Metabolic changes associated with adaptive resistance to daptomycin in Streptococcus mitis-oralis.

BACKGROUND: Viridans group streptococci of the Streptococcus mitis-oralis subgroup are important endovascular pathogens. They can rapidly develop high-level and durable non-susceptibility to daptomycin both in vitro and in vivo upon exposure to daptomycin. Two consistent genetic adaptations associated with this phenotype (i.e., mutations in cdsA and pgsA) lead to the depletion of the phospholipids, phosphatidylglycerol and cardiolipin, from the bacterial membrane. Such alterations in phospholipid biosynthesis will modify carbon flow and change the bacterial metabolic status. To determine the metabolic differences between daptomycin-susceptible and non-susceptible bacteria, the physiology and metabolomes of S. mitis-oralis strains 351 (daptomycin-susceptible) and 351-D10 (daptomycin non-susceptible) were analyzed. S. mitis-oralis strain 351-D10 was made daptomycin non-susceptible through serial passage in the presence of daptomycin. RESULTS: Daptomycin non-susceptible S. mitis-oralis had significant alterations in glucose catabolism and a re-balancing of the redox status through amino acid biosynthesis relative to daptomycin susceptible S. mitis-oralis. These changes were accompanied by a reduced capacity to generate biomass, creating a fitness cost in exchange for daptomycin non-susceptibility. CONCLUSIONS: S. mitis-oralis metabolism is altered in daptomycin non-susceptible bacteria relative to the daptomycin susceptible parent strain. As demonstrated in Staphylococcus aureus, inhibiting the metabolic changes that facilitate the transition from a daptomycin susceptible state to a non-susceptible one, inhibits daptomycin non-susceptibility. By preventing these metabolic adaptations in S. mitis-oralis, it should be possible to deter the formation of daptomycin non-susceptibility.

Characteristics of pyogenic odontogenic infection in patients attending Mulago Hospital, Uganda: a cross-sectional study.

BACKGROUND: Predisposing factors of pyogenic odontogenic infection include dental caries, pericoronitis, periodontitis, trauma to the dentition and the supporting structures or complications of dental procedures. The infections are usually polymicrobial involving normal endogenous flora. We characterised pyogenic odontogenic infection in patients attending Mulago Hospital, Uganda. RESULTS: Of the 130 patients, 62 (47.7%) were female. The most frequently involved fascial spaces were: the buccal, 52 (25.4%); submasseteric, 46 (22.4%) and the submandibular space, 36 (17.5%). Dental caries was the most prevalent predisposing factor, particularly of the lower third molar teeth. Viridans Streptococci Group and Staphylococcus aureus were the most frequent bacterial isolates: 23.5% and 19.4%, respectively. All Viridans Streptococci isolates were resistant to penicillin G, sulfamethoxazole/trimethoprim (cotrimoxazole), ampicillin and tetracycline, but susceptible to vancomycin. All Staphylococcus aureus strains were resistant to cotrimoxazole and ampicillin while retaining susceptibility to vancomycin, cefotaxime, linezolid, moxifloxacin and amoxicillin/clavulanate. Thirty five (26.9%) patients were HIV infected and the HIV status did not significantly influence the pattern of odontogenic infection. CONCLUSIONS: Dental caries was the most prevalent predisposing factor for pyogenic odontogenic infection. High prevalence of bacterial resistance to ampicillin and cotrimoxazole suggests the need for regular antibiotic susceptibility tests of isolates and rational use of antibiotics in the management of these infections. Prevention requires strengthening of oral health in the community.

[Apoptogenic activity of microbes-associants during Epstein-Barr virus infection].

AIM: Study apoptogenic activity of-microbes-associants during Epstein-Barr virus infection (EBVI) on the model of mice peritoneal macrophages in vitro. MATERIALS AND METHODS: Evaluation of apoptosis induced by bacteria isolated from EBVI patients was carried out by characteristic morphological changes of macrophages in smears stained by May-Grunwald with additional staining by Romanowsky-Giemsa. RESULTS: All the EBVI microbes-associants were established to have apoptogenic activity, however, the highest pathogenic potential was noted in Streptococcus pyogenes. CONCLUSION: The presence of apoptogenic activity in bacterial microflora accompanying EBVI against immune system cells could serve as means of their survival and be the pathogenetic basis for prolonged persistence in the organism.

