The Significance of Mesophilic Aeromonas spp. in Minimally Processed Ready-to-Eat Seafood

Phenotypic and genotypic characterization of Aeromonas hydrophila isolated from freshwater fishes at Middle Upper Egypt

Aeromonas hydrophila is a common fish pathogen and a significant foodborne pathogen of increasing public health concern. This study was conducted in Middle Upper Egypt to determine the prevalence of A. hydrophila among the diseased Oreochromis niloticus (n = 100) and Clarias gariepinus (n = 100) at Assiut and Sohag Governorates. A. hydrophila isolates (n = 44) were assessed for antimicrobial susceptibility and biofilm production. Moreover, PCR was performed to analyze the incidence of some genes in 20 isolates of A. hydrophila. The results showed that 24% and 20% of the examined O. niloticus and C. gariepinus were infected with A. hydrophila respectively, with all (100%) showing a variety of clinical signs of septicemia. A. hydrophila isolates were all biofilm producers, with varied degrees of biofilm production. 79.5% of the isolates were multidrug-resistant and had a high multiple antimicrobial resistance index > 0.2. PCR analysis revealed that all isolates carried act and blaTEM genes but not carried int2 gene. Additionally, sul1, aer, tetA, int1, and qnrA genes were present in 75%, 60%, 55%, 55% and 45% of them, respectively. This study highlights the high incidence of multidrug-resistant pathogenic A. hydrophila in the infected fishes, posing a serious risk to humans and fish.

Emergence of Aeromonas salmonicida subsp. masoucida MHJM250: unveiling pathological characteristics and antimicrobial susceptibility in golden mahseer, Tor putitora (Hamilton, 1822) in India

Aeromonas salmonicida subsp. masoucida, designated as laboratory strain MHJM250, was characterized from a naturally infected farmed golden mahseer, Tor putitora. The infected fish exhibited clinical signs of erosion at the caudal fin and hemorrhage onx the ventral body surface. Molecular identification through 16 S rDNA and phylogenetic analysis revealed 100% similarity with a known strain A. salmonicida subsp. masoucida (MT122821.1). MHJM250 exhibited positive reactions for oxidase, catalase, esculin, MR-VP, O/F and utilized arginine and lysine. It also demonstrated siderophore activity, thrived at various NaCl concentrations, hydrolyzed gelatinase, skimmed milk and casinase. In vitro studies exhibited its hemolytic nature, significant biofilm production in glucose-rich tryptone soya broth and beta-hemolysis. MHJM250 didn't produce slime and was non-precipitated upon boiling. It showed crystal violet binding characteristics and auto-agglutination with relatively weak hydrophobicity (25%). In the challenge assay, intraperitoneal administration of MHJM250 to T. pitutora fingerlings at 108 CFU mL-1 resulted in pathogenicity with 3% mortality and mild hemorrhagic symptoms. Histopathological analysis revealed degenerative changes in gill, kidney, liver, muscle, and intestine samples. The bacterium displayed resistance to several antibiotics (µg/disc); ampicillin (10 µg), ampicillin/ sulbactam (10/10 µg), clindamycin (2 µg), linezolid (30 µg), penicillin G (10 µg) and rifampicin (5 µg) and varied minimum inhibitory concentrations against oxytetracycline, erythromycin and florfenicol. Transmission electron microscopy showed its rod-shaped structure with single polar flagellum and lophotrichous flagella. An investigation on the molecular basis for virulence factors of A. salmonicida subsp. masoucida MHJM250 may offer crucial understandings to formulate disease prevention and control strategies in aquaculture.

Phylogenomics of novel clones of Aeromonas veronii recovered from a freshwater lake reveals unique biosynthetic gene clusters

Aquatic ecosystems serve as crucial reservoirs for pathogens and antimicrobial resistance genes, thus presenting a significant global health risk. Here, we investigated the phylogenomics of Aeromonas veronii from Lake Wilcox in Ontario. Among the 11 bacterial isolates, nine were identified as A. veronii. Notably, 67% of A. veronii isolates were potential human pathogens. Considerable genetic diversity was noted among the A. veronii isolates, suggesting the lake as a reservoir for multiple human pathogenic strains. Comparison of the A. veronii sequenced with global A. veronii genomes highlighted significant genetic diversity and suggests widespread dissemination of strains. All the isolates carried chromosomal genes encoding resistance to β-lactams. Although virulence gene content differed between human and non-human pathogenic strains, type III secretion systems was associated with human pathogenic isolates. The assessment of AMR genes in global isolates showed that β-lactam and tetracycline resistance genes were predominant. Although the machine learning-based pangenome-wide association approach performed did not yield any source-based genes, some genes were enriched in a few isolates from different sources. The mrkABCDF operon that mediates biofilm formation and genes encoding resistance to colistin, chloramphenicol, trimethoprim, and tetracycline were enriched in animal products, whereas macrolide resistance genes and Inc plasmid-types were linked to the aquatic environment. Novel biosynthetic gene clusters were identified, suggesting that A. veronii with varying pathogenic potential could produce unique secondary metabolites. There is a need for continuous tracking of pathogens in aquatic ecosystems to contribute to our understanding of their evolutionary dynamics and the ecological roles of their genetic elements.

IMPORTANCE

Lakes and other aquatic ecosystems can harbor harmful bacteria that can make people sick and resist antibiotics, posing a significant global health risk. In this study, we investigated Aeromonas veronii, a Gram-negative bacteria found in Lake Wilcox in Ontario. We used various techniques, including whole-genome sequencing (WGS), to analyze the bacteria and found that many of the isolates had the potential to cause human disease. We also discovered significant genetic diversity among the isolates, indicating that the lake may be a reservoir for multiple human pathogenic strains. All isolates carried genes that confer resistance to antibiotics, and some virulence genes were associated with human pathogenic isolates. This study highlights the importance of monitoring aquatic ecosystems for harmful bacteria to better understand their evolution, potential for human pathogenicity, and the ecological roles of their genetic elements. This knowledge can inform strategies for preventing the spread of antibiotic-resistant bacteria and protecting public health.

Ready to Eat Food: A Reason for Enhancement in Multidrug Resistance in Humans

The increasing trend of consuming ready-to-eat (RTE) food has become a global phenomenon, and this has raised concerns about the potential negative impacts on human health. Recent studies have shown a correlation between the consumption of RTE foods and the expansion of multidrug resistance (MDR) in humans. MDR is a significant challenge in the effective theory of infectious diseases, as it limits the effectiveness of antibiotics and other drugs used in therapy. Consumption of RTE food contribute to the development of MDR in humans. Additionally, there are potential risks of consuming RTE food contaminated with antibiotic-resistant bacteria, which can cause severe health consequences. The article highlights the need for awareness campaigns on the potential hazard related to the ingestion of RTE food and the importance of responsible and safe food production practices. It also recommends the need for regulatory bodies to establish strict guidelines for the production and distribution of RTE food to ensure that they are free from harmful contaminants and that their consumption does not lead to the development of MDR in humans. Overall, this article provides a comprehensive analysis of the potential negative impacts of RTE food consumption on human health and emphasizes the need for a more cautious approach to food consumption to protect public health.

Antibiotic-resistant bacteria contaminating leafy vegetables in Saudi Arabia's eastern region

BACKGROUND

Food-associated antibiotic-resistant bacteria can cause infections that may critically impact human health. The objectives of this study were to determine the microbial contamination level of green leafy vegetables and their antibiotic resistance pattern.

METHODS

Sixty-three samples of leafy vegetables were collected from Dammam Central Fruit and Vegetables Market from January to June 2023. The vegetables included lettuce (Lactuca sativa), parsley (Petroselinum crispum), and watercress (Nasturtium officinale). Samples were tested by standard microbiological techniques for identification and antibiotic susceptibility testing.

