Novel gold(III)-dithiocarbamate complex targeting bacterial thioredoxin reductase: antimicrobial activity, synergy, toxicity, and mechanistic insights

Introduction

Antimicrobial resistance is a pressing global concern that has led to the search for new antibacterial agents with novel targets or non-traditional approaches. Recently, organogold compounds have emerged as a promising class of antibacterial agents. In this study, we present and characterize a (C^S)-cyclometallated Au(III) dithiocarbamate complex as a potential drug candidate.

Methods and results

The Au(III) complex was found to be stable in the presence of effective biological reductants, and showed potent antibacterial and antibiofilm activity against a wide range of multidrug-resistant strains, particularly gram-positive strains, and gram-negative strains when used in combination with a permeabilizing antibiotic. No resistant mutants were detected after exposing bacterial cultures to strong selective pressure, indicating that the complex may have a low propensity for resistance development. Mechanistic studies indicate that the Au(III) complex exerts its antibacterial activity through a multimodal mechanism of action. Ultrastructural membrane damage and rapid bacterial uptake suggest direct interactions with the bacterial membrane, while transcriptomic analysis identified altered pathways related to energy metabolism and membrane stability including enzymes of the TCA cycle and fatty acid biosynthesis. Enzymatic studies further revealed a strong reversible inhibition of the bacterial thioredoxin reductase. Importantly, the Au(III) complex demonstrated low cytotoxicity at therapeutic concentrations in mammalian cell lines, and showed no acute in vivo toxicity in mice at the doses tested, with no signs of organ toxicity.

Discussion

Overall, these findings highlight the potential of the Au(III)-dithiocarbamate scaffold as a basis for developing novel antimicrobial agents, given its potent antibacterial activity, synergy, redox stability, inability to produce resistant mutants, low toxicity to mammalian cells both in vitro and in vivo, and non-conventional mechanism of action.

Antibiotic Resistance in Bacterial Pathogens

The increasing number of infections caused by antibiotic-resistant bacterial pathogens over the last few decades has become a critical global health problem, the scale of which has led to it being named a "silent pandemic" [...].

Synthesis of the cyanobacterial halometabolite Chlorosphaerolactylate B and demonstration of its antimicrobial effect in vitro and in vivo

Chlorosphaerolactylate B, a newly discovered antimicrobial halometabolite from the cyanobacterium Sphaerospermopsis sp. LEGE 00249 has been synthesized in three steps by using 12-bromododecanoic acid as starting material. A total of 0.5 g was produced for in vitro and in vivo antimicrobial efficacy testing. In vitro, the minimal inhibitory concentration (MIC) was estimated to be 256 mg/L for Staphylococcus aureus, while the minimal biofilm inhibitory concentration (MBIC) was estimated to be 74 mg/L. The in vivo study utilized a porcine model of implant-associated osteomyelitis. In total, 12 female pigs were allocated into 3 groups based on inoculum (n = 4 in each group). An implant cavity (IC) was drilled in the right tibia and followed by inoculation and insertion of a steel implant. All pigs were inoculated with 10 μL containing either: 11.79 mg synthetic Chlorosphaerolactylate B + 10⁴ CFU of S. aureus (Group A), 10⁴ CFU of S. aureus (Group B), or pure saline (Group C), respectively. Pigs were euthanized five days after inoculation. All Group B animals showed macroscopic and microscopic signs of bone infection and both tissue and implant harbored S. aureus bacteria (mean CFU on implants = 1.9 × 10⁵). In contrast, S. aureus could not be isolated from animals inoculated with saline. In Group A, two animals had a low number of S. aureus (CFU = 6.7 × 10¹ and 3.8 × 10¹, respectively) on the implants, otherwise all Group A animals were similar to Group C animals. In conclusion, synthetic Chlorosphaerolactylate B holds potential to be a novel antimicrobial and antibiofilm compound.

Clinical Escherichia coli: From Biofilm Formation to New Antibiofilm Strategies

Escherichia coli is one of the species most frequently involved in biofilm-related diseases, being especially important in urinary tract infections, causing relapses or chronic infections. Compared to their planktonic analogues, biofilms confer to the bacteria the capacity to be up to 1000-fold more resistant to antibiotics and to evade the action of the host’s immune system. For this reason, biofilm-related infections are very difficult to treat. To develop new strategies against biofilms, it is important to know the mechanisms involved in their formation. In this review, the different steps of biofilm formation in E. coli, the mechanisms of tolerance to antimicrobials and new compounds and strategies to combat biofilms are discussed.

