Aeromonas species in foods

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.

A Global Survey of Hypervirulent Aeromonas hydrophila (vAh) Identified vAh Strains in the Lower Mekong River Basin and Diverse Opportunistic Pathogens from Farmed Fish and Other Environmental Sources

Hypervirulent Aeromonas hydrophila (vAh) has emerged as the etiologic agent of epidemic outbreaks of motile Aeromonas septicemia (MAS) in high-density aquaculture of farmed carp in China and catfish in the United States, which has caused millions of tons of lost fish. We conducted a global survey to better understand the evolution, geographical distribution, and phylogeny of vAh. Aeromonas isolates were isolated from fish that showed clinical symptoms of MAS, and pure cultures were screened for the ability to utilize myo-inositol as the sole carbon source. A total of 113 myo-inositol-utilizing bacterial strains were included in this study, including additional strains obtained from previously published culture collections. Based on a gyrB phylogeny, this collection included 66 A. hydrophila isolates, 48 of which were vAh. This collection also included five new vAh isolates from diseased Pangas catfish (Pangasius pangasius) and striped catfish (Pangasianodon hypophthalmus) obtained in Cambodia and Vietnam, respectively. Genome sequences were generated from representative vAh and non-vAh isolates to evaluate the potential for lateral genetic transfer of the myo-inositol catabolism pathway. Phylogenetic analyses of each of the nine genes required for myo-inositol utilization revealed the close affiliation of vAh strains regardless of geographic origin and suggested lateral genetic transfer of this catabolic pathway from an Enterobacter species. Prediction of virulence factors was conducted to determine differences between vAh and non-vAh strains in terms of virulence and secretion systems. Core genome phylogenetic analyses on vAh isolates and Aeromonas spp. disease isolates (55 in total) were conducted to evaluate the evolutionary relationships among vAh and other Aeromonas sp. isolates, which supported the clonal nature of vAh isolates. IMPORTANCE This global survey of vAh brought together scientists that study fish disease to evaluate the evolution, geographical distribution, phylogeny, and hosts of vAh and other Aeromonas sp. isolates. In addition to vAh isolates from China and the United States, four new vAh isolates were isolated from the lower Mekong River basin in Cambodia and Vietnam, indicating the significant threat of vAh to modern aquaculture and the need for improved biosecurity to prevent vAh spread.

Effects of four different adjuvants separately combined with Aeromonas veronii inactivated vaccine on haematoimmunological state, enzymatic activity, inflammatory response and disease resistance in crucian carp

The purpose of the current study was to explore the immunomodulatory effects of different adjuvants combined with inactivated vaccines under Aeromonas veronii TH0426 infection in crucian carp. This study explored the best conditions for A. veronii as an inactivated vaccine, and included an animal safety test. Furthermore, we expressed the flagellin FlaA of the A. veronii TH0426 strain for use as an adjuvant supplemented in the diet. Crucian carp were fed 12 different experimental diets for 35 days, including the administration of 10 different adjuvants and inactivated vaccine combinations (50% aluminum hydroxide gel and inactivated vaccine combination, and inactivated vaccine with 20%, 30%, or 50% glucan, astragalus polysaccharide or flagellin), inactivated vaccine alone, and PBS control without adjuvant and inactivated vaccine. After the 42 day feeding trials, the fish were challenged with A. veronii TH0426, and the survival rate over 14 days was recorded. In addition, flagellin FlaA can be expressed normally in large amounts. All experimental groups produced higher levels of IgM serum titres than the control group in the different feeding cycles. Moreover, the activity of serum ACP, AKP, SOD, and LZM, and the expression of inflammatory factors were significantly increased in the experimental groups compared with the control group. The results of qRT-PCR analysis showed that the transcription levels of the IL-10, IL-1β, IFN-γ and TNF-α genes in heart, liver, spleen and kidney tissues were significantly enhanced by adjuvant treatment, indicating that the addition of adjuvants can significantly promote the body's inflammatory response. In addition, the phagocytic activity of leukocytes in each adjuvant treated group was significantly enhanced compared to that in the groups without adjuvant. After the A. veronii challenge, the survival rate of all adjuvant-treated groups was significantly higher than that of the control group, and the 50% flagellin adjuvant group had the highest rate of 78.37%. Overall, our findings strongly indicate that adjuvants not only significantly improve the body's immunity, but also exhibit a strong anti-infection ability. Importantly, this work provides a new perspective for the prevention and control of aquaculture diseases.

