An integrated transport mechanism of the maltose ABC importer

ATP-binding cassette (ABC) transporters use the energy of ATP hydrolysis to transport a large diversity of molecules actively across biological membranes. A combination of biochemical, biophysical, and structural studies has established the maltose transporter MalFGK₂ as one of the best characterized proteins of the ABC family. MalF and MalG are the transmembrane domains, and two MalKs form a homodimer of nucleotide-binding domains. A periplasmic maltose-binding protein (MalE) delivers maltose and other maltodextrins to the transporter, and triggers its ATPase activity. Substrate import occurs in a unidirectional manner by ATP-driven conformational changes in MalK₂ that allow alternating access of the substrate-binding site in MalF to each side of the membrane. In this review, we present an integrated molecular mechanism of the transport process considering all currently available information. Furthermore, we summarize remaining inconsistencies and outline possible future routes to decipher the full mechanistic details of transport by MalEFGK₂ complex and that of related importer systems.     

Role of K1 capsule antigen in cirrhotic patients with Escherichia coli spontaneous bacterial peritonitis in southern Taiwan

Spontaneous bacterial peritonitis (SBP) is one of the most serious complications in patients with cirrhosis. This study aimed to investigate the prevalence of SBP caused by Escherichia coli isolates with or without the K1 capsule antigen in cirrhotic patients and the outcome. From January 2004 to January 2012, a total of 54 and 41 E. coli strains derived from patients with SBP and intestinal perforation (IP), respectively, were included for comparison in this study. Bacterial characteristics including phylogenetic groups, K1 capsule antigen, and 14 virulence factor genetic determinants, as well as data regarding patient characteristics, clinical manifestations, and in-hospital deaths, were collected and analyzed. The prevalence of the K1 capsule antigen gene neuA was more common in SBP isolates compared to IP isolates (28 % vs. 10 %, p?=?0.0385). Phylogenetic groups B2 and group D were dominant in E. coli isolates with and without the K1 capsule antigen, respectively. The prevalence of virulence factors genes papG II, ompT, and usp was higher in E. coli K1 strains. There were 26 deaths (48 %) during hospitalization. Presence of the K1 capsule antigen in E. coli isolates was significantly associated with in-hospital death in cirrhotic patients with SBP (42 % vs. 14 %, p?=?0.0331). This study demonstrates a higher prevalence of the K1 capsule antigen in E. coli SBP compared to E. coli peritonitis caused by IP. There were significant associations between the K1 capsule antigen and in-hospital mortality and bacterial virulence in cirrhotic patients with E. coli SBP.     

The complex interplay among bacterial motility and virulence factors in different Escherichia coli infections

Motility mediated by the flagella of Escherichia coli is important for the bacteria to move toward host cells. Here, we present the relationship among bacterial motility, virulence factors, antimicrobial susceptibility, and types of infection. A total of 231 clinical E. coli isolates from different infections were collected and analyzed. Higher-motility strains (motility diameter ≥6.6 mm) were more common in spontaneous bacterial peritonitis (SBP) (SBP 59 %, colonization 32 %, urinary tract infection 16 %, urosepsis 34 %, and biliary tract infection 29 %; p?afa and ompT genes (p?=?0.0160 and p?=?0.0497, respectively) in E. coli strains with lower motility. E. coli isolates with higher and lower motility were in different phylogenetic groups (p?=?0.018), with a lower prevalence of A and B1 subgroups in higher-motility strains. Also, the patterns of virulence factors and antibiotic susceptibility of E. coli isolates derived from various infections were significantly different. This study demonstrates that the prevalence of higher-motility strains was greater in E. coli isolates from SBP compared to other types of infection. Various types of E. coli infection were associated with differences in bacterial motility, virulence factors, and antibiotic susceptibility. More bacterial virulence factors may be necessary for the development of extraintestinal infections caused by E. coli isolates with lower motility.     

