Peter S. Holt

Evaluation of the Efficacy of Oil-Emulsion Bacterins for Reducing Fecal Shedding of Salmonella enteritidis by Laying Hens

Two replicate experiments were conducted to test the efficacy of two different Salmonella enteritidis oil-emulsion bacterins (an experimentally prepared acetone-killed vaccine and a commercially available vaccine) for protecting laying hens against intestinal colonization following oral exposure to S. enteritidis. Each vaccine was administered twice (4 weeks apart), and all hens were challenged with 10(8) cells of a nalidixic-acid-resistant S. enteritidis strain 2 weeks after the second vaccination. Fecal samples from vaccinated and unvaccinated control hens were cultured at three weekly intervals post-challenge to determine the incidence of intestinal colonization and the numbers of S. enteritidis shed into the environment. Both vaccines significantly reduced the incidence of intestinal colonization (P < 0.05) and the mean number of S. enteritidis cells shed in the feces (P < 0.01) at 1 week post-challenge. However, the degree of protection afforded by vaccination was only partial, as more than half of the vaccinated hens still shed substantial numbers of S. enteritidis. If used in conjunction with other flock sanitation and infection-monitoring strategies, vaccination with bacterins could potentially reduce the overall level of environmental contamination and thereby also reduce the horizontal transmission of S. enteritidis within and between laying flocks.

Effect of Induced Molting on the Susceptibility of White Leghorn Hens to a Salmonella enteritidis Infection

Older white leghorn hens (more than 52 weeks old) were induced to molt using a 14-day feed-removal protocol. On day 4 of feed removal, groups of hens were infected with varying 10-fold dilutions of Salmonella enteritidis, and these hens were examined for S. enteritidis intestinal shedding 7 days later. Molting hens infected with a 10(-2) dilution of S. enteritidis shed 3-4 logs more of the organism at 7 days postinfection than the unmolted group receiving a similar dose. The mean infectious dose (ID50) for S. enteritidis in unmolted hens ranged from 0.65 x 10(4) to 5.6 x 10(4), whereas in molting hens the ID50 was found to be less than 10(1), a 2-3 log increase in the susceptibility of the hens to the organism.

The impact of different housing systems on egg safety and quality

A move from conventional cages to either an enriched cage or a noncage system may affect the safety or quality, or both, of the eggs laid by hens raised in this new environment. The safety of the eggs may be altered either microbiologically through contamination of internal contents with Salmonella enterica serovar Enteritidis (Salmonella Enteritidis) or other pathogens, or both, or chemically due to contamination of internal contents with dioxins, pesticides, or heavy metals. Quality may be affected through changes in the integrity of the shell, yolk, or albumen along with changes in function, composition, or nutrition. Season, hen breed, flock age, and flock disease-vaccination status also interact to affect egg safety and quality and must be taken into account. An understanding of these different effects is prudent before any large-scale move to an alternative housing system is undertaken.

Deposition of phage type 4 and 13a Salmonella enteritidis strains in the yolk and albumen of eggs laid by experimentally infected hens.

Because egg yolk and albumen differ substantially in their abilities to support bacterial growth, the initial level and location of Salmonella enteritidis deposition are critical for determining whether proposed standards for refrigerating eggs are likely to protect public health by preventing extensive microbial multiplication. In the present study, three groups of laying hens were infected with oral doses of approximately 10(9) cells of different S. enteritidis strains (two were phage type 4 and one was phage type 13a) in two replicate trials. For all three S. enteritidis strains, the incidence of yolk contamination (approximately 2.5% overall) was significantly greater than the incidence of albumen contamination (approximately 0.5% overall). The phage type 13a strain was less often isolated from fecal samples at 2 wk post-inoculation than were the phage type 4 strains, but no significant differences between strains were observed in the incidence of egg contamination. Most freshly laid contaminated eggs contained fewer than 1 S. enteritidis cell/ml of egg yolk or albumen, and no sample contained more than 67 S. enteritidis cells/ml.

