Abstract
Streptococcus suis is a major pathogen for swine and human. Here we aimed to know the rates of antimicrobial resistance (AMR) in invasive S. suis isolates recovered along Spain between 2016 - 2021 and elucidate their genetic origin. Antibiotic susceptibility testing was performed for 116 isolates of different genetic backgrounds and geographic origins against 18 antibiotics of 9 families. The association between AMR and genotypes and the origin of the isolates were statistically analyzed using Pearson´s chi-square test and the likelihood ratio. The antimicrobial resistant genes were identified by whole genome sequencing analysis and PCR screenings. High AMR rates (>80%) were detected for tetracyclines, spectinomycin, lincosamides, and marbofloxacin, medium (20-40%) for sulphonamides/trimethoprim, tiamulin, penicillin G, and enrofloxacin, and low (< 20%) for florfenicol, and four additional β-lactams. The occurrence of multidrug resistance was observed in 90% of isolates. For certain antibiotics (penicillin G, enrofloxacin, marbofloxacin, tilmicosin, and erythromycin), AMR was significantly associated with particular sequence types (STs), geographic regions, age of pigs, and time course. Whole genome sequencing comparisons and PCR screenings identified 23 AMR genes, of which 19 were previously reported in S. suis (aph(3')-IIIa, sat4, aadE, spw, aac(6')-Ie-aph(2'')-Ia, fexA, optrA, erm(B), mef(A/E), mrs(D), mph(C), lnu(B), lsa(E), vga(F), tet(M), tet(O), tet(O/W/32/O), tet(W)), and 4 were novel (aph(2'')-IIIa, apmA, erm(47), tet(T)). These AMR genes explained the AMR to spectinomycin, macrolides, lincosamides, tiamulin, and tetracyclines. Several genes were located on mobile genetic elements which showed a variable organization and composition. As AMR gene homologs were identified in many human and animal pathogens, the resistome of S. suis has a different phylogenetic origin. Moreover, AMR to penicillin G, fluoroquinolones, and trimethoprim related to mutations in genes coding for target enzymes (pbp1a, pbp2b, pbp2x, mraY, gyrA, parC, and dhfr). Bioinformatic analysis estimated traits of recombination on target genes, also indicative of gene transfer events. Our work evidences that S. suis is a major contributor to AMR dissemination across veterinary and human pathogens. Therefore, control of AMR in S. suis should be considered from a One Health approach in regions with high pig production to properly tackle the issue of antimicrobial drug resistance.
Highlights
Streptococcus suis is a major pathogen for swine and human
Isolates were from suckling piglets (n=11), transition pigs (n=74), and fattening pigs (n=3), but the age of the host was non-defined for 28 isolates
These sequence types (STs) were grouped in six phylogenetic eBurst Groups: eBG1 (n=42), eBG2 (n=3), eBG3 (n=4), eBG4 (n=12), eBG5 (n=33), otherwise singletons (n=22) [characterized in Uruén et al (2024)]. eBG2, eBG3, and eBG6 isolates belong to clonal complex (CC) CC16, CC24, and CC1628/1633, respectively
Summary
Streptococcus suis is a major pathogen for swine and human. Here we aimed to know the rates of antimicrobial resistance (AMR) in invasive S. suis isolates recovered along Spain between 2016 – 2021 and elucidate their genetic origin. The Gram-positive coccus Streptococcus suis is a common inhabitant of the upper respiratory tract of pigs, but it is the aetiological agent of streptococcal swine disease, a life-threatening infection characterized by the fast development of endocarditis, septicaemia, arthritis, and meningitis (Vötsch et al, 2018). It is a major cause of morbidity and mortality in sucking and transition pigs (Neila-Ibáñez et al, 2023), but can cause infections in older pigs and sows. ST1 isolates were amply recovered from diseased people (Goyette-Desjardins et al, 2014)
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