Development and performance evaluation of a microbiological method for screening and LC-MS/MS for conformation of sulfonamides in animal-derived foods.

This study developed a highly sensitive microbiological method utilizing a novel microtiter plate to screen 10 sulfonamides in chicken muscles, eggs, and prawns. This plate was fabricated from agar incorporating trimethoprim and spread with Bacillus megaterium. After residue detection by bioassay, the same test solutions were analyzed by LC-MS/MS for accurate identification and quantification. It also proved eco-friendly compared to using other quantitative methods. The residual drugs were extracted with McIlvaine buffer and purified using an Oasis® MCX cartridge. A triethylamine/methanol/water (0.5:75:24.5, v/v/v) mixture was used as the eluate. The obtained LOD values of the bioassay ranged from 5 to 25 µg kg-1 allowing the detection of the target drugs at the MRLs established in Japan. Adhering to ISO/IEC 17025 standards, the performance of the bioassay was evaluated. Based on the inhibition zone size in bioassay results, quality control yielded a Z score within ±2, indicating reasonable control over the screening process. Proficiency testing of a chicken muscle sample spiked with sulfadimidine demonstrated the inhibition zone detection of the bioassay and quantified value alignment of LC-MS/MS with reference values. In a surveillance study of 91 samples, sulfamethoxazole was detected in one prawn sample.

Development of a simple screening method for analyzing cereulide toxin in fried rice using liquid chromatography-tandem mass spectrometry.

PURPOSE: The presence of cereulide, an emetic toxin produced by Bacillus cereus, in fried rice samples is critical evidence of food poisoning even in situations where B. cereus could not be detected. This study aims to develop a screening method for analyzing cereulide in fried rice using the QuEChERS procedure and liquid chromatography-tandem mass spectrometry (LC-MS/MS). METHODS: Cereulide was identified and quantified in fried rice samples using the QuEChERS extraction method and LC-MS/MS. The accuracies of the methods were determined by analyzing fortified blank samples at two concentrations (10 and 50 µg/kg) conducted on three samples daily for five days. RESULTS: The QuEChERS procedure removed matrix compounds from fried rice. Characteristic MS/MS spectra enabled the identification of cereulide. As the matrix effects in seven fried rice samples were within ± 6%, an external solvent calibration curve could be used for quantification. This method exhibited good accuracy ranging from 88 to 89%. The relative standard deviations for both repeatability and intra-laboratory reproducibility were < 4%. These standard deviations satisfied the criteria of the Japanese validation guidelines for residues (MHLW 2010, Director Notice, Syoku-An No. 1224-1). The limit of quantification was 2 µg/kg. The applicability of this method was confirmed using the analysis of cereulide in fried rice samples incubated with emetic Bacillus cereus. CONCLUSIONS: The QuEChERS extraction procedure described herein showed substantial promise as a reliable screening tool for cereulide in fried rice sample.

Simultaneous determination of five carbapenems, highly polar antibiotics, in milk by LC-MS/MS.

The simultaneous determination of five carbapenems (biapenem, doripenem, ertapenem, imipenem, and meropenem) in raw and pasteurised bovine milk samples using LC-MS/MS was achieved and validated. Chromatographic separation was conducted on an InertSustain® AQ-C18 column using 0.1% formic acid in water and acetonitrile as the mobile phase. Target compounds were extracted using acetonitrile/water (20:80, v/v). After the removal of lipids with acetonitrile-saturated hexane, the dissolved protein was denatured with acetic acid. A portion of the supernatant was passed through an Oasis® PRiME HLB cartridge to remove the matrix. This novel method was validated in accordance with the Japanese validation guidelines and exhibited good trueness, ranging from 86.3% to 96.2%, using matrix-matched calibration curves. The relative standard deviation of repeatability ranged from 1.0% to 6.3%, and that of within-laboratory reproducibility ranged from 1.6% to 7.1%. The limit of quantification was 1.0 µg kg-1 for all analytes. None of the 60 milk samples commercially available in Tokyo contained any analytes. This novel method exhibited high-quality performance and can easily be implemented for the routine monitoring of carbapenems, which are highly polar antibiotics in milk.

Induction of open-form bile canaliculus formation by hepatocytes for evaluation of biliary drug excretion.

Biliary excretion is a major drug elimination pathway that affects their efficacy and safety. The currently available in vitro sandwich-cultured hepatocyte method is cumbersome because drugs accumulate in the closed bile canalicular lumen formed between hepatocytes and their amounts cannot be mealsured directly. This study proposes a hepatocyte culture model for the rapid evaluation of drug biliary excretion using permeation assays. When hepatocytes are cultured on a permeable support coated with the cell adhesion protein claudins, an open-form bile canalicular lumen is formed at the surface of the permeable support. Upon application to the basolateral (blood) side, drugs appear on the bile canalicular side. The biliary excretion clearance of several drugs, as estimated from the obtained permeabilities, correlates well with the reported in vivo biliary excretion clearance in humans. Thus, the established model is useful for applications in the efficient evaluation of biliary excretion during drug discovery and development.