Bacterial growth kinetics in ACD-A apheresis platelets: comparison of plasma and PAS III storage.

BACKGROUND: Our objective was to determine the growth kinetics of bacteria in leukoreduced apheresis platelets (LR-AP) in a platelet (PLT) additive solution (PAS; InterSol, Fenwal, Inc.) compared to LR-AP stored in plasma. STUDY DESIGN AND METHODS: Hyperconcentrated, double-dose LR-AP were collected from healthy donors with a separator (AMICUS, Fenwal, Inc.). LR-AP were evenly divided, InterSol was added to half (65% InterSol:35% plasma [PAS]), and PLTs in autologous plasma were used for a paired control (PL). Bacteria were inoculated into each LR-AP PAS/PL pair (0.5-1.6 colony-forming units [CFUs]/mL), and bacterial growth was followed for up to 7 days. Time to the end of the lag phase, doubling times, maximum concentration (conc-max), and time to maximum concentration (time-max) were estimated. RESULTS: Streptococcus viridans did not grow to detectable levels in either PAS or PL units. The other bacteria had no significant overall difference in the conc-max (p = 0.47) or time-max (p = 0.7) between PL and PAS LR-AP; PL had a 0.14 hours faster doubling rate (p = 0.023); and PAS had a 4.7 hours shorter lag time (p = 0.016). CONCLUSION: We observed that five index organisms will grow in LR-AP stored in a 35%:65% ratio of plasma to InterSol where initial bacterial concentrations are 0.5 to 1.6 CFUs/mL. The more rapid initiation of log-phase growth for bacteria within a PAS storage environment resulted in a bacterial concentration up to 4 logs higher in the PAS units compared to the plasma units at 24 hours, but with no difference in the conc-max. This may present an early bacterial detection advantage for PAS-stored PLTs.

Oral health of children with congenital heart disease following preventive treatment.

Congenital heart disease (CHD), abnormalities in the structural development of the heart, occurs in approximately 8:1000 live births. The causative microorganism for infective endocarditis in more than 60% of the patients with positive hemoculture of viridans streptococci (s.mutans, s.mitior) thus making it mandatory for these children to maintain their oral health. The present study assessed the oral health of children with congenital heart disease following preventive treatment. A total of 74 children with congenital heart disease were selected for the study with 30 healthy controls between the ages 5-16. The oral health was assessed by measuring the microbial counts, the OHI-S and the gingival indices. The data thus obtained were subjected to paired and unpaired t-test. Poor oral health was prevalent among these children of the study group as compared to the controls indicating a lack of sound knowledge of the maintenance of oral hygiene. Following preventive treatment the oral health improved considerably.

In vitro inferiority of ceftazidime compared with other beta-lactams for viridans group Streptococcus bacteremia in pediatric oncology patients: implications for antibiotic choices.

Viridans group Streptococcus (VGS) is a leading cause of bacteremia in pediatric oncology patients, primarily in children with acute myeloid leukemia or after hematopoietic stem cell transplantation. We retrospectively identified all positive blood cultures in oncology patients at the British Columbia Children's Hospital for a period of 54 months. VGS was the second most commonly isolated pathogen, present in 19% of all the positive blood cultures. Susceptibility analysis of 46 VGS isolates from that period was performed using the Etest method for penicillin, cefotaxime, ceftazidime, and piperacillin/tazobactam. The geometric mean minimal inhibitory concentration for ceftazidime was found to be 9 to 12-fold higher than for any other beta-lactam antibiotic. Penicillin resistance was of 13% with an additional 20% of samples with intermediate susceptibility. The study underscores the prevalence of VGS bacteremia in pediatric patients, especially with acute myeloid leukemia or postallogeneic hematopoietic stem cell transplantation, and the in vitro inferiority of ceftazidime compared with other beta-lactams in that context. We conclude that monotherapy with ceftazidime, or its use along with an aminoglycoside, is not an optimal therapy in pediatric oncology patients with febrile neutropenia.

Safety assessment of ProBiora3, a probiotic mouthwash: subchronic toxicity study in rats.

