Non Group A Streptococci especially Group C Streptococci (GCS) and Group G
Streptococci (GGS) which were long considered to be commensal organisms,
are now recognized as etiological agents of exudative pharyngitis and
pyoderma in many parts of the world(1). Post streptococcal sequelae which
were once believed to be exclusive to infections caused by Group A
Streptococci (GAS), are now known to occur following acute GGS and GCS
infections. These organisms have also been reported to cause invasive
infections similar to that caused by GAS. Due to the overlap in the
disease spectrum of GCS/GGS with that caused by GAS, it is possible that
the disease burden attributed to GGS is grossly underestimated. The
taxonomy of these organisms is debatable; however, it has been proposed
that human isolates of GGS/GCS be called S. dysgalactiae subsp.
equisimilis(2). There is extensive homology between the gene sequences
of the M protein of GGS/GCS and GAS, hence typing of these strains can be
done by emm gene sequencing(3). Since these organisms are similar
to GAS, share the same tissue niche and virulence genes, it may be
important to identify chronic carriers who may be at risk of transmitting
the infection to susceptible subjects.
We undertook a study to look for the carriage rate of
GGS and GCS in children aged 5-15 years in Corporation schools in Chennai.
We found that 65/595 (10.9%) specimens grew GGS/GCS while 41 of the 595
(6.9%) throat swabs collected grew GAS. Interestingly, though majority of
the GGS GCS (82.6%) were S. dysgalactiae subsp. equisimilis, many
of the children were found to carry strains of animal origin such as
S.equi subsp zooepedimicus (17.4%). Molecular typing of these strains
by emm gene sequencing indicated that the strains were extremely
heterogenous and were represented by 17 different emm types;
however, the type stG6792 which has been previously reported in
invasive strains was seen in all the biotypes of GGS and GCS.
Sergrouping and typing of beta hemolytic Streptococci
is done only in a few laboratories; others report beta-hemolytic
streptococcal isolates only as group A or non-group A, which would fail to
identify these potentially pathogenic organisms. Hence clinical
laboratories should be encouraged to perform group identification of all
beta-hemolytic streptococci to evaluate the role of these organisms in
invasive and non invasive infections.
References
1. Chowdhury MNH, Kambal AM, Al-Eissa YA, Khaliq MRA,
Al-Ayed IH, Al-Sanie AM. Nongroup A streptococci: are they pathogens in
the throat? J Roy Soc Health 1997; 117: 160-163.
2. Vandamme P, Pot B, Falsen E, Kersters K, Devriese
LA. Taxonomic study of Lancefield Streptococcal Groups C, G, and L
(Streptococcus dysgalactiae) and proposal of S. dysgalactiae subsp.
equisimilis subsp. nov. Int J Syst Bacteriol 1996; 46; 774-781.
3. Menon T, Lloyd C, Malathy B, Sakota V, Jackson D.
emm type diversity of beta-haemolytic streptococci recovered in
Chennai, India. J Med Microbiol 2008, 57: 540-542.