A 16-year retrospective surveillance report on the pathogenic features and antimicrobial susceptibility of Pseudomonas aeruginosa isolates from FAHJU in Guangzhou representative of Southern China

Whole-genome sequencing, multilocus sequence typing, and resistance mechanism of the carbapenem-resistant Pseudomonas aeruginosa in China

Pseudomonas aeruginosa is a significant pathogen responsible for severe multisite infections with high morbidity and mortality rates. This study analyzed carbapenem-resistant Pseudomonas aeruginosa (CRPA) at a tertiary hospital in Shandong, China, using whole-genome sequencing (WGS). The objective was to explore the mechanisms and molecular characteristics of carbapenem resistance. A retrospective analysis of 91 isolates from January 2022 to March 2023 was performed, which included strain identification and antimicrobial susceptibility testing. WGS was utilized to determine the genome sequences of these CRPA strains, and the species were precisely identified using average nucleotide identification (ANI), with further analysis on multilocus sequence typing and strain relatedness. Some strains were found to carry the ampD and oprD genes, while only a few harbored carbapenemase genes or related genes. Notably, all strains possessed the mexA, mexE, and mexX genes. The major lineage identified was ST244, followed by ST235. The study revealed a diverse array of carbapenem resistance mechanisms among hospital isolates, differing from previous studies in mainland China. It highlighted that carbapenem resistance is not due to a single mechanism but rather a combination of enzyme-mediated resistance, AmpC overexpression, OprD dysfunction, and efflux pump overexpression. This research provides valuable insights into the evolutionary mechanisms and molecular features of CRPA resistance in this region, aiding in the national prevention and control of CRPA, and offering references for targeting and developing new drugs.

Assessment of multispecies biofilm growth on root canal dentin under different radiation therapy regimens

OBJECTIVES

To assess the growth of a multispecies biofilm on root canal dentin under different radiotherapy regimens.

MATERIALS AND METHODS

Sixty-three human root dentin cylinders were distributed into six groups. In three groups, no biofilm was formed (n = 3): NoRT) non-irradiated dentin; RT55) 55 Gy; and RT70) 70 Gy. In the other three groups (n = 18), a 21-day multispecies biofilm (Enterococcus faecalis, Streptococcus mutans, and Candida albicans) was formed in the canal: NoRT + Bio) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. The biofilm was quantified (CFUs/mL). Biofilm microstructure was assessed under SEM. Microbial penetration into dentinal tubules was assessed under CLSM. For the biofilm biomass and dentin microhardness pre- and after biofilm growth assessments, 45 bovine dentin specimens were distributed into three groups (n = 15): NoRT) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm.

RESULTS

Irradiated specimens (70 Gy) had higher quantity of microorganisms than non-irradiated (p = .010). There was gradual increase in biofilm biomass from non-irradiated to 55 Gy and 70 Gy (p < .001). Irradiated specimens had greater reduction in microhardness after biofilm growth. Irradiated dentin led to the growth of a more complex and irregular biofilm. There was microbial penetration into the dentinal tubules, regardless of the radiation regimen.

CONCLUSION

Radiotherapy increased the number of microorganisms and biofilm biomass and reduced dentin microhardness. Microbial penetration into dentinal tubules was noticeable.

CLINICAL RELEVANCE

Cumulative and potentially irreversible side effects of radiotherapy affect biofilm growth on root dentin. These changes could compromise the success of endodontic treatment in oncological patients undergoing head and neck radiotherapy.

In-vitro activity of ceftolozane/tazobactam against Pseudomonas aeruginosa collected in the Study for Monitoring Antimicrobial Resistance Trends (SMART) between 2016 and 2019 in China

Ceftolozane/tazobactam (an antipseudomonal cephalosporin) in combination with a well-established β-lactamase inhibitor has not been approved to date in clinical practice in China. The aim of this study was to evaluate the in-vitro activity of ceftolozane/tazobactam and comparator agents against Pseudomonas aeruginosa with various resistance patterns. P. aeruginosa (n=2178) specimens were collected from multiple sources in seven geographic regions of China between 2016 and 2019. All isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and minimum inhibitory concentrations of various antimicrobial agents (ceftolozane/tazobactam, amikacin, tobramycin, ceftazidime, cefepime, colistin, levofloxacin, aztreonam, meropenem, imipenem and piperacillin/tazobactam) were determined using the Clinical and Laboratory Standards Institute's broth microdilution method. P. aeruginosa demonstrated considerably high rates of multi-drug resistance (MDR, 57.3%), extensive drug resistance (XDR, 43.5%) and difficult-to-treat resistance (DTR, 16.8%). The overall susceptibility of P. aeruginosa to ceftolozane/tazobactam was 81.9%, and ceftolozane/tazobactam showed diverse activity against the three resistant subsets, ranging from 28.5% against DTR P. aeruginosa to 68.9% against MDR P. aeruginosa. P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa derived from the East (Jiangzhe area) region maintained significantly lower susceptibility to ceftolozane/tazobactam compared with P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa from other regions. The susceptibility rates of P. aeruginosa isolated from diverse sources to ceftolozane/tazobactam were similar to isolates from bloodstream infections, with the highest being 88.6%. Compared with other antimicrobial agents, ceftolozane/tazobactam was more active than the β-lactams tested but was slightly less active than amikacin. Amikacin demonstrated the best activity against P. aeruginosa and the three resistant subsets. Ceftolozane/tazobactam demonstrated considerable in-vitro activity against P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa, indicating that it could be an optional therapeutic agent against P. aeruginosa.

