* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Biology Scholarship Day
Bottromycin wikipedia , lookup
List of types of proteins wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Molecular cloning wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Gene expression profiling wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Gene regulatory network wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Non-coding DNA wikipedia , lookup
Point mutation wikipedia , lookup
Community fingerprinting wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Transformation (genetics) wikipedia , lookup
Genomic library wikipedia , lookup
Endogenous retrovirus wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Genome evolution wikipedia , lookup
Genetic engineering wikipedia , lookup
“Superbugs” MRSA or Methicillin Resistant Staphyloccocus aureus What is MRSA? A common bacterium that can causes infections in different parts of the body. Usually no problem but it has become resistant to some commonly used antibiotics. Staphylococcus aureus - a short history Bacteria have very good adaptive capabilities 1940s: Penicillin was introduced - a strong selective pressure, induces mutation Bacteria can transfer traits by plasmids such as heavy metal tolerance etc Penicillin was virtually useless as an antibiotic within a decade because a plasmid spread the penicillinase (ß-lactamase) gene through the entire species of S. aureus. New antibiotics such as methicillin which were not degraded by the product of the penicillinase gene were used By 1960 methicillin resistant S. aureus (MRSA) strains were identified By the 1980s, epidemic clones of MRSA acquired multidrug resistant traits and spread worldwide to become one of the most important causes of hospital acquired infections In the early 2000s, MRSA strains carrying the Tn1546 transposon-based enterococcal vancomycin resistant mechanism were identified in clinical specimens, bringing the possibility of a totally resistant bacterial pathogen closer to reality How did this happen? Selection pressure applied S. aureus acquired a mutated gene : o the penicillinase gene (via a plasmid) o then the methicillin resistance gene mec Mec: Originated in S. scuiri another species of Staphylococcus Located in a mobile piece of DNA that contains its own enzymes for moving it around the genome This piece of DNA is called the Staphylococcal cassette chromosome mec (SCCmec) Has about 100 ORF on this element – so also contains other genes genes Mobile DNA Common in bacteria Two general types: 1. Plasmids extrachromosomal circular or linear DNA molecules which are not part of the bacterial genome carry functions advantageous to the host such as eg antibiotics or heavy metal resistance 2. Transposons jumping genes, mobile genetic elements composed of a gene coding for a special enzyme and two short flanking segments of DNA called inverted repeats How do antibiotics work? Penicillin (β-lactam) • Inhibits formation of peptidoglycan cross-links in the bacterial cell wall, normally done by PBPs (penicillin binding proteins or transpeptidases ) • The β-lactam moiety (functional group) of penicillin binds to the enzyme (PBPs) – weakens the cell wall of the bacterium and causes lysis Resistance to Penicillin • Bacteria evolved Penicillinases which hydrolysing penicillin Methicillin (also β-lactam) • Acts the same way as Penicillin • BUT insensitive to penicillinases Resistance to Methicillin • Expresses a different PBP, called PBP2a, that is resistant to methicillin • Often resistant S. aureus are resistant to other classes of antibiotics (through different mechanisms) • Accessory factors (genes) influence the level and nature of methicillin resistance Key concepts Plasmids - mobile genetic elements Bacterial conjugation Selection pressure - single drug, single mode of action, high numbers of progeny, transferable DNA elements Mutation - plasmids and transposons