Letters in Applied Microbiology最新文献

Studies have demonstrated the potential for utilizing agro-industrial byproducts for Pleurotus spp. Extracts containing polysaccharides from mushrooms obtained through solid culture, as well as from mycelial biomass obtained through liquid culture (endopolysaccharides), can regulate the immune response and increase resistance to disease. Additionally, exopolysaccharide extracts obtained from culture broth can regulate the immune response. This study aimed to utilize food industry waste to produce mycelial biomass and exopolysaccharides from Pleurotus ostreatus grown in media containing apple, grape, lemon, and orange peels. P. ostreatus produced mycelial biomass in all four residues, with the highest concentration (4.91 g L-1) in grape peels. Together with lemon and orange peels, it also produced higher concentrations of exopolysaccharides (3.22 to 3.95 g L-1). The exo- and endo-polysaccharides obtained from the culture broth and the mycelial biomass cultivated with grape peels, respectively, had α-D-glucose, α-D-galactose, α-D-xylose, and galacturonic acid as their main constituents.

Salmonella has caused widespread foodborne disease risks in China. Studies suggest that plasmid-mediated quinolone resistance (PMQR) is the main route for the spread of Salmonella's drug resistance. To establish a method for rapid detection of the genus gene invA carried by foodborne Salmonella and four PMQR genes carried by drug-resistance strains based on multiplex PCR combined with liquid chip technology. The detection limits, sensitivity, specificity, and repeatability of the method were evaluated. Our findings revealed that in terms of detection sensitivity, this method can detect the invA and qnrS with a limit as low as 5 CFU/mL. The detection limits for aac(6')-Ib-cr, oqxA, and oqxB genes were 25 CFU/mL, 10 CFU/mL, and 10 CFU/mL, respectively. In terms of specificity, no positive signals were detected for the nontarget bacteria strains and the negative control. In the repeatability experiments, the coefficient of variation (CV) for all target gene detections was <5%. In the simulation sample verification, the concordance rate with the results of conventional PCR reached 100%. Therefore, this method can provide technical support for the detection of foodborne Salmonella and PMQR genes, as well as the monitoring of drug resistance.

This study evaluated if acidifying agents used for ammonia control and pathogen reduction in poultry houses have a deleterious effect on the survival and growth of Salmonella Infantis. Changes in antimicrobial resistance (AMR) and the gene composition of the plasmid of emerging S. Infantis (pESI) were also investigated. When S. Infantis was exposed to sodium bisulfate (SBS) and acidified copper sulfate (ACS), a bacteriostatic effect on Salmonella was observed at recommended concentrations, whereas ACS at double concentration had a bactericidal effect. No difference in the maximum growth and lag phase time (P > .05) between the pESI-carrying (pESI+) and pESI-free (pESI-) strains was observed, suggesting that there was a minimal benefit or burden imposed by pESI. However, several evolved isolates of the pESI+ strains lost resistance to sulfamethoxazole and trimethoprim-sulfamethoxazole in the presence of SBS, potentially by losing the associated genes. Furthermore, applying ACS to litter microcosms post-inoculation with pESI+ strains significantly reduced the gene abundance of S. Infantis and pESI replicon (P < .05), while SBS reduced the gene abundance of pESI- strains. This study suggests that acidifiers such as ACS pose a selective pressure on pESI+  S. Infantis and broader studies are needed to investigate their efficacy for pathogen and AMR reduction in pre-harvest broiler production.