Thymol Protects Channel Catfish from Aeromonas hydrophila Infection by Inhibiting Aerolysin Expression and Biofilm Formation

Aeromonas hydrophila is an opportunistic pathogen responsible for a number of diseases in freshwater farming. Moreover, the bacterium has been identified as a zoonotic pathogen that threatens human health. Antibiotics are widely used for treatments of infectious diseases in aquaculture. However, the abuse of antibiotics has led to the emergence of antimicrobial resistant strains. Thus, novel strategies are required against resistant A. hydrophila strains. The quorum sensing (QS) system, involved in virulence factor production and biofilm formation, is a promising target in identifying novel drugs against A. hydrophila infections. In this study, we found that thymol, at sub-inhibitory concentrations, could significantly reduce the production of aerolysin and biofilm formation by inhibiting the transcription of genes aerA, ahyI, and ahyR. These results indicate that thymol inhibits the quorum sensing system. The protective effects of thymol against A. hydrophila mediated cell injury were determined by live/dead assay and lactate dehydrogenase (LDH) release assay. Moreover, the in vivo study showed that thymol could significantly decrease the mortality of channel catfish infected with A. hydrophila. Taken together, these findings demonstrate that thymol could be chosen as a phytotherapeutic candidate for inhibiting quorum sensing system-mediated aerolysin production and biofilm formation in A. hydrophila.

The use of the so-called 'tubs' for transporting and storing fresh fishery products

On-land transport/storage of fresh fishery products (FFP) for up to 3 days in 'tubs' of three-layered poly-ethylene filled with freshwater and ice was compared to the currently authorised practice (fish boxes of high-density poly-ethylene filled with ice). The impact on the survival and growth of biological hazards in fish and the histamine production in fish species associated with a high amount of histidine was assessed. In different modelling scenarios, the FFP are stored on-board in freshwater or seawater/ice (in tubs) and once on-land they are 'handled' (i.e. sorted or gutted and/or filleted) and transferred to either tubs or boxes. The temperature of the FFP was assumed to be the most influential factor affecting relevant hazards. Under reasonably foreseeable 'abusive' scenarios and using a conservative modelling approach, the growth of the relevant hazards (i.e. Listeria monocytogenes, Aeromonas spp. and non-proteolytic Clostridium botulinum), is expected to be < 0.2 log10 units higher in tubs than in boxes after 3 days when the initial temperature of the fish is 0°C ('keeping' process). Starting at 7°C ('cooling-keeping' process), the expected difference in the growth potential is higher (< 1 log10 for A. hydrophila and < 0.5 log10 for the other two hazards) due to the poorer cooling capacity of water and ice (tub) compared with ice (box). The survival of relevant hazards is not or is negligibly impacted. Histamine formation due to growth of Morganella psychrotolerans under the 'keeping' or 'cooling-keeping' process can be up to 0.4 ppm and 1.5 ppm higher, respectively, in tubs as compared to boxes after 3 days, without reaching the legal limit of 100 ppm. The water uptake associated with the storage of the FFP in tubs (which may be up to 6%) does not make a relevant contribution to the differences in microbial growth potential compared to boxes.

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.

Bacteriological, Clinical and Virulence Aspects of Aeromonas-associated Diseases in Humans

Aeromonads have been isolated from varied environmental sources such as polluted and drinking water, as well as from tissues and body fluids of cold and warm-blooded animals. A phenotypically and genotypically heterogenous bacteria, aeromonads can be successfully identified by ribotyping and/or by analysing gyrB gene sequence, apart from classical biochemical characterization. Aeromonads are known to cause scepticemia in aquatic organisms, gastroenteritis and extraintestinal diseases such as scepticemia, skin, eye, wound and respiratory tract infections in humans. Several virulence and antibiotic resistance genes have been identified and isolated from this group, which if present in their mobile genetic elements, may be horizontally transferred to other naive environmental bacteria posing threat to the society. The extensive and indiscriminate use of antibiotics has given rise to many resistant varieties of bacteria. Multidrug resistance genes, such as NDM1, have been identified in this group of bacteria which is of serious health concern. Therefore, it is important to understand how antibiotic resistance develops and spreads in order to undertake preventive measures. It is also necessary to search and map putative virulence genes of Aeromonas for fighting the diseases caused by them. This review encompasses current knowledge of bacteriological, environmental, clinical and virulence aspects of the Aeromonas group and related diseases in humans and other animals of human concern.

Molecular identification of diarrheal Aeromonas using immuno magnetic polymerase chain reaction (IM-PCR) technique: a comparative study with conventional culture method

Background

Aeromonas are ubiquitous bacteria causing many clinical conditions including acute diarrhea. Diarrheagenic Aeromonas harbors aerolysin gene secreting virulent enterotoxin, aerolysin.

