BMC Microbiology最新文献

Background: Acinetobacter baumannii is an opportunistic bacteria associated primarily with hospital-acquired infections. Its tendency to acquire or donate resistance genes to neighboring bacteria is a major concern. Tetracyclines have shown promise in treating A. baumannii infections, but tetracycline resistance is growing globally in A. baumannii isolates.

Objectives: The study aimed to study (1) the prevalence of multidrug-resistant (MDR) A. baumannii infections at Suez Canal University Hospitals, (2) the distribution of efflux pump genes AdeA &B, TetA, and TetB, and (3) the effect of efflux pump inhibitor (CCCP) on tetracycline-resistant isolates.

Methods: Clinical samples (457) were collected (blood, urine, sputum, ETA, pus, and pleural fluid), followed by A. baumannii isolation and identification, PCR detection of efflux pump genes, and detection of tetracycline susceptibility and its MIC before and after treatment with the efflux pump inhibitor (CCCP).

Results: A total of 31 A. baumannii isolates were recovered (6.78%). The highest rate of isolation was from the ICU (48.3%) from the ET aspirate samples (48.3%). The efflux system AdeA and TetB genes were distributed in 100% of isolates, whereas AdeB was found in 93.5% of isolates and the TetA gene in 87.1% of isolates. All A. baumannii isolates were MDR showing resistance to three or more classes of antibiotics. 45% of the isolates showed a 4-fold reduction of MIC and 12.9% showed a 2-fold reduction in the MIC.

Conclusions: Efflux pump is an important mechanism for tetracycline resistance among A. baumannii isolates.

Background: Listeria monocytogenes is a foodborne pathogen that can lead to severe pregnancy outcomes. This study reports the clinical and genomic characteristics of a Listeria-mediated stillbirth identified in January 2022 through the Child Health and Mortality Prevention Surveillance (CHAMPS) project in Bangladesh. The Lm-BD-CHAMPS-01 isolate was recovered from the blood and cerebrospinal fluid (CSF) of a male stillborn. Maternal history, clinical, and demographic data were collected by the CHAMPS surveillance platform. An expert panel evaluated all reports to determine the role of L. monocytogenes infection in the causal chain of stillbirth. Genomic characterization included multilocus sequence typing (MLST), core genome MLST (cgMLST), serotyping, and the presence or absence of virulence genes. Genetic divergence and phylogenetic analyses were conducted to determine the relationship with other reported isolates globally.

Results: The isolate Lm-BD-CHAMPS-01 was identified as a novel cgMLST CT11424. It belonged to ST 308, Serotype 4b, Clonal Complex 1, and Phylogenetic Lineage 1. Key L. monocytogenes virulence genes facilitating the crossing of the placental barrier, including full-length inlA, LIPI-1, and LIPI-3, were detected. The isolate was closely related to clinical L. monocytogenes isolates, as determined by GrapeTree based on cgMLST. SNP-based phylogenetic analysis found Lm-BD-CHAMPS-01 to be the most distant from other CC1 isolates in the database. Possible sources of infection included the consumption of contaminated raw vegetables or exposure to pigeons.

Conclusions: This is the first genome sequence of clinical L. monocytogenes from Bangladesh, which also caused stillbirth. Rural healthcare professionals should be aware of L. monocytogenes infection risks during pregnancy. Pregnant women should be counseled on the dangers of exposure to animals or birds and consumption of potentially contaminated raw food to prevent adverse pregnancy outcomes due to L. monocytogenes infection.

Pseudomonas aeruginosa (P. aeruginosa) and Candida albicans (C. albicans) are opportunistic pathogens whose mixed infections can exacerbate microbial dissemination and drug resistance, contributing to high mortality and morbidity rates among infected individuals. Few studies have explored the impact of C. albicans supernatant on P. aeruginosa, and the underlying mechanisms of such mixed infections remain unclear. In this study, we investigated the effects of C. albicans supernatant on biofilm formation and virulence factor activity in wild-type P. aeruginosa PAO1 and its quorum sensing-deficient mutants, ΔlasIrhlI and ΔlasRrhlR. Our results demonstrated that the biofilm formation capability and virulence were significantly higher in the PAO1 group compared to the ΔlasIrhlI and ΔlasRrhlR groups. Furthermore, exposure to C. albicans supernatant significantly enhanced both the biofilm formation and virulence of PAO1, whereas no significant changes were observed in the ΔlasIrhlI and ΔlasRrhlR mutants relative to their respective controls. These findings suggest that C. albicans supernatant may modulate P. aeruginosa biofilm formation and virulence via the las/rhl quorum sensing system.

