Sara M. Soto

Antimicrobial Resistance and Spread of Class 1 Integrons among Salmonella Serotypes

ABSTRACT The resistance profiles, for 15 antimicrobial agents, of 333Salmonella strains representing the most frequent nontyphoidal serotypes, isolated between 1989 and 1998 in a Spanish region, and 9 reference strains were analyzed. All strains were susceptible to amikacin, ceftazidime, ciprofloxacin, and imipenem, and 31% were susceptible to all antimicrobials tested. The most frequent types of resistance were to sulfadiazine, tetracycline, streptomycin, spectinomycin, ampicillin, and chloramphenicol (ranging from 46 to 22%); 13% were resistant to these six drugs. This multidrug resistance pattern was found alone or together with other resistance types within serotypes Typhimurium (45%), Panama (23%), and Virchow (4%). Each isolate was also screened for the presence of class 1 integrons and selected resistance genes therein; seven variable regions which carried one (aadA1a, aadA2, orpse-1) or two (dfrA14-aadA1a,dfrA1-aadA1a, oxa1-aadA1a, orsat1-aadA1a) resistance genes were found in integrons.

Characterization of a Self-Transferable Plasmid from Salmonella enterica Serotype Typhimurium Clinical Isolates Carrying Two Integron-Borne Gene Cassettes Together with Virulence and Drug Resistance Genes

ABSTRACT An unusual self-transferable virulence-resistance plasmid (pUO-StVR2) was found in nine multidrug-resistant (ACSSuT phenotype) Salmonella enterica serotype Typhimurium clinical isolates that were assigned to four different phage types and a single and distinctive XbaI pulsed-field gel electrophoresis profile. pUO-StVR2 is an IncFII plasmid of about 140 kb in length carrying the spvA, spvB, and spvC (Salmonella plasmid virulence) and rck (resistance to complement killing) genes. It also carries the oxa1/aadA1a (ampicillin resistance and streptomycin-spectinomycin resistance) gene cassette configuration located within a class 1 integron with qacEΔ1/sul1 (ammonium antiseptics resistance and sulfadiazine resistance); the transposon genes merA, tnpA, and tnpR (mercury resistance, transposase, and resolvase of Tn21, respectively); and the catA1 (chloramphenicol resistance) and tet(B) (tetracycline resistance) genes. The insertion of resistance genes into a Salmonella virulence plasmid constitutes a new and interesting example of plasmid evolution and presents a serious public health problem.

Extended Virulence Genotypes and Phylogenetic Background of Escherichia coli Isolates from Patients with Cystitis, Pyelonephritis, or Prostatitis

Molecular analysis of 63 Escherichia coli urine isolates showed that pyelonephritis (n=23) and prostatitis (n=17) isolates exhibited more virulence factors (VFs) among the 35 sought than did cystitis isolates (n=23). Several nontraditional VFs--including bmaE (M fimbriae), gafD (G fimbriae), fyuA (yersiniabactin receptor), ireA and iroN (novel siderophore receptors), cvaC (colicin [microcin] V), traT (serum-resistance associated), ibeA (invasion of brain endothelium), ompT (outer membrane protease T), and malX (pathogenicity island marker)--either differentiated significantly between syndromes (despite small numbers of isolates and possible multiple-comparison artifacts) or were broadly prevalent. Thus, interventions that target conserved uro-VFs may be possible, despite the likely existence of syndrome-specific pathogenetic mechanisms and/or host defense systems.

Role of efflux pumps in the antibiotic resistance of bacteria embedded in a biofilm.

Biofilms are complex microbial associations anchored to abiotic or biotic surfaces, embedded in extracellular matrix produced by the biofilms themselves where they interact with each other and the environment. One of the main properties of biofilms is their capacity to be more resistant to antimicrobial agents than planktonic cells. Efflux pumps have been reported as one of the mechanisms responsible for the antimicrobial resistance in biofilm structures. Evidence of the role of efflux pump in biofilm resistance has been found in several microorganisms such as Pseudomonas aeruginosa, Escherichia coli and Candida albicans. However, in spite of the studies on the importance of efflux pumps in biofilm growth and about their relevance in antimicrobial resistance forming biofilm, the exact role of these efflux systems has not been determined as yet.

