A total of 146 Klebsiella isolates from human asymptomatic bacteriuria (n = 73), cystitis (n = 54), and acute pyelonephritis (n = 19) were examined for the presence of particular virulence factors. Capsular type K2 was the most common serotype observed (13%). This capsule type was prevalent in isolates from asymptomatic bacteriuria and cystitis but not from pyelonephritis. Type 1 fimbriae were found significantly more often in pyelonephritis isolates than among those from asymptomatic and symptomatic lower urinary tract infection (UTI; P < .05), while no marked differences were detected with respect to the distribution of type 3 fimbriae. Serum resistance was more frequent among isolates from symptomatic (26%) than from asymptomatic UTI (18%). Enterochelin was produced by all but 1 of the isolates as determined by a bioassay. In contrast, aerobactin synthesis was rare (3%), with isolates from pyelonephritis showing the highest frequency of aerobactin production (3/19).

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A total of 92 clinical isolates of Klebsiella planticola from man was examined with respect to the production of haemagglutinins and siderophores, serum resistance and distribution of capsular types. For comparison, a group of 207 clinical isolates of K. pneumoniae was also studied. The percentages of K. planticola strains able to express mannose-sensitive haemagglutination, indicating type 1 fimbriae (83%) and mannose-resistant and Klebsiella-like agglutination, indicating type 3 fimbriae (69%), as well as to produce the siderophores enterobactin (100%) and aerobactin (2.2%) were almost identical to those of the K. pneumoniae strains. Similarly, the proportion of serum-resistant strains (30%) was comparable to that of K. pneumoniae (25%). The capsule types most often detected in K. planticola were K14 (13%), K2 (9%) and K70 (9%). The incidence of K2, which is the predominant capsular type in K. pneumoniae, was similar in both species. These findings show that K. planticola, which is being detected with increasing frequency in clinical specimens from man, has the ability to express similar putative virulence factors to K. pneumoniae, suggesting that they may have similar pathogenicity.

Extra-intestinal Hafnia alvei isolates are rarely considered to be pathogenic. To investigate whether such strains are able to produce virulence factors, a total of 70 clinical H. alvei isolates was compared with clinical extra-intestinal isolates of other members of the enterobacterial tribe Klebsiellae (Klebsiella pneumoniae, Enterobacter cloacae, Serratia marcescens). Whereas mannose-sensitive haemagglutination (MSHA) was less common in H. alvei (59%) than in K. pneumoniae (86%) and E. cloacae (89%) isolates, the incidences of mannose-resistant haemagglutination indicative of type 3 pili (MR/K-HA) and of serum resistance properties were not lower. All H. alvei strains secreted siderophores but, unlike the other enterobacterial species examined, the siderophore type was neither enterobactin nor aerobactin. Although the low pathogenicity of H. alvei isolates could not be attributed to any of the factors investigated, the mean number of factors expressed by each H. alvei isolate was signi®cantly lower than that expressed by K. pneumoniae and E. cloacae isolates but did not differ signi®cantly from that of S. marcescens. Based on these ®ndings, the low pathogenicity of H. alvei appears to be due to its low frequency of expression of virulence factors as compared with clinically signi®cant species such as K. pneumoniae and E. cloacae.

Klebsiella terrigena is very rarely isolated from humans; as yet, its clinical significance is uncertain. The aim of the present study was to evaluate whether this species is able to express putative virulence factors. A total of 72 faecal (n = 50) and clinical (n = 22) K. terrigena isolates was investigated and compared with faecal and clinical strains of K. pneumoniae. Mannose-sensitive haemagglutination (MSHA) was observed less often in K. terrigena (64-74%) than in K. pneumoniae strains. In contrast, the incidence of mannose-resistant haemagglutinin indicative of type 3 pili (MR/K-HA) (77-94%), serum resistance properties (10-23%), and production of enterobactin (100%) was similar in both species. None of the K. terrigena isolates were able to synthesize aerobactin; however, the frequency of aerobactin synthesis in K. pneumoniae was also only 5%. Serotyping showed capsular types K5 and K70 to be predominant. The virulence-associated serotype K2 was common in both K. terrigena and K. pneumoniae isolates. Taken together, the present results suggest that K. terrigena and K. pneumoniae are indistinguishable with respect to the expression of virulence factors.