Background: Xanthomonas citri subsp. citri is the causal agent of citrus canker, which causes substantial losses in citrus production. Here, we report the role of a polyketide cyclase (PKC) on the virulence in X. citri subsp. citri.

Methods: The structure of PKC was precisely predicted using Alphafold3. Promoter GUS fusion constructs and real-time quantitative reverse transcription (qRT-PCR) were employed to study the pattern of expression of the polyketide gene. A deletion mutation was created to explore the role of PKC in virulence and metabolic change.

Results: The PKC was determined to have a signal peptide, a START/RHO_alpha_C/PITP/Bet_v1/CoxG/CalC (SRPBCC) domain, and a GyrI-like small molecule binding domain. The expression of the PKC gene was induced in planta, as well as under stress by CuSO₄ and SDS. An in-frame deletion mutation resulted in a loss of virulence on the citrus hosts, which was restored by the SRPBCC domain. Furthermore, there as a remarkable reduction in the expression of type III genes, such as hrpG and hrpX. In the mutant carrying the pkc deletion, ketoleucine and acetone cyanohydrin were downregulated, and four metabolites, including D-ribose, creatine, polyoxyethylene dioleate, and cohibin C, were upregulated.

Conclusions: The overall data indicate that the PKC affects bacterial virulence by modulating the type III secretion system, possibly through the biosynthesis of particular metabolites.

Background: Ten morphologically different actinomycetes were isolated from mangrove sediments of Manakudy, Kanyakumari District, India. The potent strain was selected based on their primary screening against Gram positive Staphylococcus aureus, Enterococcus faecalis and Gram negative Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi bacterial pathogens. The selected strain was identified as Streptomyces sp CMSTAAHL-4 by 16S rRNA sequencing. The media optimization for secondary metabolites production was performed by One-Variable at a Time and Response Surface Methodology-Central Composite Design. Minimum inhibitory concentration and minimum bacterial concentration for the extracted secondary metabolites were determined. The antioxidant potential of the secondary metabolites showed that the concentration of the metabolites increases, with the percentage of inhibition. The anti-inflammatory activity of the secondary metabolites found that maximum activity was observed at 500 µg/ml of the metabolites. Alcohols, alkenes, alkynes, alkyl halides, carboxylic acids, aliphatic esters functional groups were identified by fourier transform infrared spectroscopy, gas chromatography and mass spectrometer analysis of the secondary metabolites revealed five bioactive compounds. The X-ray diffraction analysis revealed that the secondary metabolites are amorphous. The thermogravimetric analysis showed the thermal stability of secondary metabolites. Atomic force microscopy analysis revealed specific structural characteristics of the secondary metabolites, which may be associated with their potential biological activities.

Conclusions: The results showed that the antibacterial, antioxidant, and anti-inflammatory chemicals present in the isolated secondary metabolites give them therapeutic properties.

Background: The air-curing process of cigar tobacco leaves is typically conducted in an open environment, involving the participation of various microorganisms. However, the effect of microbial communities during air-curing process on the formation of flavor components remains unclear. Therefore, this study aims to reveal the dynamics of flavor components and microbial community changes, and explore the potential role of microbial communities in flavor formation during the cigar tobacco air-curing process.

Results: High-throughput sequencing analysis showed that Pantoea, Sphingomonas and Pseudomonas were the dominant bacterial genera during air-curing process, while Aspergillus was the dominant fungal genus. Subsequently, volatile flavor analysis shows that alkaloids were the most important volatile compounds in cigar leaves, followed by esters, alcohols and aldehydes. Furthermore, 38 characteristic volatile flavor compounds at different periods of air-curing were identified based on PLS-DA in different periods of air-curing. The correlation analysis between microorganisms and flavor components showed that Pantoea and Staphylococcus might promote the flavor formation from browning to post-air-curing and were positively correlated with specific flavor components like phenylacetaldehyde and acetophenone. Phoma, Mycosphaerella, Wallemia, and Cladosporium were identified as key fungal genera influencing flavor formation, as they showed positive correlations with multiple flavor components. These information enrich our understanding of the flavor formation of cigar tobacco during air curing.

Conclusions: There is a complex correlation between the microbial community and the flavor components, which may have a great influence on the flavor formation during the air-curing process of cigar leaves. Bacterial communities have higher species diversity and richness during air-curing, and have more complex correlation characteristics with volatile flavor, which may play more roles in the flavor formation. This study revealed the potential role of microbial community on flavor formation in cigar tobacco air-curing process, and provided guidance for subsequent screening of specific functional microorganisms to improve and stabilize cigar tobacco flavor.

