Although swine dysentery (SD) has been absent in US swine herds in the last 20 years, recent outbreaks have been reported in the United States and Canada (Chander et al., 2012).

In Brazil, until 2010, there were few isolated reports of SD, all of them in small herds but an increasing number of outbreaks - at least 13 - were detected in different states (Parana, São Paulo, Minas Gerais and Mato Grosso) between August and October 2012, due to delivery of contaminated replacement gilts originated from one specific multiplier to different breeding herds with no quarantine facilities. Some integrator companies were involved which escalated to wide spread infection.

In order to quantify susceptibility patterns and antimicrobial resistance, the most effective method used for the genus Brachyspira and anaerobes in general is the Minimum Inhibitory Concentration (MIC) (NCCLS, 2004).

The aim of this study was to determine patterns of Brazilian MICs for Brachyspira hyodysenteriae strains isolated from pigs with clinical disease.

Material and Methods

Samples

A total of 10 B. hyodysenteriae strains from states of Rio Grande do Sul (one), Minas Gerais (one) and Santa Catarina (eight) were isolated from clinical cases of diarrhoea and colitis referred for diagnosis and submitted for diagnostic evaluation.

Isolation

Samples of faeces and bowel were sown through swab smears on plates with selective medium for Brachyspira sp. TSA agar (Tryptic Soy Agar) with five per cent sheep blood, rifampicin (6.25mg per μl), spectinomycin (800mg per μl), vancomycin (25mg per μl), colistin (25mg per μl) (Novotna and Skardová, 2002) and incubated for at least three days at 42°C in anaerobic jars with anaerobic atmosphere.

Multiple passes were performed to obtain pure colonies using the exhaustion technique on plates with selective medium. Bacterial colonies were evaluated under phase contrast microscopy.

Histopathology

Fragments of large intestine were processed by routine histological technique of dehydration and paraffin embedding and stained with hematoxylin and eosin for histopathological evaluation.

PCR

The double amplification for B. hyodysenteriae and B. pilosicoli, according to La et al. (2006), was used. MIC: testing was performed on each isolate to tiamulin (0.063 to 8μg per ml), valnemulin (0.031 to 4μg per ml), doxycycline (0125 to 16μg per ml), tylvalosina (0.25 to 32μg per ml), lincomycin (0.5 to 64 μg per ml) and tylosin (2 to 128μg per ml) according to the specifications of VetMIC™ Brachy SVA (ver. 2).

Each well was inoculated with 0.5ml of Brain Heart Infusion Broth (BHI) and foetal bovine serum 10 per cent and about 10⁶ colony-forming units (CFU) per ml Brachyspira sp. The bacteria were harvested from a pure culture. The panels were incubated in an anaerobic atmosphere, right after inoculation stirring at 37°C for four days.

MIC was read as the lowest concentration inhibiting visible growth that is associated with increased turbidity of the medium.

Results

All samples were positive in PCR and had histopathological lesions ranging from a multifocal moderate catarrhal colitis with goblet cell hyperplasia to severe diffuse fibrinonecrotic haemorrhagic colitis associated with the accumulation of mucus in the lumen and presence spiral structures consistent with spirochaetes.

The MIC values for the 10 isolates against doxycycline, vanelmulin and tiamulin were consistently low (1 to 2mg per ml; median 2μg per mL) (1 to > 4μg per mL; median >4μg per mL) and (2 to >8μg per mL; median >8μg per mL), respectively. The MIC values were intermediate for tylvalosin (4 to >32μg per mL; median 32μg per ml) and lincomycin (16 to >64μg per mL; median 32 μg /mL) and they were high for tylosin (>128μg per ml; median >128μg per ml).

Discussion

The results were low for doxycycline, valnemulin and tiamulin, intermediate for lincomycin and tylvalosin and high for tylosin.

The findings corroborate other published results, except for tiamulin. Tiamulin results (2 to >8μg per mL; median >8μg per mL) were higher than other studies (?0,016 to >2μg per mL; median 0.25μg per mL; Hidalgo et al, 2009).

In Brazil, this drug has been used on a large scale for at least a decade and this may explain increasing resistance. Low MIC results for doxycycline confirmed the findings of other authors.

References

1. Chander Y. et al. 2012. J. Vet. Diag. Invest. 24(5), p. 903-910.
2. Hidalgo Á et al. 2009. Res. Vet. Sci. 87: p. 7-12.
3. La, T. et al. 2006. Lett. Appl. Microbiol. 42: p. 284-288.
4. NCCLS. 2004. Wayne, PA.
5. Novotná, M. et al. 2002. Veterinary Medicine– Czech, 47: 4:104–109

The paper is by Roberto Maurício Carvalho Guedes, Amanda Gabrielle de Souza Daniel, Talita Pilar Resende, Michelle de Paula Gabardo and José Paulo Hiroji Sato of the Department of Veterinary Clinic and Surgery, Department of Veterinary Pathology, Veterinary School of the Universidade Federal de Minas Gerais, Belo Horizonte, Mato Grosso, Brazil.

It was presented as a poster at the 6th International Conference on Colonic Spirochaetes in Animals and Humans 2013, University of Surrey, UK. 5-6 September 2013.

Further Reading Find out more information on swine dysentery by clicking here.

October 2013