Quinolone resistance in the food chain

Antimicrobials are used in pet animals and in animal husbandry for prophylactic and therapeutic reasons and also as growth promoters, causing selective pressure on bacteria of animal origin. The impact of quinolones or quinolone-resistant bacteria on the management of human infections may be associated with three different scenarios. (i) Quinolone-resistant zoonotic bacterial pathogens are selected and food is contaminated during slaughter and/or preparation. (ii) Quinolone-resistant bacteria non-pathogenic to humans are selected in the animal. When the contaminated food is ingested, the bacteria may transfer resistance determinants to other bacteria in the human gut (commensal and potential pathogens). And (iii) quinolones remain in residues of food products, which may allow the selection of antibiotic-resistant bacteria after the food is consumed. In this review, we analyse the abovementioned aspects, emphasising the molecular basis of quinolone resistance in Escherichia coli, Salmonella spp. and Campylobacter spp.

Quinolone-Resistant Uropathogenic Escherichia coli Strains from Phylogenetic Group B2 Have Fewer Virulence Factors than Their Susceptible Counterparts

ABSTRACT The prevalence of 31 virulence factors was analyzed among nalidixic acid-susceptible and -resistant Escherichia coli strains from phylogenetic group B2. Hemolysin, cytotoxic necrotizing factor 1, and S and F1C fimbriae genes were less prevalent among nalidixic acid-resistant E. coli strains. Quinolone resistance may be associated with a decrease in the presence of some virulence factors.

Quinolones Induce Partial or Total Loss of Pathogenicity Islands in Uropathogenic Escherichia coli by SOS-Dependent or -Independent Pathways, Respectively

ABSTRACT Escherichia coli is the most common microorganism causing urinary tract infections. Quinolone-resistant E. coli strains have fewer virulence factors than quinolone-susceptible strains. Several urovirulence genes are located in pathogenicity islands (PAIs). We investigated the capacity of quinolones to induce loss of virulence factors such as hemolysin, cytotoxic necrotizing factor 1, P fimbriae, and autotransporter Sat included in PAIs in three uropathogenic E. coli strains. In a multistep selection, all strains lost hemolytic capacity at between 1 and 4 passages when they were incubated with subinhibitory concentrations of ciprofloxacin, showing a partial or total loss of the PAI containing the hly (hemolysin) and cnf-1 (cytotoxic necrotizing factor 1) genes. RecA− mutants were obtained from the two E. coli strains with partial or total loss of the PAI. The inactivation of the RecA protein affected only the partial loss of the PAI induced by quinolones. No spontaneous loss of PAIs was observed on incubation in the absence of quinolones in either the wild-type or mutant E. coli strains. Quinolones induce partial or total loss of PAIs in vitro in uropathogenic E. coli by SOS-dependent or -independent pathways, respectively.

Relationship of Phylogenetic Background, Biofilm Production, and Time to Detection of Growth in Blood Culture Vials with Clinical Variables and Prognosis Associated with Escherichia coli Bacteremia

