Dr. Iman M. Fawzy Clinical Pathology MD, PhD Mansoura, Egypt Extended Spectrum β-Lactamases: Challenges in Laboratory Detection and Implications on Therapy Dr. Iman M. Fawzy Clinical Pathology MD, PhD Mansoura, Egypt
ESBL Extended spectrum β-lactamase (ESBL)-producing organisms pose unique challenges to clinical microbiologists, clinicians, infection control professionals and antibacterial-discovery scientists.
Why we need esbl detection? ESBL-producing Enterobacteriaceae have been responsible for numerous outbreaks of infection throughout the world ESBL pose challenging infection control issues. ESBLs are clinically significant and indicate the appropriate antibacterial agents. Unfortunately, the laboratory detection of ESBLs can be complex and, at times, misleading.
β-lactam antibiotics Penicillin Cephalosporin Monobactam Carbapenem nitrogen containing ring Bacteriocidal – mechanism is that the beta-lactam ring binds to and inactivate PBPs, preventing crosslinking of peptidoglycan = weakening = lysis
β lactamases Beta lactamases are enzymes produced by some bacteria that hydrolyze beta lactam antibiotics Penicillinases, Cephalosporinases Extended spectrum β-lactamases (ESBL) Metallo β lactamases Amp C Carbapenemase
Definition of ESBL ESBLs are enzymes hydrolyzing most penicillins and cephalosporins, and monobactam (aztreonam). but not cephamycins and carbapenems Susciptable to β-lactamase inhibitors (clavulanate, sulbactam and tazobactam) Intrinsic resistance = inherent or innate (not acquired) resistance, which is reflected in wildtype antimicrobial patterns of all or almost all representatives of a species. Intrinsic resistance is so common that susceptibility testing is unnecessary. • Acquired resistance = antimicrobial resistance in a bacterium that was previously susceptible that occurs as a result of: – Chance gene mutation – Acquisition of R genes from another bacterium
Clinical significance ESBLs destroy cephalosporins, main hospital antibiotics, given as first-line agents to many severely-ill patients, including those with intra-abdominal infections, community-acquired pneumonias and bacteraemias. Delayed recognition inappropriate treatment of severe infections caused by ESBL producers with cephalosporins ↑↑mortality .
Clinical significance ESBL-mediated resistance is not always obvious to all cephalosporins in vitro. Many ESBL producers are multi-resistant to non-β-lactam antibiotics such as quinolones, aminoglycosides and trimethoprim, narrowing treatment options.
Spread direct and indirect contact with colonized/infected patients and contaminated environmental surfaces. ESBLs are most commonly spread via unwashed hands of health care providers.
Risk factors Critically ill patients, Immunosuppression Prolonged hospital or ICU unit stay Invasive procedures: intubation, mechanical ventillation, catheter Long-term dialysis within 30 days Family member with multidrug-resistant pathogens Prior antibiotic use in last 3 months High frequency of antibiotic resistance in the community or in the specific hospital unit Patient who previously had an antibiotic-resistant organism (e.g., MRSA, VRE)
Major groups of -lactamases Functional group Major subgroup Molecular class Inhibition by clavulanate 1 C Cephalosporinases, often chromosomal enzymes in GNB but may be plasmid-encoded, confer resistance to all classes of -lactams, except carbapenems (unless combine with porin change) - 2 2a A Penicillinases, confer resistance to all penicillins, primarily from Staphylococcus and enterococci + 2b Broad-spectrum -lactamases (penicillinases/cephalosporinases) , primarily from GNB. 2be ESBLs, confer resistance to oxyimino-cephalosporins and monobactams. 2br Inhibitor-resistant TEM (IRT) -lactamases - (+ for tazobactam) 2c Carbenicillin-hydrolyzing enzymes Functional classification (Bush-Jacoby-Medeiros: 1-4) – spectrum of ATB substrate profile, enzyme inhibitor profile, enzyme net charge, hydrolysis rate, binding affinity, isoelectric focusing, protein molecular weight, amino acid composition Molecular classification (Ambler’s classification: A-D) – nucleotide and amino acid sequence
Major groups of -lactamases Functional group Major subgroup Molecular class Inhibition by clavulanate 2 2d D Cloxacillin- (oxacillin)- hydrolyzing enzymes +/- 2e A Cephalosporinases, confer resistance to monobactams + 2f Carbapenem-hydrolyzing enzymes with active site serine (serine based carbapenemases) 3 3a, 3b, 3c B Metallo--lactamases (zinc based carbapenemases), confer resistance to carbapenems and all -lactam classes, except monobactams. - 4 Miscellaneous unsequenced enzymes that do not fit into other groups Functional group classified by Bush-Jacoby-Medeiros. Molecular group classified by Ambler. Functional classification (Bush-Jacoby-Medeiros: 1-4) – spectrum of ATB substrate profile, enzyme inhibitor profile, enzyme net charge, hydrolysis rate, binding affinity, isoelectric focusing, protein molecular weight, amino acid composition Molecular classification (Ambler’s classification: A-D) – nucleotide and amino acid sequence
Selected -lactamases of gram-negative bacteria Examples Substrates Inhibition by clavulanate* Ambler’s class / Bush’s class Broad-spectrum TEM-1, TEM-2, SHV-1 Penicillin G, aminopenicillins, carboxypenicillins, piperacillin, narrow-spectrum cephalosporins +++ A / 2b OXA family Broad-spectrum group plus cloxacillin, methicillin, and oxacillin + D / 2d Extended-spectrum TEM family, SHV family Broad-spectrum group plus oxyimino-cephalosporins, and monobactam (aztreonam) ++++ A / 2be CTX-M family Expanded-spectrum group plus, for some enzymes, cefepime A Same as for CTX-M family Others (PER-1, PER-2, BES-1, GES/IBC family, SFO-1, TLA-1, VEB-1, VEB2) Same as for TEM family and SHV family *+, +++ , and ++++ denote relative sensitivity to inhibition. Peterson DL. Am J Med 2006; 119 (6 Suppl 1):S20-8.
