ESBL Producers An Increasing Problem: An Overview Of An Underrated Threat

Transcription

1 ESBL Producers An Increasing Problem: An Overview Of An Underrated Threat Hicham Ezzat Professor of Microbiology and Immunology Cairo University

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3 Introduction 1 Since the 1980s there have been dramatic shifts towards use of cephalosporins and fluoroquinolones with optimism that they would escape resistance. Unfortunately, such optimism proved to be miaplaced. The pressure of the wide and heavy use of the drugs greatly affects the resistance of bacteria causing both nosocomial and community acquired infections

4 Introduction 2 Nosocomial G-ve bacteria infections (Enteric and non fermenters) Nosocomial pneumonia is frequently associated with intubation and respiratory assistance (Ventilator associated pneumonia). Nosocomial urinary tract infections are associated with urinary catheters. Blood stream infections often arise by overspill but may arise directly with the use of intravenous lines. Wound infections.

5 Introduction 3 Community acquired G-ve bacteria infections (Enteric and non fermenters) Most bacteria causing community acquired infections accumulate resistance more slowly. However, nosocomial organisms and resistance patterns may be seen in community acquired infections.

6 Introduction 4 First described in 1983, extended-spectrum β- lactamases (ESBLs) have contributed to the dramatic increase in resistance to β-lactam agents among gram-negative bacteria. These enzymes, encoded by genes that are typically plasmid borne, hydrolyze penicillins, cephalosporins and aztreonam and are inhibited by clavulanic acid.

7 Introduction 5 Although most commonly produced by Escherichia coli and Klebsiella spp., ESBLs may be harbored by many other gram-negative bacilli as well, including but not limited to many other bacteria in the family Enterobacteriaceae. G-ve microorganisms produce extended spectrum ß-lactamases, which result in resistance to a broad range of ß-lactam antibiotics.

8 Introduction 6 Broad-spectrum β-lactam resistance among gram-negative pathogens is associated with treatment failure in the form of increased mortality, increased length of hospitalization and elevated medical costs. In general, the fourth-generation cephalosporin, cefepime, is clinically useful against organisms producing Amp C-type β- lactamases, but may be less useful in treating ESBL producing organisms.

9 Definition 1 ESBLs are enzymes that mediate resistance to extended-spectrum (third generation) cephalosporins (e.g., ceftazidime, cefotaxime, and ceftriaxone) and monobactams (e.g., aztreonam) but do not affect cephamycins (e.g., cefoxitin and cefotetan) or carbapenems (e.g., meropenem or imipenem). CDC

10 Definition 2 There is no consensus of the precise definition of ESBLs. A commonly used working definition is that the ESBLs are ß-lactamases capable of conferring bacterial resistance to the penicillins, first-, second-, and third-generation cephalosporins, and aztreonam (but not the cephamycins or carbapenems) by hydrolysis of these antibiotics, and which are inhibited by ß- lactamase inhibitors such as clavulanic acid.

11 Origin and Nature of ESBLs 1 Resistance to cephalosporins and other β-lactams may be due to production of β-lactamase enzymes, impermeability, efflux, target modification or combination. Old β-lactamase enzymes: TEM-1 is the most common plasmid-mediated β-lactamase of ampicillin resistant enteric gram-negative bacilli (for example, Escherichia coli), while SHV-1 is produced by the vast majority of Klebsiella pneumoniae. TEM-2 is a less common member of the same group with identical biochemical properties to TEM-1.

12 Origin and Nature of ESBLs 2 β-lactamase-mediated resistance to β-lactam antibiotics resulted from fundamental changes in the substrate spectra of the enzymes. Most of the currently known ESBLs are derived from the older β-lactamases. The ESBLs derived from TEM-1, TEM-2, or SHV-1 differ from their progenitors by as few as one amino acid. This results in a profound change in the enzymatic activity of the ESBLs, so that they can now hydrolyze the third-generation cephalosporins or aztreonam (hence the extension of spectrum compared to the parent enzymes).

13 Groups of ESBLs The SHV-type ESBLs may be more frequently found in clinical isolates than any other type of ESBLs. The TEM-type ESBLs are derivatives of TEM-1 and TEM-2. CTX-M enzymes are also inhibited by CA and are in the category of ESBLs. In addition, some of the enzymes of the OXA family, although belonging to functional group 2d, show a CA effect and are considered ESBLs. VEB & PER

14 Epidemiology Intensive care units are often centers of ESBL production in hospitals. Intensive care units in tertiary referral hospitals may acquire patients already colonized with ESBL producing organisms, thereby triggering an outbreak of infection. Extended-spectrum β-lactamase (ESBL) producing gram-negative bacilli are endemic in hospitals. In intensive care units, 2% prevalence of ESBLproducing organisms has been reported. Extended-spectrum β-lactamase producing flora in healthy persons 7-11% without known risk factors

15 Risk factors Nosocomial Intensive/Critical care units Prolonged hospital stays Invasive medical devices Heavy antibiotic (3 rd and 2 nd cephalosporinsaztreonam)) Community Heavy antibiotic (3 rd and 2 nd cephalosporinsaztreonam-quinolones-penicillins) Hospital in last 3 months Old age and diabetes

16 Source of Outbreaks A common environmental source of ESBL-producing organisms has occasionally been discovered. Examples have included contamination of ultrasonography coupling gel, bronchoscopes, blood pressure cuffs, and glass thermometers.esbl-producing organisms have been isolated from patients soap, sink basins, and babies baths, but the contribution of this environmental contamination to infection was impossible to determine. Present evidence suggests that transient carriage on the hands of health care workers is a more important means of transfer from patient to patient.

