Lecture 11. Introduction to Superbug Flashcards
What is a superbug?
Any strain of bacteria that has become resistant to the antibiotics that are used to treat it - Multi-Drug Resistant (MDR)
What are examples of superbugs?
Staphylococcus aureus (MRSA)
Escherichia coli
Acinetobacter spp.
Klebsiella pneumoniae
Pseudomonas aeruginosa
Mycobacterium tuberculosis
When was penicillin discovered?
1928
When was the first reported instance of penicillin-resistant S. aureus?
1944
When was Methicillin introduced to treat penicillin-resistant S. aureus?
1959
When was the first case of MRSA?
1961
What are the mechanisms of resistance?
Exposure to antibiotics selects for bacteria with mutated key genes and/or their control systems and with horizontally acquired antibiotic resistance determinants
Where is MDR Klebsiella pneumoniae spreading?
Around Eastern Europe
What are anthropogenic drivers of antibiotic resistance?
Overprescription of antibiotics and farming practices involving antibiotics
What does the Gram stain detect?
Peptidoglycan
What colour are Gram positive bacilli?
Purple
What colour are Gram negative bacilli?
Pink
What is the key problem with Gram staining?
Poor species resolution
What is biotyping?
Traditionally, strain discrimination by examining growth profiles on different substrates. Metabolic activities, colony morphology and environmental tolerances are compared. Strains are referred to as “biotypes”
What are the advantages of biotyping?
Most strains are typeable. Reproducible, relatively easy to perform and interpret
What are the disadvantages of biotyping?
Poor discriminatory power (variation in gene expression and point mutation alter metabolic activities)
What is antibiotyping (antibiogram typing)?
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
What does antibiotyping do?
The identification of new or unusual pattern of antibiotic resistance among isolates cultured from patients is often the first indication of an outbreak
What are the advantages of antibiotyping?
Almost all strains are typeable. Reproducible. Easy to perform and interpret
What are the disadvantages of antibiotyping?
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
What are the advantages of phage-typing?
Fairly reproducible, good discriminatory power and easy to interpret
What are the disadvantages of phage-typing?
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
What are bacteriophages?
Viruses that infect bacteria
What can phage-typing be used for?
Type isolates of Staphylococcus aureus and Salmonella sps. Such stains are referred as ‘phage types’
What is serotyping?
Strain discrimination on the basis of binding of antibodies of known specificity to their cell surface antigens. Target structures are lipopolysaccharides, membrane proteins, capsular polysaccharides, flagellae and fimbriae that exhibit antigenic variation. Strains differentiated by antigenic differences are known as ‘serotypes’.
What are the advantages of serotyping?
Most strains are typeable
What are the disadvantages of serotyping?
Some autoagglutinable (rough) strains are untypeable
Some methods of serotyping are technically demanding
Serotyping sometimes has poor discriminatory power (large number of serotypes, cross-reaction of antibodies with surface antigens)
