Otto L.T. Lam

Microbial chemical signaling: a current perspective

Communication among microorganisms is mediated through quorum sensing. The latter is defined as cell-density linked, coordinated gene expression in microbial populations as a response to threshold signal concentrations followed by induction of a synchronized population response. This phenomenon is used by a variety of microbes to optimize their survival in a constantly challenging, dynamic milieu, by correlating individual cellular functions to community-based requirements. The synthesis, secretion, and perception of quorum-sensing molecules and their target response play a pivotal role in quorum sensing and are tightly controlled by complex, multilayered and interconnected signal transduction pathways that regulate diverse cellular functions. Quorum sensing exemplifies interactive social behavior innate to the microbial world that controls features such as, virulence, biofilm maturation, antibiotic resistance, swarming motility, and conjugal plasmid transfer. Over the past two decades, studies have been performed to rationalize bacterial cell-to-cell communication mediated by structurally and functionally diverse small molecules. This review describes the theoretical aspects of cellular and quorum-sensing mechanisms that affect microbial physiology and pathobiology.

Bacterial lipopolysaccharides variably modulate in vitro biofilm formation of Candida species.

The objective of this study was to evaluate the effect of the bacterial endotoxin LPS on Candida biofilm formation in vitro. The effect of the LPS of Pseudomonas aeruginosa, Klebsiella pneumoniae, Serratia marcescens and Salmonella typhimurium on six different species of Candida, comprising Candida albicans ATCC 90028, Candida glabrata ATCC 90030, Candida krusei ATCC 6258, Candida tropicalis ATCC 13803, Candida parapsilosis ATCC 22019 and Candida dubliniensis MYA 646, was studied using a standard biofilm assay. The metabolic activity of in vitro Candida biofilms treated with LPS at 90 min, 24 h and 48 h was quantified by XTT reduction assay. Viable biofilm-forming cells were qualitatively analysed using confocal laser scanning microscopy (CLSM), while scanning electron microscopy (SEM) was employed to visualize the biofilm structure. Initially, adhesion of C. albicans was significantly stimulated by Pseudomonas and Klebsiella LPS. A significant inhibition of Candida adhesion was noted for the following combinations: C. glabrata with Pseudomonas LPS, C. tropicalis with Serratia LPS, and C. glabrata, C. parapsilosis or C. dubliniensis with Salmonella LPS (P<0.05). After 24 h of incubation, a significant stimulation of initial colonization was noted for the following combinations: C. albicans/C. glabrata with Klebsiella LPS, C. glabrata/C. tropicalis/C. krusei with Salmonella LPS. In contrast, a significant inhibition of biofilm formation was observed in C. glabrata/C. dubliniensis/C. krusei with Pseudomonas LPS, C. krusei with Serratia LPS, C. dubliniensis with Klebsiella LPS and C. parapsilosis/C. dubliniensis /C. krusei with Salmonella LPS (P<0.05). On further incubation for 48 h, a significant enhancement of biofilm maturation was noted for the following combinations: C. glabrata/C. tropicalis with Serratia LPS, C. dubliniensis with Klebsiella LPS and C. glabrata with Salmonella LPS, and a significant retardation was noted for C. parapsilosis/C. dubliniensis/C. krusei with Pseudomonas LPS, C. tropicalis with Serratia LPS, C. glabrata/C. parapsilosis/C. dubliniensis with Klebsiella LPS and C. dubliniensis with Salmonella LPS (P<0.05). These findings were confirmed by SEM and CLSM analyses. In general, the inhibition of the biofilm development of LPS-treated Candida spp. was accompanied by a scanty architecture with a reduced numbers of cells compared with the profuse and densely colonized control biofilms. These data are indicative that bacterial LPSs modulate in vitro Candida biofilm formation in a species-specific and time-dependent manner. The clinical and the biological relevance of these findings have yet to be explored.

A systematic review of the effectiveness of oral health promotion activities among patients with cardiovascular disease

AIMS This study aimed to review the effectiveness of oral health promotion activities conducted among patients with cardiovascular disease. METHODS AND RESULTS Three electronic databases were searched for effective papers using standardized search methods, and key findings of effective studies were summarized. The initial search yielded 3101 papers but only 8 studies met the criteria for this review: 3 were randomized controlled studies, 3 were pre-/post group interventions, 1 was a randomized split-mouth study, and 1 was a quasi-experimental study. Studies retrieved concerned oral health promotion activities in patients with coronary heart disease, hypertension, heart transplantation, and stroke. Interventions comprised periodontal treatment performed by dental personnel, and oral hygiene interventions provided by nursing home care assistants. Outcomes included improvements in periodontal health, and modifications of systemic inflammatory markers. No studies, however, evaluated the effects of oral health promotion interventions on oral microflora. CONCLUSION There are limited studies on the efficacy of oral health promotion activities in patients with cardiovascular disease, particularly stroke patients. Oral health promotion activities appear to produce improvements in periodontal health, and also result in changes to systemic markers of inflammation and endothelial function (at least) in the short term. Whether these effects can ultimately lower the risk of secondary cardiovascular events has not yet been determined.

