Cefepime vs carbapenems for treating third-generation cephalosporin-resistant AmpC ß-lactamase-hyperproducing Enterobacterales bloodstream infections: a multicenter retrospective study.

OBJECTIVES: AmpC ß-lactamase-hyperproducing Enterobacterales (ABLHE) bloodstream infections (BSI) are emerging and leading to therapeutic challenges worldwide. Prescriptions of carbapenems may lead to the emergence of resistance. This study aimed to compare cefepime with carbapenems for the treatment of third-generation cephalosporin-resistant ABLHE BSI. METHODS: This retrospective multicenter study included patients with ABLHE BSI from two tertiary hospitals in France, between July 2017 and July 2022. Non-AmpC-producing Enterobacterales, extended-spectrum ß-lactamase, and carbapenemase-producing Enterobacterales were excluded. Cefepime was prescribed only in case of minimal inhibitory concentration ≤1 mg/l. The primary outcome was 30-day in-hospital mortality from the date of index blood culture. Secondary outcomes were infection recurrence and treatment toxicity. An inverse probability of treatment weighting approach was used to balance the baseline characteristics between the two groups. RESULTS: We analyzed 164 BSI, which included 77 in the cefepime group and 87 in the carbapenem group. In the weighted cohort, the 30-day mortality rates were similar between the cefepime group (23.3%) and the carbapenem group (19.6%) with a relative risk of 1.19 (95% confidence interval, 0.61-2.33 P = 0.614). No significant difference in recurrence or toxicity was found between the two groups. CONCLUSION: This study adds evidence in favor of the use of cefepime for treating third-generation cephalosporin-resistant ABLHE BSI in case of minimal inhibitory concentration ≤ 1 mg/l, which could spare carbapenems.

Antibiotic Resistances of Enterobacteriaceae with Chromosomal Ampc in Urine Cultures: Review and Experience of a Spanish Hospital.

The Enterobacteriaceae Citrobacter freundii, Enterobacter cloacae, Klebsiella aerogenes, Morganella morganii, Providencia stuartii, and Serratia marcescens (CESPM group) produce numerous urinary tract infections (UTIs) which are difficult to treat due to their high multiresistance rate. The objectives of this study were to carry out a systematic review of antibiotic resistances by UTIs and to determine changes over time in urine cultures from a reference hospital in southern Spain. The literature was searched for European data on the resistance rates of each microorganism, and a retrospective cross-sectional descriptive study was performed in samples with suspicion of UTI from patients in Virgen de las Nieves University Hospital (Granada, Spain) between 2016 and the first half of 2021. Among 21,838 positive urine cultures, 1.85% were caused by E. cloacae, 0.77% by M. Morganii, 0.65% by K. aerogenes, 0.46% by C. freundii, 0.29% by P stuartii, and 0.25% by S. marcescens. The lowest resistance rates by microorganism were: E. cloacae to amikacin (3.47%) and imipenem (5.28%); M. morganii to piperacillin-tazobactam (1.79%), cefepime (4.76%), and tobramycin (7.74%); K. aerogenes to tobramycin (3.55%), gentamicin (4.25%), trimethoprim-sulfamethoxazole (4.96%), imipenem (5.75%), and cefepime (6.43%); C. freundii to imipenem (no resistance), nitrofurantoin (1.96%), fosfomycin (2.80%), and ertapenem (6.12%); P. stuartii to cefepime (3.28%) and ceftazidime (3.28%); and S. marcescens to gentamicin (1.8%), ciprofloxacin (3.64%), cefepime (3.70%), piperacillin-tazobactam (3.70%), and trimethoprim-sulfamethoxazole (5.45%). In our setting, CESMP Enterobacteriaceae showed the lowest resistance to piperacillin-tazobactam, cefepime, imipenem, gentamicin, and colistin, which can therefore be recommended for the empirical treatment of UTIs. The COVID-19 pandemic may have had a clinical impact in relation to the increased resistance of E. cloacae and M. morgani to some antibiotics.

