Investigation of an outbreak of CTX-M15-producing Escherichia coli of sequence types 131 and 1441 in a neonatal surgical ward: comparison of typing methods
Abstract number: O105
Karami N., Helldal L., Andersson M., Unosson C., Larsson L., Welinder-Olsson C., Ahren C., Moore E.
Objectives: The spread of E. coli producing the CTX-M-15-type of extended-spectrum b-lactamase (ESBL) was ongoing in a surgical ward caring for newborns since, at least, September 2008 and was finally recognised in late December. Various typing methods were applied and compared with pulsed-field gel electrophoresis (PFGE) to verify the outbreak and to determine the number of affected children.
Methods: Subsequent to clinical sampling, 125 children hospitalised September-December were screened for ESBL-bacteria in stool. January-June 2009, newly admitted children were screened at admission and twice weekly. 51 ESBL-E. coli isolates were detected in 26 children, of which 6 later were found to carry isolates of several PFGE-types. The 51 isolates were typed by PFGE, multiple-locus-variable number tandem repeat analysis (MLVA), a "mini" multiple-locus-sequence typing (mMLST) method (fumC, purA and dnaJ genes) and by Phene Plate (PhP) biochemical fingerprinting.
Results: When the outbreak was revealed, five children had developed infections with ESBL-E. coli of two PFGE-types, A (ST 131) and B (ST 1441), later determined to be the outbreak strains. One or both types spread to a total of 21 children. Altogether, 38 isolates (20 children) were of type A and 7 isolates (5 children) of type B. In addition six children carried isolates of six distinct PFGE-types (C-H), only found in one child each. MLVA generated the same strain differentiation profile as PFGE. mMLST accurately detected the same STs of PFGE-types as detected by standard MLST (http://mlst.ucc.ie/mlst/dbs/Ecoli), although it did not differentiate ST 131 isolates of different PFGE-types (A and C). PhP-typing differentiated isolates such that little correlation was observed with PFGE. By monitoring resistance patterns of isolates we could not predict the identity of isolates.
Conclusion: If transmission is ongoing for an extended time period, several types of ESBL-producing bacteria may be detected in an outbreak and all isolates, including screened as well as repeat isolates, should be typed to identify affected patients. Only genetic methods gave satisfactory typing results in investigating this outbreak. MLVA generated identical results as those of PFGE and is, thus, attractive, being faster, less-costly and producing results that are easier to communicate. The mMLST, although accurately detecting the STs, despite using only three house-keeping genes, was less discriminatory than PFGE or MLVA.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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