Seven-year surveillance of the prevalence of antimicrobial-resistant Escherichia coli isolates,with a focus on ST131 clones,among healthy people in Osaka,Japan

ObjectivesEscherichia coli (E. coli) is an indicator of antimicrobial resistance, and some strains of E. coli cause infectious diseases. E. coli sequence type 131 (ST131) – a global antimicrobial-resistant pandemic E. coli clone – is frequently detected in clinical specimens. Antimicrobial-resistant bacteria are monitored via national surveillance in clinical settings; however, monitoring information in non-clinical settings is limited. This study elucidated antimicrobial resistance trends of E. coli and dissemination of ST131 among healthy people in non-clinical settings.MethodsThis study collected 517 E. coli isolates from healthy people in Osaka, Japan, between 2013 and 2019. It analysed antimicrobial susceptibility of the isolates and detected the bla and mcr genes in ampicillin-resistant and colistin-resistant isolates, respectively, and the ST131 clone.ResultsAntimicrobial resistance rates of the bacteria isolated from healthy people in non-clinical settings were lower than for those in clinical settings. The resistance of the isolates to cefotaxime (4.4%) and ciprofloxacin (13.5%) gradually increased during the study period. In 23 cefotaxime-resistant isolates, the most frequent bla genes belonged to the bla_CTX-M-9 group, followed by bla_CTX-M-1 goup, bla_TEM and bla_CMY-2. One mcr-1-harbouring colistin-resistant isolate was detected in 2016. The incidence of the E. coli O25b-ST131 clone was approximately 5% until 2015 and 10% after 2016.ConclusionBoth ciprofloxacin resistance and O25b-ST131 clone frequency increased during the study period. Antimicrobial-resistant bacteria gradually spread in healthy people in non-clinical settings; one reason behind this spread was dissemination of global antimicrobial-resistant pandemic clones.     

Faropenem resistance causes in vitro cross-resistance to carbapenems in ESBL-producing Escherichia coli

ObjectiveFaropenem is an oral penem drug with activity against Gram-positive and Gram-negative bacteria, including CTX-M-15-type extended spectrum beta-lactamase (ESBL)-producing Enterobacteriales and anaerobic bacteria. As there are structural similarities, there is concern for the development of carbapenem cross-resistance; however, there are no studies confirming this. This study examined whether in vitro development of faropenem resistance in Escherichia coli isolates would result in cross-resistance to carbapenems.MethodsFour well-characterized E. coli isolates from the US Centers for Disease Control and Prevention antibiotic resistance isolate bank were utilized. Three isolates (NSF1, NSF2 and NSF3) are ESBL producers (CTX-M-15) and one (NSF4) is pan-susceptible. Faropenem minimum inhibitory concentrations (MICs) were determined and resistance was induced by serial passaging in increasing concentrations of faropenem. Susceptibility to carbapenems was determined and whole-genome sequencing (WGS) was performed to identify the underlying genetic mechanism leading to carbapenem resistance.ResultsFaropenem MIC increased from 1 mg/L to 64 mg/L within 10 days for NSF2 and NSF4 isolates, and from 2 mg/L to 64 mg/L within 7 days for NSF1 and NSF3 isolates. Reduced carbapenem susceptibility (ertapenem MIC ≥8 mg/L, doripenem/meropenem ≥2 mg/L and imipenem ≥1 mg/L) developed among three CTX-M-15-producing isolates that were faropenem-resistant, but not in NSF4 isolate that lacked ESBL enzyme. WGS analysis revealed non-synonymous changes in the ompC gene among three CTX-M-15-producing isolates, and a single nucleotide polymorphism (SNP) in the envZ gene in NSF4 isolate.ConclusionInduced resistance to faropenem causes cross-resistance to carbapenems among E. coli isolates containing CTX-M-15-type ESBL enzymes.     

