Epidemiology and clinical features of bloodstream infections caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae

Abstract

Cases of bacteremia caused by AmpC-type-beta-lactamase-producing Klebsiella pneumoniae isolates were retrospectively studied to determine the epidemiologic features and clinical outcomes of bloodstream infections. Among 389 blood isolates recovered from 1998 to 2002, 65 isolates (16.7%) were found to be extended-spectrum beta-lactamase (ESBL) or AmpC beta-lactamase producers. The beta-lactamases from 61 of the 65 isolates were characterized; 28 of 61 isolates produced AmpC-type enzymes (14 isolates each produced DHA-1 and CMY-1-like enzymes), 32 isolates produced TEM or SHV-related ESBLs, and 1 isolate produced a CTX-M-14-like enzyme. To compare the clinical features and outcomes of bloodstream infections caused by AmpC producers with those caused by TEM- or SHV-related ESBL producers, 27 patients infected with isolates producing AmpC-type enzymes (AmpC group) and 25 patients infected with isolates producing TEM- or SHV-related enzymes (ESBL group) were analyzed. There was no significant difference between the AmpC and the ESBL groups in terms of risk factors. When the initial response was assessed at 72 h after antimicrobial therapy, the treatment failure rate for the AmpC group was 51.9% (14 of 27 patients) and the 7- and 30-day mortality rates were 14.8 and 29.6%, respectively, which were similar to those for the ESBL group. When the mortality rate for the patients who received extended-spectrum cephalosporins as definitive treatment was assessed, all four patients in the DHA-1 group and one of three patients in the CMY-1-like group died. In summary, the prevalence of AmpC enzyme-producing K. pneumoniae was high at the Seoul National University Hospital, and the clinical features and outcomes for the patients infected with AmpC-producing organisms were similar to those for the patients infected with TEM- or SHV-related ESBL producers.

FIG. 1.

Plasmid agarose gel electrophoresis and Southern hybridization of DHA-1-producing isolates. Lane V517, plasmid size standards from E. coli strain V517 (18); lanes 9 to 57, DHA-1-producing plasmids from the isolates corresponding to the isolate numbers listed in Table 5; lane P, plasmid from K. pneumoniae 502321.

FIG. 2.

Dendrograms of 13 DHA-1-producing K. pneumoniae isolates (A) and 14 CMY-1-producing K. pneumoniae isolates (B). DHA-1 enzyme-producing isolates showed seven PFGE types, and CMY-1-like enzyme-producing isolates revealed two PFGE types. The strains were clustered by the unweighted pair group method with arithmetic averages. The scale indicates the percent genetic similarity. The molecular size marker is a bacteriophage lambda ladder (Bio-Rad). The numbers on the right of each lane correspond to the clinical isolate numbers in Tables 5 and 6.

FIG. 3.

Distribution of ESBL subtypes from the isolates identified each year. DHA-1-producing isolates were consistently isolated from 1998 to 2001, but CMY-1-producing isolates first appeared in 2000.