Abstract

Erysipelothrix rhusiopathiae is a gram-positive bacterium that causes erysipelas in a variety of animals including cetaceans.¹ Since there are no definitive signs or symptoms of systemic erysipelas in dolphins before death, many veterinarians will begin antibiotic treatment for captive cetaceans at the first sign of anorexia. Previous reports have listed antibiotics which should be effective in treating E. rhusiopathiae infections including penicillin G, cephalosporin, ampicillin and ciprofloxacin.^2,3,4,5 Some of these antibiotics are commonly used in the treatment of bacterial infection in captive cetaceans, but many other commonly used antibiotics such as erythromycin, kanamycin and chloramphenicol have been reported to be ineffective in treating E. rhusiopathiae infections.

This study used the Kirby-Bauer Disk-Diffusion method to test antibiotic susceptibilities of several isolates of E. rhusiopathiae cultured from deceased cetaceans. Eight bacterial cultures isolated from deceased cetaceans were identified as E. rhusiopathiae by general microbiological techniques and PCR and designated as follows: NRaD, Hong Kong I, Shedd VI, Shedd VII, Shedd VIII, UCDavis1a, UCDavis1b, and UCDavis1c. Brain-Heart Infusion (BHI) agar containing 0.05% Tween 80 was used to make agar plates for antibiotic testing. Each bacterial isolate was spread onto 12 different plates using sterile cotton swabs and filter disks containing antibiotics were added onto the plates. Sixteen disks containing different antibiotics (eight disks per plate) were added to each plate with six replicates of each plate group. The plates in group 1 included disks of penicillin, vancomycin, trimethoprim-sulfamethoxazole, ciprofloxacin, gentamycin, tetracycline, erythromycin and ampicillin. Group 2 plates had disks of clindamycin, piperacillin, kanamycin, streptomycin, cefotaxime, chloramphenicol, novobiocin and imipenum. After 48 hours incubation at thirty-seven degrees Celsius, the diameter of any zones of inhibition seen were measured in millimeters and the data was compared to published information regarding zone size and antibiotic susceptibility. All eight isolates of Erysipelothrix rhusiopathiae were resistant to cefotaxime, chloramphenicol, gentamycin, kanamycin, novobiocin, streptomycin, tetracycline, trimethoprim-sulfamethoxazole and vancomycin. All isolates were susceptible to ampicillin, clindamycin, imipenum, penicillin G and piperacillin, all of the isolates showed intermediate results for ciprofloxacin and the results for erythromycin were variable. These results matched expected results for E. rhusiopathiae except for the resistance to ciprofloxacin and cefotaxime since E. rhusiopathiae is reported as being susceptible to both of these antibiotics.

Table 1. Antibiotic testing results for 8 isolates of Erysipelothrix rhusiopathiae cultured from cetaceans.

S= Sensitive; I=Intermediate; R= Resistance
a Literature reports Erysipelothrix rhusiopathiae as being susceptible to Ciprofloxacin.
b Literature reports Erysipelothrix rhusiopathiae as having variable susceptibility to Erythromycin.
c Literature reports Erysipelothrix rhusiopathiae as being susceptible to Cefotaxime.

References

1.  Dunn J. 1990. Bacterial and mycotic diseases of cetaceans and pinnipeds. In: Dierauf, L.A. (ed.), CRC Handbook of Marine Mammal Medicine: Health, Disease, and Rehabilitation. CRC Press, Boston. Pp. 73-87.

2.  Reboli AC, WE Farrar. 1989. Erysipelothrix rhusiopathiae: an occupational pathogen. Clinical Microbiology Review 2: 354-9.

3.  Takahashi T, T Sawada, M Muramatsu, K Ohmae, N Terakado. 1984. Antibiotic resistance of Erysipelothrix rhusiopathiae strains isolated from pigs with acute septicemic erysipelas. Nippon Juigaku Zasshi 46: 921-3.

4.  Takahashi T, T Sawada, M Muramatsu, Y Tamura, T Fujisawa, Y Benno, T Mitsuoka. 1987. Serotype, antimicrobial susceptibility, and pathogenicity of Erysipelothrix rhusiopathiae isolates from tonsils of apparently healthy slaughter pigs. Journal of Clinical Microbiology 25: 536-9.

5.  Venditti M, V Gelfusa, A Tarasi, C Brandimarte, P Serra. 1990. Antimicrobial susceptibilities of Erysipelothrix rhusiopathiae. Antimicrobial Agents and Chemotherapeutics 34: 2038-40.