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 The use of larger tube-based "macrodilution" testing has been superseded by smaller "microdilution" kits.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