Antibiotics and Immunity

Thayer-Martin medium does not contain penicillin as Neisseria is susceptible to it.

Roll tube technique is used for stringent anaerobes. It provides an ideal condition for the cultivation of stringent anaerobes (redox potential below - 300 mV) which can be only achieved by the supplementation of media with reducing agents. This method consists of a roller tube in which the organism to be cultivated is immobilised on the side of the tube by a film of serum or other media.

MSA has a high concentration of sodium chloride that selects for members of the genus Staphylococcus as they can tolerate high saline levels. Organisms from other genera may grow, but very weakly.

Alkaline bile oxalate-sorbosebroth with pH 7.6 is the ideal condition for the enrichment of Yersinia enterocolitica.

This is the correct statement. Bacitracin can be used to distinguish Streptococcus pyogenes from other 'strep' bacteria because Streptococcus pyogenes is sensitive to bacitracin while others are resistant.

This is the correct answer. Teixobactin is an inhibitor of cell wall synthesis that acts primarily by binding to lipid II, a fatty molecule which is a precursor to peptidoglycan. Binding of teixobactin to lipid precursors inhibits production of the peptidoglycan layer, leading to lysis of vulnerable bacteria.

Chloramphenicol is not effective against Pseudomonas aeruginosa. Chloramphenicol resistance may be carried on a plasmid that also codes for resistance to other drugs or it is effectively pumped out by efflux pumps.

This is the correct answer. Mupirocin reversibly binds to the isoleucyl t-RNA synthetase in Staphylococcus aureus and Streptococcus, resulting in inhibition of protein synthesis.

Fourth generation cephalosporins covers Pseudomonas infection.

This statement is false. Both drugs are bacteriostatic, when used alone, but the combination shows bactericidal activity.

Trimethoprim has a very high affinity for bacterial dihydrofolate reductase. It competitively inhibits the activity of DHFR and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.

Pristinamycin belongs to the streptogramin family. It is used to treat VRE (vancomycin resistant enterococci) infections. It is effective against VRE because it inhibits protein synthesis and vancomycin acts on the cell wall. Thus, its mechanism of action is altogether different than vancomycin. It also enters the bacterial cell easily, whereas other protein inhibitors fail to do so.

Daptomycin is active against all Gram-positive organisms. They include glycopeptide resistant enterococci (GRE), Staphylococci (including methicillin resistant Staphylococcus aureus), Streptococci, corynebacteria and stationary-phase Borrelia burgdorferi persisters.

Radezolid inhibits the initiation step of protein synthesis. It targets an early step involving the binding of N-formylmethionyl-tRNA to the ribosome.

Lantibiotics are similar to bacteriocins. In fact, the lantibiotics are a class of more extensively modified bacteriocins, also called Class I bacteriocins (toxins produced by bacteria).