Gold-Derived Molecules as New Antimicrobial Agents

Antimicrobial resistance is considered one of the three most important health problems by the World Health Organization. The emergence and spread of an increasing number of antimicrobial-resistant microorganisms make this a worldwide problem. Antibiotic-resistant bacteria are estimated to be the cause of 33,000 deaths in Europe and 700,000 worldwide each year. It is estimated that in 2050 bacterial infections will cause 10 million deaths across the globe. This problem is concomitant with a decrease in the investment and, therefore, the discovery and marketing of new antibiotics. Recently, there have been tremendous efforts to find new effective antimicrobial agents. Gold complexes, with their broad-spectrum antimicrobial activities and unique modes of action, are particularly relevant among several families of derivatives that have been investigated. This mini review revises the role of gold-derived molecules as antibacterial agents.

A C∧S-Cyclometallated Gold(III) Complex as a Novel Antibacterial Candidate Against Drug-Resistant Bacteria

The worldwide emergence and spread of infections caused by multidrug-resistant bacteria endangers the efficacy of current antibiotics in the clinical setting. The lack of new antibiotics in the pipeline points to the need of developing new strategies. Recently, gold-based drugs are being repurposed for antibacterial applications. Among them, gold(III) complexes have received increasing attention as metal-based anticancer agents. However, reports on their antibacterial activity are scarce due to stability issues. The present work demonstrates the antibacterial activity of the gold(III) complex 2 stabilized as C∧S-cycloaurated containing a diphenylphosphinothioic amide moiety, showing minimum inhibitory concentration (MIC) values that ranged from 4 to 8 and from 16 to 32 mg/L among Gram-positive and Gram-negative multidrug-resistant (MDR) pathogens, respectively. Complex 2 has a biofilm inhibitory activity of only two to four times than its MIC. We also describe for the first time a potent antibacterial synergistic effect of a gold(III) complex combined with colistin, showing a bactericidal effect in less than 2 h; confirming the role of the outer membrane as a permeability barrier. Complex 2 shows a low rate of internalization in Staphylococcus aureus and Acinetobacter baumannii; it does not interact with replication enzymes or efflux pumps, causes ultrastructural damages in both membrane and cytoplasmic levels, and permeabilizes the bacterial membrane. Unlike control antibiotics, complex 2 did not generate resistant mutants in 30-day sequential cultures. We detected lower cytotoxicity in a non-tumoral THLE-2 cell line (IC50 = 25.5 μM) and no acute toxicity signs in vivo after an i.v. 1-mg/kg dose. The characterization presented here reassures the potential of complex 2 as a new chemical class of antimicrobial agents.

Microalgae and Cyanobacteria Strains as Producers of Lipids with Antibacterial and Antibiofilm Activity

Lipids are one of the primary metabolites of microalgae and cyanobacteria, which enrich their utility in the pharmaceutical, feed, cosmetic, and chemistry sectors. This work describes the isolation, structural elucidation, and the antibiotic and antibiofilm activities of diverse lipids produced by different microalgae and cyanobacteria strains from two European collections (ACOI and LEGE-CC). Three microalgae strains and one cyanobacteria strain were selected for their antibacterial and/or antibiofilm activity after the screening of about 600 strains carried out under the NoMorFilm European project. The total organic extracts were firstly fractionated using solid phase extraction methods, and the minimum inhibitory concentration and minimal biofilm inhibitory concentration against an array of human pathogens were determined. The isolation was carried out by bioassay-guided HPLC-DAD purification, and the structure of the isolated molecules responsible for the observed activities was determined by HPLC-HRESIMS and NMR methods. Sulfoquinovosyldiacylglycerol, monogalactosylmonoacylglycerol, sulfoquinovosylmonoacylglycerol, α-linolenic acid, hexadeca-4,7,10,13-tetraenoic acid (HDTA), palmitoleic acid, and lysophosphatidylcholine were found among the different active sub-fractions selected. In conclusion, cyanobacteria and microalgae produce a great variety of lipids with antibiotic and antibiofilm activity against the most important pathogens causing severe infections in humans. The use of these lipids in clinical treatments alone or in combination with antibiotics may provide an alternative to the current treatments.

Relationship between Virulence and Resistance among Gram-Negative Bacteria

Bacteria present in the human body are innocuous, providing beneficial functions, some of which are necessary for correct body function. However, other bacteria are able to colonize, invade, and cause damage to different tissues, and these are categorised as pathogens. These pathogenic bacteria possess several factors that enable them to be more virulent and cause infection. Bacteria have a great capacity to adapt to different niches and environmental conditions (presence of antibiotics, iron depletion, etc.). Antibiotic pressure has favoured the emergence and spread of antibiotic-resistant bacteria worldwide. Several studies have reported the presence of a relationship (both positive and negative, and both direct and indirect) between antimicrobial resistance and virulence among bacterial pathogens. This review studies the relationship among the most important Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) taking into account two points of view: (i) the effect the acquisition of resistance has on virulence, and (ii) co-selection of resistance and virulence. The relationship between resistance and virulence among bacteria depends on the bacterial species, the specific mechanisms of resistance and virulence, the ecological niche, and the host.

