Carbapenem resistance in Escherichia coli associated with plasmid-determined CMY-4 beta-lactamase production and loss of an outer membrane protein

Multidrug-Resistant and Extensively Drug-Resistant Escherichia coli in Sewage in Kuwait: Their Implications

In Kuwait, some sewage is discharged into the sea untreated, causing a health risk. Previously, we investigated the presence of pathogenic E. coli among the 140 isolates of E. coli cultured from the raw sewage from three sites in Kuwait. The aim of the current study was to characterize the antimicrobial resistance of these isolates and the implications of resistance. Susceptibility to 15 antibiotic classes was tested. Selected genes mediating resistance to cephalosporins and carbapenems were sought. ESBL and carbapenemase production were also determined. Two virulent global clones, ST131 and ST648, were sought. A total of 136 (97.1%), 14 (10.0%), 128 (91.4%), and 2 (1.4%) isolates were cephalosporin-resistant, carbapenem-resistant, multidrug-resistant (MDR), and extensively drug-resistant (XDR), respectively. Among the cephalosporin-resistant isolates, ampC, blaTEM, blaCTX-M, blaOXA-1, and blaCMY-2 were found. Eighteen (12.9%) samples were ESBL producers. All carbapenem-resistant isolates were negative for carbapenemase genes (blaOXA-48, blaIMP, blaGES, blaVIM, blaNDM, and blaKPC), and for carbapenemase production. Resistance rates in carbapenem-resistant isolates to many other antibiotics were significantly higher than in susceptible isolates. A total of four ST131 and ST648 isolates were detected. The presence of MDR and XDR E. coli and global clones in sewage poses a threat in treating E. coli infections.

The Genetic Characteristics and Carbapenem Resistance Mechanism of ST307 Klebsiella pneumoniae Coharbouring blaCMY-6, blaOXA-48, and a Truncated blaNDM-1

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a common nosocomial pathogen causing severe infectious diseases, and ST307 CRKP is an emerging clone. In this study, we collected five ST307 CRKP isolates, evaluated their antimicrobial susceptibility using microbroth dilution, and their clonality and population structure by PFGE, cgMLST, and SNP-based phylogenetic analysis. Then, the genome characteristics, such as antimicrobial resistance genes and plasmid profiles, were studied by subsequent genomic analysis. The plasmid transfer ability was evaluated by conjugation, and the carbapenem resistance mechanism was elucidated by gene cloning. The results showed that all five ST307 CRKP isolates harboured blaCMY-6, blaOXA-48, and blaNDM-1; however, the end of the blaNDM-1 signal peptide was interrupted and truncated by an IS10 element, resulting in the deactivation of carbapenemase. The ST307 isolates were closely related, and belonged to the globally disseminated clade. blaOXA-48 and blaNDM-1 were located on the different mobilisable IncL/M- and IncA/C2-type plasmids, respectively, and either the pOXA-48 or pNDM-1 transconjugants were ertapenem resistant. Gene cloning showed that blaCMY-6 could elevate the MICs of carbapenems up to 64-fold and was located on the same plasmid as blaNDM-1. In summary, ST307 is a high-risk clone type, and its prevalence should be given additional attention.

Carbapenemase Production and Detection of Colistin-Resistant Genes in Clinical Isolates of Escherichia Coli from the Ho Teaching Hospital, Ghana

Background

Effective and successful treatment of infectious diseases is a significant gain in clinical settings. However, resistance to antibiotics, especially the last-resort medicines, including carbapenems and colistin is on the rise.

Aim

The aim of this study was to detect carbapenemase production and colistin-resistant genes in clinical isolates of Escherichia coli. Method. The study was a cross-sectional study carried out from July 2018 to June 2019. One hundred and thirty-five nonrepetitive E. coli isolates obtained from various clinical samples were screened for carbapenemase production using meropenem (10 μg) and imipenem (10 μg) disks. Screened-positive isolates were further subjected to a confirmatory test using modified carbapenem inhibition method (mCIM). Deoxyribonucleic acid (DNA) was extracted from all the isolates to detect colistin-resistant genes by polymerase chain reaction. Data were analyzed using GraphPad Prism version 8.00 for Windows and IBM SPSS version 26 (IMB Corp. New York, USA).

Results

Of the 135 isolates, 2 were screened positive for carbapenemase production but tested negative to mCIM. With the colistin-resistant genes, only mcr-1 and mcr-2_700bp were detected in 3 of the E. coli isolates, representing 2.2%. The mcr-1 was detected in a high vaginal swab sample of a female aged between 65 and 84 years. Mcr-2_700bp was also detected in urine and blood samples of the patients.

Conclusion

The study investigated the presence of carbapenemase and colistin-resistant genes in E. coli organisms. The absence of carbapenemase in the isolates and the detection of colistin-genes call for strict infection prevention and control practices to prevent their introduction and spread to other bacterial species, respectively.

Detection of multi-resistant clinical strains of E. coli with Raman spectroscopy

In recent years, we have seen a steady rise in the prevalence of antibiotic-resistant bacteria. This creates many challenges in treating patients who carry these infections, as well as stopping and preventing outbreaks. Identifying these resistant bacteria is critical for treatment decisions and epidemiological studies. However, current methods for identification of resistance either require long cultivation steps or expensive reagents. Raman spectroscopy has been shown in the past to enable the rapid identification of bacterial strains from single cells and cultures. In this study, Raman spectroscopy was applied for the differentiation of resistant and sensitive strains of Escherichia coli. Our focus was on clinical multi-resistant (extended-spectrum β-lactam and carbapenem-resistant) bacteria from hospital patients. The spectra were collected using both UV resonance Raman spectroscopy in bulk and single-cell Raman microspectroscopy, without exposure to antibiotics. We found resistant strains have a higher nucleic acid/protein ratio, and used the spectra to train a machine learning model that differentiates resistant and sensitive strains. In addition, we applied a majority of voting system to both improve the accuracy of our models and make them more applicable for a clinical setting. This method could allow rapid and accurate identification of antibiotic resistant bacteria, and thus improve public health.

