Can MLVA Differentiate among Endemic-Like MRSA Isolates with Identical Spa-Type in a Low-Prevalence Region?

Abstract

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in Norway is low, but an endemic-like MRSA clone with Staphylococcal protein A (spa)-type t304 has been established especially in nursing homes in the Oslo region causing several large outbreaks. The challenge was that spa-typing and the gold standard Pulsed-Field Gel Electrophoresis (PFGE) were inadequate in discriminating isolates in outbreak investigations. Additional higher resolution genotyping methods were needed. The aims of this study were a) to evaluate whether Multiple-Locus Variable number of tandem repeat Analysis (MLVA) could differentiate within the PFGE clusters between epidemiologically related and unrelated endemic-like ST8-MRSA-IV-t304-PVL-neg (MRSA-t304) isolates and b) investigate the evolution of the endemic-like MRSA-t304 clone over a 15-year time period. All MRSA-t304 isolates detected in the region from 1998 through April 2013 were included. In total, 194 of 197 isolates were available for PFGE and MLVA analyses. PFGE results on isolates from 1998–2010 have been published previously. Two PFGE clusters subdivided into eight MLVA types were detected. One major outbreak clone (PFGE cluster C2/ MLVA type MT5045) appeared from 2004 to 2011 causing long-lasting and large outbreaks in seven nursing homes and one hospital. Five new MLVA types (N = 9 isolates) differing in only one VNTR compared to the outbreak clone C2/MT5045 were detected, but only one (C2/MT5044) was seen after 2011. We suggest that MLVA can replace PFGE analysis, but MLVA may not be the optimal method in this setting as it did not discriminate between all epidemiologically unrelated isolates. The results may indicate that all eight outbreaks in different locations within the PFGE C2 cluster may be branches of one large regional outbreak. The major outbreak strain C2/MT5045 may now, however, be under control, extinguished or has moved geographically.

Increasing Incidences and Clonal Diversity of Methicillin-Resistant Staphylococcus aureus in the Nordic Countries - Results From the Nordic MRSA Surveillance

“…Norway experienced several hospital acquired MRSA (HA-MRSA) outbreaks of PVL negative t304/CC8 in South Western Norway between 2004 and 2011. Since then this specific clone has become extinct, and replaced by other t304 clones more associated with the community setting (Blomfeldt et al, 2016;Di Ruscio et al, 2018). In Denmark, t304/CC6 has been associated with hospital outbreaks in recent years (Bartels et al, 2015).…”

Is increased Staphylococcus aureus colonization during military service caused by specific genotypes? Molecular examination of long‐term carriage in a prospective cohort study

“…Staphylococcus aureus microevolution was likely to occur in some degree during one year and shifts to closely related and related spa and MLVA types were observed in 17/152 (11%) recruits who were S. aureus positive at both sampling times. Genotyping applying spa and MLVA is adequate in S. aureus surveillance and outbreak investigations as these methods have high discriminatory power enabling determination of likely transmission events (8,14). Genotype was not correlated with colonization niche thus offering no explanation for the increased rate observed in throat (6).…”

“…Subtyping of isolates with the three most frequent spa types was performed using MLVA as described previously (14) per spa type/recruit/sampling time. We assumed that isolates with identical spa types detected in different sites at the same sampling time in one individual were identical strains.…”

Estandarización del análisis multi-locus de número variable de repeticiones en tándem para el estudio de Staphylococcus aureus resistentes a meticilina aislados de la comunidad en Paraguay

“…Este estudio demuestra la habilidad de la MLVA para identificar aislados genéticamente diferentes y agrupar los relacionados estrechamente entre sí, que puedan tratarse del mismo clon. Sin embargo, la metodología MLVA, al igual que otras metodologías validadas como la MLST y la tipificación del locus spA, puede agrupar como aislados idénticos a aquellos estrechamente relacionados, por lo que precisaría en algunos casos ser verificada por la PFGE, que analiza el genoma completo, lo que aumenta su poder discriminatorio 4,7,21,22 .…”