Antibiotic susceptibility of Staphylococcus aureus isolates in oral mucosa and pockets of patients with gingivitis-periodontitis

Both oral cavity and subgingival pocket are ecological niches conducive to hosting microorganisms that may act as opportunistic pathogens, such as Staphylococcus aureus and especially methicillin-resistant Staphylococcus aureus (MRSA). Early detection of MRSA is a matter of concern to Public Health. The aim of our study was to determine phenotypic and genotypic detection of methicillin resistance of S. aureus in oral mucosa and subgingival pocket in 102 patients with gingivitis-periodontitis. The prevalence of S. aureus was 10.8% (n = 11) in subgingival pocket and 19.6% (n = 20) in oral mucosa. We obtained 31 isolates of S. aureus of which 13 were mecA positive and 18 were mecA negative. Detection of mecA gene by PCR was used as the reference method to compare the results of phenotypic methods to determine methicillin resistance. Early, accurate detection of S. aureus through phenotyping and genotyping methods is crucial for assessing the colonization and preventing the spread of MRSA.     

Methicillin‐resistant staphylococci carriage in the oral cavity: a study conducted in Bari (Italy)

Oral Diseases (2010) 16 , 465–468 Objectives: The oral cavity may represent a site of colonization by antibiotic‐resistant bacteria, such as methicillin‐resistant staphylococci (MRS). To define the prevalence of staphylococci and MRS in the oral cavity, an observational study was carried out in the city of Bari (Italy). Methods: Sixty subjects were asked to provide oral samples and a questionnaire about risk factors of colonization by MRS. An enrichment medium specific for staphylococci was used for the isolation. Results: Swabs and corresponding questionnaires were available from 36 out of 60 patients. Staphylococci were isolated from seven out of 36 samples (prevalence 19.4%). Among the seven staphylococcal isolates, three were Staphylococcus aureus, and one strain, belonging to S. epidermidis species, was found to be MR (1.7%). No methicillin‐resistant S. aureus were isolated. Five out of seven staphylococcal isolates exhibited resistance to more than two classes of non‐beta‐lactams antimicrobials. None of the risk factors analysed correlated with the status of MRS carriers, except the presence of oral disease. Conclusions: The results underline the potential role of the oral cavity as a reservoir of staphylococci.     

Effect of photodynamic therapy on clinical isolates of Staphylococcus spp

Staphylococcus spp. are opportunistic microorganisms known for their capacity to develop resistance against antimicrobial agents. The objective of this study was to evaluate the effect of photodynamic therapy (PDT) on 20 Staphylococcus strains isolated from the human oral cavity, including S. aureus, S. schleiferi, S. epidermidis, S. capitis, S. haemolyticus, and S. lentus. A suspension of each Staphylococcus strain (10(6) cells/mL) was submitted to PDT using methylene blue and a low power laser. The isolated effects of methylene blue, laser treatment and ciprofloxacin were also evaluated. After the experimental treatments, 0.1 mL aliquots of the suspensions were seeded onto BHI agar for determination of the number of colony-forming units (CFU/mL). The results were analyzed by analysis of variance and Tukey's test (p < 0.05). The mean reduction in bacterial counts of the strains submitted to PDT ranged from 4.89 to 6.83 CFU (log10)/mL, with the observation of a decreasing susceptibility to treatment of S. schleiferi, S. haemolyticus, S. epidermidis, S. capitis, S. aureus, and S. lentus. The results showed that PDT was effective in reducing the number of viable cells of all clinical Staphylococcus isolates studied.     

Prevalence of oral methicillin-resistant Staphy/ococcus aureus in an institutionalized veterans population

Methicillin-resistant Staphylococcus aureus ( MRSA) is a nosocomial pathogen now of great concern in nursing homes and other institutional settings. MRSA has been well-documented to inhabit the nares, skin wounds, and respiratory tract, but little is known about its presence in the oral cavity. In this study, all patients admitted to an 80-bed VA extended care facility were cultured weekly for 12 weeks to detect the presence of MRSA in the nares, wounds, in-dwelling devices, and the oral cavity. Of a total of 107 participating subjects, 20 cultured positive for oral MRSA, yielding a prevalence of 18.7%, compared with 19.6% prevalence in the nares —the traditionally accepted screening site for MRSA. There was a 91.6% agreement between oral and nasal carriage in subjects, but four of 107 subjects (3.7%) cultured positive for oral MRSA without evidence of nasal carriage. These results suggest that oral MRSA may be more common than previously thought in high-risk settings, with a prevalence comparable with that of nasal infection. Further investigation is necessary to characterize the factors associated with the presence of MRSA in the oral cavity     

