Detection of Salmonellae in Captive and Free-Ranging Turtles Using Enrichment Culture and Polymerase Chain Reaction

Health assessment of wild speckled dwarf tortoises, CHERSOBIUS SIGNATUS

BACKGROUND

In free-ranging reptile populations, bacterial, fungal, viral and parasitic pathogens may affect hosts through impairment in movements, thermoregulation, reproduction, survival, and population dynamics. The speckled dwarf tortoise (Chersobius [Homopus] signatus) is a threatened species that is mostly restricted to the Succulent Karoo biome in South Africa, and little information on pathogens of this species is available yet. We derived baseline parameters for five males and five females that were captured to genetically enhance a conservation breeding program in Europe. Upon collection of the tortoises, ticks were removed and identified. Immediately upon arrival in Europe, ocular, nasal, oral and cloacal swabs were taken for viral, bacteriological and mycological examinations. Fecal samples were collected before and 1 month after fenbendazole treatment, and analyzed for parasites. A panel of PCR, aiming to detect herpesviruses, adenoviruses and iridoviruses, was carried out.

RESULTS

Samples were negative for viruses, while bacteriological examination yielded detectable growth in 82.5% of the swabs with a mean load of 16 × 107 ± 61 × 108 colony forming units (CFU) per swab, representing 34 bacterial species. Cloacal and oral swabs yielded higher detectable growth loads than nasal and ocular swabs, but no differences between sexes were observed. Fungi and yeasts (mean load 5 × 103 ± 13 × 103 CFU/swab) were detected in 25% of the swabs. All pre-treatment fecal samples were positive for oxyurid eggs, ranging from 200 to 2400 eggs per gram of feces, whereas after the treatment a significantly reduced egg count (90-100% reduction) was found in seven out of 10 individuals. One remaining individual showed 29% reduction, and two others had increased egg counts. In five tortoises, Nycthocterus spp. and coccidian oocysts were also identified. Soft ticks were identified as Ornithodoros savignyi.

CONCLUSIONS

Our baseline data from clinically healthy individuals will help future studies to interpret prevalences of microorganisms in speckled dwarf tortoise populations. The study population did not appear immediately threatened by current parasite presence.

How important is the eggshell as a source for initial acquisition of Salmonella in hatchling turtles?

How and when turtles first acquire gut microflora is largely speculative. In this study, the eggshell and hatching process were evaluated for their role in the initial acquisition of Salmonella, by red-eared slider turtles (Trachemys scripta elegans). First, we examined whether the eggshell is a viable substrate for bacterial persistence during incubation, and if internal egg components (i.e., albumen, yolk, and embryo) have detectable bacterial loads. Second, we experimentally manipulated Salmonella by treating eggs with combinations of Salmonella and gentamicin, an effective Gram-negative antibiotic. We found that the eggshell is a viable substrate for maintaining bacteria, as well as an effective barrier to Salmonella transmission as internal egg components were largely bacteria-free. Water samples collected 18 days post-hatch from individuals that were experimentally inoculated with a topical application of Salmonella as eggs had a higher prevalence of Salmonella than those from eggs inoculated with Salmonella but topically treated with gentamicin prior to hatching, control eggs, and eggs only treated with gentamicin, but by day 35 post-hatch there were no detectable differences among the treatment groups. Though it can also act as a barrier that prevents the bacteria from infecting the embryo prior to hatching these findings suggest that the eggshell is a likely source of Salmonella infection in turtle hatchlings.

COMPARISON OF FRESH AND FROZEN FECAL SAMPLES FOR DETECTION OF ENTERIC SALMONELLA FROM CAPTIVE INDIAN STAR TORTOISES (GEOCHELONE ELEGANS)

The use of frozen fecal samples in enrichment media to detect Salmonella spp. strains was evaluated in Indian star tortoises (Geochelone elegans) to determine the utility of this test method for field collection. Fresh fecal samples were collected from 10 captive adult Indian star tortoises. Each sample was split, with one portion in enrichment media at room temperature for 1 or 2 days before submission to a reference laboratory for standard enteric culture. The other was placed in the same enrichment media and frozen at -20°C for 2 wk. Afterwards, it was transferred to a -80°C freezer for 1 mo before submission to the same reference laboratory. These freezer temperatures and holding times were selected to replicate typical field collection procedures. Salmonella enterica was isolated from all 10 fresh samples but from only six frozen samples. Statistically, results showed no significant difference between the two methods; however, this may be due to the limited sample size, and if so, utilization of frozen fecal samples to determine Salmonella spp. prevalence may underestimate the actual prevalence.

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.

Free-living turtles are a reservoir for Salmonella but not for Campylobacter

Different studies have reported the prevalence of Salmonella in turtles and its role in reptile-associated salmonellosis in humans, but there is a lack of scientific literature related with the epidemiology of Campylobacter in turtles. The aim of this study was to evaluate the prevalence of Campylobacter and Salmonella in free-living native (Emys orbicularis, n=83) and exotic (Trachemysscripta elegans, n=117) turtles from 11 natural ponds in Eastern Spain. In addition, different types of samples (cloacal swabs, intestinal content and water from Turtle containers) were compared. Regardless of the turtle species, natural ponds where individuals were captured and the type of sample taken, Campylobacter was not detected. Salmonella was isolated in similar proportions in native (8.0 ± 3.1%) and exotic (15.0 ± 3.3%) turtles (p=0.189). The prevalence of Salmonella positive turtles was associated with the natural ponds where animals were captured. Captured turtles from 8 of the 11 natural ponds were positive, ranged between 3.0 ± 3.1% and 60.0 ± 11.0%. Serotyping revealed 8 different serovars among four Salmonella enterica subspecies: S. enterica subsp. enterica (n = 21), S. enterica subsp. salamae (n = 2), S. enterica subsp. diarizonae (n = 3), and S. enterica subsp. houtenae (n = 1). Two serovars were predominant: S. Thompson (n=16) and S. typhimurium (n=3). In addition, there was an effect of sample type on Salmonella detection. The highest isolation of Salmonella was obtained from intestinal content samples (12.0 ± 3.0%), while lower percentages were found for water from the containers and cloacal swabs (8.0 ± 2.5% and 3.0 ± 1.5%, respectively). Our results imply that free-living turtles are a risk factor for Salmonella transmission, but do not seem to be a reservoir for Campylobacter. We therefore rule out turtles as a risk factor for human campylobacteriosis. Nevertheless, further studies should be undertaken in other countries to confirm these results.

Diversity of Salmonella in biofilms and water in a headwater ecosystem

The diversity of Salmonella was analysed in biofilm and water samples from the spring and slough arms of Spring Lake, the headwaters of the San Marcos River, Texas, during the drought of 2011, with only one potential run-off event at the beginning of the study. Salmonellae were detected in semiselective enrichment cultures by end-point PCR during the entire sampling period of (11 sampling events during 2 months). From the spring arm site, 73% of the biofilms and 41% of the water samples were positive for salmonellae, while only 9% of the biofilms and 23% of the water samples were positive from the slough arm site. Salmonellae could be isolated from all positive samples, with higher diversity in biofilms compared with water samples and more strains obtained from the spring arm than from the slough arm. Differences between sites were generally caused by less frequently detected isolates, while the majority of isolates that were present in both biofilms and water from both sites was represented by three strains only. Quantification attempts by quantitative PCR directly in samples without prior enrichment did not result in a reliable detection of salmonellae, suggesting that numbers in all samples were below the detection limit.