RESULT

Eight types of bacteria belonging to six different genera were detected. Enterobacteriaceae family was represented by four genera: Klebsiella, Proteus, Morganella, and Enterobacter. The other two genera were Pseudomonas and Aeromonas. Enterobacter cloacae was the most abundant organism, followed by Pseudomonas putida and Aeromonas sobria. On the other hand, Morganella morganii, Aeromonas hydrophila, and Proteus mirabilis were the least abundant. The three vegetable types had different levels of bacterial contamination. All isolated organisms were sensitive to penicillin, cephalosporin, aminoglycoside, and fluoroquinolone. However, Klebsiella oxytoca, M. morganii, and K. pneumonia showed resistance to ampicillin. A. hydrophila, Morganella morganii, and E. cloacae showed resistance to amoxicillin. M. morganii and E. cloacae were found to be resistant to cefalotin. Moreover, A. hydrophila, M. morganii, and E. cloacae were resistant to cefoxitin. Again, A. hydrophila was found to be resistant to imipenem. Only M. morganii was resistant to Ciprofloxacin. Two isolates, P. mirabilis and M. morganii were resistant to tigecycline. Another two, M. morganii and P. mirabilis were resistant to Nitrofurantoin. Only M. morganii was found to be resistant to trimethoprim.

CONCLUSION

This study aligns with the broad consensus in the literature about the significance of bacterial contamination in vegetables and the public health implications. The unique focus on antibiotic resistance patterns adds an essential dimension to the existing body of knowledge.

Molecular detection of enterotoxins in multidrug resistant Aeromonas from ready to eat foods in North Western Himalayas: Public health significance

Aeromonas spp. are normal inhabitants of aquatic environments and are emerging foodborne bacterial pathogens. Aeromonas spp. contamination is frequent in ready-to-eat (RTE) seafood and can also occur in products prepared from milk or meat. The study determined the enterotoxin and antimicrobial susceptibility profiles of Aeromonas spp. isolates recovered from RTE milk products (n = 105), RTE meat/fish products (n = 40) and drinking water (n = 60) samples collected from tourist places in Himachal Pradesh, India, in northwestern Himalayas. 7.3 % (16/220) samples were found contaminated with Aeromonas spp. These isolates were identified as A. hydrophila (31.3 %), A. schubertii (25.0 %), A. sobria (25.0 %) and A. veronii (18.8 %). Aeromonas spp. contamination was significantly higher (14.3 %, 15/105, p = 0.0001) in RTE milk products. The contamination levels for water samples were 1.7 % whereas none of the tested RTE meat or fish products yielded Aeromonas spp. Among RTE milk products, contamination was significantly higher in paneer (South Asian soft cheese) (26.1 %, p = 0.0027) and cream (25.0 %, p = 0.046) based RTE foods. All isolates carried alt (361 bp), encoding a cytotonic heat-labile enterotoxin. Ampicillin resistance was 100 % and high levels (>30 %) of resistance were recorded for amoxicillin/clavulanic acid, amikacin, cefotaxime and ceftazidime. Six (37.5 %) isolates were multi drug resistant (MDR), showing resistance to aminoglycosides, cephams and penicillins. Isolation of alt carrying MDR isolates from RTE foods indicates that Aeromonas spp. can be potential foodborne public health threat in northwestern Himalayas.

Comprehensive analysis of predominant pathogenic bacteria and viruses in seafood products

Given the growing global demand for seafood, it is imperative to conduct a comprehensive study on the prevalence and persistence patterns of pathogenic bacteria and viruses associated with specific seafood varieties. This assessment thoroughly examines the safety of seafood products, considering the diverse processing methods employed in the industry. The importance of understanding the behavior of foodborne pathogens, such as Salmonella typhimurium, Vibrio parahaemolyticus, Clostridium botulinum, Listeria monocytogenes, human norovirus, and hepatitis A virus, is emphasized by recent cases of gastroenteritis outbreaks linked to contaminated seafood. This analysis examines outbreaks linked to seafood in the United States and globally, with a particular emphasis on the health concerns posed by pathogenic bacteria and viruses to consumers. Ensuring the safety of seafood is crucial since it directly relates to consumer preferences on sustainability, food safety, provenance, and availability. The review focuses on assessing the frequency, growth, and durability of infections that arise during the processing of seafood. It utilizes next-generation sequencing to identify the bacteria responsible for these illnesses. Additionally, it analyzes methods for preventing and intervening of infections while also considering the forthcoming challenges in ensuring the microbiological safety of seafood products. This evaluation emphasizes the significance of the seafood processing industry in promptly responding to evolving consumer preferences by offering current information on seafood hazards and future consumption patterns. To ensure the continuous safety and sustainable future of seafood products, it is crucial to identify and address possible threats.

Unveiling novel threats: Urban river isolation of Aeromonas veronii with unusual VEB-28 extended-spectrum β-lactamase and distinct mcr variants

Aeromonas spp. are frequently encountered in aquatic environments, with Aeromonas veronii emerging as an opportunistic pathogen causing a range of diseases in both humans and animals. Recent reports have raised public health concerns due to the emergence of multidrug-resistant Aeromonas spp. This is particularly noteworthy as these species have demonstrated the ability to acquire and transmit antimicrobial resistance genes (ARGs). In this study, we report the genomic and phenotypic characteristics of the A. veronii TR112 strain, which harbors a novel variant of the Vietnamese Extended-spectrum β-lactamase-encoding gene, blaVEB-28, and two mcr variants recovered from an urban river located in the Metropolitan Region of São Paulo, Brazil. A. veronii TR112 strain exhibited high minimum inhibitory concentrations (MICs) for ceftazidime (64 μg/mL), polymyxin (8 μg/mL), and ciprofloxacin (64 μg/mL). Furthermore, the TR112 strain demonstrated adherence to HeLa and Caco-2 cells within 3 h, cytotoxicity to HeLa cells after 24 h of interaction, and high mortality rates to the Galleria mellonella model. Genomic analysis showed that the TR112 strain belongs to ST257 and presented a range of ARGs conferring resistance to β-lactams (blaVEB-28, blaCphA3, blaOXA-912) and polymyxins (mcr-3 and mcr-3.6). Additionally, we identified a diversity of virulence factor-encoding genes, including those encoding mannose-sensitive hemagglutinin (Msh) pilus, polar flagella, type IV pili, type II secretion system (T2SS), aerolysin (AerA), cytotoxic enterotoxin (Act), hemolysin (HlyA), hemolysin III (HlyIII), thermostable hemolysin (TH), and capsular polysaccharide (CPS). In conclusion, our findings suggest that A. veronii may serve as an environmental reservoir for ARGs and virulence factors, highlighting its importance as a potential pathogen in public health.

Use of Matrix-Assisted and Laser Desorption/Ionization Time-of-Flight Technology in the Identification of Aeromonas Strains Isolated from Retail Sushi and Sashimi

The genus Aeromonas includes well-known pathogenic species for fishes and humans that are widely distributed in the aquatic environment and foods. Nowadays, one of the main issues related to wild Aeromonas isolates is their identification at the species level, which is challenging using classical microbiological and biomolecular methods. This study aims to test MALDI-TOF MS technology in the identification of Aeromonas strains isolated from n. 60 retail sushi and sashimi boxes using an implemented version of the SARAMIS software V4.12. A total of 43 certified Aeromonas strains were used to implement the SARAMIS database by importing the spectra obtained from their identification. The original SARAMIS version (V4.12) failed to recognize 62.79% of the certified strains, while the herein-implemented version (V4.12plus) allowed the identification of all the certified strains at least to the genus level with a match of no less than 85%. Regarding the sushi and sashimi samples, Aeromonas spp. was detected in n. 18 (30%) boxes. A total of 127 colonies were identified at the species level, with A. salmonicida detected as the most prevalent species, followed by A. bestiarum and A. caviae. Based on the results of the present study, we could speculate that MALDI-TOF technology could be a useful tool both for the food industry to monitor product contamination and for clinical purposes to make diagnoses effectively and quickly.

