Aeromonas spp. in foods: a significant cause of food poisoning?

Synergistic inhibition mechanism of pediocin PA-1 and L-lactic acid against Aeromonas hydrophila

Pediocin PA-1 (PA-1) is a membrane-targeting bacteriocin from lactic acid bacteria, which shows antimicrobial activity against a wide range of Gram-positive pathogens. However, the outer membrane of Gram-negative bacteria does not allow pediocin access to its target. In this work, the synergistic inhibitory mechanism of PA-1 with L-lactic acid against Gram-negative aquaculture and food pathogen Aeromonas hydrophila (A. hydrophila) was analyzed. The combined treatment of 3.5 mmol/L L-lactic acid and 50 μmol/L (or 30 μmol/L) PA-1 had strong bacteriostatic and bactericidal activity against A. hydrophila. Full wavelength scanning and ELISA assay revealed the release of lipopolysaccharide (LPS) from the outer membrane of A. hydrophila caused by L-lactic acid treatment. Laser confocal microscopic imaging of A. hydrophila with FITC-labeled pediocin PA-1 proved the accumulation of PA-1 on lactic acid-treated bacterial cells. PA-1 then caused a rapid dissipation of membrane potential (Δψ) and a proton gradient difference (ΔpH) in lactic acid-treated A. hydrophila. Pediocin PA-1 also caused an increase in the extracellular ATP level. Morphology revealed by SEM and TEM showed that combined treating with lactic acid and PA-1 induced vesicles on the cell surface, the outer and inner membrane disruption, and even cytoplasm leakage and cell lysis. The results proved a potential mechanism of the synergistic inhibition of lactic acid and PA-1 against A. hydrophila, by which L-lactic acid released the outer membrane LPS, making it possible for PA-1 to contact the plasma membrane of A. hydrophila, resulting in the dissipation of proton-motive force in the inner membrane and cell death.

Enterotoxin gene profile and molecular epidemiology of Aeromonas species from fish and diverse water sources

AIMS

This investigation was undertaken to study the prevalence, enterotoxin gene profile and molecular epidemiology of Aeromonads from various sources of water (182) and fish (173).

METHODS AND RESULTS

A total of 116 Aeromonas sp. were isolated, of which 48 (26·37%) were from water and 68 (34·62%) were from fish samples collected from retail markets and fish farms. The Aeromonads were recovered from all types of water sources viz. drinking water (13%), surface waters (26%) and fish ponds (69%). The most prevalent species recovered from drinking water was A. hydrophila, from fish ponds it was A. caviae, from surface water sources A. hydrophila and A. caviae were recovered more frequently, and A. hydrophila and A. veronii bv. sobria were isolated predominantly from gills of fish samples. On multiplex PCR analysis for the detection of enterotoxin genes (act, alt, ast), the above mentioned Aeromonas species frequently contained enterotoxin genes, irrespective of their sources. From isolates across all the sources, act (63%) and alt (57%) genes were encountered more frequently than ast (6%). The enterobacterial repetitive intergenic consensus sequences polymerase chain reaction was used for typing of isolates and most of the isolates from water and fish were related, owing to similar ecosystem.

CONCLUSION

A wide distribution of enterotoxin genes in Aeromonads from water and fish is a potential public health threat and molecular genotyping can be helpful to study epidemiology of the pathogen.

SIGNIFICANCE AND IMPACT OF THE STUDY

A high proportion of isolates recovered from diverse water sources, particularly potable drinking water and fish samples carried one or more enterotoxin genes thereby indicating a potential pathogenic nature of isolates from these sources. The genetic relatedness was detected amongst many isolates recovered from water sources and fish samples indicating circulation of familiar virulent clones in the aquatic environments.

