Normal Oral Microflora Research Articles

The Role of Vitamin D3 Deficiency and Colonization of the Oral Mucosa by Candida Yeast-like Fungi in the Pathomechanism of Psoriasis

Psoriasis is a chronic inflammatory skin disease with complex pathogenesis and variable severity. Performed studies have indicated the impact of vitamin D3 deficiency on the pathogenesis of psoriasis and its severity. However, there is no clear evidence of the influence of the mucosal microbiome on the onset and progression of psoriasis. This review aims to present the current evidence on the role of vitamin D3 and colonization of the oral mucosa by Candida yeast-like fungi in the pathogenesis of psoriasis. Candida albicans is a common yeast that can colonize the skin and mucosal surfaces, particularly in individuals with weakened immune systems or compromised skin barriers. In psoriasis, the skin’s barrier function is disrupted, potentially making patients more susceptible to fungal infections such as Candida. Since patients with psoriasis are at increased risk of metabolic syndrome, they may experience the vicious circle effect in which chronic inflammation leads to obesity. Vitamin D3 deficiency is also associated with microbiological imbalance, which may promote excessive growth of Candida fungi. Under normal conditions, the intestinal and oral microflora support the immune system. Vitamin D3 deficiency, however, leads to disruption of this balance, which allows Candida to overgrow and develop infections.

Intermembrane rhomboid protease activity of Rothia mucilaginosa

Rothia mucilaginosa is a part of the normal oral microflora, which has been recognized as an endodontic pathogen and is also an emerging opportunistic pathogen in immune compromised hosts. In this study, we identified the rhomboid protease in R. mucilaginosa as a candidate virulence factor. A database search identified two rhomboid genes on the genome with open reading frames of 828 bp and 822 bp, respectively. The two genes are separated by 57 bp, suggesting that they constitute a bicistronic operon. Motifs conserved among rhomboid family proteins (HxxxN, GxSG, and GxxxG) were found in their deduced amino acid sequences. The two recombinant rhomboids and the rhomboid/liposome complexes (proteoliposomes) were prepared using a wheatgerm cell-free translation system, and their serine protease activities were assessed. The two rhomboids showed serine protease activity in the form of rhomboid/liposome complex, while the recombinant rhomboids alone showed little or no activity. On the supposition of host invasion, R. mucilaginosa was cultivated in medium with type I collagen, and the rhomboid mRNA levels were examined. Real-time reverse transcription polymerase chain reaction analysis revealed that the levels of the two rhomboid mRNAs increased slightly in culture with type I collagen, although the changes were not statistically significant. These results suggested that R. mucilaginosa possesses two active rhomboids with protease activity on the membrane, and the two rhomboids may be virulence factors involved in the response to host environmental conditions.

Actinomycotic osteomyelitis of the maxilla in a female patient: A rare case report with the review of the literature.

Actinomycotic osteomyelitis is a rare chronic suppurative, granulomatous, fibrosing saprophytic infection. It is an endogenous infection caused by the Actinomyces species, which are part of the normal oral microflora. There is a male predilection for this type of infection, with the male to female ratio of 4:1. Though the etiopathogenesis of the infection is unclear, it is mostly attributed to the disruption of the normal oral microflora and the invasion of the microorganism into deeper tissues through a break in the mucosal barrier due to damage from trauma, extraction or previous injury. The portal of entry can be through the pulpal, periodontal or mucosal route, causing the purulent and necrotic infection of soft tissue, bone, or both. The diagnosis is usually considered when there is a persistent infection without the presence of regional lymphadenopathy and is usually confirmed through the histopathological depiction of the bacterial colonies - 'ray fungus' - as obtaining the positive culture of the causative microorganisms is difficult and is reported to be effective in less than 50%. Patients with such infections are managed with surgical debridement, followed by antibiotic therapy for a longer time period. Recent advances have been emphasized for an early diagnosis and a better prognosis of the therapy. Therefore, this paper aimed to present a rare case of actinomycotic osteomyelitis of the maxilla in a 45-year-old female patient, and also to review the literature on this rare infection.

Evidence on the Use of Mouthwash for the Control of Supragingival Biofilm and Its Potential Adverse Effects.

