Non-Penicillin-Susceptible Streptococcus suis Isolated from Humans

Abstract

Streptococcus suis is a pathogen that causes invasive infections in humans and pigs. In this study, 448 S. suis isolates recovered from human infections in Thailand were characterized with regard to their antimicrobial susceptibility and antimicrobial resistance genes, including, for non-penicillin-susceptible isolates, sequence analyses of five genes encoding penicillin-binding proteins (pbp1a, pbp1b, pbp2a, pbp2b, and pbp2x). All 448 isolates were susceptible to cefepime and ceftriaxone, whereas 99.6%, 91.7%, and 72.9% of the isolates were susceptible to levofloxacin, penicillin, and chloramphenicol, respectively. Almost all isolates were resistant to tetracycline (98.2%), clindamycin (94%), erythromycin (92.4%), and azithromycin (82.6%). Genes tet(O) and ermB were the predominant resistance genes detected among macrolide- and tetracycline-resistant isolates. A total of 37 out of 448 isolates (8.2%) showed intermediately resistance to penicillin. Most of these isolates (59.5%) belonged to serotype 2-ST233. Comparison of the predicted translated sequences of five PBP proteins of a penicillin-susceptible isolate (strain P1/7) to the respective PBP sequences of ten non-penicillin-susceptible isolates revealed multiple amino acid substitutions. Isolates of CC221/234 showed highly variable amino acid substitutions in all PBP proteins. An ST104 isolate had a higher number of amino acid substitutions in PBP2X. Isolates belonging to CC233/379 had numerous substitutions in PBP2B and PBP2X. ST25 isolates exhibited fewer amino acid substitutions than isolates of other STs in all five PBPs. The antimicrobial resistance of S. suis is increasing worldwide; therefore, restrictions on antimicrobial use, continuous control, and the surveillance of this bacterium throughout the pork supply chain are crucial for ensuring public health and must be a priority concern.

Genomic Characterization of Streptococcus suis Serotype 24 Clonal Complex 221/234 From Human Patients

“…As recently reported with other strains ( Bamphensin et al, 2021 ), the MIC values on penicillin revealed intermediate resistance for strains ID33329-ST221 (MIC of 0.75 μg/ml) and ID32098-ST234 (MIC of 0.38 μg/ml). These two strains had numerous substitutions in PBP2B and PBP2X, as described elsewhere ( Bamphensin et al, 2021 ). However, the strain ID39565 (ST221) was susceptible to penicillin (MIC ≤ 0.06 μg/ml) in the current study.…”

How Streptococcus suis escapes antibiotic treatments

“…This is in part due to a lower consumption of these antibiotics and/or their mechanism of resistance. For example, the main mechanism of β-lactam resistance is polymutation in pbp genes [ 62 , 65 ]. S. suis could also transfer pbp resistance alleles by HGT, but, as they are not located in MGEs, gene transfer must be mediated by natural transformation (or other methods alternative to conjugation and transduction).…”

“…Apart from mutations in pbp1a , pbp2b , and pbp2x , mutations in pbp1b , pbp2a , and pbp3 have been described in 10 β-lactam-resistant S. suis isolates [ 65 ]. As the corresponding PBPs are no key targets for β-lactam antibiotics, the contribution of these mutations to β-lactam resistance remains to be clarified.…”

Genomic characterization of Streptococcus parasuis, a close relative of Streptococcus suis and also a potential opportunistic zoonotic pathogen

“…Therefore, antimicrobial resistance (AMR) is an important public health concern. Resistance to tetracyclines, macrolides, and aminoglycosides was isolated at high rates in S. suis , particularly tetracycline and erythromycin, which are encoded by the resistance genes erm(B) and tet(O) [ 41 , 42 ]. One of the crucial problems of antimicrobial resistance is the horizontal transfer of AMRGs.…”