Allele-specific collateral and fitness effects determine the dynamics of fluoroquinolone resistance evolution.

Collateral sensitivity (CS), which arises when resistance to one antibiotic increases sensitivity toward other antibiotics, offers treatment opportunities to constrain or reverse the evolution of antibiotic resistance. The applicability of CS-informed treatments remains uncertain, in part because we lack an understanding of the generality of CS effects for different resistance mutations, singly or in combination. Here, we address this issue in the gram-positive pathogen Streptococcus pneumoniae by measuring collateral and fitness effects of clinically relevant gyrA and parC alleles and their combinations that confer resistance to fluoroquinolones. We integrated these results in a mathematical model that allowed us to evaluate how different in silico combination treatments impact the dynamics of resistance evolution. We identified common and conserved CS effects of different gyrA and parC alleles; however, the spectrum of collateral effects was unique for each allele or allelic pair. This indicated that allelic identity can impact the evolutionary dynamics of resistance evolution during monotreatment and combination treatment. Our model simulations, which included the experimentally derived antibiotic susceptibilities and fitness effects, and antibiotic-specific pharmacodynamics revealed that both collateral and fitness effects impact the population dynamics of resistance evolution. Overall, we provide evidence that allelic identity and interactions can have a pronounced impact on collateral effects to different antibiotics and suggest that these need to be considered in models examining CS-based therapies.

Semi-mechanistic modeling of resistance development to ß-lactam and ß-lactamase-inhibitor combinations.

The use of ß-lactam (BL) and ß-lactamase inhibitor (BLI) combinations, such as piperacillin-tazobactam (PIP-TAZ) is an effective strategy to combat infections by extended-spectrum ß-lactamase-producing bacteria. However, in Gram-negative bacteria, resistance (both mutational and adaptive) to BL-BLI combination can still develop through multiple mechanisms. These mechanisms may include increased ß-lactamase activity, reduced drug influx, and increased drug efflux. Understanding the relative contribution of these mechanisms during resistance development helps identify the most impactful mechanism to target in designing a treatment to counter BL-BLI resistance. This study used semi-mechanistic mathematical modeling in combination with antibiotic sensitivity assays to assess the potential impact of different resistance mechanisms during the development of PIP-TAZ resistance in a Klebsiella pneumoniae isolate expressing CTX-M-15 and SHV-1 ß-lactamases. The mathematical models were used to evaluate the potential impact of several cellular changes as a sole mediator of PIP-TAZ resistance. Our semi-mechanistic model identified 2 out of the 13 inspected mechanisms as key resistance mechanisms that may independently support the observed magnitude of PIP-TAZ resistance, namely porin loss and efflux pump up-regulation. Simulation using the resulting models also suggested the possible adjustment of PIP-TAZ dose outside its commonly used 8:1 dosing ratio. The current study demonstrated how theory-based mechanistic models informed by experimental data can be used to support hypothesis generation regarding potential resistance mechanisms, which may guide subsequent experimental studies.

Molecular relatedness of ESBL/AmpC-producing Escherichia coli from humans, animals, food and the environment: a pooled analysis.

Background: In recent years, ESBL/AmpC-producing Escherichia coli (ESBL/AmpC-EC) have been isolated with increasing frequency from animals, food, environmental sources and humans. With incomplete and scattered evidence, the contribution to the human carriage burden from these reservoirs remains unclear. Objectives: To quantify molecular similarities between different reservoirs as a first step towards risk attribution. Methods: Pooled data on ESBL/AmpC-EC isolates were recovered from 35 studies in the Netherlands comprising >27 000 samples, mostly obtained between 2005 and 2015. Frequency distributions of ESBL/AmpC genes from 5808 isolates and replicons of ESBL/AmpC-carrying plasmids from 812 isolates were compared across 22 reservoirs through proportional similarity indices (PSIs) and principal component analyses (PCAs). Results: Predominant ESBL/AmpC genes were identified in each reservoir. PCAs and PSIs revealed close human-animal ESBL/AmpC gene similarity between human farming communities and their animals (broilers and pigs) (PSIs from 0.8 to 0.9). Isolates from people in the general population had higher similarities to those from human clinical settings, surface and sewage water and wild birds (0.7-0.8), while similarities to livestock or food reservoirs were lower (0.3-0.6). Based on rarefaction curves, people in the general population had more diversity in ESBL/AmpC genes and plasmid replicon types than those in other reservoirs. Conclusions: Our 'One Health' approach provides an integrated evaluation of the molecular relatedness of ESBL/AmpC-EC from numerous sources. The analysis showed distinguishable ESBL/AmpC-EC transmission cycles in different hosts and failed to demonstrate a close epidemiological linkage of ESBL/AmpC genes and plasmid replicon types between livestock farms and people in the general population.

