Association between antimicrobial resistance and virulence in Escherichia coli

Bactericidal monoclonal antibodies specific to the lipopolysaccharide O antigen from multidrug-resistant Escherichia coli clone ST131-O25b:H4 elicit protection in mice

The Escherichia coli sequence type 131 (ST131)-O25b:H4 clone has spread worldwide and become responsible for a significant proportion of multidrug-resistant extraintestinal infections. We generated humanized monoclonal antibodies (MAbs) that target the lipopolysaccharide O25b antigen conserved within this lineage. These MAbs bound to the surface of live bacterial cells irrespective of the capsular type expressed. In a serum bactericidal assay in vitro, MAbs induced >95% bacterial killing in the presence of human serum as the complement source. Protective efficacy at low antibody doses was observed in a murine model of bacteremia. The mode of action in vivo was investigated by using aglycosylated derivatives of the protective MAbs. The significant binding to live E. coli cells and the in vitro and in vivo efficacy were corroborated in assays using bacteria grown in human serum to mimic relevant clinical conditions. Given the dry pipeline of novel antibiotics against multidrug-resistant Gram-negative pathogens, passive immunization with bactericidal antibodies offers a therapeutic alternative to control infections caused by E. coli ST131-O25b:H4.

Characterization of bacterial pathogens in rural and urban irrigation water

The study aimed to compare the bacteriological quality of an urban and rural irrigation water source. Bacterial counts, characterization, identification and diversity of aerobic bacteria were determined. Escherichia coli isolated from both sites was subjected to antibiotic susceptibility testing, virulence gene (Stx1/Stx2 and eae) determination and (GTG)5 Rep-PCR fingerprinting. Low mean monthly counts for aerobic spore formers, anaerobic spore formers and Staphylococcus aureus were noted although occasional spikes were observed. The most prevalent bacterial species at both sites were Bacillus spp., E. coli and Enterobacter spp. In addition, E. coli and Bacillus spp. were most prevalent in winter and summer respectively. Resistance to at least one antibiotic was 84% (rural) and 83% (urban). Highest resistance at both sites was to cephalothin and ampicillin. Prevalence of E. coli possessing at least one virulence gene (Stx1/Stx2 and eae) was 15% (rural) and 42% (urban). All (rural) and 80% (urban) of E. coli possessing virulence genes showed antibiotic resistance. Complete genetic relatedness (100%) was shown by 47% of rural and 67% of urban E. coli isolates. Results from this study show that surface irrigation water sources regardless of geographical location and surrounding land-use practices can be reservoirs of similar bacterial pathogens.

Burden of Bloodstream Infection Caused by Extended-Spectrum β-Lactamase–Producing Enterobacteriaceae Determined Using Multistate Modeling at a Swiss University Hospital and a Nationwide Predictive Model

Objective.

To obtain an unbiased estimate of the excess hospital length of stay (LOS) and cost attributable to extended-spectrum β-lactamase (ESBL) positivity in bloodstream infections (BSIs) due to Enterobacteriaceae.

Design.

Retrospective cohort study.

Setting.

A 2,200-bed academic medical center in Geneva, Switzerland.

Patients.

Patients admitted during 2009.

Methods.

We used multistate modeling and Cox proportional hazards models to determine the excess LOS and adjusted end-of-LOS hazard ratio (HR) for ESBL-positive and ESBL-negative BSI. We estimated economic burden as the product of excess LOS and average bed-day cost. Patient-level accounting data provided a complementary analysis of economic burden. A predictive model was fitted to national surveillance data.

Results.

Thirty ESBL-positive and 96 ESBL-negative BSI cases were included. The excess LOS attributable to ESBL-positive and ESBL-negative BSI was 9.4 (95% confidence interval [CI], 0.4–18.4) and 2.6 (95% CI, 0.7–5.9) days, respectively. ESBL positivity was therefore associated with 6.8 excess days and CHF 9,473 per BSI. The adjusted end-of-LOS HRs for ESBL-positive and ESBL-negative BSI were 0.62 (95% CI, 0.43–0.89) and 0.90 (95% CI, 0.74–1.10), respectively. After reimbursement, the average financial loss per acute care episode in ESBL-positive BSI, ESBL-negative BSI, and control cohorts was CHF 48,674, 48,131, and 13,532, respectively. Our predictive model estimated that the nationwide cost of third-generation cephalosporin resistance would increase from CHF 2,084,000 in 2010 to CHF 3,526,000 in 2015.