Characterisation of ESBL/AmpC-Producing Enterobacteriaceae isolated from poultry farms in Peninsular Malaysia.

Extended-spectrum beta-lactamases (ESBLs) and AmpC beta-lactamases (AmpCs)-producing Enterobacteriaceae have been increasingly reported and imposing significant threat to public. Livestock production industry might be the important source for clinically important ESBL-producing Enterobacteriaceae. This study aims to investigate the resistance profile, phenotypic ESBL production, beta-lactamase genes, virulence factors, and plasmid replicon types among 59 Enterobacteriaceae strains isolated from poultry faecal samples in Malaysia's commercial poultry farm. There were 38.7% and 32.3% of Escherichia coli resistant to cefotaxime and cefoxitin, respectively, while Klebsiellaspp. demonstrated resistance rate of 52.6% to both mentioned antimicrobials. Majority of the E. coli isolates carried blaTEM and blaCMY-2 group. blaSHV was the most prevalent gene detected in Klebsiellaspp., followed by blaDHA and blaTEM. Resistance to extended spectrum cephalosporin in our isolates was primarily mediated by plasmid mediated AmpC beta-lactamase such as CMY-2 group and DHA enzyme. The CTX-M genes were found in two ESBL-producing E. coli. IncF, IncI1, and IncN plasmids were most frequently detected in E. coli and Klebsiellaspp. The virulence factor, including EAST1 and pAA were identified at low frequency. This study highlights the poultry as a reservoir of resistance and virulence determinants and prevalence of plasmids in Enterobacteriaceae might drive their dissemination.

Frequency of Beta-Lactamase Antibiotic Resistance Genes in Escherichia Coli and Klebsiella pneumoniae.

BACKGROUND: This cross-sectional study was performed on isolates of Klebsiella pneumoniae, and E.coli from clinical specimens of patients admitted to Sayyad Shirazi Hospital by census sampling method in 2019. Antibiogram testing was performed using the disk diffusion method as defined by the Clinical and Laboratory Standards Organization for performing this test. Finally, the abundance of genes was evaluated by PCR using specific primers. Frequency, percentage, mean±SD were used to describe the data. Chi-square and Fisher's exact tests were used to compare the presence and absence of the studied genes alone and in the presence of each other. RESULT: This study was performed on 130 positive samples, isolated from 32 (24.6%) males and 98 (65.4%) females with a mean age of 43.78 ± 21.72. From the total number of 130 isolates, 84 (64.6%) consisted of E.coli, and 46 (35.4%) were Klebsiella. Most of the cultures were urine and vaginal (61.5%). The highest antibiotic resistance in isolates was cephalexin and cefazolin (67.9% in E.coli & 63% in Klebsiella). Colistin was identified as the most effective antibiotic (100%) in both. AMPC extendedspectrum ß-lactamase genes were present in 40 (30.8%) isolates. The highest frequency about the gene pattern of AMPC positive ß-lactamase bacteria was correlated to DHA, FOX, and CIT genes, while none of the samples contained the MOX ß-lactamase gene. E.coli and Klebsiella beta-lactamase-producing AMPC isolates were also significantly correlated with antibiotic resistance to the cephalosporin class (P <0.05). CONCLUSION: This study indicated a high percentage of resistance to third and fourth generation cephalosporins. Hence, careful antibiogram tests and prevention of antibiotic overuse in infections caused by AMPC-producing organisms and screening of clinical samples for the resistance mentioned above genes and providing effective strategies to help diagnose and apply appropriate treatments and change antibiotic usage strategies can partially prevent the transmission of this resistance.

Broiler Farms and Carcasses Are an Important Reservoir of Multi-Drug Resistant Escherichia coli in Ecuador.