Profiling and source tracking of the microbial populations and resistome present in fish products

Microorganisms in processing environments significantly impact the quality and safety of food products and can serve as potential reservoirs for antibiotic-resistant genes, contributing to public health concerns about antimicrobial resistance (AMR). Fish processing plants represent an understudied environment for microbiome mapping. This study investigated the microbial composition, prevalence of Listeria spp., and resistome structures in three catfish processing facilities in the southeastern United States. The 16S rRNA gene sequencing revealed that the observed richness and Shannon diversity index increased significantly from fish to fillet. Beta diversity analysis showed distinct clustering of microbial communities between fish, environment, and fillet samples. Fast expectation-maximization microbial source tracking (FEAST) algorithm demonstrated that the microbiota presents in the processing environment contributed 48.2 %, 62.4 %, and 53.7 % to the microbiota present on fillet in Facility 1 (F1), F2, and F3, respectively. Food contact surfaces made larger contributions compared to the non-food contact surfaces. The linear discriminant analysis of effect size (LEfSe) identified specific microbial genera (e.g., Plesiomohas, Brochothrix, Chryseobacterium and Cetobacterium) that significantly varied between Listeria spp. positive and negative samples in all three processing plants. The metagenomic sequencing results identified 212 antimicrobial resistance genes (ARGs) belonging to 72 groups from the raw fish and fish fillet samples collected from three processing plants. Although there was a significant decrease in the overall diversity of ARGs from fish to fillet samples, the total abundance of ARGs did not change significantly (P > 0.05). ARGs associated with resistance to macrolide-lincosamide-streptogramin (MLS), cationic antimicrobial peptides, aminoglycosides, and beta-lactams were found to be enriched in the fillet samples when compared to fish samples. Results of this study highlight the profound impact of processing environment on shaping the microbial populations present on the final fish product and the need for additional strategies to mitigate AMR in fish products.

Antimicrobial resistance in aeromonads and new therapies targeting quorum sensing

Aeromonas species (spp.) are well-known fish pathogens, several of which have been recognized as emerging human pathogens. The organism is capable of causing a wide spectrum of diseases in humans, ranging from gastroenteritis, wound infections, and septicemia to devastating necrotizing fasciitis. The systemic form of infection is often fatal, particularly in patients with underlying chronic diseases. Indeed, recent trends demonstrate rising numbers of hospital-acquired Aeromonas infections, especially in immuno-compromised individuals. Additionally, Aeromonas-associated antibiotic resistance is an increasing challenge in combating both fish and human infections. The acquisition of antibiotic resistance is related to Aeromonas' innate transformative properties including its ability to share plasmids and integron-related gene cassettes between species and with the environment. As a result, alternatives to antibiotic treatments are desperately needed. In that vein, many treatments have been proposed and studied extensively in the fish-farming industry, including treatments that target Aeromonas quorum sensing. In this review, we discuss current strategies targeting quorum sensing inhibition and propose that such studies empower the development of novel chemotherapeutic approaches to combat drug-resistant Aeromonas spp. infections in humans. KEY POINTS: • Aeromonas notoriously acquires and maintains antimicrobial resistance, making treatment options limited. • Quorum sensing is an essential virulence mechanism in Aeromonas infections. • Inhibiting quorum sensing can be an effective strategy in combating Aeromonas infections in animals and humans.

Insights into the mechanisms and key factors influencing biofilm formation by Aeromonas hydrophila in the food industry: A comprehensive review and bibliometric analysis

Biofilm formation by Aeromonas hydrophila in the food industry poses significant challenges to food safety and quality. Therefore, this comprehensive review aimed to provide insights into the mechanisms and key factors influencing A. hydrophila biofilm formation. It explores the molecular processes involved in initial attachment, microcolony formation, and biofilm maturation; moreover, it concurrently examines the impact of intrinsic factors, including quorum sensing, cyclic-di-GMP, the efflux pump, and antibiotic resistance, as well as environmental conditions, such as temperature, nutrient availability, and osmotic pressure, on biofilm architecture and resilience. Furthermore, the article highlights the potential of bibliometric analysis as a promising method for conceptualizing the research landscape of and identifying knowledge gaps in A. hydrophila biofilm research. The findings underscore the requirement for focused interventions that prevent biofilm development and raise food sector safety. The consolidation of current information and incorporation of bibliometric analysis enhances existing understanding of A. hydrophila biofilm formation and offers insights for future research and control strategies within a food industry context.

Aeromonas spp. in drinking water and food: Occurrence, virulence potential and antimicrobial resistance

Aeromonas sp. is a Gram-negative, non-spore-forming, rod-shaped, oxidase-positive, facultative anaerobic bacterium and a natural contaminant found in aquatic environments. Some species can invade, colonize, and damage host cells due to the presence of virulence factors, such as flagella, elastase, hemolysins, aerolysins, adhesins, enterotoxins, phospholipases and lipases, that lead to pathogenic activities. Consequently, can cause many health disorders that range from gastrointestinal problems, enteric infections, and ulcers to hemorrhagic septicemia. Aeromonas has been isolated and identified from a variety of sources, including drinking water and ready-to-eat foods (fish, meat, fresh vegetables, dairy products, and others). Some species of this opportunistic pathogen are resistant to several commercial antibiotics, including some used as a last resort for treatment, which represents a major challenge in the clinical segment. Antimicrobial resistance can be attributed to the indiscriminate use of antibiotics by society in aquaculture and horticulture. In addition, antibiotic resistance is attributed to plasmid transfer between microorganisms and horizontal gene transfer. This review aimed to (i) verify the occurrence of Aeromonas species in water and food intended for human consumption; (ii) identify the methods used to detect Aeromonas species; (iii) report on the virulence genes carried by different species; and (iv) report on the antimicrobial resistance of this genus in the last 5 years of research. Additionally, we present the existence of Aeromonas spp. resistant to antimicrobials in food and drinking water represents a potential threat to public health.

Isolation, Characterization and Genomic Analysis of a Novel Jumbo Phage, AerS_266, That Infects Aeromonas salmonicida

Aeromonas salmonicida is the causative agent of septicemia in fish, and it is associated with significant economic losses in the aquaculture industry. While piscine Aeromonas infections are mainly treated with antibiotics, the emergence of resistance in bacterial populations requires the development of alternative methods of treatment. The use of phages can be one of them. A novel A. salmonicida jumbo phage, AerS_266, was isolated and characterized. This phage infects only mesophilic A. salmonicida strains and demonstrates a slow lytic life cycle. Its genome contains 243,674 bp and 253 putative genes: 84 encode proteins with predicted functions, and 3 correspond to tRNAs. Genes encoding two multisubunit RNA polymerases, chimallin and PhuZ, were identified, and AerS_266 was thus defined as a phiKZ-like phage. While similar phages with genomes >200 kb specific to Aeromonas hydrophila and Aeromonas veronii have been previously described, AerS_266 is the first phiKZ-like phage found to infect A. salmonicida.

Predatory bacteria as potential biofilm control and eradication agents in the food industry

Biofilms are a major concern within the food industry since they have the potential to reduce productivity in situ (within the field), impact food stability and storage, and cause downstream food poisoning. Within this review, predatory bacteria as potential biofilm control and eradication agents are discussed, with a particular emphasis on the intraperiplasmic Bdellovibrio-and-like organism (BALO) grouping. After providing a brief overview of predatory bacteria and their activities, focus is given to how BALOs fulfill four attributes that are essential for biocontrol agents to be successful in the food industry: (1) Broad spectrum activity against pathogens, both plant and human; (2) Activity against biofilms; (3) Safety towards humans and animals; and (4) Compatibility with food. As predatory bacteria possess all of these characteristics, they represent a novel form of biofilm biocontrol that is ripe for use within the food industry.