Extended-Spectrum Cephalosporin-Resistant Salmonella enterica serovar Heidelberg Strains, the Netherlands(1).

Extended-spectrum cephalosporin-resistant Salmonella enterica serovar Heidelberg strains (JF6X01.0022/XbaI.0251, JF6X01.0326/XbaI.1966, JF6X01.0258/XbaI.1968, and JF6X01.0045/XbaI.1970) have been identified in the United States with pulsed-field gel electrophoresis. Our examination of isolates showed introduction of these strains in the Netherlands and highlight the need for active surveillance and intervention strategies by public health organizations.

Molecular Characterization of Extended-Spectrum-Cephalosporin-Resistant Enterobacteriaceae from Wild Kelp Gulls in South America.

Extended-spectrum-cephalosporin-resistant Enterobacteriaceae are a public health concern due to limited treatment options. Here, we report on the occurrence and the molecular characteristics of extended-spectrum-cephalosporin-resistant Enterobacteriaceae recovered from wild birds (kelp gulls). Our results revealed kelp gulls as a reservoir of various extended-spectrum cephalosporinase genes associated with different genetic platforms. In addition, we report for the first time the presence of a known epidemic clone of Salmonella enterica serotype Heidelberg (JF6X01.0326/XbaI.1966) among wild birds.

Successful control of a neonatal outbreak caused mainly by ST20 multidrug-resistant SHV-5-producing Klebsiella pneumoniae, Greece.

BACKGROUND: Extended spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-Kp) infection can cause significant morbidity and mortality in neonates. We investigated a nosocomial ESBL-Kp outbreak in a neonatal intensive care unit (NICU) of the University Hospital of Larissa (UHL), Central Greece. METHODS: A total of sixty-four ESBL-Kp were studied; twenty six isolates were recovered from the NICU and were compared with thirty-eight randomly selected isolates from different wards of the hospital during the period March- December 2012. All isolates were characterized by antimicrobial susceptibility testing, ESBL-production by double-disk synergy test, molecular typing using BOX-PCR, whereas selected isolates were further characterized by beta lactamase and virulence gene content, multilocus sequence typing and phylogenetic analysis. All neonates affected by ESBL-Kp were put under strict contact isolation, along with appropriate infection control measures. RESULTS: The outbreak strain of ST20 multidrug-resistant SHV-5-producing K. pneumoniae was identified in all infected (n = 13) and three colonized neonates. A novel ST (ST1114) was also identified among SHV-5 producers (n = 10) recovered from nine colonized infants, but it was not related with ST20. Both STs were identified only in the NICU and not in other wards of the hospital. No ESBL-Kp were isolated from the hands of the nursing staff and the environment. Although we were not able to identify the source of the outbreak, no ESBL-Kp were isolated in the NICU after this period and we assumed that the outbreak was successfully controlled. All neonates received parenteral nutrition and most of them were delivered by caesarean section and showed low gestational age (<32 weeks) and low birth weights (<1500 g). CONCLUSION: According to our knowledge, this is the first description of an outbreak of multidrug-resistant SHV-5 producing K. pneumoniae assigned to ST20.

Spread of multidrug-resistant Pseudomonas aeruginosa clones in a university hospital.

An outbreak of multidrug-resistant Pseudomonas aeruginosa (MDRPA) infections in a university hospital is described. Phenotypic and genotypic analysis of 240 isolates revealed that 152 patients, mainly in the intensive care unit (ICU), were colonized or infected with MDRPA, the majority with O11. All metallo-ß-lactamase (MBL)-positive isolates carried the bla(VIM-2) or bla(VIM-1) gene. One or more type III secretion system toxin genes were detected in most isolates. Five dominant pulsed-field gel electrophoresis (PFGE) types were characterized, associated with ST235, ST111, ST253, ST309, and ST639.

Carbapenemase-producing Pseudomonas aeruginosa from central Greece: molecular epidemiology and genetic analysis of class I integrons.

