Screening of antagonistic strains of respiratory origin and analysis of their bacteriostatic effects on pathogens

Airway commensal bacteria in cystic fibrosis inhibit the growth of P. aeruginosa via a released metabolite

In cystic fibrosis (CF), Pseudomonas aeruginosa infection plays a critical role in disease progression. Although multiple studies suggest that airway commensals might be able to interfere with pathogenic bacteria, the role of the distinct commensals in the polymicrobial lung infections is largely unknown. In this study, we aimed to identify airway commensal bacteria that may inhibit the growth of P. aeruginosa. Through a screening study with more than 80 CF commensal strains across 21 species, more than 30 commensal strains from various species have been identified to be able to inhibit the growth of P. aeruginosa. The underlying mechanisms were investigated via genomic, metabolic and functional analysis, revealing that the inhibitory commensals may affect the growth of P. aeruginosa by releasing a large amount of acetic acid. The data provide information about the distinct roles of airway commensals and provide insights into novel strategies for controlling airway infections.

Juglone Inhibits Listeria monocytogenes ATCC 19115 by Targeting Cell Membrane and Protein

Foodborne disease caused by Listeria monocytogenes is a major global food safety problem. A potential solution is the antimicrobial development of the highly bioactive natural product juglone, yet few studies exist on its antibacterial mechanism against L. monocytogenes. Thus, we aimed to elucidate the antibacterial mechanism of action of juglone against L. monocytogenes by determining the resultant cell morphology, membrane permeability, membrane integrity, and proteome changes. The minimum inhibitory concentration of juglone against L. monocytogenes was 50 μg/mL, and L. monocytogenes treated with juglone had longer lag phases compared to controls. Juglone induced L. monocytogenes cell dysfunction, leakage of potassium ions, and membrane potential hyperpolarization. Confocal laser scanning microscopy and field-emission-gun scanning electron microscope assays revealed clear membrane damage due to juglone treatment. Fourier transform infrared analyses showed that L. monocytogenes responded to juglone by some conformational and compositional changes in the molecular makeup of the cell membrane. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that juglone either destroyed proteins or inhibited proteins synthesis in L. monocytogenes. Therefore, our findings established juglone as a natural antibacterial agent with potential to control foodborne L. monocytogenes infections.

Klebsiella pneumoniae Lower Respiratory Tract Infection in a South African Birth Cohort: a Longitudinal Study

OBJECTIVES

The role of Klebsiella pneumoniae (KP) in lower respiratory tract infection (LRTI) is not well studied. We longitudinally investigated KP colonization and its association with LRTI in a South African birth cohort.

METHODS

We conducted a case-control study of infants who developed LRTI and age-matched controls, followed twice weekly through infancy. Nasopharyngeal swabs taken fortnightly and at LRTI for 33-multipex Quantitative multiplex real-time polymerase chain reaction were tested at LRTI and twice weekly from 90 days preceding LRTI. Controls were tested over the equivalent period. Multivariate models investigated the factors associated with LRTI or with KP-associated LRTI (KP-LRTI).

RESULTS

Among 885 infants, there were 439 LRTI episodes, of which 68 (15.5%) were KP-LRTI (OR 1.93; 95% CI 1.25-3.03). Infants with KP-LRTI were younger than those without KP-LRTI (median [IQR] 3.7 [2.1-5.9] vs 4.7 [2.8-7.9] months, P-value=0.009). Clinical features of KP and non-KP-LRTI were similar with 114 (26%) infants hospitalized. Prematurity (adjusted odds ratio [aOR] 11.86; 95% CI 5.22-26.93), HIV exposure (aOR 3.32; 95% CI 1.69-6.53), lower birthweight (aOR 0.68; 95% CI 0.51-0.91), and shorter breastfeeding time (aOR 0.79; 95% CI 0.65-0.96) were associated with KP-LRTI versus non-LRTI. These factors and younger age were associated with KP-LRTI versus non-KP-LRTI.

CONCLUSION

KP was associated with a substantial proportion of LRTI, particularly in premature or HIV-exposed infants in whom strategies for treatment and prevention should be strengthened.

Biocontrol Effect of Bacillus subtilis YPS-32 on Potato Common Scab and Its Complete Genome Sequence Analysis

Potato common scab is caused by Streptomyces, which resides in soil and has become a serious disease in potato planting areas worldwide. In this study, we obtained a Bacillus subtilis YPS-32 strain by natural screening, and atmospheric and room-temperature plasma (ARTP) mutagenesis and field trial results showed that B. subtilis YPS-32 has a control efficacy of 83.70% against potato common scab. The complete genome of B. subtilis YPS-32 was sequenced, and multiple genes related to the synthesis of antibiotics and plant growth promoters were detected. Based on the genomic information for B. subtilis YPS-32, the sfp gene-inactivated (related to the synthesis of secondary metabolites) mutant strain B. subtilis YPS-32Δsfp was constructed. Analysis of crude extract metabolites using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) techniques revealed that strain YPS-32 encodes antagonists, such as surfactin and fengycin, which have antimicrobial effects. This study clarifies the mode of action by which B. subtilis YPS-32 antagonizes Streptomyces scabies and provides a reference for further research on antibacterial genes in the future.

