Viridans Species Research Articles

The Effect of Oral Microbiota on the Severity and Prognosis of Stroke

The microbiome of the oral cavity plays an important role in the development and progression of various somatic diseases, including stroke. Studies show that bacteria living in the oral cavity can enter the bloodstream and contribute to inflammatory processes, which increases the risk of cardiovascular disease and stroke. It was found that in 79% of the studied stroke-related blood clots, DNA of bacteria commonly found in the oral cavity, such as streptococci of the Viridans species, was found. Periodontal pathogenic microorganisms can cause chronic inflammation and contribute to the development of atherosclerosis, which is one of the main risk factors for stroke. Dysbiosis of the oral cavity is also associated with an increase in the level of proinflammatory cytokines, which can worsen the condition of blood vessels and increase the likelihood of thrombosis. Thus, maintaining oral health and timely treatment of dental diseases can have a significant impact on reducing the risk of stroke. Understanding the relationship between the oral microbiome and the state of the cardiovascular system opens up new horizons for the development of preventive measures and therapeutic approaches to the treatment of patients at high risk of stroke.

Caries assessment and salivary microbial analysis in patients diagnosed with mucopolysaccharidosis.

Mucopolysaccharidosis (MPS) is a group of lysosomal storage disorders that cause the deposition of polysaccharides in cells. This causes systemic and oral manifestations, which can be observed clinically and radiographically. The present study aimed to assess dental caries, the effect of salivary pH, and the change of microflora on teeth in patients diagnosed with MPS. The study included children affected with mucopolysaccharidosis (n = 50) and healthy children (n = 50) in the control group between 3 and 15 years of age. The pH of saliva and decayed, missing, and filled teeth/decayed extracted and filled teeth index were noted and recorded. For the microbial analysis, saliva was inoculated into blood agar, MacConkey agar, Candida CHROMagar, and Mitis Salivarius agar, then inspected for colony-forming units, which were counted and recorded based on the colony characteristics and gram staining. Intergroup comparison of the test parameters was done using the Mann-Whitney test. P < 0.05 was considered statistically significant. The results showed significantly higher total microbial load (P = 0.00008), streptococcus viridans species (P = 0.00001), and Candida species (P = 0.0038) in the study group. The caries incidence was also higher in the study group for both primary (P = 0.0096) and permanent dentition (P = 0.0251), and salivary pH was more acidic (P = 0.00001) in the patients diagnosed with MPS. Patients diagnosed with MPS have a higher microbial load, more acidic saliva, and subsequently, a higher caries incidence than normal healthy children. Hence, regular dental evaluation, prevention, and treatment must be integrated into their health-care regimen.

Long-term outcomes of mitral valve endocarditis: improved survival through collaborative management.

Infective endocarditis (IE) of the mitral valve is an illness associated with significant morbidity and mortality. We describe the long-term outcomes of mitral valve endocarditis at a single centre. All patients who presented with IE to the study institution between 2000 and 2015 were included. Data were obtained by retrospective review of the medical records. There were 163 patients who presented with mitral valve IE. Mean age was 58 ± 16.8 years. A history of intravenous drug use was present in 18% (30/163) of patients. The most common infective agents were Staphylococcus aureus in 42% (69/163) (7% (5/69) were methicillin resistant), Streptococcus viridans species in 15% (25/163) and Enterococcus faecalis in 10% (17/163). Surgery was performed in 29% (47/163) of patients. Hospital mortality was 23% (38/163). Survival was 71% (95% confidence interval (CI) 63.1-77.6%) at 1 year, 56% (95% CI 46.0-64.9%) at 5 years and 44% (95% CI 36.4-59.7%) at 10 years follow-up. There was no survival difference between medical and surgical management (P = 0.55). On multivariate Cox regression analysis, need for renal replacement therapy (P = 0.003) and increasing age (P = 0.014) were found to be risk factors while infectious diseases consult during index admission (P = 0.007) was found to be protective. Mitral valve endocarditis is associated with survival of <50% at 10 years follow-up. Surgical and medical management were associated with similar outcomes. Increasing age and need for renal replacement therapy were associated with mortality, and infectious diseases consultation was associated with improved survival.