Objectives

To develop a molecular and immunological based method for detection of Aeromonas.

Methods

Diarrheal Aeromonas strains were identified from stool samples using culture, enterotoxicity testing using mice model. During immune magnetic polymerase chain reaction IM-PCR protocol, aerolysin specific antibodies were bound with immuno magnetic binding. Sensitivity and specificity tests for IM-PCR were conducted.

Results

There was high detection of Aeromonas using IM-PCR (12.4 %) technique when compared to low isolation with culture (5.1%). Our study confirmed that some strains of enterotoxic Aeromonas strains were uncultivable. Enterotoxicity tests on culture isolates revealed many strains were negative. IM-PCR detected high, (62/500) rate of identification of Aeromonas with aerolysin toxin gene. Aeromonas species identified after IM-PCR were A. hydrophila (40.3% ), A. veronii (17.7 %), A. caviae (14.5 %), A. trota (11.2 %), A. jandei (9.6 %) and A. schuberti (6.4%). All A. trota strains were undetected by cultivation.

Conclusion

High sensitivity and specificity of IM-PCR are due to preparation of aerolysin antibodies and immuno magnetic binding, prior to PCR. Since diseases due to Aeromonas are increasingly reported, IM-PCR is recommended for detection from clinical specimens.

Pathogens of Food Animals: Sources, Characteristics, Human Risk, and Methods of Detection

Pathogens associated with food production (livestock) animals come in many forms causing a multitude of disease for humans. For the purpose of this review, these infectious agents can be divided into three broad categories: those that are associated with bacterial disease, those that are associated with viruses, and those that are parasitic in nature. The goal of this chapter is to provide the reader with an overview of the most common pathogens that cause disease in humans through exposure via the food chain and the consequence of this exposure as well as risk and detection methods. We have also included a collection of unusual pathogens that although rare have still caused disease, and their recognition is warranted in light of emerging and reemerging diseases. These provide the reader an understanding of where the next big outbreak could occur. The influence of the global economy, the movement of people, and food makes understanding production animal-associated disease paramount to being able to address new diseases as they arise.

Gut microbiota isolated from the European pond turtle (Emys orbicularis) and its antimicrobial resistance

The aim of the study was to isolate cultivable gut microbiota from European pond turtles kept at the Lithuanian Zoo and to determine antimicrobial resistance of the isolates. The study subjects included 8 elderly turtles living at the Lithuanian Zoo for about 50 years as well as their offspring – 24 young individuals (1-2 years old) that were hatched at the same zoo. Animals were not exposed by treatment with antimicrobials during the last 3 years.

Gut samples were taken from the cloaca and inoculated onto universal media. Isolates then were identified using sequence analysis of 16S rRNA.

The antimicrobial susceptibility testing was performed using the agar diffusion method according to Kirby-Bauer. Clinical breakpoints according to CLSI whenever possible, were used for interpretation of susceptibility. Bacterial isolates resistant to at least three antimicrobials of different classes were treated as multi-resistant.

Fifty-two bacterial isolates were obtained and identified from turtle gut samples. The most prevalent genera includedAeromonas, ChryseobacteriumandCitrobacter.Fifty percent of the isolates obtained from elderly turtles (CI 95% – 19.01-80.99) and 54.8% (CI 95% – 39.75-69.85) of the isolates from young animals were identified as multi-resistant. The most common resistance rates of the isolates from both groups of the turtles were observed toward ampicillin (86.6%), ciprofloxacin (61.5%) and gentamicin (40.4%). The lowest number of resistant isolates were detected toward combination of sulfamethoxazole-trimethoprim (26.9%). The study revealed that European pond turtles kept in captivity are carriers of multi-resistant bacteria however, further studies need to be performed to investigate whether the resistant microorganisms are natural microbiota for this species or they were acquired in the zoo.

Multidrug-Resistant Aeromonas veronii Recovered from Channel Catfish (Ictalurus punctatus) in China: Prevalence and Mechanisms of Fluoroquinolone Resistance

