Characterisation of Hafnia alvei isolates from human clinical extra-intestinal specimens: haemagglutinins, serum resistance and siderophore synthesis

Extra-intestinal Hafnia alvei isolates are rarely considered to be pathogen ic. To investigate whether such strains are able to produce virulence facto rs, a total of 70 clinical H. alvei isolates was compared with clinical ext ra-intestinal isolates of other members of the enterobacterial tribe Klebsi ellae (Klebsiella pneumoniae, Enterobacter cloncae, Serratia marcescens). W hereas mannose-sensitive haemagglutination (MSHA) was less common in H. alv ei (59%) than in K, pneumoniae (86%) and E, cloacac (89%) isolates, the inc idences of mannose-resistant haemagglutination indicative of type 3 pili (M R/K-HA) and of serum resistance properties were not lower All Ii, alvei str ains secreted siderophores but, unlike the other enterobacterial species ex amined, the siderophore type was neither enterobactin nor aerobactin, Altho ugh the low pathogenicity of H, alvei isolates could not be attributed to a ny of the factors investigated, the mean number of factors expressed by eac h H. alvei isolate was significantly lower than that expressed by K, pneumo niae and E, cloncae isolates but did not differ significantly from that of S, marcescens. Based on these findings, the low pathogenicity of Ii, alvei appears to be due to its low frequency of expression of virulence factors a s compared with clinically significant species such as K, pneumoniae and E, cloacae.