Microbiological Spectrum and Antibiotic Sensitivity in Endophthalmitis: A 25-Year Review

To identify the spectrum and susceptibility pattern of pathogens responsible for culture-positive endophthalmitis referred to a single institution and investigate possible trends in both pathogens and antibiotic sensitivities over the past 25 years. A retrospective, laboratory-based study of consecutive microbiological isolates. A total of 988 consecutive culture-positive endophthalmitis isolates from 911 eyes. All culture-positive endophthalmitis isolates collected from 1987 to 2011 were identified. Susceptibility rates to a variety of antibiotics were calculated. Chi-square test for trend was used to detect changes in spectrum or susceptibility over time. Microbial spectrum and susceptibility pattern over time. A total of 988 isolates were identified from 911 eyes. The average patient age was 67 ± 18 years, and 55% of the patients were female. The most prevalent pathogens were coagulase-negative staphylococcus (39.4%), followed by Streptococcus viridans species (12.1%) and Staphylococcus aureus (11.1%). Gram-negative organisms and fungi accounted for 10.3% and 4.6% of all isolates, respectively. With the exception of 2 isolates, Enterococcus faecium and Nocardia exalbida, all the other 725 (99.7%) gram-positive bacteria tested were susceptible to vancomycin. Of the 94 gram-negative organisms tested against ceftazidime, 2 were of intermediate sensitivity and 6 were resistant. For 8 antibiotics, increasing microbial resistance over time was observed: cefazolin (P = 0.02), cefotetan (P = 0.006), cephalothin (P<0.0001), clindamycin (P = 0.04), erythromycin (P<0.0001), methicillin/oxacillin (P<0.0001), ampicillin (P = 0.01), and ceftriaxone (P = 0.006). For 3 antibiotics, increasing microbial susceptibility was observed: gentamicin (P<0.0001), tobramycin (P = 0.005), and imipenem (P<0.0001). Coagulase-negative staphylococcus remains the most frequently identified cause of endophthalmitis. Vancomycin and ceftazidime seem to be excellent empiric antibiotics for treating endophthalmitis. Although a statistically significant trend toward increasing microbial resistance against a variety of antibiotics, including cephalosporins and methicillin, was observed, a significant trend toward decreasing microbial resistance against aminoglycosides and imipenem also was detected.

Antimicrobial, anticancer and DNA binding studies of transition metal(II) complexes containing 2-phenyl-4-selenazole carboxylic acid

Three novel transition metal complexes [ML2(phen)]·H2O (M= Mn, Co, Zn; HL= C10H7O2NSe, 2-phenyl-4-selenazole carboxylic acid, phen= 1,10-phenanthroline) 1∼3 were synthesized and characterized by elemental analysis, IR spectra. Their crystal structures were deterimined by single-crystal X-ray diffraction method. The antibacterial activities of the complexes against five species of bacteria, Escherichia coli (E. coli), Staphylococcus epidermidis (S. epidermidis), Staphylococcus aureus (S. aureus), Acinetobacter baumanii (A. baumanii) and Streptococcus viridans (S. viridans), were tested respectively. The anticancer activities of the complexes against human pancreatic cancer line PANC-28 and human hepatocarcinoma line HuH7 were also studied. The interactions between the complexes and DNA were studied by ethidium bromide (EB) fluorescent probe.

Assigning strains to bacterial species via the internet.

