Effects of antibiotic-induced resistance on the growth, survival ability and virulence of Salmonella enterica.

Salmonella enterica is an important foodborne pathogen that constitutes a major health hazard. The emergence and aggravation of antibiotic-resistant Salmonella has drawn attention widely around the world. Conducting a risk assessment of antibiotic-resistant foodborne pathogens throughout the food chain is a pressing requirement for ensuring food safety. The growth, survival capability, and virulence of antibiotic-resistant Salmonella represent crucial biological characteristics that play an important role in microbial risk assessment. In this study, eight antibiotic-sensitive S. enterica strains were induced by Ampicillin (Amp) and Ciprofloxacin (CIP), respectively, and AMP-resistant and CIP-resistant mutants were obtained. The growth characteristics under different temperatures (25, 30, 35 °C), viability after exposure to heat (55, 57.5, 60 °C) and acid (HCl, pH = 3.0), the virulence potential (adhesion and invasion to Caco-2 cells, biofilm formation and motility) and the lethality in a model species (Galleria mellonella) were evaluated and compared for S. enterica strains before and after antibiotic exposure. The induction by AMP and CIP are likely to promote cross-antibiotic resistance to their antibiotic classes, ß-lactams and quinolones, as well as some compound antibiotics. It was observed that generally the antibiotic-induction-resistant strains showed decreased growth ability and lower heat resistance, although the differences were not significant at all the conditions tested. The AMP-resistant strains were significantly less acid resistance than the sensitive and the CIP-resistant ones, while exhibiting increased biofilm formation ability. In general, the antibiotic-induced resistance did not significantly affect the motility, adherence, or invasion ability of Caco-2 cells. However, CIP-resistant strains displayed lower lethality in G. mellonella infection, whereas AMP-resistant strains did not, and even two strains improved lethality. The study of the biological characteristics of antibiotic-resistant S. enterica is essential in better understanding the microbial risks to both the food chain and human health, thereby facilitating a more accurate risk assessment.

SERS determination of the antihypertensive drugs prazosin and losartan by using silver nanoparticles coated with ß-cyclodextrin.

A surface-enhanced Raman scattering (SERS) method is described for the determination of prazosin (PRH) and losartan (LOS). Silver nanoparticles modified with ß-cyclodextrin (CD-S-Ag NPs) were prepared and serve as a sensitive SERS substrate. ß-CD is both a reductant for silver ions and a host molecule that binds the analytes which leads to strong SERS enhancement. The method has distinct features: (a) The linear response extends from 0.1 to 60 µM for PRH, and from 1.0 to 100 µM for LOS; (b) the respective limits of detection are as low as 15 nM and 0.92 µM; and (c) the specific SERS bands of PRH and LOS are located at 703 and 1298 cm-1 respectively. The method was successfully applied to the determination of PRH and LOS illegally added to healthcare products. The recovery of PRH and LOS from spiked samples ranges between 91.3 and 109.3%, and from 87.4 to 105.2%, respectively, both with relative standard deviation of <5%. Graphical abstractSchematic representation of a SERS method involving ß-CD-S-Ag nanoparticles for determination of prazosin and losartan via formation of an inclusion complex.

Determination of the illegal adulteration of natural healthcare products with chemical drugs using surface-enhanced Raman scattering.

The illegal adulteration of natural healthcare products with chemical drugs can result in serious health risks for consumers. Thus there is an urgent need for a fast and precise detection method. In this research, sodium alginate (SA)-silver nanoparticles (AgNPs) were used as a substrate in surface-enhanced Raman scattering (SERS) for determining vardenafil and rosiglitazone maleate (ROS). Sodium alginate can not only reduce silver ions rapidly to AgNPs as reducing agents but can also protect AgNPs from aggregation by its use as a capping agent. The coffee ring effect has also been applied in this research to facilitate the separation and concentration of analytes. A prominent SERS enhancement can be obtained on the ring because of the electromagnetic mechanism. Both of the properties, including the use of SA and the coffee ring effect, make the method more sensitive in detecting the analytes compared to the classical AgNPs, SERS substrate which were produced using the reduction of silver nitrate with sodium citrate. The method displays a linear response for the determination of vardenafil and ROS in the 4.88-488 µg·mL-1 and 4.74-94.7 µg·mL-1 concentration ranges, and the limit of detection is as low as 1.63 µg·mL-1 and 2.20 µg·mL-1, respectively. The method was successfully applied to the detection of vardenafil and ROS in healthcare products, with recoveries between 91.52% to 107.1% and relative standard deviations of less than 4.31%. This method shows good potential for real applications.

