Open AccessPrevalence of CTX-M β-Lactamases in Philadelphia, Pennsylvania
Author(s) -
Shan E. McGettigan,
Baofeng Hu,
Kathleen Andreacchio,
Irving Nachamkin,
Paul H. Edelstein
Publication year - 2009
Publication title -
journal of clinical microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.349
H-Index - 255
eISSN - 1070-633X
pISSN - 0095-1137
DOI - 10.1128/jcm.00319-09
Subject(s) - proteus mirabilis , microbiology and biotechnology , enterobacteriaceae , cephalosporin , klebsiella , escherichia coli , biology , bacteria , klebsiella pneumoniae , proteus , antibiotics , staphylococcus aureus , genetics , gene
CTX-M β-lactamases were thought to be rare in the United States, but a recent study in Texas showed that up to 70% of extended-spectrum β-lactamase (ESBL)-containing members of theEnterobacteriaceae family were CTX-M positive (J. S. Lewis, M. Herrera, B. Wickes, J. E. Patterson, and J. H. Jorgensen, Antimicrob. Agents Chemother. 51:4015-4021, 2007). We used PCR to detect CTX-M in all 291 extended-spectrum cephalosporin-resistant gram-negative bacteria isolated in our laboratory during 2007. Thirty (48%)Escherichia coli isolates, 6 (3%)Klebsiella sp. isolates, and 7 (100%)Proteus mirabilis isolates tested were CTX-M positive, with 15% of allEnterobacteriaceae tested being positive. TheE. coli CTX-M groups were I (57%), IV (37%), II (3%), and not groupable (3%); three of the group IV isolates were positive for CTX-M-18, and three of the group I isolates were positive for CTX-M-15. One of seven positiveP. mirabilis isolates was in group II, with the remainder being positive for a CTX-M-25-like β-lactamase; and 33% of theKlebsiella sp. isolates were in group I or IV, with the remainder not being in groups I to IV. CTX-M-producing bacteria were isolated from urine (n = 13), blood (n = 13), wounds (n = 12), and the respiratory tract (n = 4). All 31 CTX-M-positive isolates tested for the presence of ESBL were confirmed to produce ESBLs by the use of tests recommended by the CLSI. Pulsed-field gel electrophoresis of the CTX-M-positive isolates showed that sixP. mirabilis isolates were clonal and that there were seven differentE. coli clusters. Five of sevenP. mirabilis isolates were from blood cultures. The CLSI tests for the confirmation of ESBL production reliably detect these isolates if both cefotaxime and ceftazidime are tested, but only about half would be classified as a possible CTX-M producers on the basis of the antibiogram alone. A new panprimer set increases the ability to detect CTX-M-producing strains. CTX-M-positive bacteria are common in our geographic region, are often invasive, and, with the exception ofP. mirabilis , are multiclonal.