ABSTRACT In patients with Escherichia coli bacteremia, data on the relationship of phylogenetic background, biofilm production, and degree of bacteremia with clinical variables and prognosis are scarce. During a 1-year period, all adults with bacteremia due to Escherichia coli diagnosed at a university center were enrolled. Determination of phylogenetic background, biofilm production, and genotyping was performed with all strains, and the time to positivity of blood culture vials was recorded. A total of 185 episodes of diverse-source E. coli bacteremia was analyzed. Strains of phylogroup D were predominant (52%). Phylogroup A isolates were associated with pneumonia and prior antibiotic intake, B1 with an abdominal source of infection, B2 with the absence of urological abnormalities, and D with urological abnormalities and age below 65 years. Resistance to antibiotics and no biofilm production were concentrated in phylogroup A strains. Biofilm production was not associated with any clinical variable. An immunocompromising condition (odds ratio [OR] = 5.01, 95% confidence interval [CI] = 1.4 to 17.9), peritonitis (OR = 17, 95% CI = 3.32 to 87), pneumonia (OR = 9.97, 95% CI = 1.96 to 50.6), and ≤7 h to bacteremia detection (OR = 4.37, 95% CI = 1.38 to 13.8) were the best predictors of a fatal outcome. Results from this study suggest that the distribution of phylogenetic backgrounds among E. coli strains involved in diverse-source bacteremia may be subject to geographical variation and that, in afflicted individuals, some high-risk sources, the patients underlying condition, and the degree of bacteremia are more important than microbial factors in determining the outcome. Time to positivity of blood culture vials may be a variable of potential clinical impact.

Review on Bacterial Stress Topics

Abstract:  A complex network of regulatory systems ensures a coordinated and effective response to different types of stress that can act on a bacterium. Bacterial stress response generates changes that influence efflux system and virulence factor expression. Thus, partial or total loss of pathogenicity islands in uropathogenic Escherichia coli can be induced by SOS‐dependent or SOS‐independent pathways related to selection of quinolone‐resistant mutants. Likewise, hyperosmolarity and some chemicals, including fluoroquinolones, salicylate, nonantimicrobial medicaments like diazepam and anti‐inflammatory drugs are all able to induce an increased active efflux, cyclohexane tolerance, loss of porins, and decreased susceptibility to multiple antimicrobials in enterobacterial strains, suggesting that bacterial response to the stress caused by an increase in osmolarity might be linked to the development of the multidrug‐resistant phenotypes. Finally, a sudden downshift of the growth temperature (cold‐shock) triggers a drastic reprogramming of bacterial gene expression to allow cell survival under the new unfavorable conditions. The strategy developed by E. coli to reach this goal consists in the induction of a set of (cold‐shock) genes whose expression is regulated at both transcriptional and posttranscriptional levels.

Expression of Interleukin-8 Receptors (CXCR1 and CXCR2) in Premenopausal Women with Recurrent Urinary Tract Infections

ABSTRACT The migration of neutrophils through infected tissues is mediated by the CXC chemokines and its receptors (CXCR1 and CXCR2). It has been proposed that a CXCR1 deficiency could confer susceptibility to acute pyelonephritis in children. The objective of the study is to assess the surface expression of CXCR1 and CXCR2 and the existence of polymorphisms in the CXCR1 gene in premenopausal women with recurrent urinary tract infections. The study included 20 premenopausal women with recurrent urinary infections, with normal urinary tracts, and without diseases potentially associated with relapsing urinary infections and 30 controls without previous urinary infections. The levels of CXCR1 and CXCR2 expression on neutrophils were measured and analyzed by flow cytometry by measuring the mean fluorescence intensity (MFI) channel. The promoter and coding regions of the CXCR1 gene were analyzed for the presence of polymorphisms by a sequence-based typing method. Patients with recurrent urinary tract infections exhibited median levels of CXCR1 expression, determined from MFI values, similar to those of the controls. The analysis of CXCR2 showed that patients with recurrent urinary infections had lower median levels of expression, determined from the MFI values, than the controls (P = 0.002, Mann-Whitney U test). No polymorphisms were detected at the promoter or at the exon 1 region of the CXCR1 gene either in the patients or in the controls. Polymorphisms were detected at the exon 2 of CXCR1, but their frequencies did not differ between patients and controls. We have found a low level of CXCR2 expression in patients with recurrent urinary tract infections. These results suggest that a low level of CXCR2 expression may increase the susceptibilities of premenopausal women to urinary tract infections.