To emphasize the importance of the appropriate use of antibiotics in aquaculture systems, the prevalence of resistance to 25 antimicrobials was investigated in 42 Aeromonas veronii strains isolated from farm-raised channel catfish in China in 2006-2012. All experiments were based on minimal inhibitory concentrations (MICs), and susceptibility was assessed according to the Clinical and Laboratory Standards Institute. Some isolates displayed antibiotic resistance to the latest-generation fluoroquinolones (i.e., ciprofloxacin, levofloxacin, and norfloxacin) in vitro. Therefore, we screened for genes conferring resistance to fluoroquinolones and performed conjugation experiments to establish the resistance mechanisms. The antibiotic resistance rates were 14.29-21.42% to three kinds of fluoroquinolones: ciprofloxacin, levofloxacin, and norfloxacin. Among the 42 strains isolated, 15 carried the qnrS2 gene. The MICs of the fluoroquinolones in transconjugants with qnrS2 were more than fourfold higher compared with the recipient. Among the fluoroquinolone-resistant A. veronii strains, eight had point mutations in both gyrA codon 83 (Ser⁸³→Ile⁸³) and parC codon 87 (Ser⁸⁷→Ile⁸⁷). However, five isolates with point mutations in parC codon 52 remained susceptible to the three fluoroquinolones. In conclusion, the mechanisms of fluoroquinolone resistance in A. veronii isolates may be related to mutations in gyrA codon 83 and parC codon 87 and the presence of the qnrS2 gene.

Pan-genome analysis of Aeromonas hydrophila, Aeromonas veronii and Aeromonas caviae indicates phylogenomic diversity and greater pathogenic potential for Aeromonas hydrophila

Aeromonas species are important pathogens of fishes and aquatic animals capable of infecting humans and other animals via food. Due to the paucity of pan-genomic studies on aeromonads, the present study was undertaken to analyse the pan-genome of three clinically important Aeromonas species (A. hydrophila, A. veronii, A. caviae). Results of pan-genome analysis revealed an open pan-genome for all three species with pan-genome sizes of 9181, 7214 and 6884 genes for A. hydrophila, A. veronii and A. caviae, respectively. Core-genome: pan-genome ratio (RCP) indicated greater genomic diversity for A. hydrophila and interestingly RCP emerged as an effective indicator to gauge genomic diversity which could possibly be extended to other organisms too. Phylogenomic network analysis highlighted the influence of homologous recombination and lateral gene transfer in the evolution of Aeromonas spp. Prediction of virulence factors indicated no significant difference among the three species though analysis of pathogenic potential and acquired antimicrobial resistance genes revealed greater hazards from A. hydrophila. In conclusion, the present study highlighted the usefulness of whole genome analyses to infer evolutionary cues for Aeromonas species which indicated considerable phylogenomic diversity for A. hydrophila and hitherto unknown genomic evidence for pathogenic potential of A. hydrophila compared to A. veronii and A. caviae.

Food Safety: Emerging Pathogens

This article presents information related to emerging pathogens that are foodborne or have the potential to be foodborne including bacteria, viruses, and parasites. The phenotypic characteristics of these pathogens, their epidemiology, prevalence in foods, and transmission routes to humans as well as means for their control are also discussed.

Emerging Aeromonas species infections and their significance in public health

Aeromonas species are ubiquitous bacteria in terrestrial and aquatic milieus. They are becoming renowned as enteric pathogens of serious public health concern as they acquire a number of virulence determinants that are linked with human diseases, such as gastroenteritis, soft-tissue, muscle infections, septicemia, and skin diseases. Proper sanitary procedures are essential in the prevention of the spread of Aeromonas infections. Oral fluid electrolyte substitution is employed in the prevention of dehydration, and broad-spectrum antibiotics are used in severe Aeromonas outbreaks. This review presents an overview of emerging Aeromonas infections and proposes the need for actions necessary for establishing adequate prevention measures against the infections.

Molecular detection of the Aeromonas virulence aerolysin gene in retail meats from different animal sources in Egypt

Meat commonly contain the same Aeromonas spp. which occur in human diarrhoeal and non-diarrhoeal faecal samples. Motile Aeromonas were isolated from 5.6% of total 302 samples. The distribution of the isolates were 5.9 and 5.2% in fresh and frozen samples, respectively. Of the 302 samples taken of the four animal meat species investigated, the genus Aeromonas were isolated in 12.3% of the fresh samples collected from buffalo meat, in 6.5% of the samples collected from sheep meat and 14.0% from the samples collected from the cattle frozen meat samples. The camel meat did not reveal any Aeromonas isolates. Aeromonas hydrophila was isolated as the most prevalent species with 6.8%, followed by Aeromonas caviae with 2.7% and Aeromonas sobria with 2.1% from the total meat samples. Aerolysin toxin gene (aerA) was detected in 3/17 isolates of A. hydrophila isolated from contaminated meat. Infection due to bacterial pathogen with such virulent factor through contact with contaminated meat while handling them, poses health hazards to humans.