Selected -lactamases of gram-negative bacteria Examples Substrates Inhibition by clavulanate* Ambler’s class/ Bush’s class AmpC ACC-1, ACT-1, CFE-1, CMY family, DHA-2, FOX family, LAT family, MIR-1, MOX-1, MOX-2 Expanded-spectrum group plus cephamycins C / 1 Carbapenemase IMP family, VIM family, GIM-1, SPM-1 (metallo-enzymes) cephamycins and carbapenems B / 3 KPC-1, KPC-2, KPC-3 Same as for IMP family, VIM family, GIM-1, and SPM-1 +++ A / 2f OXA-23, OXA-24, OXA-25, OXA-26, OXA-27, OXA-40, OXA-48 + D / 2d *+, +++ , and ++++ denote relative sensitivity to inhibition. Peterson DL. Am J Med 2006; 119 (6 Suppl 1):S20-8.
Common ESBL producers Klebsiella pneumoniae Escherichia coli Proteus mirabilis Enterobacter cloacae Non-typhoidal Salmonella (in some countries)
Common ESBL producers Type Major sources TEM, SHV E. coli, K. pneumoniae Cefotaxime hydrolyzing (CTX-M) S. Typhimurium, E. coli, K. pneumoniae Oxacillin hydrolyzing (OXA) P. aeruginosa PER-1 PER-2 P. aeruginosa, A. baumanii, S. Typhimurium S. Typhimurium VEB-1 E. coli, P. aeruginosa
Mechanisms of resistance The majority of ESBLs are acquired enzymes, encoded by plasmids. Different resistance phenotypes to: Different expression levels Different biochemical characteristics such as activity against specific β-lactams co-presence of other resistance mechanisms (other β-lactamases, efflux, altered permeability)
Survival of the fittest Resistant bacteria survive, susceptible ones die Antibiotics do not cause mutations! Antibiotics can select for the emergence and spread of resistance determinants by two different mechanisms. First, they can select for the appearance of the resistance determinant in a pathogenic species. If resistance emerges due to mutation of a cellular gene, the presence of an antibiotic in a significant concentration in the environment will provide selective advantage for survival of the resistant mutant. Second, the presence of selective concentrations of antibiotics can promote the spread of resistant strains from patient to patient by creating an environment that favours establishment of colonization with these strains. If the human gastrointestinal tract is though of as an intensely competitive environment in which many different species of bacteria compete for a limited number of resources, the presence of a resistance determinant in a given species can be a benefit in that the the level of competition for resources (normally created by the presence of competitors susceptible to the antibiotic) is reduced. In this setting, bacteria that would normally be poor competitors for limited resources can survive and even thrive. Mutant’s progeny overrun Mutant emerges slowly Sensitive cells killed by antibiotic
The Fight PG cell N O LYSIS
The Fight PG β-lactamase cell N O
The Fight PG β-lactamase Inhibitor cell N O
The Fight PG β-lactamase Inhibitor cell N O LYSIS
Sites of infection
Laboratory Detection of ESBL Phenotypic Methods Screening methods Confirmatory Methods Genotypic Methods
CLSI 2013
CLSI 2013
Confirmatory methods 1- Combination disk Uses 2 disks of 3rd cephalosporin alone and combined with clavulanic acid An increase of ≥5 mm in zone inhibition with use of the combination disk Disc with cephalosporin + clavulanic acid Disc with cephalosporin alone
CLSI 2013
CLSI 2013
Positive ESBL Cefotaxime/CA Ceftaz Cefotax Ceftaz/CA Ceftaz/CA Difference > 5 mm Positive ESBL Cefotax/CA Ceftaz Cefotax Cefotaxime/CA Negative ESBL Ceftaz/CA Ceftaz Cefotax jhindler nltn MW tele #2 2005
Difference > 5 mm Ceftazidim Cefotaxim Cefotaxim + Clav Ciftazidim + Clav
Difference > 5 mm Difference > 5 mm
Phenotypic conformation 2- Double disk approximation or double disk synergy Disk of 3rd cephalosporin placed 30 mm from amoxicillin-clavulanic acid Result: Enhanced inhibition (A keyhole or ghost zone)
Ceftriaxone Cefotaxime Amox-clav Ceftazidime Azteonam
Augmentin Cefotaxim Ceftazidim
Augmentin Ceftazidime Cefotaxime
Ceftriaxone Cefotaxime Augmentin
AMC AMC AMC
30 mm distance between discs (center to center) AMC, amoxicillin-clavulanate; CAZ, ceftazidime; CTX, cefotaxime; CRO, ceftriaxone; FEP, cefepime; CPO, cefpirome.