Antimicrobial resistance (AMR) is a major health threat for public and animal health in the twenty-first century. In Ecuador, antibiotics have been used by the poultry industry for decades resulting in the presence of multi-drug resistant (MDR) bacteria in the poultry meat production chain, with the consequent risk for public health. This study evaluated the prevalence of ESBL/AmpC and mcr genes in third-generation cephalosporin-resistant Escherichia coli (3GC-R E. coli) isolated from broiler farms (animal component), broiler carcasses (food component), and human enteritis (human component) in Quito-Ecuador. Samples were collected weekly from November 2017 to November 2018. For the animal, food, and human components, 133, 335, and 302 samples were analyzed, respectively. Profiles of antimicrobial resistance were analyzed by an automated microdilution system. Resistance genes were studied by PCR and Sanger sequencing. From all samples, 122 (91.7%), 258 (77%), and 146 (48.3%) samples were positive for 3GC-R E. coli in the animal, food, and human components, respectively. Most of the isolates (472/526, 89.7%) presented MDR phenotypes. The ESBL bla CTX-M-55, bla CTX-M-3, bla CTX-M-15, bla CTX-M-65, bla CTX-M-27, and bla CTX-M-14 were the most prevalent ESBL genes while bla CMY-2 was the only AmpC detected gene. The mcr-1 gene was found in 20 (16.4%), 26 (10.1%), and 3 (2.1%) of isolates from animal, food, and human components, respectively. The implication of poultry products in the prevalence of ESBL/AmpC and mcr genes in 3GC-R must be considered in the surveillance of antimicrobial resistance.

Investigation of plasmid mediated AmpC beta-lactamases in Escherichia coli and Klebsiella pneumoniae isolates by phenotypic and genotypic.

OBJECTIVE: To investigate the susceptibility and specificity of the phenotypic methods to determine plasmidmediated AmpC. METHODS: The cross-sectional study was conducted at Duzce University Faculty of Medicine, Microbiology Laboratory from January 2015 to June 2016, and comprised Escherichia coli and Klebsiella pneumonia isolates intermediate susceptible or resistant to cefoxitine. Combined disk diffusion test, double disc synergy test, agar gradient test and polymerase chain reaction were used to detect plasmid-mediated AmpC. RESULTS: Of the 2024 E. coli samples, 44(2.17%), and of the 792 K. pneumoniae samples, 16(2%) were included. Combined disk diffusion test had susceptibility of 68% and specificity of 50%; double disc synergy test 24% and 82%; and agar gradient test 40% and 68%. Of the isolates positively detected by polymerase chain reaction method, more than one gene region positivity was detected in 15(25%) isolates. CONCLUSION: All three phenotypic methods were found to be insufficient to detect plasmid-mediated AmpC positivity.

Plasmid-mediated resistance is going wild.

Multidrug resistant (MDR) Gram-negative bacteria have been increasingly reported in humans, companion animals and farm animals. The growing trend of plasmid-mediated resistance to antimicrobial classes of critical importance is attributed to the emergence of epidemic plasmids, rapidly disseminating resistance genes among the members of Enterobacteriaceae family. The use of antibiotics to treat humans and animals has had a significant impact on the environment and on wild animals living and feeding in human-influenced habitats. Wildlife can acquire MDR bacteria selected in hospitals, community or livestock from diverse sources, including wastewater, sewage systems, landfills, farm facilities or agriculture fields. Therefore, wild animals are considered indicators of environmental pollution by antibiotic resistant bacteria, but they can also act as reservoirs and vectors spreading antibiotic resistance across the globe. The level of resistance and reported plasmid-mediated resistance mechanisms observed in bacteria of wildlife origin seem to correlate well with the situation described in humans and domestic animals. Additionaly, the identification of epidemic plasmids in samples from different human, animal and wildlife sources underlines the role of horizontal gene transfer in the dissemination of resistance genes. The present review focuses on reports of plasmid-mediated resistance to critically important antimicrobial classes such as broad-spectrum beta-lactams and colistin in Enterobacteriaceae isolates from samples of wildlife origin. The role of plasmids in the dissemination of ESBL-, AmpC- and carbapenemase-encoding genes as well as plasmid-mediated colistin resistance determinants in wildlife are discussed, and their similarities to plasmids previously identified in samples of human clinical or livestock origin are highlighted. Furthermore, we present features of completely sequenced plasmids reported from wildlife Enterobacteriaceae isolates, with special focus on genes that could be associated with the plasticity and stable maintenance of these molecules in antibiotic-free environments.