Aeromonas spp. clinical microbiology and disease

Members of the genus Aeromonas inhabit various aquatic environments and are responsible for, and are implicated in, a number of intestinal and extra-intestinal infections in humans as well as other animals. This review focuses on invasive human infection and disease and summarizes available findings regarding the microbiology and detection of Aeromonas spp., with emphasis on successful identification and diagnosis, and the control of disease in the population. Antimicrobial resistance and therapy of Aeromonas spp. is also discussed.

The effect of preparation of cebiche on the survival of enterotoxigenic Escherichia coli, Aeromonas hydrophila, and Vibrio parahaemolyticus

BACKGROUND

Cebiche is a common dish in Latin America, prepared using raw fish mixed with vegetables and marinated with lime juice. The acidity of the lime juice is commonly believed to destroy bacteria and render cebiche as safe to eat. Little data exist concerning rates of cebiche-associated gastroenteritis outbreaks, although these may be high given the popularity of the dish.

METHODS

We inoculated raw fish with Aeromonas hydrophila, Vibrio parahaemolyticus, and enterotoxigenic Escherichia coli to determine the effect of the cebiche preparation process on bacterial viability. Raw fish were exposed to a suspension of 1.0 × 10(8) colony-forming units (CFUs) of each organism in a 50-mL solution, prior to the addition of cebiche ingredients. A typical Peruvian cebiche recipe was used combining limes, onions, sweet potatoes, cilantro, and hot peppers marinated together for 30 minutes. A homogenized mixture of the dish was then evaluated for pH and bacterial counts at 0, 10, and 30 minutes. As much as 100 µL of inocula were streaked onto tryptic soy agar (TSA) agar plates and incubated for 24 hours.

RESULTS

The initial average pH of the fish was 6.4 prior to adding cebiche ingredients and 5.0 immediately afterwards. The pH at 10- and 30-minute periods was 5.4 and 5.2, respectively. Little reduction in bacterial counts was observed at either the 10- or 30-minute time periods, with counts increasing at 30 minutes.

CONCLUSIONS

The putative bactericidal role of lime juice in the preparation process is not sufficient to reduce the microbial population present in cebiche. Pathogens may remain viable after exposure to acidic conditions. The increasing popularity of Peruvian cuisine may also lead to cebiche-associated illness outside of Latin America.

The genus Aeromonas: taxonomy, pathogenicity, and infection

Over the past decade, the genus Aeromonas has undergone a number of significant changes of practical importance to clinical microbiologists and scientists alike. In parallel with the molecular revolution in microbiology, several new species have been identified on a phylogenetic basis, and the genome of the type species, A. hydrophila ATCC 7966, has been sequenced. In addition to established disease associations, Aeromonas has been shown to be a significant cause of infections associated with natural disasters (hurricanes, tsunamis, and earthquakes) and has been linked to emerging or new illnesses, including near-drowning events, prostatitis, and hemolytic-uremic syndrome. Despite these achievements, issues still remain regarding the role that Aeromonas plays in bacterial gastroenteritis, the extent to which species identification should be attempted in the clinical laboratory, and laboratory reporting of test results from contaminated body sites containing aeromonads. This article provides an extensive review of these topics, in addition to others, such as taxonomic issues, microbial pathogenicity, and antimicrobial resistance markers.

Phylogenetic identification of Aeromonas simiae from a pig, first isolate since species description

The species Aeromonas simiae was first described on the basis of two strains (CIP 107798(T) and CIP 107797) isolated from faeces of healthy monkeys (M. fascicularis) from Mauritius, which were kept in quarantine in the Centre for Primatology, Louis Pasteur University, Strasbourg, France. In the present study, during a survey to determine the prevalence of Aeromonas at three different pig slaughterhouses at north of Portugal, a single strain MDC2374 (out of 703 isolates) was identified as A. simiae on the basis of 16S rDNA, gyrB and rpoD sequencing, confirming that traditional biochemical approaches are not resolute to identify rarely isolated Aeromonas species. To our knowledge, this is the first time since species description that A. simiae is newly isolated and identified.

Aeromonas spontaneous bacterial peritonitis: a highly fatal infectious disease in patients with advanced liver cirrhosis

BACKGROUND/PURPOSE

Aeromonas infections, rarely reported in Western countries, are not uncommon infectious diseases in Taiwan. The clinical manifestations and prognostic factors of Aeromonas spontaneous bacterial peritonitis (SBP) in patients with liver cirrhosis were investigated.

METHODS

We reviewed the medical charts and microbiological records of liver cirrhosis patients with Aeromonas SBP between January 1990 and December 2005, in a medical center in southern Taiwan.