Longitudinal study on antimicrobial consumption and resistance in rabbit farming

Reliable indicators of antimicrobial consumption (AMC) measured with harmonised data and supported by indicators for antimicrobial resistance (AMR) at herd level are necessary to target antimicrobial misuse in food-producing animals. AMC data in 2010–2015 in 32 Italian industrial rabbit holdings weighted with semester production and standardised with animal daily doses (ADDs) were collected. Herd-level AMR against eight antimicrobials was assessed in Escherichia coli, Enterococcus faecalis and Enterococcus hirae collected in 2014–2015. Escherichia coli were assessed for mcr-1 and mcr-2 genes. To produce 1?kg of live rabbit, a mean of 71.8 ADDs was used. Overall AMC reduced over time (P?<?0.05) owing to lowering consumption of tetracyclines (P?<?0.05) and colistin (P?<?0.01), but consumption of quinolones (P?<?0.05), bacitracin (P?<?0.01) and sulfonamides (P?=?0.017) increased. All except one indicator E. coli were wild-type for cefotaxime, whereas 97% displayed reduced susceptibility to tetracyclines, 89% to trimethoprim, 63% to enrofloxacin, 24% to chloramphenicol and 21% to colistin. mcr-1 was detected in 50/320 E. coli isolates from 15/32 holdings; mcr-2 was not detected in 58 isolates with colistin MIC?≥?2?mg/L. All 305 enterococci were wild-type for ampicillin, ciprofloxacin and vancomycin and displayed reduced tetracycline susceptibility. The mean antimicrobial resistance index (ARI) was 0.5 for E. coli and 0.3 for enterococci. ARI was significantly correlated with AMC at herd level for enterococci (P?=?0.008) but not E. coli where high ARI levels were found in a few holdings with low AMC.     

Pharmaceutical disposal facilitates the mobilization of resistance determinants among microbiota of polluted environment

The emergence of resistance on exposure to pharmaceuticals among microorganisms has raised serious concern in the therapeutic approach against infectious diseases. Effluents discharge from hospitals, industries, and urban settlements containing pharmaceuticals and other toxic compounds into the aquatic ecosystem selects bacterial population against them; thereby promotes acquisition and dissemination of resistant traits among the inhabitant microbiota. The present study was aimed to determine the prevalence and multidrug resistance pattern of Extended Spectrum β-lactamase (ESBL) producing and non-producing bacterial isolates from the heavily polluted Delhi stretch of river Yamuna, India. Additionally, the role of abiotic factors in the dissemination of conjugative plasmids harbouring resistance genes was also studied using E. coli J53 as recipient and resistant E. coli isolates as donor strains. Of the 227 non-duplicate bacterial isolates, 60% (136) were identified as ESBL⁺ and 40% (91) as ESBL. ESBL⁺ isolates were found highly resistant to β-lactam and non-β-lactam classes of antibiotics compared with the ESBL⁻ isolates. 68% of ESBL⁺ and 24% of ESBL⁻ isolates showed an MAR index of ≥0.5. Surprisingly, multidrug resistance (MDR), extensively drug resistance (XDR), and pandrug resistance (PDR) phenotype were observed for 78.6%, 16.9%, and 0.7% of ESBL⁺ and 90%, 3%, and none for PDR among ESBL⁻ isolates. Conjugation under different conditions showed a higher mobilization rate at neutral pH (7–7.5) for ESBL⁺ isolates. Conjugation frequency was maximum at 40 °C for the isolate E. coli MRB6 (4.1 × 10⁻⁵) and E. coli MRE32 (4.89 × 10⁻⁴) and at 35 °C for E. coli MRA11 (4.89 × 10⁻⁵). The transconjugants obtained were found tolerating different concentrations of mercuric chloride (0.0002–0.2 mg/L). Increased biofilm formation for ESBL⁺ isolates was observed on supplementing media with HgCl₂ (2 μg/mL) either singly or in combination with CTX (10 μg/mL). The present study demonstrates that anthropogenically influenced aquatic environments act as a reservoir of MDR, XDR, and even PDR strains; thereby posing a potent public health risk.     