30 mm distance between discs (center to center) AMC, amoxicillin-clavulanate; CAZ, ceftazidime; CTX, cefotaxime; CRO, ceftriaxone; FEP, cefepime; CPO, cefpirome.
Phenotypic conformation 3- Broth Microdilution MIC of 3rd cephalosporin alone and combined with clavulanic acid >3-two fold serial dilution decrease in MIC of either cephalosporin in the presence of clavulanic acid compared to its MIC when tested alone. Ceftazidim MIC =8 μg/mL Ceftazidime + Clavulanate= 1 μg/mL Or MIC ratio≥8 4- MIC broth dilution A decrease in the MIC of the combination of > 3-two fold dilutions
Phenotypic conformation 5- E-test (MIC ESBL strips) Two-sided strip containing cephalosporin on one side and cephalosporin -clavulanic acid on the other MIC ratio ≥8 >8 fold reduction in MIC in presence of CA= ESBL or Phantom zone (deformed ellipse)
Cefotaxime Cefotaxime + clavulanate
Ceftaz MIC =16 MIC= 0.25 Ceftaz/CA jhindler nltn MW tele #2 2005
Other confirmatory methods Cica b-Test uses the chromogenic cephalosporin HMRZ-86,4,5 + inhibitors to determine rapidly whether an isolate has a metallo-β-lactamase (MBL), ESBL, or hyperproduced AmpC enzyme , a control strip with no inhibitor, to detect hydrolysis of extended-spectrum cephalosporins No inhibitor Mercaptoacetic acid to inhibit MBL Clavulanate to inhibit ESBL Boronic acid to inhibit AmpC
Other confirmatory methods Brilliance ESBL agar identification of ESBL-producing E. coli, Klebsiella, Enterobacter, Serratia and Citrobacter group, directly from clinical samples. two chromogens that specifically target enzymes green and blue colonies Negative pink. Proteus, Morganella and Providencia tan-coloured colonies with a brown halo
Other confirmatory methods 6- Automated instruments Measure MICs and compare the growth of bacteria in presence of cephalosporin vs. cephalosporin -clavulanic acid
Vitek ESBL confirmatory test Phoenix ESBL test (BD) Microscan ESBL Panel
Genotypic confirmation Molecular detection PCR RFLP gene sequencing DNA microarray-based method Targets specific nucleotide sequences to detect different variants of TEM and SHV genes
Control strains
Pitfalls in ESBL tests AmpC β-lactamases third-generation cephalosporins: resistance , cephamycins, e.g. a cefoxitin: resistance Cefepime: sensitive. Carbapenemases The presence of ESBLs may also be masked by carbapenemases
ESBLs vs AmpCs ESBLs AmpCs S R Cefoxitin, cefotetan Inhibitors (pip/tazo, amp/sulbactam, amox/clav) S R Cefoxitin, cefotetan Ceftazidime, ceftriaxone Cefepime S/R
Pitfalls in ESBL tests ESBL+ AmpC β -lactamases: Especially in Enterobacter spp., Citrobacter, Morganella, Providencia and Serratia. The AmpC enzymes may be induced by clavulanate (which inhibits them poorly) and may then attack the cephalosporin, masking synergy arising from inhibition of the ESBL.
Pitfalls in ESBL tests Screening criterion for ESBL presence among AmpC‑producing Enterobacter, C. freundii and Serratia is Cefepime MIC > 1 ug/ml (inhibition zone< 26 mm). Use of Cefepime is more reliable to detect these strains because high AmpC production has little effect on cefepime activity.
