Effect of grape seed extract on quality and microbiota community of container-cultured snakehead (Channa argus) fillets during chilled storage.

Herein, the effects of grape seed extract (GSE) on the microflora and biochemical changes of container cultured snakehead (Channa argus) fillets during 11 days of chilled storage were investigated. The sensory analysis, the total number of viable colonies, the total amount of volatile basic nitrogen, and k-value analysis revealed that GSE retarded the deterioration of snakehead fillets. The degradation of inosine 5'-monophosphate and the accumulation of inosine and hypoxanthine in the GSE group were slower than these in the control group. Moreover, GSE treatment effectively decreased the accumulation of putrescine, cadaverine, and histamine. Illumina-MiSeq high throughput sequencing results showed that GSE inhibited the growth of Aeromonas on snakehead fillets. Based on the microbial enumeration, sensory analysis, and k-value, GSE prolonged the shelf life of fillets for 3 days, suggesting its potential for snakehead fillets preservation.

Application of Illumina-MiSeq high throughput sequencing and culture-dependent techniques for the identification of microbiota of silver carp (Hypophthalmichthys molitrix) treated by tea polyphenols.

This study evaluated the antimicrobial effects of tea polyphenols (TP) on changes in microbiota composition and quality attributes in silver carp fillets stored at 4 °C. During storage, TP treatment was found to be effective in enhancing sensory quality, inhibiting microbial growth, and attenuating chemical quality deterioration. Meanwhile, the composition of microbiota of silver carp fillets was investigated using culture-dependent and culture-independent methods. Initially, compared to the control, TP obviously decreased the relative abundance of Aeromonas, which allowed Acinetobacter and Methylobacterium to become the dominant microbiota in TP treated fillets on day 0. The controls, 0.5% TP-treated fillets, and 1% TP-treated fillets were rejected by sensory panelists on days 8, 12, and 12, respectively. At the time of sensory rejection, Aeromonas, followed by Acinetobacter and Pseudomonas, became the main spoilers in the control on day 8. However, TP treatment inhibited the growth of Aeromonas and Acinetobacter significantly. Consequently, Aeromonas followed by Pseudomonas and Shewanella became the predominant microbiota in all TP-treated fillets on day 12. Therefore, TP improved the quality of fillets during chilled storage, which was mainly due to their modulating effects on microbiota that resulted in the change in pattern and process of spoilage in fillets.

Long-Term Bacterial Dynamics in a Full-Scale Drinking Water Distribution System.

Large seasonal variations in microbial drinking water quality can occur in distribution networks, but are often not taken into account when evaluating results from short-term water sampling campaigns. Temporal dynamics in bacterial community characteristics were investigated during a two-year drinking water monitoring campaign in a full-scale distribution system operating without detectable disinfectant residual. A total of 368 water samples were collected on a biweekly basis at the water treatment plant (WTP) effluent and at one fixed location in the drinking water distribution network (NET). The samples were analysed for heterotrophic plate counts (HPC), Aeromonas plate counts, adenosine-tri-phosphate (ATP) concentrations, and flow cytometric (FCM) total and intact cell counts (TCC, ICC), water temperature, pH, conductivity, total organic carbon (TOC) and assimilable organic carbon (AOC). Multivariate analysis of the large dataset was performed to explore correlative trends between microbial and environmental parameters. The WTP effluent displayed considerable seasonal variations in TCC (from 90 × 103 cells mL-1 in winter time up to 455 × 103 cells mL-1 in summer time) and in bacterial ATP concentrations (<1-3.6 ng L-1), which were congruent with water temperature variations. These fluctuations were not detected with HPC and Aeromonas counts. The water in the network was predominantly influenced by the characteristics of the WTP effluent. The increase in ICC between the WTP effluent and the network sampling location was small (34 × 103 cells mL-1 on average) compared to seasonal fluctuations in ICC in the WTP effluent. Interestingly, the extent of bacterial growth in the NET was inversely correlated to AOC concentrations in the WTP effluent (Pearson's correlation factor r = -0.35), and positively correlated with water temperature (r = 0.49). Collecting a large dataset at high frequency over a two year period enabled the characterization of previously undocumented seasonal dynamics in the distribution network. Moreover, high-resolution FCM data enabled prediction of bacterial cell concentrations at specific water temperatures and time of year. The study highlights the need to systematically assess temporal fluctuations in parallel to spatial dynamics for individual drinking water distribution systems.

