Mitis Group Research Articles

The Effect of Sampling Schedule on Assessment of Dietary Measures: Evidence From Blue Monkeys (Cercopithecus mitis stuhlmanni).

Accurately assessing primate diets is important in studies of behavioral ecology and evolution. While previous research has compared sampling methods (scan, focal), we examined how sampling schedule influences accuracy of dietary measures. We define sampling schedule as the combined distribution (random vs. consecutive) and frequency of sampling days within a given month. Under field conditions, time may be required to locate a study group, and we therefore also subtracted 1, 2, or 3 h from the beginning of all non-consecutive days in each sampling schedule to mimic observation time lost to search. From a dense (near daily) 5-year record of feeding behavior derived from focal animal follows of adult females in five wild blue monkey (Cercopithecus mitis) groups, we created data subsets matching various sampling schedules, and compared monthly dietary measures calculated from each subset to those based on the full data set. These measures included (1) the proportion of observation time feeding on fruit, (2) diet composition (three top-ranked food items), (3) species richness of plant diet, (4) Shannon-Wiener diversity index based on plant species, and (5) Holmes-Pitelka index expressing dietary overlap with the previous month. We used generalized linear mixed models to assess how frequency and sampling type (a combination of distribution and hours lost) relate to a subset's deviation from the full data set, where a smaller deviation (or higher chance of matching, for diet composition) implies greater accuracy. For all dietary measures, increasing observation frequency increased accuracy. The response to distribution varied among measures, but sampling types generally differed more at lower frequencies. Deviation varied widely within and between dietary measures, and some sampling schedules resulted in values with large percentage differences from the "full" data. Accordingly, when designing and comparing studies, researchers should consider how sampling schedules may influence the accuracy of the dietary measures of interest.

A novel LAMP-based assay for the identification of Streptococcus pneumoniae and Streptococcus pseudopneumoniae in clinical isolates.

The Gram-positive bacteria Streptococcus pneumoniae is part of the Streptococcus mitis group (SMG) and causes life-threatening infections, such as pneumonia, sepsis, and meningitis. The closely related Streptococcus pseudopneumoniae has recently been shown to cause respiratory tract infections, as well as invasive infections, especially in patients with comorbidities. Due to the genetic and phenotypic similarities of species belonging to the SMG, the identification of S. pneumoniae and S. pseudopneumoniae is difficult and unreliable using phenotypic tests, as well as matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and 16S rRNA sequencing. In this study, a loop-mediated isothermal amplification (LAMP)-based assay was developed using molecular markers specific for S. pneumoniae (SPN0001) and S. pseudopneumoniae (SPPN_RS10375). The LAMP assay was evaluated using a collection of SMG clinical isolates, concluding that the method provides a correct, reliable, and fast identification of both S. pneumoniae and S. pseudopneumoniae clinical isolates.

Infective endocarditis caused by penicillin-resistant viridans group streptococci: a series of nine cases from a Spanish cohort.

Infective endocarditis (IE) caused by viridans and gallolyticus group streptococci (VGS-GGS) resistant to penicillin (PEN-R; minimum inhibitory concentration ≥4 mg/L) is rare but poses therapeutic challenges. To describe the characteristics of patients with IE caused by PEN-R VGS-GGS, focusing on antimicrobial management. Retrospective analysis of a prospective cohort of definite IE caused by PEN-R VGS-GGS between 2008 and 2023 in 40 Spanish hospitals. We describe clinical characteristics, management and outcome of the cases, and compare them to IE caused by VGS-GGS with susceptibility or susceptibility with increased exposure to penicillin (PEN-I). We identified nine cases of PEN-R VGS-GGS IE in a cohort of 1563 streptococcal IE (0.58%). All isolates belonged to S. mitis group. Three cases died during hospitalization and no relapse occurred at 3 months of follow-up. Compared to cases with susceptibility or PEN-I, PEN-R showed a higher rate of mitral location (78% versus 51%), surgical indication (67% versus 51%), and in-hospital mortality (33% versus 12%). Most cases (86%) showed resistance to third-generation cephalosporins. The preferred antibiotic regimen was beta-lactam-based: ceftriaxone plus gentamicin, penicillin plus gentamicin, ceftriaxone plus levofloxacin, and ceftaroline plus daptomycin. Two cases received a combination of vancomycin plus gentamicin. Levofloxacin was used in two cases in combination with ceftriaxone or daptomycin. All patients that received cardiac surgery were cured at the end of follow-up. IE caused by PEN-R VGS-GGS was rare and only affected mitis group streptococci. Antibiotic combination including a beta-lactam seems to be effective in its management.

