J. Stan Bailey

Universal Preenrichment Broth for the Simultaneous Detection of Salmonella and Listeria in Foods

A medium and method for preenriching food products which allow the simultaneous recovery and detection of Salmonella and Listeria are described. To prevent the pH of the medium from rapidly dropping in the presence of extraneous microorganisms found in foods, this medium, universal preenrichment (UP) broth, is highly buffered and low in carbohydrates. The medium allows sublethally injured bacteria to resuscitate and multiply to sufficiently high numbers so that highly selective, secondary enrichment media can be employed to help select the specific bacteria in question from a mixed bacterial background culture. As few as 10 heat-injured Salmonella multiplied to at least 106/ml following a 24 h enrichment in UP, even in mixtures of high levels of known competitive microflora or from naturally occurring microflora found in chicken, hot dogs, or Brie cheese. As few as 10 heat-injured Listeria monocytogenes multiplied to at least 105/ml in these same experiments. From the UP broth, secondary selective preenrichment broths which favor the growth of Salmonella or Listeria can be inoculated, and subsequent protocols for the recovery of either Salmonella or Listeria can then be followed.

Mucosal competitive exclusion to reduce Salmonella in swine.

A mucosal competitive exclusion culture has been shown to reduce or eliminate Salmonella spp. in poultry. Using similar techniques, a mucosal competitive exclusion culture from swine (MCES) was produced from the cecum of a 6-week-old pig. Suckling pigs were inoculated with 5 ml of MCES by oral gavage within 6 h postfarrowing (PF) and again at 24 h PE All pigs were challenged with 10(3) CFU of Salmonella Choleraesuis at 48 h PF by intranasal instillation, including pigs from two sows that had not been given MCES. Clinical signs and rectal swabs were monitored daily, and pigs were allowed to suckle throughout the experiment. All pigs underwent necropsy on day 7 PF, and presence of Salmonella was determined in both qualitative (10 tissues) and quantitative (two tissues) samples. Clinical signs were inapparent in all pigs throughout the experiment. Recovery of Salmonella from rectal swabs was variable. However, 28% of the gut tissues were positive from the MCES-treated pigs versus 79% from the control pigs. A 2- to 5-log10 reduction of Salmonella in the cecal contents or ileocolic junction was observed in the MCES-treated pigs when compared with the controls. These data indicate that use of MCES may be a useful approach for control of Salmonella.

Rainfall and tillage effects on transport of fecal bacteria and sex hormones 17β-estradiol and testosterone from broiler litter applications to a Georgia Piedmont Ultisol

Poultry litter provides nutrients for crop and pasture production; however, it also contains fecal bacteria, sex hormones (17beta-estradiol and testosterone) and antibiotic residues that may contaminate surface waters. Our objective was to quantify transport of fecal bacteria, estradiol, testosterone and antibiotic residues from a Cecil sandy loam managed since 1991 under no-till (NT) and conventional tillage (CT) to which either poultry litter (PL) or conventional fertilizer (CF) was applied based on the nitrogen needs of corn (Zea mays L) in the Southern Piedmont of NE Georgia. Simulated rainfall was applied for 60 min to 2 by 3-m field plots at a constant rate in 2004 and variable rate in 2005. Runoff was continuously measured and subsamples taken for determining flow-weighted concentrations of fecal bacteria, hormones, and antibiotic residues. Neither Salmonella, nor Campylobacter, nor antimicrobial residues were detected in litter, soil, or runoff. Differences in soil concentrations of fecal bacteria before and after rainfall simulations were observed only for Escherichia coli in the constant rainfall intensity experiment. Differences in flow-weighted concentrations were observed only for testosterone in both constant and variable intensity rainfall experiments, and were greatest for treatments that received poultry litter. Total loads of E. coli and fecal enterococci, were largest for both tillage treatments receiving poultry litter for the variable rainfall intensity. Load of testosterone was greatest for no-till plots receiving poultry litter under variable rainfall intensity. Poultry litter application rates commensurate for corn appeared to enhance only soil concentrations of E. coli, and runoff concentrations of testosterone above background levels.

Colonization of broiler chicks by Salmonella typhimurium definitive phage type 104.