Conclusions.

This is the first hospital-wide analysis of excess LOS attributable to ESBL positivity determined using multistate modeling to avoid time-dependent bias. These results may inform health-economic evaluations of interventions targeting ESBL control.

Escherichia coli Peritonitis in peritoneal dialysis: the prevalence, antibiotic resistance and clinical outcomes in a South China dialysis center

INTRODUCTION

Escherichia coli (E. coli) peritonitis is a frequent, serious complication of peritoneal dialysis (PD). The extended-spectrum β-lactamase (ESBL)-producing E. coli peritonitis is associated with poorer prognosis and its incidence has been on continuous increase during the last decades. However, the clinical course and outcomes of E. coli peritonitis remain largely unclear.

METHODS

All of the E. coli peritonitis episodes that occurred in our dialysis unit from 2006 to 2011 were reviewed. The polymicrobial episodes were excluded.

RESULTS

In total, ninety episodes of monomicrobial E. coli peritonitis occurred in 68 individuals, corresponding to a rate of 0.027 episodes per patient-year. E. coli was the leading cause (59.2%) of monomicrobial gram-negative peritonitis. ESBL-producing strains accounted for 35.5% of E. coli peritonitis. The complete cure rate and treatment failure rate of E. coli peritonitis were 77.8% and 10.0% respectively. Patients with preceding peritonitis had a higher risk of ESBL production as compared to those without peritonitis history [odds ratio (OR): 5.286; 95% confidence interval (CI): 2.018 - 13.843; p = 0.001]. The risk of treatment failure was significantly increased when the patient had a baseline score of Charlson Comorbidity Index (CCI) above 3 (OR: 6.155; 95% CI: 1.198 - 31.612; p = 0.03), or had diabetes mellitus (OR: 8.457; 95% CI: 1.838 - 38.91; p = 0.006), or hypoalbuminemia (≤ 30g/l) on admission (OR: 13.714; 95% CI: 1.602 - 117.428; p = 0.01). Prolonging the treatment course from 2 to 3 weeks or more reduced the risk of relapse and repeat significantly (p < 0.05).

CONCLUSIONS

E. coli peritonitis remains a common complication of PD. The clinical outcomes of E. coli peritonitis are relatively favorable despite the high ESBL rate. A history of peritonitis is associated with increased risk for ESBL development. The severity of baseline comorbidities, the presence of diabetes mellitus and hypoalbuminemia at admission are associated with poor outcomes.

CTX-M-15-D-ST648 Escherichia coli from companion animals and horses: another pandemic clone combining multiresistance and extraintestinal virulence?

OBJECTIVES

To discern the relevance of ST648 extended-spectrum β-lactamase (ESBL)-producing Escherichia coli as a putative new group of multiresistant and extraintestinal pathogenic strains in animals, its frequency, ESBL types, antimicrobial resistance patterns and virulence gene (VG) profiles should be determined and compared with ST131 strains from the same collection of strains.

METHODS

ESBL-producing E. coli isolates (n = 1152), consecutively sampled from predominantly dogs, cats and horses between 2008 and 2011, were assigned to a phylogenetic group by PCR. Partial multilocus sequence typing was performed for group D and B2 strains and strains presumed to be D-ST648 and B2-ST131 were fully typed. ESBL genes and extraintestinal pathogenic E. coli (ExPEC)-like VGs were characterized by PCR and sequence analysis and antimicrobial resistance was determined by broth dilution. Clonal analysis was done by PFGE.