Antimicrobial mouthwash improves supragingival biofilm control when used in conjunction with mechanical removal as part of an oral hygiene routine. Mouthwash is intended to suppress bacterial adhesion during biofilm formation processes and is not aimed at mature biofilms. The most common evidence-based effects of mouthwash on the subgingival biofilm include the inhibition of biofilm accumulation and its anti-gingivitis property, followed by its cariostatic activities. There has been no significant change in the strength of the evidence over the last decade. A strategy for biofilm control that relies on the elimination of bacteria may cause a variety of side effects. The exposure of mature oral biofilms to mouthwash is associated with several possible adverse reactions, such as the emergence of resistant strains, the effects of the residual structure, enhanced pathogenicity following retarded penetration, and ecological changes to the microbiota. These concerns require further elucidation. This review aims to reconfirm the intended effects of mouthwash on oral biofilm control by summarizing systematic reviews from the last decade and to discuss the limitations of mouthwash and potential adverse reactions to its use. In the future, the strategy for oral biofilm control may shift to reducing the biofilm by detaching it or modulating its quality, rather than eliminating it, to preserve the benefits of the normal resident oral microflora.

S2887 Rare Case of Capnocytophaga Causing Large Intra-Abdominal Abscess in a Cirrhotic

Introduction: Cirrhosis-associated immune dysfunction is a well-established syndrome placing affected patients at risk for severe sepsis. Thus, practitioners must remain vigilant in ruling out infectious complications in their cirrhotic population. Though most isolated pathogens are commonly seen, including E. coli, S. pneumoniae and Klebsiella, other rare species may be isolated. We present a rare case of intra-abdominal abscess secondary to Capnocytophaga in a cirrhotic patient. Case Description/Methods: A 56-year-old male with history of decompensated alcohol cirrhosis complicated by hepatic encephalopathy, spontaneous bacterial peritonitis and hepatic hydrothorax presented to the emergency room due to 3 days of increasing abdominal distension, constant burning abdominal pain, and fever of 101.4F. A CT abdomen and pelvis with IV contrast was notable for a 33.8 cm intraperitoneal abdominal abscess. Aspirate of this collection returned tan, opaque fluid. Fluid studies were notable for WBC 158,580 c/cmm, 69% segs and LD > 4500 unit/L. Fluid cultures were collected and grew Fusobacterium and Capnocytophaga. The patient did not report any recent animal exposures, abdominal procedures or dental work. After consultations with infectious disease and interventional radiology, a percutaneous drain was placed and the patient was started on oral Augmentin twice daily for several weeks. A repeat abscessogram approximately 1.5 months later showed complete resolution of the abscess and his drain was successfully removed. Discussion: There are presently six case reports of intra-abdominal infection secondary to capnocytophaga. Capnocytophaga is a gram-negative bacilli that constitute part of the normal oral microflora of humans and animals, specifically cats and dogs. Each presentation included either animal exposure or a recent intra-abdominal procedure. Of the reported cases, there were no presentations of intra-abdominal abscess. Therefore, this case presents an extremely rare case of an intraabdominal abscess secondary to capnocytophaga in a cirrhotic without any known exposures. This rare infectious complication exemplifies the need for practitioners to maintain a broad differential when pursuing infectious workups in their cirrhotic population.Figure 1.: 33.8 x 17.7 x 20.9 cm intra-abdominal abscess.

Lactobacillus fermentum and Lactobacillus crispatus Do Not Have Cytotoxic Effects on HN5 Oral Squamous Cell Carcinoma Cell Line.

Background The oral environment has a very complex normal flora and a wide variety of bacteria including lactobacilli. Studies have shown oral microbial flora has important influence in the development of oral cancer. Squamous cell carcinomas account for more than 90% of cancers in oral cavity. Lactobacilli are known as one of the newest methods for the prevention and treatment of cancers. Previous studies on the effects of probiotics on oral cancer cells are very limited, and only two species of Lactobacillus which are not present in the normal oral microflora have been studied. Due to the unknown effects of lactobacilli on oral cancer, this study aimed to investigate the effect of two species of lactobacilli of oral cavity on oral cancer cells. Methods and Materials The effects of the supernatant of two lactobacilli, namely, fermentum and crispatus were studied on HN5-cancer cells. The MTT method was used to study the effects of lactobacilli on inhibition of cancer cell growth. Results The results showed that these lactobacilli do not prevent the progression of oral cancer cells. Moreover, the results showed that the acidic medium had the most effect on reducing the growth of oral cancer cells. Conclusion Due to the different effects of lactobacilli on various cancer types, the effects of two Lactobacillus crispatus and Lactobacillus fermentum on other oral cancer cell lines may be different from what has been reported in this study.