17 Detection of ESBLs 1 Why should clinical laboratory personnel be concerned about detecting these enzymes? The presence of an ESBL-producing organism in a clinical infection can result in treatment failure if one of the previously mentioned classes of drugs is used. ESBLs can be difficult to detect because they have different levels of activity against various cephalosporins. Thus, the choice of which antimicrobial agents to test is critical. For example, one enzyme may actively hydrolyze ceftazidime, resulting in ceftazidime minimum inhibitory concentrations (MICs) of 256 µg/ml, but have poor activity on cefotaxime, producing MICs of only 4 µg/ml. If an ESBL is detected, all penicillins, cephalosporins, and aztreonam should be reported as resistant, even if in vitro test results indicate susceptibility.

18 Detection of ESBLs 2 While a variety of phenotypic and molecular methods have been successfully employed to confirm the presence of ESBLs in clinical isolates, their use is rather labor-intensive to be practical for routine screening in microbiology laboratories. There are CLSI guidelines for ESBL detection. CLSI guidelines apply only to Escherichia coli, Klebsiella spp., and Proteus mirabilis.

19 Detection of ESBLs 3 How can clinical laboratory personnel screen for ESBL production in bacteria? Screening tests for resistance Expanded screening to include special breakpoints for the three previously included antimicrobials, two cephalosporins (ceftazidime, cefpodoxime), and aztreonam, but also cefotaxime and ceftriaxone. Confirmatory tests Confirmatory testing methods for potential ESBLsproducing isolates by testing both cefotaxime and ceftazidime, alone and in combination with clavulanic acid. Testing can be performed by the broth microdilution method or by disk diffusion

20 Screening tests for ESBLs CLSI recommendations for each antibiotic should be followed (Disk inhibition or MIC). The sensitivity of screening for ESBLs in enteric organisms can vary depending on which antimicrobial agents are tested. The use of more than one of the five antimicrobial agents suggested for screening will improve the sensitivity of detection. Cefpodoxime and ceftazidime show the highest sensitivity for ESBL detection.

21 Confirmatory tests for ESBLs Phenotypic confirmation of potential ESBL-producing isolates of K. pneumoniae, K. oxytoca, or E. coli by testing both cefotaxime and ceftazidime, alone and in combination with clavulanic acid. Testing can be performed by the broth microdilution method or by disc diffusion. For MIC testing, a decrease of > 3 doubling dilutions in an MIC for either cefotaxime or ceftazidime tested in combination with 4 µg/ml clavulanic acid, versus its MIC when tested alone, confirms an ESBL-producing organism. For disc diffusion testing, a > 5 mm increase in a zone diameter for either antimicrobial agent tested in combination with clavulanic acid versus its zone when tested alone confirms an ESBL-producing organism.

22 Diffusion tests Combination discs CLSI conventional recommendations (special care with controls) Double disc synergy Major advantages of the double-disc diffusion test are that is technically simple and discs are available. However, the interpretation of the test is quite subjective and some producers may be missed. E test Reduction of MIC 8 fold

23 Dilution tests Reduction of MIC 8 fold by any agar or broth dilution synergy tests.

24 Quality Control for ESBL detection K. pneumoniae ATCC (positive control) and E. coli ATCC (negative control) should be used for quality control of ESBL tests. This is critical for combination discs.

25 Semiautomated Systems The system with the highest sensitivity for the detection of ESBLs was the Phoenix (99%), followed by the VITEK 2 (86%) and the MicroScan (84%); however, specificity was more variable, ranging from 52% (Phoenix) to 78% (VITEK 2). The performance of the semiautomated systems differed widely with the species investigated. The sensitivities of the conventional test methods ranged from 93 to 94%. The double-disk synergy test showed the highest specificity and positive predictive value among all test methods, i.e., 97% and 98%, respectively.

26 Interpretation and Reporting If an isolate is confirmed as an ESBL-producer by the CLSI-recommended phenotypic confirmatory test procedure, all penicillins, cephalosporins, and aztreonam should be reported as resistant. This list does not include the cephamycins (cefotetan and cefoxitin), which should be reported according to their routine test results. If an isolate is not confirmed as an ESBL-producer, current recommendations suggest reporting results as for routine testing. Do not change interpretations of penicillins, cephalosporins, and aztreonam for isolates not confirmed as ESBLs.

27 Treatment Recommendations None Carbapenems Quinolones Regimen Tigecycline, colistin or polymyin B Colonization Condition Blood stream infection VAP Complicated UTI Intra-abdominal infection Diabetic foot infection? If allergic to carbapenem Resistance or allergy to others

28 Infection Control Interventions Identify patients infected with ESBL-producing organisms by use of appropriate detection methods in the clinical microbiology laboratory Identify colonized patients by use of rectal swabs plated onto selective media Perform molecular epidemiologic analysis of strains from infected or colonized patients (for example, by use of pulsed-field gel electrophoresis) Institute contact isolation precautions, particularly if clonal spread is demonstrated Institute controls on antibiotic use, particularly if numerous strain types are demonstrated

29 ESBL Producers Underrating ESBL production not thought ESBL production not looked for ESBL production not reported ESBL producers treated accidentally ESBL producers propagated ESBL producers recognized as a major cause of nosocomial infections in all types of hospitals and health care centres very late if at all Industry partners role lacking or much delayed

30 Conclusion and Recommendations ESBL production thought, properly looked for, reported and ESBL producers treated. Infection control measures to prevent and control spread of ESBL producers. Alteration of antibiotic susceptibility breakpoints may become necessary but need to be carefully considered in combination with pharmacokinetic, pharmacodynamic, and clinical data.

31 Suggested Bibliography Paterson and Bonomo (Review) Livermore and Paterson CDC publications. CLSI 2005.

32 Thank You