Abstract

Captive bottlenose dolphins are susceptible to bacterial and mycotic infections. Those associated with the respiratory tract can cause significant morbidity and mortality while some remain silent. Establishing the normal baseline blowhole sample microbial flora may have practical applications in the clinical management of cetaceans as changes in this flora or the identification of a pathogen may reflect ill health or disease. In an effort to determine the normal microbial flora of these dolphins, data collected from monthly blowhole samples (May 1993-May 2000) were analyzed retrospectively. This study followed 15 captive dolphins housed in concrete pools with a semi-open, chlorinated, sand filter system where seawater is pumped from the adjacent coast. Samples were collected by holding horse blood, MacConkey, thiosulphate citrate bile sucrose, phenylethanol, Burkholderia pseudomallei selective and Sabouraud dextrose agar culture plates over the blowhole and the animal forcefully expiring onto the agar plates under trained behavior. Bacterial isolates were identified by standard techniques. Data associated with samples collected within four weeks following systemic antibiotic treatment and/or clinical presentation of respiratory diseases was excluded from this study.

A total of about 66 species were identified. Of these, seven were isolated with a frequency >2% and include: Vibrio alginolyticus (24.7%), Candida albicans (8.4%), Proteus mirabilis (6.5%), Shewenella putrefaciens (3.3%), Morganella morganii (3.1%), Staphylococcus aureus (2.4%), Pseudomonas aeruginosa (2.1%). These organisms likely constitute the normal flora of the captive dolphin upper respiratory tract. Over the course of each 12-month period of the 7 years of this study, Shewenella putrefaciens, Morganella morganii, and Pseudomonas aeruginosa were isolated at a low (~5-15%) and relatively constant frequency. In contrast, Proteus mirabilis was isolated at a frequency of~30-35% from January to March and then at a frequency of~15% throughout the remainder of the year. Isolation frequency of Vibrio alginolyticus markedly varied throughout the year with a high of ~50% in March to a low of ~20% in April and an average of~30-40% from May to February.

Commonly isolated normal flora of the cetacean's upper respiratory tract are potential pathogens. This baseline normal flora of the upper respiratory tract of captive dolphins can be a foundation for further studies and analysis on changes of microbial flora as a potential indicator of disease and adaptation to different environments.

Acknowledgements

I would like to acknowledge Drs. Mark Pokras, Alonso Aguirre and Christine Jost at the Wildlife Clinic and Center for Conservation Medicine at Tufts University. Special thanks to Dr. Sam Ridgway for his advice. This work was supported by Tufts Center for Conservation Medicine.