Novel quinoline-based derivatives as the PqsR inhibitor against Pseudomonas aeruginosa PAO1

AIMS

The emerging of drug resistant Pseudomonas aeruginosa is a critical challenge and renders an urgent action to discover innovative antimicrobial interventions. One of these interventions is to disrupt the pseudomonas quinolone signal (pqs) quorum sensing (QS) system, which governs multiple virulence traits and biofilm formation. This study aimed to investigate the QS inhibitory activity of a series of new PqsR inhibitors bearing a quinoline scaffold against Ps. aeruginosa.

METHODS AND RESULTS

The results showed that compound 1 suppressed the expression of QS-related genes and showed the best inhibitory activity to the pqs system of wild-type Ps. aeruginosa PAO1 with an IC₅₀ of 20.22 μmol l^-1 . The virulence factors including pyocyanin, total protease, elastase, and rhamnolipid were significantly suppressed in a concentration-dependent manner with the compound. In addition, 1 in combination with tetracycline inhibited synergistically the bacterial growth and suppressed the biofilm formation of PAO1. The molecular docking studies also suggested that 1 could potentially interact with the ligand-binding domain of the Lys-R type transcriptional regulator PqsR as a competitive antagonist.

CONCLUSIONS

The quinoline-based derivatives were found to interrupt the quorum sensing system via the pqs pathway and thus the production of virulence factors was inhibited and the antimicrobial susceptibility of Ps. aeruginosa was enhanced.

SIGNIFICANCE AND IMPACT OF STUDY

The study showed that the quinoline-based derivatives could be used as an anti-virulence agent for treating Ps. aeruginosa infections.

Pseudomonas aeruginosa: A typical biofilm forming pathogen and an emerging but underestimated pathogen in food processing

Pseudomonas aeruginosa (P. aeruginosa) is a notorious gram-negative pathogenic microorganism, because of several virulence factors, biofilm forming capability, as well as antimicrobial resistance. In addition, the appearance of antibiotic-resistant strains resulting from the misuse and overuse of antibiotics increases morbidity and mortality in immunocompromised patients. However, it has been underestimated as a foodborne pathogen in various food groups for instance water, milk, meat, fruits, and vegetables. Chemical preservatives that are commonly used to suppress the growth of food source microorganisms can cause problems with food safety. For these reasons, finding effective, healthy safer, and natural alternative antimicrobial agents used in food processing is extremely important. In this review, our ultimate goal is to cover recent advances in food safety related to P. aeruginosa including antimicrobial resistance, major virulence factors, and prevention measures. It is worth noting that food spoilage caused by P. aeruginosa should arouse wide concerns of consumers and food supervision department.

Quercetin modulates the gut microbiota as well as the metabolome in a rat model of osteoarthritis

Although the mechanism of osteoarthritis (OA) has been widely studied and the use of quercetin for OA therapy is well documented, the relevant characteristics of the microbiome and metabolism remain unclear. This study reports changes in the gut microbiota and metabolism during quercetin therapy for OA in a rat model and provides an integrative analysis of the biomechanism. In this study, the rats were categorized into 3 different groups: the OA model, quercetin treatment, and control groups. The OA rats was conducted using a monoiodoacetate (MIA) injection protocol. The rats in the quercetin group received daily intragastric administration of quercetin from day 1 to day 28. Stool samples were collected, and DNA was extracted. We used an integrated approach that combined the sequencing of whole 16S rRNA, short-chain fatty acid (SCFA) measurements and metabolomics analysis by mass spectrometry (MS) to characterize the functional impact of quercetin on the gut microbiota and metabolism in a rat model of OA. The use of quercetin partially abrogated intestinal flora disorder and reversed fecal metabolite abnormalities. Compared with the control rats, the OA rats showed differences at both the class level (Clostridia, Bacteroidia, and Bacilli) and the genus level (Lactobacillus and unidentified Ruminococcaceae). Acetic acid, propionic acid and 24 metabolites were significantly altered among the three groups. However, the changes were significantly abrogated in quercetin-treated OA rats. Consequently, this study provided important evidence regarding perturbations of the gut microbiome and the function of these changes in a potential new mechanism of quercetin treatment.

Analysis and Construction of a Competitive Endogenous RNA Regulatory Network of Baicalin-Induced Apoptosis in Human Osteosarcoma Cells

Background

Baicalin is an extract from the traditional Chinese herb Scutellaria baicalensis and has the potential to treat osteosarcoma (OS). However, the transcriptome-level mechanism of baicalin-mediated antitumor effects in OS has not yet been investigated. The aim of this study was to analyze the competitive endogenous RNA (ceRNA) regulatory network involved in baicalin-induced apoptosis of OS cells.

Methods

In this study, CCK-8 and flow cytometry assays were used to detect the antitumor effects of baicalin on human OS MG63 cells. Furthermore, transcriptome sequencing was employed to establish the long noncoding RNA (lncRNA), microRNA (miRNA), and mRNA profiles.

Results

Baicalin inhibited MG63 cell proliferation and induced apoptosis. Totals of 58 lncRNAs, 31 miRNAs, and 2136 mRNAs in the baicalin-treated MG63 cells were identified as differentially expressed RNAs compared to those in control cells. Of these, 2 lncRNAs, 3 miRNAs, and 18 mRNAs were included in the ceRNA regulatory network. The differentially expressed RNAs were confirmed by quantitative real-time PCR (qRT-PCR).

Conclusions

By identifying the ceRNA network, our results provide new information about the possible molecular basis of baicalin, which has potential applications in OS treatment.