Piperacillin-Tazobactam versus Other Antibacterial Agents for Treatment of Bloodstream Infections Due to AmpC ß-Lactamase-Producing Enterobacteriaceae.

In vivo induction of AmpC beta-lactamases produces high-level resistance to many beta-lactam antibiotics in Enterobacteriaceae, often resulting in the need to use carbapenems or cefepime (FEP). The clinical effectiveness of piperacillin-tazobactam (TZP), a weak inducer of AmpC beta-lactamases, is poorly understood. Here, we conducted a case-control study of adult inpatients with bloodstream infections (BSIs) due to Enterobacter, Serratia, or Citrobacter species from 2009 to 2015 to assess outcomes following treatment with TZP compared to FEP or meropenem (MEM). We collected clinical data and screened all isolates for the presence of ampC alleles by PCR. Primary study outcomes were 30-day mortality and persistent bacteremia at ≥72 h from the time of treatment initiation. Of 493 patients with bacteremia, 165 patients met the inclusion criteria, of which 88 were treated with TZP and 77 with FEP or MEM. To minimize differences between covariates, we carried out propensity score matching, which yielded 41 matched pairs. Groups only differed by age, with patients in the TZP group significantly older (P = 0.012). There were no significant differences in 30-day mortality, persistent bacteremia, 7-day mortality, or treatment escalation between the two treatment groups, including in the propensity score-matched cohort. PCR amplification and sequencing of ampC genes revealed the presence of ampC in isolates with cefoxitin MICs below 16 µg/ml, in particular in Serratia spp., and demonstrated that these alleles were highly genetically diverse. Taken together, TZP may be a valuable treatment option for BSIs due to AmpC beta-lactamase-producing Enterobacteriaceae, diminishing the need for broader-spectrum agents. Future studies are needed to validate these findings.

Beta-lactamases in Enterobacteriaceae infections in children.

Multi-drug resistance in Gram negative bacteria, particularly in Enterobacteriaceae, is a major clinical and public health challenge. The main mechanism of resistance in Enterobacteriaceae is linked to the production of beta-lactamase hydrolysing enzymes such as extended spectrum beta-lactamases (ESBL), AmpC beta-lactamases and carbapenemases (Carbapenemase Producing Enterobacteriaceae (CPE)). ESBL and CPE resistance genes are located on plasmids, which can be transmitted between Enterobacteriaceae, facilitating their spread in hospitals and communities. These plasmids usually harbour multiple additional co-resistance genes, including to trimethoprim-sulfamethoxazole, aminoglycosides, and fluoroquinolones, making these infections challenging to treat. Asymptomatic carriage in healthy children as well as community acquired infections are increasingly reported, particularly with ESBL. Therapeutic options are limited and previously little used antimicrobials such as fosfomycin and colistin have been re-introduced in clinical practice. Paediatric experience with these agents is limited hence there is a need to further examine their clinical efficacy, dosage and toxicity in children. Antimicrobial stewardship along with strict infection prevention and control practices need to be adopted widely in order to preserve currently available antimicrobials. The future development of novel agents effective against beta-lactamases producers and their applicability in children is urgently needed to address the challenge of multi-resistant Gram negative infections.

Emergence of third-generation cephalosporin-resistant Enterobacteriacae in a Japanese critical care setting.

