Effects of sub-minimum inhibitory concentrations of ciprofloxacin on enteroaggregative Escherichia coli and the role of the surface protein dispersin

A Mini-Review of Enteroaggregative Escherichia coli with a Specific Target on the Virulence Factors Controlled by the AggR Master Regulator

Enteroaggregative Escherichia coli (EAEC) strains have been linked to several outbreaks of severe diarrhea around the world, and this bacterium is now commonly resistant to antibiotics. As part of the pathophysiology of EAEC, the characteristic pattern of adherence looks like stacked bricks on the intestinal epithelium. This phenotype depends on an aggregative adhesion plasmid (pAA), which codes for a regulatory protein named AggR. The AggR protein is a master regulator that transcriptionally actives the main virulence genes in this E. coli pathotype, such as those that encode the aggregative adhesion fimbriae, dispersin and its secretion apparatus, Aar regulatory protein, and type VI secretion system. Several reports have shown that AggR positively affects most EAEC virulence genes, functioning as a classic transcriptional activator in the promoter region of these genes, interacting with the RNA polymerase. This minireview article integrates the information about virulence determinants of EAEC controlled by the AggR regulator.

Effect of sub-minimal inhibitory concentration ceftazidime on the pathogenicity of uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) is the most prevalent causative agent of urinary tract infections (UTIs). The pathogenicity of UPEC relies on the expression of virulence factors which could be regulated by intercellular signal molecules. Our previous study found that sub-minimal inhibitory concentration ceftazidime (sub-MIC CAZ) could inhibit the biofilm formation of E. coli by luxS/AI-2 or indole. Therefore, we speculated that sub-MIC CAZ might affect the pathogenic capacity of UPEC. In this study, the results showed that sub-MIC CAZ could significantly inhibit the adhesion ability, biofilm formation and swimming and swarming motilities of UPEC isolated from recurrent UTI patient. Meanwhile, obvious decreased hemolytic activity and cytotoxicity were observed in CAZ-pretreated UPEC. Furthermore, qRT-PCR results confirmed the downregulating ability of CAZ on the expression of adhesion genes, motility genes, toxin gene and signal molecule synthesis genes, which are important for virulence and biofilm formation of UPEC. Pre-treatment of UPEC with sub-MIC CAZ resulted in the reduced adhesion to human bladder epithelial cell 5637 and the decreased numbers of intracellular bacterial communities in cells. Consistent with the results in vitro, the pretreatment of CAZ resulted in the reduction of UPEC load in the bladder and the less severity of UPEC-induced inflammation compared with control group. The present study results indicated that sub-MIC CAZ could decrease the pathogenicity of UPEC and might be served as an effective antimicrobial agent to combat recurrent UTI caused by UPEC.

A review on anti-adhesion therapies of bacterial diseases

BACKGROUND

Infections caused by bacteria are a foremost cause of morbidity and mortality in the world. The common strategy of treating bacterial infections is by local or systemic administration of antimicrobial agents. Currently, the increasing antibiotic resistance is a serious and global problem. Since the most important agent for infection is bacteria attaching to host cells, hence, new techniques and attractive approaches that interfere with the ability of the bacteria to adhere to tissues of the host or detach them from the tissues at the early stages of infection are good therapeutic strategies.

METHODS

All available national and international databanks were searched using the search keywords. Here, we review various approaches to anti-adhesion therapy, including use of receptor and adhesion analogs, dietary constituents, sublethal concentrations of antibiotics, and adhesion-based vaccines.

RESULTS

Altogether, the findings suggest that interference with bacterial adhesion serves as a new means to fight infectious diseases.

CONCLUSION

Anti-adhesion-based therapies can be effective in prevention and treatment of bacterial infections, but further work is needed to elucidate underlying mechanisms.