The prevalence of an antibiotic-resistant strain of Salmonella Typhimurium definitive phage type 104 (DT104) has increased dramatically in recent years resulting in increased morbidity and mortality in both animals and humans. Colonization and shedding of Salmonella Typhimurium DT104 was studied in broiler chickens in two trials. In trial 1, 180 day-of-hatch chicks (n = 60 per group, n = 30 per replicate) were challenged with 10(6) CFU DT104 (wild-type isolate from poultry) or were commingled with a seeder chick challenged with 10(6) CFU DT104. In trial 2, 360 day-of-hatch chicks (n = 120 per treatment, n = 30 per rep) were divided into three groups. Chicks in the susceptible group were commingled with two seeder chicks that were orally challenged with 10(7) CFU/bird of a pan-sensitive strain of Salmonella Typhimurium DT104. Chicks in the resistant group were commingled with two seeder chicks that were orally challenged with 10(7) CFU/bird DT104 used in trial 1. For both trials, a control group was not exposed to DT104, composite fecal samples were evaluated twice weekly for levels of Salmonella shedding and 20 chicks per group were necropsied weekly and their cecal contents were cultured. At hatch all groups were colonized with naturally occurring Salmonella Senftenberg and Salmonella Mbandaka (trial 1) or Salmonella Senftenberg and Salmonella Ohio (trial 2) prior to exposure to DT104. Throughout the study, the level of Salmonella spp. shedding in feces (trial 1 means 3.1, 2.9, and 3.0 log10 CFU per g feces for challenged, seeder, and control groups, respectively) or ceca (trial 2 means 2.9. 2.9. and 2.5 log10 CFU per g ceca for resistant, susceptible, and control groups, respectively) did not differ among groups. In trial 1, colonization of DT104 remained constant at higher levels in the challenged group (mean 87%, P < 0.01), increased over time in the seeder group (10 to 50%, P < 0.02) and was not recovered from the control chicks. Salmonella Mbandaka colonization remained steady within each group with challenge and seeder groups maintaining higher levels of colonization than the control group. Salmonella Senftenberg colonization levels tended to decline (P = .058) over time in the challenged group (20 to 0%) and significantly decreased (P < 0.01) over time for both the seeder (80 to 0%) and control chicks (85 to 10%). In trial 2, the percentage of chicks colonized with susceptible DT104 declined (r = 0.90, P < 0.05) over the course of the trial from 45 to 0%, while recovery of the resistant DT104 persisted at a mean percentage of 27%. DT104 was not recovered from the control chicks. Salmonella Ohio colonization levels tended to decline (r = 0.79, P > 0.05) over time in the control group (75 to 20%) and significantly decreased (P < 0.05) over time in both susceptible and resistant groups (40 to 10%, r = 0.82 and 55 to 5%, r = 0.85, respectively). Salmonella Senftenberg was recovered from the control group at low frequency throughout the trial and was not recovered from the other groups. For either trial, no apparent affect on morbidity or mortality was observed. Introduction of DT104 by commingling may induce colonization resulting in persistent high levels of shedding in flocks simultaneously with other Salmonella species.

Effects of Meat Type, Storage Time and Temperature on Various Physical, Chemical and Microbiological Characteristics of Ground Pork

Whole-hog sausage was prepared from hot- and cold-boned pork raw materials to determine the effects of meat type, storage temperature and length of storage on various processing and bacteriological characteristics. Samples were stored at -1 and 4°C for 0, 28 and 56 d. Various physical, chemical and microbiological properties of the sausage were evaluated. Thiobarbituric acid (TBA) values were not affected by meat type (pre or postrigor). Hunter-Color values varied significantly among the meat types and storage temperatures. Total bacterial counts varied significantly among the hot- and cold-boned pork sausage samples (day 0). Cold-boned sausage stored at -1°C had lower plate counts of the various treatments for days 28 and 56. Pseudomonas was the predominant organism found in hotand cold-boned sausage samples. Hot-boned sausage exhibited a more diverse bacterial population than did cold-boned sausage. More gram-positive organisms were found in hot-boned sausage samples. Cold-boned sausage had a lower total bacterial count at day 0 and maintained lower counts and therefore a longer shelf life throughout the study when held at -1°C.

Bacteriological Profiles of Human Milk from Individual Donors and Pooled Samples from a Commercial Milk Bank

The bacteriological profiles of human milk samples collected from individual donors under supervised conditions of collection were compared to pooled human milk samples obtained from a commercial human milk bank. Total aerobic counts and total coliform counts of individual donor samples were lower than those of pooled, banked human milk. All of the 200 isolates from ten individual samples were staphylococci with Staphylococcus epidermidis predominating (82%). Only 1% of the isolates was identified as Staphylococcus aureus . Forty-two percent of the 100 isolates from five pooled samples were staphylococci and all of these staphylococci were coagulase-negative. Three percent of the isolates from the pooled samples were Streptococcus faecalis . The remainder (55%) were gram-negative organisms. S. epidermidis was the microorganism that was isolated most frequently from either individual (9 of 10) or pooled (3 of 5) samples.