High occurrence of carbapenem-resistant Escherichia coli isolates from healthy rabbits (Oryctolagus cuniculus): first report of blaIMI and blaVIM type genes from livestock in Tunisia

We aimed to study the antibiotic susceptibility and possible occurrence of extended-spectrum beta-lactamases (ESBL)/carbapenemase-producing Escherichia coli isolates collected from rabbits in Tunisia. In all, 35 faecal samples from healthy rabbits were collected from one farm and E. coli were isolated from three media: antibiotic-free TBX agar, TBX+2 mg l^-1 cefotaxime and TBX+1 mg l^-1 imipenem. In total, 39 E. coli isolates were recovered; the majority showed resistance to at least one antibiotic and none was ESBL producer. Carbapenem resistance was detected in 16 isolates from either selective or un-selective media. Phenotypic methods used to detect carbapenemase production showed two positive isolates by Modified Hodge Test, six metallo-carbapenemase producers (Imipenem disc+EDTA) and all were temocillin resistant (possible OXA-48 carbapenemase). bla_VIM and bla_IMP type genes were detected in two and one isolates, respectively; one of them harboured both genes. Isolates contained common genes encoding resistance to sulphonamides (sul1, sul2), tetracycline (tetA, tetB, tetC) and fluoroquinolones (qnrS, aac(6')-Ib-cr). Class 1 and 2 integrons were detected in five and four isolates, respectively. These findings highlight the importance of rabbit production as reservoir of carbapenem-resistant E. coli and argument the first report of bla_VIM and bla_IMP genes in livestock in Tunisia.

Rapid and sensitive discrimination among carbapenem resistant and susceptible E. coli strains using Surface Enhanced Raman Spectroscopy combined with chemometric tools

BACKGROUND

Raman spectroscopy is a powerful technique for the robust, reliable and rapid detection and discrimination of bacteria.

OBJECTIVES

To develop a rapid and sensitive technique based on surface-enhanced Raman spectroscopy (SERS) with multivariate data analysis tools for discrimination among carbapenem resistant and susceptible E. coli strains.

METHODS

SERS was employed to differentiate different strains of carbapenem resistant and susceptible E. coli by using silver nanoparticles (Ag NPs) as a SERS substrate. For this purpose, four strains of carbapenem resistant and three strains of carbapenem susceptible E. coli were analyzed by comparing their SERS spectral signatures. Furthermore, multivariate data analysis techniques including Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA) and Partial Least Squares-Discriminant Analysis (PLS-DA) were performed over the spectral range of 400-1800 cm^-1 (fingerprint region) for the identification and differentiation of different E. coli strains.

RESULTS

The SERS spectral features associated with resistant development against carbapenem antibiotics were separated by comparing each spectrum of susceptible strains with each resistant strain. PCA and HCA were found effective for the qualitative differentiation of all the strains analysed. PLS-DA successfully discriminated the carbapenem resistant and susceptible E. coli pellets on the strain level with 99.8 % sensitivity, 100 % specificity, 100 % accuracy and 86 % area under receiver operating characteristic (AUROC) curve.

CONCLUSION

SERS can be employed for the rapid discrimination among carbapenem resistant and susceptible strains of E. coil.

Synthesis and in Silico Modelling of the Potential Dual Mechanistic Activity of Small Cationic Peptides Potentiating the Antibiotic Novobiocin against Susceptible and Multi-Drug Resistant Escherichia coli

Cationic antimicrobial peptides have attracted interest, both as antimicrobial agents and for their ability to increase cell permeability to potentiate other antibiotics. However, toxicity to mammalian cells and complexity have hindered development for clinical use. We present the design and synthesis of very short cationic peptides (3–9 residues) with potential dual bacterial membrane permeation and efflux pump inhibition functionality. Peptides were designed based upon in silico similarity to known active peptides and efflux pump inhibitors. A number of these peptides potentiate the activity of the antibiotic novobiocin against susceptible Escherichia coli and restore antibiotic activity against a multi-drug resistant E. coli strain, despite having minimal or no intrinsic antimicrobial activity. Molecular modelling studies, via docking studies and short molecular dynamics simulations, indicate two potential mechanisms of potentiating activity; increasing antibiotic cell permeation via complexation with novobiocin to enable self-promoted uptake, and binding the E. coli RND efflux pump. These peptides demonstrate potential for restoring the activity of hydrophobic drugs.

Transcriptional response of mar, sox and rob regulon against concentration gradient carbapenem stress within Escherichia coli isolated from hospital acquired infection

Objective

The present study was carried out to investigate the transcriptional response of marA (Multiple antibiotic resistance A gene), soxS (Superoxide S gene) and rob (Right-origin-binding gene) under carbapenem stress.

Results

12 isolates were found over-expressing AcrAB-TolC efflux pump system and showed reduced expression of OmpF (Outer membrane porin) gene were selected for further study. Among them, over expression of marA and rob was observed in 7 isolates. Increasing pattern of expression of marA and rob against meropenem was observed. The clones of marA and rob showed reduced susceptibility towards carbapenems.

A Novel, Integron-Regulated, Class C β-Lactamase

AmpC-type β-lactamases severely impair treatment of many bacterial infections, due to their broad spectrum (they hydrolyze virtually all β-lactams, except fourth-generation cephalosporins and carbapenems) and the increasing incidence of plasmid-mediated versions. The original chromosomal AmpCs are often tightly regulated, and their expression is induced in response to exposure to β-lactams. Regulation of mobile ampC expression is in many cases less controlled, giving rise to constitutively resistant strains with increased potential for development or acquisition of additional resistances. We present here the identification of two integron-encoded ampC genes, bla_IDC-1 and bla_IDC-2 (integron-derived cephalosporinase), with less than 85% amino acid sequence identity to any previously annotated AmpC. While their resistance pattern identifies them as class C β-lactamases, their low isoelectric point (pI) values make differentiation from other β-lactamases by isoelectric focusing impossible. To the best of our knowledge, this is the first evidence of an ampC gene cassette within a class 1 integron, providing a mobile context with profound potential for transfer and spread into clinics. It also allows bacteria to adapt expression levels, and thus reduce fitness costs, e.g., by cassette-reshuffling. Analyses of public metagenomes, including sewage metagenomes, show that the discovered ampCs are primarily found in Asian countries.