Long-term periodical isolation of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) from Japanese children's oral cavities

IntroductionMethicillin-resistant Staphylococcus aureus (MRSA) is a major pathogen causing nosocomial infections. To control nosocomial infection in a dental hospital, periodical surveillance of MRSA from the oral cavity is very important. Furthermore, this surveillance might reveal any alteration of the incidence of MRSA among healthy children in a particular area, because many children having no systemic disease except for dental problems come to dental offices.MethodsTotally 741 children were participated in the present study; 307 in 1987–88, 103 in 1992–93, 129 in 1997– 98 and 202 in 2002–2003. S. aureus was isolated from the tongues of children without systemic diseases. All isolates were investigated for coagulase types and susceptibilities to five antibiotics.ResultsS. aureus was isolated from 33–44% of children during the examination period. The incidence of MRSA was maximal in 1992–93, and then constant at around 3%. MRSA that have type II or III coagulase were relatively dominant.ConclusionAlthough outbreaks of MRSA in Japan was decreased in the early 90's, more than 3% of children without particular risks are considered positive for MRSA.     

The prevalence and antibiotic sensitivity of oral Viridans streptococci in healthy children and children with disabilities in Kuwait

The purpose of this study was to compare the antibiotic susceptibility profiles of Viridans streptococci (VS) isolated from the oral cavity of healthy children and children with disabilities in Kuwait. Plaque samples were collected from the tooth and tongue surfaces of 102 healthy children and 102 children who were intellectually disabled and institutionalized. The resistance to seven antibiotics (amoxicillin, cephalothin, clindamycin, erythromycin, penicillin G, tetracycline, and vancomycin) was tested.
A total of 330 (44.5%) VS were isolated from the children who were healthy and 411 (55.5%) from children with disabilities. The most common isolates were S. salivarias (27.3%) in healthy children; S. sanguis (22.6%) was predominant among children who were disabled. S. mutans was found in 12.1% of the healthy children and in 16.5% of the children who were disabled. The combined percentage of resistant strains (healthy and disabled) was found to be highest with amoxicillin (43%) and lowest with vancomycin (12%). S. sanguis, S. mitis and S. oralis were more resistant in healthy children (45%, 56%, and 55% respectively) than in children with disabilities (40%, 47% and 47% respectively). S. mutans was the least resistant species to all antibiotics in both groups of children. About 56% of ali streptococci isolated from both groups were resistant to at least one of the antibiotics tested.
The data showed that there was a diference in the level of resistance of oral VS isolated from healthy children and children with disabilities to some antibiotics commonly used in dentistry.     

Staphylococcus aureus transmission through oronasal fistula in children with cleft lip and palate

Objective: To determine the presence of Staphylococcus aureus in a nasal flora and oral environment, the correlation between frequency of transmission of S. aureus and oronasal fistula size, and the pattern of methicillin resistance on S. aureus strains in children with cleft lip and palate (CLP). Design: Thirty-two CLP children with and without oronasal fistulas, ranging in age from 5 to 13 years were examined for oronasal fistula presence and size. Stimulated saliva samples and nasal swab samples were taken and investigated for S. aureus presence. S. aureus presence and counts were correlated with fistula presence and size. Results: Saliva samples showed statistical differences between the groups with and without oronasal fistulas with an area ranging from 0.80 to 28.26 mm(2). The S. aureus counts were significantly higher (r = .535, p = .002) in saliva samples from children with larger oronasal fistula. The S. aureus count was not significantly different (r = -.013, p = .942) in nasal samples compared with oronasal fistula size. Methicillin resistance with disk-diffusion method was recorded as sensitive (>/=13 mm) in all S. aureus strains. Conclusions: The results of this study indicate a positive correlation between fistula size and S. aureus transmission to one oral environment through oronasal fistulae, and a positive correlation between frequency of S. aureus transmission and fistula size. All S. aureus strains were sensitive to methicillin. These results may have implications for preventive treatment of CLP children.     

