The original indication of<unk>  was in the treatment of typhoid, but the now almost universal presence of multiple drug-resistant Salmonella typhi has meant it is seldom used for this indication except when the organism is known to be sensitive. In low-income countries, the WHO no longer recommends only<unk>  as first-line to treat meningitis, but recognises it may be used with caution if there are no available alternatives. During the last decade<unk>  has been rethought as an old agent with potential against systemic infections due to multidrug-resistant gram positive microorganisms (including vancomycin resistant enterococci). In vitro data have shown an activity against the majority (> 80%) of vancomycin resistant E. faecium strians. In the context of preventing endophthalmitis, a complication of cataract surgery, a 2017 systematic review found moderate evidence that using<unk>  eye drops in addition to an antibiotic injection (cefuroxime or penicillin) will likely lower the risk of endophthalmitis, compared to eye drops or antibiotic injections alone. Spectrum<unk>  has a broad spectrum of activity and has been effective in treating ocular infections such as conjunctivitis, blepharitis etc. caused by a number of bacteria including Staphylococcus aureus, Streptococcus pneumoniae, and Escherichia coli. It is not effective against Pseudomonas aeruginosa. The following susceptibility data represent the minimum inhibitory concentration for a few medically significant organisms. * Escherichia coli: 0.015 – 10,000 μg/mL * Staphylococcus aureus: 0.06 – 128 μg/mL * Streptococcus pneumoniae: 2 – 16 μg/mL Each of these concentrations is dependent upon the bacterial strain being targeted. Some strains of E. coli, for example, show spontaneous emergence of<unk>  resistance. Resistance Three mechanisms of resistance to<unk>  are known: reduced membrane permeability, mutation of the 50S ribosomal subunit, and elaboration of<unk>  acetyltransferase. It is easy to select for reduced membrane permeability to<unk>  in vitro by serial passage of bacteria, and this is the most common mechanism of low-level<unk>  resistance. High-level resistance is conferred by the cat-gene; this gene codes for an enzyme called<unk>  acetyltransferase, which inactivates<unk>  by covalently linking one or two acetyl groups, derived from acetyl-S-coenzyme A, to the hydroxyl groups on the<unk>  molecule. The acetylation prevents<unk>  from binding to the ribosome. Resistance-conferring mutations of the 50S ribosomal subunit are rare.<unk>  resistance may be carried on a plasmid that also codes for resistance to other drugs. One example is the ACCoT plasmid (A=ampicillin, C=chloramphenicol, Co=co-trimoxazole, T=tetracycline), which mediates multiple drug resistance in typhoid (also called R factors). As of 2014 some Enterococcus faecium and Pseudomonas aeruginosa strains are resistant to<unk> . Some Veillonella spp. and Staphylococcus<unk> itis strains have also developed resistance to<unk>  to varying degrees.
Chloramphenicol
Tetracycline
Thiamphenicol
Minocycline
Natamycin
Meropenem
Methicillin
Amikacin