Aerobic bacterial flora of the nasal cavity in Gulf of California sea lion (Zalophus californianus) pups

Abstract

Nasal swab samples from clinically healthy California sea lions pups (Zalophus californianus) from six different reproductive rookeries in the Gulf of California were collected to determine the type and frequency of the representative aerobic bacterial microflora of their nasal mucosa. A total of 114 samples were examined and 100 bacterial isolates were identified and typified by microbiological and biochemical standard tests.

Fifty four isolates corresponded to Gram positive bacteria (54%) and 46 isolates to Gram negative bacteria (46%). Fifteen bacterial genera were identified, including Micrococcus, Arcanobacterium, Corynebacterium, Moraxella, Neisseria, Escherichia, Kurthia, Acinetobacter, Staphylococcus, Brevibacillus, Bacillus, Klebsiella, Stenotrophomonas, Pseudomonas and Aeromonas. The most frequently isolated genera were Moraxella (24%), Micrococcus (18%), and Corynebacterium (15%). These results show the presence in the nasal cavity of sea lions of several microorganisms. Although considered part of the normal microflora, they may also be opportunistic pathogens for their hosts and may act as a potential natural sentinel of environmental changes.

Introduction

In general, the normal bacterial flora in a mammalian host can be considered as either resident or transitory, of which the resident population is constant for a given anatomical area at a specific age of the host animal. When resident microflora ecology becomes disturbed, the initial balance tends to be restored spontaneously. Transitory microflora however comprise microorganisms from the environment that remain for only short periods within the host. The animal’s body is not a uniform bacterial habitat as each organ system differs, creating a selective medium where certain microorganisms are more favoured than others (Sorum and Sunde, 2001, Mcfarland, 2000).

The development of the respiratory tract microflora begins at birth when the animals are exposed to a complex spectrum of microorganisms, of which those capable of adaptation or colonisation of certain mucosal areas predominate. Furthermore, the microflora of those animals that grow up in the same environment will be closely related and will be stable under specific conditions (Cangemi de Gutiérrez et al., 1999).

Bacteria, yeasts and fungi are part of the normal flora of marine mammals and a wide variety is known to be present in their environment, even though their clinical importance is often unknown (Dunn, 1990). The available information on bacterial infections in sea lions is limited and there are only a few reports of infectious diseases and isolates from animals in rehabilitation centres (Gilmartin et al., 1979, Dierauf et al., 1985, Dunn, 1990, Forshaw and Phelps, 1991, Gulland et al., 1996, Thornton et al., 1998). The aim of this work was to identify using standard biochemical tests the aerobic bacteria present in the nasal cavity of clinically healthy sea lion pups living in the wild.