BackgroundBacterial genomes are mosaic structures composed of genes present in every strain of the same species (core genome), and genes present in some but not all strains of a species (accessory genome). The aim of this study was to compare the genetic diversity of core and accessory genes of a Salmonella enterica subspecies enterica serovar Typhimurium (Typhimurium) population isolated from food-animal and human sources in four regions of Mexico. Multilocus sequence typing (MLST) and macrorestriction fingerprints by pulsed-field gel electrophoresis (PFGE) were used to address the core genetic variation, and genes involved in pathogenesis and antibiotic resistance were selected to evaluate the accessory genome.ResultsWe found a low genetic diversity for both housekeeping and accessory genes. Sequence type 19 (ST19) was supported as the founder genotype of STs 213, 302 and 429. We found a temporal pattern in which the derived ST213 is replacing the founder ST19 in the four geographic regions analyzed and a geographic trend in the number of resistance determinants. The distribution of the accessory genes was not random among chromosomal genotypes. We detected strong associations among the different accessory genes and the multilocus chromosomal genotypes (STs). First, the Salmonella virulence plasmid (pSTV) was found mostly in ST19 isolates. Second, the plasmid-borne betalactamase cmy-2 was found only in ST213 isolates. Third, the most abundant integron, IP-1 (dfrA12, orfF and aadA2), was found only in ST213 isolates. Fourth, the Salmonella genomic island (SGI1) was found mainly in a subgroup of ST19 isolates carrying pSTV. The mapping of accessory genes and multilocus genotypes on the dendrogram derived from macrorestiction fingerprints allowed the establishment of genetic subgroups within the population.ConclusionDespite the low levels of genetic diversity of core and accessory genes, the non-random distribution of the accessory genes across chromosomal backgrounds allowed us to discover genetic subgroups within the population. This study provides information about the importance of the accessory genome in generating genetic variability within a bacterial population.
SARS-CoV-2 genetic diversity has the potential to impact the virus transmissibility and the escape from natural infection- or vaccine-elicited neutralizing antibodies. Here, we report the emergence of the B.1.621 lineage, considered a variant of interest (VOI) with the accumulation of several substitutions affecting the Spike protein, including the amino acid changes I95I, Y144T, Y145S and the insertion 146 N in the N-terminal domain, R346K, E484K and N501Y in the Receptor Binding Domain and P681H in the S1/S2 cleavage site of the Spike protein. The rapid increase in frequency and fixation in a relatively short time in some cities that were near the theoretical herd immunity suggests an epidemiologic impact. Further studies will be required to assess the biological and epidemiologic roles of the substitution pattern found in the B.1.621 lineage.
BackgroundSalmonella Typhimurium ST213 was first detected in the Mexican Typhimurium population in 2001. It is associated with a multi-drug resistance phenotype and a plasmid-borne blaCMY-2 gene conferring resistance to extended-spectrum cephalosporins. The objective of the current study was to examine the association between the ST213 genotype and blaCMY-2 plasmids.ResultsThe blaCMY-2 gene was carried by an IncA/C plasmid. ST213 strains lacking the blaCMY-2 gene carried a different IncA/C plasmid. PCR analysis of seven DNA regions distributed throughout the plasmids showed that these IncA/C plasmids were related, but the presence and absence of DNA stretches produced two divergent types I and II. A class 1 integron (dfrA12, orfF and aadA2) was detected in most of the type I plasmids. Type I contained all the plasmids carrying the blaCMY-2 gene and a subset of plasmids lacking blaCMY-2. Type II included all of the remaining blaCMY-2-negative plasmids. A sequence comparison of the seven DNA regions showed that both types were closely related to IncA/C plasmids found in Escherichia, Salmonella, Yersinia, Photobacterium, Vibrio and Aeromonas. Analysis of our Typhimurium strains showed that the region containing the blaCMY-2 gene is inserted between traA and traC as a single copy, like in the E. coli plasmid pAR060302. The floR allele was identical to that of Newport pSN254, suggesting a mosaic pattern of ancestry with plasmids from other Salmonella serovars and E. coli. Only one of the tested strains was able to conjugate the IncA/C plasmid at very low frequencies (10-7 to 10-9). The lack of conjugation ability of our IncA/C plasmids agrees with the clonal dissemination trend suggested by the chromosomal backgrounds and plasmid pattern associations.ConclusionsThe ecological success of the newly emerging Typhimurium ST213 genotype in Mexico may be related to the carriage of IncA/C plasmids. We conclude that types I and II of IncA/C plasmids originated from a common ancestor and that the insertion and deletion of DNA stretches have shaped their evolutionary histories.
Polymyxins are last-resort antimicrobial agents used to treat infections caused by carbapenem-resistant Due to the worldwide dissemination of polymyxin resistance in animal and human isolates, we aimed to characterize polymyxin resistance associated with the presence of in and nonfermenter Gram-negative bacilli, using isolates collected retrospectively in Colombia from 2002 to 2016. A total of 5,887 Gram-negative clinical isolates were studied, and 513 were found to be resistant to the polymyxins. Susceptibility to colistin was confirmed by broth microdilution for all-positive isolates, and these were further subjected to whole-genome sequencing (WGS). The localization of was confirmed by S1 pulsed-field gel electrophoresis (S1-PFGE) and CeuI-PFGE hybridization. Transferability was evaluated by mating assays. A total of 12 colistin-resistant isolates recovered after 2013 harbored, including 8 , 3 serovar Typhimurium, and 1 isolate isolates were unrelated by PFGE and belonged to 7 different sequence types (STs) and phylogroups. Typhimurium and isolates belonged to ST34 and ST307, respectively. The gene was plasmid borne in all isolates but two isolates which harbored it on the chromosome. Conjugation of was successful in 8 of 10 isolates (8.2 × 10 to 2.07 × 10 cell per recipient). Plasmid sequences showed that the plasmids belonged to four different Inc groups (a new IncP-1 variant and the IncFII, IncHI1, and IncH families). Our results indicate that is circulating in clinical isolates of colistin-resistant in Colombia and is mainly harbored in transferable plasmids.
The SARS-CoV-2 genetic diversification has a potential impact in the virus escape from natural infection- or vaccine-elicited neutralizing antibodies and higher transmissibility. Here we report the emergence of novel B.1.621 variant of interest with the insertion 145N in the N-terminal domain and amino acid change N501Y, E484K, and P681H in the Receptor Binding Domain of the Spike protein. Further studies in vitro biological assays and epidemiologic analysis will allow evaluating the public health impact of B.1.621 variant.
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