Whole genome sequence analysis of Aeromonas spp. isolated from ready-to-eat seafood: antimicrobial resistance and virulence factors

Aeromonas are widespread in aquatic environments and are considered emerging pathogens in humans and animals. Multidrug resistant (MDR) Aeromonas circulating in the aquatic environment and food production chain can potentially disseminate antimicrobial resistance (AMR) to humans via the foodborne route. In this study, we aimed to investigate AMR and virulence factors of 22 Aeromonas strains isolated from ready-to-eat (RTE) seafood. A multilocus phylogenetic analysis (MLPA) using the concatenated sequences of six housekeeping genes (gyrB, rpoD, gyrA, recA, dnaJ, and dnaX) in the 22 Aeromonas genomes and average nucleotide identity (ANI) analysis revealed eight different species; A. caviae, A. dhakensis, A. hydrophila, A. media, A. rivipollensis, A. salmonicida, A. bestiarum, and A. piscicola. The presence of virulence genes, AMR genes and mobile genetic elements (MGEs) in the Aeromonas genomes was predicted using different databases. Our data showed that the genes responsible for adherence and motility (Msh type IV pili, tap type IV pili, polar flagella), type II secretion system (T2SS) and hemolysins were present in all strains, while the genes encoding enterotoxins and type VI secretion system (T6SS) including major effectors were highly prevalent. Multiple AMR genes encoding β-lactamases such as cphA and bla_OXA were detected, and the distribution of those genes was species-specific. In addition, the quinolone resistance gene, qnrS2 was found in a IncQ type plasmid of the A. rivopollensis strain A539. Furthermore, we observed the co-localization of a class I integron (intl1) with two AMR genes (sul1 and aadA1), and a Tn521 transposon carrying a mercury operon in A. caviae strain SU4-2. Various MGEs including other transposons and insertion sequence (IS) elements were identified without strongly associating with detected AMR genes or virulence genes. In conclusion, Aeromonas strains in RTE seafood were potentially pathogenic, carrying several virulence-related genes. Aeromonas carrying multiple AMR genes and MGEs could potentially be involved in the dissemination and spread of AMR genes to other bacterial species residing in the same environment and possibly to humans. Considering a One-Health approach, we highlight the significance of monitoring AMR caused by Aeromonas circulating in the food chain.

Linking microbial contamination to food spoilage and food waste: the role of smart packaging, spoilage risk assessments, and date labeling

Ensuring a safe and adequate food supply is a cornerstone of human health and food security. However, a significant portion of the food produced for human consumption is wasted annually on a global scale. Reducing harvest and postharvest food waste, waste during food processing, as well as food waste at the consumer level, have been key objectives of improving and maintaining sustainability. These issues can range from damage during processing, handling, and transport, to the use of inappropriate or outdated systems, and storage and packaging-related issues. Microbial growth and (cross)contamination during harvest, processing, and packaging, which causes spoilage and safety issues in both fresh and packaged foods, is an overarching issue contributing to food waste. Microbial causes of food spoilage are typically bacterial or fungal in nature and can impact fresh, processed, and packaged foods. Moreover, spoilage can be influenced by the intrinsic factors of the food (water activity, pH), initial load of the microorganism and its interaction with the surrounding microflora, and external factors such as temperature abuse and food acidity, among others. Considering this multifaceted nature of the food system and the factors driving microbial spoilage, there is an immediate need for the use of novel approaches to predict and potentially prevent the occurrence of such spoilage to minimize food waste at the harvest, post-harvest, processing, and consumer levels. Quantitative microbial spoilage risk assessment (QMSRA) is a predictive framework that analyzes information on microbial behavior under the various conditions encountered within the food ecosystem, while employing a probabilistic approach to account for uncertainty and variability. Widespread adoption of the QMSRA approach could help in predicting and preventing the occurrence of spoilage along the food chain. Alternatively, the use of advanced packaging technologies would serve as a direct prevention strategy, potentially minimizing (cross)contamination and assuring the safe handling of foods, in order to reduce food waste at the post-harvest and retail stages. Finally, increasing transparency and consumer knowledge regarding food date labels, which typically are indicators of food quality rather than food safety, could also contribute to reduced food waste at the consumer level. The objective of this review is to highlight the impact of microbial spoilage and (cross)contamination events on food loss and waste. The review also discusses some novel methods to mitigate food spoilage and food loss and waste, and ensure the quality and safety of our food supply.

Microbiological safety and quality of ceviche, poke, and sushi dishes sold at retail outlets in Orange County, CA

Raw, ready-to-eat (RTE) seafood products, such as ceviche, poke, and sushi, have experienced growing demand globally; however, these products have the potential to be contaminated with foodborne pathogens. The objective of this study was to determine the prevalence of Escherichiacoli/coliforms, Salmonella, and Listeria in ceviche, poke, and sushi dishes sold at the retail level in Orange County, CA, USA. Additional organisms detected during testing were also considered in the results. A total of 105 raw, RTE samples of ceviche, poke, and sushi were collected from restaurants and grocery stores in Orange County, CA. Samples were tested for Salmonella and Listeria utilizing methods from the Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM). E. coli and total coliforms were enumerated utilizing 3 M Petrifilm plates. Overall, two samples (1.9%) were positive for generic E. coli, with a range of 5-35 CFU/g. Coliforms were detected in 85 samples (81%), with a range of 5-1710 CFU/g. The average coliform levels in ceviche samples (259 CFU/g) were significantly higher than the levels in sushi samples (95 CFU/g), according to a Kruskal-Wallis H test followed by the Dunn test (p < 0.05). The coliform levels in poke samples (196 CFU/g) were not significantly different from those in ceviche or sushi. All levels of E. coli and coliforms were considered acceptable or satisfactory/borderline according to standards for RTE seafood. None of the samples tested positive for Salmonella or Listeria monocytogenes; however, other microorganisms were detected in 17 samples, including Listeria spp., Proteus mirabilis, Providencia rettgeri, and Morganella morganii. The results of this study are novel in that they present data on the microbiological safety and quality of ceviche, poke, and sushi dishes sold at retail in the United States, as well as provide a comparison across the three categories of raw, RTE seafood.

Cytotoxicity and Antimicrobial Resistance of Aeromonas Strains Isolated from Fresh Produce and Irrigation Water

The genus Aeromonas has received constant attention in different areas, from aquaculture and veterinary medicine to food safety, where more and more frequent isolates are occurring with increased resistance to antibiotics. The present paper studied the interaction of Aeromonas strains isolated from fresh produce and water with different eukaryotic cell types with the aim of better understanding the cytotoxic capacity of these strains. To study host-cell pathogen interactions in Aeromonas, we used HT-29, Vero, J774A.1, and primary mouse embryonic fibroblasts. These interactions were analyzed by confocal microscopy to determine the cytotoxicity of the strains. We also used Galleria mellonella larvae to test their pathogenicity in this experimental model. Our results demonstrated that two strains showed high cytotoxicity in epithelial cells, fibroblasts, and macrophages. Furthermore, these strains showed high virulence using the G. mellonella model. All strains used in this paper generally showed low levels of resistance to the different families of the antibiotics being tested. These results indicated that some strains of Aeromonas present in vegetables and water pose a potential health hazard, displaying very high in vitro and in vivo virulence. This pathogenic potential, and some recent concerning findings on antimicrobial resistance in Aeromonas, encourage further efforts in examining the precise significance of Aeromonas strains isolated from foods for human consumption.

Contribution of flagellar cap gene in virulence and pathogenicity of Aeromonas veronii

Aeromonas veronii is an important zoonotic and aquatic pathogen that causes a number of illnesses in both humans and animals. It is related to gastroenteritis, skin and soft tissue infections and bacteremia in humans, as well as causing significant economic losses in aquaculture owing to fish sepsis. Here, we constructed the flagellar cap gene (fliD) mutant strain of A. veronii by suicide plasmid-mediated homologous recombination system and analysed its characteristics. It was found that the deletion of fliD had no effect on growth and biochemical properties and could be inherited stably. However, the motility of A. veronii ΔfliD was significantly reduced, the flagellum was defective and the biofilm formation was attenuated compared with that of A. veronii wild-type strain. In vivo experiments revealed that the colonization capacity of ΔfliD was significantly lower than that of the wild-type strain in the period of first 24 h, and the median lethal dose (LD₅₀ ) was 56 times higher than that of the wild-type strain. The Cyprinus carpio infected with the wild-type strain indicated faster death speed and more severe clinical signs compared to ΔfliD strain. These results suggest that fliD is closely related to the virulence of A. veronii and plays an important role in pathogenicity, providing the foundation for pathogenic mechanism studies of A. veronii.

