Use of antibiotics in microbiology
Antibiotics are generally used in microbiology for antimicrobial sensitivity testing using a variety of methods, or they may be incorporated into media for use as a selective agent. Caution with their use is required for several reasons. There are many people in the community who are sensitive or allergic to various antibiotics and their overuse or misuse can lead to the development of resistant microorganisms(1).
Amoxicillin belongs to the class of antibiotics called penicillins, which are commonly used for treating bacterial infections. Penicillins are common antibiotics that can generate an allergic response. It is recommended that people who are allergic to any member of the penicillin family should avoid all contact with amoxicillin. Contact with amoxicillin can also cause irritation of the eyes, respiratory system and skin in certain individuals.
Additional issues for school science laboratories
Activities requiring the use of antibiotics require certain manipulations of microorganisms, which are not permitted in some jurisdictions. Also, the use of selective media is not allowed in most jurisdictions.
- Antibiotic sensitivity testing generally requires either lawn or broth cultures to be produced. This requires subculturing, which is a specialised technique requiring sound knowledge and expertise to minimise the risks involved. It is a skill developed with much practice. Some jurisdictions do not allow microorganisms to be subcultured.
- The type of media used should not select for pathogens (e.g., selective or enriched agars). Nutrient agar is a simple medium which supports the growth of a wide variety of bacteria and moulds and is suitable for use in school laboratories. If the activity requires the addition of amoxicillin into the agar, then this produces a medium which will select for amoxicillin resistant microorganisms.
- Antibiotic resistant bacteria need to be destroyed at 121 °C, 15 psi for 15–20 minutes using an autoclave or pressure cooker.
Science ASSIST recommendations
- Prior to carrying out any microbiological activity, a site-specific biological risk assessment(2) should be conducted to identify, assess and control any risks.
- Schools need to ensure that they have the required facilities and equipment and the necessary staff training to be able to manage the risks. If schools do not meet this criteria, then they should not undertake this level of activity safely.
- Any antibiotic, including antibiotic discs, should not be handled if the person is allergic to that particular antibiotic or class of antibiotics.
- If it is deemed appropriate to use antibiotics, then there are a wide variety of antibiotics and concentrations, including amoxicillin, available in disc form from various scientific suppliers.These are safer than an antibiotic in solution and can be readily handled wearing appropriate PPE with sterile forceps to avoid any skin contact.
- Safety data sheets should always be consulted when using any chemicals.
Currently in Australia there are differences between the state/territory educational jurisdictional policies on whether certain microbiological activities can be carried out. Schools are advised to check what activities are permitted in their jurisdiction/school sector before proceeding to work with any microorganisms.
The level of microbiological activity that involves using antibiotics should only be undertaken in schools if the following conditions apply.
- Proper facilities are in place. PC1 facilities are required. School science laboratories are generally classified as Physical Containment level 1 (PC1), if they conform to the requirements specified in Section 5 of AS/NZS 2243.3:2010 Safety in Laboratories – Microbiological safety and containment (3). If they do conform to these requirements, and there are many school labs that don’t, then they are only suitable for work with microorganisms where the hazard levels are low, and where laboratory or facility personnel can be adequately protected by standard laboratory practice(4).
- Microorganisms that are classified as Risk Group 1 are the only ones that should be used in PC1 laboratories, i.e. low risk—not associated with disease in healthy people. It should be noted that, even though some microorganisms are from RG1, some can still pose a low level of risk to the community, as they can be capable of causing disease if provided with appropriate conditions (referred to as opportunistic). People who are immunocompromised or immunosuppressed are at greater risk.
- Staff have training in microbiological skills including proficiency in aseptic technique to eliminate or minimize exposure to potentially infectious material via aerosols, splashes, ingestion, absorption and accidental inoculation, subculturing procedures, sterilisation and decontamination procedures and have the ability to identify contamination of pure cultures.
