Antimicrobial Resistance & MDRO
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Antibiotics may be bacteriostatic/bactericidal What does a bacteriostatic antibiotic do?
The antibiotic prevents the growth of bacteria
Antibiotics may be bacteriostatic/bactericidal What does a bactericidal antibiotic do?
The antibiotic kills bacteria
Various antimicrobial agents act by interfering with what? (4)
• Cell wall synthesis • Plasma membrane integrity • Nucleic acid synthesis • Ribosomal function
Antibiotic Classes What do B-Lactams do to kill bacteria? and an example?
Inhibit bacteria cell wall synthesis Eg; Amoxicillin
AMR When does AMR occur?
When microbes evolve mechanisms that protect them from the effects of antimicrobials
AMR AMR consequences (4)
• Limited treatment for infections -> delayed treatment • Increased risk of transmission • Accumulation of antimicrobial resistance • Panresistance -> microbe resistant to everything
AMR (3) Stages of AMR evolution
• Genetic mutation as a result of selective pressures • Horizontal gene transfer (HGT) • Vertical gene transfer (clonal dissemination) and subsequent transmission of resistant strains from person -> person or from other sources (animals, environmental sources)
AMR Main drivers of AMR (3)
• Overuse and misuse of antimicrobials • Poor hygiene/ sanitation • Substandard infection control measures in healthcare/agriculture
(3) Stages of horizontal gene transfer
• Transformation • Translation • Conjugation
What happens during the third stage of HGT?
Conjugation: Cells need direct contact, with this a channel forms for DNA to pass
AMR What are plasmids?
Small, extra-chromosomal DNA molecules that can replicate independently.
AMR What were antibiotics used for in agriculture and what did this promote?
Antibiotics in low concentrations were used as growth promoters for animals in agriculture. This resulted in resistance among bacteria
AMR MDRO definition
Microorganisms resistant to three or more classes of antimicrobial drugs
AMR Beta lactam antibiotics examples? (2)
• Penicillins • Carbapenems
AMR Clinically significant resistance -> Gram positive organisms examples? (4)
Staphylococcus species: 1. Staphylococcus aureus 2. Coagulase negative Staphylococci (CNS) Enterococcus species: 3. E. faecium 4. E. faecalis
AMR CNS are examples of opportunistic bacteria. Define opportunistic bacteria?
Microorganisms that don’t usually cause disease, however can become pathogenic under certain conditions -> weakened immune system - immunocompromised
Staph aureus infection associated with?
• Skin (abscesses, cellulitis) • UTI • BSI (blood stream infection) • Osteomyelitis • Foodpoisoning
Staph aureus infection treatment (2)
• Cephalexin (beta lactam) for uncomlicated skin infection • Vancomycin (glycopeptide antibiotic) for comlicated/invasive infections -> bacteraemia, pneumonia, etc.
MRSA definiton
Any strain of S. aureus that has developed (through natural selection) or acquired (throughHGT) mutiple drug resistace to several beta-lactam antibiotics, most notably methicillin
Explain how MRSA works !
• Methicillin and beta-lactams bind to and inhibit penicillin binding protein (PBP) • PBP is an enzyme that assists with peptidoglycan assembly. • When PBP is inhibited the peptidoglycan matrix cannot properly be formed and the bacterial cell will burst • An alternative penicillin binding protein is coded for, preventing methicillin binding • Confers resistance to multiple beta-lactam antibiotics (penicillin based)
Enterococcus Species Infections caused by Enterococci species? (4)
• UTIs • Bacteraemia • Endocarditis (inflammation of the endocardium) • Meningitis
Enterococcus Species Enterococcus species infection treatment? (2)
• Nitrofurantoin (nitrofuran class) for uncomplicated UTI • Vancomycin (glycopeptide class) for invasive infections
VRE VRE description
• Nosocomial pathogens that are persistant in hospital environment • Resistance to several antibiotics limits treatment options • VRE infection liked with extended hospital stays
How does vancomycin work?
• Binds to the D-Ala-D-Ala terminus of peptidoglycan precursor, inhibiting transglycosylation and transpeptidation, and causing cell wall damage