The clinical significance of beta hemolytic streptococci of the milleri group in oral abscesses

Aspirated exudate from 50 patients with oral abscesses were cultured and bacterial growth was assessed qualitatively and semi-quantitatively. Bacteria were recovered from all specimens. The mean number of species isolated per specimen was 3.6 Both facultative and obligate anaerobes were isolated from 39 (78%) specimens. The most commonly isolated facultative anaerobic species was Streptococcus virdans group, while pigmented gram negative bacilli were the most commonly isolated obligate anaerobes. Beta-hemolytic Streptococci of the "milleri" groups were recovered from 11 (22%) of the abscesses. Eight of those isolates were determined to carry Lancefield group F antigen, 2 group C, and 1 isolate was not groupable for any Lancefield antigen. These abscesses may be sequelae of oral infectious disease or trauma. Patients with oral abscesses infected with beta hemolytic Streptococci are apt to be male, and less than 35 years old. They are also likely to have a more rapid onset of infection and to require hospitalization for intensive treatment of a life threatening condition.     

Influence of oral conditions on colonization by highly toxigenic Staphylococcus aureus strains

Oral Diseases (2012) 18 , 402–409 Objectives: As the oral cavity is regarded as a relevant site for Staphylococcus aureus colonization and interhuman transmission, this study aimed to investigate whether different oral conditions influence the rates of S. aureus oral carriage and genetic characters of S. aureus isolates. Subjects and methods: Staphylococcus aureus was searched in samples collected from cheek, gingival margin, and anterior nares of 45 healthy subjects, 27 periodontitis affected subjects, and 29 subjects with fixed prosthetic restorations. Isolates were screened for 17 genetic determinants, and Partial Least Square Discriminant Analysis was performed to evaluate whether specific characters correlated with oral condition or site of isolation. Results: The three subject groups showed comparable nasal carriage rates but, both the periodontitis and prosthetic restoration groups showed significantly higher oral carriage rates, as compared to healthy subjects (P = 0.01 and 0.02, respectively). Moreover, periodontitis affected subjects hosted strains possessing a distinct genotypic and phenotypic background, characterized by the presence of a larger number of exotoxins encoding genes. Conclusions: These data confirm that the oral cavity is an important site of S. aureus colonization and demonstrate that conditions modifying the oral environment, as the presence of periodontitis and of fixed prosthetic restorations, promote S. aureus carriage and may favor the spread of more pathogenic strains.     

Antimicrobial activity of Uncaria tomentosa against oral human pathogens

Uncaria tomentosa is considered a medicinal plant used over centuries by the peruvian population as an alternative treatment for several diseases. Many microorganisms usually inhabit the human oral cavity and under certain conditions can become etiologic agents of diseases. The aim of the present study was to evaluate the antimicrobial activity of different concentrations of Uncaria tomentosa on different strains of microorganisms isolated from the human oral cavity. Micropulverized Uncaria tomentosa was tested in vitro to determine the minimum inhibitory concentration (MIC) on selected microbial strains. The tested strains were oral clinical isolates of Streptococcus mutans, Staphylococcus spp., Candida albicans, Enterobacteriaceae and Pseudomonas aeruginosa. The tested concentrations of Uncaria tomentosa ranged from 0.25-5% in Müeller-Hinton agar. Three percent Uncaria tomentosa inhibited 8% of Enterobacteriaceae isolates, 52% of S. mutans and 96% of Staphylococcus spp. The tested concentrations did not present inhibitory effect on P. aeruginosa and C. albicans. It could be concluded that micropulverized Uncaria tomentosa presented antimicrobial activity on Enterobacteriaceae, S. mutans and Staphylococcus spp. isolates.     

Incidence and characterization of Staphylococcus aureus from the tongues of children

Three hundred and seven children who had no diseases other than dental disease were examined for their oral carriage of Staphylococcus aureus, the most common persistent human pathogen. Eighty-four percent of them were positive for staphylococci, and 33% were positive for S. aureus. Among the 100 strains of S. aureus isolated, 40 strains produced enterotoxin, and 19 strains produced exfoliative toxin. Their susceptibility to antibiotics was also investigated: Six strains demonstrated resistance to methicillin (MIC greater than or equal to 12.5 microgram/mL), and 50% of the isolates were borderline resistant (MIC of 3.13 to 6.25 micrograms/mL) to the drug. These data suggest that the mouths of children could be reservoirs of pathogenic S. aureus.     

