Co1 plasmids contribute to the fitness of Salmonella Heidelberg in poultry litter

Authors: OLADEINDE, ADELUMOLA - Orise Fellow; Cook, Kimberly - Kim; ORLEK, ALEX - University Of Oxford; RITZ, CASEY - University Of Georgia; Plumblee Lawrence, Jodie; Cox Jr, Nelson; ZOCK, GREGORY - University Of Georgia; HERRINGTON, KYLER - University Of Georgia; Hall, Mary

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Salmonella enterica subsp. enterica serovar Heidelberg (S. Heidelberg) is a clinically-important serovar, linked to food-borne illness, and commonly isolated from poultry. Investigations of a large, multistate outbreak in the USA in 2011 identified poultry litter (PL) as an important extra-intestinal environment that may have selected for specific S. Heidelberg strains. In this study, we investigated the role of PL on the fitness of two S. Heidelberg strains (SH-2813 and SH-116) recovered from chicken carcass during routine US Department of Agriculture monitoring in 2013. The strains are closely related at the chromosome level, differing by only 69 single-nucleotide variants (SNVs); both harbor an IncX1 plasmid (38kb). More importantly, strain SH-116 carries 3 col plasmids including a colpVC (2kb) and two colE-like plasmids (4 and 6kb). We performed a series of controlled laboratory experiments to assess the evolution of these strains in PL that was used to raise 2 flocks of broiler chickens. The diversity of 86 strains recovered after 0, 1, 7 and 14 days of evolution in PL was determined using whole-genome sequencing (WGS). We used plasmid-specific loci for typing of acquired plasmids and quantitative and reverse-transcription PCR to determine their copy numbers and expressed transcripts. We also performed a disk diffusion susceptibility test for selected aminoglycosides and fosfomycin. The population of SH-2813 in PL decreased by 4-logs after 1 day and increased by 1.5-logs after 7 days, with a final population of log 2.5 CFU g-1 at day 14. This rebound in population after 7 days, coincided with the acquisition of 3 col plasmids in all SH-2813 strains recovered at days 7 and 14 (n=27). For SH-116, we observed a gradual decline in population and the final population was below limit of quantification. The IncX1 and colE-like plasmids belonged to MOBQ and MOBP families respectively. They were determined to be low copy number plasmids (1 –12 copies/cell) and were maintained at a ratio of 1 copy of MOBQ to 2 -12 copies of MOBP per cell. The 6kb MOBp plasmids carry 2 accessory proteins with sequences similar to a type IV toxin-antitoxin and a fragment of aminoglycoside 6-N-acetyltransferase (e-value <0.001). The colpVC is a high copy plasmid (18 – 190 /cell) and encodes only a replication protein and a hypothetical protein. The evolved SH-2813 isolates exhibited a significant decrease in their zone of inhibition to tobramycin, gentamicin, neomycin, kanamycin, and fosfomycin. These findings suggest that col plasmids may increase S. Heidelberg fitness in PL.