Classification, bacteriological findings, and analysis of sex hormone receptors and cytokine expression in mammary lesions of abattoir sows

Mammary lesions in sows can prevent suckling piglets from consuming colostrum that provides fundamental nutrients and protective immunity. Although mammary gross lesions are frequently found in sows at farms or slaughterhouses, with the exception of mastitis, they have received little research attention. In this study, we investigated mammary lesions observed in South Korean sows between 2015 and 2016. Mammary tissue samples of 82 sows showing gross lesions during meat inspection were histologically classified and immunohistochemical analysis was conducted to assess the expression of estrogen receptor (ER)-α, ER-β, and progesterone receptor (PR) for mammary hyperplastic lesions as well as that of cluster of differentiation (CD) 3, CD79a, interleukin (IL)-1α, IL-1β, IL-6, and IL-8 for mastitis. Furthermore, 20 swab samples were cultured, and the isolated bacteria were identified using polymerase chain reactions for 16S ribosomal RNA genes. The lesions were classified as hyperplasia, mastitis, or hyperplasia with mastitis. Immunohistochemistry results revealed that there was neither expression of ER-α nor of ER-β, but all examined hyperplastic samples expressed PR. In addition, there was a significant correlation between CD3 and IL-1β expressions, as well as between IL-1β and IL-6 expressions. Regarding the identity of the isolated bacteria, Pseudomonas spp. were most frequently detected. The results of this study have revealed the incidence and characteristics of porcine mammary lesions.

Incidence of Aeromonas spp. infection in fish and chicken meat and its related public health hazards: A review

Aeromonas is recognized to cause a variety of diseases in man. In humans, they are associated with intestinal and extra-intestinal infections. With the growing importance of Aeromonas as an emerging pathogen, it is important to combat this organism. It is indisputable that Aeromonas strains may produce many different putative virulence factors such as enterotoxins, hemolysins or cytotoxins, and antibiotic resistance against different antibiotics. The ability of these bacteria to grow competitively at 5°C may be indicative of their potential as a public health hazard. Comprehensive enteric disease surveillance strategies, prevention and education are essential for meeting the challenges in the years ahead. It is important for us to promote the value of enteric cultures when patients have a gastrointestinal illness or bloody diarrhea or when multiple cases of enteric disease occur after a common exposure. With the growing importance of Aeromonas as an emerging pathogen, it is important to combat this organism. It is indisputable that Aeromonas strains may produce many different putative virulence factors, such as enterotoxins, hemolysins or cytotoxins. It has been established that aerolysin is a virulence factor contributing to the pathogenesis of Aeromonas hydrophila infection. Fish and chicken play an important role in the transmission of this pathogen to humans. In the present study, the high prevalence of toxin-producing strains was found among the Aeromonas isolates. The ability of these bacteria to grow competitively at 5°C may be indicative of their potential as a public health hazard. The present review was constructed with a view to highlight the zoonotic importance of Aeromonas pathogen in fish and chicken meat.

Prevalence of listeria, Aeromonas, and Vibrio species in fish used for human consumption in Turkey

A total of 78 raw retail fish samples from 30 freshwater and 48 marine fish were examined for the presence of Listeria, Aeromonas, and Vibrio species. The overall incidence of Listeria spp. was 30% in freshwater samples and 10.4% in marine fish samples. Listeria monocytogenes (44.5%) was the most commonly isolated species in freshwater fish, and Listeria murrayi (83.5%) was the most commonly isolated species in marine fish samples. Motile aeromonads were more common in marine fish samples (93.7%) than in freshwater fish samples (10%). Vibrio alginolyticus, Vibrio fluvialis, and Vibrio damsela were isolated only in marine fish samples, representing 40.9, 38.6, and 36.3% of Vibrio isolates, respectively. In freshwater and marine fish, the highest incidences of Listeria and Aeromonas were found in skin samples; the highest incidence of Vibrio in marine fish was found in gill samples. The location of Listeria spp. and L. monocytogenes in a fish was significantly different among freshwater fish. A high incidence of these bacterial pathogens was found in the brown trout (Salmo trutta) and horse mackerel (Trachurus trachurus). Handling of contaminated fish, cross-contamination, or eating raw fish might pose a health hazard, especially in immunosuppressed individuals, elderly people, and children. This study highlights the importance of bacterial pathogens in fish intended for human consumption, but more study is needed.

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.

Putative virulence factors of the Aeromonas spp. isolated from food and environment in Abu Dhabi, United Arab Emirates

Thirty randomly selected Aeromonas isolates from food and the environment in Abu Dhabi, United Arab Emirates, were characterized for putative virulence determinants, such as production of cytotoxin, cytotonic toxin, and hemolysin and their capacity to adhere to and invade Henle 407 cells in vitro. Seventy percent of the tested isolates were cytotoxin producers, and 80% were hemolytic. Cytotoxin was produced by 6 of 7 A. hydrophila strains, 6 of 13 A. caviae strains, and 6 of 7 A. veronii bv. sobria strains, mostly from food sources. A. schubertii, A. jandaei, and A. trota also produced both cytotoxin and hemolysin. All of the 30 isolates tested adhered to Henle 407 cells, but none were able to invade the cells, as determined with the in vitro assay. However, no significant correlation of the presence of these putative virulence factors was found among these aeromonad food isolates.