Prevention of complications of iatrogenic transient bacteremia in dental practice

Transient bacteremia that occurs during invasive dental manipulations can lead to the development of severe complications in patients with diseases of the cardiovascular system, immunodeficiencies due to many factors, blood diseases, the presence of endoprostheses, etc. Antimi-crobial prevention of possible infectious-inflammatory complications of bacteremia in dentistry is an important task. The article provides data on the composition of normal oral microflora and its sensitivity to antimicrobial drugs. An algorithm for preventing complications of transient bacteremia in patients with risk factors is proposed.

ANTISEPTIC PROPERTIES OF CITRATE BUFFER

The antiseptic properties of endodontic materials are used for microbial control in root canals. Decrease in microfloria is known as one of key demands for root canal therapy. The aim of this work is to study the sensitivity of reference strains of microorganisms to citrate buffer and its combination with the antibiotic «Amoxiclav». We used the museum strains of E. coli ATCC 25922, S. aureus ATCC 25923, S. epidermidis ATCC 14990, E. faecalis ATCC 29212, M. lysodeicus ATCC 4698 and C. albicans ATCC10231 to solve this task. The disk-diffusion method for assessing the sensitivity of standard strains of microorganisms was used. We used chlorhexidine digluconate 0.05% as a control. Citrate buffer has high antibacterial activity. The combination of citrate buffer with antibiotic increases the sensitivity of all reference strains. E. coli ATCC 25922 demonstrates a moderate sensitivity to citrate buffer. This combination with an antibiotic increases the antibacterial effect in 2.3 times (p < 0.05). The sensitivity of enterococci increases towards the direction of chlorhexidine – citrate buffer – citrate buffer + «Amoxiclav». When comparing the results obtained using citrate buffer, its combination with antibiotic and chlorhexidine as a control, we should stress on the lower activity of chlorhexidine to strains of transient and normal oral microflora, which are E. coli ATCC 25922 and M. lysodeisticus ATCC 4698. On the contrary, we have revealed more pronounced action of experimental compositions against strains of pathogenic and opportunistic microorganisms, staphylococci, enterococci and yeast-like fungi that points out the advantage of citrate buffer and its combination with antibiotic «Amoxiclav» in terms of their use in the treatment of complicated caries.

Impaired salivary SIgA antibodies elicit oral dysbiosis and subsequent induction of alveolar bone loss.

Secreted IgA (SIgA) plays a central role in preventing bacterial and viral infections on mucosal surfaces by neutralizing toxins and viruses and inhibiting bacterial attachment to epithelial cells. However, the role of salivary SIgA antibodies (Abs) in regulating oral flora is still unknown. This study aimed to evaluate the association among oral bacteria, their metabolites and periodontitis in IgA-deficient (IgA KO) and wild-type (WT) control mice. Microcomputed tomography (micro-CT) analysis was used to assess alveolar bone resorption as a development of periodontitis. The bacterial profiles of saliva were determined using the next-generation sequencing assays. Furthermore, the metabolites in saliva were measured and compared using CE-TOFMS. Salivary microbiota of IgA KO mice revealed a remarkably decreased frequency of Streptococcus, and increased percentages of Aggregatibacer, Actinobacillus, and Prevotella at the genus level when compared with those of WT. Compared to WT control mice of the same age, the level of alveolar bone loss was significantly increased in IgA KO mice, and infiltration of osteoclasts was found on the surface of the alveolar bone. The metabolome profile indicated that the metabolites of IgA KO mice had greater variability in carbon metabolic, urea cycle, and lipid pathways than WT mice. These results suggest that salivary SIgA plays an important role in regulating and maintaining normal oral microflora to prevent the development of periodontal disease.

Distribution of Rothia species in root canals in a Japanese population

Rothia species are components of the normal oral microflora, which have been recognized as emerging opportunistic pathogens in immune compromised hosts. This study was performed to investigate the distribution of Rothia species in infected root canals. The correlations of clinical findings with the presence of Rothia species were also evaluated. A total of 200 root canal samples, including 92 primary infections and 108 secondary infections, were collected from 200 Japanese patients. Polymerase chain reaction (PCR) targeting the 16S rRNA gene was performed to detect three Rothia species, i.e., Rothia mucilaginosa, Rothia aeria, and Rothia dentocariosa. The detection frequencies of R. mucilaginosa, R. aeria, and R. dentocariosa were 49/200 (24.5%), 95/200 (47.5%), and 55/200 (27.5%), respectively. There were no significant differences in the detection frequencies between primary and secondary endodontic infections. The detection frequency of R. mucilaginosa in cases with gingival swelling was 42.9%, and there were significantly more cases positive than negative for this species (P = 0.042). The presence of R. aeria also showed correlations with radiolucency around the root apex (P = 0.001) and pain on percussion (P = 0.044). Quantitative real-time PCR revealed that the relative abundance of R. mucilaginosa in total bacterial counts ranged from 0.04% to 91.8%. These results indicated that Rothia species colonize root canals at relatively high frequency, and that root canals are potential reservoirs of these pathogens. The results also suggest that Rothia species are involved in the pathogenesis of apical periodontitis.