RESULTS

Forty (3.5%) ESBL-producing E. coli were determined as D-ST648, whereas B2-ST131 isolates occurred less frequently (2.8%). Although the predominant ESBL type in both groups was CTX-M-15 (72.5% versus 46.9%), ST648 strains from companion animals and horses displayed a lower variety of ESBL types (CTX-M-1, -3, -14, -15 and -61 versus CTX-M-1,-2,-14,-15,-27 and -55 and SHV-12). In contrast to ST131 strains, a higher proportion of ST648 strains showed resistance to most non-β-lactam antibiotics. Overall, VGs were less abundant in ST648 strains, although some strains had VG profiles comparable to those of ST131 strains. ExPEC-associated serotype O1:H6 was predominant (46.8%) among the ST648 strains. Some PFGE clusters comprised ST648 isolates from pets, horses and wild birds and humans included from previous studies.

CONCLUSIONS

Our findings demonstrate that certain subgroups of E. coli D-ST648-CTX-M may represent a novel genotype that combines multiresistance, extraintestinal virulence and zoonotic potential.

Shiga toxin-producing Escherichia coli

In the United States, it is estimated that non-O157 Shiga toxin-producing Escherichia coli (STEC) cause more illnesses than STEC O157:H7, and the majority of cases of non-O157 STEC infections are due to serogroups O26, O45, O103, O111, O121, and O145, referred to as the top six non-O157 STEC. The diseases caused by non-O157 STEC are generally milder than those induced by O157 STEC; nonetheless, non-O157 STEC strains have also been associated with serious illnesses such as hemorrhagic colitis and hemolytic uremic syndrome, as well as death. Ruminants, particularly cattle, are reservoirs for both O157 and non-O157 STEC, which are transmitted to humans by person-to-person or animal contact and by ingestion of food or water contaminated with animal feces. Improved strategies to control STEC colonization and shedding in cattle and contamination of meat and produce are needed. In general, non-O157 STEC respond to stresses such as acid, heat, and other stresses induced during food preparation similar to O157 STEC. Similar to O157:H7, the top six non-O157 STEC are classified as adulterants in beef by the USDA Food Safety and Inspection Service, and regulatory testing for these pathogens began in June 2012. Due to the genetic and phenotypic variability of non-O157 STEC strains, the development of accurate and reliable methods for detection and isolation of these pathogens has been challenging. Since the non-O157 STEC are responsible for a large portion of STEC-related illnesses, more extensive studies on their physiology, genetics, pathogenicity, and evolution are needed in order to develop more effective control strategies.

Protein arrays as tool for studies at the host-pathogen interface

Pathogens and parasites encode a wide spectrum of multifunctional proteins interacting to and modifying proteins in host cells. However, the current lack of a reliable method to unveil the protein-protein interactions (PPI) at the host-pathogen interface is retarding our understanding of many important pathogenic processes. Thus, the identification of proteins involved in host-pathogen interactions is important for the elucidation of virulence determinants, mechanisms of infection, host susceptibility and/or disease resistance. In this sense, proteomic technologies have experienced major improvements in recent years and protein arrays are a powerful and modern method for studying PPI in a high-throughput format. This review focuses on these techniques analyzing the state-of-the-art of proteomic technologies and their possibilities to diagnose and explore host-pathogen interactions. Major technical advancements, applications and protocol concerns are presented, so readers can appreciate the immense progress achieved and the current technical options available for studying the host-pathogen interface. Finally, future uses of this kind of array-based proteomic tools in the fight against infectious and parasitic diseases are discussed.

Multidrug resistant commensal Escherichia coli in animals and its impact for public health

