Open Access Research article

PCR-based rapid genotyping of Stenotrophomonas maltophilia isolates

Emanuela Roscetto1, Francesco Rocco1, M Stella Carlomagno1, Mariassunta Casalino2, Bianca Colonna3, Raffaele Zarrilli4 and Pier Paolo Di Nocera1*

Author Affiliations

1 Dipartimento di Biologia e Patologia Cellulare e Molecolare, Università Federico II, Via S. Pansini 5, 80131 Napoli, Italy

2 Dipartimento di Biologia, Università Roma TRE, Viale Marconi 446 Roma, Italy

3 Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Biologia Cellulare e dello Sviluppo, Università Roma La Sapienza, Via dei Sardi 70 Roma, Italy

4 Dipartimento di Scienze Mediche Preventive, Sezione di Igiene, Università Federico II, Via S. Pansini 5, 80131 Napoli, Italy

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BMC Microbiology 2008, 8:202  doi:10.1186/1471-2180-8-202

Published: 24 November 2008



All bacterial genomes contain repetitive sequences which are members of specific DNA families. Such repeats may occur as single units, or found clustered in multiple copies in a head-to-tail configuration at specific loci. The number of clustered units per locus is a strain-defining parameter. Assessing the length variability of clusters of repeats is a versatile typing methodology known as multilocus variable number of tandem repeat analysis (MLVA).


Stenotrophomonas maltophilia is an environmental bacterium increasingly involved in nosocomial infections and resistant to most antibiotics. The availability of the whole DNA sequence of the S. maltophilia strain K279a allowed us to set up fast and accurate PCR-based diagnostic protocols based on the measurement of length variations of loci carrying a variable number of short palindromic repeats marking the S. maltophilia genome. On the basis of the amplimers size, it was possible to deduce the number of repeats present at 12 different loci in a collection of S. maltophilia isolates, and therefore label each of them with a digit. PCR-negative regions were labelled 0. Co-amplification of two pairs of loci provided a 4-digit code sufficient for immediate subtyping. By increasing the number of loci analyzed, it should be possible to assign a more specific digit profile to isolates. In general, MLVA data match genotyping data obtained by PFGE (pulsed-field gel electrophoresis). However, some isolates exhibiting the same PCR profiles at all loci display distinct PFGE patterns.


The utilization of the present protocol allows to type several S. maltophilia isolates in hours. The results are immediately interpretable without the need for sophisticated softwares. The data can be easily reproducible, and compared among different laboratories.