Inhibition of Streptococcus mutans and S. sobrinus biofilms by liamocins from Aureobasidium pullulans

The aim of this study was to determine if the novel anti-streptococcal inhibitors, liamocins, also inhibit biofilm formation by S. mutans and S. sobrinus. S. mutans strain ATCC 25175 and S. sobrinus strain ATCC 33478 were tested for biofilm formation in a rapid microtiter plate (MTP) assay and the effects of added liamocins were determined. This assay measures relative biofilm growth on pin lids. Results were verified in a biofilm flow cell assay, using hydroxyapatite-coated coupons to simulate dental material. Planktonic cultures of S. mutans and S. sobrinus were inhibited by 0.1 mg liamocins/ml. When liamocins were added after the adhesion phase in a rapid microtiter plate assay, S. mutans was inhibited 53% by 5 mg liamocins/ml, while S. sobrinus was more sensitive, showing 100% inhibition at 0.5 mg liamocins/ml. When liamocins were added during the adhesion phase, biofilms of S. mutans showed 78% inhibition at 3.0 mg liamocins/ml. In a biofilm flow cell assay, liamocins added after the adhesion phase at 0.5 mg liamocins/ml inhibited biofilms of S. sobrinus, and appeared to remove biofilms over time. Liamocins were shown for the first time to inhibit biofilm formation by S. mutans and S. sobrinus. Since liamocins are specific for Streptococcus spp., they are potential new inhibitors of oral streptococcal biofilms that should not affect normal oral microflora.

Microbial Analysis and Determination of Antibiotic Susceptibility of Dental Laboratory Equipments and Laboratory Attire.

Context:This study was done to determine the level and type of microbial contamination present on the surface of various dental laboratory equipment and laboratory attire and to determine the antibiotic susceptibility pattern of these isolated pathogens.Subjects and Methods:The samples were divided into following groups: six groups of dental laboratory equipment (articulators, facebow, fox plane, polishing buff, micromotor handpiece, and surveyors) and dental attire of laboratory technicians and students. A total of 33 swabs were collected from each dental laboratory equipment, namely, articulators, facebow, fox plane, polishing buff, micromotor handpiece, and surveyors. The dental laboratory attire of students and dental technicians were analyzed separately. The swabs were collected from the laboratory attire at the end of the week, and they were washed once a week and at the beginning of the week. The groups are Group 1 – dental laboratory attire (students), Group 2 – dental laboratory attire (technicians), Group 3 – polishing buff, Group 4 – facebow, Group 5 – surveyor, Group 6 – fox plane, Group 7 – articulator, and Group 8 – micromotor handpiece. The moistened swabs were inoculated into the broth and subcultured on to the MacConkey Agar plates, and then incubated aerobically at 37°C for 24 h. The organisms were identified based on colony morphology, Gram staining, and standard biochemical tests. The antibiotic susceptibility patterns of the isolated organisms were done according to the CLSI guidelines. The collected data were statistically analyzed.Statistical Analysis Used:The data collected were entered into a Microsoft Excel Spreadsheet and analyzed using IBM SPSS Statistics, Version 22 (Armonk, NY, IBM Corp.). The frequency and mean standard deviation of the samples were analyzed using Fisher's exact value test. Percentage of resistance among the isolates to different antimicrobials was also determined.Results:The microorganisms isolated were Staphylococcus aureus, Escherichia coli, coagulase-negative Staphylococcus, Pseudomonas, Klebsiella, nonfermenting Gram-negative bacteria, and Bacillus species. The mean microbial levels in dental laboratory attire were more (5 log10 colony-forming units [CFU]) compared with dental equipment (3 log10 CFU–4 log10 CFU). Furthermore, most of the isolated organisms showed increased antimicrobial resistance.Conclusion:Majority of the isolated organisms were not a part of the normal oral microflora and are capable of causing various diseases. The increased resistance to the antimicrobials showed by the isolated organisms proves that there are increased chances of multiresistant organisms to occur in the future.