Differences in the antibiotic susceptibility of human Escherichia coli with poultry-associated and non-poultry-associated extended-spectrum beta-lactamases

The concurrent presence of bla _CTX-M-1 and bla _TEM-52 genes on similar plasmids of Escherichia coli isolated from poultry, chicken meat and humans supports the occurrence of food-borne transmission of extended-spectrum beta-lactamase (ESBL) genes. ESBL-producing E. coli (ESBL-E. coli) are most frequently detected in hospitalised patients and are known to spread in healthcare settings. We hypothesised that poultry-associated (PA) ESBL genes are predominant in the community, where acquisition is fuelled by food contamination, whereas non-PA ESBL genes are predominant in hospitals, with acquisition fuelled by cross-transmission. Then, differences in antimicrobial selective pressure in hospitals and poultry would create differences in co-resistance between PA and non-PA ESBL-E. coli. We, therefore, determined the prevalence and co-resistance of PA and non-PA ESBL-E. coli in community-acquired and nosocomial urinary tract infections in humans and bla _CTX-M-1 and bla _TEM-52 isolates from poultry. A total of 134 human ESBL-E. coli urine isolates were included in this study. Isolates containing bla _CTX-M-1 or bla _TEM-52 were considered to be PA, with the remainder being non-PA. Also, 72 poultry ESBL-E. coli were included. Minimum inhibitory concentration (MIC) values were determined by broth microdilution. The prevalence of PA ESBL genes in isolates obtained in general practice and hospitals was 28 % versus 30 % (n.s.). Human PA ESBL-E. coli were more frequently susceptible to ciprofloxacin (51 % vs. 25 %; p?=?0.0056), gentamicin (86 % vs. 63 %; p?=?.0.0082), tobramycin (91 % vs. 34 %; p?=?0.0001) and amikacin (98 % vs. 67 %; p?=?0.0001) compared to human non-PA ESBL-E. coli. PA ESBL-E. coli are not more prevalent in community acquired than nosocomial urine samples, but are more often susceptible to ciprofloxacin and aminoglycosides than non-PA ESBL-E. coli. This does not support the existence of different reservoirs of ESBL genes.     

Prevalence and risk factors for intestinal carriage of CTX-M-type ESBLs in Enterobacteriaceae from a Thai community

The incidence of infections caused by antimicrobial-resistant Enterobacteriaceae in Thailand is increasing and human intestinal flora is an important reservoir for these organisms. This study was carried out to determine the intestinal carriage of bla _CTX-M extended spectrum ß-lactamase-positive Enterobacteriaceae (ESBL + E) and AmpC-positive Enterobacteriaceae in a community setting in Northern Thailand, and to identify potential risk factors for carriage. A total of 307 fecal samples were collected from healthy volunteers in Phitsanulok province, and cefotaxime-resistant Enterobacteriaceae (CtxRE) were isolated using selective media. Polymerase chain reaction (PCR) was used to detect ESBL and AmpC genes. Risk factors were analyzed using multiple logistic regression. Genotyping was performed by multilocus sequence typing (MLST) analysis. Two hundred ninety-one CtxRE isolates were obtained and Escherichia coli was the predominant organism (66.3%). The intestinal carriage rates of bla _CTX-M ESBL + E and AmpC-positive Enterobacteriaceae were 52.1% and 6.2%, respectively. Comparative levels of bla _{CTX-M group 1} and bla _{CTX-M group 9} were found while bla _CMY-2 was the predominant genotype among AmpC genes. Co-existence of two ß-lactamase genes in a single isolate was found in 6.5% of isolates. Consumption of undercooked meat was strongly associated with intestinal carriage of bla _CTX-M ESBL + E (p = 0.003, OR = 2.133, 95% CI = 1.289–3.530). Phylogenetic grouping and MLST analysis of E. coli isolates revealed the presence of E. coli B2-ST131 (n = 8). Of these, seven carried bla _{CTX-M-group 9} and 1 carried bla _CMY-2. Our results suggest that residents in Thailand are at high risk for developing endogenous infections caused by antibiotic-resistant Enterobacteriaceae.     