Clinicomicrobiological risk factors for infective endocarditis in viridans group streptococci bacteraemia.

When to perform echocardiography to rule out infective endocarditis (IE) in patients with viridans group streptococci (VGS) bloodstream infections (BSIs) is unclear. We aimed to identify independent risk factors for IE in patients with VGS BSI. This retrospective study conducted at Seoul National University Hospital from January 2013 to December 2022 involved patients with VGS and nutritionally variant streptococcal BSI, excluding single positive blood cultures and polymicrobial BSI cases. Independent risk factors were identified by multivariate logistic regression and sensitivity analyses according to echocardiography results, VGS species or the inclusion of possible IE cases. Of 845 VGS BSI cases, 349 were analysed and 86 IE cases were identified (24.6%). In the multivariate analysis, heart valve disease [adjusted odds ratio (aOR), 14.14, 95% CI, 6.14-32.58; P < 0.001], persistent bacteraemia (aOR, 5.12, 95% CI, 2.03-12.94; P = 0.001), age (per year, aOR, 0.98; 95% CI, 0.96-1.00; P = 0.015), solid cancer (aOR, 0.26; 95% CI, 0.13-0.53; P < 0.001) and haematologic malignancy (aOR, 0.04; 95% CI, 0.01-0.41; P = 0.006) were independently associated with IE. Sensitivity analyses yielded consistent results; also, infection by a member of the mitis group was independent risk factor for IE (aOR, 6.50; 95% CI, 2.87-14.68; P < 0.001). Younger age, heart valve disease, persistent bacteraemia, absence of underlying malignancy and BSI by a member of the mitis group were independent risk factors for IE in patients with VGS BSI. Echocardiographic evaluation could be prudently considered based on these clinicomicrobiological risk factors.

Ceftriaxone-resistant viridans streptococci bacteraemia among patients treated at a large comprehensive cancer care centre: a retrospective eighteen-year study.

Viridans streptococci (VS) are opportunistic oral commensals and a common cause of bacteraemia in neutropenic patients. In this retrospective single centre cohort study, we investigated the prevalence of ceftriaxone resistance in VS (CRO-R VS) blood isolates between January 2005 and December 2022 from patients treated at a tertiary care hospital. Blood culture isolates were identified using biochemicals and mass spectrometry. Susceptibility testing was performed by Kirby-Bauer and Epsilometer tests. Demographic data, clinical outcomes and antimicrobial use were assessed through electronic medical record review. Among 791 patients with VS bacteraemia, 31 (4%) had confirmed CRO-R VS bacteraemia over the 18-year period; 20/31 (65%) were patients also treated at the Fred Hutchinson Cancer Center and were the focus of this study. Of these 20 patients, 18 (90%) had a known haematologic malignancy; 14 (70%) had undergone haematopoietic cell transplant (HCT); 18 (90%) were neutropenic at the time of culture. Two (10%) patients died within 30 days of CRO-R VS bacteraemia. All the CRO-R isolates (20/20) were members of the Streptococcus mitis group, 12 were multi-drug resistant; all were susceptible to vancomycin. Most patients received vancomycin once blood cultures were positive for a Gram-positive organism. During the study period, the frequency of VS isolate susceptibility testing increased; however, there was no concomitant increase in the percentage of CRO-R isolates at our facility. These data are important in an era where cefepime monotherapy is often used and reinforces the importance of routine resistance testing among VS bacteraemia.

Predictors of Mortality of Streptococcal Bacteremia and the Role of Infectious Diseases Consultation: A Retrospective Cohort Study.