An analysis of oral and maxillofacial pathology found in children over a 30-year period

AIM: The vast majority of oral diseases are confined to oral tissues, but numerous underlying systemic conditions may present with signs and symptoms within the oral cavity. Since the epidemiology of diseases is variable between regions, the authors carried out Europe's first paediatric-based survey of oral and maxillofacial pathology specimens submitted for diagnosis. DESIGN: All entries for specimens from children between the ages of 0 and 16 years during the 30-year period from 1973 to 2002 were retrieved and compiled into 12 diagnostic categories. RESULTS: During the study period, 4406 (8.2%) specimens came from children between the ages of 0 and 16 years, with a male to female ratio of 1.01. The diagnostic category with the largest number of specimens was tooth pathology (22.1%), followed by salivary gland disease (19.1%) and mucosal pathology (12.1%). In all, there were 114 benign tumours of nonodontogenic origin, 43 odontogenic tumours and 31 malignant tumours. The most frequently diagnosed lesions were mucous extravasation cysts, which accounted for over 16% of cases. Periapical pathology in the form of a radicular cyst, residual cyst or chronic periapical granuloma formed almost 13% of all cases. CONCLUSIONS: This survey shows that, while nearly 10% of specimens submitted to the authors' laboratory are from children under 16 years of age, the majority of lesions are of a benign nature, requiring minimal intervention; less than 1% of cases comprise malignant lesions. Odontogenic tumours are relatively rare in this age group; however, certain lesions such as adenomatoid odontogenic tumour and ameloblastic fibroma occur predominantly in children and, therefore, remain an important diagnostic consideration.     

Reduction of salivary S. aureus and mutans group streptococci by a preprocedural chlorhexidine rinse and maximal inhibitory dilutions of chlorhexidine and cetylpyridinium.

OBJECTIVES: Staphylococcus aureus and mutans group streptococci can cause, among many other diseases, infective endocarditis and postoperative infections. The reduction of the number of these microorganisms in the oral cavity prior to surgical procedures has been related to a decreased incidence of such occurrences. The aim of this study was to evaluate the effect of a single preprocedural rinse with 0.12% chlorhexidine solution (Periogard) on the salivary counts of S aureus and mutans group streptococci and determine maximal inhibitory dilutions (MID) of this and 0.05% cetylpyridinium chloride solution (Cepacol). METHOD AND MATERIALS: Saliva was collected from 60 patients before and after 30-second mouthrinses with chlorhexidine and cultured in appropriate media. The number of microorganisms was calculated based on the colony-forming units (CFUs). For the in vitro MID determination, 25 strains of S aureus were seeded in the media containing one of the sequential dilutions of both antiseptics. RESULTS: S aureus, Streptococcus mutans, and Streptococcus sobrinus were initially isolated from 45%, 63%, and 28% of the patients, respectively. After rinsing with chlorhexidine, the reductions in the CFUs were above 99% for all the studied microorganisms. In the MID determination, all isolates were inhibited with 1/20 and 1/80 dilutions of cetylpyridinium and chlorhexidine, respectively. Dose-response curves were obtained for both antiseptics. CONCLUSION: Single preprocedural chlorhexidine mouthrinse is effective in reducing salivary microorganisms to levels currently considered safe to perform invasive procedures, and it is still effective in a 1:80 dilution.     

Susceptibility and beta-lactamase-producing strains of methicillin-resistant Staphylococcus aureus

Thirty-three strains of methicillin-resistant Staphylococcus aureus (MRSA, MIC for methicillin greater than or equal to 16.0 micrograms/ml) isolated from sputum were examined for their susceptibilities against 8 antimicrobial agents. Ampicillin (ABPC), methicillin (DMPPC), cefazolin (CEZ), minocycline (MINO), erythromycin (EM), tobramycin (TOB), refampicin (RFP), and ofloxacin (OFLX) were used as the antimicrobial agents. The production of beta-lactamase was also determined. The results are as follows: 1) The highest susceptibility was given by RFP, and followed by MINO, and OFLX. All strains were resistant against EM and TOB. 2) The percentage of beta-lactamase-positive strains was 75.8%, which was distributed nearly identical among each MIC to DMPPC (72.0-77.8%). 3) Since the beta-lactamase-positive strains were found among the sensitive strains to ABPC, it was suggested that the use of beta-lactam antimicrobial agents might bring into the higher MIC value to ABPC. 4) Since there were beta-lactamase-negative strains among the resistant strains to ABPC, it was indicated that penicillin binding protein-2' might be produced by giving beta-lactam antimicrobial agents.     

