Today marks the start of Antibiotic Awareness Week – a global campaign designed to increase the awareness of antibiotic resistance and to encourage responsible use amongst the public, health professionals and policy makers to prevent the further spread of antibiotic resistance1.

Antibiotics have revolutionised modern medicine by making previously incurable illnesses like pneumonia, tuberculosis and life-threatening infections treatable2. Antibiotics are also essential to avoid infections following surgery as well as other treatments, such as chemotherapy. It is estimated that penicillin alone has saved at least 200 million lives since its first use as a medicine in 1942, making it one of the single most important advances in the history of medical science. However the overuse and misuse of antibiotics in human and animal health have resulted in the emergence and spread of antibiotic resistance. The more antibiotics are used, the less effective the become by enabling bacteria to develop resistance.

In addition to the rise in antibiotic resistance, the discovery of new antibiotics is at an all time low. It has been 30 years since a new class of antibiotics were last introduced, and only 3 of the 41 antibiotics currently in development have the potential to act against the majority of the most resistant bacteria3. Antibiotic  resistance is listed as one of the World Health Organisation’s (WHO) 10 biggest global health threats4, and it is estimated to be responsible for around 700, 000 deaths each year globally. This figure is predicted to rise to 10 million if  no action is taken3. AMR infections are estimated to cause 700,000 deaths each year globally. It is important to be able to identify the strain of bacterial infection and the antibiotics which it is resistant to or susceptible in a patient before prescribing antibiotics.

 

Antimicrobial Susceptibility Discs from Rapid Labs
Rapid Labs offer a range of antimicrobial susceptibility testing discs, recommended for use in the Kirby-Bauer method of testing for antimicrobial susceptibility from specimens of human source5. Our discs are 6.5mm in diameter and incorporate all routinely available antimicrobials at recommended concentrations. The discs are coded with a 3-letter code for the antimicrobial name, and number for concentration. With hundreds of discs available for testing a wide range of antibiotics at various strengths, please contact us for more information. Some of our commonly used products are listed below:

Amoxicillin – The most frequently used antibiotic worldwide6. Erythromycin Penicillin
Ampicillin Flucloxacillin Rifampicin – the most effective first-line drug for tuberculosis. In 2017, around 600 000 cases of TB were resistant to Rifampicin4.
Augmentin Gentamicin Streptomycin
Cefoperazone Linezolid Tetracycline
Chloramphenicol Methicillin Trimethoprin
Clindamycin Metronidazole Vancomycin

 

Test Principle

A standardised inoculum of a pure culture, isolated from a clinical sample is streaked across a designated culture medium and allowed to dry. The appropriate antimicrobial discs are then dispensed onto the culture medium. Following incubation, the agar plates are examined and zones of inhibition surrounding the discs are measured. The minimum inhibitory concentration (MIC) of the antimicrobial appears at the edge of the zone of inhibition, and represents the interaction of a critical concentration of antimicrobial on a critical microbial population. These results are compared with established zone ranges for individual antimicrobial agents to determine the most appropriate antibiotic for use in vivo.

Interpretation

Compare zone parameters with the current NCCLS Standards, interpreting as susceptible, intermediate or resistant:

  • ‘Susceptible’ – Implies that an infection due to the strain may be appropriately treated with the dosage of antimicrobial agent recommended for that type of infection and infecting species, unless otherwise contraindicated.
  • ‘Intermediate’ – Includes isolates with antimicrobial agent MICs that approach usually attainable blood and tissue levels and for which response rates may be lower than for susceptible isolates. The ‘intermediate’ category implies clinical applicability in body sites where the drugs are physiologically concentrated, or when a high dosage of a drug can be used (e.g beta-lactams). The ‘intermediate’ category also includes a ‘buffer zone’ which should prevent small, uncontrolled technical factors from causing majoy discrepancies in interpretations, especially for drugs with narrow pharmacotoxicity margins.
  • ‘Resistant’ – Not inhibited by the usually achievable systemic concentrations of the agent with normal dosage schedules and/or fall in the range where specific microbial resistance mechanisms are likely and clinical efficacy has not been reliable in treatment studies.

 

Precautions
Consultation with an infectious disease specialist is recommended for guidance in determining the need for susceptibility testing. Current editions of CLSI and EUCAST standards should be consulted for the most recent recommendations7.

 

Please get in touch if you would like more information about our antimicrobial discs by emailing medical@rapidlabs.co.uk or telephone +44 (0) 1206 250484.

 

References

  1. World Health Organisation: https://www.who.int/campaigns/world-antibiotic-awareness-week
  2. Svhwartländer (2015). Antibiotics changed modern medicine, but we must act to protect them. WHO Western Pacific Region, last accessed 18th November 2019 at http://www.wpro.who.int/china/mediacentre/releases/2015/20151119/en/
  3. Public Health England (2015). Health Matters: Antimicrobial Resistance (guidance). Last accessed 18th November at https://www.gov.uk/government/publications/health-matters-antimicrobial-resistance/health-matters-antimicrobial-resistance
  4. World Health Organisation (2019). 10 threats to global health in 2019. Last accessed 18th November 2019 at https://www.who.int/emergencies/ten-threats-to-global-health-in-2019
  5. Bauer et al (1966). Antibiotic susceptibility testing by a standardised single disk method.
  6. World Health Organisation (2018). Wide differences in antibiotic use between countries, according to new data from WHO. Last accessed 18th November 2019 at https://www.who.int/medicines/areas/rational_use/oms-amr-amc-report-2016-2018-media-note/en/
  7. American Journal of Clinical Pathology, 45: 493-496. National Committee for Clinical Laboratory Standards Performance Standards for Antimicrobial Disk Susceptibility Tests; Approved standard, M2-A8. NCCLS.