The etiological structure, biological properties of causative agents of peri-implant mucositis

The purpose was to examine the peri-implant mucositis microflora and sensitivity of dominant pathogens to antibiotics and antiseptics. Materials and methods. The study involved 43 patients with peri-implant mucositis. During the study 162 clinical strains of microorganisms were isolated and identified. Cultivation of clinical isolates was performed by the standard method, final identification was carried out with using bacteriological automatic analyzer Vitec – 2compact bioMerieux (France). Determination of sensitivity to antibiotics of pathogens was carried with disc-diffusion method; the study of sensitivity to antiseptics was carried by means of double serial dilutions method by the standard procedure approved by the Order № 167 of the Ministry of Public Health of Ukraine on “On Approval of Training Guidance “Assessment of the sensitivity of microorganisms to antibiotics”, dated by April, 5, 2007. Results. It is The microflora of peri-implant area of patients with mucositis was revealed to consist of opportunistic species. Representatives of Streptococcus spp . and Staphylococcus spp . were dominating among them, although Kocuria spp., Enterobacter spp. and yeast-like fungi Candida spp. were detected quite common. Investigated clinical strains of microorganisms had different sensitivity to antibiotics. All cultures were sensitive to fluoroquinolones, but very significant number of them showed resistance to penicillins, macrolides and lincosamides. In turn, horosten, dekasan and chlorhexidine had powerful antimicrobial effect on dominant pathogens of periimplant mucositis in patients. Moreover, the effect of decametoxine-based antiseptics on some of them significantly exceeded the activity of chlorhexidine. Conclusions. Microflora from peri-implant area of patients with peri-implant mucositis consists mainly of aerobic and facultative anaerobic microorganisms, belonging to normal oral microflora. Most of pathogens of mucositis obtaine resistance to antibiotics (penicillins, macrolides, lincosamides). Modern antiseptics horosten, decasan and chlorhexidine provide a strong antimicrobial activity against etiological pathogens of mucositis, that makes them promising for use in dental implantology.

Oral microflora and selection of resistance after a single dose of amoxicillin

The study aimed to determine the effects of a single-dose antibiotic prophylaxis on normal oral microflora. A single dose of 2 g amoxicillin was given to 29 healthy volunteers. Saliva was collected before antibiotic administration (day 1), and again on days 2, 5, 10, 17 and 24 and subjected to culturing and antibiotic sensitivity analysis. Twenty-one per cent (6/29) of the individuals carried penicillin-V- and amoxicillin-resistant viridans streptococci before antibiotic administration. After a single dose of amoxicillin there was a significant reduction in Streptococcus salivarius on days 2 and 5, a significant reduction in other viridans streptococci on day 2 and the proportion of viridans streptococci with reduced susceptibility to amoxicillin was significantly increased on days 2 and 5. A single dose of amoxicillin can cause an ecological disturbance and induce selection of resistant strains in the oral microflora.

Rothia prosthetic knee joint infection: report and mini-review.

Rothia spp. are gram-positive pleomorphic bacteria that are part of the normal oral microflora. They are associated with dental and periodontal disease, although systemic infections have also been reported. We describe the case of a 75-year-old lady with rheumatoid arthritis who presented with prosthetic knee joint infection due to Rothia aeria. We discuss its identification and the evidence regarding association of dental disease with Rothia spp. joint infections based on available literature.

Haemophilus parainfluenzae urethritis among homosexual men

Haemophilus parainfluenzae is a common inhabitant of the human upper respiratory tract of the normal oral microflora. We report three men who had been having unprotected sex with men (MSM) and subsequently acquired H. parainfluenzae urethritis, which was confirmed by 16S rRNA gene sequencing analysis. Two men were treated with ceftriaxone and doxycycline, and the third man was treated with clarithromycin. All three patients responded to treatment. This case series highlights the potential role of H. parainfluenzae as a sexually transmitted genitourinary pathogen.