Characterization of O25b-ST131 Escherichia coli Clone Producing CTX-M-15, DHA-4, and CMY-42 in Urinary Tract Infections in a Tunisian Island

The dissemination of extended-spectrum β-lactamases encoding genes in Escherichia coli, especially in the uropathogenic O25b-ST131 E. coli clone, constitutes a real concern. We aimed to identify the molecular mechanisms of resistance to cephalosporins among E. coli clinical isolates and to estimate the prevalence of the uropathogenic O25b-ST131 clone in our study. Forty-two cephalosporin-resistant E. coli implicated in urinary tract infections were collected from the Regional Hospital of a southeastern Tunisian Island from April 2015 to August 2016. Molecular screening of β-lactamases encoding genes by PCR and sequencing showed that the majority of our isolates harbored bla_CTX-M gene (bla_CTX-M-15 [n = 36], bla_CTX-M-14 [n = 2]). Nevertheless, the bla_SHV, bla_TEM, and bla_OXA-1 genes were not detected. Various class C β-lactamases encoding genes were observed in association or not with bla_CTX-M genes and were as follows: bla_ampC (n = 14), bla_CMY-42 (n = 7), bla_CMY-2 (n = 1), and bla_DHA-4 (n = 1). The research of O25b-ST131 clone was carried out by duplex PCR (pabB and trpA genes) and revealed that most of our isolates (n = 30) belonged to this clone. We also noted that the majority of our isolates belonged to the B2 phylogenetic group (n = 32), five isolates to the B1 phylogenetic group, three isolates to the D phylogenetic group, and only two isolates belonged to the A phylogenetic group. Our study provides new epidemiological information about E. coli clinical isolates in this area. Indeed, this is the first report of CTX-M-14 producing O25b-ST131 E. coli in our country and the first report of DHA-4 and CMY-42 producing E. coli in Tunisia.

Phylogenetic Diversity, Antimicrobial Susceptibility and Virulence Characteristics of Escherichia coli Isolates from Pigeon Meat

Monitoring resistance to antibiotics in wild animals may assist in evaluating tendencies in the evolution of this major public health problem. The aims of this research work were to determine the patterns of antibiotic resistance in Escherichia coli isolates from the meat of wild or domestically reared pigeons from Spain, to detect the presence of virulence and antibiotic resistance genes, and to carry out a phylogenetic classification of the isolates. Of the 37 E. coli strains tested, 32.43% of them belonged to the B2 phylogenetic group, which is often implicated in extra-intestinal infections. None of the strains showed extended-spectrum beta-lactamase activity. All the isolates presented resistance or reduced susceptibility to two or more antibiotics, with high levels of resistance to β-lactams, aminoglycosides and tetracycline. Ten resistance genes were detected, the most frequent of which were ampC, conferring resistance to ampicillin and aadA, conferring resistance to streptomycin. In total, 97.30% of the strains carried virulence factors (between one and five). The strains from pigeons reared in captivity harboured higher average numbers of resistance and virulence genes than isolates from wild pigeons. Pigeon meat is an important reservoir of E. coli with genes for antibiotic resistance and virulence having the potential to cause disease in humans.

First report on extended-spectrum beta-lactamase (ESBL) producing Escherichia coli from European free-tailed bats (Tadarida teniotis) in Portugal: A one-health approach of a hidden contamination problem

The main aim of this study was to characterize the diversity of extended-spectrum beta-lactamases (ESBLs) in Escherichia coli isolates from European free tailed-bats (Tadarida teniotis) in Portugal. ESBL-producing E. coli isolates were recovered from 14 of 146 faecal samples (9.6%) and a total of 19 isolates were completely characterized. The more prevalent beta-lactamase genes detected were bla_CTX-M-1 (57.9%) and bla_CTX-M-3 (36.8%), followed by bla_SHV (31.6%), bla_TEM (21.1%), bla_OXA (10.5%) and bla_CTX-M-9 (10.5%). Among other associated resistance genes studied, tet(A) and tet(B) were predominant and fimA was the main virulence factor detected. Phylogroups D (47.4%) and A (31.6%) were the more prevalent, followed by group B2 (21.1%). Bats are reservoirs of antimicrobial-resistant bacteria and resistance determinants and is important in further studies to identify the main sources of pollution in the environment, such as water or insects that may contain these multiresistant organisms.

First Report of SHV-148-Type ESBL and CMY-42-Type AmpC β-Lactamase in Klebsiella pneumoniae Clinical Isolates in Tunisia

Extended-spectrum beta-lactamase producing Enterobacteriaceae present a real problem worldwide. We aimed to investigate the molecular mechanisms of resistance to antibiotics among Klebsiella pneumoniae clinical isolates collected from a Hospital in the southeast of Tunisia. Eighteen cephalosporin-resistant K. pneumoniae were recovered between April 2015 and August 2016. Molecular characterization of antimicrobial resistance encoding genes was performed by PCR and sequencing. Results revealed several types of Ambler class A β-lactamase encoding genes among our isolates: [blaCTXM-15 (15), blaSHV-28 (6), blaSHV-1 (2), blaSHV-148 (1), blaSHV-61 (1), blaSHV-76 (1), blaSHV-186 (1), blaTEM-1 (8)]. The association of blaOXA-1 was observed in nine isolates. However, the class C β-lactamase encoding genes were detected in four isolates [blaCMY-4 (2), blaCMY-42 (1), blaACT-35 (1)]. Molecular typing of K. pneumoniae isolates by pulsed-field gel electrophoresis showed 16 unrelated pulsotypes proving a high diversity among our isolates. Our study provides new epidemiological information showing a huge diversity of β-lactamase encoding genes among our isolates. In fact, this is the first report of SHV-76, SHV-148, and SHV-186 in Tunisia. This is also the first report of CMY-42 and ACT-35 producing K. pneumoniae in our country.

Selection of broad-spectrum cephalosporin-resistant Escherichia coli in the feces of healthy dogs after administration of first-generation cephalosporins

Although antimicrobial products are essential for treating diseases caused by bacteria, antimicrobial treatment selects for antimicrobial-resistant (AMR) bacteria. The aim of this study was to determine the effects of administration of first-generation cephalosporins on development of resistant Escherichia coli in dog feces. The proportions of cephalexin (LEX)-resistant E. coli in fecal samples of three healthy dogs treated i.v. with cefazolin before castration and then orally with LEX for 3 days post-operation (PO) were examined using DHL agar with or without LEX (50 µg/mL). LEX-resistant E. coli were found within 3 days PO, accounted for 100% of all identified E. coli 3-5 days PO in all dogs, and were predominantly found until 12 days PO. LEX-resistant E. coli isolates on DHL agar containing LEX were subjected to antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) genotyping, β-lactamase typing and plasmid profiling. All isolates tested exhibited cefotaxime (CTX) resistance (CTX minimal inhibitory concentration ≥4 µg/mL). Seven PFGE profiles were classified into five groups and three β-lactamase combinations (bla_CMY-4 -bla_TEM-1 , bla_TEM-1 -bla_CTX-M-15 and bla_TEM-1 -bla_CTX-M-15 -bla_CMY-4 ). All isolates exhibited identical PFGE profiles in all dogs on four days PO and subsequently showed divergent PFGE profiles. Our results indicate there are two selection periods for AMR bacteria resulting from the use of antimicrobials. Thus, continuing hygiene practices are necessary to prevent AMR bacteria transfer via dog feces after antimicrobial administration.