Streptococcal bacteremia is associated with high mortality. Thia study aims to identify predictors of mortality among patients with streptococcal bacteremia. This retrospective study was conducted at the Lausanne University Hospital, Switzerland, and included episodes of streptococcal bacteremia among adult patients from 2015 to 2023. During the study period, 861 episodes of streptococcal bacteremia were included. The majority of episodes were categorized in the Mitis group (348 episodes; 40%), followed by the Pyogenic group (215; 25%). Endocarditis was the most common source of bacteremia (164; 19%). The overall 14-day mortality rate was 8% (65 episodes). The results from the Cox multivariable regression model showed that a Charlson comorbidity index >4 (P .001; hazard ratio [HR], 2.87; confidence interval [CI]: 1.58-5.22), Streptococcus pyogenes (P = .011; HR, 2.54;CI: 1.24-5.21), sepsis (P < .001; HR, 7.48; CI: 3.86-14.47), lower respiratory tract infection (P = .002; HR, 2.62; CI: 1.42-4.81), and absence of source control interventions within 48 hours despite being warranted (P = .002; HR, 2.62; CI: 1.43-4.80) were associated with 14-day mortality. Conversely, interventions performed within 48 hours of bacteremia onset, such as infectious diseases consultation (P < .001; HR, 0.29; CI: .17-.48) and appropriate antimicrobial treatment (P < .001; HR, .28; CI: .14-.57), were associated with improved outcome. Our findings underscore the pivotal role of infectious diseases consultation in guiding antimicrobial treatment and recommending source control interventions for patients with streptococcal bacteremia.

Accurate identification of Streptococcus pseudopneumoniae and other mitis group Streptococci identified as atypical Streptococcus pneumoniae in Tunisian pediatric population.

Accurate identification of Mitis group streptococci especially Streptococcus pneumoniae and Streptococcus pseudopneumoniae seems difficult due to the lack of specific and sensitive tests. We performed an approach for the identification of atypical pneumococci in pediatric Tunisian population. In this study, 49 streptococcal isolates that were considered as atypical S. pneumoniae were analyzed by: optochin susceptibility in ambient and 5% CO2 atmosphere, oxgall disk sensitivity, PCR targeting several genes and antimicrobial susceptibility.The combined results of biochemical and molecular methods showed the presence of 23 S. pneumoniae, 7 S. pseudopneumoniae, and 19 other mitis group. Among S. pseudopneumoniae, all isolates were collected from respiratory tract samples and showed a high level of resistance to β-lactams with a MIC90 of 32 mg L-1. Two isolates of S. pseudopneumoniae showed the typical phenotype of optochin resistance described in the literature. All isolates could be identified only by molecular tests. Among Streptococcus pneumonaie, all strains harbored the lytA gene and the Spn9802 fragment. But only 14 strains were encapsulated.This study describes several assays for the identification of atypical pneumococci in order to gain insights on the nature of isolate and raise alert about the presence of these strains in the pediatric Tunisian community.

Performance assessment of the Bruker Biotyper MALDI-TOF MS for the identification of difficult-to-identify viridans group streptococci.

Differentiating Streptococcus pneumoniae among nonpneumococcal viridans group streptococci (VGS) is challenging in conventional laboratories. Therefore, we aimed to evaluate the performance of the latest Bruker Biotyper matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) system in identifying VGS by comparing the results to those of the specific gene sequencing approach. Clinical isolates were initially identified using the BD Phoenix system to identify Streptococcus species. The optochin test was used to distinguish nonpneumococcal VGS from S. pneumoniae. The species of individual reference strains and clinical isolates were determined by comparing the sequences of the 16S rDNA, gyrB, sodA, groESL, or coaE genes with those in the GenBank sequence databases. We evaluated the performance of the Bruker Biotyper MALDI-TOF MS in VGS identification using two different machines with three databases. We collected a total of 103 nonpneumococcal VGS and 29 S. pneumoniae blood isolates at a medical center in northern Taiwan. Among these isolates, only seven could not be identified at the species level by the specific gene sequencing approach. We found that none of the nonpneumococcal VGS isolates were misidentified as pneumococci by the latest Biotyper system, and vice versa. However, certain strains, especially those in the mitis and bovis groups, could still not be correctly identified. The latest Bruker Biotyper 4.1 (DB_10833) showed significant improvement in identifying VGS strains. However, a specific gene sequencing test is still needed to precisely differentiate the species of strains in the mitis and bovis groups.