Streptococcus viridans are commensal bacteria that constitute a significant portion of the resident oral microflora. The objective of the present study is to investigate adverse effects, if any, of a blend of 3 natural strains, Streptococcus uberis KJ2, Streptococcus oralis KJ3, and Streptococcus rattus JH145 (probiotic mouthwash, ProBiora(3)). The blend is administered to rats orally once daily (5 days per week) at doses of 0, 10(6), or 10(9) colony-forming units of each strain for 14 weeks. No treatment-related adverse effects are observed in the physiological parameters during the study or in the evaluation of blood and tissue samples taken from the animals at the end. Results of an in vitro antibiotic susceptibility study demonstrate that all 3 ProBiora(3) strains are susceptible to commonly used therapeutic antibiotics. The results of these investigations reveal that the no-observed-adverse-effect level of the probiotic mouthwash is 2.16 x 10(9) colony-forming units per strain per kilogram of body weight per day, the highest dose used.

The clinical impact of patients with bloodstream infection with different groups of Viridans group streptococci by using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS).

The accuracy of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for identifying viridans group streptococcus (VGS) was improving. However, the clinical impact of identifying VGS had not been well recognized. Our study had comprehensively studied the clinical manifestations and outcome of VGS blood stream infection by using MALDI-TOF MS for identification.This retrospective study enrolled 312 adult patients with a monomicrobial blood culture positive for VGS. Blood culture was examined through MALDI-TOF MS.The most common VGS species were the Streptococcus anginosus group (38.8%) and Streptococcus mitis group (22.8%). Most species showed resistance to erythromycin (35.6%), followed by clindamycin (25.3%) and penicillin (12.5%). Skin and soft tissue infection and biliary tract infection were significantly related to S. anginosus group bacteremia (P = .001 and P = .005, respectively). S. mitis group bacteremia was related to infective endocarditis and bacteremia with febrile neutropenia (P = .005 and P < .001, respectively). Infective endocarditis was also more likely associated with S. sanguinis group bacteremia (P = .009). S. anginosus group had less resistance rate to ampicillin, erythromycin, clindamycin, and ceftriaxone (P = .019, <.001, .001, and .046, respectively). A more staying in intensive care unit, underlying solid organ malignancy, and a shorter treatment duration were independent risk factors for 30-day mortality. This study comprehensively evaluated different VGS group and their clinical manifestations, infection sources, concomitant diseases, treatments, and outcomes. Categorizing VGS into different groups by MALDI-TOF MS could help clinical physicians well understand their clinical presentations.

In vitro effects of commercial mouthwashes on several virulence traits of Candida albicans, viridans streptococci and Enterococcus faecalis colonizing the oral cavity.

Oral microbiota consists of hundreds of different species of bacteria, fungi, protozoa and archaea, important for oral health. Oral mycoses, mostly affecting mucosae, are mainly caused by the opportunistic pathogen Candida albicans. They become relevant in denture-wearers elderly people, in diabetic patients, and in immunocompromised individuals. Differently, bacteria are responsible for other pathologies, such as dental caries, gingivitis and periodontitis, which affect even immune-competent individuals. An appropriate oral hygiene can avoid (or at least ameliorate) such pathologies: the regular and correct use of toothbrush, toothpaste and mouthwash helps prevent oral infections. Interestingly, little or no information is available on the effects (if any) of mouthwashes on the composition of oral microbiota in healthy individuals. Therefore, by means of in vitro models, we assessed the effects of alcohol-free commercial mouthwashes, with different composition (4 with chlorhexidine digluconate, 1 with fluoride, 1 with essential oils, 1 with cetylpyridinium chloride and 1 with triclosan), on several virulence traits of C. albicans, and a group of viridans streptococci, commonly colonizing the oral cavity. For the study here described, a reference strain of C. albicans and of streptococci isolates from pharyngeal swabs were used. Chlorhexidine digluconate- and cetylpyridinium chloride-containing mouthwashes were the most effective in impairing C. albicans capacity to adhere to both abiotic and biotic surfaces, to elicit proinflammatory cytokine secretion by oral epithelial cells and to escape intracellular killing by phagocytes. In addition, these same mouthwashes were effective in impairing biofilm formation by a group of viridans streptococci that, notoriously, cooperate with the cariogenic S. mutans, facilitating the establishment of biofilm by the latter. Differently, these mouthwashes were ineffective against other viridans streptococci that are natural competitors of S. mutans. Finally, by an in vitro model of mixed biofilm, we showed that mouthwashes-treated S. salivarius overall failed to impair C. albicans capacity to form a biofilm. In conclusion, the results described here suggest that chlorhexidine- and cetylpyridinium-containing mouthwashes may be effective in regulating microbial homeostasis of the oral cavity, by providing a positive balance for oral health. On the other side, chlorhexidine has several side effects that must be considered when prescribing mouthwashes containing this molecule.