Mechanisms underlying the antimicrobial actions of the antimicrobial peptides Asp-Tyr-Asp-Asp and Asp-Asp-Asp-Tyr

The peptides Asp-Tyr-Asp-Asp (DYDD) and Asp-Asp-Asp-Tyr (DDDY) extracted from Dendrobium aphyllum have antimicrobial effects on Escherichia coli, Pseudomonas aeruginosa, and Monilia albicans, but no effects on Bacillus subtilis and Staphylococcus aureus. The effects of a hydrophobic environment on the secondary structures of these molecules were determined using circular dichroism and atomic force microscopy. Although scanning electron microscopy revealed that DDDY was more destructive to membranes than DYDD, both peptides showed antimicrobial effects against three pathogens. The minimum inhibitory concentration (MIC) of DYDD (18.075 mg/mL) against E. coli was higher than that of DDDY (4.519 mg/mL), and the influence of DYDD on the cell surface potential energy of E. coli was also greater (a decrease of 6.4 ± 0.66 mV) than that of DDDY (a decrease of 4.37 ± 0.77 mV). Moreover, the cell membrane damage and content leakage of DYDD-treated E. coli cells were more severe than those observed in the DDDY-treated cells. However, DDDY showed stronger antibacterial activity against P. aeruginosa and M. albicans than DYDD. A molecular dynamic simulation revealed that the mechanisms underlying the interaction between these two peptides and lipid bilayers were remarkably different. Therefore, two separate models were proposed to describe their antimicrobial activities.

Description and genomic characterization of Streptococcus symci sp. nov., isolated from a child's oropharynx

Using the culturomics approach, we isolated a new Streptococcus species, strain C17^T, from the oropharynx mucosa sample of a healthy 5-year-old child living in Shenyang, China. We studied the phenotypic, phylogenetic, and genomic characteristics of strain C17^T, which was identified as a Gram-positive, coccus-shaped, non-motile, aerobic, catalase-negative bacteria. Its growth temperatures ranged from 20 to 42 °C, with optimal growth at 37 °C. Acid production could be inhibited by two sugars, trehalose and raffinose. In C17^T, the reactions for enzyme lipase (C14) were confirmed to be negative, whereas those for alkaline phosphatase, α-glucosidase, and hippuric acid hydrolysis were positive. The C17^T genome contained 2,189,419 base pairs (bp), with an average G+C content of 39.95%, encoding 2092 genes in total. The 16S ribosomal RNA sequence showed 99.8% similarity with the newly identified Streptococcus pseudopneumoniae ATCC BAA-960^T. The main fatty acid components in C17^T were C16:0, C18:1 w7c, C18:0, and C18:1 w9c, all of which can be found in other species of the Streptococcus genus. Strain C17^T showed high susceptibility to clindamycin, linezolid, vancomycin, chloramphenicol, and cefepime, and moderate susceptibility to erythromycin. The obtained dDDH value between strain C17^T and the closest species was 52.9%. In addition, the whole genome sequence of strain C17^T had an 82.21–93.40% average nucleotide identity (ANI) with those strains of closely related Streptococcus species, indicating that the strain C17^T was unique among all Streptococcus species. Based on these characteristics, we determine that C17^T is a novel species, named Streptococcus symci sp. nov. (= GDMCC 1.1633 = JCM 33582).

Streptococcus xiaochunlingii sp. nov. E24 Isolated From the Oropharynx of Healthy Chinese Children

A Gram-positive, α-hemolytic, catalase-negative, facultative anaerobic and non-motile coccus was isolated form throat swabs taken from the oropharynx of healthy children. The genome was shown to be 1.950,659 bp long and contained 42.03 mol% G + C bases with 1,942 protein-coding and 53 RNA coding genes. The results of 16S rRNA gene sequencing strongly suggested that the strain is a member of the Streptococcus genus, with 98.04, 98.11, and 97.34% similarities to Streptococcus australis ATCC 700641^T, Streptococcus rubneri LMG 27207^T and Streptococcus parasanguinis ATCC 15912^T, respectively. A sodA gene comparison exhibited a sequence identity of 92.6% with the closest strain Streptococcus australis ATCC 700641^T. In silico DNA-DNA hybridization showed a highest DNA similarity value of 52% with Streptococcus australis ATCC 700641^T. Comparing 18 biochemical traits, the similarities of the Streptococcus strain E24 were 72% with Streptococcus rubneri LMG 27207^T, 78% with Streptococcus australis ATCC 700641^T and 44% with Streptococcus parasanguinis ATCC 15912^T. We suggest that based on the genotypic and phenotypic results that the strain E24 is a novel species of the Streptococcus genus and propose the name Streptococcus xiaochunlingii sp. nov. E24.

Screening of antagonistic strains of respiratory origin and analysis of their bacteriostatic effects on pathogens

Objective

To find antagonistic strains in the respiratory tract having bacteriostatic properties against common pathogens.

Methods

The oropharyngeal microbiota of five healthy children aged 4–6 years were collected and α‐hemolytic bacteria screened on 15% sheep blood agar. Bacteriostatic effects of the isolated α‐hemolytic bacteria on Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes were evaluated by the Oxford cup method. Antagonistic strains were identified by mass spectrometry, and the16S rDNAs were sequenced, and their best bacteriostatic concentrations and antagonistic spectra for Klebsiella pneumoniae, Proteus vulgaris, Enterobacter cloacae, Acinetobacter Baumanii, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes were evaluated.

Results

Of 300 isolated α‐hemolytic bacterial clones, four exhibited bacteriostatic activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Streptococcus pyogenes. Mass spectrometric analyses revealed that two of them were Streptococcus mitis and two others were Streptococcus parasanguinis strains. Further tests showed that all 4 antagonistic strains also had bacteriostatic effects on Klebsiella pneumoniae, Proteus vulgaris, Enterobacter cloacae, and Acinetobacter Baumanii, and the mode of action was not mediated by lactic acid production.

Conclusion

Four antagonistic Streptococcus strains derived from oropharyngeal microbiotas showed bacteriostatic effects on pathogens and may be involved in pharyngeal microbiome homeostasis.