Small RNA-mediated silencing of phototropin suppresses the induction of photoprotection in the green alga Chlamydomonas reinhardtii.

Small RNAs (sRNAs) form complexes with Argonaute proteins and bind to transcripts with complementary sequences to repress gene expression. sRNA-mediated regulation is conserved in a diverse range of eukaryotes and is involved in the control of various physiological functions. sRNAs are present in the unicellular green alga Chlamydomonas reinhardtii, and genetic analyses revealed that the core sRNA biogenesis and action mechanisms are conserved with those of multicellular organisms. However, the roles of sRNAs in this organism remain largely unknown. Here, we report that Chlamydomonas sRNAs contribute to the induction of photoprotection. In this alga, photoprotection is mediated by LIGHT HARVESTING COMPLEX STRESS-RELATED 3 (LHCSR3), whose expression is induced by light signals through the blue-light receptor phototropin (PHOT). We demonstrate here that sRNA-defective mutants showed increased PHOT abundance leading to greater LHCSR3 expression. Disruption of the precursor for two sRNAs predicted to bind to the PHOT transcript also increased PHOT accumulation and LHCSR3 expression. The induction of LHCSR3 in the mutants was enhanced by light containing blue wavelengths, but not by red light, indicating that the sRNAs regulate the degree of photoprotection via regulation of PHOT expression. Our results suggest that sRNAs are involved not only in the regulation of photoprotection but also in biological phenomena regulated by PHOT signaling.

[Single-laboratory Validation Study and Surveillance Using an Improved Multiresidue Analytical Method for Veterinary Drugs in Livestock Products by LC-MS/MS].

A method for the rapid analysis of multiclass residual veterinary drugs in poultry muscle, egg, and raw milk was validated in accordance with Japanese guidelines. Using LC-MS/MS, 20 veterinary drugs, including sulfonamides, coccidiostats, and macrolides were analyzed in one injection. Analytes were extracted from the samples with acetonitrile and then dehydrated and salted out using magnesium sulfate, trisodium citrate, and sodium chloride. This method was assessed by performing recovery tests of chicken muscle, duck muscle, egg, and raw milk spiked with 20 new target analytes at concentrations of 10 and 100 µg/kg. According to this method, 17 out of 20 target analytes satisfied the guideline criteria in chicken muscle and duck muscle, and all 20 target analytes met the criteria in egg and raw milk. The limit of quantification was less than MRLs for all analytes. Residues were detected in 4 out of 99 samples and analyzed using the validated method, finding that the levels of all residues were lower than the limits of quantification. These results suggest that continuous monitoring for a new trend of veterinary drugs is necessary.

Validation and application of an immunochromatographic test to detect four macrolides and two lincosamides in raw cow milk.

In this study, an immunochromatographic test (using the Charm QUAD2® Test) was used to screen for residual macrolides and lincosamides in raw cow's milk. The validation parameters (selectivity/specificity, detection capability (CCß), and ruggedness) were in agreement with the requirements of[EC] 2021. The selectivity of the immunochromatographic test was verified by the negative results of microbiological tests. The false-positive rate was 0%. The CCß values of the immunochromatographic test for various antibiotics in milk were as follows: erythromycin 0.02 mg/kg, spiramycin 0.1 mg/kg, tilmicosin 0.025 mg/kg, tylosin 0.05 mg/kg, lincomycin 0.15 mg/kg, and pirlimycin 0.15 mg/kg. The determined CCß values were lower than the respective maximum residue limits (MRLs; regulatory limits in Japan) for milk, except for lincomycin (equal to the MRL). The presence of antibiotic groups other than macrolides and lincosamides did not interfere with the specificity of the test. It showed no significant difference in lot-to-lot repeatability. The results obtained by the two researchers showed no significant differences. Finally, the test was applied to milk samples obtained from a tylosin-treated cow. The outcome was positive and in agreement with the results of the chemical analytical and microbiological methods. Therefore, this validated immunochromatographic test is expected to be suitable for routine analysis to ensure milk safety.

Proteomic identification and quantification of Clostridium perfringens enterotoxin using a stable isotope-labelled peptide via liquid chromatography-tandem mass spectrometry.

PURPOSE: Detection of Clostridium perfringens enterotoxin (CPE) in human stool is critical evidence of food poisoning. However, processing patient-derived samples is difficult and very few methods exist to confirm the presence of CPE. In this study, a technique was developed using proteomic analysis to identify and quantify CPE in artificial gut fluid as an alternative. METHODS: The standard CPE was spiked into artificial gut fluids, and effective methods were developed by employing both a stable isotope-labelled internal standard peptide and liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: Proteotypic peptide EILDLAAATER formed by tryptic digestion was selected for quantitation of CPE. The peptide was identified using product ion spectra. Although the nontoxic peptides originating from CPE showed very low detectability in extraction and tryptic digestion, they could be detected with sufficient sensitivity using the method we developed. Based on a spiked recovery test at two concentrations (50 and 200 µg/kg), the recovery values were 85 and 78%, respectively. The relative standard deviations of repeatability and within-laboratory reproducibility were less than 8 and 11%, respectively. These standard deviations satisfied the criteria of the Japanese validation guidelines for residues (MHLW 2010, Director Notice, Syoku-An No. 1224-1). The limit of quantification (LOQ) was estimated to be 50 µg/kg. The combination of the product ion spectra and relative ion ratio supported CPE identification at the LOQ level. CONCLUSIONS: To the best of our knowledge, this is the first report of proteomic analysis of CPE using LC-MS/MS. The method would greatly help in assessing CPE reliably.