Bioprocessing and integration of a high flux screening systematic platform based on isothermal amplification for the detection on 8 common pathogens

During a large variety of common pathogens, E. coli, P. aeruginosa, MRSA, MRCNS, V. parahaemolyticus, L. monocytogenes and Salmonella are the leading pathogens responsible for large number of human infections and diseases. In this study, a high flux screening based on nucleic acid isothermal amplification technique has been developed. For the 8 common pathogens, species-specific targets had been selected and analyzed for their unique specificity. After optimization, separate LAMP reaction assays had been bioprocessed and integrated into one systematic detection platform, including 8 strips (PCR tubes) and 96-well plates. Eight standard strains verified for the accuracy. Application of the established high flux screening platform was used for detection for 48 samples in 4 different 96-well plates, with 2 groups of 2 operators using double-blind procedure. The accuracy of 100% was obtained, with the total time consumption as 66-75 min (for 12 samples detection on 8 different pathogens). As concluded, through the bioprocess of the systematic platform based on LAMP technique, it's been demonstrated to be capable of simultaneous detection of 8 pathogens, with high sensitivity, specificity, rapidity and convenience.

"One-step" characterization platform for pathogenic genetics of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is an important human pathogen causing a variety of life-threatening diseases. In recent years, the health problem caused by S. aureus contaminated food has become a global health problem. S. aureus can express various pathogenic factors, mainly used for adhesion, colonization, invasion and infection of the host. Therefore, rapid and accurate detection of virulence genes in S. aureus is necessary to prevent outbreaks caused by this pathogen. PCR is a useful tool for rapid detection of foodborne pathogens. The objective of this study was to detect the presence of major toxin genes in S. aureus, including sea, seb, sec, see, pvl and tsst, by using a PCR plate. Of the 13 strains tested, 12 (92.3%) were found to be positive for one or more toxin genes. This study realized the one-step detection of main toxin factors in S. aureus.

Pathogenic and Virulence Factor Detection on Viable but Non-culturable Methicillin-Resistant Staphylococcus aureus

Food safety and foodborne infections and diseases have been a leading hotspot in public health, and methicillin-resistant Staphylococcus aureus (MRSA) has been recently documented to be an important foodborne pathogen, in addition to its recognition to be a leading clinical pathogen for some decades. Standard identification for MRSA has been commonly performed in both clinical settings and food routine detection; however, most of such so-called "standards," "guidelines," or "gold standards" are incapable of detecting viable but non-culturable (VBNC) cells. In this study, two major types of staphylococcal food poisoning (SFP), staphylococcal enterotoxins A (sea) and staphylococcal enterotoxins B (seb), as well as the panton-valentine leucocidin (pvl) genes, were selected to develop a cross-priming amplification (CPA) method. Limit of detection (LOD) of CPA for sea, seb, and pvl was 75, 107.5, and 85 ng/μl, indicating that the analytical sensitivity of CPA is significantly higher than that of conventional PCR. In addition, a rapid VBNC cells detection method, designated as PMA-CPA, was developed and further applied. PMA-CPA showed significant advantages when compared with PCR assays, in terms of rapidity, sensitivity, specificity, and accuracy. Compared with conventional VBNC confirmation methods, the PMA-CPA showed 100% accordance, which had demonstrated that the PMA-CPA assays were capable of detecting different toxins in MRSA in VBNC state. In conclusion, three CPA assays were developed on three important toxins for MRSA, and in combination with PMA, the PMA-CPA assay was capable of detecting virulent gene expression in MRSA in the VBNC state. Also, the above assays were further applied to real samples. As concluded, the PMA-CPA assay developed in this study was capable of detecting MRSA toxins in the VBNC state, representing first time the detection of toxins in the VBNC state.

Development of a Direct and Rapid Detection Method for Viable but Non-culturable State of Pediococcus acidilactici

Pediococcus acidilactici may significantly reduce the pH-value, and thus has different influence, including serving as a probiotic in human microbiota but a spoilage in human food as it could change the flavor. Pediococcus acidilactici is also capable of entering into the viable but non-culturable (VBNC) state causing false negative results of standard culture-based detection method. Thus, development of detection method for VBNC state P. acidilactici is of great significance. In this study, propidium monoazide (PMA) combined with cross priming amplification (CPA) was developed to detect the VBNC cells of P. acidilactici and applied on the detection in different systems. With detection limit of 10⁴ cells/ml, high sensitivity, and 100% specificity, PMA-CPA can successfully detect VBNC cells of P. acidilactici and be applied in with high robustness.

Direct Detection of Viable but Non-culturable (VBNC) Salmonella in Real Food System by a Rapid and Accurate PMA-CPA Technique

Salmonella enterica is a typical foodborne pathogen with multiple toxic effects, including invasiveness, endotoxins, and enterotoxins. Viable but nonculturable (VBNC) is a type of dormant form preserving the vitality of microorganisms, but it cannot be cultured by traditional laboratory techniques. The aim of this study is to develop a propidium monoazide-crossing priming amplification (PMA-CPA) method that can successfully detect S. enterica rapidly with high sensitivity and can identify VBNC cells in food samples. Five primers (4s, 5a, 2a/1s, 2a, and 3a) were specially designed for recognizing the specific invA gene. The specificity of the CPA assay was tested by 20 different bacterial strains, including 2 standard S. enterica and 18 non-S. enterica bacteria strains covering Gram-negative and Gram-positive isolates. Except for the two standard S. enterica ATCC14028 and ATCC29629, all strains showed negative results. Moreover, PMA-CPA can detect the VBNC cells both in pure culture and three types of food samples with significant color change. In conclusion, the PMA-CPA assay was successfully applied on detecting S. enterica in VBNC state from food samples.