Usefulness of Chromogenic CromoCen® AGN agar medium for the identification of the genus Aeromonas: Assessment of faecal samples.

Selective screening media for the detection and identification of Aeromonas strains are needed to guide primary isolation procedures in the clinical laboratory. This study compared the selective CromoCen® AGN chromogenic agar medium for the detection and identification of Aeromonas strains that were isolated from various samples against the conventional selective agar media that are commonly used for the isolation of this organism in food, environmental and clinical samples. The Miles and Misra and ecometric methods were used to evaluate the microbiological performance of CromoCen® AGN chromogenic agar medium, which was shown to be satisfactory. A total of 14 reference Aeromonas strains, 44 wild strains and 106 clinical stool specimens were examined using both non-chromogenic selective agars that are commonly used for Aeromonas isolation and CromoCen® AGN agar. The latter exhibited 94.73% sensitivity and 100% specificity for the various samples. On CromoCen® AGN agar medium, Aeromonas formed colonies with light green, greenish and salmon pigments with or without a surrounding wide transparent zone (halo) of 2-3mm in diameter around the entire border. This medium is recommended for the isolation and potential identification of the Aeromonas genus.

Pioneer colonizer microorganisms in biofilm formation on galvanized steel in a simulated recirculating cooling-water system.

Some bacteria have a higher tendency to produce biofilm than others. Especially, Pseudomonas and Aeromonas strains are acknowledged to be pioneer colonizers and are predominant in biofilm formation. We examined biofilm formation and first attachment maintance of biofilms of Pseudomonas spp., Pseudomonas aeruginosa, Aeromonas spp, sulphate reducing bacteria and filamentous fungi. A simulated recirculating cooling-water system was used. Heterotrophic bacteria counts on galvanized steel and glass surfaces rose during the tidy period of 720 hours. In addition, we determined that although Pseudomonas spp., Pseudomonas aeruginosa and Aeromonas spp. were the pioneer colonizers, they surprisingly could not be determined in the biofilms on both types of surface after 456 hours. Sulphate reducing bacteria were observed in biofilms on both surfaces from the outset of the experiments. Filamentous fungi were seen on the galvanized steel and glass surfaces after 0.5 h.

[Postoperative infection of an epigastric hematoma caused by Aeromonas veronii biovar sobria]. / Postoperative Infektion eines epigastrischen Hämatoms mit Aeromonas veronii biovar sobria.

HISTORY: A 52-year-old man with a gastric signet-ring cell carcinoma but without acute symptoms was admitted for reconstructive surgery of the gastrointestinal tract. INVESTIGATIONS: Before the present surgery all functional and radiological tests merely confirmed the previously known disease. Except for mild anemia and abnormal electrolytes all laboratory tests were within normal limits. COURSE, DIAGNOSIS AND TREATMENT: The patient underwent reconstructive surgery of the gastrointestinal tract, namely an ascending sigmoidostomy and resection of an enterocutaneous fistula. For a few days the postoperative development was as expected and the drain, placed during surgery, was removed at the expected time. 9 days postoperatively the patient developed signs of an infection (fever up to 38.8 degrees C, increased WBC and raised C-reactive protein levels). Computed tomography (CT) of the abdomen revealed an epigastric tumor measuring 6 x 5 cm. CT-guided needle aspiration of this lesion showed macroscopic signs of an infected hematoma. A pigtail catheter was successfully implanted for continuous drainage. Both the fluids obtained from CT-guided aspiration and the pigtail drain grew Aeromonas veronii biovar sobria when cultured on standard blood agar. Administration of both cefotaxim and metronidazole for 10 days produced a decrease in the inflammatory parameters. The abdominal CT at that time showed a noticeable regression of the epigastric mass so that the patient was discharged from hospital 3 weeks after surgery. CONCLUSION: This case emphasizes the importance of adequately dosed antibiotic therapy, also for unusual bacteria such as species of Aeromonas.

Effects of linear cationic alpha-helical antimicrobial peptides on immune-relevant genes in trout macrophages.