[Surveillance of Acaricides in Honey].

By using the LC-MS/MS method developed by us, we determined the residual amounts of acaricides in honey samples commercially available in Tokyo from April 2015 to March 2021. The results of analyzing 127 honey samples, amitraz was detected in 85 samples at the level of 1.1-34.1 µg/kg. Propargite was detected in 3 samples at 2.4-3.8 µg/kg. None of them was beyond the Japanese MRLs or uniform limits. In these survey for 6 years, amitraz was detected in high rate throughout the year. But, the present results imply that amitraz has been used properly in actual bee-keeping because of no violation of MRL and less fluctuation in the detected levels. On the other hand, propargite was detected at the levels over LOQ in domestic honey samples for the first time in 2020, which may suggest a new trend of acaricide use in apiculture in Japan.

Monitoring of residual antibacterial agents in animal and fishery products in Tokyo from 2003 to 2019: application and verification of a screening strategy based on microbiological methods.

Residual antibacterial agents in 5909 animal and fishery products in Tokyo, Japan, were investigated over 17 consecutive years (2003-2019). Monitoring of 32 antibacterial agents (lincosamides, macrolides, penicillins, quinorones and tetracyclines) per product was accomplished via two steps: screening (by microbiological methods) and confirmation (by instrumental methods). Microbiological screening methods identified presumptive groups and determined semi-quantitative values. The instrumental methods quantified 81 residues of 11 different antibacterial agents in 72 samples. The screening strategy based on microbiological methods demonstrated the following: (i) the majority of the samples (over 99%) met Japanese regulations, (ii) using multiple methods provided a reliable inspection system with accurate quantitative values and (iii) there was a constant presence of tetracyclines and unexpected residues (lincomycin and norfloxacin) in various products. Thus, this long-term monitoring and screening strategy provided evidence that the frequencies and trends of residual antibacterial agents not only enhance food safety but also help to prevent antimicrobial resistance.

[Determination of Antibacterial Agents for Animals in Swine Muscles by Microbiological Screening and LC-MS/MS].

The determination of antibacterial agents for animals in swine muscles was improved by microbiological screening and liquid chromatography-mass spectrometry (LC-MS/MS) analyses. In the first instance, the residual drugs were extracted from the samples using the Na2EDTA-McIlvaine buffer (pH 6.0). Subsequently, the agents were purified utilizing a PLS-3 cartridge and extracted with acetonitrile. Considering the microbiological methods, the sensitivities of the investigated drugs were higher and the test plate conditions were improved using a new reference organism Geobacillus stearothermophilus. As a result, a microbiological screening approach able to detect 33 drugs at MRL was developed in Japan. Remarkable, no false positives were detected. Moreover, the same preparation method enabled rapid and reliable microbiological screening, resulting in efficient screening with no undeterminable results.

Development of an alternative approach for detecting botulinum neurotoxin type A in honey: Analysis of non-toxic peptides with a reference labelled protein via liquid chromatography-tandem mass spectrometry.

In this study, we developed a reference labelled protein containing the partial amino acid sequence of botulinum neurotoxin type A (BoNTA). We also applied it as an internal standard to detect specific and non-toxic peptides originated from BoNTA in honey with the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Original proteins in the honey sample were collected through a two-step process that included solubilisation and trichloroacetic acid (TCA) precipitation. Solubilisation by adding water enabled processing of proteins in honey. TCA precipitation collected proteins without specific binding. The combination of protein alkylation and an appropriate enzyme-to-protein ratio ensured feasibility of tryptic digestion. A desalting process eliminated a large amount of salts and other tryptic peptides in the honey sample. The use of the reference labelled protein enabled compensation for tryptic digestion efficiency and electrospray ionisation efficiency based on LC-MS/MS measurement. After the peptide selection and protein BlastP analysis, five unique peptides were chosen. The non-toxic peptides originating from BoNTA were reliably detected using LC-MS/MS based on a multiple-reaction monitoring mode. Detection of several peptides ensured screening of BoNTA in honey samples. Based on the responses, the proteotypic peptide LYGIAINPNR was selected as the quantitative peptide. Due to maintaining the relative ion ratios, the selective transition completely identified the non-toxic peptides. The intensity of the transitions established a detection limit of BoNTA estimated to be 9.4 ng mL-1. Although extraction efficiency was not evaluated using the BoNTA standard, the results suggested this method may be used for quantification of BoNTA in honey. The method was applied to 19 honey samples purchased in Tokyo; none of them was found to contain the target toxin. Overall, the method is expected to accelerate BoNTA monitoring for food safety.