Production of a monoclonal antibody against Aeromonas hydrophila and its application to bacterial identification

AIMS

to develop a monoclonal antibody (MAb) for the rapid detection of Aeromonas hydrophila in human faeces.

METHODS AND RESULTS

A monoclonal antibody with strong specificity against Aer. hydrophila was obtained by the fusion of myeloma cells and splenocytes of a mouse immunized with vegetative cells of Aer. hydrophila ATCC 7966, followed by a two-step selection against other species of the genera. ELISA analyses revealed that MAb 5F3 strongly reacts with all the Aer. hydrophila strains evaluated, showing a just basal reactivity against other species of the genera, especially Aer. sobria and Aer. caviae.

CONCLUSIONS

MAb 5F3 was characterized as an IgG that recognized a polypeptide of approximately 110 kDa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This MAb could be used to detect Aer. hydrophila in human stool samples.

Prevalence and molecular characterization of Aeromonas spp. in ready-to-eat foods in Italy

A survey was carried out in Italy to ascertain the prevalence of Aeromonas spp. in ready-to-eat foods (vegetables, cheeses, meat products, and ice creams) and the level of molecular heterogeneity of the isolates found by macrorestriction analysis of genomic DNA with pulsed-field gel electrophoresis (PFGE). In total, 46 (14.4%) of the 320 food samples examined were found positive for Aeromonas spp. The highest percentages of isolation were discovered in vegetables, particularly lettuce (45.0%), endive (40.0%), and rucola (20.0%). Ricotta was the only cheese type analyzed that showed a high frequency of isolation (45.0%). Among meat products, salami and raw ham (25.0% of samples positive) and, to a lesser extent, baloney (5.0%) were found positive for Aeromonas spp. Aeromonas hydrophila was the most common isolate from foods of animal origin, whereas Aeromonas caviae was the dominant species in vegetables. No motile aeromonads were found in ice cream samples. Aeromonas isolates showed a high level of genetic heterogeneity, because 24 PFGE patterns were identified among 27 A. hydrophila strains and 20 PFGE patterns were found in 23 A. caviae isolates. In conclusion, consumers of ready-to-eat foods in Italy are regularly exposed to many genetically distinct strains of A. hydrophila and A. caviae without evident signs of malaise, and therefore, few of these strains, if any, are likely to be pathogenic.

Bactérias do gênero Aeromonas em água de matadouro bovino

Verificou-se a ocorrência de bactérias do gênero Aeromonas em amostras de água (abastecimento/residuária) obtidas em matadouro bovino. Analisaram-se a água utilizada nas dependências internas, a água dos currais, utilizada na dessedentação, pré-higienização e tranqüilização dos animais e a água residuária da lavagem das carcaças. Das 30 amostras representativas de cada tipo, bactérias do gênero Aeromonas foram isoladas em 10 (33,3%) amostras da água dos currais e em 10 (33,3%) amostras da água residuária da lavagem de carcaças. Nenhuma das amostras da água tratada de abastecimento das instalações revelou-se positiva no isolamento. As espécies isoladas foram Aeromonas hydrophila em duas (2,2%) e Aeromonas caviae em 19 (21,1%) amostras. Uma cepa considerada atípica foi isolada da água dos currais. Os resultados evidenciaram que a água dos currais pode ser uma importante fonte de contaminação, principalmente para a pele, e através dela as Aeromonas sp. podem chegar à sala de matança.

Note: susceptibility to chlorine of Aeromonas hydrophila strains

The susceptibility of five Aeromonas hydrophila strains and one Escherichia coli strain to chlorine was studied under carefully controlled laboratory conditions. Of the Aer. hydrophila strains, two were from untreated water, two from tap water (immediately downstream of a water treatment plant) and one from the DSM collection. The study included disinfectant concentration (0.1, 0.2 and 0.5 mg l-1), pH (6, 7 and 8) and temperature (4, 21 and 32 degrees C) as controlled variables. The results indicated that the untreated water strains, the DSM strain and the E. coli strain were inactivated within 1 min of chlorine treatment. The strains from chlorinated water (TW11 and TW27) showed a different susceptibility to chlorine disinfection, the rate of inactivation being greater at pH6 than at pH8 for both strains. Under the standard conditions of temperature 21 degrees C, pH7 and chlorine concentration 0.2 mg l-1, an increase or decrease of approximately 1 log unit in the number of bacteria did not affect the kill rate of the strains TW11 and TW27.