First description of OXA-48-producing Escherichia coli and the pandemic clone ST131 from patients hospitalised at a military hospital in Algeria

The aim of the study was to assess the frequency and diversity of carbapenemases and extended-spectrum β-lactamases (ESBL) produced by Escherichia coli isolates from patients hospitalised in the Regional Military Hospital of Constantine (Algeria). E. coli isolates were collected over a 2-year period from patients presenting E. coli infections. Strains with reduced susceptibility to ertapenem and/or positive for ESBL were characterised with regard to antibiotic resistance, bla genes, phylogenetic groups, O25 serotyping, quinolone resistance, repetitive sequence-based polymerase chain reaction (rep-PCR) profiles and multi-locus sequence typing (MLST). Of the 448 isolated E. coli, 94 (20.9 %) were multidrug-resistant. One of them (1.1 %) produced a bla _OXA-48 and was identified as a B1 ST5 strain. The transposon bearing this gene was Tn1999.2. This strain was isolated from a patient coming from a border province with Tunisia, where this carbapenemase is endemic. In addition, 84 (18.8 %) isolates among them produced an ESBL with predominance (97.6 %) of bla _CTX-M-15, which was coupled with qnr genes in 10.9 %. ESBL-producing strains were mainly detected in phylogroups D and A. They displayed 20 rep-PCR profiles and all the clonally related isolates were of the same sequence type (ST). Ten strains (9.4 %) belonged to the pandemic clone ST131. This study describes for the first time the presence of OXA-48-producing E. coli and the emergence of the intercontinental ST131 bla _CTX-15-producing E. coli strains in Algeria.     

Determination of intimin and Shiga toxin genes in Escherichia coli isolates from gastrointestinal contents of healthy broiler chickens in Kerman City, Iran

Shiga toxin-producing Escherichia coli (STEC) strains have emerged as food poisoning pathogens which can cause severe diseases in humans. Poultry can be readily and persistently colonized, leading to the excretion of the STEC strains in the gastrointestinal contents and becoming a potential risk for human infection. Two hundred and ninety E. coli isolates were recovered from the cecum and jejunum contents of 145 broiler chickens during the slaughter. The isolates were examined to determine the phylotypes and prevalence of stx1, stx2, and eae genes. E. coli isolates were segregated in four main phylogenetic group A (60.69 %), B1 (8.62 %), B2 (9.31 %), and D (21.38 %). The isolates from the cecal contents belonged to A (68.27 %), B1 (1.38 %), B2 (13.10 %), and D (17.24 %) phylogenetic groups. The E. coli isolates from the contents of the jejunum indicated that the isolates were distributed in four phylogenetic groups including 53.11 % (77 isolates) in A, 15.86 % (23 isolates) in B1, 5.52 % (8 isolates) in B2, and 25.51 % (37 isolates) in D group. Nine isolates (3.10 %) were positive for eae and stx2 genes. None of the isolates contained the stx1 gene. The positive isolates were distributed in three phylo-groups and four phylogenetic subgroups A (A₀, A₁), B1, and D (D₁, D₂). The four eae- and stx2-positive isolates from the cecal contents belonged to A₀, A₁, and D₁ phylo-subgroups; whereas five eae- and stx2-positive isolates from the jejunum contents fell into A₀, A₁, and D₁ phylo-subgroups and B1 phylo-group.     

TLR4 inhibition impairs bacterial clearance in a therapeutic setting in murine abdominal sepsis

Objective and design

To investigate the therapeutic effect of E5564 (a clinically used TLR4 inhibitor) in murine abdominal sepsis elicited by intraperitoneal infection with a highly virulent Escherichia coli in the context of concurrent antibiotic therapy.

Methods

Mice were infected with different doses (~2 × 10⁴–2 × 10⁶ CFU) of E. coli O18:K1 and treated after 8 h with ceftriaxone 20 mg/kg i.p. combined with either E5564 10 mg/kg i.v. or vehicle. For survival studies this treatment was repeated every 12 h. Bacterial loads and inflammatory parameters were determined after 20 h in peritoneal lavage fluid, blood, liver and lung tissue. Plasma creatinin, AST, ALT and LDH were determined to assess organ injury.

Results

E5564 impaired bacterial clearance under the antibiotic regime after infection with a low dose E. coli (1.7 × 10⁴ CFU) while renal function was slightly preserved. No differences were observed in bacterial load and organ damage after infection with a tenfold higher (1.7 × 10⁵ E. coli) bacterial dose. While treatment with E5564 slightly attenuated inflammatory markers provoked by the sublethal doses of 104–105 E. coli under the antibiotic regime, it did not affect lethality evoked by infection with 1.7 × 106 E. coli.

