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Identification of factors that led to the development of pig-associated epidemic MRSA clone

Subject Area Veterinary Medical Science
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 389553136
 
Final Report Year 2023

Final Report Abstract

Aim of this German-Chinese joint project was to identify factors that contributed to the development of an epidemic pig-associated livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) clone. In particular, the German project partners (i) characterized the porcine LA-MRSA CC398 lineage currently dominating in Germany, (ii) analysed novel mobile genetic elements (MGEs) identified among German and Chinese porcine LA-MRSA isolates, and (iii) investigated whether the successful LA-MRSA lineages CC398 in Germany and CC9 in China, respectively, could have had an advantage in host colonization due to certain metabolic properties. The 178 porcine LA-MRSA CC398 isolates collected in the German national resistance monitoring program GERM-Vet from 2007 to 2019 displayed close phylogenetic relationships but a wide molecular variety. Several toxinencoding genes were detected. The isolates harboured a wide range of antimicrobial resistance (AMR) properties mirroring the proportions of the classes of antimicrobial agents applied in veterinary medicine in Germany. Multiple novel or rare AMR genes were identified, such as the phenicol-lincosamide-oxazolidinone-pleuromutilin-streptogramin A resistance gene cfr and the pleuromutilin-lincosamide-streptogramin A resistance gene vga(C). Many AMR genes were part of MGEs, such as small transposons or plasmids, and might therefore be easily transferred via horizontal gene transfer. A novel SCCmec type V variant was detected that was composed of a type V SCCmec element, a novel pseudo-SCC element and a remnant of a type XII SCCmec element. Two new members of the Tn554 transposon family were designated as Tn553 and Tn560, respectively. Tn553 preferred a different integration site than other Tn554 transposons and carried a complete blaZ-blaR1-blaI betalactamase operon. Tn560 harboured a multiresistance gene cluster comprising the spectinomycin resistance gene spcV, a new spc variant, the pleuromutiline-lincosamidestreptogramin A resistance gene lsa(E) and the lincosamide resistance gene lnu(B). The novel macrolide-lincosamide-streptogramin B resistance gene erm(54) was located on a nonconjugative plasmid together with an ica cluster for biofilm formation and cadmium, mercury and copper resistance genes. Metabolic variations did most likely not play a key role in the emergence of two different epidemic LA-MRSA clones in Germany and China. However, unfavourable metabolic properties of the Chinese LA-MRSA CC9 clone might support its ongoing gradual replacement by the superior LA-MRSA CC398 clone through livestock trade and human occupational exposure. Since the CC398 lineage has a greater pathogenicity, the public health risk posed by LA-MRSA from pigs might rise in the future. Thus, large-scale surveillance of LA-MRSA is important to early detect new emerging possibly more dangerous variants and to prevent their further dissemination among pig farms and introduction into the human community.

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