Enterococcus faecalis inhibits Klebsiella pneumoniae growth in polymicrobial biofilms in a glucose-enriched medium

Catheter-related urinary tract infections are one of the most common biofilm-associated diseases. Within biofilms, bacteria cooperate, compete, or have neutral interactions. This study aimed to investigate the interactions in polymicrobial biofilms of Klebsiella pneumoniae and Enterococcus faecalis, two of the most common uropathogens. Although K. pneumoniae was the most adherent strain, it could not maintain dominance in the polymicrobial biofilm due to the lactic acid produced by E. faecalis in a glucose-enriched medium. This result was supported by the use of E. faecalis V583 ldh-1/ldh-2 double mutant (non-producer of lactic acid), which did not inhibit the growth of K. pneumoniae. Lyophilized cell-free supernatants obtained from E. faecalis biofilms also showed antimicrobial/anti-biofilm activity against K. pneumoniae. Conversely, there were no significant differences in planktonic polymicrobial cultures. In summary, E. faecalis modifies the pH by lactic acid production in polymicrobial biofilms, which impairs the growth of K. pneumoniae.

The Usefulness of Microalgae Compounds for Preventing Biofilm Infections

Biofilms play an important role in infectious diseases. It has been estimated that most medical infections are due to bacterial biofilms, and about 60-70% of nosocomial infections are also caused by the formation of a biofilm. Historically, microalgae are an important source of bioactive compounds, having novel structures and potential biological functions that make them attractive for different industries such as food, animal feed, aquaculture, cosmetics, and pharmaceutical. Several studies have described compounds produced by microalgae and cyanobacteria species with antimicrobial activity. However, studies on the antibiofilm activity of extracts and/or molecules produced by these microorganisms are scarce. Quorum-sensing inhibitor and anti-adherent agents have, among others, been isolated from microalgae and cyanobacteria species. The use of tools such as nanotechnology increase their power of action and can be used for preventing and treating biofilm-related infections.

Inhibition of Bacterial and Fungal Biofilm Formation by 675 Extracts from Microalgae and Cyanobacteria

Bacterial biofilms are complex biological systems that are difficult to eradicate at a medical, industrial, or environmental level. Biofilms confer bacteria protection against external factors and antimicrobial treatments. Taking into account that about 80% of human infections are caused by bacterial biofilms, the eradication of these structures is a great priority. Biofilms are resistant to old-generation antibiotics, which has led to the search for new antimicrobials from different sources, including deep oceans/seas. In this study, 675 extracts obtained from 225 cyanobacteria and microalgae species (11 phyla and 6 samples belonging to unknown group) were obtained from different culture collections: The Blue Biotechnology and Ecotoxicology Culture Collection (LEGE-CC), the Coimbra Collection of Algae (ACOI) from Portugal, and the Roscoff Culture Collection (RCC) from France. The largest number of samples was made up of the microalgae phylum Chlorophyta (270) followed by Cyanobacteria (261). To obtain a large range of new bioactive compounds, a method involving three consecutive extractions (hexane, ethyl acetate, and methanol) was used. The antibiofilm activity of extracts was determined against seven different bacterial species and two Candida strains in terms of minimal biofilm inhibitory concentration (MBIC). The highest biofilm inhibition rates (%) were achieved against Candida albicans and Enterobacter cloacae. Charophyta, Chlorophyta, and Cyanobacteria were the most effective against all microorganisms. In particular, extracts of Cercozoa phylum presented the lowest MBIC₅₀ and MBIC₉₀ values for all the strains except C. albicans.

Relationship Between Biofilm Formation and Antimicrobial Resistance in Gram-Negative Bacteria

Gram-negative microorganisms are a significant cause of infection in both community and nosocomial settings. The increase, emergence, and spread of antimicrobial resistance among bacteria are the most important health problems worldwide. One of the mechanisms of resistance used by bacteria is biofilm formation, which is also a mechanism of virulence. This study analyzed the possible relationship between antimicrobial resistance and biofilm formation among isolates of three Gram-negative bacteria species. Several relationships were found between the ability to form biofilm and antimicrobial resistance, being different for each species. Indeed, gentamicin and ceftazidime resistance was related to biofilm formation in Escherichia coli, piperacillin/tazobactam, and colistin in Klebsiella pneumoniae, and ciprofloxacin in Pseudomonas aeruginosa. However, no relationship was observed between global resistance or multidrug-resistance and biofilm formation. In addition, compared with other reported data, the isolates in the present study showed higher rates of antimicrobial resistance. In conclusion, the acquisition of specific antimicrobial resistance can compromise or enhance biofilm formation in several species of Gram-negative bacteria. However, multidrug-resistant isolates do not show a trend to being greater biofilm producers than non-multiresistant isolates.