Susceptibility to five antifungals of Aspergillus fumigatus strains isolated from chronically colonised cystic fibrosis patients receiving azole therapy

Exposure of Aspergillus fumigatus to stressful antifungal therapies may result in decreased susceptibility. The aim of the present work was to evaluate the susceptibility to azole and non-azole antifungals of 159 isolates of A. fumigatus collected from cystic fibrosis (CF) patients receiving azole antifungal therapy. The genetic diversity of the fungal isolates was assessed using microsatellite genotyping, and some strains were found in patient's sputum samples more than 4 years apart. No resistant isolates [minimal inhibitory concentration (MIC)/minimal effective concentration (MEC) ≥4 μg/mL] were identified to the antifungals amphotericin B, caspofungin, itraconazole and voriconazole. A single A. fumigatus isolate was identified outside of the epidemiological cut-off of 0.25 μg/mL for posaconazole. Susceptibility of the recurrent isolates was in agreement with the susceptibility of the first isolate identified (100% essential agreement). Even after azole exposure, several recurrent A. fumigatus strains were detected in the subsequent sputum samples. Development of resistance in A. fumigatus to antifungals appears to be rare amongst CF patients. However, it remains crucial to evaluate the importance of antifungal agents for allergic fungal diseases.     

Antimicrobial susceptibility of Escherichia coli from community-acquired urinary tract infections in Europe: the ECO·SENS study revisited

This study determined the antimicrobial susceptibility of Escherichia coli causing community-acquired, acute, uncomplicated, non-recurrent urinary tract infection in unselected women aged 18-65 years and compared the results with those obtained 8 years earlier in the first ECO·SENS study (1999-2000). During 2007-2008, urine samples were taken from 1697 women in Austria, Greece, Portugal, Sweden and the UK. The countries were chosen to represent areas of Europe indicated to have more (Greece and Portugal) or less (UK, Austria and Sweden) problems with resistance. Antimicrobial susceptibility testing of 903 E. coli isolates (150-200 isolates per country) to 14 antimicrobials was performed by disk diffusion using European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. In E. coli, resistance to mecillinam, cefadroxil (representing oral cephalosporins), nitrofurantoin, fosfomycin trometamol, gentamicin and the third-generation cephalosporins cefotaxime and ceftazidime was <2%, with the following exceptions: gentamicin in Portugal (2.8%); fosfomycin in Greece (2.9%); and cephalosporins in Austria (2.7-4.1%). Resistance levels were higher for amoxicillin/clavulanic acid (2.0-8.9%) and ciprofloxacin (0.5-7.6%) and much higher to ampicillin (21.2-34.0%), sulfamethoxazole (21.2-31.3%), trimethoprim (14.9-19.1%) and trimethoprim/sulfamethoxazole (14.4-18.2%). Resistance to quinolones and trimethoprim increased between the ECO·SENS I (1999-2000) and ECO·SENS II (2007-2008): nalidixic acid 4.3% to 10.2%; ciprofloxacin 1.1% to 3.9%; and trimethoprim 13.3% to 16.7%. In the previous study, no isolates with extended-spectrum β-lactamase were found; however, in the present study 11 isolates were identified as having either CTX-M or AmpC.     

Piperacillin-Tazobactam-Resistant/Third-Generation Cephalosporin-Susceptible Escherichia coli and Klebsiella pneumoniae Isolates: Resistance Mechanisms and In vitro-In vivo Discordance

We previously reported the detection of Escherichia coli and Klebsiella pneumoniae that displayed in vitro piperacillin-tazobactam (TZP) resistance but were susceptible to third-generation cephalosporins (TZP-R/Ceph3-S). In this study, we assessed the phenotypic and genotypic profiles of 12 clinical non-clonal TZP-R/Ceph3-S E. coli and K. pneumoniae isolates derived from bloodstream infections. Whole-genome sequencing revealed that most of the TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined harbored bla_TEM-1 and bla_SHV-1 genes, respectively, but none harbored extended-spectrum β-lactamase, AmpC β-lactamase or carbapenemase genes. Increasing the tazobactam concentration from 4 mg/L to 16 mg/L restored TZP in vitro susceptibility among E. coli isolates expressing TEM-1, but had minimal impact on the susceptibility of K. pneumoniae to TZP. Real-time qPCR analysis showed that bla_TEM-1 expression was amplified in TZP-R E. coli upon incubation with sub-inhibitory TZP concentrations. Using an immunocompetent murine septicemia model, the efficacy of TZP against TZP-R/Ceph3-S isolates was assessed using TZP doses that mimicked human plasma exposures following intravenous (IV) administration of TZP 4.5 g q6h over 0.5 h for 24 h. Efficacy was assessed by survival through 96 h. There was high mortality in untreated control mice for all tested isolates. Compared with controls, TZP human-simulated exposure significantly improved survival for all TZP-R/Ceph3-S E. coli and K. pneumoniae isolates examined (P < 0.05). Thus, TZP was associated with remarkable in vivo activity against TZP-R/Ceph3-S E. coli and K. pneumoniae despite the observed resistance in vitro.     