RESULTS

Thirty-one liver cirrhosis patients developed Aeromonas SBP within a 16-year period. The majority (26, 84%) had concurrent Aeromonas bacteremia. A. sobria (55%) and A. hydrophila (45%) were the causative species. The predominant clinical manifestations included fever (84%), abdominal pain (74%), hypotension on admission (48%), altered mental status (45%), and acute renal failure (42%). Gram-negative bacilli were found in Gram staining of ascitic fluids in 27% of 26 patients, while aeromonads were isolated from ascitic fluids in 55% of 31 patients. The yield rate of ascitic fluid cultures decreased greatly, if paracentesis was performed at > 3 hours after the administration of antimicrobial therapy. All but one patient received in-vitro-active antimicrobial agents within 48 hours, but the all-cause mortality rate was 56%. Initial high Pitt's bacteremia score was independently associated with a fatal outcome in multivariate analysis.

CONCLUSION

Aeromonas SBP is a fatal disease, and must be included in the differential diagnosis of SBP in patients with advanced liver cirrhosis in endemic areas.

High frequency of hemolytic and cytotoxic activity in Aeromonas spp. isolated from clinical, food and environmental in Rio de Janeiro, Brazil

Molecular study of aerolysin and cytotonic enterotoxin genes by PCR and colony blot hybridization was performed in 117 strains of Aeromonas spp. isolated from different sources. Homogeneous distribution of these genes in A. hydrophila complex strains was observed. For A. caviae and A. sobria complex strains, aerolysin genes were more frequent than cytotonic enterotoxins genes. Of 64 A. caviae complex strains, only one (1.5%) amplified the 451 bp product for the aer gene, however, the same primers detected a 400 bp product in 50 (78%) strains. This product was sequenced and had two short regions with homology to several hemolysin genes. The genotype aer (+)/aerA(+)/hly (+)/ast (+)/alt (+) was detected in six A. hydrophila strains from food and environmental source. The most common genotype found in A. hydrophila strains was hly (+) (85%) and aerA(+) (78.7%), while in A. caviae complex strains was aerA(+) (32.8%). All A. veronii complex sobria strains were aer (+)/aerA(+). All A. caviae and A. hydrophila were positive when tested with aer probe using the colony blot test. Thirty-seven percent of A. hydrophila and 53% of A. caviae tested were positive for ast probe. Eighty-nine percent of samples were cytotoxic in Vero cells. Our data demonstrated that Aeromonas spp. can harbor and express virulence genes and reinforce the potential of Aeromonas as a human pathogen.

Multiplex PCR detection of enterotoxin genes in Aeromonas spp. from suspect food samples in northern Taiwan

Aeromonads possess an array of virulence factors and are causative agents of a number of human infections. Among them, genes of one cytotoxic (Act) and two cytotonic (Alt, Ast) enterotoxins are implicated in a human diarrheal disease. A rapid, specific, simultaneous detection of these enterotoxin genes in suspected food poisoning samples is not yet reported. Hence, a multiplex PCR assay was designed to amplify the cytotoxic (act), heat-labile cytotonic (alt), and heat-stable cytotonic (ast) enterotoxin genes of aeromonads. The PCR assay was tested with 133 Aeromonas spp. isolated from suspect food poisoning samples and retail samples of poultry and fish from wet markets in and around Taipei, Northern Taiwan. The Aeromonas spp. isolates were divided into six genotypes based on absence or presence of one or more enterotoxin genes. Of these 133 isolates, Aeromonas caviae (52.5%) and Aeromonas hydrophila (43.4%) were the most frequently isolated species from food poisoning samples and retail samples, respectively. Among the species, A. hydrophila had a significantly higher proportion for harboring three enterotoxin genes than had the others, whereas Aeromonas encheleia, considered a nonpathogen, was found harboring three enterotoxin genes. The multiplex PCR assays are rapid and specific, and provide a useful tool for the detection and genotyping of enterotoxin genes of aeromonads.

Enterobacteriaceae and related organisms isolated from shell eggs collected during commercial processing