There are increasing evidence of the potential role of antimicrobial peptides in the regulation of immune responses in mammalian species. However, the effects of these peptides in fish have yet to be investigated. In this study, we examined the transcriptional expression profile of representative immune-relevant genes in a trout macrophage cell line, RTS11, in response to three linear cationic alpha-helical antimicrobial peptides (insect cecropin B, fish pleurocidin and a cecropin analogue CF17). The expression levels of two pro-inflammatory genes, interleukin-1 beta (IL-1 beta) and cyclo-oxygenase-2 (COX-2), increased in the peptide-treated RTS11 cells. The peptides did not appear to affect the expression levels of representative genes associated with antigen presentation, interferon response or JAK/STAT signal transduction. Furthermore, the induction of IL-1 beta and COX-2 in RTS11 by lipopolysaccharide was not adversely affected by these three antimicrobial peptides. Overall, the data indicate a pro-inflammatory effect of the three cationic antimicrobial peptides in the inflammatory response of salmonid species, suggesting a potential application of these peptides as immune adjuvant for fish vaccination.

Factors affecting biosurfactant production by oil degrading Aeromonas spp. isolated from a tropical environment.

An Aeromonas spp. was isolated from tropical estuarine water. The organism grew on crude oil and produced biosurfactant that could emulsify hydrocarbons. The peak growth and biosurfactant production was on the 8th day. The organism grew on a range of hydrocarbons that include crude oil and hexadecane while no growth was recorded on some hydrocarbons that include benzene. The biosurfactant produced by the organism emulsified a range of hydrocarbons with diesel (E24=65) as the best substrate and hexane (E24=22) as the poorest. After purification, the biosurfactant was found to contain about 38% carbohydrate and an unidentified lipid. No protein was present in the purified biosurfactant. Production of biosurfactant was highest in medium with glucose and lowest in the medium with diesel+acetate. Soybean was the best nitrogen source for biosurfactant production. The activity of the biosurfactant was enhanced optimally at NaCl concentration of 5%, pH of 8.0 and temperature of 40 degrees C. The biosurfactant retained 77% of its original activity after 120 min of exposure to heat at a temperature of 100 degrees C. Biosurfactant may be produced with this organism using non-hydrocarbon substrates such as glucose and soybean that are readily available and would not require extensive purification for use in food and pharmaceutical industries.

Diversidade e perfil plasmidial de bactérias do gênero Aeromonas isoladas de ambientes aquáticos do Estado de São Paulo / Diversity and plasmidial profile of bactéria of the genus Aeromonas isolated from aquatic evironments os State of São Paulo

Introdução: O gênero Aeromonas é ubiqüitário no ambiente aquático e já foi isolado de água doce, salgada, salobra, mineral, poluída ou tratada. Várias espécies de Aeromonas apresentam fatores de virulência e podem estar relacionadas a uma série de doenças para seu hospedeiro. Objetivo: Estudar a diversidade e caracterizar molecularmente através do perfil plasmidial, as diferentes espécies do gênero Aeromonas provenientes de corpos hídricos de São Paulo. Métodos: Foram coletadas 19 amostras de água, sendo 11 amostras de água doce, 1 de água salobra,e 7 de água salgada. As amostras foram concentradas através de membrana filtrante e enriquecidas em 100mL de água peptonada alcalina 1por cento. As amostras foram estriadas em placas de petri contendo diferentes meios de cultivo. As colônias típicas foram submetidas a provas bioquímicas para a identificação das espécies. Foi feito o levantamento bibliográfico do Índice de qualidade de Água (IQA) na CETESB, dos pontos de coleta analisados. Para análise do perfil plasmidial, foi utilizada a metodologia descrita por BIRNBORN e DOLU (1979). Resultados: As espécies de Aeromonas foram isoladas em 84,2por cento dos ambientes isolados; segundo os dados do CETESB, 58,3por cento das amostras apresentaram condições favoráveis de qualidade de água; 43,2por cento das cepas isoladas apresentaram pelo menos um plasmídio. Conclusões: Concluiu-se que esses organismos estão amplamente distribuídos no ambiente aquático e que as espécies de Aeromonas não apresentam o mesmo perfil plasmidial, Os organismos isolados dos ambientes estudados podem representar risco à saúde.

External decontamination of wild leeches with hypochloric acid.