Empirical treatment of lower urinary tract infections in the face of spreading multidrug resistance: in vitro study on the effectiveness of nitroxoline

The spread of antimicrobial resistance challenges the empirical treatment of urinary tract infections (UTIs). Among others, nitrofurantoin is recommended for first-line treatment, but acceptance among clinicians is limited due to chronic nitrofurantoin-induced lung toxicity and insufficient coverage of Enterobacteriaceae other than Escherichia coli. Nitroxoline appears to be an alternative to nitrofurantoin owing to its favourable safety profile, however data on its current in vitro susceptibility are sparse. In this study, susceptibility to nitroxoline was tested against 3012 urinary clinical isolates (including multidrug-resistant bacteria and Candida spp.) by disk diffusion test and/or broth microdilution. At least 91% of all Gram-negatives (n?=?2000), Gram-positives (n?=?403) and yeasts (n?=?132) had inhibition zone diameters for nitroxoline ≥18?mm. Except for Pseudomonas aeruginosa, nitroxoline MIC₉₀ values were ≤16?mg/L and were 2- to >16-fold lower compared with nitrofurantoin. In extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus (MRSA), MIC₉₀ values of nitroxoline were two-fold higher compared with non-ESBL-producing enterobacteria and methicillin-susceptible S. aureus (MSSA). The in vitro efficacies of nitroxoline and nitrofurantoin against ATCC strains of E. coli, Enterococcus faecalis and Proteus mirabilis were compared by time–kill curves in Mueller–Hinton broth and artificial urine. Nitroxoline was non-inferior against E. coli, P. mirabilis and E. faecalis in artificial urine. In conclusion, nitroxoline showed a broad antimicrobial spectrum, with inhibition zone diameters and MICs of nitroxoline well below the EUCAST breakpoint for E. coli for most organisms, and thus may also be a target for therapy of uncomplicated UTIs.     

Activity of ceftolozane-tazobactam against Gram-negative pathogens isolated from lower respiratory tract infections in the Asia-Pacific region: SMART 2015-2016

The aim of this study was to investigate the susceptibility of respiratory Gram-negative bacteria to ceftolozane/tazobactam and other antibiotics in the Asia-Pacific region during 2015-2016. MICs were determined using the CLSI standard broth microdilution method and interpreted accordingly. Pseudomonas aeruginosa (1574 isolates), Klebsiella pneumoniae (1226), Acinetobacter baumannii (627) and Escherichia coli (476) accounted for 73.1% of 5342 Gram-negative respiratory pathogens. Susceptibility to ceftolozane/tazobactam of individual Enterobacteriaceae was >80%, except for Enterobacter cloacae (76.6%). Ceftolozane/tazobactam inhibited 81.9% of K. pneumoniae and 91.9% of E. coli, with respective MIC₅₀/MIC₉₀ values of 0.5/>32 and 0.25/2 mg/L. For carbapenem-susceptible, ESBL-producing K. pneumoniae and E. coli, susceptibility was 65.5% and 93.3%, respectively, and respective MIC₅₀/MIC₉₀ values were 2/>32 and 0.5/2 mg/L. Bla_{CTX-M-1 group} was most prevalent in selected ESBL-producing K. pneumoniae (40 of 54 isolates) and E. coli (15 of 22 isolates), with ceftolozane/tazobactam susceptibility rates of 50% and 80%, respectively. Bla_SHV-ESBL was the second most prevalent, and ceftolozane/tazobactam inhibited 20% of 20 K. pneumoniae isolates with bla_SHV-ESBL. The only effective antibiotics for carbapenem-non-susceptible K. pneumoniae (111 isolates) and E. coli (24 isolates) were amikacin and colistin. Ceftolozane/tazobactam was effective against almost all tested P. aeruginosa and carbapenem-non-susceptible strains, with susceptibility of 92.3% and 72.8%, respectively; the respective MIC₅₀/MIC₉₀ values were 1/4 and 2/>32 mg/L. The high susceptibility of ceftolozane/tazobactam remained in different age groups, patient locations, recovery times and countries, except Vietnam. In conclusion, ceftolozane/tazobactam was effective against most respiratory Gram-negative pathogens in the Asia-Pacific region; however, the emergence of carbapenem resistance mandates ongoing surveillance.     