Molluscs-A ticking microbial bomb

Bivalve shellfish consumption (ark shells, clams, cockles, and oysters) has increased over the last decades. Following this trend, infectious disease outbreaks associated with their consumption have been reported more frequently. Molluscs are a diverse group of organisms found wild and farmed. They are common on our tables, but unfortunately, despite their great taste, they can also pose a threat as a potential vector for numerous species of pathogenic microorganisms. Clams, in particular, might be filled with pathogens because of their filter-feeding diet. This specific way of feeding favors the accumulation of excessive amounts of pathogenic microorganisms like Vibrio spp., including Vibrio cholerae and V. parahaemolyticus, Pseudomonas aeruginosa, Escherichia coli, Arcobacter spp., and fecal coliforms, and intestinal enterococci. The problems of pathogen dissemination and disease outbreaks caused by exogenous bacteria in many geographical regions quickly became an unwanted effect of globalized food supply chains, global climate change, and natural pathogen transmission dynamics. Moreover, some pathogens like Shewanella spp., with high zoonotic potential, are spreading worldwide along with food transport. These bacteria, contained in food, are also responsible for the potential transmission of antibiotic-resistance genes to species belonging to the human microbiota. Finally, they end up in wastewater, thus colonizing new areas, which enables them to introduce new antibiotic-resistance genes (ARG) into the environment and extend the existing spectrum of ARGs already present in local biomes. Foodborne pathogens require modern methods of detection. Similarly, detecting ARGs is necessary to prevent resistance dissemination in new environments, thus preventing future outbreaks, which could threaten associated consumers and workers in the food processing industry.

Epidemiological characteristics, virulence potential, antimicrobial resistance profiles, and phylogenetic analysis of Aeromonas caviae isolated from extra-intestinal infections

Objective

Aeromonas caviae (A. caviae) is one of the major etiological agents in human intestinal infections reported to be associated with a broad spectrum of extra-intestinal infections with increasing incidence over recent years. Although previous studies have established its significance as a causative agent of both bloodstream and gastrointestinal infections, the characteristics of A. caviae that cause extra-intestinal infections remain unilluminated.In this single-center retrospective study, we investigated epidemiological characteristics, antimicrobial resistance genes and phenotypes, virulence genes, and phyloevolution of 47 clinical A. caviae isolated from patients with extra-intestinal infections from 2017 to 2020.

Methods

A. caviae strains were identified by biochemical tests and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF/MS), ultimately confirmed to species level by whole-genome sequencing (WGS). Antimicrobial resistance and virulence genes were identified using the Comprehensive Antibiotic Resistance Database (CARD) and the virulence factor database (VFDB), respectively. Phylogenetic analysis of 47 clinical strains was performed by combining with 521 A. caviae strains from NCBI database.

Results

A. caviae was an opportunistic pathogen in immunocompromised patients, especially those with underlying hepatobiliary diseases and malignancies. 19 out of 47 isolates were identified as multidrug resistance (MDR) strains. Piperacillin-tazobactam, levofloxacin, gentamicin, amikacin with a resistance rate of less than 10% remained as options to treat extra-intestinal infections. 24 out of 47 isolates exhibited non-susceptibility to cephalosporins and cephamycins, all of which carried β-lactamase gene, including bla _MOX, bla _PER-3, bla _OXA, bla _NDM, and bla _CphA. Most stains (98%, 46/47) carried at least one of the virulence genes, but extra-intestinal infections had a low mortality rate. Phylogenetic analysis indicated the risk of nosocomial transmission but revealed no outbreak. However, the emergence of MDR and β-lactamase resistance genes in extra-intestinal isolates of A. caviae is becoming an increasing risk to public health and requires attention.

Conclusions

This study strengthen our understanding of A.caviae isolated from extra-intestinal infections. It may contribute to the management of extra-intestinal infections as well as the prevention and control of drug resistance.

A Novel Aeromonas popoffii Phage AerP_220 Proposed to Be a Member of a New Tolavirus Genus in the Autographiviridae Family

Aeromonas popoffii is one of the environmental Aeromonas species. A number of factors of virulence have been described for this species and it has been reported as a causative agent of urinary tract infection. The first A. popoffii bacteriophage AerP_220 along with its host strain A. popoffii CEMTC 4062 were isolated from river water. The phage has a podovirus morphotype, shows a narrow host range and is lytic against the host strain. The AerP_220 genome comprises 45,207 bp and does not contain genes responsible for antibiotic resistance and toxin production. Fifty-nine co-directional putative ORFs were found in the AerP_220 genome. Thirty-three ORFs encoded proteins with predicted functions; the products of 26 ORFs were hypothetical proteins. AerP_220 genome analysis revealed that this phage can be considered a novel species within the Autographiviridae family. Comparative genomic and proteomic analysis revealed that AerP_220 along with the Aeromonas phage vB_AspA_Tola (OM913599) are members of a new putative Tolavirus genus in the family Autographiviridae. The Gajwadongvirus and proposed Tolavirus genera along with Pantoea phage Nufs112 and phage Reminis could form a new Tolavirinae subfamily within the Autographiviridae family.

Growth and Spoilage Potential of an Aeromonas salmonicida Strain in Refrigerated Atlantic Cod (Gadus morhua) Stored under Various Modified Atmospheres

Aeromonas spp. are ubiquitous aquatic bacteria, frequently isolated from seafood. The growth and spoilage potential of an inoculated strain of Aeromonas salmonicida (SU2) in Atlantic cod (Gadus morhua) fillets were assessed as a function of various modified atmospheres (MA) (CO2 (67%) with O2 (33%) or N2 (33%), and vacuum packaging (VP)) under refrigerated storage (4 °C) for 13 days. Additionally, the general microbiological quality was assessed by quantifying total aerobic psychrotrophic count (PC), total aerobic plate count (APC), and H2S-producing bacteria. A selection of spoilage metabolites was quantified by nuclear magnetic resonance (NMR) spectroscopy. The MA containing CO2/O2 and CO2/N2 significantly inhibited the growth of the inoculated strain throughout storage (p < 0.001), whereas VP allowed for a 3-log increase of Aeromonas in 13 days. No significant effect of the inoculation with A. salmonicida on spoilage metabolite production was detected. Applying O2 instead of N2 in the CO2-enriched atmosphere resulted in a significantly lower PC for 10 days, and H2S-producing bacteria were inhibited in both MAs compared to vacuum. This study provides data that can be used as a basis to further elucidate the role of bacteria belonging to the genus Aeromonas as potential spoilage organisms in marine fish species.

Effects of antibiotics on Vietnam koi, Anabas testudineus, exposed to Aeromonas dhakensis as a co-infection

The dietary effects of antibiotics on aquatic disease is circumstantial and has not been investigated under infections. the efficacy of erythromycin, after 10 days in use and 10 days off, on the survival and infection rate of (Anabas testudineus) after co-infection with antibiotic-resistant Aeromonas dhakensis (isolate NV5M or V7L). The mortality rate observed in non-medicated groups of co-infected fish (93.3 and 100%) was significantly higher (p < 0.05) than that in the medicated group of naturally infected fish (NIF) (53.3%) but not significantly different to that in medicated groups of co-infected fish (66.6% and 86.6%). In particular, the loads of invasive erythromycin-resistant bacteria (ERB) were markedly higher (p < 0.05, 3.5-4.8 times) in the kidney of co-infected fish medicated for 5 days than those in NIF. The measure of ERB in the kidney of fish co-infected with isolate V7L, whether medicated or not for 10 days, was significantly higher (p < 0.05) than that in non-medicated NIF and also that in the medicated group of fish co-infected with isolate NV5M. In addition to the elevation of gut-derived ERB invasion and colonization in the kidney, synergistic effects of the competition between mixed pathogens caused by co-infection and medication might result in a high fish mortality rate. Further investigation of antibiograms and/or new strategies for aquatic disease control should be undertaken with mixed infections and interaction of pathogens to achieve the optimal treatment effect.

Emergence of extensively drug-resistant Aeromonas hydrophila complex isolated from wild Mugil cephalus (striped mullet) and Mediterranean seawater

Background and Aim:

Antibiotic resistance has been a progressively documented problem, resulting in treatment failure in humans and animals. This study aimed to investigate the antimicrobial susceptibility and virulence of extensively drug-resistant (XDR) Aeromonas spp. in wild Mugil cephalus and its surrounding seawater along the coastal road of Port Said, Egypt.

Materials and Methods:

Specimens were examined bacteriologically, confirmed biochemically, and tested for their sensitivity against 11 antimicrobial agents. Molecular confirmation of the obtained isolates by 16S rRNA was performed, followed by the detection of antimicrobial resistance and virulence genes.