BackgroundMethods for assigning strains to bacterial species are cumbersome and no longer fit for purpose. The concatenated sequences of multiple house-keeping genes have been shown to be able to define and circumscribe bacterial species as sequence clusters. The advantage of this approach (multilocus sequence analysis; MLSA) is that, for any group of related species, a strain database can be produced and combined with software that allows query strains to be assigned to species via the internet. As an exemplar of this approach, we have studied a group of species, the viridans streptococci, which are very difficult to assign to species using standard taxonomic procedures, and have developed a website that allows species assignment via the internet.ResultsSeven house-keeping gene sequences were obtained from 420 streptococcal strains to produce a viridans group database. The reference tree produced using the concatenated sequences identified sequence clusters which, by examining the position on the tree of the type strain of each viridans group species, could be equated with species clusters. MLSA also identified clusters that may correspond to new species, and previously described species whose status needs to be re-examined. A generic website and software for electronic taxonomy was developed. This site allows the sequences of the seven gene fragments of a query strain to be entered and for the species assignment to be returned, according to its position within an assigned species cluster on the reference tree.ConclusionThe MLSA approach resulted in the identification of well-resolved species clusters within this taxonomically challenging group and, using the software we have developed, allows unknown strains to be assigned to viridans species via the internet. Submission of new strains will provide a growing resource for the taxonomy of viridans group streptococci, allowing the recognition of potential new species and taxonomic anomalies. More generally, as the software at the MLSA website is generic, MLSA schemes and strain databases for other groups of related species can be hosted at this website, providing a portal for microbial electronic taxonomy.

Mef(A), mef(E) and a new mef allele in macrolide-resistant Streptococcus spp. isolates from Norway

To type mef genes in a nationwide collection of clinical isolates of Streptococcus pneumoniae and Streptococcus pyogenes as well as pharyngeal carrier strains of viridans streptococci in Norway. Erythromycin-resistant mef-positive multilocus sequence-typed (MLST) clinical isolates of S. pneumoniae (n = 36) and S. pyogenes (n = 12) from the National Surveillance Program for Antimicrobial Resistance (NORM) as well as viridans streptococci (n = 20) from healthy adults were included. PCR-amplified mef genes were initially discriminated by BamHI digestion. Selected mef genes from representatives of different sequence types (STs) of S. pneumoniae (n = 11) and S. pyogenes (n = 4), and viridans group streptococcal species (n = 8) were typed by sequencing and their strains examined for co-resistances. Hydropathy plots of different mef-encoded proteins were performed. A predominance of mef(A) was detected in S. pneumoniae (23/36) and S. pyogenes (9/12) due to the clonal spread of ST9 and ST39, respectively. mef(E) was the most widely distributed mef determinant occurring in nine different STs of S. pneumoniae and in four different viridans species. A new mef allele was identified in two STs of S. pyogenes. mef(E) is the most widely distributed mef determinant in Norwegian clinical strains of S. pneumoniae and pharyngeal carrier strains of various viridans streptococci. However, mef(A) is more prevalent in S. pneumoniae and S. pyogenes due to clonal spread. A new mef allele was found in two different STs of S. pyogenes.

Unintended Benefit to the Donor of Bacterial Screening of Platelets, Pheresis Donations.