Resistance to third-generation cephalosporins in Escherichia coli in the French community: The times they are a-changin'?

ObjectivesSince the early 2000s, Escherichia coli resistance to third-generation cephalosporins (3GCs) has been increasing in all European countries, mainly due to the spread of extended spectrum β-lactamases (ESBLs). Here we present a retrospective study that combines resistance of E. coli to 3GCs and quinolones with data on antibiotic use in the community in a region of Northeastern France.MethodsSince 2012, an observational surveillance of antimicrobial resistance and antibiotic use in the community was conducted: data on antimicrobial resistance in E. coli isolates were collected from 11 private laboratories, and consumption data were collected from the three main healthcare insurances.ResultsA significant decrease in the prevalence of resistance to 3GCs (from 5.6% to 4.2%; P < 0.001), nalidixic acid (from 16.7% to 14.8%; P = 0.004) and ciprofloxacin (from 10.9% to 8.1%; P < 0.001) was reported between 2015 and 2017. Although total antibiotic consumption did not vary significantly between 2012 and 2017, a decrease in the consumption of 3GCs (–32.%; P < 0.001) and quinolones (–25.5%; P < 0.001) was observed.ConclusionHere we report a decrease in the prevalence of E. coli isolates resistant to 3GCs and quinolones in outpatients in the context of significant decreasing consumption of these two antibiotic classes.     

Spread of multidrug-resistant IncHI1 plasmids carrying ESBL gene blaCTX-M-1 and metabolism operon of prebiotic oligosaccharides in commensal Escherichia coli from healthy horses,France

The objective of the study was to identify the genetic determinants and characteristics of expanded-spectrum cephalosporin (ESC) resistance in commensal Escherichia coli from healthy horses in France in 2015. Faecal samples from 744 adult horses were screened for ESC-resistant E. coli isolates. The extended-spectrum beta-lactamase (ESBL)/AmpC resistance genes were identified using polymerase chain reaction (PCR) and sequencing. ESC phenotypes were horizontally transferred by conjugation or transformation. Plasmids carrying ESBL/AmpC genes were typed by PCR-based replicon typing, restriction fragment length polymorphism (RFLP), and plasmid multilocus sequence typing (pMLST). The ESC-resistant E. coli isolates were typed by XbaI macrorestriction analysis. Sixteen of 41 stables harboured at least one horse carrying ESC-resistant E. coli. The proportion of individually tested horses carrying ESC-resistant E. coli was 8.5% (28/328). Fifty non-redundant ESC-resistant E. coli isolates showing a great diversity of XbaI macrorestriction profiles belonged mainly to phylogroup B1, and were negative for major E. coli virulence genes, indicating they are commensal isolates. ESBL bla_CTX-M genes were dominant (bla_CTX-M-1, n=34; bla_CTX-M-2, n=8; bla_CTX-M-14, n=2) and located on conjugative plasmids belonging to various incompatibility groups (IncHI1, IncI1, IncN, IncY, or non-typeable). Among these, the multidrug-resistant IncHI1-pST9 plasmids were dominant and simultaneously harboured the bla_CTX-M-1/2 genes and an operon enabling the metabolism of short-chain fructo-oligosaccharides (scFOS). In conclusion, commensal E. coli of French horses displayed a significant distribution of IncHI1-pST9 plasmids carrying both the bla_CTX-M-1/2 gene and the fos metabolism operon. This finding highlights the risk of co-selection of multidrug-resistant IncHI1 plasmids carrying ESBL genes possibly mediated by the use of scFOS as prebiotic in horses.     