Prevalence, antimicrobial resistance and serotype distribution of group B streptococcus isolated among pregnant women and newborns in Rabat, Morocco

Purpose. Group B streptococcus (GBS) is an important cause of neonatal sepsis worldwide. Data on the prevalence of maternal GBS colonization, risk factors for carriage, antibiotic susceptibility and circulating serotypes are necessary to tailor adequate locally relevant public health policies.Methodology. A prospective study including pregnant women and their newborns was conducted between March and July 2013 in Morocco. We collected clinical data and vagino-rectal and urine samples from the recruited pregnant women, together with the clinical characteristics of, and body surface samples from, their newborns. Additionally, the first three newborns admitted every day with suspected invasive infection were recruited for a thorough screening for neonatal sepsis. Serotypes were characterized by molecular testing.Results. A total of 350 pregnant women and 139 of their newborns were recruited. The prevalence of pregnant women colonized by GBS was 24 %. In 5/160 additional sick newborns recruited with suspected sepsis, the blood cultures were positive for GBS. Gestational hypertension and vaginal pruritus were significantly associated with a vagino-rectal GBS colonization in univariate analyses. All of the strains were susceptible to penicillin, while 7 % were resistant to clindamycin and 12 % were resistant to erythromycin. The most common GBS serotypes detected included V, II and III.Conclusion. In Morocco, maternal GBS colonization is high. Penicillin can continue to be the cornerstone of intrapartum antibiotic prophylaxis. A pentavalent GBS vaccine (Ia, Ib, II, III and V) would have been effective against the majority of the colonizing cases in this setting, but a trivalent one (Ia, Ib and III) would only prevent 28 % of the cases.

Escherichia coli: an old friend with new tidings

Escherichia coli is one of the most-studied microorganisms worldwide but its characteristics are continually changing. Extraintestinal E. coli infections, such as urinary tract infections and neonatal sepsis, represent a huge public health problem. They are caused mainly by specialized extraintestinal pathogenic E. coli (ExPEC) strains that can innocuously colonize human hosts but can also cause disease upon entering a normally sterile body site. The virulence capability of such strains is determined by a combination of distinctive accessory traits, called virulence factors, in conjunction with their distinctive phylogenetic background. It is conceivable that by developing interventions against the most successful ExPEC lineages or their key virulence/colonization factors the associated burden of disease and health care costs could foreseeably be reduced in the future. On the other hand, one important problem worldwide is the increase of antimicrobial resistance shown by bacteria. As underscored in the last WHO global report, within a wide range of infectious agents including E. coli, antimicrobial resistance has reached an extremely worrisome situation that ‘threatens the achievements of modern medicine’. In the present review, an update of the knowledge about the pathogenicity, antimicrobial resistance and clinical aspects of this ‘old friend’ was presented.

Vaginal versus Obstetric Infection Escherichia coli Isolates among Pregnant Women: Antimicrobial Resistance and Genetic Virulence Profile

Vaginal Escherichia coli colonization is related to obstetric infections and the consequent development of infections in newborns. Ampicillin resistance among E. coli strains is increasing, which is the main choice for treating empirically many obstetric and neonatal infections. Vaginal E. coli strains are very similar to extraintestinal pathogenic E. coli with regards to the virulence factors and the belonging to phylogroup B2. We studied the antimicrobial resistance and the genetic virulence profile of 82 E. coli isolates from 638 vaginal samples and 63 isolated from endometrial aspirate, placental and amniotic fluid samples from pregnant women with obstetric infections. The prevalence of E. coli in the vaginal samples was 13%, which was significant among women with associated risk factors during pregnancy, especially premature preterm rupture of membranes (p<0.0001). Sixty-five percent of the strains were ampicillin-resistant. The E. coli isolates causing obstetric infections showed higher resistance levels than vaginal isolates, particularly for gentamicin (p = 0.001). The most prevalent virulence factor genes were those related to the iron uptake systems revealing clear targets for interventions. More than 50% of the isolates belonged to the virulent B2 group possessing the highest number of virulence factor genes. The ampicillin-resistant isolates had high number of virulence factors primarily related to pathogenicity islands, and the remarkable gentamicin resistance in E. coli isolates from women presenting obstetric infections, the choice of the most appropriate empiric treatment and clinical management of pregnant women and neonates should be carefully made. Taking into account host-susceptibility, the heterogeneity of E. coli due to evolution over time and the geographical area, characterization of E. coli isolates colonizing the vagina and causing obstetric infections in different regions may help to develop interventions and avoid the aetiological link between maternal carriage and obstetric and subsequent puerperal infections.