In the United States, commercial shell eggs are washed and graded before retail. Since passage of the Egg Products Inspection Act in 1971, processing guidelines have been set to ensure that external and internal characteristics are maintained. However, less is known about how commercial processing affects the safety of shell eggs. To identify enteric bacteria entering plants and persisting throughout processing, eggs were collected from 3 US commercial shell egg-processing plants on 3 separate visits. On each plant visit, 12 eggs were collected from each of 12 sites along the processing line: accumulator, prewash rinse, first washer, second washer, sanitizer rinse, dryer, oiler, check detection/scales, 2 egg grader/packer head lanes, rewash belt entrance, and rewash belt exit. Each egg was sampled by a rinse technique, and the rinsate was plated onto violet red bile glucose agar with overlay for the detection and enumeration of Enterobacteriaceae. From each plate, up to 5 colonies were randomly selected and isolated for identification to genus or species by using biochemical tests. Several genera and species were detected at each of the 3 plants. Sites from which the greatest numbers of isolates were identified were those collected from eggs during preprocessing (accumulator, prewash rinse) or from eggs judged as dirty (rewash belt entrance or exit). Sites yielding the smallest number of isolates were those during or at the end of processing. Escherichia coli and Enterobacter spp. were isolated from each of the 9 plant visits. Other genera isolated from at least 1 of the 3 plants included Cedecea, Citrobacter, Erwinia, Hafnia, Klebsiella, Kluyvera, Leclercia, Morganella, Proteus, Providencia, Rahnella, Salmonella, and Serratia. Non-Enterobacteriaceae isolated and identified included Aeromonas, Chryseomonas, Listonella, Pseudomonas, Sphingobacterium, Vibrio, and Xanthomonas. All of the genera and species were recovered less frequently from fully processed eggs than from unwashed eggs, indicating that shell eggs are less contaminated with bacteria as a result of commercial washing procedures.

An investigation of the Gamma hypothesis: A predictive modelling study of the effect of combined inhibitors (salt, pH and weak acids) on the growth of Aeromonas hydrophila

The Gamma hypothesis, that multiple inhibitory factors combine independently, is the underlying hypothesis for the quantification of the Hurdle concept used in food manufacture. The literature, however, is confused as to whether interactive effects exist and under which circumstances they occur, if at all. Using the method of time to detection (TTD), the inhibitory effect of pH, salt and specific weak acids (acetic, propionic, sorbic and benzoic) and combinations of these with respect to the growth of Aeromonas hydrophila (ATCC 7966) were analysed. A model based on the relative rate to detection described all combinations analysed as having independent effects on the TTD. No synergistic interactions were found between pH and salt, between pH and individual weak acids or between combinations of weak acids and pH for any of the systems under study. This study supports the validity of the Gamma concept -- that individual environmental effects act independently and should, in turn, facilitate attempts to model the growth of other microorganisms under a variety of conditions.

Methodological Quality Assessment of Review Articles Evaluating Interventions to Improve Microbial Food Safety

Review articles are a means of summarizing the potentially vast volume of research on a topic. However, the methodological quality of review articles varies, and reviews on the same topic may reach different conclusions. We evaluated 65 review articles published between 2000 and 2005 that addressed the effectiveness of microbial food safety interventions, using criteria for methodological soundness developed in the medical field. Overall, the methodological quality of the review articles was poor, with none of the reviews providing information on the method of locating primary research studies or the inclusion/exclusion criteria for selecting primary studies. None of the reviews included a critical appraisal of the methodological quality of the primary studies. Less than half of the reviews stated a focused research question, explored possible reasons for differences in the results of primary studies, discussed the generalizability of results, or proposed directions for future research. There is a need to improve the methodological quality of review articles on microbial food safety interventions if they are to be of use in policy and decision making.

Biochemical and molecular characterization of tetracycline-resistant Aeromonas veronii isolates from catfish

Eighty-one tetracycline-resistant Aeromonas sp. strains were isolated from farm-raised catfish. Morphological and biochemical characteristics indicated that 23 of the 81 aeromonads were Aeromonas hydrophila, 7 isolates were Aeromonas trota, 6 isolates were Aeromonas caviae, 42 isolates were Aeromonas veronii, and 3 isolates were Aeromonas jandaei. However, the AluI and MboI restriction fragment length polymorphism (RFLP) patterns of the PCR-amplified 1.4-kb 16S rRNA gene from all 81 tetracycline-resistant aeromonads from catfish were identical to the RFLP banding patterns of A. veronii ATCC 35626, indicating that all 81 isolates were strains of A. veronii. A multiplex PCR assay successfully amplified the 5 tetracycline-resistant genes (tetA to E) from the genomic DNA of all 81 isolates. The assay determined that tetE was the dominant gene occurring in 73/81 (90.0%) of the aeromonads. Plasmids (2.0 to 20 kb) were isolated from 33 of the 81 isolates. Dendrogram analysis of the SpeI pulsed-field gel electrophoresis identified 15 distinct macrorestriction patterns among the isolates. Our results indicate the need for use of 16S rRNA in the identification of Aeromonas spp. and the prevalence of catfish as a reservoir of tet genes.