Diverse prevalence of 16S rRNA methylase genes armA and rmtB amongst clinical multidrug-resistant Escherichia coli and Klebsiella pneumoniae isolates

In this study, 112 Escherichia coli and 55 Klebsiella pneumoniae isolates with a multidrug-resistant (MDR) phenotype were collected from 2007 to 2009. All isolates simultaneously exhibited resistance to cefotaxime (or ceftazidime), ciprofloxacin (or levofloxacin) and amikacin. Plasmid-mediated 16S rRNA methylases, including armA, rmtA, rmtB, rmtC, rmtD, rmtE and npmA, were detected by polymerase chain reaction (PCR) amplification. Common β-lactamase genes, including bla_TEM, bla_SHV, bla_CTX-M, bla_PER, bla_VEB, bla_GES and bla_OXA, as well as plasmid-mediated bla_AmpC and plasmid-mediated quinolone resistance (PMQR) determinants, including qnrA, qnrB, qnrS, qepA and aac(6′)-Ib-cr, were also screened. The transferable capacity of resistance plasmids was established by conjugation testing. The genetic relatedness of isolates was analysed by pulsed-field gel electrophoresis (PFGE). Only armA and rmtB genes were detected in this study. Data showed that 93.8% of MDR E. coli and 94.5% of MDR K. pneumoniae carried at least one of armA or rmtB. The armA and rmtB genes were present in 11.6% and 82.1% of MDR E. coli, respectively. In parallel, 58.2% and 40.0% of MDR K. pneumoniae were armA- and rmtB-positive, respectively. Furthermore, the qepA gene was present in 66.3% of rmtB-carrying MDR E. coli, but it was rarely detected in MDR K. pneumoniae. Approximately 71.9% of armA-positive MDR K. pneumoniae simultaneously co-carried qnrB and bla_DHA. Moreover, 78.1% and 63.6%, respectively, of armA-positive and rmtB-positive MDR K. pneumoniae strains harboured qnr alleles and 53.1% and 59.1% harboured aac(6′)-Ib-cr. In addition, MDR E. coli strains exhibited a low prevalence of qnr alleles and aac(6′)-Ib-cr. PFGE analysis revealed divergent genetic relatedness, suggesting horizontal dissemination of armA and rmtB along with common β-lactamases and PMQR determinants amongst clinical MDR E. coli and K. pneumoniae isolates.     

Another look at differences in the susceptibility of Escherichia coli and Klebsiella pneumoniae to cephalothin and cefazolin

The significance of in vitro susceptibility tests on Enterobacteriaceae to cephalothin and cefazolin has not been exactly defined in the guidelines of the National Committee for Clinical Laboratory Standards. In the hope of clarifying this confusion, we provide additional information from an ancillary study of the Taiwan Surveillance of Antimicrobial Resistance 1998 (TSAR I). There were 505 Escherichia coli and 227 Klebsiella pneumoniae isolates susceptible to cephalothin, reported by 42 participating hospitals. The susceptibility of these isolates were re-tested at the Microbial Infections Reference Laboratory using cefazolin, with the result that 72% of the 252 cephalothin-resistant E. coli isolates and 24% of the 41 cephalothin-resistant K. pneumoniae isolates were found to be susceptible to cefazolin. We further surveyed the availability of cephalothin and cefazolin in Pharmacy Departments; all of the TSAR I hospitals had cefazolin available in their pharmacies. The resistance rate of E. coli was significantly lower for 12 hospitals that had cefazolin in both pharmacy and laboratory compared with 11 hospitals that had cefazolin available in pharmacy but cephalothin in laboratory. In addition, for all the hospitals that had cephalothin available for clinical use, the resistance rate was twice as low in two hospitals reporting cefazolin susceptibility as in the seven hospitals reporting cephalothin susceptibility. Our findings suggest that inappropriate selection of cephalothin and cefazolin for susceptibility testing contribute to inaccurate indications of in vivo activity for first generation cephalosporins in the treatment of E. coli infections.     

Prévalence de la résistance d’Escherichia coli isolés de prélèvements d’origine urinaire ou gastro-intestinale vis-à-vis de l’association amoxicilline-acide clavulanique et de divers antibiotiques

This study evaluates the prevalence of the resistance of E. coli against amoxicillin-clavulanic acid (AMC), and analyzed the results according to the susceptibility testing methods. Strains tested with the ATB Expression were more resistant than with the E-test or the reference agar dilution methods, resulting in an apparent high frequency of resistance for E. coli. The rate of E. coli resistant to AMC is low: 3.2% and 2% for strains isolated from urinary tract (UT) and gastrointestinal tract (GIT). Moreover, 67% of the strains with reduced susceptibility had MICs ≤ 8 mg/L. The percentage of resistance to nalidixic acid, norfloxacin and ciprofloxacin were 17.9%, 11.3% and 10.6% for the UT strains and 5%, 8.5% and 5.1% for the GIT strains, respectively. Considering the increase of fluoroquinolone resistance, AMC remains a useful antibiotic for the treatment of E. coli infections.     