Results:

Aeromonas spp. was recovered from fish (44%) and water samples (36%). A. hydrophila was the most prevalent identified strain, followed by Aeromonas sobria, Aeromonas caviae, and Aeromonas schubertii. Moreover, 90% of the tested isolates were multidrug-resistant (MDR), while 26.67% were XDR. Tested isolates were resistant to b-lactams and sulfonamides (100%), oxytetracycline (90%), and streptomycin (62.22%) but completely susceptible to cefotaxime. XDR isolates successfully amplified resistance genes (bla_TEM , sul1, and tetA(A)) but not the (aadA1) gene, although there was phenotypic resistance to streptomycin on plates. All XDR isolates carry the cytotoxic enterotoxin gene (act), but alt gene was detected in only one isolate (12.5%).

Conclusion:

Data in this study provide a recent update and highlight the role of wild mullet and seawater as reservoirs for MDR and XDR Aeromonas spp. that may pose a risk to humans as food-borne infection or following direct contact.

Aeromonas: the multifaceted middleman in the One Health world

Aeromonas is at the interface of all the One Health components and represents an amazingly sound test case in the One Health approach, from economic loss in aquaculture tochallenges related to antibiotic-resistant bacteria selected from the environment. In human health, infections following leech therapy is an outstanding example of such One Health challenges. Aeromonads are not only ubiquitous environmental bacteria, able to rapidly colonize and cause opportunistic infections in humans and animals, they are also capable of promoting interactions and gene exchanges between the One Health components. This makes this genus a key amplifier of genetic transfer, especially of antibiotic resistance genes.

Effect of spatio-temporal variables, host fish species and on-farm biosecurity measures on the prevalence of potentially pathogenic Aeromonas species in freshwater fish farms

AIMS

To determine the prevalence of Aeromonas species in freshwater fish farms, factors affecting their prevalence and virulence factors associated with each species.

METHODS AND RESULTS

In a cross-sectional study from 128 farms in four districts of Uttar Pradesh, India, 11 species of Aeromonas were identified by gyrB sequencing including the first report of Aeromonas crassostreae from fish. Four species of Aeromonas were more prevalent (MP) in fish farms, A. veronii bv. sobria (50.0%) was the highest, followed by A. caviae (18.8%), A. veronii bv. veronii (11.7%) and A. dhakensis (7.0%). The less prevalent (LP) species were A. hydrophila, A. media, A. jandaei, A. allosaccharophila, A. salmonicida, A. crassostreae and A. taiwanensis. Spatial variation in the prevalence of Aeromonas species was observed. Dominance of biovar sobria ranged from 33.3 to 68.6%, notably lesser in farms with on-farm biosecurity measures. The prevalence of biovar veronii was significantly associated with pangas fish, rainy season and farms with on-farm biosecurity measures. The prevalence of LP species was significantly higher in mrigal fish and winter season. Multiple virulence factors (>6) were detected in 70.2% of the Aeromonas species. Significant association of β-hemolysin, DNase, slime production, act, ahh1, aexT and lip was observed with different species of Aeromonas. Moreover, 75.8% of Aeromonas species possessed one or more enterotoxins genes (act/alt/ast).

CONCLUSION

Significant association of spatio-temporal variables, host fish species and on-farm biosecurity measures were observed on the prevalence of some of the Aeromonas species in freshwater fish farms. Most of the Aeromonas species harboured virulence factors indicating their potential for pathogenicity.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that determined the prevalence and identified the factors that affect the prevalence of Aeromonas species in freshwater fish farms. This information will be useful in managing Aeromonas infection in fish and their risks to public health.

Ready-to-Eat Sandwiches as Source of Pathogens Endowed with Antibiotic Resistance and Other Virulence Factors

The aim of this study was to evaluate and characterize the bacterial load present in twenty-four Ready-To-Eat (RTE) sandwiches, purchased at refrigerated vending machines and supermarkets in the province of Modena (Italy). We isolated 54 bacterial strains, including pathogens of interest in food safety, such as Listeria, Staphylococcus, Enterococcus, Yersinia, Aeromonas and Acinetobacter spp. Phenotypic tests have been performed on these pathogens to detect the presence of virulence factors, such as gelatinase production and hemolytic capability. To test their antibiotic resistance features, the minimum inhibitory concentration (MIC) against eight commonly used antibiotics (Amikacin, Ciprofloxacin, Ampicillin, Oxacillin, Imipenem, Tetracycline, Erythromycin and Vancomycin) was also evaluated. The results showed that among the 54 isolates, fifty percent (50%) belonged to harmless microorganisms (Leuconostoc and Lactococcus), whereas the remaining fifty percent (50%) included pathogenic bacteria (Listeria ivanovii, Listeria monocytogenes, Staphylococcus aureus, Yersinia, and Citrobacter spp.), species responsible for pathologies often difficult to treat due to the presence of antibiotic resistance features. This study demonstrates the importance of thorough controls, both during the production and marketing of RTE food like sandwiches, to avoid reaching the infectious load and the onset of pathologies, particularly dangerous for old and immunocompromised patients.

Maltose promotes crucian carp survival against Aeromonas sobrial infection at high temperature

Temperature influences fish’s susceptibility to infectious disease through an immune response. However, the mechanism underlying this regulation is yet to be elucidated. In this study, we compared the susceptibility of crucian carp that were grown at 18°C and 33°C, respectively, to Aeromonas sobrial infection and found that crucian carp was more susceptible when grown at 33°C. These distinct susceptibilities of fish at different temperatures to infection may partially be explained by their differences in the metabolism as revealed by comparative metabolomics profiling: crucian carp demonstrated enhanced TCA cycle but reduced fatty acid biosynthesis; Our study also found that maltose was the most suppressed metabolite in fish grown at 33°C. Importantly, exogenous injection of maltose enhances crucian carp survival grown at 33°C by 30%. Further study showed that exogenous maltose downregulated the production of several cytokines but enhanced the lysozyme (lyz) and complement component c3, which involves the humoral innate immunity. Our results suggest that maltose promotes the survival of crucian carp likely through fine tuning the immune gene expression, and this finding provides a novel approach to manage bacterial infection.

Virulence and antimicrobial resistance potential of Aeromonas spp. associated with shellfish

Aeromonas spp. are associated with seafood-related outbreaks worldwide. In seafood industry, shellfish play a major role in global seafood production. With this emerging trend of shellfish consumption, shellfish-related bacterial infections are being reported frequently. Aeromonas spp. are natural contaminants found in shellfish. Although 36 species have been identified, some species including Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii biotype sobria have dragged major attention as foodborne pathogenic bacteria. The ability to elaborate a variety of virulence factors of Aeromonas spp. contributes to the pathogenic activities. Also, emerging antimicrobial resistance in Aeromonas spp. has become a huge challenge in seafood industry. Furthermore, multidrug resistance increases the risk of consumer health. Studies have supplied pieces of evidence about the emerging health risk of Aeromonas spp. isolated from seafood. Therefore, the present review was intended to highlight the prevalence, virulence and antimicrobial resistance of Aeromonas spp. isolated from various types of shellfish.

Prevalence, Virulence Gene Distribution and Alarming the Multidrug Resistance of Aeromonas hydrophila Associated with Disease Outbreaks in Freshwater Aquaculture

The study aims to evaluate the infection prevalence, virulence gene distribution and antimicrobial resistance of Aeromonas hydrophila associated in diseased outbreaks of cultured freshwater fish in Northern Vietnam. The confirmed A. hydrophila were screened for the presence of the five pitutative-virulence genes including aerolysin (aerA), hemolysin (hlyA), cytotonic enterotoxin (act), heat-labile cytotonic enterotoxin (alt), and heat-stable enterotoxin (ast), and examined the susceptibility to 16 antibiotics. A total of 236 A. hydrophila isolates were recovered and confirmed from 506 diseased fish by phenotypic tests, PCR assays, and gyrB, rpoB sequenced analyses, corresponding to the infection prevalence at 46.4%. A total of 88.9% of A. hydrophila isolates harbored at least one of the tested virulence genes. The genes aerA and act were most frequently found (80.5% and 80.1%, respectively) while the ast gene was absent in all isolates. The resistance to oxacillin, amoxicillin and vancomycin exhibited the highest frequencies (>70%), followed by erythromycin, oxytetracycline, florfenicol, and sulfamethoxazole/trimethoprim (9.3–47.2%). The multiple antibiotic resistance (MAR) index ranged between 0.13–0.88 with 74.7% of the isolates having MAR values higher than 0.2. The results present a warning for aquaculture farmers and managers in preventing the spread of A. hydrophila and minimizing antibiotic resistance of this pathogen in fish farming systems.

