Streptococcus pneumoniae acquires genes for resistance to antibiotics such as streptomycin (Str) or trimethoprim (Tmp) by recombination via transformation of DNA released by other pneumococci and closely related species. Using naturally transformable pneumococci, including strain D39 serotype 2 (S2) and TIGR4 (S4), we studied whether pneumococcal nasopharyngeal transformation was symmetrical, asymmetrical, or unidirectional. Incubation of S2Tet and S4Str in a bioreactor simulating the human nasopharynx led to the generation of SpnTet/Str recombinants. Double-resistant pneumococci emerged soon after 4 h postinoculation at a recombination frequency (rF) of 2.5 × 10−4 while peaking after 8 h at a rF of 1.1 × 10−3. Acquisition of antibiotic resistance genes by transformation was confirmed by treatment with DNase I. A high-throughput serotyping method demonstrated that all double-resistant pneumococci belonged to one serotype lineage (S2Tet/Str) and therefore that unidirectional transformation had occurred. Neither heterolysis nor availability of DNA for transformation was a factor for unidirectional transformation given that the density of each strain and extracellular DNA (eDNA) released from both strains were similar. Unidirectional transformation occurred regardless of the antibiotic-resistant gene carried by donors or acquired by recipients and regardless of whether competence-stimulating peptide-receptor cross talk was allowed. Moreover, unidirectional transformation occurred when two donor strains (e.g., S4Str and S19FTmp) were incubated together, leading to S19FStr/Tmp but at a rF 3 orders of magnitude lower (4.9 × 10−6). We finally demonstrated that the mechanism leading to unidirectional transformation was due to inhibition of transformation of the donor by the recipient.

Background: Migrants in sub-Saharan Africa are at increased risk of HIV acquisition after migration, but little is known about their sexual partners at place of destination.Setting: Rakai Community Cohort Study (RCCS) in Uganda. Methods:From 1999 to 2016, persons aged 15-49 years were surveyed in the RCCS and reported on their 4 most recent sexual partners in the last year. We compared the characteristics of sexual partners reported by migrants moving into RCCS communities in the last 2 years (ie, in-migrants) with those of long-term residents with no recent migration history. Among a subset of participants in cohabitating epidemiologically linked couples of known HIV serostatus, we also assessed prevalence of having $1 untreated HIV-positive partner among in-migrants and long-term residents.Results: One hundred sixteen thousand seven hundred forty-four sexual partners were reported by 29,423 participants. The sexual partnerships of in-migrants were significantly less likely to be marital, more likely to span community boundaries, and shorter in duration than those of long-term residents. In-migrants also reported more sexual partners and were less likely to know their partner's HIV status or to have told their partner their HIV status. Among 7558 epidemiologically linked couples, HIV-negative in-migrants were more likely to partner with untreated HIV-positive persons compared with HIV-negative longterm residents (women: 6.3% vs. 4.1%; prevalence risk ratio = 1.77, 95% confidence interval: 1.49 to 2.11; men: 6.9% vs. 3.9%; prevalence risk ratio = 1.72, 95% confidence interval: 1.38-2.14). Conclusion:There is a higher frequency of risky sexual behaviors among the partnerships of in-migrants compared with those of longterm residents. Among cohabitating couples, in-migrants are more likely to partner with untreated HIV-positive individuals.

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