ESBL and carbapenemase-producing Gram-negative infection

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

ESBL and carbapenemase describe resistance mechanisms, not a clinical syndrome. E. coli, Klebsiella species and other Enterobacterales may colonise the gut silently or cause cystitis, pyelonephritis, biliary or abdominal infection, pneumonia, device infection and bacteraemia. The anatomical focus and physiology determine urgency; the mechanism and MIC determine which antibiotic reaches a reliable exposure.

ESBL enzymes, commonly CTX-M types, inactivate extended-spectrum cephalosporins and aztreonam. Carbapenemases are more heterogeneous: KPC is a serine enzyme inhibited by avibactam and vaborbactam; OXA-48-like enzymes are inhibited by avibactam but not reliably by vaborbactam; metallo-beta-lactamases hydrolyse carbapenems but spare aztreonam, which may still be destroyed by co-produced ESBL or AmpC.

Treatment belongs to the local microbiology and antimicrobial-stewardship system because prevalence, formulary access, susceptibility methods and dosing support differ. A label from months ago informs empirical coverage but does not prove the current organism. Conversely, standard sepsis regimens may be inactive in a currently colonised high-risk patient, so previous laboratory data must be accessible at the bedside.

Key points

Extended-spectrum beta-lactamases hydrolyse most penicillins and third-generation cephalosporins but usually leave carbapenems active; co-resistance to quinolones and co-trimoxazole is common.
Carbapenemase-producing Enterobacterales carry enzymes such as KPC, OXA-48-like, NDM, VIM or IMP; the enzyme class predicts which newer beta-lactam combination can work.
Colonisation of the bowel, urine around a catheter or a chronic wound does not itself require antibiotics; treat an attributable clinical infection, not the resistance result.
Obtain blood and high-quality source cultures before antimicrobials when safe and retrieve every previous isolate, susceptibility, carbapenemase result and overseas healthcare exposure.
For severe ESBL bloodstream or non-urinary infection, meropenem 1 g intravenously every eight hours is a common first-line regimen pending site, MIC and renal review.
For susceptible uncomplicated lower UTI, nitrofurantoin or another narrow oral agent can spare carbapenems; never extrapolate that susceptibility to pyelonephritis or sepsis.
NICE restricts ceftazidime-avibactam to severe resistant Gram-negative infection with specialist advice, supported susceptibility and no suitable alternative; it is particularly useful for OXA-48-like and selected KPC producers.
CPE control requires immediate IPC notification, risk-based single-room or cohort care, contact precautions, flags, transfer communication and contact screening; routine antibiotic decolonisation is not recommended.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Plasmid-mediated ESBL

Mobile CTX-M and related enzymes spread between Enterobacterales and hydrolyse extended-spectrum cephalosporins, often alongside non-beta-lactam resistance genes.

Carbapenemase acquisition

KPC, OXA-48-like, NDM, VIM and IMP enzymes hydrolyse carbapenems with distinct inhibitor profiles and epidemic potential.

Healthcare selection

Broad antibiotics, devices, critical care, prolonged admission and overseas healthcare select resistant bowel flora and facilitate patient-to-patient transmission.

Community reservoir

ESBL-producing E. coli also circulates outside hospitals through household, food, animal and international-travel networks, commonly causing recurrent UTI.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Beta-lactam hydrolysis
Enzymes cleave the antibiotic beta-lactam ring before it can bind penicillin-binding proteins and interrupt cell-wall construction.
2
Co-resistance platforms
Mobile plasmids often carry quinolone, aminoglycoside and trimethoprim resistance determinants, narrowing useful oral and intravenous options together.
3
Gut colonisation
Resistant Enterobacterales persist in intestinal flora without symptoms and later seed urinary, biliary, abdominal or bloodstream infection.
4
Protected source persistence
Biofilm on catheters and bacteria within obstructed or undrained systems survive active serum antibiotic concentrations until physical source control.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Silent gastrointestinal carriage

A rectal screen identifies resistant Enterobacterales without fever, local symptoms or tissue invasion; this changes IPC and future empirical decisions, not treatment.

Urinary infectionRed flag

Dysuria and frequency suggest lower UTI, while fever, loin pain, vomiting or sepsis indicates upper-tract or bloodstream involvement requiring systemic exposure.

Intra-abdominal sourceRed flag

Biliary obstruction, perforation, anastomotic leak or abscess causes pain and sepsis and needs drainage or surgery alongside active antibiotics.