The Distribution of Eight Antimicrobial Resistance Genes in Streptococcus oralis, Streptococcus sanguinis, and Streptococcus gordonii Strains Isolated from Dental Plaque as Oral Commensals.

It has been proposed that oral commensal bacteria are potential reservoirs of a wide variety of antimicrobial resistance genes (ARGs) and could be the source of pathogenic bacteria; however, there is scarce information regarding this. In this study, three common streptococci of the mitis group (S. oralis, S. sanguinis, and S. gordonii) isolated from dental plaque (DP) were screened to identify if they were frequent reservoirs of specific ARGs (blaTEM, cfxA, tetM, tetW, tetQ, ermA, ermB, and ermC). DP samples were collected from 80 adults; one part of the sample was cultured, and from the other part DNA was obtained for first screening of the three streptococci species and the ARGs of interest. Selected samples were plated and colonies were selected for molecular identification. Thirty identified species were screened for the presence of the ARGs. From those selected, all of the S. sanguinis and S. oralis carried at least three, while only 30% of S. gordonii strains carried three or more. The most prevalent were tetM in 73%, and blaTEM and tetW both in 66.6%. On the other hand, ermA and cfxA were not present. Oral streptococci from the mitis group could be considered frequent reservoirs of specifically tetM, blaTEM, and tetW. In contrast, these three species appear not to be reservoirs of ermA and cfxA.

Evaluation of Immulex S. pneumoniae Omni test for the direct detection of S. pneumoniae from positive blood cultures

Rapid and early identification of Streptococcus pneumoniae from positive blood cultures is crucial for the management of patients with bloodstream infections (BSI). Many identification systems in microbiology laboratories have difficulty differentiating S. pneumoniae from other closely related species in the Streptococcus mitis group. To overcome this limitation, we developed a rapid workflow in our laboratory combining direct MALDI-TOF MS identification with the Immulex S. pneumoniae Omni test (SSI Diagnostica, Denmark) for rapid detection of S. pneumoniae directly from positive blood cultures. The workflow was evaluated using 51 Streptococcus isolates. Compared to conventional biochemical testing, our new workflow demonstrates 100 % specificity and sensitivity for the detection and differentiation of S. pneumoniae from other closely related species. Our new workflow is accurate, cost-effective, and can easily be implemented in microbiology laboratories that already perform direct MALDI-TOF identification from positive blood cultures to improve the management of patients with invasive pneumococcal disease. ImportanceInvasive pneumococcal disease remains a major public health problem worldwide. Reducing the time to identify Streptococcus pneumoniae in positive blood cultures allows patients to be treated sooner with more targeted and effective antibiotics. We evaluated a two-step protocol where positive blood cultures are first tested directly by MALDI-TOF MS and any samples containing Streptococcus species are tested by Immulex S. pneumoniae Omni test to both detect and differentiate S. pneumoniae from other closely related Streptococcus species. Our study results showed 100 % sensitivity and specificity, and a much faster turn-around time than conventional methods.

Use of 16s rRNA Gene Sequencing for the Identification of Viridans Group Streptococci.

Streptococci belonging to the viridans group are gram-positive bacteria residing as commensals in the upper respiratory, gastrointestinal, and genital tracts in humans. Though they are largely known to be commensals, they may also cause life-threatening infections like infective endocarditis, septicemia, pyogenic infections, pneumonia, and meningitis. The viridans group streptococci (VGS) are usually identified by biotyping; however, species discrimination is not always possible by phenotypic characterization. We identified 53 isolates from blood cultures of patients with infective endocarditis and compared the results ofbiotyping with 16s rRNA gene sequencing for species identification. Organisms belonging to the mitis group were the most common. 16s rRNA gene polymerase chain reaction and sequencing were useful in identifying the etiological agents at the species level.S.oraliswas the most common etiological agent.

Dynamic interactions between Candida albicans and different streptococcal species in a multispecies oral biofilm.