Colonization of Specific Regions of the Reproductive Tract and Deposition at Different Locations Inside Eggs Laid by Hens Infected with Salmonella Enteritidis or Salmonella Heidelberg

Abstract Internal contamination of eggs by Salmonella Enteritidis has been a significant source of human illness for several decades and is the focus of a recently proposed U.S. Food and Drug Administration regulatory plan. Salmonella Heidelberg has also been identified as an egg-transmitted human pathogen. The deposition of Salmonella strains inside eggs is apparently a consequence of reproductive tissue colonization in infected laying hens, but the relationship between colonization of specific regions of the reproductive tract and deposition in different locations within eggs is not well documented. In the present study, groups of laying hens were experimentally infected with large oral doses of Salmonella Heidelberg, Salmonella Enteritidis phage type 13a, or Salmonella Enteritidis phage type 14b. For all of these isolates, the overall frequency of ovarian colonization (34.0%) was significantly higher than the frequency of recovery from either the upper (22.9%) or lower (18.1%) regions of the oviduct. No significant differences were observed between the frequencies of Salmonella isolation from egg yolk and albumen (4.0% and 3.3%, respectively). Some significant differences between Salmonella isolates were observed in the frequency of recovery from eggs, but not in the frequency or patterns of recovery from reproductive organs. Accordingly, although the ability of these Salmonella isolates to colonize different regions of the reproductive tract in laying hens was reflected in deposition in both yolk and albumen, there was no indication that any specific affinity of individual isolates for particular regions of this tract produced distinctive patterns of deposition in eggs.

Microbiological and Histopathological Effects of an Induced-Molt Fasting Procedure on a Salmonella enteritidis Infection in Chickens

A study was undertaken to determine if a 2-week feed-removal protocol, as is used by industry to induce a molt in aging hens, would affect the course of a Salmonella enteritidis infection. White leghorn hens aged 69-84 weeks were deprived of feed to induce a molt, and on day 4 of the fast, the birds were orally infected with 5 x 10(6) S. enteritidis. S. enteritidis organisms were enumerated in the spleen on day 6 and from the alimentary tract on days 7, 14, 21, 28, and 35. Little difference was detected in numbers of S. enteritidis from spleens of molted and unmolted hens. Significantly more molted hens shed detectable intestinal S. enteritidis than unmolted hens on day 14 (one of two trials) and day 21 (one of two trials). Intestinal levels of S. enteritidis were increased 100- to 1000-fold in the molted birds on day 7 (one of two trials) and day 14 (two of two trials), and many of the hens exhibited bloody alimentary secretions. Histological examination of the intestinal tract of S. enteritidis-infected molted hens showed increased inflammation in the epithelium and lamina propria of colons and ceca, compared with unmolted infected hens.

Colonization of Reproductive Organs and Internal Contamination of Eggs After Experimental Infection of Laying Hens with Salmonella heidelberg and Salmonella enteritidis

Internal contamination of eggs laid by hens infected with Salmonella enteritidis has been a prominent international public health issue since the mid-1980s. Considerable resources have been committed to detecting and controlling S. enteritidis infections in commercial laying flocks. Recently, the Centers for Disease Control and Prevention also reported a significant association between eggs or egg-containing foods and S. heidelberg infections in humans. The present study sought to determine whether several S. heidelberg isolates obtained from egg-associated human disease outbreaks were able to colonize reproductive tissues and be deposited inside eggs laid by experimentally infected hens in a manner similar to the previously documented behavior of S. enteritidis. In two trials, groups of laying hens were orally inoculated with large doses of four S. heidelberg strains and an S. enteritidis strain that consistently caused egg contamination in previous studies. All five Salmonella strains (of both serotypes) colonized the intestinal tracts and invaded the livers, spleens, ovaries, and oviducts of inoculated hens, with no significant differences observed between the strains for any of these parameters. All four S. heidelberg strains were recovered from the interior liquid contents of eggs laid by infected hens, although at lower frequencies (between 1.1% and 4.5%) than the S. enteritidis strain (7.0%).