Computer aided assignment of motile Aeromonas strains to genospecies level by standard biochemical tests

A procedure is given for differentiation of motile Aeromonas spp. Based on nine to 12 biochemical properties it allows an assignment of isolated Aeromonas strains first to phenotypes and, in the second step, to hybridization groups (HGs) 1-13 as well as to the genotypically defined species Aer. allosaccharophila and Aer. encheleia. The computer aided classification is carried out according to the principles of numerical taxonomy. Using this differentiation scheme 23 Aeromonas strains, which were isolated from food, and two reference strains were speciated. A total of 16 strains were assigned to Aer. hydrophila, six strains to Aer. caviae and one strain to Aer. sobria. Of the 16 Aer. hydrophile strains, 11 were attached to HG 1, one to HG 2 and four could not be classified clearly as HG 3 or HG 1. All six Aer. caviae isolated were assigned to HG 5 and the Aer. sobria strain was ranked among HG 8. The reference strains were assigned to the same genotypes by this method than by DNA-DNA hybridization assays.

Incidence and toxigenicity of Aeromonas hydrophila in seafood

Three selective media, Oxoid Aeromonas agar (OA), blood ampicillin agar (BA) and starch ampicillin agar (SA) were used to evaluate the presence of Aeromonas hydrophila in 66 samples of oyster, shrimp, fish and surimi products. Oyster had the highest incidence, with 50% positive, whilst no A. hydrophila was found in the surimi. Of the three selective media, BA displayed the highest recovery rate of A. hydrophila from seafood. Forty-eight isolates from this survey were tested for their capability to produce hemolysin and cytotoxin. Hemolysin was produced by 79.2% of the isolates and cytotoxin was produced by 91.7% of the isolates in brain heart infusion broth. One of the toxin-producing isolates from oyster, strain 8-169, was further tested for growth and toxin production in oyster, shrimp and fish at various temperatures. This particular isolate grew best and had highest toxin production in oyster. Hemolysin and cytotoxin were produced earlier at 28 degrees C than at 37 degrees C, and titers of hemolysin were also higher at 28 degrees C. At 5 degrees C, it was able to grow and produce hemolysin in oyster.

Fate of Aeromonas and Yersinia on modified-atmosphere-packaged (MAP) cod and trout

The growth/survival of Aeromonas spp. and Yersinia enterocolitica on cod and trout stored in two modified atmospheres at 0 degrees, 5 degrees and 12 degrees C was compared with that on aerobically stored fish. Both organisms grew on aerobically stored fish at all three temperatures. Growth on the modified-atmosphere-stored fish was never greater and was generally markedly less than on aerobically stored fish. This reduction in growth was greater in the higher carbon dioxide-containing atmosphere and at the lower temperature(s).

Distribution of Aeromonas phenospecies and genospecies among strains isolated from water, foods or from human clinical samples

A total of 332 Aeromonas spp. originating from drinking water (n = 75), fresh water (n = 57), chicken and ground beef (107), human faecal samples in association with travelling (n = 49), human faecal samples not associated with travelling (n = 38), and six strains from human blood cultures were studied by phenotypic methods and by using analysis of ribopatterns as a molecular method for the identification of the 13 known hybridization groups (HGs). Also included were the reference strains of each HG. A. hydrophila HG 1, A. caviae HG 4 and A. veronii biotype sobria HG 8/10 were the most important genospecies identified in human faecal samples. A. hydrophila HG 2 and A. media HG 5B predominated in drinking water and A. hydrophila HG 2 and HG 3, A. media HG 5A and HG 5B predominated in fresh water. In drinking water only one isolate was A. hydrophila HG 1 and two isolates were A. caviae HG 4. Clinically important Aeromonas spp. HG 1 (A. hydrophila), HG 4 (A. caviae) and HG 8/10 (A. veronii biotype sobria) were common in chicken and ground beef. In contrast to the drinking water samples, HG 5A was common in chicken and ground beef samples. Atypical, unidentified isolates were most often found in fresh water samples (12/57 strains). Although water has been suspected of being an important source of human aeromonas infections, clinically important HGs were found to be in the minority among Aeromonas spp. identified in drinking water or fresh water. The distribution of Aeromonas spp. HGs among drinking water, chicken and ground beef samples was also different, suggesting that contamination of meat or chicken may not originate from water.

