Background:
Antimicrobial resistance among pneumococci has greatly increased over the past two to three
decades. Resistance to tetracycline (
tet
(M)), chloramphenicol (
cat
) and macrolides (
erm
(B) and/or
mef
(A/E)) is
generally conferred by acquisition of specific genes that are associated with mobile genetic elements, including
those of the Tn
916
and Tn
5252
families. The first tetracycline-, chloramphenicol- and macrolide-resistant
pneumococci were detected between 1962 and 1970; however, until now the oldest pneumococcus shown to
harbour Tn
916
and/or Tn
5252
was isolated in 1974. In this study the genomes of 38 pneumococci isolated prior to
1974 were probed for the presence of
tet
(M),
cat, erm
(B),
mef
(A/E) and
int
(integrase) to indicate the presence of
Tn
916/
Tn
5252
-like elements.
Results:
Two Tn
916
-like,
tet
(M)-containing, elements were identified among pneumococci dated 1967 and 1968.
The former element was highly similar to that of the PMEN1 multidrug-resistant, globally-distributed pneumococcal
reference strain, which was isolated in 1984. The latter element was associated with a streptococcal phage. A third,
novel genetic element, designated ICE
Sp
PN1, was identified in the genome of an isolate dated 1972. ICE
Sp
PN1
contained a region of similarity to Tn
5252
, a region of similarity to a pneumococcal pathogenicity island and novel
lantibiotic synthesis/export-associated genes.
Conclusions:
These data confirm the existence of pneumococcal Tn
916
elements in the first decade within which
pneumococcal tetracycline resistance was described. Furthermore, the discovery of ICE
Sp
PN1 demonstrates the
dynamic variability of pneumococcal genetic elements and is contrasted with the evidence for Tn
916
stability.