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Analysis of a Cell Wall Mutant Highlights Rho-Dependent Genome Amplification Events in Staphylococcus aureus
Publication . Portela, Raquel; Faria, Nuno A.; Miragaia, Maria; Mwangi, Michael; de Lencastre, Hermínia; Tomasz, Alexander; Sobral, Rita G.; UCIBIO - Applied Molecular Biosciences Unit; DCV - Departamento de Ciências da Vida; Molecular, Structural and Cellular Microbiology (MOSTMICRO); Instituto de Tecnologia Química e Biológica António Xavier (ITQB); American Society for Microbiology
In a study of antibiotic resistance in Staphylococcus aureus, specific cell wall mutants were previously generated for the peptidoglycan biosynthesis gene murF, by the insertion of an integrative plasmid. A collection of 30 independent mutants was obtained, and all harbored a variable number of copies of the inserted plasmid, arranged in tandem in the chromosome. Of the 30 mutants, only 3, F9, F20 and F26, with a lower number of plasmid copies, showed an altered peptidoglycan structure, lower resistance to β-lactams and a different loss-of-function mutation in rho gene, that encodes a transcription termination factor. The rho mutations were found to correlate with the level of oxacillin resistance, since genetic complementation with rho gene reestablished the resistance and cell wall parental profile in F9, F20 and F26 strains. Furthermore, complementation with rho resulted in the amplification of the number of plasmid tandem repeats, suggesting that Rho enabled events of recombination that favored a rearrangement in the chromosome in the region of the impaired murF gene. Although the full mechanism of reversion of the cell wall damage was not fully elucidated, we showed that Rho is involved in the recombination process that mediates the tandem amplification of exogeneous DNA fragments inserted into the chromosome
Exploring the food production chain as a source of bacteria resistant to last-resort antibiotics
Publication . Cabral, Laura Mariana Gouveia; Miragaia, Maria; Bouchami, Ons
Antibiotic-resistant bacteria spread through the food chain is a public health problem. However, the role of the meat production chain in antibiotic resistance dissemination is still unknown. Of concern is the emergence of resistance to antibiotics that are the last resort for human infection treatment.
Samples collected along the pig processing chain in 2016, from live pigs to slaughterhouse operators, were screened for Gram-negative bacteria and staphylococci resistant to linezolid, tigecycline and colistin. Gram-negative bacteria resistant to last-resort antibiotics and representative staphylococci were identified by 16S rRNA/ tuf sequencing and susceptibility to other antibiotics was also evaluated. The whole genome was sequenced, and bioinformatics tools were used to determine the content in antimicrobial resistance genes and characterize the bacterial genetic background. Cross-transmission along the pig production chain was evaluated by single nucleotide polymorphisms (SNPs) analysis.
Overall, 34% of Gram-negative isolates were tigecycline resistant and 13% were colistin-resistant, being mainly from the operators and live pigs. Genes oqxA/oqxB, encoding multidrug efflux pumps, were carried by 71% of tigecycline-resistant Enterobacteriaceae, but colistin-resistant determinants were not found. Resistance to these last-resort antibiotics was probably associated with the overexpression of the efflux pumps (tigecycline) and mutations in genes involved in lipid A biosynthesis (colistin). We detected no resistance to last-resort antibiotics among staphylococci, but resistance to beta-lactams, tetracyclines and macrolides was frequent. Although we did not identify transmission of Gram-negative bacteria resistant to last-resort antibiotics, closely related S. hyicus were found in equipment, operators, and pigs.
Results suggest that slaughterhouses are reservoirs for multidrug-resistant bacteria, including those resistant to last-resort antibiotics and confirmed the occurrence of bacterial transmission between different sampling sites. The fact that high rates of resistance to last-resort antibiotics were
detected, highlights the importance and urgency of taking action on both surveillance and control of these bacteria in the veterinary setting.
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Fundação para a Ciência e a Tecnologia
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3599-PPCDT
Número da atribuição
PTDC/CVT-CVT/29510/2017