 human illnesses FSIS estimates that 182,060 human illnesses were caused by consumption of were caused by consumption of S. enteritidisS. enteritidis--contaminated shell eggs in 2000.contaminated shell eggs in 2000.

September, 2004: FDA proposes regulations for September, 2004: FDA proposes regulations for shell egg production that include mandatory testing shell egg production that include mandatory testing of environmental samples (and eggs, if necessary) of environmental samples (and eggs, if necessary) from commercial laying flocks.from commercial laying flocks.

Common Risk Reduction Common Risk Reduction Practices for S. enteritidis in Practices for S. enteritidis in

Poultry FlocksPoultry Flocks

Using uninfected chicksUsing uninfected chicksEffective pest controlEffective pest controlCleaning and disinfection between flocksCleaning and disinfection between flocksHeightened biosecurityHeightened biosecurityWashing and refrigeration of eggsWashing and refrigeration of eggsVaccinationVaccination

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100100

% of states% of states

Changes in Human S. enteritidis Incidence in 31 StatesChanges in Human S. enteritidis Incidence in 31 Statesafter Implementation of Egg Quality Assurance Programsafter Implementation of Egg Quality Assurance Programs

DecreasedDecreased IncreasedIncreased Source: CDC

Proposed FDA Regulations forProposed FDA Regulations forShell Egg ProducersShell Egg Producers

Purchase chicks from uninfected (NPIPPurchase chicks from uninfected (NPIP--certified) certified) breeder flocks.breeder flocks.Maintain pest control and biosecurity programs.Maintain pest control and biosecurity programs.Test laying house environmental samples for Test laying house environmental samples for S. enteritidisS. enteritidis at 40at 40--45 weeks of age and after45 weeks of age and afterinduced molting.induced molting.If environment positive for If environment positive for S. enteritidisS. enteritidis, , clean/disinfect thoroughly between flocks and test clean/disinfect thoroughly between flocks and test eggs. If eggs positive, divert for pasteurization.eggs. If eggs positive, divert for pasteurization.Store eggs under refrigeration at 45Store eggs under refrigeration at 45°° F.F.

11 22 33 44Weeks post-inoculationWeeks post-inoculation

0055

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% positive% positive

Recovery of S. enteritidis from eggslaid by experimentally infected hens

ShellsShells YolksYolks AlbumensAlbumens

What are the research needs of What are the research needs of regulatory agencies and the poultry regulatory agencies and the poultry

industry regarding industry regarding SalmonellaSalmonella in eggs?in eggs?

Sources of Information:

2004 USDA2004 USDA--FSIS Risk Assessment for FSIS Risk Assessment for Salmonella enteritidisSalmonella enteritidis in Eggsin EggsEgg Nutrition Center Food Safety Egg Nutrition Center Food Safety Advisory PanelAdvisory PanelAmerican Egg Board Open HouseAmerican Egg Board Open House

PostPost--Harvest (Egg Processing) Harvest (Egg Processing) Research NeedsResearch Needs

Prevalence of pathogens on egg shells Prevalence of pathogens on egg shells before and after processingbefore and after processingEffectiveness of egg sanitizersEffectiveness of egg sanitizersValidation of current and prospective Validation of current and prospective regulatory provisionsregulatory provisions

Egg Processing Safety, Quality, Egg Processing Safety, Quality, and Securityand Security

Deana Jones Deana Jones –– Food Technologist Food Technologist (Lead Scientist)(Lead Scientist)

Michael Musgrove Michael Musgrove –– Food TechnologistFood Technologist

Effects of commercial cool water washing on pathogen detection in shell eggs

• Egg surface temperature was significantly reduced when eggs were washed with a combination of warm and cool water.

• Enterobacteriaceae frequency was not different between wash water temperature treatments for offline eggs.

• Listeria was detected in cool wash water at the offline facility but not on or in any eggs.

• Salmonella and Campylobacter were detected within the shells of 3 and 2 (of 384) samples, respectively. All positive samples were from cool water treated eggs.

• More work needs to be conducted to determine the feasibility of cool water washing of shell eggs, including examining detergents designed for cooler temperatures.

Correlation of shell strength and Salmonella Enteritidis infection

• Eggshell quality has always been difficult to quantify due to variable nature of eggs

• Advent of more objective detection devices has eliminated much of the testing variability

• A highly invasive inoculation method was utilized, yet it was very difficult to detect SE in the egg. Positive egg contents were only found after pre-enrichment.