Acetaldehyde production from ethanol by oral streptococci.

Alcohol is a well documented risk factor for upper digestive tract cancers. It has been shown that acetaldehyde, the first metabolite of ethanol is carcinogenic. The role of microbes in the production of acetaldehyde to the oral cavity has previously been described in several studies. In the present study, the aim was to investigate the capability of viridans group streptococci of normal oral flora to produce acetaldehyde in vitro during ethanol incubation. Furthermore, the aim was to measure the alcohol dehydrogenase (ADH) activity of the bacteria. Eight clinical strains and eight American Type Culture Collection (ATCC) strains of viridans group streptococci were selected for the study. Bacterial suspensions were incubated in two different ethanol concentrations, 11 mM and 1100 mM and the acetaldehyde was measured by gas chromatography. ADH-activity was measured by using a sensitive spectroscopy. The results show significant differences between the bacterial strains regarding acetaldehyde production capability and the detected ADH-activity. In particular, clinical strain of Streptococcus salivarius, both clinical and culture collection strains of Streptococcus intermedius and culture collection strain of Streptococcus mitis produced high amounts of acetaldehyde in 11 mM and 1100 mM ethanol incubation. All these four bacterial strains also showed significant ADH-enzyme activity. Twelve other strains were found to be low acetaldehyde producers. Consequently, our study shows that viridans group streptococci may play a role in metabolizing ethanol to carcinogenic acetaldehyde in the mouth. The observation supports the concept of a novel mechanism in the pathogenesis of oral cancer.

Effects of tigecycline, linezolid and vancomycin on biofilms of viridans streptococci isolates from patients with endocarditis.

BACKGROUND: Endocarditis, and prosthetic valve endocarditis in particular, is a serious disease with high morbidity and mortality. We investigate the effects of tigecycline, linezolid and vancomycin on biofilms of viridans group streptococci (VGS) isolated from patients with definite native or prosthetic valve endocarditis. METHODS AND RESULTS: Ten of 20 VGS blood stream isolates from patients with endocarditis formed biofilms in the microtiter plate biofilm model. The minimal inhibitory concentrations (MIC) for tigecycline, linezolid and vancomycin were determined using the microdilution broth method. Biofilms were grown for 24 hours and were incubated with tigecycline, linezolid and vancomycin at increasing concentrations from 1-128x MIC of the isolate being tested. Biofilm thickness was quantified by measuring the optical density (OD) after dyeing it with crystal violet. The incubation of the biofilms with tigecycline, linezolid or vancomycin resulted in a significant reduction of OD compared to the control biofilm without antibiotic (p<0.05). The optical density ratio (Odr) decreased significantly at 2x MIC for tigecycline, and at 8x MIC for linezolid and vancomycin (p<0.05). Although biofilms persisted even at the highest antibiotic concentrations of 128x MIC, bacterial growth was eradicated starting at concentrations of 16x MIC for vancomycin and of 32x MIC for linezolid, but not for tigecycline, up to a concentration of 128x MIC. CONCLUSIONS: In the present study on viridans streptococci isolated from patients with endocarditis, tigecycline and linezolid reduced the density of the biofilms as effectively as vancomycin. However, linezolid and vancomycin were bactericidal at higher concentrations. Linezolid and vancomycin at very high doses may be useful in the treatment of biofilm-associated diseases caused by VGS infections.

[Influence of penicillin minimum inhibitory concentration in the synergy between penicillin and gentamicin in viridans-group streptococci]. / Influencia de la concentración inhibitoria mínima de penicilina en la acción sinérgica de su combinación con gentamicina frente a estreptococos del grupo viridans.