Healthcare-associated sepsisRed flag

Ventilation, central or urinary devices, critical care, prolonged antibiotics and overseas healthcare create infection risk from a previously silent resistant reservoir.

Treatment failureRed flag

Persistent fever, bacteraemia or organ dysfunction despite reported susceptibility should prompt dose, infusion, renal clearance, mechanism and source-control review.

Red flags requiring action

Shock, rising lactate, altered consciousness, oliguria or respiratory failure requires immediate broad active intravenous therapy and source control.
Previous carbapenemase-producing Enterobacterales, overseas hospitalisation, transfer from an outbreak facility or a known colonised household contact should trigger urgent IPC and empirical-treatment review.
Pyelonephritis, obstruction, renal abscess or bacteraemia must not be treated with nitrofurantoin or oral fosfomycin because tissue and serum exposure are inadequate.
Persistent bacteraemia despite an apparently susceptible drug raises inadequate exposure, undrained source, infected device, heteroresistance or emergence of resistance.
NDM, VIM or IMP metallo-beta-lactamase is not inhibited by avibactam alone; mechanism-specific combination or cefiderocol decisions require specialist laboratory evidence.
Pregnancy, renal failure, augmented renal clearance, epilepsy, valproate therapy and severe beta-lactam allergy can materially alter carbapenem or novel-agent prescribing.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line blood and source culturesFirst stepFirst line
Why
Identify the current pathogen and susceptibility from blood, urine, deep tissue, bile, drainage or another true infection focus.
Interpretation and limitations
Collect before antibiotics when safe and replace chronic-catheter urine before sampling where feasible. Superficial swabs and old isolates may reflect colonisation.
02
Phenotypic susceptibility testing
Why
Determine which agents are active at the infection site and flag ESBL or carbapenem resistance.
Interpretation and limitations
Interpret current MICs with EUCAST methods and clinical site. An in-vitro urinary option may not achieve bloodstream, renal-parenchymal or lung exposure.
03
Carbapenemase identification
Why
Differentiate KPC, OXA-48-like, NDM, VIM, IMP and other mechanisms using rapid molecular or antigen methods.
Interpretation and limitations
Mechanism directs novel beta-lactam choice and IPC epidemiology. Send discordant or unusual isolates to the specialist or reference laboratory.
04
Source imaging
Why
Detect obstruction, abscess, infected collection, biliary disease or device complication needing physical control.
Interpretation and limitations
Use renal ultrasound or CT, abdominal CT, biliary imaging or site-specific studies according to symptoms; antibiotics alone cannot sterilise an obstructed infected system.
05
CPE screening
Why
Identify gastrointestinal carriage in defined healthcare contacts, admissions or people with previous overseas or outbreak exposure.
Interpretation and limitations
Use rectal swab or faecal testing according to the UKHSA framework and local algorithm; negative screens do not erase a previous confirmed carrier flag automatically.
06
Renal and pharmacokinetic assessment
Why
Select beta-lactam dose and infusion that maintains adequate time above the MIC without neurotoxicity.
Interpretation and limitations
Measure current creatinine clearance and reassess daily in sepsis; augmented clearance, dialysis and rapidly changing kidney function require pharmacist-led adjustment.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Asymptomatic colonisation

A positive rectal, chronic-wound or catheter specimen without attributable clinical disease reflects carriage and should not trigger antibiotics.

AmpC production

Inducible or derepressed AmpC causes cephalosporin resistance through a different enzyme and changes beta-lactam interpretation despite similar reports.

Non-enzymatic carbapenem resistance

Porin loss plus ESBL or AmpC, efflux and target changes can raise carbapenem MICs without a transmissible carbapenemase.

Resistant non-fermenter

Pseudomonas and Acinetobacter use different resistance mechanisms and require organism-specific agents rather than an Enterobacterales pathway.

Non-infectious inflammation

Drug reaction, malignancy, thrombosis and inflammatory disease can coexist with resistant colonisation and falsely attribute fever to a screen result.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01CULTURE FIRSTIdentify infection and resistance historyFirst stepA patient with ESBL or CPE risk develops local symptoms, fever, sepsis or a new positive culture.

1Perform ABCDE and obtain blood plus high-quality source cultures before antimicrobials if collection is immediate; do not delay resuscitation or an active first dose in shock.
2Retrieve previous species, MICs and carbapenemase results, overseas or outbreak healthcare and recent antibiotics and devices.
3Distinguish asymptomatic colonisation, asymptomatic bacteriuria and catheter growth from a clinical infection using symptoms, physiology and specimen quality.
4Alert microbiology for empirical selection and IPC for CPE risk, isolation, screening and transfer communication.

