Lecture 2: Introduction to Superbugs Flashcards
What are superdrugs?
Superbugs are bacterial strains that have become resistant to multiple antibiotics used for treatment (Multi-Drug Resistant - MDR).
Give some examples of superbugs
- Staphylococcus aureus (MRSA)
- Escherichia coli
- Acinetobacter spp.
- Klebsiella pneumoniae
- Pseudomonas aeruginosa,
- Mycobacterium tuberculosis
Historical Insight
Alexander Fleming (1945 Nobel Lecture) warned that inappropriate antibiotic use could lead to resistance by allowing bacteria to “learn” to resist penicillin.
Describe the timeline of resistance development of S.aureus to penicllin
- 1940s-1950s: Penicillin used to treat Staphylococcus aureus.
- 1944: First reported case of penicillin-resistant S.aureus
- 1959: Introduction of Methicillin to treat penicillin-resistant S.aureus
- 1961: British scientists reported the first case of MRSA
- 1968: First reported human case of MRSA in the United States
- 2002: First documented case of VRSA (vancomycin-resistant Staphylococcus aureus) in the United States
What does VRSA stand for?
vancomycin-resistant Staphylococcus aureus
What did resistance to vancomycin first develop in?
Resistance to vancomycin developed in Enterococcus and it is now quite common in Enterococcus
Is it true that VRSA strains are still quite rare?
Yes
Describe the mechanism of antibiotic resistance
- Resistance arises due to exposure to antibiotics, especially at sub-therapeutic doses. This selects for bacteria with mutated key genes (e.g, up-regulation of β-lactamases; down-regulation of porins; up-regulation of efflux pumps…)
- These genetic information will pass from one generation to the next within a family
Vertical Gene Transfer - The genetic information can also spread across several bacterial species
Horizontal Gene Transfer via the plasmids
What are the anthropogenic drivers of antibiotic resistance?
- Farming practices
- Horticultural practices
- Veterinary practices
- Healthcare practices
How do farming practices drive antibiotic resistance?
Use of antibiotics as animal growth promoters
Many animals routinely fed (subtherapeutic) doses of β-lactams, erythromycin and tetracycline as growth promoters
How do horticultural practices drive antibiotic resistance?
Antibiotics sprayed on crops, to reduce bacterial growth
E.g, Californian soft fruit are routinely sprayed with tetracycline to reduce bacterial growth
How do verterinary practices drive antibiotic resistance?
Over-prescription of antibiotics for treatment of pets
How do healthcare practices contribute to antibiotic resistance?
Overprescription by GPs, especially for viral infections like respiratory tract infections.
Unregulated access to antibiotics in developing countries.
How did Covid 19 contribute to increased antibiotic resistance?
Lack of clear protocols led to increased inappropriate antibiotic use.
What are the 2 types of resistance mechanisms for antibiotic resistance?
Intrinsic Antibiotic Resistance
&
Acquired Antibiotic Resistance
What is intrinsic resistance?
Naturally occurring, e.g., Gram-negative bacteria with double membranes that inhibit drug entry.
What is extrinsic resistance?
Results from genetic changes like acquiring β-lactamase genes or efflux pumps.
Describe non-specific antibiotic resistance
Affects multiple antibiotics via mechanisms such as:
- Efflux pumps (removing antibiotics).
- Reduced membrane porins (limiting drug entry).
Describe specific antibiotic resistance
- Targets a particular antibiotic or class. Examples:
- Production of enzymes like β-lactamases.
- Mutations at antibiotic target sites (e.g., ribosomes).(to resist macrolides.
)
Describe how resistance to beta-lactam antibiotics can occur?
① mutation of PBP, lowering the affinity for penicillins, etc
② down-regulation of porins in Gram-negative bacteria;
③ acquisition of β-lactamase- ESBL (extended spectrum β-lactamase);
④ up-regulation of efflux pumps
Describe how resistance to quinolones may occur
① Mutations in gyrase weaken quinolone-enzyme interactions
② Plasmid – encoded Qnr proteins decrease topoisomerase–DNA binding
③ A plasmid-encoded enzyme acetylates ciprofloxacin, decreasing its effectiveness.