Conclusions

The impact of TLR4 inhibition during abdominal sepsis by virulent E. coli bacteria is only beneficial at low infection grade at cost of bactericidal activity.     

Occurrence of virulence genes, 16S rRNA methylases,and plasmid-mediated quinolone resistance genes in CTX-M-producing Escherichia coli from Pakistan

The aim of the study was to conduct a comprehensive molecular characterization of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli collected from Pakistan. Genetic relatedness among 98 ESBL-producing E. coli was measured by pulsed-field gel electrophoresis (PFGE). The presence of genes encoding ESBLs, virulence factors (VFs), 16S rRNA methylases, plasmid-mediated quinolone resistance (PMQR) encoding elements, plasmid replicon types, phylogenetic groups of E. coli, prevalence of the worldwide disseminated clone E. coli ST131, and phylogrouping of CTX-M enzymes was investigated by polymerase chain reaction (PCR). All isolates carried bla _CTX-M genes and, except for one isolate from CTX-M phylogroup 9, they all belonged to CTX-M phylogroup 1. The isolates were genetically diverse with PFGE. Phylogenetic group D (36 %) was most abundant in this collection of E. coli, whereas isolates belonging to B2 (22 %) had the highest content of virulence genes. PMQR genes were found in 84.6 % of the isolates; among them, 93 % isolates were positive for variants of acetyltransferases (aac(6′)-lb-cr), whereas qnrB, qepA, and qnrS were present in 11 %, 5 %, and 4 % of the isolates, respectively. Only 3 % of the isolates contained genes encoding 16S rRNA methylases. The most abundant replicon type was IncF (96 %), and 18 % of the isolates belonged to the ST131 clone. Out of 34 investigated VFs, 24 genes encoding different types of adhesins, protectins, toxins, siderophores, and other VFs were found. Although the isolates in this collection were highly resistant to many antimicrobials, susceptibility to amikacin and meropenem was retained.     

The impact of inoculum size on the activity of cefoperazone-sulbactam against multidrug resistant organisms

Objectives

This study aims to assess the in vitro activity of cefoperazone alone and different cefoperazone-sulbactam ratios against different inoculum sizes of multidrug resistant organisms.

Characterization of carbapenem-resistant <Emphasis Type="Italic">Escherichia coli</Emphasis> and <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis> from a healthcare region in Hong Kong

Carbapenem-resistant Enterobacteriaceae represents a major public health issue. This study investigated the clonality and resistance mechanisms of 92 carbapenem-resistant E. coli (n?=?21) and K. pneumoniae (n?=?71) isolates collected consecutively from clinical specimens and patients at high risk of carriage between 2010 and 2012 in a healthcare region in Hong Kong. Combined disk tests (CDTs) and the Carba NP test were used for phenotypic detection of carbapenemases. PCR assays were used to detect carbapenemase genes. All isolates were intermediate or resistant to at least one carbapenem. Nine (9.8 %) isolates were genotypic carbapenemase producers and included six K. pneumoniae (one ST1306/bla _IMP-4, one ST889/bla _IMP-4, two ST11/bla _KPC-2, one ST258/bla _KPC-2, one ST483/bla _NDM-1) and three E. coli (one ST131/bla _IMP-4, two ST744/ bla _NDM-1) isolates. All nine isolates carrying carbapenemase genes could be detected by the CDTs and the Carba NP test. PCR identified bla _CTX-M and bla _AmpC alone or in combination in 77.8 % (7/9) and 96.4 % (80/83) of the carbapenemase-producers and non-producers, respectively. Porin loss was detected in 22.2 % (2/9) and 59.0 % (49/83) of the carbapenemase-producers and non-producers, respectively. Overall, the E. coli clones were diverse (14 different STs), but 36.6 % (26/71) of the K. pneumoniae isolates belonged to ST11. In conclusion, the prevalence of carbapenemases among carbapenem-nonsusceptible E. coli and K. pneumoniae remained low in Hong Kong. Porin loss combined with AmpC and/or CTX-M type ESBL was the major mechanism of carbapenem resistance in the study population.     