The oral cavity is colonized by a plethora of bacteria, fungi, and archaea, including streptococci of the mitis group (MSG) and the yeast Candida albicans. This study aims to investigate the role of streptococcal species in the development of oral biofilm and the cross-kingdom interactions between some of the members of the commensal MSG and the pathogen yeast C. albicans using a multispecies supragingival biofilm model. A total of nine different in vitro biofilms were grown, quantified with culture analyses, and visually examined with confocal laser scanning microscopy (CLSM). A four-species biofilm without any streptococcal species was used as a basic biofilm. In each subsequent inoculum, one species of MSG was added and afterward combined with Streptococcus mutans. The eight-species biofilm contained all eight strains used in this study. Culture analyses showed that the presence of S. mutans in a four-species biofilm with Streptococcus oralis or S. oralis subsp. tigurinus did not differ significantly in C. albicans colony-forming unit (CFU) counts compared to biofilms without S. mutans. However, compared to other mitis species, Streptococcus gordonii combined with S. mutans resulted in the lowest CFUs of C. albicans. Visual observation by CLSM showed that biofilms containing both S. mutans and one species of MSG seemed to induce the formation of filamentous form of C. albicans. However, when several species of MSG were combined with S. mutans, C. albicans was again found in its yeast form.

Performance of Two Matrix-Assisted Laser Desorption Ionization-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) Systems for Identification of the Viridans Group Streptococci.

Due to similar colony morphology among viridans group streptococci (VGS), the differentiation of VGS species remains difficult in routine clinical microbiology. Recently, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) has been described as a fast method for identifying various bacteria at species level, and also for the VGS strains. A total of 277 VGS isolates were identified with the two MALDI-TOF MS systems (VITEK MS and Bruker Biotyper). The tuf and rpoB gene sequencing was used as the reference identification method for comparison. Based on tuf and rpoB gene sequencing, 84 isolates were S. pneumoniae and 193 strains were other VGS isolates including S. anginosus group (n=91, 47.2%), S. mitis group (n=80, 41.5%), S. bovis group (n=11, 5.7%), S. salivarius group (n=10, 5.2%), and S. mutans group (n=1, 0.5%). VITEK MS and Bruker Biotyper accurately identified 94.6% and 89.9% of all VGS isolates, respectively. VITEK MS showed better identification results than Bruker Biotyper for S. mitis group including S. pneumoniae and S. bovis group, but for other VGS isolates, two MALDI-TOF MS systems showed comparable identification performance. However, VITEK MS was able to identify S. gallolyticus to the subspecies level with high-confidence (S. gallolyticus ssp. pasteurianus), while the Bruker Biotyper system could not. While Bruker Biotyper system could be able to correctly differentiate the subspecies of S. salivarius from S. vestibularis, VITEK MS poorly identify. This study demonstrated that two MALDI-TOF MS systems allowed discrimination for most VGS isolates with different identification performance, but Bruker Biotyper could produce more misidentifications and VITEK MS system. It is crucial to be familiar with the performance of MALDI-TOF MS systems used in clinical microbiology.

Species designation of streptococci causing infective endocarditis in patients with mitral valve prolapse

Viridans group streptococci (VGS) have been previously linked to infective endocarditis (IE) in patients with mitral valve prolapse (MVP). The species identification of VGS is now available in clinical laboratories; however, it has not been examined in MVP IE. Therefore, we detailed the clinical profile, species designations, and antibiotic susceptibility of VGS isolates from patients with MVP IE. We retrospectively queried all adults with MVP and a definite or possible IE diagnosis seen at medical centers of the Mayo Clinic Enterprise from January 2009 to December 2021. Data, including clinical characteristics, comorbidities, microbiology, and outcomes, were extracted from electronic health records. VGS isolates from patients with MVP and IE were subclassified into mutans, salivarius, anginosus, sanguinis, and mitis groups. A total of 38 patients with MVP with IE due to streptococcal species were included. Overall, median age was 62.4 years and 32% of patients were females. The most prevalent comorbidities were diabetes mellitus (26%), hypertension (21%), heart failure (16%), and malignancy (16%). A total of (37%) patients presented with an embolic event at the time of their IE diagnosis, 27 (66%) required valve surgery, and no patient died within the hospital stay. The Streptococcus mitis group was the predominant (n=17, 45%) species designation; S. anginosus and S. sanguinis were identified in three (8%) each; S. mutans in two (5%); and S. salivarius in one (3%).Non-VGS streptococcal pathogens included S. agalactiae in three patients (8%), S. equi in two (5%), and S. dysgalactiae and S. bovis in one each (3%). VGS were identified in five (13%) patients, but species designation was not done. No penicillin resistance was identified among the isolates. The S. mitis group was the predominant species in our investigation. Continued evaluation of VGS species should be considered to profile the IE risk based on species identification.