구강 내 Helicobacter pylori

Helicobacter pylori(H. pylori) associated with gastritis and gastric cancer is mainly detected dental plaque and saliva in the oral cavity. Most infection is probably acquired in childhood, but the route of transmission is not clear. The oral cavity has been indicated as secondary reservoir of H. pylori, and may therefore be argued in the route of transmission and reinfection of the stomach which follows treatment of H. pylori infection. So this review aimed to discuss about H. pylori in the oral cavity. H. pylori in stomach can appear in the oral cavity by gastroesophageal reflex or vomiting, but infection of stomach and oral cavity is different. Diagnostic methods are serological method, urea breath test, PCR method, urease test, histologic method and so on. Nested PCR recommend for detection of H. pylori in saliva and dental plaque. H. pylori infection in the oral cavity appear variously and is no relation with dental diseases. The antimicrobial mouthrinse recommend in patients with periodontal diseases because of high detection rate fo H. pylori. Thus H. pylori may be considered as the normal oral microflora.

The Oral Cavity, Biofilms and Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is the most prevalent infection in intensive care units (ICUs) and second only to urinary tract sepsis amongst hospital-acquired infections. The endotracheal tube is an important component in the pathogenesis of VAP, as it both subverts the normal defence mechanisms of the respiratory tract and offers a surface that can support biofilm growth, thereby providing a reservoir of potential respiratory pathogens. Traditionally recognized VAP pathogens include Staphylococcus aureus and Gram-negative bacteria such as Pseudomonas aeruginosa and members of the Enterobacteriaceae family. These microorganisms are not recognized as members of the normal oral microflora, but are thought to infect the lungs endogenously via the oropharyngeal route. Prior to entering the lower respiratory tract, there is evidence that the oral cavity does become colonised by respiratory pathogens. In this regard, it is probable that the normal oral microflora is an influencing factor for VAP, either through affecting recruitment of respiratory pathogens to oral plaque, or to biofilms that develop in the endotracheal tube. Indeed the ability of several Streptococcus species belonging to the normal oral microflora to promote recruitment of bacteria to plaque biofilm through production of extracellular glucans has long been recognised. Recent studies have indeed highlighted that poor oral hygiene is a risk factor for VAP and therefore the maintenance of adequate oral health care in ventilated patients represents an important preventative strategy. Keywords: Biofilm, endotracheal tube, oral hygiene, ventilator-associated pneumonia, intensive care units, hospital-acquired infections, respiratory tract, respiratory pathogens, Staphylococcus aureus, Pseudomonas aeruginosa

Salivaricin G32, a Homolog of the PrototypeStreptococcus pyogenesNisin-Like Lantibiotic SA-FF22, Produced by the Commensal SpeciesStreptococcus salivarius

Salivaricin G32, a 2667 Da novel member of the SA-FF22 cluster of lantibiotics, has been purified and characterized from Streptococcus salivarius strain G32. The inhibitory peptide differs from the Streptococcus pyogenes—produced SA-FF22 in the absence of lysine in position 2. The salivaricin G32 locus was widely distributed in BLIS-producing S. salivarius, with 6 (23%) of 26 strains PCR-positive for the structural gene, slnA. As for most other lantibiotics produced by S. salivarius, the salivaricin G32 locus can be megaplasmid encoded. Another member of the SA-FF22 family was detected in two Streptococcus dysgalactiae of bovine origin, an observation supportive of widespread distribution of this lantibiotic within the genus Streptococcus. Since the inhibitory spectrum of salivaricin G32 includes Streptococcus pyogenes, its production by S. salivarius, either as a member of the normal oral microflora or as a commercial probiotic, could serve to enhance protection of the human host against S. pyogenes infection.

Enterococcus faecalis infection in root canals - host-derived or exogenous source?

Enterococcus faecalis is associated with a significant number of refractory endodontic infections. Previous studies report a prevalence of Ent. faecalis ranging from 24% up to 77% in teeth with failed endodontic treatment. The origin of the micro-organism remains unclear, as enterococci do not belong to the normal oral microflora. The aim of this study was to determine whether these enterococci were of endogenous or exogenous origin. Fifty consecutive patients with apical periodontitis in need of endodontic orthograde re-treatment were included. Samples were collected from root canals, saliva and faeces and subjected to microbiological culturing. The genetic relationship between Ent. faecalis from root canals and isolates from the different host sources was determined using pulsed-field gel electrophoresis. In 16% (8/50) of the patients, enterococci were collected from the root canal samples. The genetic analysis showed that the isolates from the root canals were not related to those from the normal gastrointestinal microflora. None of these patients had enterococci in their saliva samples. Endodontic infections with Ent. faecalis are probably not derived from the patient's own normal microflora, which indicates that these infections ent. faecalis are of exogenous origin. This is the first study to genetically compare endodontic infectious Ent. faecalis isolates with isolates from the hosts' own normal microflora.