Enzymatic activity potency in Candida albicans is depends on different pH levels. This study investigates the importance of matching in vitro pH conditions to those encountered at infection sites. A total of 20 vulvovaginitis C. albicans isolates were investigated for phospholipase, proteinase, and esterase activities. The activities were measured at three pH levels (4, 5, and 7) representing for the healthy vaginal range, potential infection condition, and a standard in vitro reference point, respectively. Specific media were used to assess enzyme activity. Phospholipase and proteinase activity were significantly higher at acidic pH compared to neutral pH. In contrast, esterase activity showed a slight increase at neutral pH. Analysis revealed significant differences in enzyme activity between pH 5 and 7, highlighting the importance of using pH-relevant conditions for studying Candida virulence. This study reveals that the acidic vaginal pH characteristic of C. albicans infections significantly enhances the activity of its key damaging enzymes. This highlights the limitations of using a standard pH protocol for enzyme activity analysis. By employing pH-mimicking conditions, future research can unlock a deeper understanding the actual C. albicans virulence that might occur in site of infection. Data analysis should consider beyond this factor.

This study aimed to evaluate the antimicrobial susceptibility and clonal relatedness of Klebsiella pneumoniae isolates recovered from the milk of cows with mastitis in a large-scale study that clinical severity was scored. A total of 48 K. pneumoniae complex isolates were subjected to in vitro antimicrobial susceptibility tests (AST), PCR for carbapenemase-encoding genes, and molecular typing by pulsed-field gel electrophoresis (PFGE). Thirteen isolates, selected by PFGE type and AST results were subjected to whole-genome sequencing (WGS) for the identification of sequence types (STs) and the detection of antimicrobial resistance genes and virulence-encoding genes. A total of 39 different PFGE restriction profiles were identified. Thirteen different STs, including two novel STs, were identified among the 13 sequenced strains. The blaCTX-M-8, qnrE1, aadA2, cmlA4, dfrA15, sul1, tetA, and tetB genes were identified. Two isolates presented the yersiniabactin-encoding gene ybtAEPQSTUX. Klebsiella pneumoniae isolates from the milk of cows with mastitis clinically scored revealed high genetic diversity, according to both PFGE and MLST analysis, as well as harboring resistance genes commonly found in human clinical isolates.

Mycoplasma pneumonia (MP) is a common pathogen of human respiratory infections and one of the leading causes of community-acquired pneumonia. Early and rapid diagnosis of its infection is crucial for clinical treatment decisions. In this study, we innovatively combined recombinase polymerase amplification with Pyrococcus furiosus Argonaute protein (PfAgo) to establish a novel molecular diagnostic method for MP. This assay demonstrated high specificity with no cross-reactivity with other common respiratory pathogens. The limit of detection was 2 × 104 copies μl-1. Furthermore, evaluation using 37 clinical samples showed 100% specificity and 86.36% sensitivity compared to quantitative real-time polymerase chain reaction (qPCR). The entire workflow, including sample preparation, can be completed within 2.5 h and requires only basic instrumentation. This method holds great potential for application in primary healthcare settings and resource-limited regions.

This study aimed to explore the cultivable actinobacterial diversity in Krem Dam cave, Meghalaya, India, and to evaluate their biotechnological potential through antimicrobial activity, plant growth-promoting traits, and metabolic pathway prediction. Sediment samples were collected from five locations within the cave, pretreated, and cultured on selective media to isolate actinobacteria. Isolates were characterized morphologically, physiologically, and chemotaxonomically, followed by 16S rDNA sequencing for molecular identification. The PAPRICA pipeline was used to predict metabolic pathways from 16S rDNA sequences. Antimicrobial activity was assessed against Gram-positive, Gram-negative bacteria, and Candida species using cross-streak and agar-well diffusion methods, while biosynthetic gene clusters (PKS-I, PKS-II, and NRPS) were screened via polymerase chain reaction (PCR). Plant growth-promoting (PGP) traits, including IAA production, phosphate solubilization, siderophore activity, and nitrogen fixation were evaluated, along with antagonism against phytopathogens and seedling vigor in tomato. Forty-eight isolates were identified, predominantly Streptomyces thermocarboxydus-related strains, with one Amycolatopsis species. Seventy-seven percent harbored at least one biosynthetic gene cluster, and significant antimicrobial activity was observed, particularly against Gram-positive bacteria. Several isolates exhibited multiple PGP traits, and two (KD-21, KD-29) enhanced tomato seedling vigor. The study concludes that Krem Dam cave harbors diverse, bioactive actinobacteria with promising applications in pharmaceuticals and sustainable agriculture, warranting further metabolomic and genomic investigations.