Combined host-guest complex with coffee-ring effect for constructing ultrasensitive SERS substrate for phenformin hydrochloride detection in healthcare products.

Phenformin hydrochloride (PHE), once used as a traditional anti-diabetic drug, has now been banned due to significant side effects. However, the phenomenon of the illegal addition of PHE to hypoglycemic healthcare products is still rampant. Thus, the detection of illegally added PHE is urgently needed. Surface-enhanced Raman scattering (SERS) is a promising candidate for this purpose, but the weak affinity between PHE and bare metal (Au or Ag) limits direct SERS detection of PHE. In this paper, we prepared Ag nanoparticles coated with ß-cyclodextrin (AgNP@ß-CD), which display the coffee-ring effect, that can be used for PHE sensing. ß-CD-functionalized nanoparticles could capture the analyte and fix the molecular orientation in the hydrophobic cavity. The coffee-ring effect could improve the SERS effect through a higher concentration of the analyte, higher density of nanoparticles, and more hot spots. The SERS performance of the AgNP@ß-CD substrate was characterized by using o-phenylenediamine dihydrochloride as a probe molecule. The excitation wavelength and pH value were optimized. A linear response for PHE detection is in the 7.0 × 10-8-1.0 × 10-6 mol L-1 concentration range, and the limit of detection is as low as 8.0 × 10-9 mol L-1. This AgNP@ß-CD coffee-ring effect substrate was applied to the detection of PHE in healthcare products, with recoveries between 95.3 and 105.0% and relative standard deviations of less than 5.16%. It is anticipated that the AgNP@ß-CD substrate will also have great potential for the monitoring of other aromatic drugs in healthcare products.

Prevalence, antibiotic resistance and molecular characterization of Staphylococcus aureus in ready-to-eat fruits and vegetables in Shanghai, China.

Staphylococcus aureus (S. aureus) is one of the foodborne pathogens. This study aimed to investigate the prevalence of S. aureus in ready-to-eat (RTE) fruits and vegetables in Shanghai, China. We evaluated antibiotic resistance patterns and genetic diversity of isolates through whole genome sequencing. Our findings demonstrated that out of 143 market samples, 47 (32.87%) tested positive for S. aureus, with the prevalence rates ranging from 10% to 57.14% among 12 types of RTE fruits and vegetables. Most isolates were resistant to trimethoprim-sulphamethoxazole, oxacillin, and ampicillin. We identified a total of 15 antibiotic resistance genes associated with resistance to 6 antibiotics, such as fosfomycin, fluoroquinolone, and ß-lactam. Adhesion genes and enterotoxin genes, including icaA, icaB, icaC, set, seg, and sec, were also identified. Seven multi-locus sequence types (MLST) were detected, two of which were novel (ST7208 and ST7986). Notably, ST705-t529 (34.04%) and ST6-t701 (27.79%) represented the predominant types of S. aureus. Furthermore, three of the isolates were confirmed to be methicillin-resistant S. aureus by mecA genes. Taken together, our results highlight the high prevalence of S. aureus in RTE fruits and vegetables, posing a potential threat to food safety, particularly due to its high level of antibiotic resistance.

Growth, biofilm formation, and motility of Listeria monocytogenes strains isolated from food and clinical samples located in Shanghai (China).