BACKGROUND: Multidrug-resistant Pseudomonas aeruginosa is a serious challenge for antimicrobial therapy of nosocomial infections, as it possesses several mechanisms of antimicrobial resistance. In Central Greece, a sudden increase of infections caused by carbapenem-resistant P. aeruginosa was observed during 2011, indicating the need for further analysis. METHODS: Five-hundred and sixty-eight P. aeruginosa isolates were collected consecutively during an 8-month period in 2011 from inpatients treated in three hospitals in the Thessaly region (1,000,000 habitants) of Greece. Carbapenem-resistant P. aeruginosa (n = 284) were characterized by antimicrobial susceptibility testing and ß-lactamase content, and the genetic relatedness of carbapenemase-producing isolates was assessed by BOX-PCR, multilocus sequence typing, and eBURST analysis. Mapping of the class I integrons of Verona integron-encoded metallo-ß-lactamase (VIM)-carrying isolates was also performed, and clinical data of the VIM producers were reviewed. RESULTS: Eighty (14.1%) out of the 568 P. aeruginosa isolates recovered from clinical specimens were VIM producers. Multilocus sequence typing revealed high prevalence of the international clones ST111 and ST235 among blaVIM-2- and blaVIM-4-positive isolates, respectively. blaVIM-17 was identified in an isolate of a novel sequence type (ST1457). blaVIM gene cassettes were carried by five distinct class I integrons, including two novel ones. CONCLUSIONS: Since the first report of VIM-producing P. aeruginosa in 2000, this microorganism still remains among the most prevalent multidrug resistant pathogens in Greece. The spread of VIM-producers belonging to the most common international clones (ST111 and ST235), the spread of integrons of divergent structures, and the emergence of novel integrons underscore their ongoing evolution.

Factors influencing linezolid-nonsusceptible coagulase-negative staphylococci dissemination among patients in the intensive care unit: a retrospective cohort study.

BACKGROUND: The aim of the present study was to identify risk factors for linezolid-nonsusceptible coagulase-negative staphylococci (CNS) dissemination in the intensive care unit. METHODS: Among the 246 patients included, 33 revealed a linezolid-nonsusceptible CNS-positive culture specimen, 68 were positive for linezolid-susceptible CNS and 145 served as controls. Isolates were characterized by phenotypic and genotypic methods to species level, susceptibility to antistaphylococcal agents and clones. RESULTS: Among the 33 linezolid-nonsusceptible CNS patients, 29 revealed Staphylococcus epidermidis and 4 Staphylococcus capitis. All S. epidermidis strains belonged to the ST22 clone (by multilocus sequence typing), 26 carried both C2534T and T2504A and 3 strains were C2543T mutations. S. capitis strains were stratified as a common pulsed-field gel electrophoresis type and carried the G2576T mutation. Risk factors for linezolid-nonsusceptible CNS isolation were linezolid administration and mean number of linezolid-nonsusceptible CNS-positive patients in nearby beds per day. CONCLUSIONS: These results reinforce the aspect of rational antibiotic usage, but also highlight the need for strict infection control measures to prevent the dissemination of linezolid-nonsusceptible CNS.

Longitudinal Study of Dynamic Epidemiology of Extended-Spectrum Beta-Lactamase-Producing Escherichia coli in Pigs and Humans Living and/or Working on Pig Farms.

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacterales have been increasingly isolated from pigs, highlighting their potential for transmission to humans living and/or working within pig farms. As longitudinal data on the prevalence and the molecular characteristics of such isolates from the high-risk farming population remain scarce, we performed a long-term study on 39 Dutch pig farms. Fecal samples from pigs, farmers, family members, and employees were collected during four sampling occasions with a 6-month period. The presence of ESBL-producing Enterobacterales and their molecular characteristics (ESBL gene, plasmid, and sequence types) were determined by standard methods. Data on personal and farm characteristics were collected using questionnaires. ESBL-producing Escherichia coli was present in pigs at least once for 18 of 39 farms and in 17 of 146 farmers, family members, and/or employees. Among these 417 E. coli isolates, blaCTX-M-1 was the most frequently observed ESBL gene in pigs (n = 261) and humans (n = 25). Despite the great variety in plasmid (sub)types and E. coli sequence types (STs), we observed genetic similarity between human- and pig-derived isolates in (i) ESBL gene, plasmid (sub)type, and ST, suggesting potential clonal transmission in seven farms, and (ii) only ESBL gene and plasmid (sub)type, highlighting the possibility of horizontal transfer in four farms. Five pig farmers carried ESBL producers repeatedly, of whom two carried an identical combination of gene, plasmid (sub)type, and ST over time. Human ESBL carriage was associated with both presence of ESBL producers in pigs and average number of hours working on the pig farm per week, while prolonged human carriage was observed only incidentally. IMPORTANCE Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli represents a public health hazard due to reduced therapeutic options for the treatment of infections. Although direct contact with pigs is considered a risk factor for human ESBL-producing E. coli carriage through occupational exposure, nationwide data regarding the occurrence of such isolates among pigs and humans living and/or working on farms remain scarce. Therefore, we determined (i) the longitudinal dynamics in prevalence and molecular characteristics of ESBL-producing E. coli in Dutch pig farmers and their pigs over time and (ii) the potential transmission events between these reservoirs based on genetic relatedness and epidemiological associations in longitudinal data. Our data suggesting the possibility of clonal and horizontal dissemination of ESBL-producing Escherichia coli between pigs and pig farmers can be used to inform targeted intervention strategies to decrease the within-farm human exposure to ESBL-producing E. coli.