Abstract Background: Our blood center began routine screening of Single Donor Platelets, Pheresis (SDP) for bacteria on December 15, 2003 using aerobic culture bottles with the BacT Alert® 3D System. SDP units are held a minimum of 24 hours prior to sampling and then are labeled and released while the culture bottles are incubated for five days. Case Study: A 77-year old female donated a SDP and concurrent Plasma. Pre-donation platelet count was 328 x103/μL and hemoglobin level was 15.0 g/dL. Collection was uneventful with no error codes received from the equipment. Sample for was obtained on day-1, inoculated in an aerobic culture bottle, and incubated. The inoculated bottle showed growth of bacteria at 19.6 hours of the culture period. SDP had not been distributed and was recultured. Repeat culture was performed on day-2 and it also showed growth at 13.4 hours. The concurrent plasma was thawed and cultured and did not show any growth. A gram stain of the positive culture bottle revealed gram-positive cocci in chains that were later identified as Streptococcus viridans. The donor was notified of the culture results. The donor denied any skin rash or infection, sore throat, fractures, heart or lung conditions. She denied fever, chills or any acute illness. Her chronic conditions included hypertension treated with Lisinopril. She was also receiving thyroid replacement for hypothyroidism and Asiphex for gastro esophageal reflux disease (GERD). She denied any GI or GU symptoms. The culture results were mailed to the donor so that she could share them with her personal physician. The donor is a frequent apheresis donor and has donated 54 SDPs over the past seven years. Three previous donations immediately prior to the current donation were found to be negative after 5-day culture. On day 18, the donor felt weak and tired but without fever or other symptoms and she went to see her physician. The physician obtained a blood culture that grew bacteria the next day. Further testing identified the organism as Streptococcus salivarius, a viridans species. Donor was then hospitalized for five days to begin intravenous Ceftriaxone. Further antibiotic treatment was given at home via a peripherally inserted central (PIC) line. The donor had a three-year history of a benign heart murmur. The PIC line was removed with the completion of the antibiotic treatment on day 65. The donor remained asymptomatic throughout the treatment. Two trans-thoracic and two trans-esophageal echocardiograms were negative for bacterial endocarditis. However, mild idiopathic hypertrophic subaortic stenosis was discovered. The donor had dental work done two months prior to the time the bacteremia was found. However, she had one SDP donation that was culture negative after the dental work. The cause of the donor’s bacteremia remains obscure. Discussion: Although the screening of Platelets, Pheresis is for the protection of the patient who will receive the product, this case shows that the detection of the bacteria also may benefit the donor. In our case, aymptomatic Streptococcus viridans bacteremia would not have been recognized if it were not detected by culturing her SDP. The donor was grateful for the information that lead to the early detection of blood stream infection that resulted in successful treatment. The donor continues to ask that she be able to donate when eligible.

Infective endocarditis: a diagnostic and therapeutic challenge for the new millennium.

This review on infective endocarditis (IE) is based on clinical studies carried out in Göteborg since 1984, data obtained from a Swedish national registry of IE since 1995 and existing literature. IE is still a great challenge in medicine, although improved bacteriological and echocardiographical techniques have facilitated diagnosis. In Sweden the incidence of IE is about 6 per 100,000 inhabitants a year. During recent decades IE has changed character. Patients are older, fever is often the only major symptom and a new murmur is less frequent. Streptococci, including viridans species and staphylococci, are still the most common bacteria found. Antibiotic treatment for 4-6 weeks may reduce mortality of IE to 30-50%. For further reduction, heart surgery is necessary in 20-25% of patients in order to remove infected tissues and restore valve function. Rapid diagnosis, careful antibiotic treatment and optimal surgery may reduce mortality associated with treatment to 10%. Antibiotic treatment is still mainly empiric. Penicillin and aminoglycoside for 2 weeks only seem to be effective in uncomplicated IE caused by alpha-streptococci. Otherwise, 4 weeks of treatment is needed, but aminoglycoside treatment may be reduced to 1 week in general and 2 weeks for enterococcal infections.

Growth of Viridans streptococci on human serum alpha1-acid glycoprotein.

Viridans streptococci have emerged as major opportunistic pathogens. We suggest that for these bacteria to proliferate in vivo and cause disease, they must utilize host tissue components. We have therefore examined the ability of all recognized species of viridans streptococci to liberate and utilize the constituent sugars of the glycans of the extensively sialylated human serum alpha1-acid glycoprotein (AGP) as the sole source of carbohydrate to support in vitro growth. Analysis of residual glycans following bacterial growth was performed by high-pH anion exchange chromatography with pulsed amperometric detection and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Only those species which produced sialidase-namely, Streptococcus oralis, S. intermedius, and S. defectivus--grew on AGP. The extent of degradation of glycans was dependent on the particular glycosidases produced by the bacteria. S. defectivus produced only a sialidase which released the terminal N-acetylneuraminic acid residues of the glycans, and the liberated sugar was utilized. S. intermedius also produced beta-galactosidase and beta-N-acetylglucosaminidase, which removed galactose and N-acetylglucosamine from desialylated glycans, all of which again were utilized by the organism. S. oralis produced beta-galactosidase, beta-N-acetylglucosaminidase, and alpha-fucosidase and novel alpha- and beta-mannosidases which were apparent only from the analysis of the residual sugars of AGP. S. oralis cleaved all the sugars from AGP except for 22% of the N-acetylglucosamine. The residual N-acetylglucosamine residues remaining were those linked to the asparagine of the peptide backbone. All the monosaccharides released by S. oralis from AGP, with the exception of fucose, were utilized. Sialidase production may be a key factor for growth of these species of viridans streptococci on glycoproteins in vivo, since they are commonly associated with extra-oral diseases, with S. oralis emerging as an important pathogen.

