Rapid Bacterial Recognition over a Wide pH Range by Boronic Acid-Based Ditopic Dendrimer Probes for Gram-Positive Bacteria

Abstract

We have developed a convenient and selective method for the detection of Gram-positive bacteria using a ditopic poly(amidoamine) (PAMAM) dendrimer probe. The dendrimer that was modified with dipicolylamine (dpa) and phenylboronic acid groups showed selectivity toward Staphylococcus aureus. The ditopic dendrimer system had higher sensitivity and better pH tolerance than the monotopic PAMAM dendrimer probe. We also investigated the mechanisms of various ditopic PAMAM dendrimer probes and found that the selectivity toward Gram-positive bacteria was dependent on a variety of interactions. Supramolecular interactions, such as electrostatic interaction and hydrophobic interaction, per se, did not contribute to the bacterial recognition ability, nor did they improve the selectivity of the ditopic dendrimer system. In contrast, the ditopic PAMAM dendrimer probe that had a phosphate-sensing dpa group and formed a chelate with metal ions showed improved selectivity toward S. aureus. The results suggested that the targeted ditopic PAMAM dendrimer probe showed selectivity toward Gram-positive bacteria. This study is expected to contribute to the elucidation of the interaction between synthetic molecules and bacterial surface. Moreover, our novel method showed potential for the rapid and species-specific recognition of various bacteria.

Boronic Acid-Based Dendrimers with Various Surface Properties for Bacterial Recognition with Adjustable Selectivity

“…Previous studies have shown that S. aureus grows at pH 4.0− 9.8 28 and E. coli thrives at pH 4.5−9.0. 29 Figure 2A shows that whereas B-PAMAM(+), which is based on the PAMAM(G4) dendrimer, selectively recognized Gram-positive bacteria (including S. aureus IAM1011), producing aggregates and decreasing turbidity, 21,23 B-PAMAM(−), which is based on the PAMAM(G3.5) dendrimer, did not cause any changes in both E. coli K12W3110 and S. aureus IAM1011 suspensions. The results indicate that negatively charged dendrimer probes fail to recognize bacteria because of the repulsive force produced between the probes and bacteria having a negatively charged surface.…”

“…35 We had previously reported that boronic acid has the potential to form bonds with the cis-diols of saccharides on the surface of both Gram-positive and Gram-negative bacteria. 23 We considered that the binding force of boronic acid groups was stronger for Gram-positive bacteria than for Gramnegative bacteria. However, as indicated in Figures 2 and 3, boronic acid itself could not recognize bacteria, and the presence of electrostatic interaction was crucial for the recognition.…”

“…The compound was the same as that previously reported. 23 Synthesis of B-PAMAM(−). Synthetic compound 2 (15.5 mg, 8.0 equiv, 75 μmol), PAMAM(G3.5) dendrimer (1.5 mL, 1.0 equiv, 9.4 μmol), and DMT-MM (104 mg, 40 equiv, 376 μmol) were dissolved in methanol (3.5 mL) and the reaction mixture was stirred at room temperature for 2 days.…”

“…The recognition was observed as an aggregation of complexes between bacteria and probes, which resulted in the decrease in turbidity. We also investigated the supramolecular interactions of B-PAMAM and found that PAMAM’s supramolecular interaction alone was unable to recognize Gram-positive bacteria but it enhanced the recognition of boronic acids. , However, the effect of the PAMAM dendrimer core and the mechanism of selectivity toward Gram-positive bacteria were not studied.…”

“…B-PAMAM(−) has PAMAM(G3.5)-type carboxylic acid and phenylboronic acid terminus. Pseudozwitterionic NH 2 -B-PAMAM has all types of terminal substituents (PAMAM(G3.5)-type carboxylic acid, PAMAM(G4)-type amine, and phenylboronic acid).Previously reported B-PAMAM(+) had PAMAM(G4)-type amine and phenylboronic acid terminus 23.…”