ability of the bacteria to resist or inactivate the antibiotic. specimens for antibiotic sensitivity testing are ideally collected before treatment is started. a sample may be taken from the site of a suspected infection; such as a blood culture sample when bacteria are suspected to be present in the bloodstream (bacteraemia), a sputum sample in the case of a pneumonia, or a urine sample in the case of a urinary tract infection. sometimes multiple samples may be taken if the source of an infection is not clear. these samples are transferred to the microbiology laboratory where they are added to culture media, in or on which the bacteria grow until they are present in sufficient quantities for identification and sensitivity testing to be carried out. when antibiotic sensitivity testing is completed, it will report the organisms present in the sample, and which antibiotics they are susceptible to. although antibiotic sensitivity testing is done in a laboratory (in vitro), the information provided about this is often clinically relevant to the antibiotics in a person (in vivo). sometimes, a decision must be made for some bacteria as to whether they are the cause of an infection, or simply commensal bacteria or contaminants, such as staphylococcus epidermidis and other opportunistic infections. other considerations may influence the choice of antibiotics, including the need to penetrate through to an infected site (such as an abscess), or the suspicion that one or more causes of an infection were not detected in a sample. history since the discovery of the beta-lactam antibiotic penicillin, the rates of antimicrobial resistance have increased. over time, methods for testing the sensitivity of bacteria to antibiotics have developed and changed. alexander fleming in the 1920s developed the first method of susceptibility testing. the "gutter method" that he developed was a diffusion method, involving an antibiotic that was diffused through a gutter made of agar. in the 1940s, multiple investigators, including pope, foster and woodruff, vincent and vincent used paper discs instead. all these methods involve testing only susceptibility to penicillin. the results were difficult to interpret and not reliable, because of inaccurate results that were not standardised between laboratories. dilution has been used as a method to grow and identify bacteria since the 1870s, and as a method of testing the susceptibility of bacteria to antibiotics since 1929, also by alexander fleming. the way of determining susceptibility changed from how turbid the solution was, to the ph (in 1942), to optical instruments. the use of larger tube-based "macrodilution" testing has been superseded by smaller "microdilution" kits. in 1966, the world health organisation confirmed the kirby-bauer method as the standard method for susceptibility testing; it is simple, cost-effective and can test multiple antibiotics. the etest was developed in 1980 by bolmstrӧm and eriksson, and maldi-tof developed in 2000s. an array of automated systems has been developed since and after the 1980s. pcr was the first genetic test available and first published as a method of detecting antibiotic susceptibility in 2001. further research point-of-care testing is being developed to speed up the time for testing, and to help practitioners avoid prescribing unnecessary antibiotics in the style of precision medicine. traditional techniques typically take between 12 and 48 hours, although it can take up to five days. in contrast, rapid testing using molecular diagnostics is defined as "being feasible within an 8-h(our) working shift". progress has been slow due to a range of reasons including cost and regulation. additional research is focused at the shortcomings of current testing methods. as well as the duration it takes to report phenotypic methods, they are laborious, have difficult portability and are difficult to use in resource-limited settings, and have a chance of cross-contamination. as of 2017, point-of-care resistance diagnostics were available for methicillin-resistant staphylococcus aureus (mrsa), rifampin-resistant mycobacterium tuberculosis (tb), and vancomycin-resistant enterococci (vre) through genexpert by molecular diagnostics company cepheid. quantitative pcr, with the view of determining the percent of a detected bacteria that possesses a resistance gene, is being explored. whole genome sequencing of isolated bacteria is also being explored, and likely to become more available as costs decrease and speed increases over time. additional methods explored include microfluidics, which uses a small amount of fluid and a variety of testing methods, such as optical, electrochemical, and magnetic. such assays do not require much fluid to be tested, are rapid and portable. the use of fluorescent dyes has been explored. these involve labelled proteins targeted at biomarkers, nucleic acid sequences present within cells that are found when the bacterium is resistant to an antibiotic. an isolate of bacteria is fixed in position and then dissolved. the isolate is then exposed to fluorescent dye, which will be luminescent when viewed. improvements to existing platforms are also being explored, including improvements in imaging systems that are able to more rapidly identify the mic in phenotypic samples; or the use of bioluminescent enzymes that reveal bacterial growth to make changes more easily visible. bibliography burnett d (2005). the science of laboratory diagnosis. chichester, west sussex, england hoboken, nj: wiley. isbn 978-0-470-85912-4. oclc 56650888. ford, m (5 june 2019). medical microbiology. oxford university press. isbn 978-0-19-881814-4. mahon c, lehman d, manuselis g (2018). textbook of diagnostic microbiology (6 ed.). elsevier health sciences. isbn 978-0-323-48212-7. mcpherson, ra; pincus, mr (2017). henry's clinical diagnosis and management by laboratory methods (23 ed.). elsevier health sciences. isbn 978-0-323-41315-2.