To investigate the role of bacterial cofactors in the development of urogenital cancer, we took vaginal and preputial swabs for bacterial isolation from 148 free-ranging and 48 stranded California sea lions (Zalophus californianus), including 13 animals with urogenital carcinoma. Aerobic bacteria were isolated from 116 (78.4 percent) wild sea lions and 100 percent of stranded animals. A total of 394 isolates were identified representing 51 unique bacterial species. The mean number of isolates per animal was 2.0 ± 1.6 (median = 2, range from 0 to 7) and increased with age in the wild group. There was no difference in the number of isolates per animal between wild and stranded adults. Cytological examination of vaginal or preputial smears showed a majority (69.5 percent, 56/82) of animals examined had no or mild inflammation. The most common bacteria isolated from the wild sea lions were Psychrobacter phenylpyruvicus (39 isolates), non-hemolytic Streptococcus (35 isolates), Corynebacterium spp. (30 isolates), and Escherichia coli (20 isolates). More bacterial types were isolated from stranded animals than wild animals (32 vs. 24) and there was significantly less growth of Psychrobacter phenylpyruvicus, Corynebacterium spp., Moraxella-like spp. in the stranded animals.
We obtained bacterial cultures from 13 sea lions with urogenital carcinoma. Bacterial growth occurred in all cases resulting in 34 isolates from 15 different bacterial species with a median of three (x = 2.6 ± 1.4, range 1-5) isolates per animal. Beta-hemolytic Streptococcus was the most frequently isolated bacterium from carcinoma cases (7 isolates, 53.8 percent). Female California sea lions with urogenital carcinomas were 38.3 (95 percent CI, 2.5-1886.3) times more likely to have beta-hemolytic streptococci then females stranded for other causes, but males with carcinomas were not (OR = 1.2, 95 percent C.I., 0.1-15.6) more likely to have beta-hemolytic streptococci. No other bacteria were significantly associated with the presence of urogenital carcinomas.
Chlamydia PCR was performed on DNA extracted from swabs from 59 wild, 28 stranded, and six carcinoma adult sea lions. All samples were negative for Chlamydia spp.
The urogenital carcinomas of sea lions were strongly associated with beta-hemolytic streptococci in the females, suggesting that the organism may play a role in the development of the disease; however, because no association was found in the males with urogenital carcinomas, there appears to be a connection between gender and the prevalence of beta-hemolytic Streptococcus in animals with carcinomas.