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Published on: March 3, 2023
Prevalence of CTX-M beta-lactamases in Philadelphia, Pennsylvania
Shannon E McGettigan1, Baofeng Hu, Kathleen Andreacchio
1Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104-4283, USA.
Abstract:
CTX-M beta-lactamases were thought to be rare in the United States, but a recent study in Texas showed that up to 70% of extended-spectrum beta-lactamase (ESBL)-containing members of the Enterobacteriaceae 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 all Enterobacteriaceae tested being positive. The E. 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 positive P. mirabilis isolates was in group II, with the remainder being positive for a CTX-M-25-like beta-lactamase; and 33% of the Klebsiella 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 six P. mirabilis isolates were clonal and that there were seven different E. coli clusters. Five of seven P. 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 of P. mirabilis, are multiclonal.
Insights
CTX-M beta-lactamases are common in Enterobacteriaceae in the US, with 15% of isolates testing positive. CTX-M-producing bacteria are often invasive and can be detected using PCR and CLSI tests.
Area of Science:
- Microbiology
- Molecular Biology
- Clinical Science
Background:
- CTX-M beta-lactamases were previously considered rare in the United States.
- A recent study in Texas indicated a high prevalence of CTX-M in extended-spectrum beta-lactamase (ESBL)-containing Enterobacteriaceae.
Purpose of the Study:
- To determine the prevalence of CTX-M beta-lactamases in extended-spectrum cephalosporin-resistant gram-negative bacteria isolated in a laboratory setting.
- To characterize the types of CTX-M enzymes and their genetic relatedness in these isolates.
Main Methods:
- Polymerase chain reaction (PCR) was used to detect CTX-M genes in 291 gram-negative bacterial isolates.
- Isolates were identified as Escherichia coli, Klebsiella sp., and Proteus mirabilis.
- Pulsed-field gel electrophoresis (PFGE) was employed to assess the clonality of CTX-M-positive isolates.
Main Results:
- 15% of all Enterobacteriaceae tested were CTX-M positive, with 48% of Escherichia coli, 3% of Klebsiella sp., and 100% of Proteus mirabilis isolates being positive.
- CTX-M groups I and IV were most common in E. coli, while P. mirabilis isolates harbored a CTX-M-25-like enzyme.
- CTX-M-producing bacteria were isolated from various clinical sources, including urine, blood, and wounds. Six P. mirabilis isolates were clonal, and seven E. coli clusters were identified.
Conclusions:
- CTX-M-producing bacteria are common in the studied geographic region and frequently associated with ESBL production.
- These CTX-M-positive bacteria are often invasive, with P. mirabilis isolates showing clonality and E. coli isolates exhibiting multiclonal spread.
- Standard CLSI tests can reliably detect ESBL production, but antibiograms alone may underestimate CTX-M prevalence. A new panprimer set enhances CTX-M detection capabilities.
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