Environmental phosphate differentially affects virulence phenotypes of uropathogenic Escherichia coli isolates causative of prostatitis

K-12 Escherichia coli cells grown in static media containing a critical phosphate (Pi) concentration ≥25 mM maintained a high polyphosphate (polyP) level in stationary phase, impairing biofilm formation, a phenomenon that is triggered by polyP degradation. Pi concentration in human urine fluctuates according to health state. Here, the influence of environmental Pi concentration on the occurrence of virulence traits in uropathogenic E. coli (UPEC) isolated from acute prostatitis patients was evaluated. After a first screening, 3 isolates were selected according to differential biofilm formation profiles depending on media Pi concentration. For each isolate, biofilm positive and negative conditions were established. Regardless of the isolate, biofilm formation capacity was accompanied with curli and cellulose production and expression of some key virulence factors associated with adhesion. When the selected isolates were grown in their non-biofilm-forming condition, low concentrations of nalidixic acid and ciprofloxacin induced biofilm formation. Interestingly, similar to laboratory strains, polyP degradation induced biofilm formation in the selected isolates. Data demonstrated the complexity of UPEC responses to environmental Pi and the importance of polyP metabolism in the virulence of clinical isolates.

First report of a Klebsiella pneumoniae ST466 strain causing neonatal sepsis harbouring the blaCTX-M-15 gene in Rabat, Morocco

Klebsiella pneumoniae is one of the Gram-negative bacilli most commonly found in urine of pregnant women and causing neonatal sepsis. The aim of this study was to analyse in terms of epidemiology and antimicrobial resistance of 23 K. pneumoniae isolates collected from vaginal swabs or urine of pregnant women, from pharyngeal and ear swabs of apparently healthy newborns and from peripheral cultures and hemocultures of newborns with suspected invasive neonatal infection in Rabat, Morocco. The prevalence of K. pneumoniae was 0.6 and 0.9% among pregnant women and neonates, respectively. These strains showed lower antimicrobial resistance levels regarding the developed countries. Thus, only one strain from a neonate presented an ESBL. This is the first report of a K. pneumoniae strain causing neonatal sepsis harbouring the blaCTX-M-15 gene in an IncFII plasmid and belonging to ST466 in this area.

Impact of quinolone-resistance acquisition on biofilm production and fitness in Salmonella enterica

OBJECTIVES

To investigate the potential relationship between quinolone resistance and biofilm production in a collection of Salmonella enterica clinical isolates and in S. enterica serovar Typhimurium serial mutants with increasing resistance to ciprofloxacin.

METHODS

Nalidixic acid susceptibility and biofilm formation were assessed in a collection of 122 S. enterica clinical isolates. An in vitro quinolone-resistant mutant, 59-64, was obtained from a biofilm-producing and quinolone-susceptible clinical isolate, 59-wt, in a multistep selection process after increasing ciprofloxacin concentrations. The quinolone resistance mechanisms [target gene and multidrug resistance (MDR) regulatory mutations, MICs of several antibiotics, cell envelope protein analysis, real-time PCR and ciprofloxacin accumulation] were characterized for mutant strains. In addition, analysis of fitness, biofilm formation, rdar morphotype and expression of biofilm-related genes by real-time PCR were also determined.

RESULTS

Nalidixic acid-susceptible S. enterica strains were more prevalent in producing biofilm than the resistant counterparts. Strain 59-64 acquired five target gene mutations and showed an MDR phenotype. AcrAB and acrF overexpression were ruled out, whereas TolC did show increased expression in 59-64, which, in addition, accumulated less ciprofloxacin. Consistently, increased ramA expression was seen in 59-64 and attributed to a mutation within its promoter. Reduced biofilm production related to diminished csgB expression as well as reduced fitness was seen for 59-64, which was unable to form the rdar morphotype.

CONCLUSIONS

Quinolone resistance acquisition may be associated with decreased production of biofilm due to lower csgB expression. Efflux, biofilm production and fitness seem to be interrelated.

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.

Salicylate increases the expression of marA and reduces in vitro biofilm formation in uropathogenic Escherichia coli by decreasing type 1 fimbriae expression

Escherichia coli is one of the most frequent bacteria implicated in biofilm formation, which is a dynamic process whose first step consists in bacteria adhesion to surfaces through type 1 fimbriae. Salicylate induces a number of morphological and physiological alterations in bacteria including the activation of the transcriptional regulator MarA. In this report the effects of salicylate on biofilm formation and their relationship with MarA were studied. An inverse relationship was observed between in vitro biofilm formation and salicylate concentration added to the culture medium. Salicylate increases the expression of marA and decreases the expression of fimA and fimB genes in the wild-type strain. In addition, the fimA and fimB expression was decreased in a MarR mutant in which marA was also overexpressed. In conclusion, the expression of type 1 fimbriae in presence of salicylate may be regulated by the level of marA expression through fimB regulator, albeit through neither the ompX nor the tolC genes.

CTX-M-15-producing enteroaggregative Escherichia coli as cause of travelers' diarrhea

Travelers’ diarrhea is a major public health problem. From patients in whom diarrhea developed after travel to India, 5 enteroaggregative Escherichia coli strains carrying β-lactamase CTX-M-15 were identified; 3 belonged to clonal complex sequence type 38. This β-lactamase contributes to the multidrug resistance of enteroaggregative E. coli, thereby limiting therapeutic alternatives.