BACKGROUND: Medicinal leech, Hirudo medicinalis, has been used in plastic and reconstructive surgery, to relieve venous congestion and to improve the microrevascularization of flaps. In many countries, wild leeches are still provided from local markets and utilised with antibiotic prophylaxies. In this research, results of identification of bacteria in the transport fluid is reported, oral and intestinal floras and the antibiograms of the identified microorganisms are investigated. Also, to avoid possible infections, the ability of hypochloric acid, a disinfectant, to suppress the relevant microorganisms without changing the life style and behavior of leeches in terms of sucking function, is investigated. METHODS: Bacterial identifications and antibiograms of oral and intestinal flora and transport medium were performed for 10 leeches. The optimum concentration of hypochloric acid which eliminated microorganisms without affecting the viability and sucking function of the leeches were determined by dilution of hypochloric acid to 100, 50, 25, 12.5, 6.25 ppm concentrations in different groups of 25 leeches. Finally, 20 leeches were applied atraumatically to the bleeding areas of rats, the duration of suction was determined and compared statistically between the leeches treated and not treated with hypochloric acid solution. RESULTS: Aeromonas hydrophilia was the most commonly identified microorganism and found to be resistant to first generation cephalosporins, frequently used in prophylaxis at surgical wards. In the next stages of the study, the leeches were subjected to a series of diluted hypochloric acid solutions. Although disinfection of the transport material and suppression of the oral flora of hirudo medicinalis were successful in 100, 50, 25, 12.5, 6.25 ppm concentrations; 12.5 ppm solution was the greatest concentration in which hirudo medicinalis could survive and sucking function was not affected significantly. CONCLUSIONS: External decontamination of wild leeches with 12.5 ppm hypochloric acid enables bacterial suppression without causing negative effects on leech sucking function and life.

Control of Aeromonas on minimally processed vegetables by decontamination with lactic acid, chlorinated water, or thyme essential oil solution.

Aeromonas is an opportunistic pathogen, which, although in low numbers, may be present on minimally processed vegetables. Although the intrinsic and extrinsic factors of minimally processed prepacked vegetable mixes are not inhibitory to the growth of Aeromonas species, multiplication to high numbers during processing and storage of naturally contaminated grated carrots, mixed lettuce, and chopped bell peppers was not observed. Aeromonas was shown to be resistant towards chlorination of water, but was susceptible to 1% and 2% lactic acid and 0.5% and 1.0% thyme essential oil treatment, although the latter provoked adverse sensory properties when applied for decontamination of chopped bell peppers. Integration of a decontamination step with 2% lactic acid in the processing line of grated carrots was shown to have the potential to control the overall microbial quality of the grated carrots and was particularly effective towards Aeromonas.

Lateral flagella are required for increased cell adherence, invasion and biofilm formation by Aeromonas spp.

Two types of flagella are responsible for motility in mesophilic Aeromonas strains. A polar unsheathed flagellum is expressed constitutively that allows the bacterium to swim in liquid environments and, in media where the polar flagellum is unable to propel the cell, Aeromonas express peritrichous lateral flagella. Recently, Southern blot analysis using a DNA probe based on the Aeromonas caviae Sch3N lateral flagellin gene sequence showed a good correlation between strains positive for the DNA probe, swarming motility and the presence of lateral flagella by microscopy. Here, we conclude that the easiest method for the detection of the lateral flagellin gene(s) is by PCR (polymerase chain reaction); this showed good correlation with swarming motility and the presence of lateral flagella. This was despite the high degree of DNA heterogeneity found in Aeromonas gene sequences. Furthermore, by reintroducing the laf (lateral flagella) genes into several mesophilic lateral-flagella-negative Aeromonas wild-type strains, we demonstrate that this surface structure enhances the adhesion to and invasion of HEp-2 cells and the capacity for biofilm formation in vitro. These results, together with previous data obtained using Laf- mutants, demonstrate that lateral flagella production is a pathogenic feature due to its enhancement of the interaction with eukaryotic cell surfaces.

Immunity induced shortly after DNA vaccination of rainbow trout against rhabdoviruses protects against heterologous virus but not against bacterial pathogens.

It was recently reported that DNA vaccination of rainbow trout fingerlings against viral hemorrhagic septicaemia virus (VHSV) induced protection within 8 days after intramuscular injection of plasmid DNA. In order to analyse the specificity of this early immunity, fish were vaccinated with plasmid DNA encoding the VHSV or the infectious haematopoietic necrosis virus (IHNV) glycoprotein genes and later challenged with homologous or heterologous pathogens. Challenge experiments revealed that immunity established shortly after vaccination was cross-protective between the two viral pathogens whereas no increased survival was found upon challenge with bacterial pathogens. Within two months after vaccination, the cross-protection disappeared while the specific immunity to homologous virus remained high. The early immunity induced by the DNA vaccines thus appeared to involve short-lived non-specific anti-viral defence mechanisms.