Diversity and Antimicrobial Activity towards Listeria spp. and Escherichia coli among Lactic Acid Bacteria Isolated from Ready-to-Eat Seafood

Biopreservation is a food preservation technology using microorganisms and/or their inherent antimicrobial metabolites to inhibit undesirable microorganisms. The aim of the present study was to explore the diversity and antimicrobial activity of lactic acid bacteria (LAB) strains (n = 99) isolated from ready-to-eat (RTE) seafood (cold-smoked salmon (CSS), gravlax, and sushi) towards two strains of Listeria monocytogenes (CCUG 15527, F11), Listeria innocua (CCUG 15531) and Escherichia coli (CCUG 38079). The LAB strains were assigned to five different genera (Carnobacterium spp., Lactobacillus spp., Leuconostoc spp., Weissella spp., and Enterococcus sp.) by sequencing a 1150 bp stretch of the 16S rRNA gene. A significant association between the seafood source and the distribution of LAB genera was found (p < 0.001), of which Leuconostoc spp. were most prevalent in sushi and Carnobacterium sp. and Lactobacillus sp. were most frequently isolated from CSS and gravlax. Antimicrobial activity among the LAB was significantly affected by LAB genera (F= 117.91, p < 0.001, one-way ANOVA), product of origin (F = 3.47, p < 0.05), and target (F = 4.64, p = 0.003). LAB isolated from sushi demonstrated a significantly higher antimicrobial effect than LAB from CSS and gravlax (p < 0.05). In general, a significantly higher antimicrobial activity was found towards Listeria spp. than E. coli (p < 0.05). However, Leuconostoc spp. demonstrated similar antimicrobial effects towards E. coli and Listeria spp., except for L. monocytogenes F11 being more sensitive (p < 0.05). This study suggested that seafood-derived LAB strains could be selected for technological application in RTE seafood systems.

Studies on The Inhibitory Properties of Leaf Ethanolic Extracts Obtained from Ficus (Moraceae) Species Against Aeromonas Spp. Strains

Introduction

The most frequently isolated bacteria in Polish aquaculture are of the Aeromonas genus; also pathogenic to human fish consumers, they cause substantial economic losses, and require antibiotic therapy to treat. Antibiotic residues in animal-derived food provoke concern. The aim of the study was to appraise the antimicrobial activity of ethanolic extracts of Ficus plant species against Aeromonas strains.

Material and Methods

Leaves of 41 Ficus species were collected from two Ukrainian botanic gardens. They were crushed, washed, homogenized in ethanol and centrifuged, and the supernatants were applied in the Kirby–Bauer disc-diffusion method to assess the susceptibility to them of Aeromonas hydrophila, A. sobria, and A. salmonicia subsp. salmonicida isolates confirmed as K886, K825, and St30 strains. Analogous assessment was also made of these bacteria’s susceptibility to sulfonamides, quinolones, tetracyclines, and one amphenicol. Data were analysed statistically.

Results

The majority of the extracts considerably inhibited bacterial growth, A. sobria being susceptible to 14 Ficus species, A. salmonicida subsp. salmonicida to 13, and A. hydrophila to 10.

Conclusion

Treatment with plant extracts has promise as an alternative to antibiotic therapy. Botanic gardens may offer new sources of plant-derived agents with a broad spectrum of biological and antimicrobial action. Further research will be useful to broaden knowledge of Ficus’ therapeutic potential.

Outer Membrane Vesicles Released From Aeromonas Strains Are Involved in the Biofilm Formation

Aeromonas spp. are Gram-negative rod-shaped bacteria ubiquitously distributed in diverse water sources. Several Aeromonas spp. are known as human and fish pathogens. Recently, attention has been focused on the relationship between bacterial biofilm formation and pathogenicity or drug resistance. However, there have been few reports on biofilm formation by Aeromonas. This study is the first to examine the in vitro formation and components of the biofilm of several Aeromonas clinical and environmental strains. A biofilm formation assay using 1% crystal violet on a polystyrene plate revealed that most Aeromonas strains used in this study formed biofilms but one strain did not. Analysis of the basic components contained in the biofilms formed by Aeromonas strains confirmed that they contained polysaccharides containing GlcNAc, extracellular nucleic acids, and proteins, as previously reported for the biofilms of other bacterial species. Among these components, we focused on several proteins fractionated by SDS-PAGE and determined their amino acid sequences. The results showed that some proteins existing in the Aeromonas biofilms have amino acid sequences homologous to functional proteins present in the outer membrane of Gram-negative bacteria. This result suggests that outer membrane components may affect the biofilm formation of Aeromonas strains. It is known that Gram-negative bacteria often release extracellular membrane vesicles from the outer membrane, so we think that the outer membrane-derived proteins found in the Aeromonas biofilms may be derived from such membrane vesicles. To examine this idea, we next investigated the ability of Aeromonas strains to form outer membrane vesicles (OMVs). Electron microscopic analysis revealed that most Aeromonas strains released OMVs outside the cells. Finally, we purified OMVs from several Aeromonas strains and examined their effect on the biofilm formation. We found that the addition of OMVs dose-dependently promoted biofilm formation, except for one strain that did not form biofilms. These results suggest that the OMVs released from the bacterial cells are closely related to the biofilm formation of Aeromonas strains.

Occurrence, diversity and temperature-dependent growth kinetics of Aeromonas spp. in lettuce

Bagged, pre-cut and prewashed lettuce products are marketed as ready to eat. This concept poses a food safety concern, due to lack of efficient hurdles to eliminate possible microbial contaminants from the fresh produce and/or the processing itself. Aeromonas spp. are potential foodborne pathogens that are frequently isolated from lettuce. High counts of, e.g., A. hydrophila have been found in retail ready-to-eat (RTE) vegetable salads. The aim of this study was to assess the general microbiological quality, the occurrence and diversity of potential human pathogenic mesophilic Aeromonas spp. of retail RTE lettuce products. Additionally, temperature-dependent growth kinetic parameters of Aerobic Plate Counts (APC) and Aeromonas spp. in one selected RTE lettuce product, rocket lettuce, were quantified by performing storage experiments at 4 °C, 8 °C and 12 °C. The Aeromonas isolates were further characterized regarding pathogenic traits and phylogenetic relationship. The overall hygienic quality of the lettuce products was unsatisfactory, as 60% of the products had an APC level higher than 7.0 log CFU/g. Presumptive Aeromonas spp. were detected in 52% of the samples, levels ranging from approximately 2.0-6.0 log CFU/g. Significantly lower counts of APC and Aeromonas spp. were found in uncut and unwashed products. Presumptive Aeromonas spp. were able to proliferate in rocket lettuce stored at 4 °C (μmax = 0.39 ± 0.06/d and μmax = 0.43 ± 0.05/d for lettuce from producers A and B, respectively), and μmax was approximately 2× higher at 8 °C and 3× higher at 12 °C. Eighty-four percent of the collected isolates were identified as A. media, based on partial gyrB sequencing. Additionally A. salmonicida and A. bestiarum were detected. The pathogenic potential in this material was high, most of the isolates harbored at least one of the toxin genes, act, ast, alt.