Genetic environment of sul genes and characterisation of integrons in Escherichia coli isolates of blood origin in a Spanish hospital

The prevalence and characterisation of integrons and the genetic environment of sulphonamide resistance genes were studied in 135 Escherichia coli isolates recovered from blood cultures in a Spanish hospital during 2007. Class 1 and 2 integrons were identified in 54 isolates (intI1, 52 isolates; intI2, 1 isolate; and intI1 + intI2, 1 isolate). Of the 53 intI1-positive isolates, 36 (67.9%) contained the classic class 1 integron including the qacEΔ1–sul1 region, and 11 different gene cassette arrangements were demonstrated in 33 of these isolates. Seventeen intI1-positive isolates lacked the qacEΔ1–sul1 region, and 8 gene cassette arrangements were demonstrated in 12 of these isolates. Seventy-one isolates showed a sulphonamide-resistant phenotype, 63 of which contained sul genes. The sul1 gene was associated with intI1 in 36 of 42 sul1-positive isolates, and the sul3 gene was associated with non-classic class 1 integrons in 5 of 7 sul3-positive isolates. Finally, sul2 was found associated with strA–strB genes in 32 of 35 sul2-positive isolates, identifying 11 genetic structures, 1 of them presenting the IS150 element disrupting the strB gene; this structure was included in GenBank with accession no. FJ705354. Almost one-half of the E. coli isolates from blood cultures contained integrons and sul genes. Moreover, sul genes were detected in different structures, one of them new, and could be important determinants in antibiotic resistance dissemination.     

Acute uncomplicated cystitis: from surveillance data to a rationale for empirical treatment

The objectives of this study were to explore the epidemiological features and resistance rates in uropathogens isolated from cases of acute uncomplicated cystitis (AUC) in Greece, and subsequently to guide empirical treatment. Urine samples from outpatients aged >16 years were cultured and for each uropathogen isolated non-susceptibility to orally administered antimicrobial agents was defined. Demographic and clinical data were provided in questionnaire form. From January 2005 to March 2006 a total of 1936 non-duplicate positive urinary cultures were collected and 889 AUC cases were evaluated. Escherichia coli was the main aetiological agent (83%). In the AUC group, non-susceptibility rates for E. coli isolates were as follows: amoxicillin 25.8%; co-trimoxazole 19.2%; cefalothin 14.9%; nitrofurantoin 10.7%; amoxicillin/clavulanic acid 5.2%; nalidixic acid 6%; mecillinam 3.4%; ciprofloxacin 2.2%; cefuroxime 1.7%, and fosfomycin 1.6%. Amoxicillin and/or co-trimoxazole use in the previous 3 months was significantly associated with isolation of a co-trimoxazole-resistant E. coli isolate. The same applied for previous use of a fluoroquinolone agent and isolation of a ciprofloxacin-resistant E. coli isolate. In conclusion, increased co-trimoxazole non-susceptibility rates undermine its use as a first-line agent in empirical treatment, especially in cases of recent use of co-trimoxazole and/or amoxicillin. Fluoroquinolones display potent in vitro activity against community uropathogens, but prudent use is warranted for uncomplicated infections. Mecillinam and nitrofurantoin could serve as effective front-line agents in an effort to design fluoroquinolones-sparing regimens.     

