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PubMed2004

Molecular basis of resistance to macrolides and other antibiotics in commensal viridans group streptococci and Gemella spp. and transfer of resistance genes to Streptococcus pneumoniae.

We assessed the mechanisms of resistance to macrolide-lincosamide-streptogramin B (MLS(B)) antibiotics and related antibiotics in erythromycin-resistant viridans group streptococci (n = 164) and Gemella spp. (n = 28). The macrolide resistance phenotype was predominant (59.38%); all isolates with this phenotype carried the mef(A) or mef(E) gene, with mef(E) being predominant (95.36%). The erm(B) gene was always detected in strains with constitutive and inducible MLS(B) resistance and was combined with the mef(A/E) gene in 47.44% of isolates. None of the isolates carried the erm(A) subclass erm(TR), erm(A), or erm(C) genes. The mel gene was detected in all but four strains carrying the mef(A/E) gene. The tet(M) gene was found in 86.90% of tetracycline-resistant isolates and was strongly associated with the presence of the erm(B) gene. The cat(pC194) gene was detected in seven chloramphenicol-resistant Streptococcus mitis isolates, and the aph(3')-III gene was detected in four viridans group streptococcal isolates with high-level kanamycin resistance. The intTn gene was found in all isolates with the erm(B), tet(M), aph(3')-III, and cat(pC194) gene. The mef(E) and mel genes were successfully transferred from both groups of bacteria to Streptococcus pneumoniae R6 by transformation. Viridans group streptococci and Gemella spp. seem to be important reservoirs of resistance genes.

Anti-Bacterial Agents↗
PubMed2026

FMT alleviates multidrug-resistant Salmonella enterica-induced diarrhea and is associated with loss of IncHI2A-associated resistance determinants in mice.

INTRODUCTION: Multidrug-resistant (MDR) Salmonella enterica (S. enterica) poses a serious threat to animal and public health because of increasingly limited treatment options. Fecal microbiota transplantation (FMT) is a potential microbiota-based intervention; however, its effects on MDR Salmonella infection and pathogen-associated antibiotic resistance gene (ARG) dynamics remain unclear. METHODS: A murine diarrhea model was established using the clinical MDR S. enterica isolate P174, and infected mice were treated with FMT. Clinical symptoms, intestinal pathology, transcriptional inflammatory responses, gut microbiota composition, and ARG profiles of recovered Salmonella isolates were evaluated. Whole-genome sequencing was used to characterize resistance determinants, and the stability of ARGs and IncHI2A backbone markers was further assessed during 19 in vitro passages. RESULTS: FMT reduced diarrhea, promoted body weight recovery, and alleviated intestinal tissue injury and inflammatory cell infiltration. Colonic expression of Tnf, Il1b, and Il6 decreased, whereas Il10 expression increased. FMT was also associated with partial recovery of gut microbial diversity, increased relative abundances of Lactobacillus, Bifidobacterium, and other commensal anaerobic taxa, and reduced Salmonella abundance. Whole-genome sequencing showed that bla OXA-1, floR, oqxA, and oqxB were co-localized on an IncHI2A-associated plasmid sequence. Loss of these resistance determinants increased over time in isolates recovered from FMT-treated mice, whereas no loss of the four ARGs or the IncHI2A backbone markers repB and parB was detected during 19 in vitro passages. Among isolates showing simultaneous loss of all four ARGs, nearly all also lacked detectable repB and parB, whereas isolates with partial ARG loss retained both markers. These patterns were consistent with both backbone-associated loss and resistance-region deletion or rearrangement. Most ARG-loss isolates showed reduced antimicrobial resistance. DISCUSSION: FMT alleviated MDR S. enterica-induced intestinal disease and was associated with partial recovery of gut microbiota characteristics and increased instability and loss of IncHI2A-associated resistance determinants in vivo. These findings suggest a potential association between intestinal microbial ecological changes and altered maintenance patterns of resistance-associated genetic elements in MDR S. enterica.

Salmonella enterica↗