Utilization of sialic acid by viridans streptococci.

The importance of viridans streptococci as agents of serious extra-oral diseases, including endocarditis, is now recognized. We have tested the hypothesis that the ability to utilize sialic acid as a nutrient source may play a role in the proliferation of these organisms. The type strains of the 15 presently recognized species of viridans streptococci and two clinical isolates-S. oralis (AR3), isolated from a patient with infective endocarditis, and S. intermedius (UNS35), a brain abscess isolate-were studied for their ability to utilize sialic acid. Only S. oralis, S. sanguis, S. gordonii, S. mitis ("oralis group") S. intermedius, S. anginosus, S. constellatus ("milleri group"), and S. defectivus ("nutritionally variant group") were able to use sialic acid (N-acetylneuraminic acid) efficiently as a sole carbon source. Formate, acetate, and ethanol were produced as the major metabolic end-products of sialic acid metabolism, while corresponding glucose-grown cultures produced lactate as the major metabolic end-product. Utilization of sialic acid was independent of the production of sialidase. Cell-free extracts of sialic acid-grown cultures expressed elevated levels of N-acetylneuraminate pyruvate-lyase (NPL; the first enzyme in the intracellular catabolism of sialic acid) and N-acetylglucosamine-6-phosphate (GlcNAc-6-P) deacetylase and glucosamine-6-phosphate (GlcN-6-P) deaminase (enzymes involved in the intracellular catabolism of N-acetylglucosamine). These activities were repressed by growth in the presence of glucose. The intracellular fate of sialic acid, after cleavage by NPL into N-acetylmannosamine (ManNAc) and pyruvate, is uncertain, but the elevated levels of GlcNAc-6-P deacetylase and GlcN-6-P deaminase in sialic acid-grown cells suggest that phosphorylation and isomerization are possible steps in the metabolism of ManNAc to generate an intermediate common to the pathway of N-acetylglucosamine metabolism. The species of viridans streptococci that have the ability to utilize sialic acid are those most commonly associated with extra-oral diseases, and this ability is likely to play a role in the persistence and survival of these infecting organisms in vivo.

Streptococcus crista sp. nov., a Viridans Streptococcus with Tufted Fibrils, Isolated from the Human Oral Cavity and Throat

We studied strains of an unusual streptococcus that superficially resembles Streptococcus sanguis but has fibrils that are arranged in lateral tufts. These strains were originally isolated from human throats and oral cavities and have been referred to previously as "Streptococcus sanguis I," the "CR group," and the "tufted-fibril group." Until now, insufficient phenotypic data have been available to allow reliable differentiation of these strains from other viridans streptococcal species, particularly the species in the S. sanguis group. Recently, workers have proposed a scheme of phenetic tests that is based on 4-methylumbelliferyl-linked substrates and conventional biochemical tests and allows the tufted-fibril group to be differentiated; these organisms differ from other viridans species in being able to hydrolyze arginine but not esculin and in producing alpha-L-fucosidase but not beta-glucosidase or alkaline phosphatase. These data, together with the results of our DNA-DNA hybridization experiments and the unusual ultrastructure of the tufted-fibril strains as determined by electron microscopy, demonstrate that these organisms represent a new species, for which the name Streptococcus crista is proposed. The DNA base composition is 42.6 to 43.2 mol% G + C. The type strain is strain CR311 (= NCTC 12479).