A Meta-Analysis of the Prevalence of Class 1 Integron and Correlation with Antibiotic Resistance in Pseudomonas aeruginosa Recovered from Iranian Burn Patients

The role of integrons has been highlighted in antibiotic resistance among Pseudomonas aeruginosa isolates. Therefore, we here reviewed the prevalence of class 1 integrons and their correlations with antibiotic resistance of P. aeruginosa isolated from Iranian burn patients. This review was conducted according to the guidelines of Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA). Cross-sectional and cohort studies published from January 1, 2000 until December 31, 2018 were enrolled. Meta-analysis was performed by Comprehensive Meta-Analysis (CMA) software using the random effects model, Cochran's Q, and I2 tests. Publication bias was estimated by Funnel plot and Egger's linear regression test. Nine out of 819 studies met the eligibility criteria. The overall combined prevalence of class 1 integrons in P. aeruginosa isolates was 69% (95% confidence interval [CI]: 50.5-83%). The highest combined resistance was reported against Cloxacillin (87.7%), followed by Carbenicillin (79.1%) and Ceftriaxone (77.3%). The combined prevalence of multidrug-resistant (MDR) isolates was 79.3% (95% CI: 31.1-97%). Also, a significant correlation was noted between the presence of class 1 integrons and antibiotic resistance in 55.5% of the included studies (P < .05). The results showed high prevalence of class 1 integrons, antibiotic resistance, and MDR strains in P. aeruginosa isolated from Iranian burn patients. Also, most of the included studies showed a significant correlation between the presence of class 1 integrons and antibiotic resistance.

Study on the Viable but Non-culturable (VBNC) State Formation of Staphylococcus aureus and Its Control in Food System

A Viable but non-culturable (VBNC) state is a bacterial survival strategy under reverse conditions. It poses a significant challenge for public health and food safety. In this study, the effect of external environmental conditions including acid, nutrition, and salt concentrations on the formation of S. aureus VBNC states at low temperatures were investigated. Different acidity and nutritional conditions were then applied to food products to control the VBNC state formation. Four different concentration levels of each factor (acid, nutrition, and salt) were selected in a total of 16 experimental groups. Nutrition showed the highest influence on the VBNC state formation S. aureus, followed by acid and salt. The addition of 1% acetic acid could directly kill S. aureus cells and inhibit the formation of the VBNC state with a nutrition concentration of 25, 50, and 100%. A propidium monoazide-polymerase chain reaction (PMA-PCR) assay was applied and considered as a rapid and sensitive method to detect S. aureus in VBNC state with the detection limit of 104 CFU/mL.

Study on the virulome and resistome of a vancomycin intermediate-resistance Staphylococcus aureus

Methicillin-resistant S. aureus (MRSA) has been considered a potential "Super Bugs", responsible for various infectious diseases. Vancomycin has been the most effective antibitic to treat MRSA originated infections. In this study, we aimed at investigating the genomic features of a vancomycin intermediate-resistance S. aureus strain Guangzhou-SauVS2 isolated from a female patient suffering from chronic renal function failure, emphasizing on its antimicrobial resistance and virulence determinants. The genome has a total length of 2,605,384 bp and the G+C content of 33.21%, with 2,239 predicted genes annotated with GO terms, COG categories, and KEGG pathways. Besides the carriage of vancomycin b-type resistance protein responsible for the vancomycin intermediate-resistance, S. aureus strain Guangzhou-SauVS2 showed resistance to β-lactams, quinolones, macrolide, and tetracycline, due to the acquisition of corresponding antimicrobial resistance genes. In addition, virulence factors including adherence, antiphagocytosis, iron uptake, and toxin were determined, indicating the pathogenesis of the strain.

Microbiome characterization and re-design by biologic agents for inflammatory bowel disease insights

The therapeutic effect of inflammatory bowel disease has improved in the past decades, but most of patients cannot tolerate, do not respond to drugs, or relapse after treating with conventional therapy. Therefore, new and more effective treatment methods are still needed in treatment of IBD. In this review, we will discuss the relevant mechanisms and the latest research progress of biologics (anti-TNF treatments, interleukin inhibitors, integrin inhibitors, antisense oligonucleotide, and JAK inhibitors) for IBD, focus on the efficacy and safety of drugs for moderate-to-severe IBD, and summarize the clinical status and future development direction of biologics in IBD.

High-flux simultaneous screening of common foodborne pathogens and their virulent factors

Rapid and sensitive detection techniques for foodborne pathogens are important to the food industry. However, traditional detection methods rely on bacterial culture in combination with biochemical tests, a process that typically takes 4-7 days to complete. In this study, we described a high-flux polymerase chain reaction (PCR) method for simultaneous detection of nine targeted genes (rfbE, stx1, stx2, invA, oprI, tlh, trh, tdh, and hlyA) with multiplex strains. The designed primers were highly specific for their respective target gene fragments. As the selected primers follow the principles of similar melting and annealing temperature, all the targeted genes could be detected for one strain with the same PCR program. Combining with 96-well PCR plate, by adding a single different gene to each well in each row, both the ATCC strains (E. coli, Salmonella spp., V. parahaemolyticus, L. monocytogenes, P. aeruginosa, S. aureus) and the clinical strains (E. coli, P. aeruginosa, S. aureus) were simultaneously detected to carry their specific and virulence genes. Therefore, using 96-well PCR plate for PCR amplification might be applied to high-flux sequencing of specific and virulence genes.