Factors affecting susceptibility of Staphylococcus aureus to antibacterial agents

Staphylococcus aureus is a major human pathogen that causes suppurative diseases, toxic shock syndrome, pneumonia, food poisoning, and staphylococcal scalded skin syndrome (SSSS). S. aureus can also cause osteomyelitis and radicular cysts that impact dental health. β-lactam antibiotics are frequently used for the treatment of S. aureus infections, but the emergence of methicillin-resistant S. aureus (MRSA) has caused serious problems for the antibiotic treatment of S. aureus infections. PBP2′ has a low affinity for methicillin antibiotics and is one of the factors responsible for resistance to these antibiotics. However, clinical MRSA isolates show various levels of resistance to methicillin that are not determined by the amount of PBP2′, indicating that other factors are also involved. Furthermore, while vancomycin is very effective against MRSA, vancomycin-resistant and vancomycin-intermediate S. aureus have recently been reported. Many studies have been undertaken to better understand methicillin and vancomycin resistance mechanisms through identification of the factors affecting susceptibility to β-lactams. We recently demonstrated that MRSA showed resistance to antimicrobial peptides produced by humans that are a component of the innate immune system, in addition to various antibiotics.     

Staphylococcus lugdunensis--a potential pathogen in oral infection.

OBJECTIVE: The purpose of this study was to investigate the pathogenicity of Staphylococcus lugdunensis in acute oral infection. STUDY DESIGN: S. lugdunensis was isolated from patients with acute oral infections and from healthy control subjects. Antibiotic susceptibility, in vitro cellular toxicity, in vivo virulence, and hemolytic activity testing and dot blot analysis were performed. The statistical significance of in vitro cellular toxicity was determined by means of analysis of variance. RESULTS: Isolated from the infected patients, S. lugdunensis showed resistance to penicillin, ampicillin, methicillin, cephalothin, and clindamycin, exhibited virulence in vivo, and showed delta-like hemolysin activity. Four of the 6 strains of S. lugdunensis gave synergistic hemolysis. In dot blot analysis, S. lugdunensis showed a positive reaction to the probe of the delta-hemolysin gene in S. aureus. CONCLUSIONS: The results suggest that S. lugdunensis may be a potential pathogen in acute oral infection.     

Mutans streptococci strains prevalence before and after cavity preparation during Atraumatic Restorative Treatment

Critics argue that all carious dentine is not removed from the hand-prepared cavity during the Atraumatic Restorative Treatment (ART) procedure, and that the caries process is soon resumed. The aim of this study was to determine the effectiveness of ART in removing carious tissue, by investigating the numbers of mutans streptococci and lactobacilli, with emphasis on the prevalence of Streptococcus mutans and Streptococcus sobrinus strains before, and after ART treatment of dental caries. Two microbiology samples were collected. The first sample was removed from the centre of the carious lesion at the enamel-dentine junction, and the second was collected from the centre of the hard cavity wall above the pulp, after the soft infected dentine had been manually removed. A total of 71 mutans streptococci isolates from 31 children and 40 carious teeth were subcultured, biochemically characterised and genotyped by the arbitrarily primed polymerase chain reaction (AP-PCR). Results showed a significant decrease in TVC (P<0.0001), mutans streptococci (P < 0.0001) and lactobacilli (P = 0.0002) after cavity preparation. AP-PCR identified S. mutans strains that were undetectable during biotyping, and divided clinical isolates into two main clusters. In all, 63% (45/71) of isolates from the carious lesions comprised S. mutans strains. After cavity preparation, this was reduced to 35% (25/71), of which 30% (21/71) were S. mutans and the remaining 6% (4/71) S. sobrinus strains. The number of mutans streptococci strains was below detectable levels in 19 of the prepared cavities. The significant decrease in bacteria after manual cavity preparation demonstrates the reliability of a standardized ART technique, yet the presence of S. mutans strains shows that the effectiveness of the ART procedure can vary during treatment and between dental practitioners.     

Incidence and risk factors for infection in oral cancer patients undergoing different treatments protocols