Ciprofloxacin-resistant Escherichia coli in Central Greece: mechanisms of resistance and molecular identification.

BACKGROUND: Fluoroquinolone resistant E. coli isolates, that are also resistant to other classes of antibiotics, is a significant challenge to antibiotic treatment and infection control policies. In Central Greece a significant increase of ciprofloxacin-resistant Escherichia coli has occurred during 2011, indicating the need for further analysis. METHODS: A total of 106 ciprofloxacin-resistant out of 505 E. coli isolates consecutively collected during an eight months period in a tertiary Greek hospital of Central Greece were studied. Antimicrobial susceptibility patterns and mechanisms of resistance to quinolones were assessed, whereas selected isolates were further characterized by multilocus sequence typing and ß-lactamase content. RESULTS: Sequence analysis of the quinolone-resistance determining region of the gyrA and parC genes has revealed that 63% of the ciprofloxacin-resistant E. coli harbored a distinct amino acid substitution pattern (GyrA:S83L + D87N; ParC:S80I + E84V), while 34% and 3% carried the patterns GyrA:S83L + D87N; ParC:S80I and GyrA:S83L + D87N; ParC:S80I + E84G respectively. The aac (6')-1b-cr plasmid-mediated quinolone resistance determinant was also detected; none of the isolates was found to carry the qnrA, qnrB and qnrS.Genotyping of a subset of 35 selected ciprofloxacin-resistant E. coli by multilocus sequence typing has revealed the presence of nine sequence types; ST131 and ST410 were the most prevalent and were exclusively correlated with hospital and health care associated infections, while strains belonging to STs 393, 361 and 162 were associated with community acquired infections. The GyrA:S83L + D87N; ParC:S80I + E84V substitution pattern was found exclusively among ST131 ciprofloxacin-resistant E. coli. Extended-spectrum ß-lactamase-positive ST131 ciprofloxacin-resistant isolates produced CTX-M-type enzymes; eight the CTX-M-15 and one the CTX-M-3 variant. CTX-M-1 like and KPC-2 enzymes were detected in five and four ST410 ciprofloxacin-resistant E. coli isolates, respectively. CONCLUSIONS: Our findings suggest that, ST131 and ST410 predominate in the ciprofloxacin resistant E. coli population.

Design principles of collateral sensitivity-based dosing strategies.

Collateral sensitivity (CS)-based antibiotic treatments, where increased resistance to one antibiotic leads to increased sensitivity to a second antibiotic, may have the potential to limit the emergence of antimicrobial resistance. However, it remains unclear how to best design CS-based treatment schedules. To address this problem, we use mathematical modelling to study the effects of pathogen- and drug-specific characteristics for different treatment designs on bacterial population dynamics and resistance evolution. We confirm that simultaneous and one-day cycling treatments could supress resistance in the presence of CS. We show that the efficacy of CS-based cycling therapies depends critically on the order of drug administration. Finally, we find that reciprocal CS is not essential to suppress resistance, a result that significantly broadens treatment options given the ubiquity of one-way CS in pathogens. Overall, our analyses identify key design principles of CS-based treatment strategies and provide guidance to develop treatment schedules to suppress resistance.

Occurrence and Molecular Characteristics of Extended-Spectrum Beta-Lactamase-Producing Enterobacterales Recovered From Chicken, Chicken Meat, and Human Infections in Sao Paulo State, Brazil.