AIM: Extended-spectrum beta-lactamases and AmpC beta-lactamases give resistance to Enterobacteriaceae against cephalosporins, which are important drugs in various clinical settings. Within 5 days, a total of eight strains of Citrobacter freundii and two strains of Escherichia coli, all of which were resistant to third-generation cephalosporins, were isolated from six different patients in a critical care center. We carried out epidemiological and genetic studies to confirm the situation to be an outbreak by a single strain or a beta-lactamase-producing gene. METHODS: A review of patients' clinical data, pulsed-field gel electrophoresis epidemiological study against the strains, and polymerase chain reaction analysis for the detection of extended-spectrum beta-lactamase genes (TEM, SHV, CTX-M-1, CTX-M-2, and CTX-M-9) and multiplex polymerase chain reaction analysis for plasmid-mediated AmpC-beta-lactamase genes were carried out. RESULTS: Pulsed-field gel electrophoresis showed none of the subjects were genetically identical organisms. However, all strains possessed either extended-spectrum beta-lactamases (TEM, CTX-M-2, and CTX-M-9) or AmpC-beta-lactamases. One patient carried both extended-spectrum beta-lactamase- and AmpC- beta-lactamase-producing organisms. CONCLUSION: This study revealed that various types of easily transmittable drug resistance genes exist in the critical care setting concurrently. This case was not an outbreak of such strains, but the present situation might indicate a more serious condition than a mere outbreak of a single resistant strain. Enterobacteriaceae that possess extended-spectrum beta-lactamases or AmpC-beta-lactamases are increasingly common in many medical institutions in Japan, and constitutive monitoring of drug-resistant organisms and proper contact precautions are essential to prevent possible outbreaks.

Detection of ESBL among AmpC producing enterobacteriaceae using inhibitor-based method.

INTRODUCTION: The occurrence of multiple ß-lactamases among bacteria only limits the therapeutic options but also poses a challenge. A study using boronic acid (BA), an AmpC enzyme inhibitor, was designed to detect the combined expression of AmpC ß-lactamases and extended-spectrum ß-lactamases (ESBLs) in bacterial isolates further different phenotypic methods are compared to detect ESBL and AmpC. METHODS: A total of 259 clinical isolates of Enterobacteriaceae were isolated and screened for ESBL production by (i) CLSI double-disk diffusion method (ii) cefepime- clavulanic acid method (iii) boronic disk potentiation method. AmpC production was detected using cefoxitin alone and in combination with boronic acid and confirmation was done by three dimensional disk methods. Isolates were also subjected to detailed antibiotic susceptibility test. RESULTS: Among 259 isolates, 20.46% were coproducers of ESBL and AmpC, 26.45% were ESBL and 5.40% were AmpC. All of the 53 AmpC and ESBL coproducers were accurately detected by boronic acid disk potentiation method. CONCLUSION: The BA disk test using Clinical and Laboratory Standards Institute methodology is simple and very efficient method that accurately detects the isolates that harbor both AmpCs and ESBLs.

An Increase in the Clinical Isolation of Acquired AmpC beta-Lactamase-Producing Klebsiella pneumoniae in Korea from 2007 to 2010

We investigated the occurrence and genetic basis of AmpC beta-lactamase (AmpC)-mediated antibiotic resistance, by examining Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis isolates at a university hospital, from 2007 to 2010. The ampC genes were detected by multiplex AmpC PCR, and AmpC-positive strains were subjected to DNA sequencing. Extended-spectrum beta-lactamase (ESBL) production was assessed using the ESBL disk test based on the utilization of boronic acid. Carbapenem-resistant isolates were further investigated by the modified Hodge test, a carbapenemase inhibition test and SDS-PAGE experiments. AmpC expression was detected in 1.6% of E. coli (39 DHA-1, 45 CMY-2, and 1 CMY-1) isolates, 7.2% of K. pneumoniae (39 DHA-1, 45 CMY-2, and 1 CMY-1) isolates, and 2.5% of P. mirabilis (8 CMY-2 and 1 CMY-1) isolates. Of the 198 acquired AmpC producers, 58 isolates (29.3%) also produced an ESBL enzyme. Among the acquired AmpC-producing K. pneumoniae isolates, the minimum inhibitory concentration (MIC) MIC50/MIC90 values for cefoxitin, cefotaxime, cefepime, imipenem, and meropenem were >32/>32, 16/>32, 1/16, 0.25/0.5, and or =2 microg/mL for 2 K. pneumoniae isolates, both of which carried the blaDHA-1 gene with a loss of OmpK36 expression, but were negative for carbapenemase production. The acquisition of AmpC-mediated resistance in K. pneumoniae isolates increased, as did the proportion of AmpC and ESBL co-producers among the hospital isolates. The accurate identification of isolates producing AmpCs and ESBLs may aid in infection control and will assist physicians in selecting an appropriate antibiotic regimen.

