Birds as vectors of enteric pathogens
A survey of individual faecal samples from seagulls showed that the presence of Salmonella was associated with feeding habits. Up to 55% of gulls feeding on sources of sewage were carrying the organism, and the range of serotypes found were similar to those in the human population. In rural gulls having access to other sources of food, salmonellae were not found. Similarly other bird species studied, rooks, geese and pigeons which do not feed at sources of sewage, did not harbour the organism. The relationship between feeding habits and faecal microflora was also demonstrated in a study of the antibiotic resistant coliforms in bird faeces. In gulls feeding at sewage outfalls the levels and ratio of coliforms resistant to the antibiotics chloramphenicol, ampicillin, tetracycline and streptomycin were similar to those found in the sewage, whereas in other wild bird species antibiotic resistant coliforms were infrequently isolated. In comparison the microflora of intensively reared poultry had a completely different pattern, determined by the presence of antibiotics used for disease prevention and medication. The antibiotic resistance pattern of the faecal coliforms of birds can therefore serve as indicators of their feeding habits. Campylobacters were present in all groups of birds studied. There was no relationship to feeding habits or disease. The organism may be part of the normal faecal microflora. In gulls, C.coli was the main biotype, but in geese, rooks and pigeons C.jejuni predominated, suggesting these latter bird species may have a role in the transmission of Campylobacter. An initial study of the carriage of Listeria monocytogenes by birds showed that gulls feeding on sewage had the highest levels of carriage, especially of the haemolytic, pathogenic serotypes I and 4. In other bird species Listeria was either absent or there was a low incidence of non-haemolytic and non-pathogenic strains.