Investigation of carbapenem resistance and the first identification of Klebsiella pneumoniae carbapenemase (KPC) enzyme among Escherichia coli isolates in Turkey: A prospective study

BACKGROUND

The aim of this study was to determine the presence of carbapenem resistance and carbapenemase production in Escherichia coli isolates from clinical samples in Turkey.

METHODS

The prospective study included a total of 4.052 Escherichia coli isolates collected from patients admitted to a hospital from March 2011 to May 2012. We used ertapenem disc for screening carbapenemase production, and the confirmation was performed by using Etest. The resistance mechanisms and genetic relatedness of the carbapenem resistant strains were investigated by using PCR (polymerase chain reaction) and pulsed-field gel electrophoresis (PFGE), respectively.

RESULTS

Among the 4.052 E. coli isolates, 24 (0.59%) were found to be carbapenem resistant. Of these, only 5 isolates were positive for OXA-48 and 2 isolates were positive for Klebsiella pneumoniae carbapenemase (KPC)-2. The KPC-2 producing E. coli strains (n = 2) were both isolated from the same patient. The bla_KPC genes were confirmed using DNA sequence analysis. The genetic relationship between the 24 E. coli strains studied by PFGE revealed that the strains were genetically unrelated.

CONCLUSIONS

This article confirms, to our knowledge for the first time, the detection of KPC-2-producing E. coli in Turkey, with OXA-48 being the most frequent carbapenemase in the study.

Distribution and Classification of Serine β-Lactamases in Brazilian Hospital Sewage and Other Environmental Metagenomes Deposited in Public Databases

β-lactam is the most used antibiotic class in the clinical area and it acts on blocking the bacteria cell wall synthesis, causing cell death. However, some bacteria have evolved resistance to these antibiotics mainly due the production of enzymes known as β-lactamases. Hospital sewage is an important source of dispersion of multidrug-resistant bacteria in rivers and oceans. In this work, we used next-generation DNA sequencing to explore the diversity and dissemination of serine β-lactamases in two hospital sewage from Rio de Janeiro, Brazil (South Zone, SZ and North Zone, NZ), presenting different profiles, and to compare them with public environmental data available. Also, we propose a Hidden-Markov-Model approach to screen potential serine β-lactamases genes (in public environments samples and generated hospital sewage data), exploring its evolutionary relationships. Due to the high variability in β-lactamases, we used a position-specific scoring matrix search method (RPS-BLAST) against conserved domain database profiles (CDD, Pfam, and COG) followed by visual inspection to detect conserved motifs, to increase the reliability of the results and remove possible false positives. We were able to identify novel β-lactamases from Brazilian hospital sewage and to estimate relative abundance of its types. The highest relative abundance found in SZ was the Class A (50%), while Class D is predominant in NZ (55%). CfxA (65%) and ACC (47%) types were the most abundant genes detected in SZ, while in NZ the most frequent were OXA-10 (32%), CfxA (28%), ACC (21%), CEPA (20%), and FOX (19%). Phylogenetic analysis revealed β-lactamases from Brazilian hospital sewage grouped in the same clade and close to sequences belonging to Firmicutes and Bacteroidetes groups, but distant from potential β-lactamases screened from public environmental data, that grouped closer to β-lactamases of Proteobacteria. Our results demonstrated that HMM-based approach identified homologs of serine β-lactamases, indicating the specificity and high sensitivity of this approach in large datasets, contributing for the identification and classification of a large number of homologous genes, comprising possible new ones. Phylogenetic analysis revealed the potential reservoir of β-lactam resistance genes in the environment, contributing to understanding the evolution and dissemination of these genes.

In vitro bactericidal activity of Berberis aristata extract against clinical isolates of carbapenem-resistant Escherichia coli

BACKGROUND

Berberis aristata is known to contain a variety of phenolic compounds, flavonoids such as quercetin attributing towards its holistic capability of mitigating multidrug resistance.

METHODS

B. aristata stem bark extract was prepared and characterized using phytochemical and bioactivity-based fingerprinting. Anti-oxidant and anti-lipid peroxidation profiling was also done in conjunction with in vitro anti-microbial efficacy testing against the test microorganism i. e., New Delhi Metallo-β-lactamase-1 (NDM-1) Escherichia coli.

RESULTS

Aquo-alcoholic (1:1) extract of B. aristata (PTRC-2111-A), containing 3.0±0.02 µg of QUERCETIN/mg of dried extract, exhibited [flavonoid/polyphenol: F/P (quercetin %) ~ 0.16(0.06 %)]. The bioactivity fingerprint profile of PTRC-2111-A included IC50 ratio [DPPH/NOS]=0.064 as functional standardized value having IC50 (DPPH Scavenging)=16±0.5 µg/mL and IC50 (Nitric Oxide Scavenging)=250±0.5 µg/mL respectively. The reducing ability and anti-lipid peroxidation equivalent (extract: standard) of PTRC-2111-A with respect to standard was estimated to be 3.44 (ascorbic acid) and 0.78 (quercetin) respectively. In vitro anti-microbial activity evaluated against sts-09 multidrug-resistant strain of carbapenem-resistant E. coli was found to be 25 µg/mL.

CONCLUSIONS

B. aristata was found to contain a number of phytoconstituents, which acts in a synergistic manner to provide significant bactericidal potential against carbapenem-resistant E. coli.

Whole-genome typing and characterization of blaVIM19-harbouring ST383 Klebsiella pneumoniae by PFGE, whole-genome mapping and WGS

OBJECTIVES

We utilized whole-genome mapping (WGM) and WGS to characterize 12 clinical carbapenem-resistant Klebsiella pneumoniae strains (TGH1-TGH12).

