Changing epidemiology of MRSA-CC398 in Spanish hospitals located in areas with different pig farming densities: a 2023 multicentre study

Abstract

Background: Livestock-associated (LA)-MRSA of CC398 lineage is related to the pig environment, although it also colonizes/infects humans. Tetracycline resistance (TETR) is a phenotypic marker of LA-MRSA-CC398.

Objectives: To determine the prevalence and changing epidemiology of LA-MRSA-CC398 in seven Spanish hospitals (H1-H7) located in areas with different pig farming densities (PFDs) (extremely high, very high, medium, and very low: EH/VH/M/VL), and to identify other non-CC398-LA-MRSA clones.

Methods: MRSA-TETR isolates (n = 165) obtained from hospitals H1-H7 over 6 months in 2023 were characterized with respect to genetic lineages/antimicrobial resistance and virulence/immune evasion cluster of CC398 and non-CC398. Results were compared with a previous multicentre study from 2016.

Results: We identified 86/165 MRSA-TETR isolates (52.1%) as being MRSA-CC398. A significant difference in MRSA-CC398/MRSA prevalence was detected between hospitals located in EH-PFD areas (H1 and H2, > 25%) and the one in a VL-PFD area (H7, 0%). Prevalences in the range 6.4%-12.2% were found in hospitals in M- and VH-PFD areas (H3-H6). Fourteen spa-types were identified among MRSA-CC398 isolates, with t011/t034 predominating (68.3%), followed by t1451/t1255 (13%). All but two MRSA-CC398 isolates were scn-negative (human adaptation marker). Among the 79 non-CC398-MRSA-TETR isolates, CC5, CC1 and CC8 predominated (45.6%, scn-negative). The prevalences of the scn gene among non-CC398-MRSA-TETR isolates in hospitals of EH-, VH-, M- and VL-PFD areas were 77.8%, 50%, 18.75% and 0%, respectively (significant correlation, P < 0.05). This study shows that MRSA-CC398 isolates are prevalent in hospitals located in EH-PFD areas but absent in the hospital of the VL-PFD area. Moreover, an increase in both PFD and prevalence of MRSA-CC398/MRSA in hospitals H3-H6 was observed in the 2023 study compared with the 2016 study.

Conclusions: A significant increase and more genetic diversity of predominant lineages of CC398-MRSA-TETR were observed in hospitals located in M- to VH-PFD areas.