• Correlation analysis did not find any strong positive or negative correlations between shell strength and SE contamination within the range of shell strengths detected in the current study

Recovery of Salmonella from commercial shell eggs by two methods

• Utilized shell rinse and shell crush and rub• Monitored for naturally occurring Salmonella• Shell rinse recovered 4.8% positives• Shell crush and rub recovered 5.3% positives• Occasionally only one method was positive for

Salmonella per sample• Using both methods increased sensitivity,

although in most cases, crushing provided more sensitive detection

Impact of commercial processing on the incidence of Salmonella on shell eggs

Salmonella No. of isolates Sample typeTyphimurium 21 Eggshell

1 Tap waterTyphimurium

(Copenhagen)4 Eggshell

4-12:i:-monophasic 2 EggshellHeidelberg 9 EggshellKentucky 1 Eggshell

1 Wash waterTotal 39

PrePre--Harvest (Egg Production) Harvest (Egg Production) Research Needs: Stress and Immunity Research Needs: Stress and Immunity

IssuesIssues

Effects of induced molting (by feed Effects of induced molting (by feed withdrawal and alternative methods) on withdrawal and alternative methods) on immune responsiveness and susceptibility immune responsiveness and susceptibility to to SalmonellaSalmonella infectioninfectionStress associated with other management Stress associated with other management practices and effects on immune practices and effects on immune responsivenessresponsivenessProtection by vaccination and stress effects Protection by vaccination and stress effects on vaccine efficacyon vaccine efficacy

Stress Effects on Immunity and Stress Effects on Immunity and Physiology of PoultryPhysiology of Poultry

Peter Holt Peter Holt –– Immunologist Immunologist (Lead Scientist)(Lead Scientist)

Randle Moore Randle Moore –– Veterinarian/PhysiologistVeterinarian/Physiologist

Effect of Feed Deprivation and Recovery from Feed Deprivation Over Time on:

Effect of Feed Deprivation and Recovery from Feed Deprivation Over Time on:

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Effect of Feed Deprivation on in Vitro Tissue Invasion of Salmonella enteritidis

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Effect of Induced Molting on Levels of SE in Flies vs on Floor

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Isolation of S. Enteritidis from Fly Interior vs Exterior

Treatment Exterior Interior

Nonmolt 8/10 9/10

Molt 9/10 9/10

Isolation of S. Enteritidis from Internal Organs

Treatment Sal. Gland Crop Gut

Nonmolt 0/10 1/10 10/10

Molt 0/10 3/10 8/10

PrePre--Harvest (Egg Production) Harvest (Egg Production) Research Needs: Pathogenesis IssuesResearch Needs: Pathogenesis Issues

Prevalence, level, and site of egg contamination; Prevalence, level, and site of egg contamination; growth kinetics of growth kinetics of SalmonellaSalmonella in eggs during in eggs during storage; effects of refrigeration on bacterial growth storage; effects of refrigeration on bacterial growth in eggsin eggsThe evolution (and identification) of The evolution (and identification) of SalmonellaSalmonellastrains able to contaminate eggsstrains able to contaminate eggsGenetic differences between Genetic differences between SalmonellaSalmonella strains that strains that can be used to establish epidemiological can be used to establish epidemiological relationships (including sources and routes of relationships (including sources and routes of transmission)transmission)

Controlling Egg Contamination Controlling Egg Contamination with Salmonella enterica by with Salmonella enterica by

Understanding its Evolution and Understanding its Evolution and PathobiologyPathobiology

Jean GuardJean Guard--Bouldin Bouldin ––Veterinarian/Molecular Biologist (Lead Scientist)Veterinarian/Molecular Biologist (Lead Scientist)

Richard Gast Richard Gast -- MicrobiologistMicrobiologist(Research Leader)(Research Leader)

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days postinoculationdays postinoculation

Mean Duration of Salmonella RecoveryMean Duration of Salmonella Recoveryfrom Fecal Samplesfrom Fecal Samples

Parent strainsParent strains Passaged strainsPassaged strains

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% positive% positive

Salmonella Recovery from EggsSalmonella Recovery from Eggs

Parent strainsParent strains Passaged strainsPassaged strains

PT8PT8 PT13aPT13a0055

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S. enteritidis penetration into egg yolksS. enteritidis penetration into egg yolks

7° / 24 hours7° / 24 hours 30° / 24 hours30° / 24 hours

Phenotype canPhenotype can vary dramatically within vary dramatically within serotype and phage typeserotype and phage type

biofilmnegative

PT13APT13A

= EggContamination

PT13APT13A

≠EggContamination

biofilmpositive

SNP portfolio of Salmonella Enteritidis

6, 36%

12, 12%

13, 2%

14, 3%

15, 6%

16, 3%

17, 3%

8, 1%

11, 1%

18, 10%1, 3%

2, 2%3, 3%

4, 2%

5, 2%

9, 9%10, 1% 7, 2%

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Work in progress from Jean Guard Bouldin, DVM, Ph.D., USDA-ARS-ESQRU, Athens GA

The Future of Salmonella The Future of Salmonella Control in EggControl in Egg--Laying Chickens?Laying Chickens?

Detecting and protecting against specific Salmonella Detecting and protecting against specific Salmonella serotypes can be essential for responding to urgent or serotypes can be essential for responding to urgent or

severe threats to public health, but the most costsevere threats to public health, but the most cost--effective effective and sustainable approaches to controlling foodand sustainable approaches to controlling food--borne borne

disease are based on risk reduction practices that address disease are based on risk reduction practices that address a broad spectrum of current and emerging pathogens.a broad spectrum of current and emerging pathogens.