- Staff are able to demonstrate good microbiological technique, competency and confidence when performing procedures, interpretations and outcomes of activities, and competency in microbiological hazard awareness to maximise the student experience in microbiology.
- Suitable PPE is provided, this includes a lab coat and safety glasses. Cuts are covered with a waterproof dressing and consideration is given to the wearing of disposable gloves.
- An autoclave or pressure cooker is available for sterile preparation of agar/broth etc. and for decontamination.
Action of antibiotics
Antibiotics kill or inhibit certain microorganisms. Many common antibiotics inhibit bacterial growth by inhibiting protein synthesis. Amoxicillin acts on cell wall synthesis by inhibiting the formation of the peptidoglycan cross-link, a major component in gram-positive bacteria. The cell wall is weakened and ultimately ruptures.
Antibiotic sensitivity testing
The sensitivity of microorganisms to antibiotics is a common and important technique in microbiology laboratories. Common antibiotic sensitivity methods include dilution methods, disc diffusion methods, E-testing and some automated testing systems. The results from antibiotic testing are used for selecting the correct antibiotic for therapy against an infecting organism.
For further information on this subject take a look at Science ASSIST's 'Guidelines for best practice for Microbiology in Australian Schools' document: https://assist.asta.edu.au/resource/4196/guidelines-best-practice-microb...
(1) ‘Antibiotics’ Microbiology online website, http://www.microbiologyonline.org.uk/about-microbiology/microbes-and-the... (Accessed 15 February 2016)
(2) US Department of Health and Human Services. 2009. ‘Section II—Biological Risk Assessment’ in Biosafety in microbiological and biomedical laboratories (BMBL), 5th Edition, pp 9–21, Centers for Disease and Control Prevention website, https://www.cdc.gov/labs/pdf/CDC-BiosafetyMicrobiologicalBiomedicalLabor... (Link updated January 2019)
(3) Standards Australia. 2010. AS NZS 2243.3-2010. Safety in Laboratories – Microbiological safety and containment. Sydney, Australia
(4) ‘Microbiology’, October 2013, University of Sydney WHS website, https://intranet.sydney.edu.au/services/safety-wellbeing/standards-guidelines.html
‘Agar diffusion test’, Wikipedia website, https://en.wikipedia.org/wiki/Agar_diffusion_test (February 2016)
‘Allergic reactions to antibiotics’, healthdirect Australia website, https://www.healthdirect.gov.au/allergic-reactions-to-antibiotics (October 2014)
‘Amoxicillin’, US National Library of Medicine website, https://medlineplus.gov/druginfo/meds/a685001.html (January 2010)
‘Amoxicillin’ Safety Data Sheet Version 5.3, Sigma-Aldrich website http://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=AU&lang... (December 2015)
‘Antibiotic allergy clinical update’, Australian society of clinical immunology and allergy website, https://allergy.org.au/hp/papers/allergic-reactions-to-antibiotics/ (May 2015)
See the 'Susceptibility testing of antiseptics and disinfectants' Standard Operating Procedure in Science ASSIST's 'Guidelines for best practice for microbiology in Australian Schools'. (Added October 2019).
‘Antibiotic susceptibility discs and ejector packs’ Southern Biological website, ‘Mastring antibiotic sets’, Southern Biological website, https://www.southernbiological.com/mastring-antibiotic-sets/ (Updated October 2019).
Australian Government, Department of Health and Department of Agriculture. 2015. Responding to the threat of antimicrobial resistance. Australia’s First National Antimicrobial Resistance Strategy 2015–2019, Australian Government, Department of Health website. To download this document, click here.
Bio-Rad. 2011. ‘Disks for antibiotic susceptibility testing’ Bio-Rad website. https://commerce.bio-rad.com/webroot/web/pdf/inserts/CDG/en/Literature/inserts/66098_01_2011_GB.pdf
‘Growth medium’, Wikipedia website, https://en.wikipedia.org/wiki/Growth_medium (February 2016)