203. Comparison of the number of genome-wide single nucleotide polymorphisms (SNPs) among epidemiologically-related and -unrelated methicillin-resistant Staphylococcus aureus (MRSA) isolates of indistinguishable genotype by PCR-based open-reading frame typing (POT) kit
Session: Poster Abstract Session: Diagnostics: Bacteriology, Sequencing, and Resistance
Thursday, October 27, 2016
Room: Poster Hall
Background: PCR-based open-reading frame typing (POT) for methicillin-resistant Staphylococcus aureus(MRSA), a genotyping method based on the results of 22 multiplex PCR, was developed for outbreak investigation, and a commercial POT kit is now commonly used in the clinical settings in Japan. Identical POT results for epidemiologically-related isolates typically suggest possible transmission. However, isolates with no apparent epidemiological relationship sometimes yield the same POT type. In the current study, we compared the numbers of the genome-wide single nucleotide polymorphisms (SNPs) among two sets of MRSA isolates of the same POT type, namely epidemiologically-related and -unrelated ones.

Methods: Two sets of 5 MRSA isolates yielding the identical POT type were investigated: Isolates of POT type A, from the same ward and department for 10 months, were suspected to be involved in nosocomial transmission. Isolates of POT type B were from inpatients with no apparent epidemiological relationship in the same period. All clinical isolates were from inpatients in a teaching hospital in Japan. Genotypic characterization was performed by using Cica Geneus Staph POT KIT (Kanto Chemical, Tokyo, Japan) as well as multilocus sequence typing, SCCmec-typing, and spa-typing. Genome-wide sequences of the isolates were acquired by Illumina MiSeq. SNPs were identified by mapping to the closest reference sequence by bwa. Only SNPs confirmed by the robust data in all 5 isolates and a reference sequence were extracted. The number of SNPs was estimated by pairwise comparison among isolates of each POT type.

Results: Isolates of POT type A were ST5/SCCmec II and spa-t002, whereas isolates of POT type B were ST1/SCCmec IV and spa-t1784. The numbers of pairwise SNPs among isolates of POT type A were 1-20, and 2 pairs with only one SNP were identified among them. In contrast, there were 40-83 pairwise SNPs among isolates of POT type B except one pair with 8 SNPs.

Conclusion: Even if POT types were indistinguishable, the number of genome-wide SNPs was, in most cases, smaller among isolates with epidemiological relationship than among isolates without apparent epidemiological relationship. Presumption of the relatedness of the isolates with uncertain epidemiological background from the POT-kit results should be prudent, as the manufacturer recommends.

Tomoo Saga, MD, PhD1,2, Rumi Tatsuko, MT1, Kotaro Aoki, MPAS2, Ayumi Omokawa, MD, PhD1, Yuki Moritoki, MD, PhD1, Akiko Shimizu-Saga, MD, PhD1, Noriko Kobayashi, MT, PhD1, Shigeharu Ueki, MD, PhD1, Yoshikazu Ishii, PhD2, Kazuhiro Tateda, MD2 and Makoto Hirokawa, MD, PhD1, (1)Akita Univ. Hosp., Akita, Japan, (2)Toho Univ. Sch. of Med., Tokyo, Japan


T. Saga, None

R. Tatsuko, None

K. Aoki, None

A. Omokawa, None

Y. Moritoki, None

A. Shimizu-Saga, None

N. Kobayashi, None

S. Ueki, None

Y. Ishii, None

K. Tateda, None

M. Hirokawa, None

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