In vivo trials. Phages 151, 25, and 10 were used at a lower
titer (9.0 log10 PFU ml1, trial 1) and a higher titer (11.0 log10
PFU ml1, trial 2) in separate in vivo trials to reduce the numbers
of Nalr S. enterica serotype Enteritidis P125109, Hadar 18, and
Typhimurium 4/74 bacteria colonizing the ceca of broiler chickens.
When the phages were administered at 9.0 log10 PFU, no
significant reductions in the cecal carriage of Salmonella in the
phage-treated broilers was recorded for any of the serotypes
tested over the 6-day duration of the trial. This was despite a
significant increase in the titers of phage 151 (5.2 1.63 log10
PFU g1 cecal content compared with controls) within 24 h of
phage administration (data not shown). The phages were rapidly
removed from the chicken intestine in the absence of Salmonella
hosts (group B) and were below the limit of detection after 48 h
(151) or 72 h (10, 25). In the second trial, the chickens were
sacrificed over a period of 3 days only, as the results from trial 1
indicated that any decrease in Salmonella numbers following
phage treatment should be apparent in this period (data not
shown). The results of this second trial are presented in Fig. 3.
The higher phage titer corresponded to a significant reduction in
the mean cecal colonization by S. enterica serotypes Enteritidis
P125109 and Typhimurium 4/74 after 24 h (1.53 2.38 and
3.48 1.88 log10 CFU g1 cecal content, respectively, compared
with the control groups [5.77 1.85 and 5.67 0.41 log10 CFU
g1 cecal content]). These reductions in cecal colonization were
significant for both S. enterica serotypes Enteritidis (P
0.0000001) and Typhimurium (P 0.000001) by a single-factor
ANOVA. No significant differences between control and phagetreated
groups were recorded for birds colonized with S. enterica
serotype Hadar 18 (5.77 0.45 and 5.34 0.34 log10 CFU g1
cecal content for phage-treated and control groups, respectively).