ESBL+ AmpC Amox-Clav Cefepime
ESBL+ AmpC
ESBL+ AmpC Cefotaxime Cefoxitin Cefipime Augmentin Cefpodoxime + Clavulanic Cefpodoxime Ceftazidime
ESBL+ AmpC ESBL and AmpC ESBL positive clavulanate enhancement present AmpC positive cefepime: S cefoxitin: R
ESBL+ AmpC AmpC Fox: R Clav: R ESBL Zone enhancement
AmpC AmpC cefepime : S cefoxitin : R no clavulanate enhancement= ESBL negative
ESBL+ Carbapenemase ESBL + carbapenemases ESBL positive clavulanate enhancement present carbapenemase production resistance to carbapenem agents
ESBLs and the inoculum effect In vitro: the MICs of cephalosporins rise as the inoculum of ESBL- producing organisms increases. In vivo: Intra-abdominal abscesses and pneumonia are some of the clinical settings where organisms are present in high-inoculum, physicians should avoid cephalosporins if risk of ESBL-producing organism is suspected.
Two antibiograms of ESBL producing strain Two antibiograms of ESBL producing strain. Note the difference in zones and synergistic effect around the amoxicillin-clavulanate pills due to different inoculum concentration.
Reporting If ESBL: Resistant, for all penicillins, cephalosporins, and monobactams Report beta lactam inhibitor drugs as they test. If ESBL is not detected, report drugs as tested.
Treatment Carbapenems are the drugs of choice. Unfortunately, use of carbapenems has been associated with the emergence of carbapenem-resistant bacterial species It may be advisable to use non carbapenem antimicrobials as the first line treatment in the less severe infections with ESBL producing strains.
-lactam/-lactamase inhibitor on treatment of ESBL-producing organisms Most ESBLs are susceptible to clavulanate and tazobactam in vitro, nevertheless some ESBL producers are resistant to -lactamase inhibitor due to Hyperproduction of the ESBLs → overwhelm inhibitor Co-production of inhibitor-resistant penicillinases or AmpC enzyme Relative impermeability of the host strain -lactam/-lactamase inhibitor should not be used to treat serious infections with ESBL-producing organisms.
Summary of cephamycins on treatment of ESBL-producing organisms Limited clinical data Generally effective against Enterobacteriaceae producing TEM-, SHV-, and CTX-M-derived ESBLs Reports of cephamycins resistance development during prolonged therapy Loss of outer membrane porin (porin deficient mutant) Acquisition of plasmid-mediated AmpC -lactamase (ACT-1)
ESBL are Emerging Challenges multiple enzymes High-Risk clones globally disseminated hospital, community acquired High rates Challenge of intestinal carriage extra-human reservoirs
ESBL are more complex Antibacterial choice is often complicated by multi-resistance. Many ESBL producing organisms also express AmpC β-lactamases may be co-transferred with plasmids mediating aminoglycoside resistance. there is an increasing association between ESBL production and fluoroquinolone resistance
Prevention ICU is hot spot Hands of healthcare workers, family, visitors thermometer Ultrasound gel Flag records Education Contact precautions Transfer between wards & hospitals
Still the best way to prevent spread of infections and drug resistance is ……
Prevention Individual patient level Institutional level Avoid use of cephalosporins, aztreonam Avoid unnecessary use of invasive devices Ensure good hand hygiene before and after patient-care activities Institutional level Restrict use of 3rd-generation cephalosporins Isolation of patient Investigate environmental contamination
Recommendations Older agents such as aminoglycosides need reappraisal to spare the selective pressures of a carbapenem. new trials of cephalosporin/β-lactamase inhibitors can be predicted oral carbapenems are urgently needed
Recommendations Empirical treatment strategies may need to be re-thought where there is a significant risk. Use a carbapenem until the infection has been proved NOT to involve an ESBL producer, then to step down to a narrower- spectrum ab .
Recommendations Optimize appropriate use of antimicrobials The right agent, dose, timing, duration, route Help reduce antimicrobial resistance The combination of effective antimicrobial supervision and infection control has been shown to limit the emergence and transmission of antimicrobial-resistant bacteria Dellit TH et al. Clin Infect Dis. 2007;44(2):159–177; . Drew RH. J Manag Care Pharm. 2009;15(2 Suppl):S18–S23; Drew RH et al. Pharmacotherapy. 2009;29(5):593–607.
Take Home Messages ESBL-producing bacterial infection is an emerging problem worldwide. These organisms are associated with multi-drug resistance causing high rate of mortality and treatment failure. The significant risk factors for ESBL-producing bacterial infection are prior use of antibiotics, especially 3rd generation cephalosporins, and critically ill or debilitated patients. Need the ESBL-laboratory testing for establish the problem. Carbapenems is the drug of choice for serious ESBL-producing bacterial infection. Avoiding overuse or misuse of 3rd generation cephalosporins and implementing isolation and contact precaution to prevent and control the ESBL outbreak.
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