Formation and Control of the Viable but Non-culturable State of Foodborne Pathogen Escherichia coli O157:H7

As a common foodborne pathogen, Escherichia coli O157:H7 produces toxins causing serious diseases. However, traditional methods failed in detecting E. coli O157:H7 cells in the viable but non-culturable (VBNC) state, which poses a threat to food safety. This study aimed at investigating the formation, control, and detection of the VBNC state of E. coli O157:H7. Three factors including medium, salt, and acid concentrations were selected as a single variation. Orthogonal experiments were designed with three factors and four levels, and 16 experimental schemes were used. The formation of the VBNC state was examined by agar plate counting and LIVE/DEAD^® BacLight^TM bacterial viability kit with fluorescence microscopy. According to the effects of environmental conditions on the formation of the VBNC state of E. coli O157:H7, the inhibition on VBNC state formation was investigated. In addition, E. coli in the VBNC state in food samples (crystal cake) was detected by propidium monoazide-polymerase chain reaction (PMA-PCR) assays. Acetic acid concentration showed the most impact on VBNC formation of E. coli O157:H7, followed by medium and salt concentration. The addition of 1.0% acetic acid could directly kill E. coli O157:H7 and eliminate its VBNC formation. In crystal cake, 25, 50, or 100% medium with 1.0% acetic acid could inhibit VBNC state formation and kill E. coli O157:H7 within 3 days. The VBNC cell number was reduced by adding 1.0% acetic acid. PMA-PCR assay could be used to detect E. coli VBNC cells in crystal cake with detection limit at 10⁴ CFU/ml. The understanding on the inducing and inhibitory conditions for the VBNC state of E. coli O157:H7 in a typical food system, as well as the development of an efficient VBNC cell detection method might aid in the control of VBNC E. coli O157:H7 cells in the food industry.

Development and Application of a Simple "Easy To Operate" Propidium Monoazide-Crossing Priming Amplification on Detection of Viable and Viable But Non-culturable Cells of O157 Escherichia coli

O157 Escherichia coli is one of the most important foodborne pathogens causing disease even at low cellular numbers. Thus, the early and accurate detection of this pathogen is important. However, due to the formation of viable but non-culturable (VBNC) status, the golden standard culturing methodology fails to identify O157 E. coli once it enters VBNC status. Crossing priming amplification (CPA) is a novel, simple, easy-to-operate detection technology that amplifies DNA with high speed, efficiency, and specificity under isothermal conditions. The objective of this study was to firstly develop and apply a CPA assay with propidium monoazide (PMA) for the rapid detection of the foodborne E. coli O157:H7 in VBNC state. Five primers (2a/1s, 2a, 3a, 4s, and 5a) were specially designed for recognizing three targets, which were rfbE, stx1, and stx2, and evaluated for its effectiveness in detecting VBNC cell of E. coli O157:H7 with detection limits of pure VBNC culture at 10³, 10⁵, and 10⁵ colony-forming units (CFUs)/ml for rfbE, stx1, and stx2, respectively, whereas those of food samples (frozen pastry and steamed bread) were 10³, 10⁵, and 10⁵ CFUs/ml. The application of the PMA-CPA assay was successfully used on detecting E. coli O157:H7 in VBNC state from food samples. In conclusion, this is the first development of PMA-CPA assay on the detection of VBNC cell, which was found to be useful and a powerful tool for the rapid detection of E. coli O157:H7 in VBNC state. Undoubtedly, the PMA-CPA method can be of high value to the food industry owing to its various advantages such as speed, specificity, sensitivity, and cost-effectiveness.

Effect of Environmental Conditions on the Formation of the Viable but Nonculturable State of Pediococcus acidilactici BM-PA17927 and Its Control and Detection in Food System

Objective: This study aimed to investigate the effect of environmental conditions including nutrient content, acetic acid concentration, salt concentration, and temperature on the formation of viable but nonculturable (VBNC) state of Pediococcus acidilactici, as well as its control and detection in food system. Methods: Representing various environmental conditions in different food systems, 16 induction groups were designed for the formation of VBNC state of P. acidilactici. Traditional plate counting was applied to measure the culturable cell numbers, and Live/Dead Bacterial Viability Kit combined with fluorescent microscopy was used to identify viable cells numbers. The inhibition of bacterial growth and VBNC state formation by adjusting the environmental conditions were investigated, and the clearance effect of VBNC cells in crystal cake system was studied. In addition, a propidium monoazide-polymerase chain reaction (PMA-PCR) assay was applied to detect the VBNC P. acidilactici cells in crystal cake food system. Results: Among the environmental conditions included in this study, acetic acid concentration had the greatest effect on the formation of VBNC state of P. acidilactici, followed by nutritional conditions and salt concentration. Reducing nutrients in the environment and treating with 1.0% acetic acid can inhibit P. acidilactici from entering the VBNC state. In the crystal cake system, the growth of P. acidilactici and the formation of VBNC state can be inhibited by adding 1.0% acetic acid and storing at -20°C. In crystal cake system, the PMA-PCR assay can be used to detect VBNC P. acidilactici cells at a concentration higher than 10⁴ cells/ml. Conclusion: The VBNC state of P. acidilactici can be influenced by the changing of environmental conditions, and PMA-PCR assay can be applied in food system for the detection of VBNC P. acidilactici cells.