Celulitis facia odontogénica severa infrecuent causada por citrobacter freunddii productora de ampc en un paciente con diabetes mellitus 2. reporte de caso / Uncmmon severe oodontogenic facial cellulitis caused by ampcproducing citrobacter freundii in a patient with type 2 diabetes mellitus. case report / Celulite facial odontogênica sevea infrequente causada por citrobacter freundii produtora de ampc em um paciente com diabetes mellitus 2. relatório e caso

El manejo de la celulitis facial odontogénica no deja de ser un tema controversial en el campo de la cirugía oral y maxilofacial; los principios quirúrgicos y terapéuticos han sido sometidos a modificacio nes basadas en los hallazgos clínicos, imagenológicos y microbiológicos a través del tiempo. En pacientes con diabetes mellitus 2 se incrementa el riesgo a sufrir infecciones bacterianas oportunistas con tiempos de hospitalización más prolongados que la población no diabética. La literatura es clara estableciendo las diferencias clínicas y microbiológicas de la celulitis facial odontogénica en este grupo de pacientes, sin embargo, no existe un protocolo médico quirúrgico destinado a ellos. El microorganismo comúnmente aislado es Klebsiella pneumoniae, mientras Citrobacter freundii es inusual en las infecciones odontogénicas, su capacidad para producir betalactamasas de amplio espectro (AmpC) le permite bloquear la acción de los antibióticos de uso empírico en Cirugía Oral y Maxilofacial. A continuación, presentamos el caso de una paciente de 61 años con diabetes Mellitus tipo 2 y celulitis facial odontogénica por Citrobacter freundii productora de AmpC.

The management of odontogenic facial cellulitis is still a controversial issue in the field of Oral and Maxillofacial Surgery. Surgical and therapeutic principles have undergone modifications based on clinical findings, imaging and microbiological over time. In patients with type 2 Diabetes Mellitus the risk of opportunistic bacterial infections is increased thus suffering longer hospitalization periods than the nondiabetic population. The literature is clear by setting the clinical and microbiological differences of odontogenic facial cellulitis in this group of patients, but there is no surgical medical protocol for them. Klebsiella pneumoniae is the most common microorganism isolated while Citrobacter freundii is unusual in relation to oral infections; their ability to produce ESBLs (AmpC) allows them to block the action of empirical antibiotics used in Maxillofacial Surgery. We present the case of a 61 year old patient with type 2 Diabetes Mellitus and odontogenic facial cellulitis caused by AmpCproducing Citrobacter freundii.

O tratamento da celulite facial odontogênica não deixa de ser um tema controverso no campo da Cirurgia Oral e Maxilofacial; os princípios cirúrgicos e terapêuticos foram submetidos a modificações baseadas nos descobrimentos clínicos, imagenológicos e microbiológicos através do tempo. Em pacientes com Diabetes Mellitus 2 aumenta o risco de sofrer infecções bacterianas oportunistas com tempos de hospitalização mais prolongados que na população não diabética. A literatura é clara estabelecendo as diferenças clínicas e microbiológicas da Celulite Facial Odontogênica neste grupo de pacientes; porém, não existe um protocolo médico cirúrgico destinado a eles. O microrganismo comunmente isolado é o Klebsiella pneumoniae, enquanto que o Citrobacter freundii é inusual nas infecções odontogênicas, sua capacidade para produzir betalactamases de amplo espectro (AmpC) lhe permite bloquear a ação dos antibióticos de uso empírico em Cirurgia Oral e Maxilofacial. A seguir apresentamos o caso de uma paciente de 61 anos com Diabetes Mellitus tipo 2 e celulite facial odontogênica por Citrobacter freundii produtora de AmpC.