METHODS

All strains were screened for carbapenemase genes by PCR, and typed by MLST, PFGE (XbaI) and WGM (AflII) (OpGen, USA). WGS (Illumina) was performed on TGH8 and TGH10. Reads were de novo assembled and annotated [SPAdes, Rapid Annotation Subsystem Technology (RAST)]. Contigs were aligned directly, and after in silico AflII restriction, with corresponding WGMs (MapSolver, OpGen; BioNumerics, Applied Maths).

RESULTS

All 12 strains were ST383. Of the 12 strains, 11 were carbapenem resistant, 7 harboured blaKPC-2 and 11 harboured blaVIM-19. Varying the parameters for assigning WGM clusters showed that these were comparable to STs and to the eight PFGE types or subtypes (difference of three or more bands). A 95% similarity coefficient assigned all 12 WGMs to a single cluster, whereas a 99% similarity coefficient (or ≥10 unmatched-fragment difference) assigned the 12 WGMs to eight (sub)clusters. Based on a difference of three or more bands between PFGE profiles, the Simpson's diversity indices (SDIs) of WGM (0.94, Jackknife pseudo-values CI: 0.883-0.996) and PFGE (0.93, Jackknife pseudo-values CI: 0.828-1.000) were similar (P = 0.649). However, the discriminatory power of WGM was significantly higher (SDI: 0.94, Jackknife pseudo-values CI: 0.883-0.996) than that of PFGE profiles typed on a difference of seven or more bands (SDI: 0.53, Jackknife pseudo-values CI: 0.212-0.849) (P = 0.007).

CONCLUSIONS

This study demonstrates the application of WGM to understanding the epidemiology of hospital-associated K. pneumoniae. Utilizing a combination of WGM and WGS, we also present here the first longitudinal genomic characterization of the highly dynamic carbapenem-resistant ST383 K. pneumoniae clone that is rapidly gaining importance in Europe.

Antibacterial properties of L-amino acid oxidase: mechanisms of action and perspectives for therapeutic applications

Venom, the mucus layer covering the body surface, ink glands, mammary glands, milk, and various animal secretory functions as both a physical and chemical defense barrier against bacteria and virus infections. Previously, several studies reported that L-amino acid oxidases (LAAOs) present in animal secretary fluids have strong antimicrobial activities and selective cytotoxic activities against Gram-positive and Gram-negative bacteria, various pathogenic bacteria, viruses, and parasite species. These LAAOs catalyze oxidative deamination of an L-amino acid substrate with the generation of hydrogen peroxide. The antibacterial activity of LAAOs is completely inhibited by catalase; thus, LAAOs kill bacteria by the hydrogen peroxide generated from the oxidation of L-amino acid substrates. This review focuses on the selective, specific, and local antibacterial actions of various LAAOs that may be used as novel therapeutic agents against infectious diseases. LAAOs that are suitable leads for combating multidrug-resistant bacterial infections are also studied.

Detection of expanded-spectrum β-lactamases in Gram-negative bacteria in the 21st century

Emerging β-lactamase-producing-bacteria (ESBL, AmpC and carbapenemases) have become a serious problem in our community due to their startling spread worldwide and their ability to cause infections which are difficult to treat. Diagnosis of these β-lactamases is of clinical and epidemiological interest. Over the past 10 years, several methods have been developed aiming to rapidly detect these emerging enzymes, thus preventing their rapid spread. In this review, we describe the range of screening and detection methods (phenotypic, molecular and other) for detecting these β-lactamases but also whole genome sequencing as a tool for detecting the genes encoding these enzymes.

The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria

The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.

Risk factors for the acquisition of carbapenem-resistant Escherichia coli at a tertiary care center in South Korea: a matched case-control study

BACKGROUND

Carbapenem resistance among gram-negative bacilli is an emerging threat worldwide. The objective of this study was to identify risk factors for the acquisition of carbapenem-resistant Escherichia coli (CRE).

METHODS

We conducted a matched case-control study comprising 57 cases of acquisition of CRE and 114 controls (1:2 matched) selected from patients with a culture of carbapenem-susceptible E coli between January 2006 and December 2010 at a 2000-bed tertiary care center in South Korea.

RESULTS

On univariate analysis, previous use of carbapenem (P < .01), fluoroquinolone (P < .01), and glycopeptide (P < .01), as well as length of hospital stay (P < .05), were significantly associated with CRE acquisition. On multivariate analysis, previous use of carbapenem (odds ratio [OR], 4.56; 95% confidence interval [CI] 1.44-14.46; P = .01) and previous use of fluoroquinolone (OR, 2.81; 95% CI, 1.14-6.99; P = .03) were independent risk factors.

CONCLUSIONS

At this institute, the antibiotic selective pressure of carbapenems and fluoroquinolones was shown to be an important risk factor for the acquisition of CRE.

Cephalosporin resistance among animal-associatedEnterobacteria: a current perspective

Beta-lactam antimicrobials are an important class of drugs used for the treatment of infection. Resistance can arise by several mechanisms, including the acquisition of genes encoding beta-lactamases from other bacteria, alterations in cell membrane permeability and over expression of endogenous beta-lactamases. The acquisition of beta-lactamase resistance genes by both Salmonella and Escherichia coli appears to be on the rise, which may pose potential problems for the treatment of infections in both human and animal medicine. The prudent use of clinically important antimicrobials is therefore critical to maintain their effectiveness. Where possible, the use of newer generation cephalosporins should be limited in veterinary medicine.

Updated molecular epidemiology of carbapenem-non-susceptible Escherichia coli in Taiwan: first identification of KPC-2 or NDM-1-producing E. coli in Taiwan

BACKGROUND

The global spread and increasing incidence of carbapenem-resistant Enterobacteriaceae have resulted in treatment and public health concerns. Here, we present an investigation of the molecular mechanisms and clonality of carbapenem-non-susceptible Escherichia coli (CnSEC) based on a nationwide survey in Taiwan.

METHODS

We collected 32 and 43 carbapenem-non-susceptible E. coli isolates in 2010 and 2012, respectively. The genes encoding cabapenemases and plasmidic AmpC-type and extended-spectrum β-lactamases (EBSLs) were analyzed by polymerase chain reaction (PCR). The major porin channels OmpF and OmpC were evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Molecular typing was performed with pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST).