BACTÉRIAS DO GÊNERO AEROMONAS NO FLUXOGRAMA DE BENEFICIAMENTO DO LEITE TIPO A E SEU COMPORTAMENTO FRENTE À AÇÃO DE ANTIMICROBIANOS

RESUMO Objetivando verificar os possíveis pontos de contaminação e disseminação de bactérias do gênero Aeromonas, foram analisadas amostras de leite colhidas em diferentes pontos do fluxograma de beneficiamento em uma granja de leite tipo A. De 80 amostras analisadas, Aeromonas spp. foram isoladas em 37 (46,25%) delas. Foram colhidas 20 amostras de cada ponto da linha de produção e revelaram-se positivas no isolamento, 90% (18/20) das amostras de leite cru, 30% (6/ 20) das de leite da saída do pasteurizador, 40% (8/20) das de leite do tanque de abastecimento da máquina de empacotar e 25% (5/20) das amostras do leite pronto para consumo. Dentre as espécies foram identificadas Aeromonas sobria em 40,54% das amostras, Aeromonas hydrophila e Aeromonas caviae em 21,62% delas, Aeromonas veronii em 10,81% e Aeromonas schubertii em 2,7%. Das cepas isoladas, 37 foram submetidas a testes de sensibilidade a antimicrobianos. Destas, 100% foram resistentes à ampicilina, 75,67% à cefalotina, 64,86% à cefoxitina e 48,64% ao aztreonam. As drogas as quais as cepas mostraram-se menos resistentes foram, cloranfenicol, netilmicina, amicacina, gentamicina, tetraciclina e tobramicina. Os resultados obtidos demonstram que bactérias do gênero Aeromonas resistentes a vários antimicrobianos podem estar presentes no leite tipo A, o que faz com que este produto possa determinar risco à saúde da população consumidora, e que deve servir de alerta aos serviços de saúde pública.

Development of a rapid identification method for Aeromonas species by multiplex-PCR

Existing biochemical methods cannot distinguish among some species of Aeromonads, while genetic methods are labor intensive. In this study, primers were developed to three genes of Aeromonas: lipase, elastase, and DNA gyraseB. In addition, six previously described primer sets, five corresponding to species-specific signature regions of the 16S rRNA gene from A. veronii, A. popoffii, A. caviae, A. jandaei, and A. schubertii, respectively, and one corresponding to A. hydrophila specific lipase (hydrolipase), were chosen. The primer sets were combined in a series of multiplex-PCR (mPCR) assays against 38 previously characterized strains. Following PCR, each species was distinguished by the production of a unique combination of amplicons. When the assays were tested using 63 drinking water isolates, there was complete agreement in the species identification (ID) for 59 isolates, with ID established by biochemical assays. Sequencing the gyrB and the 16S rRNA gene from the remaining four strains established that the ID obtained by mPCR was correct for three strains. For only one strain, no consensus ID could be obtained. A rapid and reliable method for identification of different Aeromonas species is proposed that does not require restriction enzyme digestions, thus simplifying and speeding up the process.

Growth of Aeromonas hydrophila in the whey cheeses Myzithra, Anthotyros, and Manouri during storage at 4 and 12 degrees C

The fresh whey cheeses Myzithra, Anthotyros, and Manouri were inoculated with Aeromonas hydrophila strain NTCC 8049 (type strain) or with an A. hydrophila strain isolated from food (food isolate) at levels of 3.0 to 5.0 x 10(2) CFU/g of cheese and stored at 4 or 12 degrees C. Duplicate samples of cheeses were tested for levels of A. hydrophila and pH after up to 29 days of storage. At 4 degrees C, A. hydrophila grew in Myzithra and Anthotyros with a generation time of ca. 19 h, but no growth was observed in Manouri. In Myzithra, average maximum populations of 8.87 log CFU/g (type strain) and 8.79 log CFU/g (food isolate) were recorded after 20 and 22 days of storage at 4 degrees C, respectively. The average maximum populations observed in Anthotyros stored at 4 degrees C were 6.72 log CFU/g (food isolate) and 6.13 log CFU/g (type strain) and were observed after 15 and 16 days of storage, respectively. A. hydrophila grew rapidly and reached high numbers in cheeses stored at 12 degrees C. The average generation times were 3.7 and 3.9 h (Myzithra), 4.1 and 6.1 h (Anthotyros), and 8.0 and 9.2 h (Manouri) for the type strain and the food isolate, respectively. Among the different whey cheese trials, the highest A. hydrophila population recorded (10.13 log CFU/g) was in Myzithra that had been inoculated with the food isolate after 8 days of storage at 12 degrees C. To prevent A. hydrophila growth in whey cheeses, efforts must be focused on preventing postprocessing contamination and temperature abuse during transportation and storage.