Isolation of Salmonella enterica Serovar Enteritidis from Houseflies (Musca domestica) Found in Rooms Containing Salmonella Serovar Enteritidis-Challenged Hens

ABSTRACT Houseflies (Musca domestica) released into rooms containing hens challenged with Salmonella enterica serovar Enteritidis (Salmonella serovar Enteritidis) rapidly became contaminated with Salmonella serovar Enteritidis. Forty to 50% of the flies were contaminated at 48 h, and the percentage increased to 50 to 70% at 4 and 7 days postexposure and then decreased to 30% at day 15. Initial attempts at recovering surface organisms for culture using an aqueous rinse were largely unsuccessful, while cultures of internal contents readily recovered Salmonella serovar Enteritidis. However, when 0.5% detergent was incorporated into the rinse, high recovery levels of bacteria were observed from both external and internal culture regimens, indicating equal distribution of the organism on and in the fly and a tighter interaction of the organism with the host than previously thought. Salmonella serovar Enteritidis was isolated routinely from the fly gut, on rare occasions from the crop, and never from the salivary gland. Feeding contaminated flies to hens resulted in gut colonization of a third of the birds, but release of contaminated flies in a room containing previously unchallenged hens failed to result in colonization of any of the subject birds. These results indicate that flies exposed to an environment containing Salmonella serovar Enteritidis can become colonized with the organism and might serve as a source for transmission of Salmonella serovar Enteritidis within a flock situation.

Evaluation of the Efficacy of an Oil-Emulsion Bacterin for Protecting Chickens Against Salmonella enteritidis

To assess the potential protective efficacy of a Salmonella enteritidis bacterin, an acetone-killed oil-emulsion vaccine was prepared from a phage type 13a S. enteritidis strain and administered subcutaneously to hens in two experiments. Hens were housed individually, and every other hen was vaccinated (at 23 weeks of age in one experiment and at 45 weeks in the other). A second (booster) bacterin injection was administered 6 weeks later in both experiments. Three weeks after the second vaccination, all hens were challenged with an oral dose of approximately 10(9) cells of a heterologous (phage type 14b) S. enteritidis strain. In both trials, S. enteritidis was isolated from fewer internal organs (spleens, ovaries, and oviducts) and pools of egg contents from vaccinated hens than from unvaccinated control hens. Vaccination did not, however, affect the percentage of hens that shed S. enteritidis in feces in either experiment.

Microbiological analysis of the early Salmonella enteritidis infection in molted and unmolted hens

A study was conducted in which the early kinetics (4 hr to 96 hr) of an infection by Salmonella enteritidis in older white leghorn hens was examined, and a molt was induced through withholding feed to determine its effect on the progression of this infection. Molted and unmolted hens were orally infected with 5-10 x 10(6) S. enteritidis on day 4 of the feed removal. At 4, 24, 48, 72, and 96 hr postinfection, liver, spleen, ileum, colon, cecum, and feces were removed from six hens per group and sampled for the presence of the challenge organism. By 24 hr postinfection, S. enteritidis was most prevalent in the cecum and feces of unmolted hens, and this prevalence continued throughout the experimental period. In molted hens, however, S. enteritidis could be detected in a high percentage (90-100%) of colon, cecum, and feces samples at 24 to 96 hr postinfection and in 67% or more of ileum samples at 48 to 96 hr postinfection, indicating a much wider distribution of the S. enteritidis along the intestinal tract than in unmolted hens. The numbers of S. enteritidis recovered from these alimentary samples were also significantly higher in molted than unmolted hens. S. enteritidis could not be detected in livers or spleens of either treatment group at 4 or 24 hr postinfection. At 48, 72, and 96 hr postinfection, 50% or more of the livers and spleens in both the molted and unmolted hens were positive for the challenge organism, but significantly more S. enteritidis was recovered from the organs of the molted hens at these three sampling times.(ABSTRACT TRUNCATED AT 250 WORDS)