Short communicationThe upper respiratory tract is a natural reservoir of haemolytic Mannheimia species associated with ovine mastitis
Introduction
Mannheimia haemolytica is an opportunistically pathogenic organism and an obligate commensal of the upper respiratory tract of ruminants. It is the major organism involved in bovine respiratory disease and can cause ovine pneumonia and septicaemia (Boyce et al., 2004, Kirk and Glenn, 1996). Together with Mannheimia glucosida, they are known to be important causes of intramammary infection in sheep (Omaleki et al., 2010, Omaleki et al., 2011). Lamb suckling has been suggested as an important route for transferring M. haemolytica from the nasopharynx of lambs to the ewe’s udder, as isolates obtained from the ovine respiratory tract had similar pathogenicity for ovine mammary tissue to those obtained from mammary secretions or mastitic milk (Fragkou et al., 2011). Studies have demonstrated that M. haemolytica cannot be isolated from the teat skin before lambing or after weaning, also indicating the likely role of lambs in transferring this organism from their oral cavity to the ewe’s udder (Jones and Watkins, 1998). Colonisation of papilloma-like scabby lesions of the teat with different serotypes of M. haemolytica, including serotype A11 of the former [P.] haemolytica, latterly reclassified as M. glucosida, has also been reported, suggesting that these lesions can act as a source for contamination of the teat canal after lamb suckling (Burriel, 1997).
There are no published data investigating the genetic associations between isolates of Mannheimia species from the nasopharynx of sheep and those causing mastitis. Therefore, this study aimed to identify isolates of M. haemolytica and M. glucosida from the nasopharynx of sheep and compare the isolates previously found to be associated with ovine mastitis with those obtained from nasal swabs.
Section snippets
Materials and methods
Three Poll Dorset flocks were included in this study. Flock A had a history of clinical mastitis caused by Mannheimia species at a prevalence of up to 5% over the previous three years, flock J had had a mastitis outbreak in 2009 with 10% of lactating ewes affected (Omaleki et al., under revision), and flock K had had a prevalence of mastitis of less than 2% over the past three years. The three flocks were located in different regions of Victoria, Australia: flock A in the north-east, flock J in
Results
Haemolytic Mannheimia sp. isolates were obtained from 13 of the 26 nasal swabs collected in flock A (50%), with 4 of them identified as M. haemolytica and 9 as M. glucosida (31% and 69% of the haemolytic Mannheimia spp. isolates respectively) (Supplementary Table 1). The nasal swab isolates from this flock were designated with a lower case letter “a”. In this flock, the M. haemolytica isolate a11, obtained from a nasal swab of a lamb in December 2010, was closely related to mastitis isolates
Discussion
Lamb suckling has been suggested to be an important means of infecting the ewe’s udder with different bacteria, as an increase in bacteriologically positive teat secretions of ewes is observed after they have suckled their lambs (Fragkou et al., 2011, Gougoulis et al., 2008). In one study, M. haemolytica was isolated from 63% of samples collected from the tonsils of lambs over 6 weeks (Fragkou et al., 2011). Comparison of the 16s rRNA gene sequence of a M. haemolytica isolate obtained from milk
Conflict of interest
The authors declared that they had no conflicts of interest with respect to their authorship or the publication of this article.
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