Leukemia and risk of recurrent Escherichia coli bacteremia: genotyping implicates E. coli translocation from the colon to the bloodstream

In patients with leukemia, the portal(s) and reasons for the persistence of an Escherichia coli recurrent bacteremia remain unclear. Adult Hematology Clinic (AHC) databases at the State Clinical Hospital in Gdańsk were reviewed to evaluate the frequency of E. coli bacteremia between 2002 and 2005. Blood and bowel E. coli strains were obtained and the genetic relatedness of the strains was analyzed. The rate of E. coli bacteremia per 1,000 admissions at the AHC was higher (85.0) than in the other clinics of the hospital (2.9), p?<?0.001. A higher mortality was observed in patients with a history of E. coli versus non-E. coli bacteremia [30/95 (31 %) vs. 53/430 (12 %), p?<?0.001]; 72.8 % of patients with leukemia had an unknown source of bacteremia. In 2005, 6 out of 25 (24 %) patients with leukemia had ≥2 episodes of E. coli-positive blood cultures. These gastrointestinal E. coli isolates were replaced within 3–8 weeks with a new E. coli H genotype. A recurrent episode of bacteremia was usually caused by an infection with a transient E. coli H genotype identical to that found in the subject’s bowel. Consistent with the definition of bowel/blood translocation, the bowel appeared to be a portal for E. coli in these subjects and, hence, a clear source for their recurring bacteremia.     

Several hPepT1-transported drugs are substrates of the Escherichia coli proton-coupled oligopeptide transporter YdgR

Proton-dependent oligopeptide transporters (POTs) are secondary active transporters found in all kingdoms of life. POTs utilize the proton electrochemical gradient for the uptake of nutrient dipeptides and tripeptides. The human POT hPepT1 is known to transport a number of drugs. As part of ongoing studies on substrate specificities of POTs from Escherichia coli, our aim in this study was to investigate whether bacterial POTs could also transport these drugs. For this, we selected the common orally administered drugs sulpiride, bestatin, valacyclovir, ampicillin and oseltamivir, that are all transported by hPepT1. The transport of these drugs was evaluated using the prototypical POT YdgR from E. coli. The transport studies were pursued through combining cell-based assays with liquid chromatography–tandem mass spectrometric (LC–MS/MS) analysis. These investigations revealed that YdgR from E. coli is able to transport five (sulpiride, bestatin, valacyclovir, ampicillin and oseltamivir) drugs. Furthermore, cells not overexpressing YdgR were also able to transport these drugs in a POT-like manner. Orthologues of YdgR are found in several species in the gut microbiome; hence, our findings could have implications for further understanding about the interaction between gut microbes and orally administered drugs.     

Association between dementia and reduced walking ability and 30-day mortality in patients with extended-spectrum beta-lactamase-producing <Emphasis Type="Italic">Escherichia coli</Emphasis> bacteremia

Previous studies have shown controversial results of factors associated with short-term mortality in patients with extended-spectrum beta-lactamase (ESBL)-producing E. coli bacteremia and no research has investigated the impact of the geriatric assessment criteria on short-term mortality. Our objective was to determine whether dementia and walking ability are associated with 30-day mortality in patients with ESBL-producing E. coli bacteremia. All blood bottle cultures, analyzed from January 2008 to April 2015, in the Bacteriology Department of a 2,600-bed, university-affiliated center, Nantes, France, were retrospectively extracted. Factors associated with short-term mortality in patients with ESBL-producing E. coli bacteremia: 140 patients with an ESBL-producing E. coli bloodstream infection were included; 22 (15.7%) patients died within 30 days following the first positive blood bottle culture of ESBL-producing E.coli. In multivariate analysis, a reduced ability to walk (OR = 0.30; p = 0.021), presence of dementia (OR = 54.51; p = 0.040), a high Sepsis-related Organ Failure Assessment (SOFA) score (OR = 1.69; p < 0.001), presence of neutropenia (OR = 12.94; p = 0.049), and presence of a urinary tract infection (OR = 0.07; p = 0.036), were associated with 30-day mortality. Our findings provide new data showing an independent association between 30-day mortality with dementia and reduced walking ability, in patients with ESBL-producing E. coli bacteremia. These criteria should be considered in the therapeutic management of patients with ESBL-producing E. coli bacteremia.     