④ Plasmid-encoded efflux pumps decrease the concentration of quinolones in the cell.
Describe how resistance to Aminoglycosides may occur
Aminoglycosides can be modified by acetyltransferases
Methylation of the 16S rRNA by ribosomal methyltransferase prevent Aminoglycosides from binding to this target
Which multi-drug -resistant bacteria is a rising threat?
Klebsiella pneumoniae
K. pneumoniae: causes the disease Klebsiella pneumonia, with destructive changes to human lungs, inflammation and haemorrhage that sometimes produces a thick, bloody, mucoid sputum (currant jelly sputum).
Where is there a high prevalence of Klebsiella pneumoniae
High prevalence in Greece and Italy (>50% of isolates resistant in 2010).
What is typing important for?
- Necessary for controlling outbreaks and tracking the spread of resistance. (ie k pneuomniae)
- Helps in epidemiological studies and implementing control measures.
Describe typing with gram stain
Gram stain detects peptidoglycan.
It is a valuable diagnostic tool.
Not all bacteria can be classified by this technique
Gram-variable groups
Gram-indeterminate groups
key problem: poor species resolution
What are the phenotypic methods of typping?
Biotyping
Antibiotyping
Phage Typing
Serotyping
Describe biotypingstrain discrimination on the basis of antibiotic resistance.
Comparison of susceptibility of different isolates to a set of antibiotics. Isolates differing in their susceptibilities are considered as different strains.
- Examines growth profiles, metabolic activities, and colony morphology./ a method of identifying and classifying organisms based on their metabolic activities, environmental tolerances, and other characteristics./The identification of different bacteria types based on reaction to biochemical tests.
- Advantages: Reproducible, easy to perform.
- Disadvantages: Limited discriminatory power due to variation in gene expression and point mutation alter metabolic activities
What is Antibiotyping?
- strain discrimination on the basis of antibiotic resistance.
Comparison of susceptibility of different isolates to a set of antibiotics. Isolates differing in their susceptibilities are considered as different strains. - Advantages: almost all strains are typeable. Reproducible. Easy to perform and interpret
- Disadvantages: acquisition of antibiotic determinants, point mutations and gene expression changes can alter patterns of antibiotic resistance quickly, reducing discriminatory power
What is phage typing?
:strain discrimination on the basis of resistance to various bacteriophage.
Strains are characterised by their resistance or susceptibility to a standard set of bacteriophages and relies on the presence or absence of particular receptors on the bacterial surface that are used by the virus.
Advantages: Fairly reproducible, good discriminatory power and easy to interpret.
Disadvantages: This technique requires maintenance of biologically active ‘phages and hence is available only at reference centres. Even for experienced workers, the technique is time-consuming. Many strains are non-typeable.
Define serotypoing
Differentiates strains by antigenic properties (e.g., lipopolysaccharides, flagella).
Strains differentiated by antigenic differences known as ‘serotypes’.
Common for Salmonella (over 2,600 serotypes identified).
Disadvantages: Technically demanding, cross-reactivity issues.
Describe the genotypic methods of typing
- DNA-based techniques like:
RAPD (Random Amplification of Polymorphic DNA).
PFGE (Pulsed Field Gel Electrophoresis).
MLST (Multilocus Sequence Typing).
Provide superior strain discrimination and reveal genetic relationships.
Summary
There are global present and rising threats from multi-drug resistant pathogenic bacteria
Inappropriate use antibiotics is the primary cause of the development and spread of antibiotic resistance.
We need accurate typing methods to examine the natural history of spread of a new variant and to apply control measures
Phenotyping methods take some way towards identification, but nucleic acid techniques should show superior strain discrimination.
Exam Preparation
Focus on:
Antibiotic resistance mechanisms.
Examples of superbugs.
Spread of resistance via gene transfer.
Drivers of resistance spread.
Principles of typing methods.
Exam Preparation
Focus on:
Antibiotic resistance mechanisms.
Examples of superbugs.
Spread of resistance via gene transfer.
Drivers of resistance spread.
Principles of typing methods.
phenotypic vs genotypic typing
- Phenotypic methods are easy but lack precision.
- Genotypic methods provide detailed information but are resource-intensive.
