Resistance to an antibiotic to which a bacterium is innately susceptible. It occurs when a bacterium acquires the ability to resist the actions of a particular antibiotic through either genetic mutation or horizontal gene transfer.

A microbiological test to determine whether bacteria are susceptible or resistant to an antibiotic. Also called 'antimicrobial sensitivity testing'.

An enzyme that can break down carbapenem antibiotics.

A discriminating concentration used in the interpretation of susceptibility tests to define isolates as susceptible or resistant.

A way of assessing whether a beta-lactamase is affected by an inhibitor. This helps identify the type of beta-lactamase. For each test, separate disks containing the antibiotic tested alone and in combination with an inhibitor are applied to the inoculated agar. The inhibition zone around the disk with the test antibiotic alone is compared with the zone around the test disk combined with the inhibitor. Sets of disks are commercially available to do this type of testing.

A test most frequently used to detect ESBL. It involves applying a disk containing the test antibiotic (mostly a cephalosporin) next to a disk containing an inhibitor (mostly clavulanic acid) on an inoculated agar plate. If ESBL is present, there is a distorted zone on the side of the test antibiotic nearest the inhibitor disk. Standard AST disks are commonly used for this.

A disk diffusion test used to study the macrolide lincosamide streptogramin resistance (MLSB), both constitutive and inducible, as well as macrolide streptogramin resistance (MSB) in Staphylococcus aureus. This applies to macrolides (such as erythromycin) inducing resistance to the lincosamide, clindamycin. This resistance mechanism could not be detected if clindamycin was tested alone. The ‘D’ refers to the shape of the zone around the clindamycin disk which is flattened on one side giving a ‘D’ shape.

Transport proteins in the bacterial membrane that actively transport antibiotics out of the bacterial cell.

An agreed concentration of antibiotic that defines a wild type microorganism. The ECOFF reflects the ability to detect resistance mechanisms that may or may not be clinically significant in a susceptibility test.

A Europe-based organisation that promotes international laboratory standards and guidelines for performing antibiotic susceptibility tests.

Bacteria which produce extended-spectrum beta-lactamases (ESBLs) making them more resistant to broad-spectrum cephaolsporins.

Methods based on the detection of genes.

A simple means of determining MIC. It uses thin plastic test strips that are impregnated on the underside with a dried antibiotic concentration gradient and are marked on the upper surface with a concentration scale. These are placed on an inoculated agar plate. After overnight incubation, the tests are read by viewing the strips from the top of the plate. The MIC can be read at the point where the zone of inhibition meets the test strip.

Bacteria that do not retain crystal violet dye in the Gram-staining test.

Bacteria with a thick peptidoglycan layer in their cell wall that is stained blue–purple by the Gram stain dye.

Infections that develop as a direct result of medical or surgical treatment or contact in a healthcare setting, such as a hospital, residential care home or nursing home.

The process of transferring genetic information between two unrelated cells. It is the primary mechanism of spreading antibiotic resistance because it allows bacteria to spread antibiotic resistance genes rapidly between different species.

A substance which stops an enzyme from working, thereby neutralising it. Beta-lactamase inhibitors are drugs that are co-administered with beta-lactam antimicrobials to overcome antimicrobial resistance by inhibiting serine beta-lactamases.

A short DNA sequences that can move from one site to another on a chromosome or to another chromosome or plasmid.

A means of testing for antimicrobial resistance mechanism. It involves testing a range of individual antimicrobials and other reagents, the ‘panel’. The pattern of resistance can be interpreted to predict the mechanism. This is often performed by an automated system. These systems have enhanced computer software for analysing test results for atypical patterns and unusual resistance phenotypes.

The innate ability of a bacterial species to resist the action of an antibiotic owing to the bacteria’s structural or functional characteristics.

A mass spectrometry technique used to rapidly and accurately identify organisms to species level.

The lowest concentration of an antimicrobial agent that inhibits the visible growth of a microorganism.

Bacteria that are resistant to at least two antimicrobials.

A concept that recognises the interdependency of human health, animal health and the ecosystems in which they evolve.

A group of bacterial genes, usually encoding proteins with related functions, that are under the control of a single regulatory DNA region.

Bacterial membrane proteins that have an important role in cell wall synthesis. They are a specific target of beta-lactamases.

Methods that rely on observable characteristics of the strain being tested.

A circular, non-chromosomal piece of DNA often carrying genes associated with a particular function, e.g. antibiotic resistance.

A technique used to create copies of specific DNA sequences from a DNA template.

A transmembrane protein complex that allows the movement of small molecules across the bacterial outer membrane.

The monitoring of an individual test or process to ensure that quality requirements are being met.

Activities and processes that identify and minimise errors and ensure laboratory quality. For example, quality control, quality assurance and quality management system.

A sequence of DNA that encodes the amino acid sequence of a particular protein that confers resistance to an antimicrobial.

A document detailing how routine laboratory processes and procedures should be performed.

The combined effect of two or more things being greater than the sum of their individual effects.

Segments of DNA that are capable of independently replicating themselves and inserting the copy into a new position within the same or another chromosome or plasmid.

Strains of Staphylococcus aureus bacteria that have intermediate resistance to the antimicrobial vancomycin.

Strains of Enterococci that resist treatment with the antimicrobial vancomycin.

Strains of Staphylococcus aureus bacteria that resist treatment with the antimicrobial vancomycin.

The ability of a pathogen to cause disease.

This is the predominant phenotype or genotype in a population.

A machine, piece of equipment, or vehicle that you can trust to work well and that you can use to do a lot of work.

The clear region around a disc impregnated with antimicrobial in a disk diffusion test. It indicates that the isolate being tested is susceptible to the antimicrobial.

The capacity for transmitting disease to humans from other vertebrate animals (e.g. pigs, poultry, dogs), which are the natural hosts of the pathogens.

An enzyme that can break down penicillin, conferring resistance on the strain of bacterium carrying the gene for this enzyme. It is sometimes called penicillinase.