Differences in production of several extracellular virulence factors in clinical and food Aeromonas spp. strains

Production of several extracellular virulence factors (lipase, protease and haemolysin) was compared in 15 Aeromonas spp. isolated from faeces of patients with Aeromonas-associated gastroenteritis and 81 strains isolated from food. Strains from food did not show differences in production of these factors when compared with strains isolated from faeces. However, if strains were considered in relation to autoagglutination (AA) character, the AA+ differed from AA- strains in lipase and protease production. Supernatant fluids of AA+ food and human strains showed 2.5-fold more protease production than that observed in AA- strains. These two characteristics of certain Aeromonas strains could be related with the more virulent capacity.

Comparison of seven selective media for the isolation of mesophilic Aeromonas species in fish and meat

Seven selective agar media and two enrichment broths were evaluated for their suitability for the isolation of mesophilic Aeromonas species from meat, fish, and shellfish samples. In a first trial, aeromonads were inoculated in fish and meat samples and reisolated using all selected media. For qualitative isolation, enrichment in alkaline peptone water (pH 8.7 +/- 0.1) at 28 degrees C and subsequent plating onto sheep blood agar supplemented with 30 mg/L ampicillin (ASBA 30) and bile salts-irgasan-brilliant green agar (BIBG) at 35 degrees C led to the best results. For quantitative assays, direct plating on the same agar media is recommended. In a second trial, 829 meat, fish, and shellfish samples were investigated with the same methods. The results show that BIBG is the most selective medium and that presumptive identification of aeromonads on ASBA 30 is very easy. Finally, we could confirm the opinion of other workers that optimal recovery of mesophilic Aeromonas spp. requires the use of more than one agar medium.

An example of the stages in the development of a predictive mathematical model for microbial growth: the effects of NaCl, pH and temperature on the growth of Aeromonas hydrophila

The stages involved in developing a predictive model are illustrated using data describing the effects of temperature (3-20 degrees C), NaCl concentration (0.5-4.5% w/v) and pH (4.6-7.0) on the aerobic growth of Aeromonas hydrophila (cocktail of 6 strains). Optical density measurements using micro-titre plates were used as an initial screen, to determine the appropriate sampling times for viable counts to be made and to determine the approximate boundaries for growth. Growth curves were generated from viable counts and fitted using a modified Gompertz equation. Quadratic response surface equations were fitted to the log of lag and generation times, in response to the variables of temperature, NaCl and pH (in terms of hydrogen ion concentration). The effects of various combinations of these controlling factors are described. Comparisons between predicted growth rates and lag times from our response surface equations and other models for growth of A. hydrophila, developed with viable count data and optical density measurements, are made, together with comparisons with data from the literature on the growth of this bacterium in foods.

Virulence factors in clinical and food isolates of Aeromonas species

Virulence factors were compared in 15 Aeromonas spp. isolated from faeces of patients with Aeromonas-associated gastroenteritis and in 81 strains isolated from food. Strains from food did not show differences in the distribution of virulence factors when compared with strains isolated from faeces. However, 88.8% of Aeromonas strains isolated from food were capable of producing possible virulence factors. Characterization of 28 autoagglutinating (AA+) Aeromonas spp. indicated that the human strains differed from the food strains in hemagglutinating and hemolytic capacities. These results suggest that autoagglutination associated with hemagglutinating and hemolytic capacities in food strains may be a helpful indicator of potential pathogenicity.

