Abstract
Following the identification of a case of severe clinical mastitis in a Saanen dairy goat (goat A), an average of 26 lactating goats in the herd was monitored over a period of 11 months. Milk microbiological analysis revealed the presence of Pseudomonas aeruginosa in 7 of the goats. Among these 7 does, only goat A showed clinical signs of mastitis. The 7 P. aeruginosa isolates from the goat milk and 26 P. aeruginosa isolates from environmental samples were clustered by RAPD-PCR and PFGE analyses in 3 genotypes (G1, G2, G3) and 4 clusters (A, B, C, D), respectively. PFGE clusters A and B correlated with the G1 genotype and included the 7 milk isolates. Although it was not possible to identify the infection source, these results strongly suggest a spreading of the infection from goat A. Clusters C and D overlapped with genotypes G2 and G3, respectively, and included only environmental isolates. The outcome of the antimicrobial susceptibility test performed on the isolates revealed 2 main patterns of multiple resistance to beta-lactam antibiotics and macrolides. Virulence related phenotypes were analyzed, such as swarming and swimming motility, production of biofilm and production of secreted virulence factors. The isolates had distinct phenotypic profiles, corresponding to genotypes G1, G2 and G3. Overall, correlation analysis showed a strong correlation between sampling source, RAPD genotype, PFGE clusters, and phenotypic clusters. The comparison of the levels of virulence related phenotypes did not indicate a higher pathogenic potential in the milk isolates as compared to the environmental isolates.
Highlights
Pseudomonas aeruginosa is an aerobic, motile, Gram-negative rod, widely present in the environment, e.g. in water and in humid settings [1], but it is an important opportunistic pathogen for humans, plants and animals
The adaptive behavior of P. aeruginosa is possible thanks to its genetic flexibility which is supported by an extended genome, containing a high number of accessory genes [3]
Genome sequencing of the extensively studied P. aeruginosa strain PAO1 revealed the presence of a great number of genes involved in metabolic adjustment, transport, and release of organic elements, as well as numerous chemotaxis systems [19, 20]
Summary
Pseudomonas aeruginosa (family Pseudomonadaceae) is an aerobic, motile, Gram-negative rod, widely present in the environment, e.g. in water and in humid settings [1], but it is an important opportunistic pathogen for humans, plants and animals. A reduction in the clinical symptoms was observed but, at the same time, the monthly Dairy Herd Improvement (DHI) data of this goat revealed a remarkable increase in milk SCC, from an average of 4.150 x cells/ml from April to August 2007, to 4.787 x cells/ml in September 2007. After this single outbreak, all the lactating goats were monitored for 1 year, and milk samples were collected before dry off (November 2007 and October 2008) and after kidding (April 2008).
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