of Salmonella Bacteriophages from Swine Effluent
M. R. McLaughlin,* M. F. Balaa, J.
Sims, and R. King
United States Department of Agriculture, Agricultural Research
Service, Waste Management and
Forage Research Unit, Mississippi State, MS 39762.
Bacteriophages (phages) associated with Salmonella
were collected from nine swine manure lagoons in Mississippi.
Phages were isolated by an enrichment protocol or directly
from effluent. For enrichment, chloroform-treated samples
were filtered (0.22 m) and selectively
enriched by adding a cocktail of Salmonella strains
in trypticase soy broth. After overnight incubation at 35oC,
chloroform was added and samples stored at 5oC.
Enriched samples were tested by double agar layer (DAL) plaque
assay against individual Salmonella isolates. Phage
titers of 2.9 x108 to 2.1 x109 plaque
forming units (pfu) per mL were produced, but estimation of
phage titers in lagoons was not possible. For direct isolation,
effluent was clarified by centrifugation, filtered (0.22 m),
and used in DAL plaque assays to select single-plaque isolates
for 15 Salmonella strains. Plaque counts varied among
Salmonella strains and lagoons. The most sensitive
strain for direct phage recovery was ATCC 13311. Phage titers
estimated by direct isolation with ATCC 13311 ranged among
lagoons from 12 to 148 pfu per mL. In limited host range tests,
66 isolates recovered by the enrichment protocol produced
plaques only on Enteritidis and Typhimurium strains of Salmonella
and none produced plaques on lagoon isolates of Citrobacter,
Escherichia, Proteus, Providencia, or Serratia.
Electron microscopy (EM) showed purified enrichment isolates
had Podoviridae morphology (tailless 50- nm icosahedral
heads with tail spikes). Electron microscopy of clarified
concentrated effluent showed 5.5:1 tailless to tailed phages.
The isolated phages have potential as typing reagents, specific
indicators, and biocontrol agents of Salmonella.