Reduction, Prevention, and Control of Salmonella enterica Viable but Non-culturable Cells in Flour Food

The processing and storage conditions of flour food inevitably pose environmental stress, which promote bacteria to enter a viable but non-culturable (VBNC) state. The existence of VBNC cells causes false-negative detection in traditional culture-based detection methods, resulting in food quality and safety issues. This study aimed at investigating the influence factors including nutrition, acid, salt, and temperature for the entry into a VBNC state of Salmonella enterica and an efficient detection method. During induction with multi-stress conditions, nutrition starvation antagonizes with low-level acidity. Besides, high-level acidity was considered as an inhibitor for VBNC induction. Four inducers including nutrition starvation, salt stress, low-level acidity, and low temperature were concluded for a VBNC state. In addition, the keynote conditions for S. enterica entering a VBNC state included (i) nutrient-rich acidic environment, (ii) oligotrophic low-acidity environment, and (iii) oligotrophic refrigerated environment. Based on the keynote conditions, the environmental conditions of high acidity (1.0% v/v acetate) with low temperature (-20°C) could successfully eliminate the formation of S. enterica VBNC cells in flour food. In addition, combining with propidium monoazide pretreatment, PCR technology was applied to detect S. enterica VBNC cells. The sensitivity of the PMA-PCR technology was 10⁵ CFU/ml in an artificially simulated food system. The results derived from this study might aid in the detection and control of VBNC state S. enterica in flour food products.

First Report on the Rapid Detection and Identification of Methicillin-Resistant Staphylococcus aureus (MRSA) in Viable but Non-culturable (VBNC) Under Food Storage Conditions

Formation of viable but non-culturable (VBNC) status in methicillin-resistant Staphylococcus aureus (MRSA) has never been reported, and it poses a significant concern for food safety. Thus, this study aimed to firstly develop a rapid, cost-effective, and efficient testing method to detect and differentiate MRSA strains in the VBNC state and further apply this in real food samples. Two targets were selected for detection of MRSA and toxin, and rapid isothermal amplification detection assays were developed based on cross-priming amplification methodology. VBNC formation was performed for MRSA strain in both pure culture and in artificially contaminated samples, then propidium monoazide (PMA) treatment was further conducted. Development, optimization, and evaluation of PMA-crossing priming amplification (CPA) were further performed on detection of MRSA in the VBNC state. Finally, application of PMA-CPA was further applied for detection on MRSA in the VBNC state in contaminated food samples. As concluded in this study, formation of the VBNC state in MRSA strains has been verified, then two PMA-CPA assays have been developed and applied to detect MRSA in the VBNC state from pure culture and food samples.

Pseudomonas aeruginosa quorum sensing inhibition by clinical isolate Delftia tsuruhatensis 11304: involvement of N-octadecanoylhomoserine lactones

Pseudomonas aeruginosa is one of the most common opportunistic pathogens that use quorum sensing (QS) system to regulate virulence factors expression and biofilm development. Delftia sp. 11304 was selected among 663 Gram-negative clinical isolates based on its QS inhibitory activity against P. aeruginosa MMA83 clinical isolate. Whole genome sequencing identified this isolate as D. tsuruhatensis and revealed genetic armamentarium of virulence factors and antibiotic resistance determinants. Ethyl acetate extract of D. tsuruhatensis 11304 culture supernatant (QSI extract) prevented biofilm formation of P. aeruginosa MMA83, but was unable to cause biofilm decomposition. QSI extract showed a synergistic effect in combination with meropenem and gentamycin, against P. aeruginosa MMA83. A dose-dependent reduction of the virulence factors: elastase, rhamnolipid and pyocyanin production by P. aeruginosa MMA83 and significant downregulation of lasI, lasR, rhlI, rhlR, pqs and mvfR expression were observed. Matrix-assisted Laser Desorption Ionization (MALDI) mass spectrometry of D. tsuruhatensis 11304 QSI extract revealed the presence of N-acyl homoserine lactones (AHL) with chain lengths of C12 to C18. The main ion peak was identified as N-octadecanoylhomoserine lactone (C₁₈-HSL). Commercial C₁₈-HSL (20 µM) reduced pyocyanin production as well as mRNA level of the lasI gene. A novel AHL species, dihydroxy-N-octadecanoylhomoserine lactone, was also described.

Biofilm Formation of Staphylococcus aureus under Food Heat Processing Conditions: First Report on CML Production within Biofilm

This study aimed to evaluate the Staphylococcus aureus biofilm formation and Nε-carboxymethyl-lysine generation ability under food heat processing conditions including pH (5.0-9.0), temperature (25 °C, 31 °C, 37 °C, 42 °C and 65 °C), NaCl concentration (10%, 15% and 20%, w/v) and glucose concentration (0.5%, 1%, 2%, 3%, 5%, 10%, w/v). S. aureus biofilm genetic character was obtained by PCR detecting atl, ica operon, sasG and agr. Biofilm biomass and metabolic activity were quantified with crystal violet and methyl thiazolyl tetrazolium staining methods. S. aureus biofilm was sensitive to food heat processing conditions with 37 °C, pH 7.0, 2% glucose concentration (w/v) and 10% NaCl concentration (w/v) were favorable conditions. Besides, free and bound Nε-carboxymethyl-lysine level in weak, moderate and strong biofilm were detected by optimized high performance liquid chromatography tandem mass spectrometry. Nε-carboxymethyl-lysine level in S. aureus biofilm possessed a significant gap between strong, moderate and weak biofilm strains. This investigation revealed the biological and chemical hazard of Staphylococcus aureus biofilm to food processing environment.

Microbial virulence, molecular epidemiology and pathogenic factors of fluoroquinolone-resistant Haemophilus influenzae infections in Guangzhou, China

BACKGROUND

Fluoroquinolone-resistant Haemophilus influenzae (FRHI) has been reported worldwide but remain unclear in China.