This study aimed to investigate the phylogenetic diversity and epidemiology of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae from chicken, chicken meat, and human clinical isolates in Sao Paolo, Brazil, and characterize their respective ESBL-encoding plasmids. Three hundred samples from chicken cloaca, chicken meat, and clinical isolates were phenotypically and genotypically assessed for ESBL resistance. Isolates were identified by MALDI TOF-MS and further characterized by MLST analysis and phylogenetic grouping. ESBL genes were characterized and their location was determined by I-Ceu-I-PFGE and Southern blot, conjugation, transformation, and PCR-based replicon typing experiments. Thirty-seven ESBL-producing isolates (28 E. coli and 9 K. pneumoniae) that were positive for the bla CTX-M-1 or bla CTX-M-2 gene groups were obtained. Two isolates were negative in the transformation assay, and the chromosomal location of the genes was deduced by Southern blot. The bla CTX-M genes identified were carried on plasmid replicon-types X1, HI2, N, FII-variants, I1 and R. The E. coli isolates belonged to nine sequence types, while the K. pneumoniae isolates belonged to four sequence types. The E. coli isolates belonged to phylotype classification groups A, B1, D, and F. This study demonstrated that isolates from cloacal swabs, chicken meat, and human feces had genetic diversity, with a high frequency of bla CTX-M-15 among chickens, chicken meat, and human feces. Thus, this reinforces the hypothesis that chickens, as well as their by-products, could be an important source of transmission for ESBL-producing pathogens to humans in South America.

Identification of antibiotic collateral sensitivity and resistance interactions in population surveillance data.

BACKGROUND: Collateral effects of antibiotic resistance occur when resistance to one antibiotic agent leads to increased resistance or increased sensitivity to a second agent, known respectively as collateral resistance (CR) and collateral sensitivity (CS). Collateral effects are relevant to limit impact of antibiotic resistance in design of antibiotic treatments. However, methods to detect antibiotic collateral effects in clinical population surveillance data of antibiotic resistance are lacking. OBJECTIVES: To develop a methodology to quantify collateral effect directionality and effect size from large-scale antimicrobial resistance population surveillance data. METHODS: We propose a methodology to quantify and test collateral effects in clinical surveillance data based on a conditional t-test. Our methodology was evaluated using MIC data for 419 Escherichia coli strains, containing MIC data for 20 antibiotics, which were obtained from the Pathosystems Resource Integration Center (PATRIC) database. RESULTS: We demonstrate that the proposed approach identifies several antibiotic combinations that show symmetrical or non-symmetrical CR and CS. For several of these combinations, collateral effects were previously confirmed in experimental studies. We furthermore provide insight into the power of our method for multiple collateral effect sizes and MIC distributions. CONCLUSIONS: Our proposed approach is of relevance as a tool for analysis of large-scale population surveillance studies to provide broad systematic identification of collateral effects related to antibiotic resistance, and is made available to the community as an R package. This method can help mapping CS and CR, which could guide combination therapy and prescribing in the future.

Manganese complex [Mn(CO)3(tpa-κ3N)]Br increases antibiotic sensitivity in multidrug resistant Streptococcus pneumoniae.

OBJECTIVES: The emergence of multidrug-resistance (MDR) in Streptococcus pneumoniae clones and non-vaccine serotypes necessitate the development of novel treatment strategies. This work aimed to determine the efficacy of the Mn complex [Mn(CO)3(tpa-κ3N)]Br against clinically important MDR strains of S. pneumoniae. METHODS: Twenty MDR clinicalS. pneumoniae strains were included in this study. Minimum inhibitory concentrations (MICs) of [Mn(CO)3(tpa-κ3N)]Br were determined via broth microdilution alone and in combination with other antimicrobial agents using checkerboard assays and/or disc diffusion tests. In vitro efficacy was assessed by time-kill assays while in vivo efficacy was tested using the insect model Galleria mellonella. RESULTS: [Mn(CO)3(tpa-κ3N)]Br showed moderate in vitro efficacy against S. pneumoniae coupled with bactericidal activity. Checkerboard and disc diffusion assays showed synergy between [Mn(CO)3(tpa-κ3N)]Br and tetracycline, and the combination of both agents caused rapid kill-kinetics and reduced the MIC below the susceptibility breakpoint of 1 mg/L even for tetracycline-resistant strains of S. pneumoniae. Similar results were observed for the erythromycin- and the co-trimoxazole-Mn complex combination. In the G. mellonella infection model, mortality and morbidity rates at 96 h were significantly lower in larvae treated with [Mn(CO)3(tpa-κ3N)]Br than phosphate buffered saline, while treatment with the tetracycline-Mn complex combination was superior to monotherapy, resulting in significantly lower mortality and morbidity rates (p < 0.049). CONCLUSIONS: We show that [Mn(CO)3(tpa-κ3N)]Br has in vitro and in vivo antibacterial activity against clinically relevant strains of S. pneumoniae and has the potential to be used in combination with currently available antibiotics to increase their effectiveness against MDR S. pneumoniae.