Prevalence of Escherichia coli among samples collected from the genital tract in pregnant and nonpregnant women: relationship with virulence

Escherichia coli are enteric Gram-negative bacilli that can colonize the female genital tract and become implicated in different infections in pregnant women, including intra-amniotic infection, puerperal infections and neonatal infections. The virulence profiles of E. coli isolates from vaginal swabs from pregnant and nonpregnant women were compared. The hly-, cnf-, pap- and iroN-genes were found significantly more frequently in E. coli isolated from pregnant women in comparison with those isolated from nonpregnant women. Escherichia coli from pregnant women seem to be more virulent than from nonpregnant women developing severe infections, thereby increasing possible neonatal sepsis.

Prevalence of enterotoxins among Escherichia coli isolates causing bacteraemia

The most frequent cause of bacteraemia among Gram-negative bacteria is Escherichia coli. Analysis of the genes encoding the Shigella enterotoxin 1 (ShET-1), ShET-2, enteroaggregative heat stable toxin 1 (EAST-1) toxins and AggR factor in E. coli strains causing bacteraemia revealed that set1 genes were presented significantly more frequently among quinolone-susceptible strains (P<0.0001), in phylogenetic group B2 (P=0.0004) and in biofilm strains (P=0.02). In contrast, sen genes were significantly more frequent among nalidixic acid-resistant isolates (15% vs. 6%, P=0.046) and in phylogenetic group B1 (P=0.0001). This is the first study in which ShET1, ShET2 and EAST-1 have been found in E. coli collected from blood.

Human migration and infectious diseases

Emerging infectious diseases (EID) are defined as diseases that have appeared recently or that have recently increased in their frequency, geographical distribution or both. Commercial globalisation, population movements and environmental changes are the main factors favouring the international spread of microorganisms. Transport and communication development constitutes also a remarkable factor in the worldwide dispersion of microorganisms. The mass movement of large numbers of people creates new opportunities for the spread and establishment of common or novel infectious diseases. A surveillance system to detect emergent and re‐emergent infections, a rapid responsiveness of healthcare systems and laboratories, vector control, and the provision of healthcare education programmes to inform the population of how to avoid infections are needed in order to stop the spread of infectious diseases.

Biofilm formation in uropathogenic Escherichia coli strains: relationship with prostatitis, urovirulence factors and antimicrobial resistance

PURPOSE

Escherichia coli strains are the most frequent cause of urinary tract infections. Biofilm formation allows the strains to persist a long time in the genitourinary tract and interfere with bacterial eradication. We determined the possible relationships between the different urinary tract infections, and in vitro biofilm formation, the presence of urovirulence factors and nalidixic acid resistance.

MATERIALS AND METHODS

A total of 151 E. coli strains collected from patients with cystitis (44 strains), pyelonephritis (75) and prostatitis (32) were analyzed for in vitro biofilm formation, the phylogenetic group, the presence of several urovirulence factors and resistance to nalidixic acid.

RESULTS

E. coli strains causing prostatitis produced biofilm in vitro more frequently than those causing other urinary tract infections and had a higher frequency of hemolysin (p = 0.03 and 0.0002, respectively). However, only hemolysin was independently associated with prostatitis. On the other hand, strains forming biofilm presented a significantly higher frequency of hemolysin and type 1 fimbriae expression.

CONCLUSIONS

Although hemolysin is the main virulence factor by which E. coli causes acute prostatitis, the association between hemolysin and biofilm formation may result in increased ability of E. coli strains to persist in the prostate.

Implication of biofilm formation in the persistence of urinary tract infection caused by uropathogenic Escherichia coli

Escherichia coli is the most frequent microorganism involved in urinary tract infection (UTI). Acute UTI caused by uropathogenic E. coli (UPEC) can lead to recurrent infection, which can be defined as either re-infection or relapse. E. coli strains causing relapse (n = 27) and re-infection (n = 53) were analysed. In-vitro production of biofilm, yersiniabactin and aerobactin was significantly more frequent among strains causing relapse. Biofilm assays may be helpful in selecting patients who require a therapeutic approach to eradicate persistent biofilm-forming E. coli strains and prevent subsequent relapses.

Detection of virulence determinants in clinical strains of Salmonella enterica serovar Enteritidis and mapping on macrorestriction profiles

A total of 80 strains of Salmonella enterica serovar Enteritidis, causing gastroenteritis (G) or bacteraemia (B), and three control strains (C), were subjected to: (i) detection of 14 chromosomally and 1 plasmid-located virulence genes by PCR, (ii) detection of DNA polymorphisms by XbaI and BlnI PFGE, and cluster analysis, (iii) mapping of the 15 screened sequences on macrorestriction profiles and (iv) comparison of the screening and mapping results with data available for other Salmonella strains. Identical virulence genotypes and very similar macrorestriction profiles were shown by most S. Enteritidis strains. However, a number of B strains belonged to genomic types with polymorphisms affecting fragments carrying (SPI2-slyA), (SPI2-slyA-phoP/Q-agfA), (SPI4 and/or stn) and spvC. The information obtained provides the basis for further studies on the genetic background of virulence and the molecular epidemiology of S. Enteritidis.

