Characterization of Pasteurella spp. Strains Isolated from Human Infections
Introduction
Bacteria belonging to the Pasteurellaceae family (i.e., organisms of the genera Pasteurella, Mannheimia, Actinobacillus and Haemophilus) have a high degree of host specificity (Frederiksen, 1993). In contrast to Haemophilus spp., Pasteurella spp. are not commensals of human beings although some strains may be present as a transient part of the normal flora (Avril et al., 1990). Human isolates of Pasteurella spp. are usually clinically significant, these bacteria being responsible for infections related to direct (e.g., bites or scratches) or indirect animal exposure (Weber et al., 1981). Such isolates consist mainly of Pasteurella multocida subspecies multocida, but other species or subspecies have been reported (Holst et al., 1992).
Capsular material is an important determinant of the virulence of Pasteurella species. Five capsular groups have been described for strains of the “P. multocida complex” (i.e., P. multocida subspecies and Pasteurella canis, the latter formerly known as “P. multocida dog-type”). Group B and E strains of P. multocida have been isolated from bovine haemorrhagic septicaemia in many parts of the world; in Europe, however, group E strains have not been isolated, and group B strains have been isolated only in Eastern Europe (Kedrak and Borkowska-Opacka, 2001). F type strains have been isolated from ducks and fowls (Rimler and Rhoades, 1987). A and D strains, which have been isolated from many domesticated and wild animal species, are the groups most frequently isolated from human infections (Carter, 1962).
The aim of the present work was to reconsider the distribution of species and capsular groups (A and non-A) of Pasteurella spp. isolates from human infections in relation to sites of infection and, when a direct contact was known, to animal species.
Section snippets
Bacterial Strains
Over a 12-year period (1983–1994) 143 Pasteurella strains, isolated from human infections in five medical microbiology laboratories, were collected. An isolate from a clinical sample was suspected to be a Pasteurella strain if it was a gram-negative, non-motile and microaerophilic bacterium which did not grow on Drigalski or McConkey medium, gave positive reactions for catalase (10% H2O2) and oxidase (1% tetramethylparaphenylenediamine) and was susceptible to the O/129 compound
Identification
The 143 strains were identified as follows: P. multocida (128), P. canis (9), Pasteurella dagmatis (4), and Pasteurella stomatis (2). No strain was classified in any of the other species described by Mutters et al. (1985) or in the previously described “taxon 16” (Bisgaard and Mutters, 1988). Acidification tests in sorbitol and dulcitol showed that of the 128 strains of P. multocida, 112 were P. multocida subsp. multocida (sorbitol positive and dulcitol negative), 13 were P. multocida subsp.
Discussion
The results confirm the high prevalence of P. multocida among strains of Pasteurella species isolated from man (Holst et al., 1992, Ganière et al., 1993). Identification of strains according to the classification of Mutters et al. (1985) revealed a large predominance of the subspecies multocida; the subspecies septica accounted for 9% of all strains, and only three strains were identified as P. multocida subsp. gallicida. Wild birds and fowls are the usual sources of P. multocida subsp.
Acknowledgements
We acknowledge Christian Le Goff (CIRAD-EMVT, Maisons-Alfort) for serogrouping and colleagues who have send us Pasteurella strains, especially Jacques Vaucel (Hôpital Yves Le Foll, Saint Brieuc).
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