A systematic review and meta-analysis of clinical, microbiological, and behavioural aspects of oral health among patients with stroke.

OBJECTIVE The objective of this study was to review clinical, microbiological, and immunological aspects of oral health, as well as oral health related behaviours among patients following stroke. DATA SOURCES A structured search strategy was applied to three electronic databases to identify relevant papers. STUDY SELECTION The initial search yielded 19,927 papers, 60 potentially relevant studies (Kappa: 0.974) and 23 relevant papers (Kappa: 0.965) in accordance with the inclusion criteria. Outcomes regarding tooth condition, periodontal condition, oral hygiene status, and dental attendance were pooled for seven meta-analyses. Narrative summaries were provided for those outcomes which could not be pooled for meta-analysis. RESULTS The standardized differences in mean values of the parameters (fixed effect, random effect model) for patients with stroke compared to control groups were: number of teeth (-0.325, -0.271), DMFT (0.246, 0.246), oral hygiene status - plaque index (0.305, 0.356) and gingival index (0.716, 0.653), periodontal health status - clinical attachment loss (0.437, 0.490) and probing depth (0.470, 0.579). In addition, a lower chance of dental attendance was observed among patients with stroke (odds ratio: 0.493, 0.480). For those outcomes which could not be pooled for meta-analysis, it was not possible to draw any qualitative conclusion due to the equivocal results of these studies. CONCLUSIONS There is an increasing interest in oral health of patients with stroke. Patients with stroke had a poorer clinical oral health status across a range of parameters (tooth loss, dental caries experience, and periodontal status). Coupled with this, their dental attendance was less frequent. Further studies employing standardized assessments of oral health/oral health behaviour can confirm these oral health disparities. CLINICAL SIGNIFICANCE With comprehensive literature search, this systematic review and meta-analysis indicated a poorer oral health status and less frequent dental attendance behaviour among patients with stroke.

Effect of oral hygiene interventions on opportunistic pathogens in patients after stroke

BACKGROUND Despite the role of the oral cavity as a reservoir of opportunistic pathogens for infection in patients following stroke, the evaluation of the effects of oral hygiene interventions has been largely neglected. METHODS This randomized clinical trial included 102 patients undergoing hospital-based rehabilitation for stroke. Patients were randomized to one of 3 groups: oral hygiene instruction (OHI) only; OHI and 0.2% chlorhexidine mouth rinse twice daily; or OHI, 0.2% chlorhexidine mouth rinse twice daily, and assisted brushing twice weekly. Oral samples were obtained at baseline and after 3 weeks for detection of Staphylococcus aureus, aerobic and facultatively anaerobic gram-negative bacilli, and yeasts. RESULTS Almost three-quarters (72.8%) of the patients harbored oral anaerobic gram-negative bacilli at baseline, and more than half had detectable S aureus (56.8%) and yeasts (59.3%). Percentage frequencies and viable counts of pathogens remained relatively stable during the course of the clinical trial, and no significant differences were observed among the 3 patient groups. CONCLUSIONS In our study cohort, there was no significant difference in the effectiveness of the 3 different oral hygiene interventions on the prevalence or viable counts of oral opportunistic pathogens.

Effectiveness of oral hygiene interventions against oral and oropharyngeal reservoirs of aerobic and facultatively anaerobic gram-negative bacilli.

BACKGROUND Aerobic and facultatively anaerobic gram-negative bacilli (AGNB) are opportunistic pathogens and continue to cause a large number of hospital-acquired infections. AGNB residing in the oral cavity and oropharynx have been linked to nosocomial pneumonia and septicemia. Although AGNB are not considered members of the normal oral and oropharyngeal flora, medically compromised patients have been demonstrated to be susceptible to AGNB colonization. METHODS A literature search was conducted to retrieve articles that evaluated the effectiveness of oral hygiene interventions in reducing the oral and oropharyngeal carriage of AGNB in medically compromised patients. RESULTS Few studies have documented the use of mechanical oral hygiene interventions alone against AGNB. Although a number of studies have employed oral hygiene interventions complemented by antiseptic agents such as chlorhexidine and povidone iodine, there appears to be a discrepancy between their in vitro and in vivo effectiveness. CONCLUSION With the recognition of the oral cavity and oropharynx as a reservoir of AGNB and the recent emergence of multidrug and pandrug resistance in hospital settings, there is a pressing need for additional high-quality randomized controlled trials to determine which oral hygiene interventions or combination of interventions are most effective in eliminating or reducing AGNB carriage.