METHODS

A total of 402 H. influenzae isolates collected from 2016 to 2017 were included. Antimicrobial susceptibility on 10 antibiotics was performed, and minimum inhibitory concentration of ciprofloxacin- and nalidixic acid-resistant strains were further determined by E-test strips, with risk factors also evaluated. Strains with resistance or reduced susceptibility to ciprofloxacin were subjected to sequencing of the quinolone resistance-determining regions (QRDR) and plasmid-mediated quinolone resistance genes by sequencing, with multi-locus sequence typing.

RESULTS

2.2% of H. influenzae strains were non-susceptible (7/402, 1.7%) or susceptible (2/402, 0.5%) to ciprofloxacin but NAL-resistant by E-test, and multidrug resistance was more common in fluoroquinolones non-susceptible H. influenzae group (p = 0.000). Infection risk factors included invasive procedure (p = 0.011), catching cold/previous contact with someone who had a cold (p = 0.019), fluoroquinolones use during previous 3 months (p = 0.003). With none of mutations obtained in gyrB, parE and other plasmid-mediated quinolone resistance genes, 7 and 4 strains were found for Ser-84-Leu substitutions in gyrA and one amino acid substitution in the QRDR of gyrA linked with one amino acid substitution in the QRDR of parC, respectively. In addition, five sequence types (ST) were identified, with ST1719 firstly found.

CONCLUSIONS

For the first time, this study has reported the incidence, risk factors, molecular determinants on fluoroquinolones resistance and ST of FRHI strains in mainland China, representing the first evidence of mutation of gyrA and parC in China and the new ST1719 worldwide.

In vitro antibacterial and early stage biofilm inhibitory potential of an edible chitosan and its phenolic conjugates against Pseudomonas aeruginosa and Listeria monocytogenes

In the present study, the antibacterial potential of chitosan grafted with phenolics (CPCs) such as caffeic acid (CCA), ferulic (CFA), and sinapic acid (CSA) were evaluated against foodborne pathogens like Pseudomonas aeruginosa (PA) and Listeria monocytogenes (LM). The geometric means of minimum inhibitory concentration (MIC range 0.05-0.33 mg/ml), bactericidal concentration (MBC range 0.30-0.45 mg/ml), biofilm inhibitory concentration (BIC range 0.42-0.83 mg/ml), and biofilm eradication concentration (BEC range 1.71-3.70 mg/ml) of CPCs were found to be lower than the MIC (0.12-1.08 mg/ml), MBC (0.17-1.84 mg/ml), BIC (4.0-4.50 mg/ml), and BEC (17.4-23.0 mg/ml) of unmodified chitosan against PA and LM. CPCs attenuated the biofilms of PA and LM by increasing the membrane permeability of bacteria embedded within the biofilms. Further, sub MIC of CPCs (0.5 × MIC) significantly reduced the biofilm adhesion (p < 0.001) by representative strains of LM (CCA: 72.2 ± 3.5, CFA: 79.3 ± 0.9, and CSA: 74.9 ± 1.5%) and PA (CCA: 64 ± 1.1, CFA: 67.8 ± 0.8, and CSA: 65.7 ± 4.9%). These results suggested the antibacterial and anti-biofilm potential of CPCs that can be exploited to control foodborne pathogenic infections.

The fingerprint mapping and genotyping systems application on methicillin-resistant Staphylococcus aureus

As a typical Gram-positive microorganism, S. aureus was recognized as common foodborne pathogenic bacteria in food industry. To study their individuality and pathogenicity mechanism, thirty-three Staphylococci strains were applied to the investigation with the identification of MRSA by PCR targeting on S. aureus specific 16S rRNA and femA genes as well as methicillin-resistant mecA and orfX elements by multiplex-PCR assay. Fingerprinting mapping was then employed using three typing systems (KZ/M13, IS256 and ERIC2) to genotype 33 MRSA strains. As the result indicated, all 33 Staphylococci strains were identified as MRSA. However, diversity occurred among different fingerprinting system results. KZ/M13 system and IS256 system both typed 10 genotypes while ERIC2 system had 8 genotypes. Based on the genotyping results, a discussion was performed in typing ability, discriminatory ability and accordance ratio. Given the above studies, a novel rapid detection method for MRSA was conducted with multiplex-PCR, which possessed rapidity and accuracy. Meanwhile, three fingerprinting systems showed high sensitivity, resolution and classification ratio in MRSA typing. These methods have a broad application prospect in food safety and epidemiology in the future.

Physical relation and mechanism of ultrasonic bactericidal activity on pathogenic E. coli with WPI

OBJECTIVE

This study aimed to investigate the physical relation and mechanism of bactericidal activity on pathogenic E. coli by ultrasonic field with whey protein isolate (WPI).

METHODS

Ultrasound treatment was performed under the conditions of intensity at 65 W/cm², pulse duty ratio at 0.5 for 0-15 min with WPI concentration ranged from 0 to 10%. Viscosity, granularity, surface hydrophobicity, free radical scavenging activity, and thermal denaturation were assessed by rotational viscometer, Malvern Mastersizer 2000 particle size analyzer, fluorescent probe ANS method, DPPH method, and differential scanning calorimetry, respectively.

RESULTS

The thermal denaturation of WPI was not altered by ultrasound field, but the viscosity of WPI was increased upon 10 min treatment. Additionally, its ability to scavenge free radicals and hydrophobicity were increased. The result also showed that the bacteria viability was improved by WPI during ultrasound treatment. However, the WPI protection was decreased by the prolonged treatment.

CONCLUSION

Ultrasound treatment resulted in the increasing of the viscosity, free radicals scavenging activity and hydrophobicity of WPI which led to reduced bactericidal activity on E. coil, while WPI protection was disintegrated by prolonged treatment.