Bacillus thuringiensis Berliner is a well-known biocontrol agent that produces insecticidal crystal proteins encoded by cry genes, which are effective against various insect orders. However, only a limited number of B. thuringiensis strains are known to be toxic to white grubs, a major pest of coconut, groundnut, and sugarcane that can cause up to 70%-80% yield losses. In this study, five indigenous B. thuringiensis strains, isolated from soil and Anomala elata cadavers, were screened for toxicity against second-instar Holotrichia serrata larvae, a highly destructive white grub species. Among them, the strain NBAIR BtAe exhibited the highest toxicity with an LC₅₀ of 115.36 μg mL-1. Whole-genome sequencing of NBAIR BtAe revealed a 5.67 Mb circular chromosome with 35.64% GC content. BtToxin_Digger analysis identified a novel cry gene with 39.57% similarity to cry21Aa2, along with other virulence genes including zwa6, zwa5A, chitinase C, inhA1, inhA2, bmp1, spp1Aa1, enhancin, and tpp80Ab1-like. These genes were validated through PCR. Additionally, genes encoding secondary metabolites such as lanthipeptides, paenilamicin, petrobactin, bacillibactin, and fengycin were detected. The presence of diverse pesticidal and antimicrobial genes highlights the potential of NBAIR BtAe as a promising candidate for bioinsecticide development targeting H. serrata in integrated pest management programs.

Mycoplasma genitalium is challenging to work with and new methods are needed to study this bacterium directly in clinical samples. This study designed and validated a proof-of-concept polymerase chain reaction (PCR)-based 'tiling' methodology to sequence M. genitalium genomes. Primers were designed to produce 2.5 kb amplicons covering the 580 kb genome with a minimum overlap of 100 bp. Analysis was performed using the laboratory strain G37 and a clinical isolate. Amplicons were sequenced on the Oxford Nanopore MinION using ligation sequencing. Reads were mapped to a reference to produce a consensus genome. A total of 262 primer pairs were designed and amplification was successful for 99.5% (261/262) of 2.5 kb amplicons, with G37 genome coverage of 99.5% (mean read depth, 1973X). Using larger 5kb amplicons, amplification was successful for 92.4% (121/131) of primer pairs, with a coverage of 92.2% (mean read depth, 223X). When validated on a clinical isolate, 98.3% coverage was achieved (read depth, 443X). In conclusion, this study developed a PCR-based tiling approach to whole genome sequencing of M. genitalium by designing and validating a set of 262 primer pairs.

This study uses whole genome sequencing (WGS) to identify beta-lactam resistance-associated mutations in in vitro selected Staphylococcus aureus subsp. aureus ATCC 25923 strains, and correlates the findings with isolates collected from mastitis-infected dairy cows. Resistance was induced in a susceptible strain of S. aureus subsp. aureus ATCC 25923 through serial in vitro exposure to ampicillin sodium salt, cefapirin, cefuroxime sodium salt, and cefquinome. The resulting resistant isolates exhibited thousands of fold increases in minimum inhibitory concentrations (MICs), compared to the susceptible strain. In the absence of antimicrobial selection pressure, the MIC decreased by up to 32-fold, indicating a significant restoration of antimicrobial susceptibility. WGS identified resistance-associated mutations in the penicillin-binding proteins, ABC transporter ATP-binding protein, cell wall-active antibiotics response protein, cyclic-di-AMP phosphodiesterase, and two-component system sensor histidine kinase. Additionally, these mutations were investigated in the S. aureus isolates collected from mastitis-infected dairy cows. These isolates shared the same resistance-associated mutations as in vitro-selected strains. These findings demonstrate that resistance mutations identified through in vitro selection are also present in clinical isolates, highlighting the clinical applicability of in vitro selection for understanding antimicrobial resistance in mastitis-associated S. aureus.