RESULTS

The resistance rates of CnSEC isolates to cefazolin, cefotaxime, cefoxitin, ceftazidime, and ertapenem were all 100%, and most (94.7%) isolates were CMY producers. The main mechanism of CnSEC in Taiwan is via plasmidic AmpC β-lactamase CMY-2 and DHA-1 in combination with the loss of OmpC/F. In 2010, one isolate was confirmed to harbor blaIMP-8; a KPC-2 producer and an NDM-1 producer were detected in 2012. No isolate had VIM- or OXA-carbapenemases. ST131 was the predominant ST type (33.3%). PFGE revealed no large cluster in CnSEC isolates in Taiwan.

CONCLUSIONS

The co-existence of plasmidic AmpC β-lactamase and outer membrane protein loss is the main mechanism for CnSEC in Taiwan. The emergence of KPC-2 and NDM-1 in 2012 and the predominance of ST131 warrant close monitoring and infection control.

No evidence so far for the dissemination of carbapenemase-producing Enterobactericeae in the community in Switzerland

BACKGROUND

Carbapenemase-producing Enterobacteriaceae represent an increasing threat to public health and to the treatment of serious nosocomial infections. The aim of this study was to screen for the presence of carbapenemase-producing Enterobacteriaceae in human carriers in community settings in Switzerland, a country representative of central Europe.

FINDINGS

Three hundred and fourteen stool samples of healthy staff members of a meat-processing company and 291 fecal swabs from primary care patients were recovered in Switzerland between April 2012 and July 2012 and were tested for carbapenemase-producing Enterobacteriaceae isolates by selecting for growth on a carbapenem-containing selective medium. Six resulting isolates (5 Escherichia coli and 1 Citrobacter youngae) were subjected to antimicrobial susceptibility tests and PCR analysis by screening for the carbapenemase genes bla OXA-48, bla VIM, bla NDM-1, and bla KPC as well as for the extended-spectrum ß-lactamase genes bla TEM, bla SHV, bla CTX-M and bla CMY-2. No carbapenemase genes were detected. Resistance to ß-lactam antibiotics was due to carriage of the extended-spectrum ß-lactamase CTX-M-15 in 4 isolates, to CTX-M-14 in one further isolate and to the plasmidic AmpC-ß-lactamase CMY-2 in one isolate.

CONCLUSIONS

These results show that carbapenemase-producing Enterobacteriaceae are as yet not present in the community. Continuous surveillance is necessary to anticipate future trends in the prevalence and dissemination of carbapenem resistant isolates in the population.

Extended-spectrum β lactamase-producing gram-negative bacteria: clinical profile and outcome in a neonatal intensive care unit

BACKGROUND & AIMS

Multidrug-resistant extended-spectrum 3 lactamase-producing bacteria (ESBL) have emerged as a common problem globally. However, data regarding clinical profile and outcome in neonates infected with ESBL-producing gram-negative bacteria are sparse.

METHODS

A retrospective study was undertaken of all neonates admitted between April 2002 and May 2003 to the neonatal intensive care unit, Safdarjang Hospital, New Delhi who had blood cultures positive for gram-negative bacteria. The clinical profile and outcome in each patient was obtained from the case notes. The mortality and morbidity of the ESBL (cases) and non-ESBL groups were compared. Data were analysed using the chi(2) and Student's t-tests.

RESULTS

There were 75 cases of gram-negative septicaemia, 46 newborns (61.3%) were infected with ESBL-producing strains and 63 case records were available. ESBL production was associated with prematurity (24/38 vs 9/25, p=0.03), prolonged rupture of membranes (14/38 vs 2/25, p=0.01) and previous antibiotic administration to the infant (15/38 vs 1/25, p=0.002). Fifty per cent of infants with early-onset sepsis and 82.1% with late-onset sepsis were infected with ESBL strains. Newborns with ESBL sepsis were more likely to manifest persistent thermal instability (13/38 vs 3/25, p=0.04) and pre-feed gastric aspirates (18/38 vs 3/25, p=0.004). More than 90% of ESBL isolates were susceptible to carbapenems, cefperazone-sulbactam and piperacillin-tazobactam. The mean length of nursery stay (15.8 vs 10.7, p=0.02) and mortality (23.6 vs 4.0%, p= 0.07) were higher in the ESBL group and onset of feeds was delayed (7.6 vs 3.9 days, p=0.007) in this group.

CONCLUSIONS

Isolation of ESBL in cases of early-onset sepsis indicates that ESBL producers might have percolated into the community. Early suspicion of ESBL-producing isolates in cases of neonatal sepsis can facilitate prompt institution of appropriate empirical therapy and lead to an improved outcome.

Involvement of MarR and YedS in carbapenem resistance in a clinical isolate of Escherichia coli from China

A carbapenem-resistant clinical isolate of Escherichia coli, which lacked OmpF and OmpC porins, carried a marR mutation and expressed a functional yedS, a normally nontranslated gene. MarR and YedS are described here as having effects on the ability of this strain to resist carbapenems. Additionally, expression of YedS was regulated by the small RNA MicF in a MarA-dependent way. These findings illustrate how broadly bacteria can mutate within a selective clinical setting, in this case, resistance to carbapenems, by altering three porin genes and one regulatory gene.

Loss of outer membrane protein C in Escherichia coli contributes to both antibiotic resistance and escaping antibody-dependent bactericidal activity

Outer membrane proteins (OMPs) serve as the permeability channels for nutrients, toxins, and antibiotics. In Escherichia coli, OmpA has been shown to be involved in bacterial virulence, and OmpC is related to multidrug resistance. However, it is unclear whether OmpC also has a role in the virulence of E. coli. The aims of this study were to characterize the role of OmpC in antimicrobial resistance and bacterial virulence in E. coli. The ompC deletion mutant showed significantly decreased susceptibility to carbapenems and cefepime. To investigate the survival of E. coli exposed to the innate immune system, a human blood bactericidal assay showed that the ompC mutant increased survival in blood and serum but not in complement-inactivated serum. These effects were also demonstrated in the natural selection of OmpC mutants. Also, C1q interacted with E. coli through a complex of antibodies bound to OmpC as a major target. Bacterial survival was increased in the wild-type strain in a dose-dependent manner by adding free recombinant OmpC protein or anti-C1q antibody to human serum. These results demonstrated that the interaction of OmpC-specific antibody and C1q was the key step in initiating the antibody-dependent classical pathway for the clearance of OmpC-expressing E. coli. Anti-OmpC antibody was detected in human sera, indicating that OmpC is an immunogen. These data indicate that the loss of OmpC in E. coli is resistant to not only antibiotics, but also the serum bactericidal effect, which is mediated from the C1q and anti-OmpC antibody-dependent classical pathway.