Analysis of adherence of Streptococcus defectivus and endocarditis-associated streptococci to extracellular matrix

Pathogenesis of nutritionally variant streptococcal (NVS) endocarditis initiates with bacterial attachment to and colonization of the damaged heart valve surface. Underlying extracellular matrix (ECM) exposed to the environment during damage to cardiac endothelium provides additional receptors that could be involved in bacterial adherence. The ability of NVS and endocarditis-associated streptococci to bind ECM was investigated by using an enzyme-linked immunosorbent assay system that incorporated ECM secreted by baby hamster kidney and human umbilical vein endothelial cells in culture. Streptococcus defectivus, the major species isolated from NVS endocarditis cases, bound ECM of fibroblasts and endothelial cells, indicating that the ECM molecule involved in the binding was a common constituent of diverse matrices. The specific binding of S. defectivus to ECM was demonstrated by saturation binding and specific antibody inhibition studies. Of the 15 S. defectivus strains analyzed, 13 bound ECM, whereas Streptococcus adjacens and NVS serotype III strains were unable to bind the matrix. This selective binding suggested that S. defectivus binds to heart valves through a mechanism different from those of other NVS in subacute bacterial endocarditis. A survey of non-NVS streptococcal endocarditis isolates demonstrated that S. mutans, S. mitis, S. sanguis, and S. faecalis also bound ECM, whereas other viridans species were unable to bind the matrix.

Investigation of a Streptococcus viridans Pseudobacteremia Epidemic at a University Teaching Hospital

AbstractFor several months in 1986, an outbreak of Streptococcus viridans pseudobacteremia occurred at a large teaching hospital. All sources of laboratory blood culture contamination were excluded. A retrospective epidemiological study indicated that one phlebotomist, “P,” collected a disproportionate number of the positive blood cultures. Further comparison of the paired blood culture results from the three months when the incidence was highest revealed a good concordance of results among all other phlebotomists (Kappa = 0.5), while P's results concurred with others less frequently than would be expected even by chance (Kappa &lt; 0.0). Clinical follow-up showed that P did not routinely wear gloves while drawing blood and had eczema of the hands. Skin scrapings from the hands, right index finger/fingernail grew predominantly S viridans species that were compatible with those recovered from contaminated blood cultures. This epidemic demonstrated the need for early detection of this source as a cause of nosocomial pseudobacteremia.

Investigation of a Streptococcus viridans pseudobacteremia epidemic at a university teaching hospital.

For several months in 1986, an outbreak of Streptococcus viridans pseudobacteremia occurred at a large teaching hospital. All sources of laboratory blood culture contamination were excluded. A retrospective epidemiological study indicated that one phlebotomist, "P," collected a disproportionate number of the positive blood cultures. Further comparison of the paired blood culture results from the three months when the incidence was highest revealed a good concordance of results among all other phlebotomists (Kappa = 0.5), while P's results concurred with others less frequently than would be expected even by chance (Kappa less than 0.0). Clinical follow-up showed that P did not routinely wear gloves while drawing blood and had eczema of the hands. Skin scrapings from the hands, right index finger/fingernail grew predominantly S viridans species that were compatible with those recovered from contaminated blood cultures. This epidemic demonstrated the need for early detection of this source as a cause of nosocomial pseudobacteremia.

Multiple brain abscesses secondary to dental caries and severe periodontal disease

A case is reported in which an intra-oral focus of sepsis is thought to have resulted in the patient developing multiple brain abscesses without the presence of lung infection or cardiac valvular disease. The link between the two sites of infection is supported by the isolation of two Streptococcus viridans species normally associated with dental caries and periodontal disease. The management of multiple brain abscesses is discussed.

Nutritionally variant streptococci from corneal ulcers in horses.

Of 24 isolates of nutritionally variant streptococci recovered from equine corneal ulcers, 22 were tested for growth requirements, physiological and biochemical reactions, and susceptibility to different antimicrobial agents. Satisfactory growth was obtained by supplementing blood agar and Todd-Hewitt broth with pyridoxal hydrochloride, and all of the media for the culture and the biochemical testing were supplemented with 0.002% of this substance. Biochemical patterns of 12 of the isolates resembled those of two viridans streptococcal species, Streptococcus intermedius and Streptococcus constellatus. Patterns of 10 isolates did not resemble those of any recognized viridans species. All of the isolates were inhibited by less than or equal to 0.25 microgram of erythromycin per ml, less than or equal to 4 micrograms of chloramphenicol per ml, and less than or equal to 4 micrograms of gentamicin per ml, and all but two were inhibited by less than or equal to 0.1 microgram of penicillin per ml.