Penicillin resistance rates higher than 60% have been recorded in viridans group streptococci by some authors during the 90's and recently such resistance was associated with higher levels of mortality in bacteremia. The lowest minimum inhibitory concentration of penicillin for which synergy with aminoglycosides is not yet possible is still unknown. In order to try to dilucidate this puzzle, a study on the susceptibility to penicillin of 28 strains of viridans group streptococci isolated from significant samples in the Hospital de Pediatría "Prof. Dr. Juan P. Garrahan" was carried out. Seven mitis group isolates presenting different susceptibility patterns were selected for performing time-killing curves with penicillin, gentamicin, and penicillin plus gentamicin, using higher and lower penicillin concentrations than their minimal inhibitory concentrations. Synergy was not observed when the penicillin concentration was lower than the minimum inhibitory concentration, at least in these strains with minimum inhibitory concentrations of gentamicin > or = 16 microg/ml. When using penicillin in higher concentrations than the minimum inhibitory concentration, synergy was found in five of the seven strains. Aminoglycoside-modifying enzymes were found in the two other streptococci.

Viridans group streptococcal infections among children with cancer and the importance of emerging antibiotic resistance.

Viridans group streptococci (VGS) are major pathogens among children with cancer or receiving hematopoietic stem cell transplantation and are associated with considerable morbidity and mortality rates. The incidence and severity of VGS infections have increased during the past 15 years and account for as many as one third of all bacteremic episodes. Risk factors include severe neutropenia, mucositis, gastrointestinal toxicity, pneumonia, younger age, and high-intensity chemotherapy (especially cytosine arabinoside). VGS no longer can be assumed to be susceptible to penicillin because as many as 37 percent of VGS isolates harbor high levels of resistance (minimum inhibitory concentration >4 microg/mL). Furthermore, resistance to multiple classes of antibiotics, including beta-lactams and fluoroquinolones, has now been documented and is increasing in prevalence. In this article, we present a brief overview of VGS, describe the clinical spectrum of VGS-related diseases in children with cancer, and review the recent data regarding the incidence, clinical significance, and management of emerging antibiotic resistance among VGS.

Oral bacteria resistant to mercury and to antibiotics are present in children with no previous exposure to amalgam restorative materials.

Dental plaque from 76 children without amalgam restorations was screened for bacteria resistant to mercuric chloride. Seventy-one per cent of the children harboured mercury-resistant oral bacteria and the median percentage of the total oral microflora resistant to mercuric chloride was 0.007% (range 0-5.3%). Eighty-seven mercury-resistant bacteria were isolated and 86% of these were streptococci with Streptococcus mitis predominating. Sixty per cent of the mercury-resistant isolates were also resistant to at least one of the four antibiotics tested (penicillin, ampicillin, erythromycin and tetracycline) with resistance to tetracycline (40% of isolates) most frequently encountered.

Is hydrogen peroxide responsible for the inhibitory activity of alpha-haemolytic streptococci sampled from the nasopharynx?

OBJECTIVE: The inhibitory effect of alpha-haemolytic Streptococci (AHS) in vitro on the three commonest otitis media pathogens, Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, was previously investigated. The aim of this study was to determine the mechanism of this inhibitory activity. MATERIAL AND METHODS/RESULTS: When fractions of AHS filtrate were assayed to determine their inhibitory activity after size-exclusion chromatography, the inhibitory activity was found in the fractions with a low molecular weight. The inhibitory effect was completely reversed when catalase was added to the cell-free filtrate of AHS. A quantitative method also revealed high production (approximately 3 mmol/l) of hydrogen peroxide in the AHS filtrate with the best inhibitory activity. Electron microscopy of bacteria exposed to AHS filtrate with an inhibitory effect showed changes similar to bacteria exposed to hydrogen peroxide. CONCLUSIONS: We conclude that the inhibitory effect of AHS is most likely due to the production of hydrogen peroxide. The significance of hydrogen peroxide production of AHS is discussed in relation to the non-specific and specific mucosal defence systems.

Influence of the probiotic Streptococcus salivarius strain M18 on indices of dental health in children: a randomized double-blind, placebo-controlled trial.