After the era of plentiful antibiotics we are alarmed by the increasing number of antibiotic resistant strains. The genetic flexibility and adaptability of Escherichia coli to constantly changing environments allows to acquire a great number of antimicrobial resistance mechanisms. Commensal strains of E. coli as versatile residents of the lower intestine are also repeatedly challenged by antimicrobial pressures during the lifetime of their host. As a consequence, commensal strains acquire the respective resistance genes, and/or develop resistant mutants in order to survive and maintain microbial homeostasis in the lower intestinal tract. Thus, commensal E. coli strains are regarded as indicators of antimicrobial load on their hosts. This chapter provides a short historic background of the appearance and presumed origin and transfer of antimicrobial resistance genes in commensal intestinal E. coli of animals with comparative information on their pathogenic counterparts. The dynamics, development, and ways of evolution of resistance in the E. coli populations differ according to hosts, resistance mechanisms, and antimicrobial classes used. The most frequent tools of E. coli against a variety of antimicrobials are the efflux pumps and mobile resistance mechanisms carried by plasmids and/or other transferable elements. The emergence of hybrid plasmids (both resistance and virulence) among E. coli is of further concern. Co-existence and co-transfer of these "bad genes" in this huge and most versatile in vivo compartment may represent an increased public health risk in the future. Significance of multidrug resistant (MDR) commensal E. coli seem to be highest in the food animal industry, acting as reservoir for intra- and interspecific exchange and a source for spread of MDR determinants through contaminated food to humans. Thus, public health potential of MDR commensal E. coli of food animals can be a concern and needs monitoring and more molecular analysis in the future.

A novel form of bacterial resistance to the action of eukaryotic host defense peptides, the use of a lipid receptor

Host defense peptides show great potential for development as new antimicrobial agents with novel mechanisms of action. However, a small number of resistance mechanisms to their action are known, and here, we report a novel bacterial resistance mechanism mediated by a lipid receptor. Maximin H5 from Bombina maxima bound anionic and zwitterionic membranes with low affinity (Kd > 225 μM) while showing a strong ability to lyse (>55%) and penetrate (π > 6.0 mN m(-1)) these membranes. However, the peptide bound Escherichia coli and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) membranes with higher affinity (Kd < 65 μM) and showed a very low ability for bilayer lysis (<8%) and partitioning (π > 1.0 mN m(-1)). Increasing levels of membrane DMPE correlated with enhanced binding by the peptide (R(2) = 0.96) but inversely correlated with its lytic ability (R(2) = 0.98). Taken with molecular dynamic simulations, these results suggest that maximin H5 possesses membranolytic activity, primarily involving bilayer insertion of its strongly hydrophobic N-terminal region. However, this region was predicted to form multiple hydrogen bonds with phosphate and ammonium groups within PE head-groups, which in concert with charge-charge interactions anchor the peptide to the surface of E. coli membranes, inhibiting its membranolytic action.

The anticancer drug tirapazamine has antimicrobial activity against Escherichia coli, Staphylococcus aureus and Clostridium difficile

Rapidly increasing bacterial resistance to existing therapies creates an urgent need for the development of new antibacterials. Tirapazamine (TPZ, 3-amino-1,2,4-benzotriazine 1,4 dioxide) is a prodrug undergoing clinical trials for various types of cancers. In this study, we showed that TPZ has antibacterial activity, particularly at low oxygen levels. With Escherichia coli, TPZ was bactericidal under both aerobic and anaerobic conditions. Escherichia coli mutants deficient in homologous recombination were hypersusceptible to TPZ, suggesting that drug toxicity may be due to DNA damage. Moreover, E. coli strains deleted for genes encoding putative reductases were resistant to TPZ, implying that these enzymes are responsible for conversion of the prodrug to a toxic compound. Fluoroquinolone-resistant E. coli strains were as susceptible to TPZ as a wild-type strain. Methicillin-resistant Staphylococcus aureus strains were also susceptible to TPZ (MIC = 0.5 μg mL(-1) ), as were pathogenic strains of Clostridium difficile (MIC = 7.5 ng mL(-1) ). TPZ may merit additional study as a broad-spectrum antibacterial, particularly for anaerobes.

Four main virotypes among extended-spectrum-β-lactamase-producing isolates of Escherichia coli O25b:H4-B2-ST131: bacterial, epidemiological, and clinical characteristics

