Objective—To investigate the effect of an Escherichia
coli that produced microcin 24 (Mcc24) on shedding
of Salmonella enterica serotype Typhimurium in swine
and evaluate evidence of in vivo activation of the
Mcc24-mediated, multiple-antibiotic resistance ( mar)
Animals—36 crossbred weaned pigs.
Procedure—24 pigs were allocated to 2 groups
(12 pigs/group). Pigs in 1 group received daily oral
administration of an Mcc24-producing E coli, whereas
the other group received a non–Mcc24-producing E
coli. All pigs were challenge exposed with Salmonella
Typhimuriumχ4232. A third group of 6 pigs received
Mcc24-producing E coli and was challenge exposed
with an Mcc24-sensitive, marA-deleted strain of
SalmonellaTyphimurium 4232. After challenge exposure,
fecal samples from all pigs were cultured to
detect shedding of Salmonella Typhimurium and
Salmonella Typhimurium isolates were screened for
resistance to ciprofloxacin. Fecal samples were collected
throughout the study, and tissue samples were
collected during necropsy.
Results—Differences in shedding of Salmonella
Typhimurium were not detected between groups
receiving Mcc24-producing or non–Mcc24-producing
E coli. No significant differences were found in quantitative
analysis between groups receiving Mcc24-producing and non–Mcc24-producing E coli. Evidence
of maractivation was not detected.
Conclusions and Clinical Relevance—Microcin-producing
E coli did not exert an effect on shedding of
Salmonella Typhimurium or maractivation in pigs. It may
be difficult or impractical to create the conditions
required for Mcc24 to be an effective part of a food safety
intervention to reduce shedding of Salmonella
Typhimurium. (Am J Vet Res 2004;65:1616–1620)
To evaluate the efficacy of tulathromycin for prevention of abortion in pregnant ewes when administered within 24 hours after experimental inoculation with Campylobacter jejuni.
20 pregnant ewes between 72 and 92 days of gestation.
All ewes were inoculated with a field strain of C jejuni (8.5 × 108 to 10.6 × 108 CFUs, IV). Eighteen hours later, ewes received either tulathromycin (1.1 mL/45 kg [2.4 mg/kg], SC; n = 10) or sterile saline (0.9% NaCl) solution (1.1 mL/45 kg, SC; sham; 10). Ewes were euthanized immediately after observation of vaginal bleeding, abortion, or completion of a 21-day observation period. Necropsy was performed on all ewes, and tissue specimens were obtained for bacterial culture and histologic examination.
1 sham-treated ewe and 1 tulathromycin-treated ewe developed signs of severe endotoxemia and were euthanized within 24 hours after C jejuni inoculation. Seven sham-treated and 2 tulathromycin-treated ewes developed vaginal bleeding or aborted and were euthanized between 4 and 21 days after C jejuni inoculation. The proportion of tulathromycin-treated ewes that developed vaginal bleeding or aborted during the 21 days after C jejuni inoculation (2/9) was significantly less than that for the sham-treated ewes (7/9).
CONCLUSIONS AND CLINICAL RELEVANCE
Results suggested that administration of tulathromycin to pregnant ewes following exposure to C jejuni was effective in decreasing the number of C jejuni–induced abortions. Because of concerns regarding the development of macrolide resistance among Campylobacter strains, prophylactic use of tulathromycin in sheep is not recommended.