The current review focuses on the studies conducted on the colonization of microorganisms on orthodontic ligatures during orthodontic treatment. The fixed orthodontic appliances have long been associated with an increase in plaque accumulation, bacterial colonization, and resultant enamel decalcification. Voluminous research has been carried out on the microbial colonization of even newer orthodontic materials such as elastomeric ligatures with an evidence of variably increased microbial counts during orthodontic treatment. However, conclusive material-based data for minimal microbial colonization to establish acceptance criteria for the use of elastomeric ligatures are hardly available. Thus, there is a need for further studies with dual emphasis on exploring microbial associations based on surface chemistries of different elastomers and their requisite modifications for hampering microbial biofilms to evolve efficacious oral health friendly orthodontic ligatures.

The absence of PtsN, the terminal phosphoacceptor of the phosphotransferase system comprising PtsP-PtsO-PtsN, in Escherichia coli confers a potassium-sensitive ( ) of 200 to 400 mM that is thought to be required for optimal functioning of several metabolic processes (reviewed in references 1 and 2). In addition, K ϩ is a major determinant in the maintenance of cell turgor, so that an increase in osmolarity of the medium is associated with increased [K ϩ ] i (3-6). K ϩ has also been proposed to act as a second messenger (2, 7).The maintenance of cytoplasmic K ϩ pools in E. coli is achieved through the balance of activities of K ϩ uptake systems Kdp, Trk, and Kup (formerly known as TrkD) on the one hand and of an as yet unidentified K ϩ efflux system or systems on the other (1, 2). The well-studied K ϩ efflux systems KefG/B and KefF/C are known to act as K ϩ /H ϩ antiporters, with K ϩ efflux and concomitant H ϩ influx leading to cytoplasmic acidification, serving to mitigate the detrimental effects of endogenous or exogenous electrophiles (reviewed in reference 8). A residual K ϩ transport activity, TrkF, present in a kdp kup trk triple K ϩ transporter-defective mutant is thought to represent a mode of K ϩ uptake occurring through systems that do not normally transport K ϩ (9), and an as yet uncharacterized turgor-activated efflux system is also believed to exist (10).The Kdp transporter, encoded by genes of the kdpFABC operon, is a high-affinity K ϩ uptake system (11, 12) that is transcriptionally induced when the external K ϩ concentration ([K ϩ ] e ) becomes limiting for growth (13,14). More recent studies have shown that expression and/or activity of the Kdp transporter is also inhibited by [K ϩ ] e s above 5 mM (15, 16). The Trk and Kup systems, in contrast, are low-affinity K ϩ uptake systems that are constitutively expressed (1, 2). Of these systems, Kup is a standalone K ϩ transporter, whereas the Trk system is a multicomponent system, and a null mutation in trkA, coding for the regulatory subunit, disables the Trk system (2). The presence of multiple transport systems for K ϩ allow, within the limits of its osmoregulatory capacity, robust growth of E. coli in media with a wide range of [K ϩ ] e s. In E. coli, components of the phosphotransferase system (PTS) mediate uptake of carbohydrates, wherein transport of the incoming sugar is coupled to its phosphorylation (reviewed in references 17, 18, 19, and 20). In each of these systems, a phosphate moiety is transferred from phosphoenolpyruvate (PEP) to the particular sugar via a multiprotein phosphorelay mechanism. E. coli also possesses a PTS comprising PtsP-PtsO-PtsN, with a PEP-dependent phosphorelay operating in the same sequence (21-23). However, the phosphorylation substrate of PtsN is unknown. Given that ptsN and ptsO are member genes of the rpoN operon (21), PtsP, PtsO, and PtsN have also been referred to as EI Ntr , Npr, and EIIA Ntr , respectively. A recent study has shown that the phosphorylation state of PtsN can be modulated, depending u...

BackgroundBesides, other factors, the choice of materials used as orthodontic ligatures could be one of the many tools to counter the effects of microbial adhesion, that culminates into dental ailments. Therefore, we assessed bacterial adhesion on elastomeric ligatures with special reference to coloured elastomeric rings during orthodontic treatment.Material and MethodsA split mouth study, involving 240 samples of different elastomeric ligatures from forty orthodontic patients possessing good oral hygiene was carried out. The archwire was ligated to the brackets on both arches with elastomeric rings (superslick, clear transparent , blue and pink) at predetermined quadrants. After six weeks, ligatures from second premolars were removed and processed for bacterial enumeration using standard techniques. Bacterial counts were also determined for stimulated saliva samples taken at 0 and 6 weeks.ResultsA statistically significant difference in bacterial counts was obtained amongst different elastomeric modules used. Maximum bacterial counts were found on conventional pigmented elastomeric modules, followed by Superslick module and clear module. More number of bacteria associated with the conventional pink as compared to the conventional blue pigmented modules, however it was not statistically significant. The three bacterial genera Streptococcus Staphylococcus and Aerobic Lactobacilli adhered to elastomeric modules in following predominant pattern i.e. Conventional pink>Conventional Blue>Superslick>Clear.ConclusionsThe studies evidenced colour and material dependent bacterial colonization on orthodontic modules and could be an indicator of bacterial biofilm forming potential based on surface chemistries and a clinically efficacious tool to redesign conventional and modified elastomeric rings as orthodontic ligation accessories. Key words:Bacterial colonization, biofilm, coloured elastomers, orthodontic ligatures.

High temperature requirement A (HtrA) are allosterically regulated enzymes wherein effector binding to the PDZ domain triggers proteolytic activity. Yet, it remains unclear if the inter-residue network governing allostery is conserved across HtrA enzymes. Here, we investigated and identified the interresidue interaction networks by molecular dynamics simulations on representative HtrA proteases, Escherichia coli DegS and Mycobacterium tuberculosis PepD, in effector-bound and free forms. This information was used to engineer mutations that could potentially perturb allostery and conformational sampling in a different homologue, M. tuberculosis HtrA. Mutations in HtrA perturbed allosteric regulation�a finding consistent with the hypothesis that the inter-residue interaction network is conserved across HtrA enzymes. Electron density from data collected on cryo-protected HtrA crystals revealed that mutations altered the topology of the active site. Ensemble models fitted into electron density calculated from room-temperature diffraction data showed that only a fraction of these models had a catalytically competent active site conformation alongside a functional oxyanion hole thus providing experimental evidence that these mutations influenced conformational sampling. Mutations at analogous positions in the catalytic domain of DegS perturbed the coupling between effector binding and proteolytic activity, thus confirming the role of these residues in the allosteric response. The finding that a perturbation in the conserved inter-residue network alters conformational sampling and the allosteric response suggests that an ensemble allosteric model best describes regulated proteolysis in HtrA enzymes.