High flux isothermal assays on pathogenic, virulent and toxic genetics from various pathogens

Toxins, encoding by virulence factors, are significant cause of food-borne illnesses and death in the worldwide. Loop-mediated isothermal amplification (LAMP) is one of the widely used methodologies because of the high sensitivity, specificity and rapidity. Nowadays, LAMP has been regarded as an innovative gene amplification technology and emerged as an alternative to PCR-based methodologies in identification of the pathogenic virulent and toxic genetics. The high sensitivity of LAMP enables detection of the pathogens in sample materials even without time consuming and sample preparation. Therefore, we review the typical characteristics of LAMP assay, recent advance in detection of virulence factors and the application of LAMP assay on detection of four commonly virulence factors. As concluded, with the advantages of rapidity, simplicity, sensitivity, specificity and robustness, LAMP is capable of identification the virulence factors. Moreover, the main purpose of this review is to provide theory support for the application of LAMP assay on the virulence factors identification.

Correlation and in vitro mechanism of bactericidal activity on E. coli with whey protein isolate during ultrasonic treatment

OBJECTIVE

This study aimed to investigate correlation and in vitro mechanism of bactericidal activity on E. coli with whey protein isolate (WPI) during ultrasonic treatment.

METHODS

The structural changes of WPI under ultrasonic field were studied by amino-acid analyzer, circular dichroism, SDS-PAGE, and spectrophotometer.

RESULTS

With the increasing of WPI concentration added during ultrasonic treatment, the survival rate of E. coli increased. The influence of WPI on bactericidal activity under ultrasonic treatment might due to the change of tertiary and higher level structures, not by the primary structure, and had little relation with secondary structure.

CONCLUSION

The influence of WPI on bactericidal activity during ultrasonic treatment might due to the change of the tertiary structure and higher level structures.

Integron mediated bacterial resistance and virulence on clinical pathogens

Integron was recognized as mobile elements responsible for the emergence and diffusion of antibiotic resistance, virulence and pathogenicity. The existence of resistant integron in pathogens may consequently lead to the increasing number of clinical failures in bacterial mediated diseases, as well as the expenses. In this study, a total of 22 clinical pathogens (including E. faecalis, S. aureus, K. pneumoniae, Enterobacter, P. aeruginosa and Acinetobacter) were subjected to the identification of class 1-class 3 integrons and drug resistant gene cassettes by high flux LAMP method. According to the results, the clinical isolates were screened as carrying class 1 integron with dfrA12-orfF-aadA2 cassette array, class 1 integron with dfrA17-aadA5 cassette array, class 1 integron with aadA2 cassette, class 1 integron with bla_VIM2 cassette, class 1 and class 2 integron with dfrA1-sat1-aadA1 and dfrA12-orfF-aadA2 cassette arrays simultaneously, which was accordantly with the previous data. The optimized high flux LAMP assay was proceeded in water bath at 65 °C for 60 min and determined by naked eye, with the time consumption restricted within 2.5 h. Prior to conventional PCR method, the high flux LAMP assay was demonstrated as a highly-specific and highly-sensitive method. This study offered a valid LAMP method in resistance integrons detection for laboratory use, which was time-saving and easy-determination.

Study on the excision and integration mediated by class 1 integron in Streptococcus pneumoniae

As a novel antibiotic resistance mobile element, integron was recognized as a primary source of antibiotic genes among Gram-positive organisms for its excision and integration of exogenous genes. In this study, Streptococcus pneumoniae was subjected to investigate the excision and integration of class 1 integron with eight different plasmids. As the results indicated, excision in both att site and gene cassettes were successfully observed, which was further confirmed by integration assays and PCR amplification. The observation of class 1 integron mediated excision and integration of various exogenous antibiotics resistance genes may raise the attention of integrons as novel antibiotic resistance determinant in Gram-positive bacteria, especially in Streptococcus.

Effect of aminoglycosides on the pathogenic characteristics of microbiology

Infections caused by pathogen remain to be one of the most important global health issues, and scientists are devoting themselves to seeking effective treatments. Aminoglycoside antibiotics are one kind of widely used antibiotics because of the good efficiency and broad antimicrobial-spectrum. However, it causes some unexpected effects on the pathogenic characteristics of microbiology during the treatment, such as drug resistance and biofilm promotion. Drug resistance is partly due to antibiotics abuse. Simultaneously, aminoglycoside is documented to make divergent effects on biofilm based on their concentrations. Here, we review the mechanism of drug resistance caused by long-term use of aminoglycoside antibiotics, the effects of antibiotic concentration on biofilm formation and the negative effects on intestinal flora to provide theoretical supports for rational use of antibiotics.

Pathogenic features and characteristics of food borne pathogens biofilm: Biomass, viability and matrix

Biofilm is a ubiquitous growth pattern of bacterial species survival but is notorious for its threat on public health and food contamination. Extensive studies of the biofilm structure, formation, quantification, quorum sensing system and underlying control strategies have been reported during the past decades. Insightful elucidation of the pathogenic features and characteristic of bacterial biofilm can facilitate in devising appropriate control strategies for biofilm eradication. Therefore, this review mainly summarized the pathogenic features of biofilms from food borne microorganisms, including the biomass (which could be quantified using crystal violet and fluorogenic dye Syto9 assays), viability (which could be determined by tetrazolium salts, fluorescein diacetate, resazurin staining and alamar blue assays) and matrix (which are commonly detected by dimethyl methylene blue and wheat germ agglutinin assays). In addition, three features were further compared with its particular benefits in specific application.