The prevalence of dental caries continues to increase, and novel strategies to reverse this trend appear necessary. The probiotic Streptococcus salivarius strain M18 offers the potential to confer oral health benefits as it produces bacteriocins targeting the important cariogenic species Streptococcus mutans, as well as the enzymes dextranase and urease, which could help reduce dental plaque accumulation and acidification, respectively. In a randomized double-blind, placebo-controlled study of 100 dental caries-active children, treatment with M18 was administered for 3 months and the participants were assessed for changes to their plaque score and gingival and soft-tissue health and to their salivary levels of S. salivarius, S. mutans, lactobacilli, ß-haemolytic streptococci and Candida species. At treatment end, the plaque scores were significantly (P = 0.05) lower for children in the M18-treated group, especially in subjects having high initial plaque scores. The absence of any significant adverse events supported the safety of the probiotic treatment. Cell-culture analyses of sequential saliva samples showed no differences between the probiotic and placebo groups in counts of the specifically enumerated oral micro-organisms, with the exception of the subgroup of the M18-treated children who appeared to have been colonized most effectively with M18. This subgroup exhibited reduced S. mutans counts, indicating that the anti-caries activity of M18 probiotic treatments may be enhanced if the efficiency of colonization is increased. It was concluded that S. salivarius M18 can provide oral health benefits when taken regularly.

Euthermic endocarditis.

BACKGROUND: Most patients with infective endocarditis (IE) manifest fever. Comparison of endocarditis patients with and without fever, and whether the lack of fever in IE is a marker for poorer outcomes, such as demonstrated in other severe infectious diseases, have not been defined. METHODS AND RESULTS: Cases from the Mayo Clinic, Rochester, Minnesota, Division of Infectious Diseases IE registry, a single-center database that contains all cases of IE treated at our center. Diagnosis date between 1970 and 2006, which met the modified Duke criteria for definite endocarditis, without fever was included. There were 240 euthermic endocarditis cases included in this analysis, with 282 febrile controls selected by frequency matching on gender and decade of diagnosis. Euthermic patients had a median age of 63.6 years (± 16.1) as compared to 59.0 years (± 16.4) in the febrile control group (p=0.001). Median (IQR) symptom duration prior to diagnosis was 4.0 (1.0, 12.0) weeks in the euthermic group compared to 3.0 (1.0, 8.0) weeks in the febrile controls (p= 0.006). From unadjusted analyses, survival rates were 87% in euthermic cases versus 83% in febrile controls across 28-day follow-up (p=0.164), and 72% in euthermic group cases versus 69% in febrile controls across 1-year follow-up (p=0.345). Also unadjusted, the 1-year cumulative incidence rate of valve surgery was higher in euthermic cases versus febrile controls (50% vs. 39%, p= 0.004). CONCLUSIONS: Patients with euthermic endocarditis are older, and lack of fever was associated with longer symptom duration and delayed diagnosis prior to IE diagnosis. Despite a higher unadjusted rate of valve surgery in euthermic patients, the result was not significant when adjusting for baseline confounders. Differences in survival rates at both 28-days and 365-days were not statistically significant between the two groups.

Antibacterial activity of yoghurt against viridans streptococci in vitro.

OBJECTIVE: Yoghurt consumption leads to a selective decrease in the oral level of mutans streptococci. It is not clear whether this decrease is due to the bactericidal activity of yoghurt or other mechanisms. The present study investigated the differences in susceptibility to yoghurt between several strains of viridans streptococci. DESIGN: The sources of variation were minimised, at the expense of the external validity of the study, using culture collection strains. Each strain was tested separately on five occasions in planktonic form and logarithmic growth phase. Two strains of each of the following Streptococcus species were tested: mutans, sobrinus, gordonii, oralis, parasanguinis and sanguinis. One millilitre [10(8) colony-forming units (cfu)] of each strain was incubated (37 degrees C, 60min) with 9mL of fat-free plain yoghurt containing Streptococcus thermophilus and Lactobacillus bulgaricus (10(8) and 10(7)cfu/g, respectively) in gently vortexed tubes. Survival rates were calculated every 15min by dividing the number of viable cells, obtained using conventional laboratory procedures, by the baseline number. RESULTS: Survival rates were 8% (S. mutans 6519T), 12% (S. mutans 31738), 35% (S. oralis 25671) and >50% (all other species tested) after 15min, and 0.01% (S. mutans) and >10% (all other species tested) after 30min. Overall, S. parasanguinis and S. sobrinus were the most resistant species. When heat-treated yoghurt (<10cfu/g bacteria and inactivated bacteriocins) was used, this antibacterial activity was not found. CONCLUSION: In vitro, yoghurt with live bacteria showed selective anti-mutans activity, suggesting that the overall decrease in mutans streptococci in vivo could be due to a bactericidal effect on S. mutans but not on S. sobrinus.