Quinolones induce partial or total loss of pathogenicity islands in uropathogenic Escherichia coli by SOS-dependent or -independent pathways, respectively

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.

[Different antibiotic resistance mechanisms associated with integrons in clinical isolates of Salmonella typhimurium]

Antibiotic resistance in clinical isolates of Salmonella typhimurium has steadily risen in recent years. Some of the resistance genes may be carried into integrons. In this study, integrons, both from 10 epidemiologically related and unrelated S. typhimurium clinical isolates, were characterized, showing that epidemiologically different strains can carry the same integron, and that epidemiologically related strain can carry different integrons. Among the resistance genes detected in this study were genes encoding b-lactamases (bla(oxa-30) in two strains, and bla(pse-1) in five strains, one of which was carrying this cassette in two different integrons); aminoglycoside-modifying enzymes (aadA2 in four strains, one of which was carrying this cassette in two different integrons, and aadA1 in six strains); as well dihydrofolate reductases (dfrAI in three strains).

In vitro fluoroquinolone-resistant mutants of Salmonella enterica serotype Enteritidis: analysis of mechanisms involved in resistance

This study analysed the mechanisms involved in the acquisition of resistance to quinolones in mutants obtained in vitro of Salmonella enterica serotype Enteritidis. Two nalidixic acid-resistant (minimal inhibitory concentrations, MIC>256 mg/l), ciprofloxacin-susceptible (MIC 0.5 mg/l) clinical isolates of Salmonella Enteritidis with a mutation at amino acid codon Ser-83 of the gyrA gene were grown on plates containing increasing concentrations of ciprofloxacin. The increase in MIC to ciprofloxacin, sparfloxacin and trovafloxacin was totally or partially associated with over-expression of an AcrAB-like efflux pump. In addition, unidentified mechanism(s) may have been involved in the increased MIC to these antimicrobials. This study demonstrated that AcrAB-like efflux pumps appear to play a relevant role in the increase in MIC to some quinolones although, other, as yet undefined, mechanisms may be involved.

Antimicrobial resistance in clinical isolates of Salmonella enterica serotype Enteritidis: relationships between mutations conferring quinolone resistance, integrons, plasmids and genetic types

In 481 clinical isolates of Salmonella enterica serotype Enteritidis collected from a Spanish region in 2000, 108, 83 and four isolates were resistant, respectively, to nalidixic acid, ampicillin or both. Nalidixic acid resistance was the result of DNA gyrase mutations involving the codons Asp-87 (97 isolates) and Ser-83 (15 isolates) of the gyrA gene; no mutations in parC were detected. In ampicillin-resistant strains, blaTEM genes located on plasmids and/or the chromosome were implicated. Five plasmids containing blaTEM1-like genes were identified, ranging from 7 to 100 kb, four of which were self-transferable; one of these contained a class 1 sul1 integron with an aadA1a gene cassette. This integron was also found on the chromosome of an isolate resistant to ampicillin, streptomycin and sulfadiazine. A relationship between a 40 kb self-transferable plasmid and strains of Salmonella Enteritidis phage type 6a with a distinctive RAPD profile was established.

Class 1 integron-borne gene cassettes in multidrug-resistant Yersinia enterocolitica strains of different phenotypic and genetic types

Seventy nine strains of Yersinia enterocolitica resistant to one or more antimicrobials were analyzed for integrons. Only class 1 sul1 integrons containing aadA1a (28 strains), aadA1a-dfr1-sat1 (2 strains), and dfr1-aadA1a (1 strain) gene cassettes were found. The first two types were found in clinical isolates belonging to serotype O:3, biotypes 2 to 4, and eight combined ribotypes, and the third was found in the reference strain, CECT4054 (O:8). All screened resistance markers were found in strains with and without integrons (except for chloramphenicol resistance, encoded by catA1 gene, which was only present in strains with integrons), but in different resistance profiles (R profiles). A profile (ampicillin, streptomycin, sulfadiazine, and trimethoprim resistance, encoded by the tem1, aadA1a, sul1, and dfr1 genes, respectively) was found in strains, with and without integrons. Integrons and some of the resistance genes are located on plasmids with sizes ranging between 65 and 140 kb. This is the first report of class 1 integrons in Y. enterocolitica.