Bloodstream infections caused by <Emphasis Type="Italic">Escherichia coli</Emphasis> producing AmpC β-lactamases: epidemiology and clinical features

The aim of the study was to investigate the epidemiology and clinical features of bloodstream infections due to Escherichia coli producing AmpC β-lactamases (AmpC-Ec-BSI). In a multi-centre case–control study, all third-generation-cephalosporin-resistant Escherichia coli BSI (3GC-Ec-BSI) isolates were analysed. Acquired bla _AmpC (bla _ac-AmpC) detection was done by polymerase chain reaction (PCR) and sequencing. Chromosomal bla _AmpC (bla _c-AmpC) expression was quantified by real-time PCR. Cases were patients with AmpC-Ec-BSI. Controls were patients with cephalosporin-susceptible E. coli BSI, matched 1:1 by sex and age. Demographics, comorbidities, intrinsic and extrinsic risk factors for antimicrobial resistance, clinical presentation and outcomes were investigated. Among 841 E. coli BSI, 17 were caused by AmpC-Ec (2 %). Eleven isolates (58.8 %) had bla _ac-AmpC and six were bla _c-AmpC overproducers. The mean age of cases was 66.2 years and 71 % were men. Cases were more frequently healthcare-related (82 vs. 52 % controls, p?<?0.05) and presented more intrinsic and extrinsic risk factors. At least one risk factor was present in 94.1 % of cases vs. 41.7 % of controls (p?=?0.002). Severity and length of stay (LOS) were higher among cases (mean Pitt Score 2.6 vs. 0.38 in controls, p?=?0.03; LOS 17.5 days vs. 6 in controls, p?=?0.02). Inappropriate empirical therapy (IET) was administered to 70.6 % of cases and 23.5 % of controls (p?<?0.003). No differences were found in terms of cure rate at the 14th day and mortality. Bloodstream infections due to AmpC-Ec (mostly plasmid-mediated) are infrequent in our area. AmpC-Ec-BSI affects mainly patients with intrinsic risk factors and those with previous antibiotic exposure. A high proportion received IET.     

Patterns and trends of pediatric bloodstream infections: a 7-year surveillance study

We characterize the epidemiology of pediatric bloodstream infections (BSIs) in Switzerland. We analyzed pathogen distribution and resistance patterns in monomicrobial and polymicrobial BSIs in children from 2008 to 2014 using data from the Swiss antibiotic resistance centre (ANRESIS). A confirmatory statistical analysis was performed comparing pathogens and resistance across 20 acute care hospitals. We identified 3,067 bacteremia episodes, of which 1,823 (59 %) were considered true BSI episodes. Overall, S. aureus (16.5 %, 300) was the most frequent pathogen, followed by E. coli (15.1 %, 276), coagulase-negative staphylococci (CoNS, 12.9 %, 235), S. pneumoniae (11.1 %, 202) and non-E. coli Enterobacteriaceae (8.7 %, 159). S. aureus and E. coli showed similar frequencies in all of the variables analyzed (e.g., hospital acquisition, hospital type, medical specialty). The proportion of these microorganisms did not change over time, resistance rates remained low (4.3 % methicillin resistance in S. aureus; 7.3 % third-/fourth-generation cephalosporin resistance in E. coli), and no significant resistance trends were observed. We observed a 50 % increase of CoNS BSIs from 2008 (9.8 %, 27) to 2014 (15.2 %, 46, p value for trend?=?0.03). S. pneumoniae decreased from 17.5 % (48) to 6.6 % (20) during that timeframe (p for trend?=?0.007). S. aureus and E. coli remained the most significant pathogens among pediatric BSIs in Switzerland, exhibiting low resistance rates. CoNS accounted for a greater proportion of BSIs over time. The decrease in bacteremic pneumococcal infections can likely be attributed to the introduction of the 13-valent conjugate vaccine in 2011.     