Carbapenems: past, present, and future

In this review, we summarize the current "state of the art" of carbapenem antibiotics and their role in our antimicrobial armamentarium. Among the β-lactams currently available, carbapenems are unique because they are relatively resistant to hydrolysis by most β-lactamases, in some cases act as "slow substrates" or inhibitors of β-lactamases, and still target penicillin binding proteins. This "value-added feature" of inhibiting β-lactamases serves as a major rationale for expansion of this class of β-lactams. We describe the initial discovery and development of the carbapenem family of β-lactams. Of the early carbapenems evaluated, thienamycin demonstrated the greatest antimicrobial activity and became the parent compound for all subsequent carbapenems. To date, more than 80 compounds with mostly improved antimicrobial properties, compared to those of thienamycin, are described in the literature. We also highlight important features of the carbapenems that are presently in clinical use: imipenem-cilastatin, meropenem, ertapenem, doripenem, panipenem-betamipron, and biapenem. In closing, we emphasize some major challenges and urge the medicinal chemist to continue development of these versatile and potent compounds, as they have served us well for more than 3 decades.

Detection and spread of carbapenem-resistant Citrobacter freundii in a teaching hospital in China

BACKGROUND

We examined the detection and spread of carbapenem-resistant Citrobacter freundii in Huashan Hospital, Shanghai, China between 2005 and 2008.

METHODS

Twenty-three isolates of carbapenem-resistant C freundii collected in our hospital underwent resistant gene amplification by polymerase chain reaction, followed by minimal inhibitory concentration (MIC) analysis. Molecular epidemiologic analyses included pulsed-field gel electrophoresis and case study.

RESULTS

Analysis of MICs with amikacin, gentamicin, cefotaxime, ceftazidime, cefepime, imipenem, meropenem, ertapenem, cefoxitin, piperacillin-tazobactam, and ciprofloxacin characterized the isolates as highly resistant to antimicrobials. Colistin, tigecycline, minocycline, and doxycycline to all C freundii isolates had lower MICs than the other antimicrobials tested, with MIC(50)/MIC(90) values of 0.5/1, 1/1, 4/8, and 4/4 mg/L, respectively. Molecular typing using pulsed-field gel electrophoresis classified the isolates into 4 groups, of which 15 isolates belonged to a single clone. In total, all of the isolates produced KPC-2-type carbapenemase, of which most were likely to couple with CTX-M-type extended-spectrum β-lactamases and plasmid-mediated CMY-2-type AmpC enzyme. Subsequent clinical investigations involving the general status of patients, the ward, and antimicrobial and therapeutic outcomes showed that a carbapenem-resistant clone had spread critically in the Department of Neurosurgery. Potential risk factors were identified, including invasive procedures, surgical operations, use of indwelling urine catheters, and number of sickbed changes.

CONCLUSION

The spread of carbapenem-hydrolyzing C freundii isolates has emerged in regional hospitals in China. Multidrug-resistant mechanisms of strains severely hamper control efforts. Our findings should alert clinicians to issues involved with preventing the spread of carbapenem-resistant C freundii.

ACT-6, a novel plasmid-encoded class C β-lactamase in a Klebsiella pneumoniae isolate from China

The purpose of this study was to investigate the phenotypic and molecular characterization of a novel plasmid-mediated AmpC-type β-lactamase in Klebsiella pneumoniae E701 isolated from Anhui province in China. In comparison with the ACT-1, sequence analysis revealed that there were 43 point mutations in the coding gene, and 10 of which led to amino-acid substitution. Resistance could be transferred by conjugation or transformation with plasmid DNA into E. coli JM109, which was due to the production of a β-lactamase with an isoelectric point of 8.4 named ACT-6. Cloning, expression, purification and kinetics were carried out to study the characterization of the novel AmpC-type β-lactamase. The results of MIC determinations and substrate profiles showed there was no significant difference in the activities of the novel enzyme and ACT-1. Moreover, the class 1 integron and the whole open reading frame of the novel AmpC-type β-lactamase from K.pneumoniae E701 were detectable in the same size plasmid. This is the first report on the emergence of the novel ACT-6 type β-lactamases in K. pneumoniae.

Phenotypic and biochemical comparison of the carbapenem-hydrolyzing activities of five plasmid-borne AmpC β-lactamases

The CMY-2, ACT-1, DHA-1, ACC-1, and FOX-1 enzymes are representative of five plasmid-mediated AmpC (pAmpC) β-lactamase clusters. Resistance to imipenem has been reported in Enterobacteriaceae as a result of pAmpC expression combined with decreased outer membrane permeability. The aim of this study was to determine the role of different pAmpCs in carbapenem resistance and to define the structure/activity relationship supporting carbapenemase activity. The ampC genes encoding the five pAmpCs and the chromosomal AmpC of Escherichia coli EC6, which was used as a reference cephalosporinase, were cloned and introduced into wild-type E. coli TOP10 and OmpC/OmpF porin-deficient E. coli HB4 strains. The MICs of β-lactams for the recombinant strains revealed that CMY-2, ACT-1, and DHA-1 β-lactamases conferred a high level of resistance to ceftazidime and cefotaxime once expressed in E. coli TOP10 and reduced significantly the susceptibility to imipenem once expressed in E. coli HB4. In contrast, FOX-1 and ACC-1 enzymes did not confer resistance to imipenem. Biochemical analysis showed that CMY-2 β-lactamase and, to a lesser extent, ACT-1 exhibited the highest catalytic efficiency toward imipenem and showed low K(m) values. A modeling study revealed that the large R2 binding site of these two enzymes may support the carbapenemase activity. Therefore, CMY-2-type, ACT-1-type, and DHA-1-type β-lactamases may promote the emergence of carbapenem resistance in porin-deficient clinical isolates.

