Methods: MiSeq NextGen DNA sequencing of the ampicillin-resistant P. shigelloides type strain following DNA extraction and digestion yielded 655,994 reads. Due to the lack of an annotated reference strain, we identified contigs of homology from two P. shigelloides reference genomes. Concurrently, we compiled known ampicillin resistance (beta-lactamase) genes from three genetically similar human pathogens Escherichia coli, Aeromonas hydrophila, and Vibrio cholera and systematically compared the sequences to P. shigelloides contigs using the publically available software, nucleotide BLAST (Basic Local Alignment Search Tool; NCBI). Knowing that P. shigelloides are aquatic, we also compared the contigs to beta-lactamase genes of aquatic Enterobacteriaceae family species Dickeya, Erwinia, Edwardsiella, Cronobacter, Pantoea and Morganella.
Results: Thirty-five homologous beta-lactamase sequences from ten bacterial species did not show significant regions of overlap with 53 P. shigelloides type strain DNA contigs that had significant homology to our type strain reads.
Conclusion: Our results could signify that the ampicillin resistance mechanism(s) for P. shigelloides may be novel, although investigation of penicillin binding protein modifications is also required. Elucidation of the mechanism(s) of ampicillin resistance by this pathogen would allow for more targeted therapies for these infections as well as shed light into antibiotic resistance mechanisms of pathogens.