Evaluation of the Rapid Strep system for the identification of clinical isolates of Streptococcus species.

A total of 247 strains of streptococci isolated from humans were tested for identification in the Rapid Strep system. The identification rates and identification levels were different for each Streptococcus species. Our data indicate that the Rapid Strep system will identify nearly all the beta-hemolytic Streptococcus species if serological procedures are used in conjunction with the rapid physiological procedures. Of the group D streptococci, 98% of the enterococci and 95% of the non-enterococci were correctly identified. Of the commonly occurring viridans species, 85% were correctly identified, but only 10% of the less frequently occurring viridans species were identified. A total of 90% of the Streptococcus pneumoniae and 60% of the Aerococcus strains were correctly identified.

Exogenous thymidine and reversal of the inhibitory effect of sulfamethoxazole-trimethoprim on streptococci

The practice of using sulfamethoxazole-trimethoprim (SXT) for the selective isolation of Streptococcus pyogenes and as a taxonomic character in the presumptive identification of streptococci was applied to 17 strains of different groups of streptococci to determine their characteristic behaviour in the presence of exogenous thymidine. Streptococcus pyogenes, Streptococcus agalactiae and group D enterococci utilized thymidine, the first two species obtaining a maximum reversal of the inhibitory effect of SXT at thymidine concentrations of 1.2 micrograms/ml and 0.6 micrograms/ml or higher, respectively. For group D enterococci, the degree of reversal of the inhibitory effect was proportional to the thymidine concentration. In contrast, the four viridans species studied (Streptococcus sanguis I, Streptococcus salivarius, Streptococcus mitis and Streptococcus sanguis II) and Streptococcus pneumoniae were unable to utilize thymidine from an exogenous source and thus growth remained inhibited even at the highest concentrations of thymidine tested. For selective isolation and identification of streptococci only stable media with batch-to-batch consistency are recommended together with a known quantity of thymidine.

Antimicrobial Susceptibilities of Species of Viridans Streptococci

Sixty-three strains of viridans streptococci (12 strains of Streptococcus mutans, 12 of Streptococcus mitis, nine of Streptococcus sanguis type I, 12 of S. sanguis type II, 10 of Streptococcus MG-intermedius, and eight of Streptococcus anginosus-constellatus) were tested for susceptibility to 12 antibiotics by a microdilution method. The antibiotics tested were: penicillin, ampicillin, nafcillin, cephalothin, cefamandole, vancomycin, streptomycin, kanamycin, amikacin, netilmicin, gentamicin, and rifampin. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) extended over a 512-fold range. Penicillin G was the most active antimicrobial agent, with MICs of 0.06-4 /pg/ml and MBCs of 0.06->8 /Lg/ml. A concentration of 0.06 /g/ml was inhibitory and bactericidal, respectively, to 12 and 12 of the 12 strains of S. mutans, five and four of the 12 strains of S. mitis, nine and four of the nine strains of S. sanguis type I, nine and four of the 12 strains of S. sanguis type II, nine and four of the 10 strains of Streptococcus MG-intermedius, and six and two of the eight strains of S. anginosus-constellatus. The activity of ampicillin was similar to that of penicillin G, but cephalothin and cefamandole were less active; 0.125 and 0.5 /ug/ml, respectively, inhibited and killed 50% of the 63 strains. Vancomycin (1 Iug/ml) inhibited 54 and killed 19 strains. Gentamicin and netilmicin were the most active of the five aminoglycosides tested, but at a concentration of 8 pg/ml, they inhibited and killed, respectively, only 37% and 15% of the 63 strains. Rifampin (0.06 /pg/ml) inhibited 49 but killed only seven strains. In general, S. mitis and S. sanguis type II required higher concentrations of antibiotics for inhibition and killing than did the other species of viridans streptococci tested.