A total of 1,021 extended-spectrum-β-lactamase-producing Escherichia coli (ESBLEC) isolates obtained in 2006 during a Spanish national survey conducted in 44 hospitals were analyzed for the presence of the O25b:H4-B2-ST131 (sequence type 131) clonal group. Overall, 195 (19%) O25b-ST131 isolates were detected, with prevalence rates ranging from 0% to 52% per hospital. Molecular characterization of 130 representative O25b-ST131 isolates showed that 96 (74%) were positive for CTX-M-15, 15 (12%) for CTX-M-14, 9 (7%) for SHV-12, 6 (5%) for CTX-M-9, 5 (4%) for CTX-M-32, and 1 (0.7%) each for CTX-M-3 and the new ESBL enzyme CTX-M-103. The 130 O25b-ST131 isolates exhibited relatively high virulence scores (mean, 14.4 virulence genes). Although the virulence profiles of the O25b-ST131 isolates were fairly homogeneous, they could be classified into four main virotypes based on the presence or absence of four distinctive virulence genes: virotypes A (22%) (afa FM955459 positive, iroN negative, ibeA negative, sat positive or negative), B (31%) (afa FM955459 negative, iroN positive, ibeA negative, sat positive or negative), C (32%) (afa FM955459 negative, iroN negative, ibeA negative, sat positive), and D (13%) (afa FM955459 negative, iroN positive or negative, ibeA positive, sat positive or negative). The four virotypes were also identified in other countries, with virotype C being overrepresented internationally. Correspondingly, an analysis of XbaI macrorestriction profiles revealed four major clusters, which were largely virotype specific. Certain epidemiological and clinical features corresponded with the virotype. Statistically significant virotype-specific associations included, for virotype B, older age and a lower frequency of infection (versus colonization), for virotype C, a higher frequency of infection, and for virotype D, younger age and community-acquired infections. In isolates of the O25b:H4-B2-ST131 clonal group, these findings uniquely define four main virotypes, which are internationally distributed, correspond with pulsed-field gel electrophoresis (PFGE) profiles, and exhibit distinctive clinical-epidemiological associations.

Fluoroquinolone-resistant Haemophilus parasuis isolates exhibit more putative virulence factors than their susceptible counterparts

The prevalence of 23 putative virulence factors among fluoroquinolone-susceptible and -resistant Haemophilus parasuis isolates was analyzed. Putative hemolysin precursor, fimbrial assembly chaperone, and type I site-specific restriction modification system R subunit genes were more prevalent among fluoroquinolone-resistant H. parasuis isolates than among fluoroquinolone-susceptible H. parasuis isolates. Fluoroquinolone resistance may be associated with an increase in the presence of some virulence factors.

Presence of multi-drug resistant pathogenic Escherichia coli in the San Pedro River located in the State of Aguascalientes, Mexico

Contamination of surface waters in developing countries is a great concern. Treated and untreated wastewaters have been discharged into rivers and streams, leading to possible waterborne infection outbreaks and may represent a significant dissemination mechanism of antibiotic resistance genes. In this study, the water quality of San Pedro River, the main river and pluvial collector of the Aguascalientes State, Mexico was assessed. Thirty sample locations were tested throughout the River. The main physicochemical parameters of water were evaluated. Results showed high levels of fecal pollution as well as inorganic and organic matter abundant enough to support the heterotrophic growth of microorganisms. These results indicate poor water quality in samples from different locations. One hundred and fifty Escherichia coli were collected and screened by PCR for several virulence genes. Isolates were classified as either pathogenic (n = 91) or commensal (n = 59). The disc diffusion method was used to determine antimicrobial susceptibility to 13 antibiotics. Fifty-two percent of the isolates were resistant to at least one antimicrobial agent and 30.6% were multi-resistant. Eighteen E. coli strains were quinolone resistant of which 16 were multi-resistant. Plasmid-mediated quinolone resistance (PMQR) genes were detected in 12 isolates. Mutations at the Ser-83→Leu and/or Asp-87→Asn in the gyrA gene were detected as well as mutations at the Ser-80→Ile in parC. An E. coli microarray (Maxivirulence V 3.1) was used to characterize the virulence and antimicrobial resistance genes profiles of the fluoroquinolone-resistant isolates. Antimicrobial resistance genes such as bla TEM, sulI, sulII, dhfrIX, aph3 (strA), and tet (B) as well as integrons were found in fluoroquinolone (FQ) resistance E. coli strains. The presence of potential pathogenic E. coli and antibiotic resistance in San Pedro River such as FQ resistant E. coli could pose a potential threat to human and animal health.