Ingested blood contributes to the specificity of the symbiosis of Aeromonas veronii biovar sobria and Hirudo medicinalis, the medicinal leech.

Hirudo medicinalis, the medicinal leech, usually carries in its digestive tract a pure culture of Aeromonas veronii bv. sobria. Such specificity is unusual for digestive tracts that are normally colonized by a complex microbial consortium. Important questions for the symbiotic interaction and for the medical application after microvascular surgery are whether other bacteria can proliferate or at least persist in the digestive tract of H. medicinalis and what factors contribute to the reported specificity. Using a colonization assay, we were able to compare experimentally the ability of clinical isolates and of a symbiotic strain to colonize H. medicinalis. The symbiotic A. veronii bv. sobria strain proliferated well and persisted for at least 7 days inside the digestive tract. In contrast, the proliferation of Pseudomonas aeruginosa and Staphylococcus aureus was inhibited inside the animal compared to growth in the in vitro control, indicating that the ingested blood was modified within the digestive tract. However, both strains were able to persist in the digestive tract for at least 7 days. For an Escherichia coli strain, the viable counts decreased approximately 1, 000-fold within 42 h. The decrease of viable E. coli could be prevented by interfering with the activation of the membrane-attack complex of the complement system that is present in blood. This suggests that the membrane-attack complex remained active inside H. medicinalis and prevented the proliferation of sensitive bacteria. Thus, antimicrobial properties of the ingested vertebrate blood contribute to the specificity of the A. veronii-H. medicinalis symbiosis, in addition to modifications of the blood inside the digestive tract of H. medicinalis.

Enhancement of anti-Aeromonas salmonicida activity in Atlantic salmon (Salmo salar) macrophages by a mannose-binding lectin.

We investigated the effects of a calcium-dependent mannose-binding lectin isolated from the serum of Atlantic salmon on Aeromonas salmonicida viability and the anti-A. salmonicida activity of Atlantic salmon macrophages. In the absence of other factors, binding of this lectin at concentrations of 0.8, 4.0 and 20.0 ng ml(-1) to virulent A. salmonicida failed to significantly reduce (P> 0.05) cell viability. However, binding of the lectin to A. salmonicida did result in significant (P < or = 0.05) dose-dependent increases in phagocytosis, and bactericidal activity. Significant increases (P < or = 0.05) were also observed in phagocyte respiratory burst activity within the lectin concentration range of 4.0-20.0 ng ml(-1) but the stimulation was not dose dependent at these lectin concentrations. At the lowest lectin concentration tested (0.32 ng ml(-1)), a significant decrease (P < or = 0.05) in respiratory burst was observed. The structure and activity of this lectin are similar to that of mammalian mannose-binding lectins, which are known to play a pivotal role in innate immunity. The presence of this lectin may be an important defense mechanism against Gram-negative bacteria such as A. salmonicida.

Prevalencia de Aeromonas app. en agua de superficie / Prevalence of Aeromonas spp. in surface water

Evidencias microbiológicas, clínicas, inmunológicas y epidemiológicas han demostrado la enteropatogenicidad de algunas cepas de Aeromonas. La principal fuente de infección es el agua y estos microorganismos han sido hallados virtualmente en todos los ambientes acuáticos. Adicionalmente, algunas Aeromonas, incluyendo las cepas enterotoxigénicas, son capaces de crecer rápidamente a temperatura de 5ºC y aun de producir toxinas. Los productos vegetales regados con aguas contaminadas pueden alcanzar niveles críticos de Aeromonas después de ser mantenidos bajo refrigeración, y constituyen así un riesgo para la salud pública al ser consumidos son cocción en forma de ensaladas. Se realizó el presente estudio con el propósito de evaluar este riesgo. Las muestras de agua de superficie fueron sembradas en placas de agar ampicilina almidón y de agar inositol-verde brillante-sales biliares. 100 ml de cada muestra fueron filtradas a través de una membrana Milhpoce de 0.45 µm. Los filtros fueron colocados en agua peptonada alcali como medio de enriquecimiento durante 24h a 35ºC. Un asa impregnada con el enriquecimiento fue utilizada para el aislamiento en superficie de los agares selectivos mencionados. Las colonias presuntivas fueron identificadas mediante el sistema API 20E. El nivel de prevalencia de Aeromonas en las muestras analizadas fue del 17.8 por ciento. Se observó una mayor frecuencia de aislamiento cuando se empleaba la técnica de enriquecimiento A.Veronii biotipo sobria (anteriormente A. sobria) fue la especie más frecuentemente hallada. Debido a que esta especie ha estado asociada con la mayor virulencia, el uso de agua contaminada para el riego de los productos vegetales que van a ser conservados bajo refrigeración y consumidos crudos puede representar un riesgo para la salud pública

Adherence of Aeromonas caviae to human cell lines Hep-2 and Caco-2.