Sub-minimum inhibitory concentrations of ceftazidime inhibit Pseudomonas aeruginosa biofilm formation

Pseudomonas aeruginosa exhibits the biofilm mode of growth and causes chronic as well as acute infections in humans. Several reports have shown that the treatments with sub-minimum inhibitory concentrations (sub-MICs) of antimicrobial agents influence biofilm formation by P. aeruginosa. The antibiotic ceftazidime (CAZ) is used to treat P. aeruginosa infections, but few studies have examined the effects of β-lactams on biofilm formation by P. aeruginosa. In this study, we investigated the role of sub-MICs of CAZ in the formation of P. aeruginosa biofilms. 1/4 × MIC CAZ reduced the biofilm volume of P. aeruginosa PAO1, as quantified by crystal violet staining. The formation of P. aeruginosa PAO1 biofilms treated with 1/4 × MIC CAZ were observed by confocal laser scanning microscopy. They were more heterogeneous than the PAO1 biofilms without CAZ treatment. Furthermore, sub-MICs of CAZ inhibited the twitching motility, which played an important role in mature biofilm formation. 1/4 × MIC CAZ also reduced the gene expressions of lecA, lecB, pel and psl, which mediate the adhesion and polysaccharide matrix synthesis of P. aeruginosa. These effects suggest that sub-MICs of CAZ may affect a number of stages of biofilm formation. Investigating the effects of sub-MIC antibiotics on targeted bacterial biofilm may lead to the development of future antibiotic treatment modalities.

Alterations of growth rate and gene expression levels of UPEC by antibiotics at sub-MIC

The host is the main environment for bacteria, and they also expose to many antibiotics during the treatment of infectious diseases in host body. In this study, it was aimed to investigate possible changes in growth rate and expression levels of three virulence genes (foc/foc, cnf1, and usp) in a uropathogenic E. coli standard strain within the presence of ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole. The UPEC C7 strain was grown on tryptic soy broth-TSB (control), TSB + ciprofloxacin, TSB + nitrofurantoin, and TSB + trimethoprim-sulfamethoxazole for determination of both growth rate and gene expression level. Antibiotics were added according to their sub-minimal inhibition concentrations. E-test was used to determine MIC values of antibiotics. Growth changes were measured in absorbance 600 nm during 24-h period. Total RNA isolations were performed after incubation for 24 h at 37 °C. Gene expression levels were determined by quantitative PCR. Tukey's post hoc test was used for statistical analysis. According to absorbance values, it has been shown that only ciprofloxacin and trimethoprim-sulfamethoxazole have lead significant decrease on growth rate. We also detected statistically significant differences in each gene expression levels for all antibiotics via relative quantification analysis. Fold changes in gene expression was found 0.65, 1.42, 0.23 for foc/foc gene; 0.01, 0.01, 2.84 for cnf1 gene; and 0.1, 0.01, 0.01 for usp gene in the presence of ciprofloxacin, nitrofurantoin, and trimethoprim/sulfamethoxazole, respectively. This investigation has shown that antibiotics can play a role as an environmental factor which may determine the pathogenicity of bacteria in vivo.

Inhibition of enteroaggregative Escherichia coli cell adhesion in-vitro by designed peptides

Enteroaggregative Escherichia coli (EAEC) bears remarkable capacity to adhere the host intestinal mucosal surface and results in acute or persistent childhood diarrhea worldwide. In this study, an attempt has been made to inhibit EAEC cell adherence in-vitro using synthetic peptides. E. coli isolates (n = 54) were isolated from the stool samples of clinically diagnosed pediatric diarrheal patients. 92.8% isolates showed different types of aggregative adherence patterns with HEp-2 cells. AAF-II (Aggregative Adherence Fimbriae-II) EAEC exhibited the maximum ability to form biofilm and intracellular survival. Peptides were designed against the high antigenic epitopic regions of AAF-II adhesin of EAEC O42 using prediction algorithms like BcePred and ProPred software to block the EAEC cell adhesion in-vitro. Peptides P2 (DITITPATNRDVNV) and P3 (MRIKAWGEANHGQL) demonstrated higher inhibition of EAEC cell adhesion than P1 (GMQGSITPAIPLRPG). Interestingly, increasing the pre-incubation time of the peptides with HEp-2 cells from 1 h to 2 h showed the maximum inhibition. The data suggested the potential role of P2 and P3 peptides in successfully blocking the binding of AAF-II EAEC with HEp-2 cell receptors. Hence, the peptides may be efficacious in designing new chemotherapeutic for the management of EAEC mediated diarrhea.

