1.Distribution of virulence genes and the molecular epidemiology of Streptococcus pyogenes clinical isolates by emm and multilocus sequence typing methods
Siti Nur Adila Hamzah ; Mohd Nasir Mohd Desa ; Azmiza Syawani Jasn ; Niazlin Mohd Taib ; Siti Norbaya Masri ; Rukman Awang Hamat
The Medical Journal of Malaysia 2021;76(2):164-170
Background: Streptococcus pyogenes has a variety of
virulence factors and the predominant invasive strains differ
according to specific emm types and geographical
orientation. Although emm typing is commonly used as the
gold standard method for the molecular characterisation,
multilocus sequence typing (MLST) has become an
important tool for comparing the genetic profiles globally.
This study aimed to screen selected virulence genes from
invasive and non-invasive clinical samples and to
characterise the molecular epidemiology by emm typing and
MLST methods.
Materials and Methods: A total of 42 S. pyogenes isolates
from invasive and non-invasive samples collected from two
different tertiary hospitals were investigated for the
distribution of virulence factors and their molecular
epidemiology by emm and multilocus sequence typing
methods. Detection of five virulence genes (speA, speB,
speJ, ssa and sdaB) was performed using multiplex
polymerase chain reaction (PCR) using the standard primers
and established protocol. Phylogenetic tree branches were
constructed from sequence analysis utilised by neighbour
joining method generated from seven housekeeping genes
using MEGA X software.
Results: Multiplex PCR analysis revealed that sdaB/speF
(78.6%) and speB (61.9%) were the predominant virulence
genes. Regardless of the type of invasiveness, diverse
distribution of emm types/subtypes was noted which
comprised of 27 different emm types/subtypes. The
predominant emm types/subtypes were emm63 and emm18
with each gene accounted for 11.8% whereas 12% for each
gene was noted for emm28, emm97.4 and emm91. The MLST
revealed that the main sequence type (ST) in invasive
samples was ST402 (17.7%) while ST473 and ST318 (12% for
each ST) were the major types in non-invasive samples. Out
of 18 virulotypes, Virulotype A (five genes, 55.6%) and
Virulotype B (two genes, 27.8%) were the major virulotypes
found in this study. Phylogenetic analysis indicated the
presence of seven different clusters of S. pyogenes.
Interestingly, Cluster VI showed that selected emm/ST types
such as emm71/ST318 (n=2), emm70.1/ST318 (n=1),
emm44/ST31 (n=1) and emm18/ST442 (n=1) have clustered
within a common group (Virulotype A) for both hospitals
studied.
Conclusion: The present study showed that group A
streptococcci (GAS) are genetically diverse and possess
virulence genes regardless of their invasiveness. Majority of
the GAS exhibited no restricted pattern of virulotypes except
for a few distinct clusters. Therefore, it can be concluded
that virulotyping is partially useful for characterising a
heterogeneous population of GAS in hospitals.