Viridans streptococci in endocarditis and neutropenic sepsis: biofilm formation and effects of antibiotics.

OBJECTIVES: Viridans group streptococci (VGS) are a frequent cause of bacterial endocarditis or sepsis in patients with neutropenia. Endocarditis in particular, is associated with plaque formation on the endocardium and valve leaflets whereas VGS septicaemia in neutropenic patients is caused by the influx of oral flora bacteria through mucositic lesions. This study examined the in vitro potency for biofilm formation of clinical VGS bloodstream isolates, and the effects of antibiotics on these biofilms. METHODS: During the years 1998-2000, 40 VGS bloodstream isolates from 18 patients with endocarditis and 22 patients with severe sepsis and neutropenia were collected. The MICs of penicillin, teicoplanin and moxifloxacin were determined using the microdilution broth method according to NCCLS criteria. Biofilms were grown in microtitre plates, dyed with Crystal Violet, and the mean optical density (OD) was used for quantification. Biofilms were incubated with penicillin, teicoplanin and moxifloxacin at various concentrations starting with the MICs for the respective isolates tested. RESULTS: Isolates from eight out of 18 patients with endocarditis and six out of 22 patients with neutropenia formed biofilms (not significant). For the 14 isolates, the MIC(90)s (range) of penicillin, teicoplanin and moxifloxacin were 0.5 mg/L (0.001-0.5), 0.125 mg/L (0.025-0.125) and 0.5 mg/L (0.05-0.5), respectively. Generally, biofilms persisted although incubated with the antibiotics up to concentrations of 128 x MIC. However, the ODs of biofilms after incubation with an antibiotic were significantly lower than the ODs of biofilms without antibiotic (P<0.05). A significant decrease in the biofilms with increasing antibiotic concentrations was observed for teicoplanin and moxifloxacin, but not for penicillin G. CONCLUSIONS: VGS isolated from patients with endocarditis and patients with sepsis and neutropenia form biofilms. Biofilms persist even when exposed to antibiotics at concentrations up to 128 x MIC. Nevertheless, teicoplanin and moxifloxacin reduced the density of the biofilms at concentrations >/=16 x MIC. Thus, testing the effects of antibiotics on biofilms may supply useful information in addition to standard in vitro testing, particularly in diseases where biofilm formation is involved in the pathogenesis.

Accuracy of phenotypic and genotypic testing for identification of Streptococcus pneumoniae and description of Streptococcus pseudopneumoniae sp. nov.

We have identified an unusual group of viridans group streptococci that resemble Streptococcus pneumoniae. DNA-DNA homology studies suggested that a subset of these isolates represent a novel species that may be included in the S. oralis-S. mitis group of viridans group streptococci. We suggest that this novel species be termed Streptococcus pseudopneumoniae. A combination of phenotypic and genetic reactions allows its identification. S. pseudopneumoniae strains do not have pneumococcal capsules, are resistant to optochin (inhibition zones, less than 14 mm) when they are incubated under an atmosphere of increased CO2 but are susceptible to optochin (inhibition zones, >14 mm) when they are incubated in ambient atmospheres, are not soluble in bile, and are positive by the GenProbe AccuProbe Pneumococcus test. The bile solubility test is more specific than the optochin test for identification of S. pneumoniae. Genetic tests for pneumolysin (ply) and manganese-dependent superoxide dismutase (sodA) and identification tests with a commercial probe, AccuProbe Pneumococcus, do not discriminate between the new species and S. pneumoniae.