Evaluation of Prevalence, Homology and Immunogenicity of Dispersin among Enteroaggregative Escherichia coli Isolates from Iran

Background:

Diarrhea, caused by enteroaggregative Escherichia coli (EAEC), is an important infection leading toillness and death. Numerous virulent factors have been described in EAEC. However, their prevalence was highly variable among EAECs of distinct geographic locations. Studies have shown that dispersin (antiaggregation protein, aap) is one of the important and abundant virulent factors in EAEC. In this study, we aimed to determine the presence, conservation, and immunogenicity of aap gene in EAEC isolated from Iranian patients.

Methods:

PCR amplification of aap gene in the EAEC isolates was performed, and the aap gene was cloned in pBAD-gIIIA vector. The sequence of aap gene was analyzed using the ExPASy and BLAST tools. The expression of aap gene was performed in E. coli Top10, and expression confirmation was carried out by SDS-PAGE and Western-blot techniques. Rabbits were immunized with purified dispersin protein emulsified with Freund’s adjuvant. Sera were collected and examined for antibody response. Finally, invitro efficacy of dispersin and anti-dispersin was evaluated.

Results:

The results of PCR showed the presence of aap gene in all of the EAEC isolates with significant homology. Finally, the significant difference between the levels of IgG response in dispersin-injected rabbits and control group was observed.

Conclusion:

Our results were in accordance with other studies that reported the presence of dispersin in the EAEC isolates with high conservation and immunogenicity. Hence, dispersin could be a promising candidate for any probable prevention against EAEC infections.

Effects of intracanal irrigant MTAD Combined with nisin at sub-minimum inhibitory concentration levels on Enterococcus faecalis growth and the expression of pathogenic genes

Exposure to antibiotics is considered to be the major driver in the selection of antibiotic-resistant bacteria and may induce diverse biological responses in bacteria. MTAD is a common intracanal irrigant, but its bactericidal activity remains to be improved. Previous studies have indicated that the antimicrobial peptide nisin can significantly improve the bactericidal activity of MTAD against Enterococcus faecalis. However, the effects of MTAD and its modification at sub-minimum inhibitory concentration (sub-MIC) levels on Enterococcus faecalis growth and the expression of pathogenic genes still need to be explored. In this study, the results of post-antibiotic effects (PAE) and post-antibiotic sub-MIC effects (PASME) showed that MTADN (nisin in combination with MTAD) had the best post-antibiotic effect. E. faecalis after challenge with MTAD was less sensitive to alkaline solutions compared with MTAN (nisin in place of doxycycline in MTAD) and MTADN. E. faecalis induced with sub-MIC of MTAD generated resistance to the higher concentration, but induction of E. faecalis with MTAN did not cause resistance to higher concentrations. Furthermore, real-time polymerase chain reaction (RT-PCR) showed that the stress caused by sub-MIC exposure to MTAD, MTAN, or MTADN resulted in up- or down-regulation of nine stress genes and four virulence-associated genes in E. faecalis and resulted in different stress states. These findings suggested that nisin improved the post-antibacterial effect of MTAD at sub-MIC levels and has considerable potential for use as a modification of MTAD.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Animal models of enteroaggregative Escherichia coli infection