A simple method to differentiate three classes of cholesterol-dependent cytolysins

Cholesterol-dependent cytolysins (CDCs) are proteinaceous toxins widely distributed in gram-positive pathogenic bacteria. CDCs can be classified into three groups (I–III) based on the mode of receptor recognition. Group I CDCs recognize cholesterol as their receptor. Group II CDC specifically recognizes human CD59 as the primary receptor on the cell membrane. Only intermedilysin from Streptococcus intermedius has been reported as a group II CDC. Group III CDCs recognize both human CD59 and cholesterol as receptors. CD59 contains five disulfide bridges in its tertiary structure. Therefore, we treated human erythrocytes with dithiothreitol (DTT) to inactivate CD59 on membranes. Our data showed that DTT treatment caused a complete loss of recognition of intermedilysin and an anti-human CD59 monoclonal antibody. In contrast, this treatment did not affect the recognition of group I CDCs, judging from the fact that DTT-treated erythrocytes were lysed with the same efficiency as mock-treated human erythrocytes. The recognition of group III CDCs toward DTT-treated erythrocytes was partially reduced, and these results are likely due to the loss of human CD59 recognition. Therefore, the degree of human CD59 and cholesterol requirements of uncharacterized group III CDCs frequently found in Mitis group streptococci can be easily estimated by comparing the amounts of hemolysis between DTT-treated and mock-treated erythrocytes.

Peculiarities of Periodontal Pocket Microbiome in Patients with Generalized Periodontitis in the Post-COVID Period

The oral cavity, like the lungs, is often referred to as the «ecological niche of commensal, symbiotic, and pathogenic organisms», and the emigration and elimination of microbes between them are constant, ensuring a healthy distribution of saprophytic microorganisms that maintains organ, tissue, and immune homeostasis. The prolonged hospital stays due to COVID-19 complications, cross-infection, oxygenation therapy through the mask or incubation, and long-term intravenous infusions limit the patient’s ability to care about the oral cavity, regularly clean teeth, floss interdental, etc., which creates extremely favorable conditions for colonization by aerobic and anaerobic pathogens of the oral cavity and periodontal pockets and leads to the rapid progression of chronic generalized periodontitis in this category of patients in the future. The goal of the study was to assess the state of the microbiome of the periodontal pockets of dental patients in the post-covid period. Methods. The object of the study was 140 patients with generalized periodontitis of the I and II stages of development in the chronic course (GP), among which 80 patients had coronavirus disease in the closest past. The patients were randomized by age, sex, and stage of GP development. The diagnosis of periodontal disease was established according to the classifi cation by Danilevskyi. The bacteriological material for aerobic and facultative anaerobic microflora and yeast-like fungi was collected from periodontal pockets with a calibrated bacteriological loop and immediately seeded on blood agar. Results. Significant qualitative and quantitative changes in the nature of the oral microbiocenosis were observed in patients with GP after the recent coronavirus disease, compared with similar patients who did not suffer from COVID-19. We have noticed almost complete disappearance of bacteria that belong to the transient representatives of the oral microflora such as Neisseria, corynebacteria (diphtheria), micrococci, and lactobacilli. The main resident representatives of the oral microflora, i.e., α-hemolytic Streptococci of the mitis group, were found in all healthy individuals and patients of groups A and C, but in 30.0±4.58% of patients in group B, α-hemolytic streptococci in the contents of periodontal pockets are present in quantities not available for detection by the applied method (&lt;2.7 lg CCU/mL). In terms of species, Streptococcus oralis and Streptococcus salivarius are more characteristic in gingival crevicular fluid in healthy individuals (93.8% of selected strains). In 68.4±3.32% of patients in group A, 64.0±3.43% of patients in group B, and 67.5±3.76% of patients in group C, the dominant species were Streptococcus gordonii and Streptococcus sanguinis (p&lt;0.01), which increased pathogenic potential as they produce streptolysin-O, inhibit complement activation, bind to fibronectine, actively form biofilms on the surface of tooth enamel and gum epithelial surface, and can act as an initiator of adhesion of periodontal pathogens. The other representatives of the resident microflora of the oral cavity — Stomatococcus mucilaginosus and Veillonella parvula for the patients of group C are also found in periodontal pockets with a signifi cantly lower index of persistence and minimal population level. In the post-covid period, both the population level and the frequency of colonization of periodontal pockets by Staphylococci and β-hemolytic Streptococci decreases rapidly. For these patient groups, unlike for those that did not suff er from COVID-19, we did not find any case of colonization with Staphylococcus aureus, as well as β-hemolytic Streptococci and epidermal Staphylococcus were also absent. The most characteristic in the post-covid period is a decrease in the proportion of α-hemolytic Streptococci, an increase in the proportion of yeast-like fungi of Candida species, as well as the appearance of a significant number of gram-negative rod-shaped bacteria (Enterobacteria and Pseudomonads). In periodontal patients, the microbial count is approximately 2 orders of magnitude lower than in those with GP who did not suffer from COVID-19 (p&lt;0.05). Conclusions. The overpassed coronavirus disease due to intensive antibiotic therapy leads to a marked decrease in the number of viable saprophytic microorganisms in the periodontal pockets of patients with GP. In the post-covid period for the patients with GP, there is a decrease in the level of colonization of periodontal pockets by species of resident oral microflora — α-hemolytic Streptococci, reduction of resident microorganism’s species, and almost complete disappearance of transient microfl ora. On the other hand, the frequency of colonization of periodontal pockets by fungi species, enterobacteria, and pseudomonads significantly increases. There are more expressed disorders in the periodontal pocket’s microbiome for the patients with a severe and complicated course of coronavirus disease, such as post-covid pulmonary fibrosis, which requires reconsideration of approaches to therapeutic and pharmacological treatment in this category of patients.