Listeria monocytogenes is a common foodborne pathogen that frequently causes global outbreaks. In this study, the growth characteristics, biofilm formation ability, motility ability and whole genome of 26 L. monocytogenes strains isolated from food and clinical samples in Shanghai (China) from 2020 to 2022 were analyzed. There are significant differences among isolates in terms of growth, biofilm formation, motility, and gene expression. Compared with other sequence type (ST) types, ST1930 type exhibited a significantly higher maximum growth rate, the ST8 type demonstrated a stronger biofilm formation ability, and the ST121 type displayed greater motility ability. Furthermore, ST121 exhibited significantly high mRNA expression levels compared with other ST types in virulence genes mpl, fbpA and fbpB, the quorum sensing gene luxS, starvation response regulation gene relA, and biofilm adhesion related gene bapL. Whole-genome sequencing (WGS) analyses indicated the isolates of lineage I were mostly derived from clinical, and the isolates of lineage II were mostly derived from food. The motility ability, along with the expression of genes associated with motility (motA and motB), exhibited a significantly higher level in lineage II compared with lineage I. The isolates from food exhibited significantly higher motility ability compared with isolates from clinical. By integrating growth, biofilm formation, motility phenotype with molecular and genotyping information, it is possible to enhance comprehension of the association between genes associated with these characteristics in L. monocytogenes.

Comparative Analysis of Growth, Survival, and Virulence Characteristics of Listeria monocytogenes Isolated from Imported Meat.

Listeria monocytogenes is an important foodborne pathogen with worldwide prevalence. Understanding the variability in the potential pathogenicity among strains of different subtypes is crucial for risk assessment. In this study, the growth, survival, and virulence characteristics of 16 L. monocytogenes strains isolated from imported meat in China (2018-2020) were investigated. The maximum specific growth rate (µmax) and lag phase (λ) were evaluated using the time-to-detection (TTD) method and the Baranyi model at different temperatures (25, 30, and 37 °C). Survival characteristics were determined by D-values and population reduction after exposure to heat (60, 62.5, and 65 °C) and acid (HCl, pH = 2.5, 3.5, and 4.5). The potential virulence was evaluated via adhesion and invasion to Caco-2 cells, motility, and lethality to Galleria mellonella. The potential pathogenicity was compared among strains of different lineages and subtypes. The results indicate that the lineage I strains exhibited a higher growth rate than the lineage II strains at three growth temperatures, particularly serotype 4b within lineage I. At all temperatures tested, serotypes 1/2a and 1/2b consistently demonstrated higher heat resistance than the other subtypes. No significant differences in the log reduction were observed between the lineage I and lineage II strains at pH 2.5, 3.5, and 4.5. However, the serotype 1/2c strains exhibited significantly low acid resistance at pH 2.5. In terms of virulence, the lineage I strains outperformed the lineage II strains. The invasion rate to Caco-2 cells and lethality to G. mellonella exhibited by the serotype 4b strains were higher than those observed in the other serotypes. This study provides meaningful insights into the growth, survival, and virulence of L. monocytogenes, offering valuable information for understanding the correlation between the pathogenicity and subtypes of L. monocytogenes.

Sensitive Detection of Rhodamine B in Condiments Using Surface-Enhanced Resonance Raman Scattering (SERRS) Silver Nanowires as Substrate.

In this paper, a facile large-scale preparation of surface-enhanced resonance Raman scattering (SERRS) substrates for the determination of Rhodamine B (RhB) based on silver nanowires (Ag NWs) has been developed. The morphology, structure, and properties of as-prepared Ag NWs are characterized using ultraviolet-visible (UV-Vis) spectroscopy, field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD), respectively. Ag NWs were assembled onto glass slides through a self-assembly method. Moreover, in our experiment, as-prepared Ag NWs@glass were used as a SERRS substrate to detect RhB at the excitation wavelength of 532 nm. Experimental conditions such as pH value and soaking time on SERRS performance were studied and optimized. Under the optimized conditions, the SERRS intensity at 1648 cm-1 exhibited a linear relationship with the concentration of RhB in the range of 1.0 × 10-9-1.0 × 10-5 mol L-1 and detection limit (signal-to-noise ratio [S/N] = 3) is as low as 0.3 nmol L-1. The corresponding correlation coefficient of the linear equation was 0.996. This method based on Ag NWs@glass for the detection of RhB in three kinds of condiment was investigated. The limits of detection (LODs) for RhB were 0.35 µg/g in chili powder, 0.14 µg/g in chili sauce, and 0.02 µg/g in Chinese prickly ash. The relative standard deviations (RSD) were between 2.18% and 4.56% (n = 3) and recoveries at three levels were in the range of 80.0-98.7% for different spiked food products. Moreover, the results showed that the proposed method was sensitive, convenient, and feasible for the determination of RhB in condiments.