Lecture 11

Superbug – any bacteria strain that has developed resistance to most of antibiotics used to treat it (MDR) – multi drug resistance When you are exposing people to small conc of antiobitoitcs, some strains that are mutant are selected – strains that have mutation sin key genes (target of antibiotics) lead to change in affinity in target for antibiotics Horizontally acquired antibiotic resistant determinants is another way antibiotic resistance occurs. Klebsiella pneumonia is a threat in becoming a superbug Anthropogenic drivers of AMR Farming practices – 13 million KG of antibiotics used as growth promotes in animals Healthcare practices Veterinarian practices – overprescribed antibiotics for pets All these facts leads to community acquired resistance

Common colds are 9 times out of 10 ar etreated with antibiotics when it is not necessary – leads to AMR We need to understand the natural history of a disease and develop ways to control its spread for these, we need to characterise bacterial pathogen variants gram staining is a very efficient way to distinguish different strains of bacteria there are gram variable groups – bacteria that switch from gram negative to gram positive gram indeterminate groups – they don’t stain main disadvantage of gram staining is that it has poor species resolution biotyping method used to differentiate different strains based on growth requirement of bacteria

• Look at metabolic activity
• Ability to produce different enzymes
• Ability to grow under different conditions   Advantage of biotyping:   Most strains are typeable, reproducible, relatively easy to perform and interpret   Disadvantage of biotyping: poor discriminatory power (variation in gene expression and point mutation alter metabolic activities)   Antibiotyping   Strain discrimination based on antibiotic resistance   Comparison of susceptibility of different isolates to a set of antibiotics. Isolates differing in their susceptibilities are considered as different strains   When new antibiotic resistance is identified, it suggests new outbreak   Advantage: almost all strains are typeable   Disadvantage: acquisition of antibiotic determinants, point mutations and gene expression changes can alter patterns of antibiotic resistance quickly, reducing discriminatory power.   Bacteriophage: viruses that infect bacteria

Phage typing: Few drops of different phage’s applied to bacteria After incubation phage’s that produce lysis are the specific ones 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 Advantage: fairly reproducible, good discriminatory power and easy to interpret Disadvantage: requires maintenance of biologically active phage’s and hence is available only at reference centres.

• Technique can be time consuming   Serotyping: strain discrimination based on binding of antibodies of known specificity to their cell surface antigen. Target structures are lipopolysaccharides, membrane proteins, capsular pollysacharides   The difference between serotype 1 and serotype 2 depends on the specific virus or bacteria being referred to, as different pathogens can have different serotypes.   Advantage: most strains are typeable   Disadvantage: some autoagglutinable strains are untypeable
• Some methods of serotyping are technically demanding   Using molecular nucleic acid based techniques is more effective in differentiating different strains and allows better understanding of the genetic relationships of strains   RAPD : ramdom amplification of polymorphic DNA   PFGE : Pulsed field gel electrophoresis   AFLP : amplified fragment length polymorphism