02ESBLTreat ESBL infection by siteAn ESBL-producing Enterobacterales isolate causes clinical infection and carbapenem resistance is not present.

1For severe bloodstream, abdominal, pulmonary or upper-urinary infection, use meropenem 1 g intravenously every eight hours with renal adjustment and prolonged infusion according to local policy.
2For stable susceptible disease, narrow to an active oral agent only after source control, haemodynamic recovery and confirmation that it achieves exposure at the site.
3For uncomplicated lower UTI, use nitrofurantoin, pivmecillinam, fosfomycin or another locally recommended susceptible option rather than a carbapenem.
4Reserve ceftazidime-avibactam, meropenem-vaborbactam and cefiderocol for carbapenem-resistant infection or another defined specialist reason.

03CPEMatch treatment to carbapenemaseClinical infection is caused by carbapenemase-producing Enterobacterales.

1PreferredAlternativeFor OXA-48-like infection, use susceptibility-confirmed ceftazidime-avibactam when no narrower suitable alternative exists; it is the preferred mechanism-aligned novel agent.
2For KPC infection, select ceftazidime-avibactam or meropenem-vaborbactam from susceptibility, site, previous exposure, renal function and local formulary.
3For NDM or another metallo-beta-lactamase, use cefiderocol or a specialist simultaneous ceftazidime-avibactam plus aztreonam regimen when laboratory testing supports it.
4Do not add aminoglycoside, colistin or tigecycline routinely to an active modern beta-lactam; combination toxicity requires a specific resistant-organism or salvage rationale.

04SOURCE CONTROLRemove protected infection fociObstruction, abscess, infected line, necrotic tissue, prosthesis or ongoing abdominal contamination accompanies infection.

1Decompress an infected obstructed urinary or biliary system urgently and drain abdominal, pelvic or soft-tissue collections.
2Remove an implicated vascular or urinary device when feasible and replace chronic urinary catheters before a diagnostic culture.
3Repeat blood cultures until clearance for bacteraemia and investigate persistent positivity for endovascular, deep or retained-device disease.
4Set duration from focus, drainage, clinical response and clearance rather than extending broad therapy solely because the isolate is resistant.

05CONTAINPrevent CPE transmissionCPE carriage or infection is suspected or confirmed in a healthcare setting.

1Use a single room with en-suite facilities where possible or cohort under IPC advice, with standard and contact precautions and dedicated equipment.
2Screen contacts and high-risk admissions according to the UKHSA CPE framework rather than improvising a universal sampling schedule.
3Place a durable electronic flag and communicate status before every transfer, dialysis attendance, procedure, care-home return or readmission.
4Do not prescribe antibiotics or faecal decolonisation products to eradicate asymptomatic carriage; stewardship and hand, device and environmental hygiene are the control measures.

Key medicines and prescribing safety6 treatments · regimens, roles and cautions

First-line carbapenem for severe ESBL bloodstream or non-urinary infection and selected unstable upper-urinary disease.

Meropenem

Give 1 g intravenously every eight hours for severe ESBL infection, using an extended infusion and higher site-specific dose only under the local protocol, with renal adjustment.

Review seizure risk, allergy, renal function and major reduction of valproate concentrations; do not use merely to treat colonisation or uncomplicated susceptible cystitis.

Carbapenem-sparing of antipseudomonal activity for appropriate once-daily definitive treatment or outpatient therapy.

Ertapenem

Give 1 g intravenously every 24 hours for selected stable susceptible ESBL infection after source control, with renal adjustment.

Avoid in shock, severe hypoalbuminaemia, CNS infection or where Pseudomonas or Acinetobacter coverage is needed; confirm susceptibility and stewardship approval.

NICE-supported option for severe drug-resistant Gram-negative infection, especially susceptible OXA-48-like and selected KPC producers with no suitable alternative.

Ceftazidime-avibactam

Give 2 g/0.5 g intravenously every eight hours infused over two hours, adjusting for renal function and infection site under microbiology supervision.

It is inactive against metallo-beta-lactamases alone, resistance can emerge, and rapidly improving renal function risks underdosing; pair with aztreonam only under a validated specialist protocol.

Mechanism-aligned option for susceptible KPC-producing Enterobacterales infection.