Outbreaks and sporadic cases of Salmonella serovar panama studied by DNA fingerprinting and antimicrobial resistance

In the Principality of Asturias (PA), Spain. three Salmonella serovar Panama outbreaks were registered in August 1998. In order to achieve an accurate identification of the strains implicated in the outbreaks and to study the molecular epidemiology of this serovar in the PA, the isolates collected over 1990-1999 were examined by DNA fingerprinting and antimicrobial resistance analysis. The origin of the isolates was: human (65, of which 20 were associated with the three outbreaks), octopus (2), beef (2), eggs (7), poultry faeces (2), sea water (5), sewage (2) and unknown (1). Sixteen lineages were defined by ribotyping, enterobacterial repetitive intergenic consensus sequences analysis, and randomly amplified polymorphic DNA segment analysis. One lineage was endemic in the PA and was also represented by isolates from other Spanish regions. The organisms of this lineage can be differentiated (by resistance-, plasmid- and integron-profiles) into 19 types. The three outbreaks were caused by organisms falling into a single type (nalidixic acid-resistant, plasmid- and integron-free) belonging to the endemic lineage, which was associated with poultry as the reservoir. Isolates showing drug-resistance (71%) fell into six lineages and 23 types. Ten multidrug-resistant types carried class I integrons with three types of variable regions containing resistance gene cassettes.

Multidrug resistance is mediated by large plasmids carrying a class 1 integron in the emergent Salmonella enterica serotype [4,5,12:i:-]

A multidrug-resistant Salmonella enterica serotype [4,5,12:i:-] clone carried a class 1 integron harboring dfrA12 and aadA2 gene cassettes and bla(TEM-1), aac(3)-IV, cmlA1, and tetA genes located in large plasmids of about 140 kb (carrying spv) or 120 kb (lacking spv). Several segregants, lacking multidrug resistance, contained a plasmid smaller than the parental one and no longer hybridized with probes for the lost resistances. The genes mediating resistance to ampicillin, chloramphenicol, and tetracycline in the [4,5,12:i:-] clone are different from those found in the pentadrug-resistant serotype Typhimurium DT104 clone.

Usefulness of genetic typing methods to trace epidemiologically Salmonella serotype Ohio

Different genetic typing procedures were applied in an epidemiological study of Salmonella serotype Ohio. Isolates that generated identical DNA fingerprints (HinclI ribotypes, ERIC and RAPD profiles) were clustered into the same lineage, and the addition of data from plasmid, integron and resistance profiles was used to differentiate types. Results led to the determination of the endemic and the emergent epidemic types at specific times, and to ascertain the clinical and epidemiological impact of each type. In the series analysed (47 clinical isolates and 3 non-clinical isolates) 11 lineages and 32 types were found. Two lineages were considered prevalent and endemic, and during an epidemiological alert (Spain, 1998) a re-emergence and spread of organisms mainly from the most frequent lineage had occurred. The combination of H-ribotype with ERIC profile, as primary markers, and resistance profile with plasmid profile, as secondary markers, was shown to be the most useful tool to trace epidemiologically Ohio.

Molecular characterisation of emergent multiresistant Salmonella enterica serotype [4,5,12:i:-] organisms causing human salmonellosis

Salmonella multidrug-resistant clinical organisms identified as serotype [4,5,12:i:-] were typed using selected genetic procedures and compared with typhimurium organisms collected in the same Spanish region. Results showed a low genetic heterogeneity among [4,5,12:i:-] organisms, which generated identical ribotypes and similar but not identical XbaI PFGE, RAPD, and plasmid profiles. Multidrug resistance could be eliminated by curing and seems to be mediated by 140-kb (spvC+) and 120-kb (spvC-) non-self-transferable plasmids. The [4,5,12:i:-] organisms fall into a single genetic lineage, which emerged in 1997 and presents a different degree of genetic relationship with typhimurium lineages.

Potential of three-Way randomly amplified polymorphic DNA analysis as a typing method for twelve Salmonella serotypes

The potential of a three-way randomly amplified polymorphic DNA (RAPD) procedure (RAPD typing) for typing Salmonella enterica strains assigned to 12 serotypes was analyzed. The series of organisms used included 235 strains (326 isolates) collected mainly from clinical samples in the Principality of Asturias and 9 reference strains. RAPD typing was performed directly with broth cultures of bacteria by using three selected primers and optimized PCR conditions. The profiles obtained with the three primers were used to define RAPD types and to evaluate the procedure as a typing method at the species and serotype levels. The typeability was 100%; the reproducibility and in vitro stability could be considered good. The concordance of RAPD typing methods with serotyping methods was 100%, but some profiles obtained with two of the three primers were obtained with strains assigned to different serotypes. The discrimination index (DI) within the series of organisms was 0.94, and the DI within serotypes Typhimurium, Enteritidis, and Virchow were 0.72, 0.52, and 0.66, respectively. Within these serotypes the most common RAPD types were differentiated into phage types and vice versa; combining the types identified by the two procedures (RAPD typing and phage typing) resulted in further discrimination (DI, 0. 96, 0.74, and 0.87, respectively). The efficiency, rapidity, and flexibility of the RAPD typing method support the conclusion that it can be used as a tool for identifying Salmonella organisms and as a typing method that is complementary to serotyping and phage typing methods.