Evaluation of the MicroScan NegCombo Panel Type 44 for Detection of Extended-Spectrum beta-Lactamase among Clinical Isolates of Escherichia coli, Klebsiella species, and Proteus mirabilis / 대한진단검사의학회지

BACKGROUND: Accurate and rapid detection of extended-spectrum beta-lactamases (ESBLs) is important in guiding proper antimicrobial therapy for infected patients. We evaluated the performance of MicroScan NegCombo Type 44 panel (Dade Behring, USA), which was developed to confirm ESBL-producing Enterobacteriaceae using ceftazidime/clavulanate and cefotaxime/clavulanate. METHODS: From August 30 to September 20, 2007, 206 non-duplicate clinical isolates, including 106 Escherichia coli, 81 Klebsiella pneumoniae, 11 Klebsiella oxytoca, and 8 Proteus mirabilis were subcultured and tested with Type 32 and Type 44 panels. The results were compared with those of the CLSI phenotypic confirmatory test (CLSI-PCT) and disk approximation test (DAT). Isolates not susceptible to cefotetan or flagged as "Possible ESBL, unable to interpret confirm test (Possible ESBL)" on Type 44 panel were tested with boronic acid disks to confirm AmpC beta-lactamases (AmpC) production. RESULTS: Of the 206 isolates tested, 44 (21.4%) produced ESBL by CLSI-PCT or DAT, including 27 E. coli, 14 K. pneumoniae, 2 K. oxytoca, and 1 P. mirabilis. Thirty-eight isolates flagged as "Confirmed ESBL" on Type 44 panel were all confirmed as ESBL-producers. Of 14 K. pneumoniae flagged as "Possible ESBL", 6 were confirmed as ESBL and AmpC co-producers and 8 as AmpC-producers. CONCLUSIONS: Type 44 panel showed an excellent performance in detecting ESBL-producing E. coli, Klebsiella spp., and P. mirabilis. When flagged as "Confirmed ESBL", no other confirmatory test was necessary to report as ESBL; however, "Possible ESBL" required a differential test for AmpC production.

New Method for Detecting Plasmid-mediated AmpC Beta-lactamases / 中华医院感染学杂志

OBJECTIVE To establish a convenient method for detecting plasmid-mediated AmpC beta-lactamases in Enterobacteriaceae lacking chromosomal AmpC beta-lactamases and to investigqte their genotype.METHODS Fifteen isolates of Klebsiella pneumoniae were collected and the diameters of inhibitory zone of cefoxitin in combination with or without cloxacillin were measured separately by standard disc diffusion test.The M3D assay was used as control method.And the activity of AmpC beta-lactamases of all isolates was simultaneously assayed.Multiplex PCR was performed to determine the genotype of AmpC beta-lactamases.RESULTS Among 15 isolates,8 isolates were identified to have plasmid-mediated AmpC beta-lactamases.The sensitivity and specificity of AmpC beta-lactamases phenotypic confirmatory test were 100%.Eight of 15 isolates were identified to be DHA-1 beta-lactamases by multiplex PCR.CONCLUSIONS The new AmpC beta-lactamases phenotypic confirmatory test is a reliable method for detecting plasmidmediated AmpC beta-lactamases in Enterobacteriaceae lacking chromosomal AmpC beta-lactamases.DHA-1 beta-lactamases are the main genotypes of plasmid-mediated AmpC beta-lactamases in Hubei Province of China.

Plasmid-encoded AmpC beta-lactamases: how far have we gone 10 years after the discovery?

The dogma that ampC genes are located exclusively on the chromosome was dominant until about 10 years ago. Since 1989 over 15 different plasmid-encoded AmpC beta-lactamases have been reported from several countries. Most of these enzymes evolved in two clusters. The major cluster includes several enzymes with a high similarity to CMY-2, which is the closest related chromosomal AmpC enzyme of Citrobacter freundii. A second cluster centers around CMY-1. It is less homogeneous and not closely related chromosomal AmpC enzymes. Molecular diversification by amino acid substitutions does not usually translate into a change in the resistance phenotype. At this time, CMY-2 appears to be the most prevalent and widely distributed. Further global increase of prevalence and diversity of plasmidic AmpC beta-lactamases have to be anticipated in the next millenium.