New research that is easily missed because of the increasingly unusual use of cc398 instead of the more usual st398. Both refer to the same troublesome strain.
Humans first, maybe, but the conclusion seems clear enough
and implicates livestock, and by extension antibiotic use in livestock creating antibiotic resistant features, before spreading to humans. The public health risks are once again confirmed.
"Our
findings strongly support the idea that livestock-associated MRSA CC398
originated as MSSA in humans. The jump of CC398 from humans to livestock was
accompanied by the loss of phage-carried human virulence genes, which likely
attenuated its zoonotic potential, but it was also accompanied by the
acquisition of tetracycline and methicillin resistance. Our findings exemplify
a bidirectional zoonotic exchange and underscore the potential public health
risks of widespread antibiotic use in food animal production."
Staphylococcus aureus CC398: Host Adaptation
and Emergence of Methicillin Resistance in Livestock
- Address
correspondence to Lance B. Price, lprice@tgen.org.
1. Editor Fernando Baquero, Ramón y Cajal University
Hospital
ABSTRACT
Since its discovery in the early
2000s, methicillin-resistant Staphylococcus aureus (MRSA) clonal complex 398 (CC398) has
become a rapidly emerging cause of human infections, most often associated with
livestock exposure. We applied whole-genome sequence typing to characterize a
diverse collection of CC398 isolates (n = 89), including MRSA and
methicillin-susceptible S. aureus (MSSA) from animals and humans
spanning 19 countries and four continents. We identified 4,238 single
nucleotide polymorphisms (SNPs) among the 89 core genomes. Minimal homoplasy
(consistency index = 0.9591) was detected among parsimony-informative SNPs, allowing
for the generation of a highly accurate phylogenetic reconstruction of the
CC398 clonal lineage. Phylogenetic analyses revealed that MSSA from humans
formed the most ancestral clades. The most derived lineages were composed
predominantly of livestock-associated MRSA possessing three different
staphylococcal cassette chromosome mec element (SCCmec) types (IV, V, and VII-like)
including nine subtypes. The human-associated isolates from the basal clades
carried phages encoding human innate immune modulators that were largely
missing among the livestock-associated isolates. Our results strongly suggest
that livestock-associated MRSA CC398 originated in humans as MSSA. The lineage
appears to have undergone a rapid radiation in conjunction with the jump from
humans to livestock, where it subsequently acquired tetracycline and
methicillin resistance. Further analyses are required to estimate the number of
independent genetic events leading to the methicillin-resistant sublineages,
but the diversity of SCCmec subtypes is suggestive of strong and
diverse antimicrobial selection associated with food animal production.
IMPORTANCE Modern food animal production is characterized
by densely concentrated animals and routine antibiotic use, which may
facilitate the emergence of novel antibiotic-resistant zoonotic pathogens. Our
findings strongly support the idea that livestock-associated MRSA CC398
originated as MSSA in humans. The jump of CC398 from humans to livestock was
accompanied by the loss of phage-carried human virulence genes, which likely
attenuated its zoonotic potential, but it was also accompanied by the
acquisition of tetracycline and methicillin resistance. Our findings exemplify
a bidirectional zoonotic exchange and underscore the potential public health risks
of widespread antibiotic use in food animal production.
FOOTNOTES
·
Citation Price LB, et al. 2012. Staphylococcus
aureus CC398: host
adaptation and emergence of methicillin resistance in livestock. mBio
3(1):e00305-11. doi:10.1128/mBio.00305-11.
- Received 19 December 2011
- Accepted 3 January 2012
- Published 21 February 2012
- Copyright © 2012 Price et al.
This is an open-access article distributed
under the terms of the Creative Commons Attribution-Noncommercial-Share Alike
3.0 Unported License, which permits unrestricted noncommercial use,
distribution, and reproduction in any medium, provided the original author and
source are credited.