The emergence of multidrug-resistant (MDR) Raoultella isolates is linked to the acquisition of antibiotic resistance genes (ARGs) with plasmids playing a pivotal role in this process. While plasmid-mediated transmission of ARGs in Raoultella has been extensively reported, limited attention has been given to genetically dissecting the modular structures of plasmids. This study aims to elucidate the genomic features of novel incompatible plasmids in MDR Raoultella by presenting 13 complete plasmid sequences from four isolates, along with an analysis of 16 related plasmids from GenBank. These 29 plasmids were classified into five distinct groups: IncFII single-replicon plasmids, dual-replicon plasmids containing the IncFII replicon, IncHI plasmids, IncR plasmids, and IncX8 plasmids. A new incompatible group, IncFII_p23141-CTXM, was identified, alongside five newly designated Inc groups based on previously determined sequences, namely IncFII_{pKPC2_EC14653}, IncFII_pCP020359, IncFII_pCP024509, IncFII_pKOX-137, and IncFII_pKDO1. Furthermore, this research marks the first report of four Inc groups of plasmids within Raoultella, namely IncFII_p23141-CTXM plasmid, IncFII_{pKPC2_EC14653} plasmid, IncX8 plasmid, and IncFII_pCP020359: IncFIB-7.1 dual-replicon plasmid. Moreover, novel mobile genetic elements, including two unit transposons (Tn6806 and Tn6891), one IS-based transposition unit (Tn6561), and four insertion sequences (ISRor6, ISRor7, ISRor8, and ISRor9) were discovered. Notably, this is the first report of mcr-9 in clinical Raoultella strains. At least 49 ARGs conferring resistance against 11 different categories of antimicrobials were identified on these 13 plasmids. Overall, this research deepens the understanding of incompatible plasmids in Raoultella, serving as a reference for exploring antibiotic resistance profiles and plasmid diversity in MDR Raoultella.

Background: Enterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), and can cause severe cerebral complications and even fatality in children younger than 5 years old. However, there is no specific medication for EV71 infection in clinical practice. Our previous studies had identified the 6-thioguanine (6-TG), an FDA-approved anticancer drug, as a potential antiviral agent, but its anti-EV71 activity is largely unknown, therefore, we aim to explore the antiviral effect of 6-TG on EV71.

Results: 6-TG significantly suppressed EV71 mRNA level, VP1 protein expression, and viral progeny production in HT-29 cells. In EV71-infected HT-29 cells, the 50% cytotoxicity concentration of 6-TG (CC₅₀) was > 2000 µM and the 50% inhibitory concentration of 6-TG against EV71 (IC₅₀) was 0.9302 µM. Interestingly, the selectivity index (SI) value of 6-TG against EV71 was > 2150.1, which was higher than the SI value (> 66.7) of ribavirin. Mechanistically, 6-TG treatment reduced the expression of baculoviral IAP repeat containing 3 (BIRC3), and further inhibited EV71 replication by attenuating BIRC3-mediated the complete autophagy.

Conclusions: 6-TG exerted a significant inhibitory effect on EV71 infection in vitro and prevented EV71-induced the complete autophagy by decreasing BIRC3 expression. Our work provided a basis for the further development of 6-TG as a therapy for EV71-associated HFMD.

Background: The excessive use of antibiotics is a major contributor to the global issue of antimicrobial resistance (AMR), a significant threat to human and animal health. Hence, assessing new strategies for managing Multi-Drug Resistant (MDR) microorganisms is vital. In this study, the use of mechanically isolated mature adipose cells (MIMACs) and their lysate (Adipolysate) as a new sustainable antimicrobial agent was assessed against Methicillin-resistant Staphylococcus aureus (MRSA).

Conclusions: The minimum volume of MIMACs achieved complete bacterial inhibition (Minimum Lethal volume) was 75 µl and 100 µl for bacterial concentration of 10¹⁰ and 10¹² cfu/ml, respectively. Direct bacterial membrane attachment and intracellular capture was visualized under light and electron microscopy. Adipolysate was characterized via GC-MS, the fatty acid profile demonstrated several components with known antimicrobial properties. The tested Adipolysate revealed inhibition zone of diameter 25.33 ± 0.88 mm against the tested S. aureus strain, compared with the inhibition zone of Vancomycin (24.0 ± 0.00 mm) and Erythromycin (30.0 ± 0.00). The study revealed the potential effects of MIMACs and Adipolysate as sustainable, natural, and robust antimicrobial agents. However, these preliminary results will be further investigated to understand the mechanism of action and explore possible applications in various fields.