Emergence and outbreaks of CTX-M beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae strains in a Tunisian hospital

Abstract

Sixty-two isolates of Enterobacteriaceae (35 Escherichia coli and 27 Klebsiella pneumoniae isolates) producing CTX-M-type beta-lactamases were collected between March 2000 and June 2003 in different wards of Charles Nicolle Hospital in Tunis (Tunisia). Sequencing identified the bla(CTX-M-15) determinant in 55 isolates and bla(CTX-M-16) in 7 isolates. The CTX-M-15-producing strains were isolated in several wards and consisted mainly of two successive clonal groups of E. coli and a major clonal group of K. pneumoniae. The second clonal group of E. coli belonged to phylogenetic group B2 and harbored more virulence factors than the first clonal group. Among the 22 transconjugants or electroporants obtained with selected E. coli and K. pneumoniae CTX-M-15-producing strains, a predominant plasmid restriction pattern was obtained with 17 isolates. The four CTX-M-16-producing strains of E. coli yielded the same pulsed-field gel electrophoresis (PFGE) pattern, while the three CTX-M-16-producing strains of K. pneumoniae yielded two different PFGE patterns. All of the CTX-M-16-producing isolates were recovered in the pediatric ward and had the same plasmid restriction pattern.

FIG. 1.

PFGE patterns of K. pneumoniae strains carrying bla_CTX-M genes. Lanes 1 to 13, Kp19, Kp20, Kp65, Kp18, Kp15, Kp61, Kp67, Kp62, Kp69, Kp13, Kp14, Kp56, and Kp30 corresponding to molecular types K1, K4, K4, K9, K6, K4, K4, K4, K4, K3, K7, K1, and K4, respectively.

FIG. 2.

Number of patients infected by clonal strains of E. coli and K. pneumoniae producing CTX-M-type β-lactamases and isolated at Charles Nicolle Hospital between March 2000 and June 2003. Bar with horizontal hatching, E. coli clone E1 (CTX-M-15); bar with vertical hatching, E. coli clone E2 (CTX-M-16); bar with horizontal dashes, E. coli clone E3 (CTX-M-15); bar with vertical dashes, E. coli clone E6 (CTX-M-15); light-gray bar, K. pneumoniae clone K1 (CTX-M-16); dark-gray bar, K. pneumoniae clone K4 (CTX-M-15).

FIG. 3.

HpaI-digested plasmid profiles of transconjugants or electroporants producing CTX-M-16. Lanes 1 to 4, electroporants of Ec3, Ec38, Kp12, and Kp19, respectively; lane 5, transconjugant Ec7; lane M, molecular weight marker, 1-kb DNA ladder (Bio-Rad).

FIG. 4.

Projections of the bacterial and clinical variables of the 35 E. coli strains on F1/F2 planes computed by factorial analysis of correspondence. A, B2, and D, phylogenetic groups A, B2, and D; E1 to E7, E. coli molecular types 1 to 7; CTX15 and CTX16, β-lactamase types CTX-M-15 and CTX-M-16; urine, blood, and other, urinary tract infection, bacteremia, and other infections; 2000 to 2003, years of isolation. The nine VFs are named as in Table 1.

FIG. 5.

Projections of the bacterial and clinical variables of the 27 K. pneumoniae strains on F1/F2 planes computed by factorial analysis of correspondence. K1 to K9, K. pneumoniae molecular types 1 to 9; CTX15 and CTX16, β-lactamase types CTX-M-15 and CTX-M-16; urine, blood, and other, urinary tract infection, bacteremia, and miscellaneous infections; 2000 to 2003, years of isolation.