Human Practices Increasing Antibiotic Resistance
Start with what an antibiotic actually is. An antibiotic is a drug that exploits a difference between a bacterium and one of your own cells. Bacteria build a peptidoglycan cell wall you do not have; they run a 70S ribosome where yours is 80S; they coil their DNA with their own gyrase; they must manufacture folate from scratch where you simply eat it. Every antibiotic class targets one of these bacteria-only features, which is exactly why it can poison the microbe without poisoning the patient. Hold on to that single idea, because resistance is nothing more than a bacterium finding a way to keep using the feature the drug was attacking.
If you accept that, the rest follows by simple logic. Bacteria divide in minutes, mutate constantly, and trade genes with their neighbours. Any drug that kills the susceptible majority hands the surviving minority an empty world to repopulate. So resistance is not bad luck or a manufacturing flaw — it is the predictable, almost mechanical result of putting a selective pressure on a fast-evolving population. Antibiotic resistance is evolution under pressure, happening on a timescale of days.
The basic chain is therefore:
antibiotic exposure -> susceptible organisms killed -> resistant organism or gene survives the cull -> survivor multiplies and spreads through patient, facility, community, animals or environment -> later treatment failure
This chapter builds in that order: first why resistance is inevitable (the mechanisms), then how human practice accelerates it, and only then how O&G should respond. O&G uses antibiotics constantly — caesarean prophylaxis, maternal and puerperal sepsis, chorioamnionitis, miscarriage and termination complications, urinary infection, sexually transmitted infections (STIs), pelvic inflammatory disease (PID) and surgical prophylaxis — so the specialist who understands the mechanism owns a core patient-safety skill, not an abstract one.
What Antibiotics Attack, and Why That Defines Resistance
Before resistance can make sense, the target has to make sense. Each major class exploits one bacteria-specific weakness. Once you can name the weakness, the matching resistance mechanism is obvious: the bacterium simply protects, hides, alters or destroys that one point of attack.
| Class (examples) | Bacteria-only target it attacks | How resistance defeats that attack |
|---|---|---|
| Beta-lactams — penicillins, cephalosporins, carbapenems | Penicillin-binding proteins (PBPs) that cross-link the peptidoglycan wall | Beta-lactamase enzymes destroy the drug; altered PBPs no longer bind it |
| Glycopeptides — vancomycin | Building blocks of the peptidoglycan wall | Modified wall precursors the drug cannot grip; an outer membrane that keeps it out of Gram-negatives |
| Aminoglycosides, macrolides, tetracyclines, clindamycin | The bacterial 70S ribosome (protein synthesis) | Modifying enzymes inactivate the drug; the ribosomal binding site is altered; efflux pumps expel tetracyclines |
| Fluoroquinolones | DNA gyrase / topoisomerase (DNA coiling) | A mutated gyrase the drug no longer fits |
| Rifampicin | Bacterial RNA polymerase | A single point change in the polymerase abolishes binding |
| Sulphonamides + trimethoprim | The folate-synthesis pathway bacteria must run themselves | Alternative or insensitive enzymes that bypass the block |
| Metronidazole | Activated only inside anaerobes; damages microbial DNA | Reduced drug activation in less-anaerobic conditions |
The teaching point is that resistance is target-specific. A beta-lactamase makes an organism untouchable by penicillins yet says nothing about its response to a quinolone. This is why "resistant" is never a single property — an organism is resistant to a named drug by a named mechanism, and why the laboratory susceptibility report, not a memorised rule, decides therapy.
How Resistance Develops
Resistance has two halves: a genetic origin (where the resistant trait comes from) and an ecological fate (how it then takes over). Both must be present for resistance to matter clinically.
| Mechanism | Meaning | Clinical implication |
|---|---|---|
| Mutation | A random DNA copying error alters the target, the entry point or an enzyme | Resistance can arise spontaneously during ordinary replication, before the drug ever arrives |
| Selection | The antibiotic kills susceptible organisms and leaves the resistant few to repopulate | Every unnecessary course rewards whatever can survive it |
| Horizontal gene transfer | Plasmids, transposons ("jumping genes") and conjugation through pili move ready-made resistance genes between bacteria | Resistance can jump between species without any new mutation — one organism's solution becomes another's |
| Enzymatic destruction | The drug is chemically broken down before it acts | Beta-lactamases, including extended-spectrum forms |
| Target modification | The drug's binding site is changed so it no longer fits | Altered PBPs (MRSA), altered ribosomes, altered gyrase |
| Efflux pumps | The drug is actively pumped back out | A common route to multidrug resistance |
| Reduced permeability | The drug cannot get in | Gram-negative porin loss; the outer membrane that already excludes vancomycin |
| Biofilm | Organisms encased in a self-made matrix resist both drug and immune attack | Catheters, chronic wounds, retained devices |
Two of these deserve emphasis because they explain hospital outbreaks. Horizontal gene transfer means a resistance gene that arose once, anywhere, can be donated wholesale to an unrelated species — a single conjugation event can hand a harmless gut commensal the machinery to defeat a last-line drug. And a biofilm lowers the dose needed to establish infection while raising the dose needed to clear it: the presence of a foreign body such as a cannula or catheter can cut the infecting inoculum a thousand-fold, which is why device discipline is an antibiotic-resistance issue, not just an infection-control one.
Subtherapeutic exposure is especially dangerous. If concentrations are too low to kill but high enough to pressure the organism, resistant subpopulations gain a decisive advantage — the drug culls their competitors without removing them. This happens through wrong dose, missed doses, poor-quality or counterfeit medicines, prolonged low-level exposure or inadequate tissue penetration (a particular trap in obesity and in poorly perfused infected tissue).
How Human Practice Creates a Selective Medium
The laboratory selects organisms by choosing culture conditions that favour one group over another. Clinical practice can accidentally do the same inside a patient or ward.
| Human action | Selective medium created | Likely result |
|---|---|---|
| Cephalosporin exposure without enterococcal activity | Susceptible flora suppressed while enterococci survive | Enterococcal superinfection or colonisation in hospital settings |
| Repeated azoles without confirming Candida | Susceptible C. albicans suppressed | Non-albicans Candida or non-infective vulval disease is missed |
| Broad anaerobic and Gram-negative cover for vague discharge | Vaginal and gut competitors disrupted | Resistant colonisers and recurrent dysbiosis become more likely |
| Long catheter dwell time plus antibiotics | Device biofilm with repeated drug exposure | Resistant catheter-associated UTI risk rises |
| Partial STI treatment without partner care | Organisms repeatedly exposed during reinfection cycles | Persistent transmission and repeated community antibiotic pressure |
| Underdosed prophylaxis in obesity or delayed theatre timing | Tissue concentrations below effective levels at incision | Infection occurs despite "antibiotics given", leading to further treatment |