PREdIctoRS of oRAL HEALtH-RELAtEd QuALIty of LIfE In PAtIEntS foLLoWInG StRoKE

Objectives: To explore the influence of socio-demographic and clinical oral health factors on oral health-related quality of life (OHRQoL) in patients after stroke, and to monitor OHRQoL outcomes following the provision of an in-hospital oral health intervention programme. Design: OHRQoL was measured before and after randomization and provision of oral health promotion interventions in a prospective clinical trial. Subjects: Eighty-one patients admitted to a stroke rehabilitation ward. Methods: OHRQoL was assessed using the Oral Health Impact Profile-14 (OHIP-14) and Oral Health Transition Scale upon admission and 3 weeks later following provision of an oral health promotion programme. Potential factors were examined for their association with OHRQoL outcomes. Results: Lack of a regular daily brushing habit was significantly associated with 6 of 8 transition scale items (p < 0.01) at baseline, while significant improvements in OHRQoL were observed over the course of the clinical trial for all patients as a whole (p < 0.05). Conclusion: OHRQoL is compromised following stroke and may be influenced by the lack of a regular daily brushing habit during hospitalization. The early re-establishment of an oral hygiene protocol is a priority in stroke rehabilitation wards in order to improve clinical oral health and OHRQoL.

Oral health promotion interventions on oral reservoirs of staphylococcus aureus: a systematic review

The oral cavity serves as a reservoir of Staphylococcus aureus for infection of the lower respiratory tract and cross-infection to other patients. This systematic review was designed to examine the effectiveness of oral health promotion interventions on this pathogen. The PubMed, ISI Web of Science, and Cochrane Library databases were searched for clinical trials assessing the effect of oral health promotion interventions on oral and oropharyngeal carriage of S. aureus. Oral health promotion interventions on oral reservoirs of S. aureus in both systemically healthy and medically compromised groups consisted of oral hygiene interventions only. There was a lack of evidence pertaining to the effectiveness of mechanical oral hygiene interventions against this pathogen. Chlorhexidine delivered in oral hygiene products such as mouthrinses, gels, and sprays appeared to have some utility against S. aureus, although some studies found equivocal effects. There was a dearth of studies investigating the efficacy of other chemical agents. Although many chemical agents contained in oral hygiene products have proven in vitro activity against S. aureus, their clinical effectiveness and potential role as adjuncts or alternative therapies to conventional treatment remain to be confirmed by further high-quality randomized controlled trials.

Oral health promotion interventions on oral yeast in hospitalised and medically compromised patients: a systematic review

Yeast are major aetiological agents of localised oral mucosal lesions, and are also leading causes of nosocomial bloodstream infections. The purpose of this systematic review was to examine the effectiveness of oral health promotion interventions on the prevalence and incidence of these opportunistic oral pathogens in hospitalised and medically compromised patients. The PubMed, ISI Web of Science and Cochrane Library databases were searched for clinical trials assessing the effect of oral health promotion interventions on oral yeast. Chlorhexidine delivered in a variety of oral hygiene products appeared to have some effect on oral yeast, although some studies found equivocal effects. Although a wide array of other compounds have also been investigated, their clinical effectiveness remains to be substantiated. Likewise, the utility of mechanical oral hygiene interventions and other oral health promotion measures such as topical application of salivary substitute, remains unsettled. Although many chemical agents contained in oral hygiene products have proven in vitro activity against oral yeast, their clinical effectiveness and potential role as adjuncts or alternative therapies to conventional treatment remains to be confirmed by further high‐quality randomised controlled trials. This is pertinent, given the recent emergence of yeast resistance to conventional antifungal agents.

A new elusive otodontid shark (Lamniformes: Otodontidae) from the lower Miocene, and comments on the taxonomy of otodontid genera, including the ‘megatoothed’ clade

Abstract We describe a new large otodontid lamniform shark, Megalolamna paradoxodon gen. nov. et sp. nov., chronostratigraphically restricted to the early Miocene (Aquitanian–Burdigalian). This new species is based on isolated teeth found from five globally distributed localities: the Jewett Sand in southern California, USA; the Pungo River Formation of North Carolina, USA; the Chilcatay Formation of Peru; the Oi Formation in Mie Prefecture, Japan; and the O’oshimojo Formation in Nagano Prefecture, Japan. Extrapolations based on available published data on modern macrophagous lamniforms suggest that the largest specimen of M. paradoxodon gen. nov. et sp. nov. possibly came from an individual that measured at least 3.7 m in total length. All specimens came from deposits in the mid-latitudinal zones representing shallow-water, shelf-type, coastal environments. Its dentition likely exhibited monognathic heterodonty suited for capturing and cutting relatively large prey (e.g. medium-sized fishes). We recommend the genus Otodus to include sharks of the ‘megatoothed’ (e.g. megalodon) lineage in order to avoid Otodus paraphyly. We also propose the following phylogenetic hypothesis: [Kenolamna + [Cretalamna + [Megalolamna + Otodus]]]. ZooBank LSID for the genus Megalolamna is: urn: lsid:zoobank.org:act:B4791DEF-4D96-4FEB-9B7B-0EF816B96079 ZooBank LSID for the species Megalolamna paradoxodon is: urn:lsid:zoobank.org:act:7D3D7442-53C6-43A2-9E8D-6339729565B6