[Interpretive reading of enterobacteria antibiograms]

The resistance pattern observed in the antibiogram of an isolate should be the sum of its natural resistance pattern, characteristic of the species, plus the acquired resistances. In Enterobacteriaceae, the production of inactivating enzymes is the main mechanism of resistance to beta-lactams and aminoglycosides. Each one of these enzymes recognizes one or more specific beta-lactams or aminoglycosides as substrate. This substrate specificity implies a specific resistance pattern from which we can deduce the enzymes present in the isolate. However, enzymatic-mediated resistance is not the only mechanism implicated and resistance is frequently multifactorial. Resistance to quinolones is mainly due to precise, sequential chromosomal mutations that can be selected by fluoroquinolone treatments. Recently, certain plasmid-mediated genes which code enzymes that modify quinolones or that are target protectors have been implicated in the low level resistance to quinolones.

Carbapenem-resistant KPC-2-producing Escherichia coli in a Tel Aviv Medical Center, 2005 to 2008

All of the carbapenem-resistant Escherichia coli (CREC) isolates identified in our hospital from 2005 to 2008 (n = 10) were studied. CREC isolates were multidrug resistant, all carried bla(KPC-2), and six of them were also extended-spectrum beta-lactamase producers. Pulsed-field gel electrophoresis indicated six genetic clones; within the same clone, similar transferable bla(KPC-2)-containing plasmids were found whereas plasmids differed between clones. Tn4401 elements were identified in all of these plasmids.

Molecular characterization of biofilm formation and attachment of Salmonella enterica serovar typhimurium DT104 on food contact surfaces

The molecular mechanism of biofilm formation by Salmonella Typhimuriun DT104 was characterized for a better understanding of its attachment and colonization in food processing environments. A library of random mutagenized clones was screened for phenotypic analyses of their ability to form biofilm, pellicle, curli, and cellulose. The genes identified were involved in lipopolysaccharide synthesis, assembly of flagella, regulation of rRNA biosynthesis, and outer membrane transportation and signaling. The insertion of transposon in flgK, rfbA, nusB, and pnp genes resulted in decreased biofilm formation. Alterations of flagellar and lipopolysaccharide production were confirmed in the flgK mutant and rfbA mutant, respectively. Biofilm formation by these four mutants in meat and poultry broths and their attachment on surfaces of stainless steel and glass were significantly reduced compared with those of the wild-type strain (P < 0.05). On the contrary, the mutation of STM4263 and yjcC genes in Salmonella Typhimuriun DT104 resulted in increased biofilm formation and attachment of the species in tested broths and on contact surfaces. Our findings suggest that many factors, such as production of exopolymeric substances and their efficient transportation through outer membrane, expression of flagella, and regulation of exoribonucleases and RNA-binding protein, could be involved in biofilm formation and attachment of Salmonella Typhimurium DT104 on contact surfaces.

Paradoxical effect of Klebsiella pneumoniae OmpK36 porin deficiency

AIM

To evaluate the effect of defined mutations in the major OmpK35 and OmpK36 porins in Klebsiella pneumoniae on the activity of two common plasmid-mediated AmpC enzymes.

METHODS

Naturally occurring conjugative plasmids containing bla(DHA-1) and bla(CMY-2) were obtained from K. pneumoniae isolates in western Sydney. These were moved into K. pneumoniae ATCC13883 and isogenic porin knockouts Kp885 (DeltaompK35) and Kp886 (DeltaompK36), created by homologous recombination of kanamycin resistance cartridges into the specified genes, and their antimicrobial susceptibilities compared.

RESULTS

beta-lactam resistance was greater in the presence of CMY-2-containing plasmids than DHA-1-containing plasmids, and higher in K. pneumoniae than Escherichia coli. Neither cefepime nor imipenem resistance was observed, and DHA-mediated cefotaxime and ticarcillin/clavulanate resistance was unexpectedly reduced from 8-24 (CTX) and >256 (TIM) mg/L in Kp13883 to 1-2 (CTX) and 32-48 mg/L (TIM) in the isogenic DeltaompK36 porin knockout Kp886.

CONCLUSIONS

AmpC plasmids in particular are an important cause of transmissible resistance to ticarcillin/clavulanate in K. pneumoniae, but probably not in E. coli. Single knockouts of OmpK35 and OmpK36 porins in K. pneumoniae do not significantly increase antibiotic resistance in K. pneumoniae, and a paradoxical lowering of resistance to CTX and TIM is seen with deletion of ompK36. This has potentially important clinical implications.

AmpC beta-lactamases

SUMMARY

AmpC beta-lactamases are clinically important cephalosporinases encoded on the chromosomes of many of the Enterobacteriaceae and a few other organisms, where they mediate resistance to cephalothin, cefazolin, cefoxitin, most penicillins, and beta-lactamase inhibitor-beta-lactam combinations. In many bacteria, AmpC enzymes are inducible and can be expressed at high levels by mutation. Overexpression confers resistance to broad-spectrum cephalosporins including cefotaxime, ceftazidime, and ceftriaxone and is a problem especially in infections due to Enterobacter aerogenes and Enterobacter cloacae, where an isolate initially susceptible to these agents may become resistant upon therapy. Transmissible plasmids have acquired genes for AmpC enzymes, which consequently can now appear in bacteria lacking or poorly expressing a chromosomal bla(AmpC) gene, such as Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis. Resistance due to plasmid-mediated AmpC enzymes is less common than extended-spectrum beta-lactamase production in most parts of the world but may be both harder to detect and broader in spectrum. AmpC enzymes encoded by both chromosomal and plasmid genes are also evolving to hydrolyze broad-spectrum cephalosporins more efficiently. Techniques to identify AmpC beta-lactamase-producing isolates are available but are still evolving and are not yet optimized for the clinical laboratory, which probably now underestimates this resistance mechanism. Carbapenems can usually be used to treat infections due to AmpC-producing bacteria, but carbapenem resistance can arise in some organisms by mutations that reduce influx (outer membrane porin loss) or enhance efflux (efflux pump activation).

Seagulls of the Berlengas natural reserve of Portugal as carriers of fecal Escherichia coli harboring CTX-M and TEM extended-spectrum beta-lactamases

Escherichia coli isolates containing the following extended-spectrum beta-lactamases have been detected in 11 of 57 fecal samples (19.3%) in Berlengas Island seagulls: TEM-52 (eight isolates), CTX-M-1 (one isolate), CTX-M-14a (one isolate), and CTX-M-32 (one isolate). Most of the extended-spectrum beta-lactamase-positive isolates harbored class 1 or class 2 integrons, which included different antibiotic resistance gene cassettes.