Oral mitis group streptococci reduce infectivity of influenza A virus via acidification and H2O2 production.

Members of the mitis group streptococci are the most abundant inhabitants of the oral cavity and dental plaque. Influenza A virus (IAV), the causative agent of influenza, infects the upper respiratory tract, and co-infection with Streptococcus pneumoniae is a major cause of morbidity during influenza epidemics. S. pneumoniae is a member of mitis group streptococci and shares many features with oral mitis group streptococci. In this study, we investigated the effect of viable Streptococcus oralis, a representative member of oral mitis group, on the infectivity of H1N1 IAV. The infectivity of IAV was measured by a plaque assay using Madin-Darby canine kidney cells. When IAV was incubated in growing culture of S. oralis, the IAV titer decreased in a time- and dose-dependent manner and became less than 100-fold, whereas heat-inactivated S. oralis had no effect. Other oral streptococci such as Streptococcus mutans and Streptococcus salivarius also reduced the viral infectivity to a lesser extent compared to S. oralis and Streptococcus gordonii, another member of the oral mitis group. S. oralis produces hydrogen peroxide (H2O2) at a concentration of 1-2 mM, and its mutant deficient in H2O2 production showed a weaker effect on the inactivation of IAV, suggesting that H2O2 contributes to viral inactivation. The contribution of H2O2 was confirmed by an inhibition assay using catalase, an H2O2-decomposing enzyme. These oral streptococci produce short chain fatty acids (SCFA) such as acetic acid as a by-product of sugar metabolism, and we also found that the inactivation of IAV was dependent on the mildly acidic pH (around pH 5.0) of these streptococcal cultures. Although inactivation of IAV in buffers of pH 5.0 was limited, incubation in the same buffer containing 2 mM H2O2 resulted in marked inactivation of IAV, which was similar to the effect of growing S. oralis culture. Taken together, these results reveal that viable S. oralis can inactivate IAV via the production of SCFAs and H2O2. This finding also suggests that the combination of mildly acidic pH and H2O2 at low concentrations could be an effective method to inactivate IAV.