The determination of antimicrobial susceptibility by MIC and epidemiological cut-off values and the detection of resistance genes in Aeromonas species isolated from cultured fish

The present study was aimed at determining antimicrobial susceptibility by a CLSI standard microdilution testing protocol and detecting the resistance genes of motile Aeromonas species isolated from cultured fish. The importance of the minimum inhibitory concentrations was assessed based on statistically determined epidemiological cut-off values calculated by normalized resistance analysis. Unfortunately, CLSI epidemiological cut-off values are available only for Aeromonas salmonicida, and there is no further detailed data on Aeromonas isolated from aquatic animals. The antimicrobial susceptibilities of pre-identified motile Aeromonas species to florfenicol, tetracycline and sulfamethoxazole were determined by calculating epidemiological cut-off values with fully automated and freely available Excel spreadsheets, applying the normalized resistance interpretation (NRI) method. Furthermore, the presence of the antimicrobial resistance genes floR, tetA, tetB, tetC, tetD, tetE, tetH, sulI, sulII and sulIII was detected by PCR analysis and confirmed by sequence analysis. The presence of up to six different genes (multiple antimicrobial resistance) was determined in the Aeromonas isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: Significance and Impact of the Study: In this study, we investigated phenotypic and genotypic antimicrobial resistance characteristics by a novel method based on epidemiological cut-off values. This is the second comprehensive study on the antimicrobial susceptibility characteristics of Aeromonas species using NRI and epidemiological cut-off values. The present research is related to our previous researches focussed on the identification of motile Aeromonads, their prevalence in relation to different fish lengths, seasons and regions, and covered the investigation of Lactococcus garvieae, Yersinia ruckeri, Flavobacterium spp., Enterobacter spp. and Citrobacter spp.

An in silico analysis of acquired antimicrobial resistance genes in Aeromonas plasmids

Sequences of 105 Aeromonas species plasmids were probed for acquired anti-microbial resistance (AMR) genes using a bioinformatics approach. The plasmids showed no positive linear correlation between size and GC content and up to 55 acquired AMR genes were found in 39 (37%) plasmids after in silico screening for resistance against 15 antibiotic drug classes. Overall, potential multiple antibiotic resistance (p-MAR) index ranged from 0.07 to 0.53. Up to 18 plasmids were predicted to mediate multiple drug resistance (MDR). Plasmids pS121-1a (A. salmonicida), pWCX23_1 (A. hydrophila) and pASP-a58 (A. veronii) harboured 18, 15 and 14 AMR genes respectively. The five most occurring drug classes for which AMR genes were detected were aminoglycosides (27%), followed by beta-lactams (17%), sulphonamides (13%), fluoroquinolones (13%), and phenicols (10%). The most prevalent genes were a sulphonamide resistant gene Sul1, the gene aac (6')-Ib-cr (aminoglycoside 6'-N-acetyl transferase type Ib-cr) resistant to aminoglycosides and the blaKPC-2 gene, which encodes carbapenemase-production. Plasmid acquisition of AMR genes was mainly inter-genus rather than intra-genus. Eighteen plasmids showed template or host genes acquired from Pseudomonas monteilii, Salmonella enterica or Escherichia coli. The most occurring antimicrobial resistance determinants (ARDs) were beta-lactamase, followed by aminoglycosides acetyl-transferases, and then efflux pumps. Screening of new isolates in vitro and in vivo is required to ascertain the level of phenotypic expression of colistin and other acquired AMR genes detected.

An Update on the Genus Aeromonas: Taxonomy, Epidemiology, and Pathogenicity

The genus Aeromonas belongs to the Aeromonadaceae family and comprises a group of Gram-negative bacteria widely distributed in aquatic environments, with some species able to cause disease in humans, fish, and other aquatic animals. However, bacteria of this genus are isolated from many other habitats, environments, and food products. The taxonomy of this genus is complex when phenotypic identification methods are used because such methods might not correctly identify all the species. On the other hand, molecular methods have proven very reliable, such as using the sequences of concatenated housekeeping genes like gyrB and rpoD or comparing the genomes with the type strains using a genomic index, such as the average nucleotide identity (ANI) or in silico DNA–DNA hybridization (isDDH). So far, 36 species have been described in the genus Aeromonas of which at least 19 are considered emerging pathogens to humans, causing a broad spectrum of infections. Having said that, when classifying 1852 strains that have been reported in various recent clinical cases, 95.4% were identified as only four species: Aeromonas caviae (37.26%), Aeromonas dhakensis (23.49%), Aeromonas veronii (21.54%), and Aeromonas hydrophila (13.07%). Since aeromonads were first associated with human disease, gastroenteritis, bacteremia, and wound infections have dominated. The literature shows that the pathogenic potential of Aeromonas is considered multifactorial and the presence of several virulence factors allows these bacteria to adhere, invade, and destroy the host cells, overcoming the immune host response. Based on current information about the ecology, epidemiology, and pathogenicity of the genus Aeromonas, we should assume that the infections these bacteria produce will remain a great health problem in the future. The ubiquitous distribution of these bacteria and the increasing elderly population, to whom these bacteria are an opportunistic pathogen, will facilitate this problem. In addition, using data from outbreak studies, it has been recognized that in cases of diarrhea, the infective dose of Aeromonas is relatively low. These poorly known bacteria should therefore be considered similarly as enteropathogens like Salmonella and Campylobacter.

Prevalence of virulence and antimicrobial resistance genes in Aeromonas species isolated from marketed cockles (Tegillarca granosa) in Korea

This study aimed to examine incidence, virulence and antimicrobial properties in Aeromonas spp. isolated from cockles (Tegillarca granosa) in Korea. Firstly, genomic DNA was extracted from 32 Aeromonas spp. isolates, and PCR screening for virulence, antimicrobial resistance genes was carried out. The disk diffusion assay was used to examine antimicrobial susceptibility. Aeromonas spp. isolates comprised, A. hydrophila (n = 8), A. veronii (n = 15), A. media (n = 2), A. salmonicida (n = 2), A. allosaccharophila (n = 1), A. bestiarum (n = 1), A. culicicola (n = 1), A. enteropelogenes (n = 1) and A. rivipollensis (n = 1). High prevalence of virulence-related genes reported as; act (69%), alt (47%), ast (41%), aerA (56%), lip (50%), ahyB (47%), ser (28%), fla (66%), gcat (44%), ascV (50%) and hlyA (72%). All isolates were multidrug resistant, while highest resistance level observed for ampicillin (100%), followed by imipenem (81%), rifampicin (78%), cephalothin (72%), piperacillin (47%) and Colistin sulfate (31%). The presence of bla_SHV , bla_CTX , tetE, aac(6')-Ib, strA-strB, qnrS, qnrB and IntI1 genes were reported in varying combinations. Nevertheless, bla_TEM , bla_IMP , tetA, tetB, qnrA, qnrB and aphAI-IAB genes and the class1 integron were not detected. The high occurrence of virulence and antimicrobial resistance genes in cockles reveals that it can be a potential health risk source for consumers.

Use of Autochthonous Lactobacilli to Increase the Safety of Zgougou

Seeds of Pinus halepensis are used for preparing zgougou, a spontaneously fermented matrix giving juice and seeds debris, consumed in many Arabian countries, including Tunisia. In the same way as all the food processes based on spontaneous fermentation, zgougou hides health risks due to eventual pathogenic microorganisms and derived toxins. This study aimed at investigating the effect of the use of autochthonous Lactobacillus paraplantarum A1 and Lactobacillus plantarum A2, as fermentation starters, on the microbiological characteristics, profiles of volatile organic compounds (VOC), antibacterial and antioxidant activities of juice and seeds debris from zgougou. The starter lactobacilli inhibited undesired bacteria (e.g., Enterobacter and Aeromonas) and coccus-shaped lactic acid bacteria, as shown by culture-dependent and-independent methods. The inhibitory effect was more evident in juice than in seeds debris. Some VOC (ethanol, acetoin, phenol,2-methoxy and caryophyllene) were present at higher concentrations in juice and seeds obtained upon spontaneous fermentation, compared to the samples deriving from fermentation with lactobacilli. The latter samples were characterized by higher concentrations of acetic acid, decane, 1-nonanol, bornyl acetate and bornyl formate. In addition, they showed a wider spectrum of antibacterial activity than spontaneously fermented juice and seeds. The use of autochthonous lactobacilli did not relevantly affect the antioxidant activity of zgougou. When juice from lactobacilli-driven fermentation was used to prepare a traditional Tunisian pudding ("Assidat-Zgougou"), it improved color and odor with respect to the pudding containing juice from spontaneous fermentation. This study showed that the use, at laboratory scale, of autochthonous lactobacilli is a feasible biotechnological tool to outgrow undesired bacteria, thus improving the safety of zgougou juice. Future studies should be undertaken to confirm the observed benefits at industrial scale.