Enteroaggregative Escherichia coli (EAEC) has been acknowledged as an emerging cause of gastroenteritis worldwide for over two decades. Epidemiologists are revealing the role of EAEC in diarrheal outbreaks as a more common occurrence than ever suggested before. EAEC induced diarrhea is most commonly associated with travelers, children and immunocompromised individuals however its afflictions are not limited to any particular demographic. Many attributes have been discovered and characterized surrounding the capability of EAEC to provoke a potent pro-inflammatory immune response, however cellular and molecular mechanisms underlying initiation, progression and outcomes are largely unknown. This limited understanding can be attributed to heterogeneity in strains and the lack of adequate animal models. This review aims to summarize current knowledge about EAEC etiology, pathogenesis and clinical manifestation. Additionally, current animal models and their limitations will be discussed along with the value of applying systems-wide approaches such as computational modeling to study host-EAEC interactions.

Anti-adhesion methods as novel therapeutics for bacterial infections

Anti-adhesion therapies for bacterial infections offer an alternative to antibiotics, with those therapies bacteria are not killed but are prevented from causing harm to a host by inhibiting adherence to host cells and tissues, a prerequisite for the majority of infectious diseases. The mechanisms of these potential therapeutic agents include inhibition of adhesins and their host receptors, vaccination with adhesins or analogs, use of probiotics and dietary supplements that interfere with receptor-adhesin interactions, subminimal inhibitory concentrations of antibiotics and manipulation of hydrophobic interactions. Once developed, these drugs will contribute to the arsenal for fighting infectious disease in the future, potentially subverting antibiotic resistance.

Clinical implications of enteroadherent Escherichia coli

Pathogenic Escherichia coli that colonize the small intestine primarily cause gastrointestinal illness in infants and travelers. The main categories of pathogenic E. coli that colonize the epithelial lining of the small intestine are enterotoxigenic E. coli, enteropathogenic E. coli, and enteroaggregative E. coli. These organisms accomplish their pathogenic process by a complex, coordinated multistage strategy, including nonintimate adherence mediated by various adhesins. These so called "enteroadherent E. coli" categories subsequently produce toxins or effector proteins that are either secreted to the milieu or injected to the host cell. Finally, destruction of the intestinal microvilli results from the intimate adherence or the toxic effect exerted over the epithelia, resulting in water secretion and diarrhea. In this review, we summarize the current state of knowledge regarding these enteroadherent E. coli strains and the present clinical understanding of how these organisms colonize the human intestine and cause disease.

Simulation model to predict the fate of ciprofloxacin in the environment after wastewater treatment

The extent hospital effluent contributes to antimicrobial presence in the environment and its impact on resistance dissemination remains unknown. To investigate the fate of the antimicrobial ciprofloxacin in hospital effluent a Monte Carlo simulation model was developed to model levels from hospital use to wastewater treatment plant (WWTP) effluent release, in addition to modeling resistance formation potential, hazard quotient (HQ) and swimmer exposure. The mean predicted concentration (PC) of ciprofloxacin in hospital effluent, urban effluent, WWTP effluent, sludge, soil and sea water was 579, 6.06, 2.59, 3.48, 0.006 and 0.15 mg/m(3), respectively. A parallel surveillance study confirmed levels of ciprofloxacin above or below the limit of detection. The model predicted levels would never exceed the ECOSAR toxicity value. The model predicted a 98% probability of ciprofloxacin exhibiting a HQ > 1 (low toxicity concern). The mean ciprofloxacin PC in WWTP effluent was less than the minimum inhibitory concentration (MIC). The probability of conditions in WWTP effluent being favorable for resistance at 20% and 80% of the MIC was 3% and 72%, respectively. In all instances, when the MIC was bound, the probability for resistance formation within soil and sea water was < 1%. The probability of a swimmer being exposed to a level of ciprofloxacin greater than the acceptable daily intake was negligible. The study concluded that release of hospital effluent into the environment may lead to concentrations of ciprofloxacin which are of low toxicity concern but may be conducive to resistance formation and allow for the dissemination of resistance.