Meropenem-vaborbactam

Give 2 g/2 g intravenously every eight hours infused over three hours, with creatinine-clearance adjustment under the local restricted-antimicrobial pathway.

Vaborbactam does not reliably inhibit OXA-48-like or metallo-beta-lactamases; review allergy, renal function, seizures, valproate interaction and susceptibility.

Reserved option for susceptible carbapenem-resistant Gram-negative infection, including selected metallo-beta-lactamase producers.

Cefiderocol

Give 2 g intravenously every eight hours infused over three hours, with dose-frequency changes for renal impairment or augmented renal clearance under specialist protocol.

Use only with microbiology and infection approval, mechanism and MIC review; monitor renal dosing, C. difficile, superinfection and the clinical response closely.

Narrow carbapenem-sparing oral treatment when infection is confined to the bladder.

Nitrofurantoin

For susceptible uncomplicated lower UTI, give modified-release nitrofurantoin 100 mg orally twice daily for three days in a non-pregnant woman or seven days in a man under UK local guidance.

Do not use for fever, pyelonephritis, prostatitis or bacteraemia; check renal function, pregnancy near term and pulmonary, hepatic or neurological toxicity.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Septic shock

Initially inactive empirical therapy permits unchecked endotoxin-associated inflammation, circulatory failure, severe multiorgan injury and increased mortality.

Recurrent urinary infection

Persistent bowel carriage, stones, obstruction, prostate involvement or urinary devices cause repeated episodes with progressively limited oral options.

Healthcare outbreak

Unrecognised CPE carriage spreads through hands, equipment, sinks and shared care networks, disrupting high-risk clinical services.

Emergent treatment resistance

Suboptimal exposure or prolonged novel-agent use selects beta-lactamase mutations, permeability changes or new resistance during therapy.

Antibiotic collateral harm

Broad therapy causes C. difficile, microbiome disruption, organ toxicity and further resistance selection in the patient and care environment.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review cultures, MICs and carbapenemase result daily and narrow as soon as an active site-appropriate agent is defined.
Track renal function and recalculate novel beta-lactam dosing frequently during sepsis, dialysis or rapid recovery; underexposure selects failure and resistance.
Repeat blood cultures to clearance in bacteraemia and monitor drainage, obstruction relief and device removal rather than using inflammatory markers alone.
Watch for neurotoxicity, C. difficile, cytopenia, liver injury, hypersensitivity and drug interactions, particularly valproate loss with carbapenems.
IPC should document screening results, precautions, electronic alerts, exposed contacts and communication across discharge and transfer.
Follow local laboratory, IPC and UKHSA routes for CPE surveillance and outbreak reporting; carriage does not create an indication for antimicrobial treatment.
After treatment, do not perform routine clinical cultures to prove eradication in an asymptomatic carrier; investigate only a new clinical syndrome or IPC-directed screen.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Mechanism predicts inhibitor

Avibactam inhibits KPC and OXA-48-like enzymes, vaborbactam principally protects against KPC, and neither alone inhibits NDM, VIM or IMP.

Site overrides laboratory shorthand

An antibiotic reported susceptible for bladder infection can be unsafe for renal tissue or blood because the achievable exposure is different.

Colonisation guides empiricism

A prior CPE screen should shape urgent empirical treatment in sepsis, but it does not prove that an asymptomatic current culture needs therapy.

New agents need protection

Using novel beta-lactams for ordinary ESBL disease consumes options needed for carbapenem resistance and increases selective pressure for emerging resistance.

Clearance is not decolonisation

Successful treatment of bacteraemia removes infection while bowel carriage may persist for months, so IPC flags and future risk assessment remain important.

11Common pitfallsFrequent interpretation and management errors.

01
Do not treat a positive rectal screen, asymptomatic catheter urine or colonised wound with systemic antibiotics.
02
Do not use nitrofurantoin or oral fosfomycin for pyelonephritis, prostatitis or bloodstream infection.
03
Do not assume every carbapenem-resistant isolate has the same enzyme; KPC, OXA-48-like and metallo-beta-lactamases require different agents.
04
Do not use ceftazidime-avibactam alone for NDM, VIM or IMP infection, because avibactam does not inhibit metallo-beta-lactamases.
05
Do not add nephrotoxic combination agents routinely when one active modern beta-lactam is available.
06
Do not remove CPE alerts or contact precautions simply because infection treatment has ended or one screening swab is negative.