Interrogation of the contribution of (endo)lysin domains to tune their bacteriolytic efficiency provides a novel clue to design superior antibacterials

Bacteriophage-derived endolysins and bacterial autolysins (hereinafter lysins) represent a completely new class of efficient antibacterials. They prevent the development of bacterial resistance and help protect commensal microbiota, producing cell wall lysis. Here we have investigated whether the acquisition of enzymatic active domains (EADs) and cell wall binding domains (CWBDs) of balancing efficiencies could be a way of tuning natural lysin activity. The concept was applied to produce a chimeric lysin of superior antibacterial capacity using the endolysin Skl and the major pneumococcal autolysin LytA. Combination of the Skl EAD and the cell wall choline-binding domain (CBD) of LytA in the chimera QSLA increased the bacterial killing by 2 logs or more compared to parental enzymes at an equal concentration and extended the substrate range to resistant and emergent pneumococci and other pathogens of the mitis group. Contrarily, QLAS, containing LytA EAD and Skl CBD, was inactive against all tested strains, although domain structures were preserved and hydrolysis of purified cell walls maintained in both chimeras. As a whole, our study provides a novel clue to design superior lysins to fight multidrug-resistant pathogens based on domain selection, and a powerful in-vivo active lysin (QSLA) with promising therapeutic perspectives.

Investigating the Streptococcus sinensis competence regulon through a combination of transcriptome analysis and phenotypic evaluation.

Streptococcus sinensis is a recently identified member of the Mitis group of streptococci. This species has been associated with infective endocarditis; however its mechanisms of pathogenesis and virulence are not fully understood. This study aimed to investigate the influence of the competence-stimulating peptide (CSP) and the competence regulon quorum-sensing circuitry (ComABCDE) on subsequent gene transcription and expression, as well as resultant phenotypes. In this study we confirmed the native CSP identity, ascertained when endogenous CSP was produced and completed a transcriptome-wide analysis of all genes following CSP exposure. RNA sequencing analysis revealed the upregulation of genes known to be associated with competence, biofilm formation and virulence. As such, a variety of phenotypic assays were utilized to assess the correlation between increased mRNA expression and potential phenotype response, ultimately gaining insight into the effects of CSP on both gene expression and developed phenotypes. The results indicated that the addition of exogenous CSP aided in competence development and successful transformation, yielding an average transformation efficiency comparable to that of other Mitis group streptococci. Additional studies are needed to further delineate the effects of CSP exposure on biofilm formation and virulence. Overall, this study provides novel information regarding S. sinensis and provides a substantial foundation on which this species and its role in disease pathogenesis can be further investigated.

Distribution of two-component signal transduction systems BlpRH and ComDE across streptococcal species.

Two-component signal transduction (TCS) systems are important regulatory pathways in streptococci. A typical TCS encodes a membrane-anchored sensor kinase (SK) and a cytoplasmic response regulator (RR). Approximately, 20 different types of TCSs are encoded by various streptococci. Among them, two TCSs, in particular BlpRH and ComDE, are required for bacteriocins production and competence development. The SK component of these two TCSs is highly similar and belongs to the protein kinase-10 (HPK-10) subfamily. While these two TCSs are present in streptococci, no systematic studies have been done to differentiate between these two TCSs, and the existence of these pathways in several species of the genus Streptococcus is also unknown. The lack of information about these pathways misguided researchers for decades into believing that the Streptococcus mutans BlpRH system is a ComDE system. Here, we have attempted to distinguish between the BlpRH and ComDE systems based on the location of the chromosome, genomic arrangement, and conserved residues. Using the SyntTax and NCBI databases, we investigated the presence of both TCS systems in the genome of several streptococcal species. We noticed that the NCBI database did not have proper annotations for these pathways in several species, and many of them were wrongly annotated, such as CitS or DpiB instead of BlpH. Nevertheless, our critical analyses led us to classify streptococci into two groups: class A (only the BlpRH system) and class B (both the BlpRH and ComDE systems). Most of the streptococcal groups, including bovis, pyogenic, mutans, salivarius, and suis, encode only the BlpRH system. In contrast, only in the mitis and anginosus groups were both the TCS systems present. The focus of this review is to identify and differentiate between the BlpRH and ComDE systems, and discuss these two pathways in various streptococci.