Fish: serologic evidence of infection with human pathogens

Detection of Salmonella in the intestine of Hypostomus plecostomus from the upper San Marcos River, Texas

The prevalence of salmonellae in the intestines of the invasive suckermouth catfish Hypostomus plecostomus was assessed in the San Marcos River, just down-stream of its spring-fed headwaters. In 2014, H. plecostomus, sediment, and water samples were collected during 15 sampling events. A combination of semi-selective enrichment and quantitative polymerase chain reaction (qPCR) revealed the presence of salmonellae in 45% of the fish intestines across the entire year, with a prevalence range of 13-100% per sampling event. Repetitive element sequence-based PCR (rep-PCR) and multi-locus sequence typing (MLST) revealed a high diversity of salmonellae from fish intestine samples at individual sampling times, single or multiple presence of rep-PCR patterns and serotypes within individual fish, and identical rep-PCR patterns and serotypes for different fish within and across sampling events. Overall, 15 serotypes were identified by MLST, with a diversity range between one and seven serotypes per sampling event. Some serotypes were retrieved only once, while others were detected more frequently. A few serotypes were retrieved at several sampling times, nearly evenly distributed over the entire sampling period. Prevalence and diversity were independent of precipitation events, indicating the potential presence of environmental strains that are capable of long-term persistence in the environment.

Characterization of the Cultivable Gut Microflora in Wild-Caught Mediterranean Fish Species

Background: Microflora of the gastrointestinal tract plays important roles in food digestion, nutrient absorption and in host defense against ingested pathogens. Several studies have focused on the microflora of farmed fishes, but the gut flora of wild fishes remains poorly characterized. The aim of this work was to provide an overview of the bacteria colonizing the gut of wild-caught fishes and to determine whether some bacterial species can be pathogenic.

Results: We isolated cultivable bacteria from fifteen wild-caught Mediterranean fish species corresponding to different habitat, diet and origin. Bacterial species identity was determined by 16s rRNA gene sequencing for the 61 isolates. The potential pathogenicity of isolated bacteria was investigated using fruit fly (Drosophila melanogaster) and zebrafish (Danio rerio) as model organisms. Two bacterial strains (Serratia sp. and Aeromonas salmonicida) were lethal when microinjected to Drosophila, while zebrafish did not develop any disease when exposed to any of 34 isolated bacterial strains. However, it was interesting to note that two bacterial strains (Shewanella and Arthrobacter) isolated from marine fishes were able to colonize the guts of freshwater zebrafish.

Conclusion: The results of this study give an overview of the bacterial species found in the guts of wild fishes living off Beirut seashore. It shows that some parameters believed to be limiting factors to host-gut colonization by bacteria can be overcome by some species. This pilot study could be extended by sampling a larger number of fish species with several specimens per fish species, and by identifying uncultivable bacteria that reside in the fish guts. Our results may have implications for the utilization of certain bacterial species in fish farming or their use as bio-indicators for water and/or food quality.

Salmonellae in fish feces analyzed by in situ hybridization and quantitative polymerase chain reaction

The potential of fish to transfer salmonellae from heterogeneous aquatic biofilms into feces was assessed in controlled aquarium studies with Suckermouth Catfish Hypostomus plecostomus and with biofilms inoculated with salmonellae. Neither the presence of catfish nor inoculation with salmonellae had detectable effects on the abundance of the microbial community. Densities of the microbial community were about 10(5) cells/mL in the water during a 1-week period, whereas densities of the microbial community increased 10-fold (10(6) to 10(7) cells/mg) in catfish feces during the same period. Salmonellae were detected by both quantitative polymerase chain reaction (qPCR) and situ hybridization in water samples immediately after inoculation, in numbers of about 10(4) cells/mL, representing up to 20% of the cells of the microbial community. Numbers decreased by three orders of magnitude within the first 3 d of the study, which represented only 0.01% of the community, and became undetectable after day 5. In catfish feces, numbers of Salmonella initially increased to up to 6% of the cells of the community but then declined. These results suggest that Salmonella are not biomagnified during gut passage, and thus, fish only provide a means for the translocation of this pathogen.

Phenotypic characterization of human pathogenic bacteria in fish from the coastal waters of South West Cameroon: public health implications

Increasing economic and recreational opportunities, attractive scenery and a perception of a better quality of life are luring people to the coast. Unfortunately, these activities together with the commensurate increase in population in the area inevitably result in pollution of coastal waters with excessive microorganisms and other pollutants. Microbial pollutants not only contaminate the coastal water but also aquatic food sources, thus posing a health risk to consumers. Fish is a major source of protein in Cameroon, especially in the coastal areas. In this study, we investigated the microbiological quality of fish from the Limbe and Tiko beaches in South West Cameroon from May to October 2007. We isolated human pathogenic bacteria from three anatomic sites (skin, gills, intestine) of 50 fish (150 specimens) and investigated their susceptibility patterns to a battery of antibiotics. Data were analyzed statistically using chi2 with significance set at p < .05. Eleven bacterial species were identified, including Escherichia coli type 1 (20.8%), Citrobacter fruendii (16.4%), Proteus vulgaris (13%), Klebsiella pneumoniae (12.1%), Klebsiella ozaenae (7.7%), Enterobacter cloacae (7.2%), Klebsiella oxytoca (5.8%), Serratia marcescens (4.8%), Serratia odorifera (4.8%), Hafnia alvei (4.4%) and Proteus penneri (2.9%). More contaminated fish were found at Limbe beach than at Tiko beach (61.4% versus 38.6%, respectively (p < .05)). When ranking contamination with respect to anatomic site, skin was the most contaminated (40.6%) specimen and gills the least (28.5%). Ciprofloxacillin, ofloxacillin, and cotrimoxazole were the most effective antibiotics against all isolates, exhibiting 100% sensitivity. Almost half of the isolates (45.7%) were resistant to ampicillin. The results of our study demonstrate that fish from the coastal waters of South West Cameroon are a source of human pathogenic and opportunistic bacteria; hence this finding has public health implications.