ABSTRACT: BACKGROUND: Over the past decade, advances in the field of cancer treatments have been counterbalanced by a rising number of immunosuppressed patients with a multitude of new risk factors for infection. Hence, the aim of this study was to determine risk factors, infectious pathogens in blood and oral cavity of oral cancer patients undergoing different treatment procedures. METHODS: The present prospective cohort analysis was conducted on the patients undergoing treatment in the radiotherapy unit of Regional Cancer Institute, Pt. B.D. Sharma University of Health Sciences, Rohtak, Haryana, during the period of January 2007 to October 2009. Total 186 patients with squamous cell carcinoma of oral cavity were analyzed in the study. Based on treatment procedures patients were divided into three groups, group I were under radiotherapy, group II under chemotherapy and group III were of radio chemotherapy together. Clinical isolates from blood and oral cavity were identified by following general microbiological, staining and biochemical methods. The absolute neutrophile counts were done by following the standard methods. RESULTS: Prevalent bacterial pathogens isolated were Staphylococcus aureus, Escherichia coli, Staphylococcus epidermidis, Pseudomonas aeruginosa, Klebsiella pneumonia, Proteus mirabilis, Proteus vulgaris and the fungal pathogens were Candida albicans, Aspergillus fumigatus. The predominant gram negative bacteria, Pseudomonas aeruginosa and Klebsiella pneumonia were isolated from blood of radiotherapy and oral cavity of chemotherapy treated cases respectively. The predominance of gram positive bacteria (Staphylococcus aureus and Staphylococcus epidermidis) were observed in blood of chemotherapy, radio chemotherapy cases and oral cavity of radiotherapy, radio chemotherapy treated cases. Our study also revealed the presence of C. albicans fungi as most significant oral cavity pathogens in radiotherapy and radio chemotherapy cases. CONCLUSION: Gram positive bacteria and Gram negative were reported from the blood of all the three groups' patients. Oral mucositis played a significant role in oral cavity infection and make patients more prone to C. albicans infection.     

Risk Factors for Methicillin-Resistant Staphylococcus aureus (MRSA) and Use of a Nasal Mupirocin Ointment in Oral Cancer Inpatients.

PURPOSE: Elimination of methicillin-resistant Staphylococcus aureus (MRSA) is of critical importance in oral and maxillofacial surgery because control is very difficult once infection of an oral tumor or oral wound with MRSA is established. PATIENTS AND METHODS: We retrospectively investigated the risk factors for acquiring MRSA in 518 patients with oral cancer among 1,877 inpatients in our department between 1984 and 2005. RESULTS: The patients with oral cancer demonstrated a high rate of MRSA colonization and infection (77.8%) relative to the population as a whole with MRSA isolated percentage in our department after 1991. The risk factors for MRSA in oral cancer patients are also related to systemic diseases and physiological and iatrogenic conditions, including cerebrovascular diseases (77.8%), peripheral arterial catheterization (69.2%), diabetes (50.0%), tracheotomy (50.0%), renal failure (50.0%), long-term broad-spectrum antibiotic use (45.7%), and malnutrition (43.3%). However, the highest risk of MRSA seems to be related to poor hygienic care. CONCLUSIONS: Beginning in 1999, we implemented a strategy for reducing infection by MRSA that included nasal mupirocin ointment for patients at high risk of MRSA; since then, the detection rate has decreased. We suggest that the administration of nasal mupirocin ointment and provision of scrupulous hygienic care for high-risk patients are useful and effective measures for decreasing the incidence of MRSA infection.     

Antibiotic resistance and production of inhibitory substances among bacterial strains isolated from the oral cavities of BALB/c mice

In the oral cavities of BALB/c mice, microbial population levels are regulated by multifactorial processes. Factors include the production of inhibitory substances and the exchange of genetic material. In this work, 371 isolates from different sites (saliva, tongue, teeth, and mucosa) of the oral cavities of BALB/c mice were screened for resistance to antibiotics and antimicrobial activity. Antibiotic-resistant strains represented 25% of the total flora. Among the predominant species, all the S. faecalis isolates showed multiresistance, and 23% of the Lactobacillus murinus isolates and 15% of the Staphylococcus aureus were resistant to at least one antibiotic. Resistance to aminoglycosides (neomycin, streptomycin, kanamycin, and gentamicin) was most frequently encountered. In S. faecalis, high levels of resistance were recorded to neomycin and streptomycin but not to gentamicin or kanamycin. Macrolides (M), lincosamides (L), streptogramin B (S), tetracycline (Tc), and chloramphenicol (Cm) resistance was also present in multiresistance patterns, especially among S. faecalis isolates. Hemolytic (Hly+) streptococci were less resistant to MLS, Tc, and Cm than were non-hemolytic (Hly-) isolates. Resistance to beta-lactam antibiotics was detected only among staphylococci and with a low prevalence (4%). The frequencies of strains producing antimicrobial substances against the indicator strains (S. mutans LG-1, S. sanguis Ny 101, and A. viscosus Ny 1) were high for L. murinus (76%) and S. faecalis (57% for Hly- and 90% for Hly+), but low for S. aureus (7%). These results indicate that the indigenous oral flora could interfere with colonization by allochthonous micro-organisms and that resistance patterns should be taken into account for the elimination of the oral indigenous flora by antibiotic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)