MI11.1-3 | Antimicrobial Resistance & Stewardship — Glossary

Resistance that develops in previously susceptible organisms through mutation or horizontal acquisition of resistance genes.

A coordinated set of interventions to optimise antimicrobial use in healthcare — ensuring appropriate drug, dose, route, and duration while minimising resistance selection.

The ability of a microorganism to survive and grow in the presence of an antimicrobial agent that would normally inhibit or kill it.

An enzyme produced by bacteria that hydrolyses the beta-lactam ring of penicillins, cephalosporins, and related antibiotics, rendering them inactive.

A beta-lactamase capable of hydrolysing carbapenems; includes metallo-beta-lactamases (NDM-1), KPC, and OXA types.

Numerical MIC or zone diameter threshold established by the Clinical and Laboratory Standards Institute to classify organisms as Susceptible, Intermediate, or Resistant to specific antibiotics.

Direct cell-to-cell transfer of plasmid DNA through a sex pilus; the most clinically significant mechanism of horizontal resistance gene transfer.

The practice of switching from empirical broad-spectrum antibiotic therapy to narrower-spectrum targeted therapy once culture and susceptibility results are available.

An AST method using antibiotic-impregnated paper disks on agar; zone of inhibition diameter is compared to CLSI/EUCAST breakpoints to determine S/I/R.

A membrane transporter protein that actively exports antibiotics from the bacterial cytoplasm, reducing intracellular drug concentration.

A plasmid-encoded beta-lactamase capable of hydrolysing extended-spectrum cephalosporins and monobactams, but inhibited by beta-lactamase inhibitors and not carbapenems.

Six clinically critical drug-resistant organisms: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species.

Transfer of genetic material between organisms other than from parent to offspring; key mechanism for spread of resistance genes across bacterial species.

Naturally occurring resistance that is an inherent characteristic of a microbial species, present before any antibiotic exposure.

Converting from intravenous to oral antibiotic therapy when a patient is clinically stable and an oral agent with adequate bioavailability is available.

An annual cumulative summary of antimicrobial susceptibility rates for common organisms isolated at a specific institution; used to guide empirical antibiotic therapy choices.

Non-susceptibility to at least one agent in three or more antimicrobial categories.

The lowest concentration of an antimicrobial that inhibits visible bacterial growth in vitro under standardised conditions.

S. aureus carrying the mecA gene, which encodes PBP2a — a penicillin-binding protein with low affinity for all beta-lactams, rendering the entire class ineffective.

A zinc-dependent carbapenemase first described in 2008 from a Swedish patient treated in New Delhi; confers resistance to all beta-lactams including carbapenems; not inhibited by tazobactam.

Non-susceptibility to all agents in all antimicrobial categories; no standard treatment options available.

Extrachromosomal circular DNA capable of autonomous replication; the primary vehicle for multiple antibiotic resistance gene dissemination.

A serum biomarker elevated in bacterial infections; used in PCT-guided protocols to shorten antibiotic duration in CAP and sepsis without worsening outcomes.

An AMSP strategy in which antibiotic prescriptions are reviewed in real time by an ASP team, with direct recommendations to prescribers for optimisation.

Enterococcus carrying vanA/B genes that alter the peptidoglycan terminus, preventing vancomycin binding.

Non-susceptibility to at least one agent in all but two or fewer antimicrobial categories.