The microbiology of minimally processed fresh fruits and vegetables

Minimally processed fresh (MPF) fruits and vegetables are good media for growth of microorganisms. They have been involved in outbreaks because of the consumption of products contaminated by pathogens. They are also sensitive to various spoilage microorganisms such as pectinolytic bacteria, saprophytic Gram-negative bacteria, lactic acid bacteria, and yeasts. Contamination of MPF fruits and vegetables occurs at every stage of the food chain, from cultivation to processing. Polluted environments during cultivation or poor hygienic conditions in processing increase the risk of contamination with foodborne pathogens. Although MPF fruits and vegetables may harbor psychrotrophic microorganisms such as fluorescent pseudomonads or Listeria monocytogenes, good control of refrigeration temperature limits growth of spoilage and pathogenic microorganisms. Modified atmospheres are often efficient to maintain or improve visual organoleptic quality of MPF fruits and vegetables, but their effects on microorganisms are inconsistent. Chemical disinfection can partially reduce the initial bacterial contamination; irradiation seems to be more efficient. The applications of legislations and quality assurance systems to control contamination, survival, and growth of foodborne pathogens in MPF fruits and vegetables are discussed.

The public health significance of Aeromonas spp. in foods

There is now evidence that some strains of Aeromonas species are enteropathogens. Such strains possess virulence properties, such as the ability to produce enterotoxins, cytotoxins, haemolysins and/or the ability to invade epithelial cells. Strains with these properties are common contaminants of drinking water and a wide range of foods. Contact or consumption of contaminated water, especially in summer, is a major risk factor in Aeromonas-associated gastroenteritis. Aeromonas-contaminated foods may also be vehicles of infection. Given the properties of strains that have been described in foods it has been suggested that food-borne illness could result not only from colonization and in vivo expression of virulence factors, but possibly also by intoxication following ingestion of foods that have been stored for a period of time, even under refrigeration. This paper reviews what is known about Aeromonas spp. in foods, their expression of virulence determinants, particularly at refrigeration temperatures, and the questions remaining to be answered to evaluate the risk they pose, so that an appropriate public health response can be determined.

Thermal Inactivation of Aeromonas hydrophila As Affected by Sodium Chloride and Ascorbic Acid

The combined effects of sodium chloride (0, 1.0, 1.5, and 3.0%) and ascorbic acid (0, 1.0, and 2.0 mmol/liter) with mild heat (46°C) on the survival of Aeromonas hydrophila were evaluated. Because of the nonlinear nature of the survivor curves obtained, several equations yielding an R 2 (coefficient of multiple determination) of ≅ 1 were tested. The equation that most closely fit the curvature of the observed data set was a hyperbolic function. Equation coefficients were combined to obtain a so-called death value. This value (46.67% explained variance) was calculated by extracting the larger eigenvalue and the relative eigenvector from the correlation matrix of the coefficients. the effects of the experimental factors on the death value were described by a quadratic response surface model. Results revealed that the death value was not influenced by the presence of ascorbic acid. However, increased mortality resulted from the interaction between sodium chloride and ascorbic acid.

Distribution of mesophilic Aeromonas species in raw and ready-to-eat fish and meat products in Switzerland

A total of 829 poultry, meat, shellfish and fish products commonly consumed in Switzerland were qualitatively and quantitatively examined for the presence of mesophilic Aeromonas spp. Overall, aeromonads occurred in 24.1% of the samples. Raw food products were frequently contaminated (e.g. 94.1% in minced meat), with colony counts up to 6.0 x 10(6)/g. Some ready-to-eat products had a relatively high percentage of positive samples as well, such as cooked ham in slices (38.2%), mortadella (12.9%), smoked cooked sausage (15.6%), hot and cold smoked fish (10.9-14.3%) and gravad salmon (10.5%). Colony counts, however, were somewhat lower (up to 1.7 x 10(3)/g). The high contamination rate of cooked or hot smoked foods suggests recontamination after cooking or smoking, e.g., at the slicing and packaging stage. 61.2% of the identified strains were Aeromonas hydrophila, followed by 22.5% Aeromonas caviae and 16.3% Aeromonas sobria.

Occurrence of Aeromonas spp. in samples of ground meat and chicken

Aeromonas spp. was commonly isolated from ground meat and chicken samples at the retail level. The dominant species in ground meat were A. hydrophila and A. caviae. In chicken, A. sobria was common while A. caviae was isolated infrequently. Although A. hydrophila was isolated from 75% of ground meat samples and 62% of chicken samples, DL-lactate-positive A. hydrophila (genospecies 1) was isolated from only 25 or 37% or respective samples. Sorbitol-positive A. hydrophila (genospecies 3) was common in both ground meat and chicken.