Adherence of Aeromonas caviae to HEp-2 and Caco-2 cell monolayers was investigated with 24 clinical isolates. Growth phase, temperature, multiplicity of infection and length of incubation affected adherence. Treatment of the bacteria with trypsin, sodium metaperiodate, mechanical shearing and the addition of cytochalasin B and cycloheximide to the monolayer significantly reduced the adherence capabilities of the strains investigated. The use of chloramphenicol to inhibit protein synthesis reduced the adhesive capabilities of bacteria grown in liquid medium and those subjected to mechanical shearing. Light microscopy, scanning and transmission electron microscopy were employed in the investigation of bacteria-bacteria and bacteria-monolayer interactions and indicated similarities with the aggregative adherence patterns of the Enterobacteriaceae. The presence of extracellular bacterial appendages and their correlation with increased adhesive capacity may indicate a role in the process of adherence.

Especies de aeromonas asociadas a diarrea: características microbiológicas y clínicas / Species of aeromonas associated a diarrhea: characteristic microbiological and clinical

Para estudiar las características microbiológicas y clínicas de Aeromonas sp. asociada a Enfermedad Diarreica Aguda (EDA) se analizaron, desde junio de 1993 1 diciembre de 1994, 397 muestras de heces de niños menores de cinco años con EDA y 121 asintomáticos. Fueron aisladas en una frecuencia de 11,8 y 5,8 por ciento en los casos de EDA y control, respectivamente. A.hydrophila y A.caviae fueron las especies más aisladas en ambos casos. Como patógenos únicos se encontraron en un 38,3 por ciento, y asociados en un 61,7 por ciento. La presentación del cuadro clínico fue 50 por ciento de tipo disentérico: 33,33 por ciento de tipo secretorio y 16.66 por ciento de tipo indeterminado. El mejor medio de cultivo fue el DNA-ampicilina. Se obtuvo un 1 por ciento con producción de H2S y un 5 por ciento fermentadoras de la lactosa. En las cepas se detectó por lo menos dos de las enzimas estudiadas; en base a esto, existe una importante circulación de este género con capacidad de producir EDA

Utilization of transferrin and salmon serum as sources of iron by typical and atypical strains of Aeromonas salmonicida.

The ability of typical and atypical strains of Aeromonas salmonicida to utilize non-haem sources of protein-bound iron was evaluated. (i) In a plate bioassay, the suppression of growth imposed on typical and atypical A. salmonicida by addition of the high-affinity iron chelator ethylenediamine-di(o- hydroxyphenylacetic acid) (EDDA) to the growth medium was reversed by the addition of 30% or 90% iron-saturated bovine or human transferrin (Tf) or lactoferrin (Lf) to the growth medium. (ii) The mechanism of obtaining iron from Tf was investigated by the addition of bovine Tf contained within a dialysis bag. The reversal of iron-restricted growth suppression differed between the strains in that the atypical strains were unable to utilize Tf contained within a dialysis bag while the typical strains were able to do so. This suggested a siderophore-mediated uptake of iron from Tf by the typical strains, which are known to produce siderophores while atypical strains do not. (iii) A solid-phase binding assay using horseradish-peroxidase-conjugated or biotinylated Tf or Lf failed to detect Tf/Lf-binding activity using whole typical or atypical cells. (iv) When atypical extracellular products (ECP) plus bovine Tf or salmon serum were enclosed in a dialysis bag, diffusible products were released which could reverse the EDDA-imposed growth suppression of an atypical strain. This reversal was negated by inhibition of the ECP metalloprotease with EDTA. (v) Purified 70 kDa serine protease of a typical strain was able to digest bovine Tf to low molecular mass fragments as observed in SDS-PAGE. These results indicate that typical and atypical strains of A. salmonicida differ in their mechanism of utilization of non-haem protein- bound sources of iron. Typical strains utilize Tf via a siderophore-mediated mechanism and are also able to digest Tf with the extracellular serine protease. Atypical strains utilize Tf by a siderophore-independent mechanism probably involving the proteolytic degradation of Tf by the extracellular metalloprotease.