Emergence of a new mutation and its accumulation in the topoisomerase IV gene confers high levels of resistance to fluoroquinolones in Escherichia coli isolates

Mutations in DNA gyrase and topoisomerase IV genes are the main mechanisms of resistance to quinolones. In this study, we determined mutations in gyrA, gyrB, parC and parE among 57 ciprofloxacin-resistant Escherichia coli isolates from a South Korean hospital and analysed the relationship between the minimal inhibitory concentrations (MICs) of fluoroquinolones and mutations in the topoisomerase IV gene. All ciprofloxacin-resistant E. coli isolates carried double mutations in gyrA and at least a single mutation in parC; some isolates also carried a single mutation in parE. The most common mutations were S83L and D87N in gyrA, S80I in parC and S458A in parE, which accounted for 25% of isolates. Single mutations in parE at L445I, S458P and S458W were identified for the first time. Double mutations in parC and a combination of single mutations in parC and parE significantly increased the MIC values of fluoroquinolones. In vitro induction of resistance to ciprofloxacin showed that double mutations in gyrA were a prerequisite to conferring a resistant phenotype to fluoroquinolones, and an additional mutation in the topoisomerase IV gene increased the MIC values of ciprofloxacin. In conclusion, emergence of a new mutation in parC and parE and its accumulation induces high levels of resistance to fluoroquinolones in E. coli.     

Geographic distribution of fluoroquinolone-resistant Escherichia coli strains in Asia

Fluoroquinolone (FQ) resistance is usually caused by point mutations within the quinolone resistance-determining regions (QRDRs) of gyrA, gyrB, parC and/or parE. However, little is known about the worldwide increase in FQ-resistant Escherichia coli or, more specifically, about the geographical distribution of QRDR mutations and the clonal spread of isolates. In this study, we analysed 68 FQ-resistant E. coli isolates from eight Asian countries using QRDR amino acid mutation patterns and examined their susceptibility to FQs. Of the isolates, 38% had mutations at S83 and D87 of GyrA and S80 of ParC (MM/?/M?/?) and 34% had mutations at S83 and D87 of GyrA, S80 of ParC and S458 of ParE (MM/?/M?/M). MIC₅₀ values (minimum inhibitory concentrations for 50% of the isolates) for isolates with at least mutation at S458 of ParE for ciprofloxacin and prulifloxacin were relatively higher than MIC₅₀ values of isolates without this mutation. Based on their geographic distribution and the QRDR mutation patterns, the isolates were divided into a common type in which the organisms were isolated from three or more countries, and a local type in which the isolates were from one or two countries. Mutation types at S83L and D87N in GyrA and S80I in ParC with no or another site in the QRDR were the most frequent among the FQ-resistant isolates, especially among the common type. Gene typing indicated that isolates in the common type were not similar between countries. These data suggest that the increase in FQ-resistant E. coli strains is mainly generated by mutations in the QRDR in each geographical area rather than through intercontinental spread.     

Extended-spectrum cephalosporins and the inoculum effect in tests with CTX-M-type extended-spectrum β-lactamase-producing Escherichia coli: Potential clinical implications of the revised CLSI interpretive criteria

Based on the new recommendations of the Clinical and Laboratory Standards Institute (CLSI), the revised cephalosporin breakpoints may result in many CTX-M-producing Escherichia coli being reported as susceptible to ceftazidime. We determined the activity of ceftazidime and other parenteral β-lactam agents in standard- and high-inoculum minimum inhibitory concentration (MIC) tests against CTX-M-producing E. coli isolates. Antimicrobial susceptibility was determined using a broth microdilution MIC method with inocula that differed 100-fold in density. An inoculum effect was defined as an eight-fold or greater increase in MIC on testing with the higher inoculum. When the revised CLSI ceftazidime breakpoint of 4 μg/mL was applied, 34 (34.3%) of the 99 CTX-M-producers tested were susceptible. More specifically, for 42 CTX-M-14-producing E. coli isolates, 32 (76.2%) were susceptible at 4 μg/mL. Cefotaxime, ceftazidime, cefepime and piperacillin/tazobactam were found to be associated with inoculum effects in 100% of the evaluable tests for extended-spectrum β-lactamase-producing E. coli isolates. The MIC₅₀ (MIC required to inhibit 50% of isolates) of ceftazidime was 16 μg/mL in the standard-inoculum tests and >512 μg/mL in the high-inoculum tests. In the high-inoculum tests including isolates encoding CTX-M-14, ceftazidime was dramatically affected, with susceptibility decreasing from 82.1% of isolates inhibited at 4 μg/mL in the standard-inoculum tests to 0% at high inoculum. Although further studies may demonstrate that ceftazidime has a role in the treatment of infections caused by these organisms, we suggest that until more data become available, clinicians should be cautious about treating serious CTX-M-producing E. coli infections with ceftazidime or cefepime.