Antibiotic sensitivity of E. coli and Salmonella isolated from different water sources in Kashmir, India

The objective of the present study was to determine the prevalence of Salmonella and Escherichia coli, the serotypes involved and the antibiogram of the various isolates obtained from different sources of water supply (streams, Dal Lake, tube wells and community supply water) in Kashmir, India, during the years 2009–2010. A total of 100 samples, 25 from each source, were taken for the present study. All samples were evaluated for the presence of Salmonella and E. coli, stereotyped and tested for antimicrobial susceptibility. A total of 60 isolates of E. coli and 12 isolates of Salmonella were obtained. The antimicrobial susceptibilities of different isolates of E. coli and Salmonella from different water sources were examined by disc diffusion method. The high in vitro sensitivity was shown by 100 % of E. coli isolates for ciprofloxacin, 95 % for amoxycillin/clavulanic acid, 93.33 % for each of cephotaxime and amikacin and 91.67 % for lavofloxacin and gentamicin. The isolates registered an intermediate response to rifampicin (85.00 %), lomefloxacin (83.33 %) and norfloxacin (83.33 %) and showed resistance to erythromycin (98.33 %). The isolates of Salmonella were 100 % sensitive for gentamicin, 91.67 % for each of cefixime, ciprofloxacin, amikacin and lavofloxacin; 83.33 % for each of cephotaxime and amoxycillin/clavulanic acid and showed resistance to erythromycin (100 %), nalidixic acid (100 %) and rifampicin (91.67 %). The isolates, however, showed an intermediate resistance to lomefloxacin (83.34 %) and norfloxacin (66.67). The high incidence of multi-drug-resistant strains of E. coli and Salmonella is due to injudicious use of antibiotics and exchange of antibiotic resistance among bacterial populations.     

Testing the mutant selection window hypothesis with Escherichia coli exposed to levofloxacin in a rabbit tissue cage infection model

The purpose of this study was to test the mutant selection window (MSW) hypothesis with Escherichia coli exposed to levofloxacin in a rabbit model and to compare in vivo and in vitro exposure thresholds that restrict the selection of fluoroquinolone-resistant mutants. Local infection with E. coli was established in rabbits, and the infected animals were treated orally with various doses of levofloxacin once a day for five consecutive days. Changes in levofloxacin concentration and levofloxacin susceptibility were monitored at the site of infection. The MICs of E. coli increased when levofloxacin concentrations at the site of infection fluctuated between the lower and upper boundaries of the MSW, defined in vitro as the minimum inhibitory concentration (MIC₉₉) and the mutant prevention concentration (MPC), respectively. The pharmacodynamic thresholds at which resistant mutants are not selected in vivo was estimated as AUC₂₄/MPC > 20 h or AUC₂₄/MIC > 60 h, where AUC₂₄ is the area under the drug concentration time curve in a 24-h interval. Our finding demonstrated that the MSW existed in vivo. The AUC₂₄/MPC ratio that prevented resistant mutants from being selected estimated in vivo is consistent with that observed in vitro, indicating it might be a reliable index for guiding the optimization of antimicrobial treatment regimens for suppression of the selection of antimicrobial resistance.     

Determination of phylogenetic background,fimbrial genes,and antibiotic susceptibility of Escherichia coli isolates from urinary tract infections in Bam region,Iran

Phylogenetic analysis have shown that Escherichia coli (E. coli) strains segregate in four main phylogenetic groups A, B1, B2, and D. E. coli fimbriae increase invasive capability of bacteria to renal tissues. The purpose of this study was to determine the distribution of phylogenetic groups/subgroups among fimbrial genes and antibiotic resistance patterns of E. coli isolates from urinary tract infections (UTI), in Bam (southeast of Iran). A total of 122 E. coli isolates from patients with UTI, which were confirmed by biochemical tests, were collected. Antibiotic susceptibility of isolates was examined against six antibiotic agents by disk diffusion method. DNA was extracted and examined for detection of phylogenetic group/subgroups and also for determination of afaI BC, sfa/focDE, and papEF genes using PCR technique. E. coli isolates were distributed in phylogroups A (45.08 %), D (43.45 %), B2 (7.83 %), and B1 (4.09 %). The examined isolates belonged to six phylogenetic subgroups A₀ (28.69 %), D₂ (24.59 %), D₁ (18.85 %), A₁ (16.39 %), B_2–3 (7.39 %), and B₁ (4.09 %). Fimbrial genes were found in 27.85 % of isolates. Phylogroups A and D were more prevalent in antibiotic resistance patterns than other phylogenetic groups. The findings of the current study showed that A and D phylogenetic groups were dominant among our isolates. These results differ with that of other researches in other parts of the world. Further studies are required to clarify the phylogenetic background in Bam area. Antibiotic resistant seems to be a common feature of most E. coli isolates in this area.