Detection of salmonellae from fish in a natural river system

Sediment, water, and fish gut samples taken at three sites near the headwaters of the San Marcos River, Texas, were analyzed for salmonellae Salmonella spp. by culture and molecular techniques. While enrichment cultures from sediment and water samples from the two uppermost sites were negative for salmonellae in polymerase chain reaction analyses, both sediment and water samples were positive at the downstream site. At all sites, salmonellae were present in the guts of different fishes (e.g., largemouth bass Micropterus salmoides, channel catfish Ictalurus punctatus, common carp Cyprinus carpio, and suckermouth catfish Hypostomus plecostomus). The highest percentage of detection (33% of analyzed fish) occurred at the downstream site, whereas detection percentages at the upper two sites were 18% and 17%. Detection of salmonellae was usually limited to one segment of the gut (i.e., upper or lower part). Serovars were highly variable among individuals and differed between the upper and lower gut in the only individual (a common carp) that had salmonellae in both gut segments. In situ hybridization demonstrated that salmonellae were normally associated with particulate material in the gut and occurred in highly variable numbers ranging from an occasional organism to a majority of the gut microbe population. These results demonstrate the presence of different serovars of potentially human pathogenic salmonellae among four ecologically distinct fishes within natural environments. They also suggest that salmonellae are not components of the indigenous microbial community in fish intestines but rather are ingested with particulate material.

Involvement of Enterobacter cloacae in the mortality of the fish, Mugil cephalus

AIMS

To identify the causative agent of the mortality in the fish, Mugil cephalus, in Muttukadu lagoon.

METHODS AND RESULTS

An enteric bacterium from the kidneys of moribund fish M. cephalus, was isolated and identified as Enterobacter cloacae (MK). Mugil cephalus was experimentally infected by this isolate and was re-isolated from the kidneys of the moribund fish. Enterobacter cloacae isolates from the lagoon water (MW1, MW2 and reference strain ATCC 13047) and the reference strain were not able to induce similar pathogenesis. The putative factor imparting pathogenicity to the MK isolate was identified as a cationic molecule, which migrated towards the cathode on agarose gel electrophoresis.

CONCLUSIONS

The Ent. cloacae (MK) isolate harbouring a cationic factor was the causative agent for the mortality of M. cephalus, found in Muttukadu lagoon.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reveals that human enteric bacteria MK which is considered as nonpathogenic to fish, may become pathogenic to fish when it harbours this cationic factor. This cationic factor is found to be pathogenic to the fish M. cephalus leading to mortality. It was also found to be pathogenic to mice. Therefore, the shuttling of Ent. cloacae, harbouring cationic factor, between human and fish may be of human health importance.

Food borne microbial pathogens of cultured aquatic species

This article provides a broad overview of microbial pathogens associated with marine and fresh water aquatic animals, including Vibrio species, Escherichia coli, Streptococcus iniae, Salmonella species, and Edwardsiella tarda. Historically, cultured fish were not considered important vectors of human pathogens. This situation is changing, partly due to increasing animal densities as a consequence of a rapidly growing industry and partly due to increasing awareness by health care providers of pathogens in aquatic species that may result in human illness. Concerns facing the industry are also discussed along with possible solutions.

Immune response of Tilapia aurea exposed to Salmonella typhimurium

Tilapia aurea showed a specific immune response to Salmonella typhimurium. S. typhimurium was introduced into the gut of T. aurea by force-feeding. S. typhimurium was isolated from the fish viscera after 15 days, but at 30 days viable cells were not detected. T. aurea had an antibody titer to S. typhimurium after 30 days which was fivefold greater than the natural background antibody titer. An elevated antibody titer was not indicative of active bacterial infection.

Acute phase (C-reactive) protein-like macromolecules from rainbow trout (Salmo gairdneri)

A protein which reacts with the Cx-polysaccharide of Streptococcus pneumoniae and is inhibited by phosphorylcholine was isolated from the serum of rainbow trout by affinity chromatography. The protein, which exists in monomeric and oligomeric forms in non-immune trout serum, is very similar with regard to specificity and size to the Cx-reactive protein from rabbits. A semi-quantitative analytical method for evaluating bacterial agglutination with an electronic particle counter and size distribution analyzer was developed to compare natural and acute serum levels of trout and rabbit Cx-reactive proteins. Results indicate that the poikilotherm has much higher concentrations in normal serum. The trout serum protein can also be rapidly induced to yet higher levels by both chemical and physical stress. The implications for such a protein in the teleost's natural defense system and overall homeostasis are discussed.

Antibodies against enteric bacteria in brown bullhead catfish (Ictalurus nebulosus, LeSueur) inhabiting contaminated waters

Brown bullhead catfish were collected from sewage- and acid mine waste-polluted waters in an attempt to detect antibodies against human enteric bacteria in their sera and to investigate the association of antibody response with environmental conditions. Agglutination antigens prepared from isolates obtained from water collected at the same locations as the fish habitats were used to demonstrate such antibodies. The results showed large percentages of reactive sera for common isolates such as Escherichia coli and Enterobacter cloacae as well as lesser incidences of antibodies to other, less common isolates. In general, fish with the highest titres were collected from habitats with higher coliform counts. Acid mine drainage reduced the total coliform counts, but did not appear to affect the titers of sera from fish collected from water so affected. It was concluded that the bottom-feeding catfish might be a better subject for the study of fish as an ecological indicator of fecal pollution in acid-polluted waters.