Antibiotic production in Streptomyces is organized by a division of labor through terminal genomic differentiation.

One of the hallmark behaviors of social groups is division of labor, where different group members become specialized to carry out complementary tasks. By dividing labor, cooperative groups increase efficiency, thereby raising group fitness even if these behaviors reduce individual fitness. We find that antibiotic production in colonies of Streptomyces coelicolor is coordinated by a division of labor. We show that S. coelicolor colonies are genetically heterogeneous because of amplifications and deletions to the chromosome. Cells with chromosomal changes produce diversified secondary metabolites and secrete more antibiotics; however, these changes reduced individual fitness, providing evidence for a trade-off between antibiotic production and fitness. Last, we show that colonies containing mixtures of mutants and their parents produce significantly more antibiotics, while colony-wide spore production remains unchanged. By generating specialized mutants that hyper-produce antibiotics, streptomycetes reduce the fitness costs of secreted secondary metabolites while maximizing the yield and diversity of these products.

High Prevalence of Intra-Familial Co-colonization by Extended-Spectrum Cephalosporin Resistant Enterobacteriaceae in Preschool Children and Their Parents in Dutch Households.

Extended-spectrum cephalosporin-resistant (ESCR) Enterobacteriaceae pose a serious infection control challenge for public health. The emergence of the ESCR phenotype is mostly facilitated by plasmid-mediated horizontal extended-spectrum ß-lactamases (ESBLs) and AmpC gene transfer within Enterobacteriaceae. Current data regarding the plasmid contribution to this emergence within the Dutch human population is limited. Hence, the aim of this study was to gain insight into the role of plasmids in the dissemination of ESBL/AmpC genes inside Dutch households with preschool children and precisely delineate co-colonization. In 87 ESCREnterobacteriaceae from fecal samples of parents and preschool children within 66 Dutch households, genomic localization, plasmid type and insertion sequences linked to ESBL/AmpC genes were determined. Chromosomal location of ESBL/AmpC genes was confirmed when needed. An epidemiologically relevant subset of the isolates based on household co-carriage was assessed by Multilocus Sequence Typing and Pulsed-Field Gel Electrophoresis for genetic relatedness. The narrow-host range I1α and F plasmids were the major facilitators of ESBL/AmpC-gene dissemination. Interestingly, we documented a relatively high occurrence of chromosomal integration of typically plasmid-encoded ESBL/AmpC-genes. A high diversity of non-epidemic Escherichia coli sequence types (STs) was revealed; the predominant STs belonged to the pandemic lineages of extraintestinal pathogenic E. coli ST131 and ST69. Intra-familiar co-carriage by identical ESCREnterobacteriaceae was documented in 7 households compared to 14 based on sole gene typing, as previously reported. Co-carriage was more frequent than expected based on pure chance, suggesting clonal transmission between children and parents within the household.

Occurrence and characterization of extended-spectrum cephalosporin-resistant Enterobacteriaceae in healthy household dogs in Greece.

Extended-spectrum cephalosporin- and/or carbapenem-resistant (ESCR and/or CarbR) Enterobacteriaceae constitute a public health hazard because of limited treatment options and are endemic among humans in Greece. Recently, ESCR and CarbREnterobacteriaceae have been increasingly isolated from companion animals, stressing their potential role as a reservoir for humans. However, the presence of ESCR bacteria in companion animals within Greek households has not been determined yet. Genes conferring the ESCR and CarbR phenotype were detected among canine isolates and their chromosomal or plasmid location was determined. Standard methods were applied for plasmid characterization. The clonal relatedness of the recovered isolates was examined by multilocus sequence typing (MLST). Here, we report the first findings on the presence of ESCREnterobacteriaceae in healthy Greek dogs. ESCREscherichia coli isolates were associated with different sequence types (STs), including the human pandemic ST131 clone. The occurrence of human-related ESBL/pAmpC genes, plasmid types and/or strain STS in this animal reservoir suggests possible bilateral transmission.