Submitted to: Analytical and Bioanalytical Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/8/2008
Publication Date: 5/1/2008
Citation: Irwin, P.L., Nguyen, L., Chen, C., Paoli, G. 2008. Binding of Nontarget Organisms to Anti-Salmonella and Anti-E. coli O157 Immunomagnetic Beads: Most Probable Composition of Background Eubacteria. Analytical and Bioanalytical Chemistry. 391:525-536. Interpretive Summary: The contamination of foods with pathogenic bacteria (e.g., Salmonella or E. coli O157:H7) may lead to substantial food poisoning epidemics. In order to sensitively detect food poisoning bacteria certain isolation methods, such as the well-known immunomagnetic bead (IMB) technique for separating and concentrating these bacteria, have been developed. Unfortunately, the level of pathogenic bacteria in foods is very low relative to the concentration of benign bacteria. Thus, IMB methods for extracting pathogenic bacteria from foods also capture some of the good bacteria thereby limiting the functionality of these methods. In this report we present the most probably occurring nontarget organisms in several foods which bind nonspecifically to commercial IMBs. This information is useful to microbiologists in the detection of pathogenic bacteria from foods using IMBs protocols.
Technical Abstract: We present herein the composition of bacterial communities occurring in ground chicken and the changes which arise in these populations based upon non-selective partitioning by commercially-available Dynal anti-Salmonella and anti-E. coli O157 immunomagnetic beads (IMB). In a trial survey of various food items (ground chicken, salad bar lettuce, ground beef, and fresh shrimp) we found that ground chicken possessed a bacterial population which adhered best to commercial IMBs. For this reason all detailed population evaluations were based upon results from ground chicken purchased from a local supermarket at 4 different harvests over a period of one year. Three random samplings, each of ca. 25 grams, were made at each “harvest”. Our enumeration and colony selection protocol was based upon a 6×6 drop plate method using a dilution which produced ca. 4-10 colonies per drop. DNA was extracted from each colony and the composition of Eubacteria in each of these harvests was determined by sequence-based identification of 16S rDNA amplicons. The Gram positive bacteria Brochothrix thermosphacta and Carnobacterium maltaromticum were be the most commonly found organism in both the total chicken wash (PBS) and in the IMB-bound (PBS-washed) fraction. The remaining background organisms (Gram negative) which also adhered to varying degrees to commercial IMBs were: Pseudomonas oleovorans, Acinetobacter lwoffi, Serratia antarcticum or S. proteamaculans, and Rahnella. We found that most of these background organisms grew well at 5 degree C with doubling times ranging from ca. 5-19 hours and several did not survive at 37 deg (D value of 3-7 hours). A large number of the organisms were also cladistically evaluated based on rDNA basepair disparities: all Brochothrices were monophyletic; 12 different Pseudomonads; 8 Carnobacteria; 7 Acinetobacteres; 4 Serratiae; 2 Rahnellae.