Antibiotic Resistance Pattern and Distribution of pslA Gene Among Biofilm Producing Pseudomonas aeruginosa Isolated From Waste Water of a Burn Center

Novel strategies for vancomycin-resistant Enterococcus faecalis biofilm control: bacteriophage (vB_EfaS_ZC1), propolis, and their combined effects in an ex vivo endodontic model

BACKGROUND

Endodontic treatment failures are predominantly attributed to Enterococcus faecalis (E. faecalis) infection, a Gram-positive coccus. E. faecalis forms biofilms, resist multiple antibiotics, and can withstand endodontic disinfection protocols. Vancomycin-resistant strains, in particular, are challenging to treat and are associated with serious medical complications.

METHODS

A novel phage, vB_EfaS_ZC1, was isolated and characterized. Its lytic activity against E. faecalis was assessed in vitro through time-killing and biofilm assays. The phage's stability under various conditions was determined. Genomic analysis was conducted to characterize the phage and its virulence. The phage, propolis, and their combination were evaluated as an intracanal irrigation solution against a 4-week E. faecalis mature biofilm, using an ex vivo infected human dentin model. The antibiofilm activity was analyzed using a colony-forming unit assay, field emission scanning electron microscopy, and confocal laser scanning microscopy.

RESULTS

The isolated phage, vB_EfaS_ZC1, a siphovirus with prolate capsid, exhibited strong lytic activity against Vancomycin-resistant strains. In vitro assays indicated its effectiveness in inhibiting planktonic growth and disrupting mature biofilms. The phage remained stable under wide range of temperatures (- 80 to 60 °C), tolerated pH levels from 4 to 11; however the phage viability significantly reduced after UV exposure. Genomic analysis strongly suggests the phage's virulence and suitability for therapeutic applications; neither lysogeny markers nor antibiotic resistance markers were identified. Phylogenetic analysis clustered vB_EfaS_ZC1 within the genus Saphexavirus. The phage, both alone and in combination with propolis, demonstrated potent antibiofilm effects compared to conventional root canal irrigation.

CONCLUSION

Phage vB_EfaS_ZC1 demonstrates a promising therapy, either individually or in combination with propolis, for addressing challenging endodontic infections caused by E. faecalis.

Aerobic granular sludge formation and stability in enhanced biological phosphorus removal system under antibiotics pressure: Performance, granulation mechanism, and microbial successions

Wastewater containing antibiotics can pose a significant threat to biological wastewater treatment processes. This study investigated the establishment and stable operation of enhanced biological phosphorus removal (EBPR) by aerobic granular sludge (AGS) under mixed stress conditions induced by tetracycline (TC), sulfamethoxazole (SMX), ofloxacin (OFL), and roxithromycin (ROX). The results show that the AGS system was efficient in removing TP (98.0%), COD (96.1%), and NH₄⁺-N (99.6%). The average removal efficiencies of the four antibiotics were 79.17% (TC), 70.86% (SMX), 25.73% (OFL), and 88.93% (ROX), respectively. The microorganisms in the AGS system secreted more polysaccharides, which contributed to the reactor's tolerance to antibiotics and facilitated granulation by enhancing the production of protein, particularly loosely bound protein. Illumina MiSeq sequencing revealed that putative phosphate accumulating organisms (PAOs)-related genera (Pseudomonas and Flavobacterium) were enormously beneficial to the mature AGS for TP removal. Based on the analysis of extracellular polymeric substances, extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and microbial community, a three-stage granulation mechanism was proposed including adaption to the stress environment, formation of early aggregates and maturation of PAOs enriched microbial granules. Overall, the study demonstrated the stability of EBPR-AGS under mixed antibiotics pressure, providing insight into the granulation mechanism and the potential use of AGS for wastewater treatment containing antibiotics.

Phenotypic and genotypic characterization of clinical Pseudomonas aeruginosa

Objectives

Pseudomonas aeruginosa is an opportunistic pathogen that can cause many nosocomial infections. Biofilm formation, drug resistance, and motility contribute to virulence in P. aeruginosa. This study assessed the colistin minimum inhibitory concentration (MIC), biofilm formation, presence of mod A and psl A genes, and types of motilities in multidrug-resistant (MDR) and multidrug-susceptible (MDS) P. aeruginosa.

Methods

Sixty-two P. aeruginosa from pus and 18 from urine samples were studied for their susceptibility to commonly used antibiotics, colistin MIC by agar dilution, and biofilm-forming ability by the microtiter plate method. All MDR and MDS P. aeruginosa isolates were tested for the presence of mod A and psl A genes by PCR, and different types of motilities using specific media.

Results

Among the 40 MDR and 40 MDS isolates, 17 each were colistin-resistant and 23 each were colistin-intermediate. Nine MDR pus isolates and three MDR urine isolates showed all three types of motilities. Thirteen MDS pus isolates and four MDS urine isolates showed both swimming and swarming motility. MDS isolates did not show twitching motility. A higher number of MDR strains were strong biofilm producers (n = 19), whereas a higher number of MDS strains (n = 24) were moderate biofilm producers (p = 0.023). Twenty-seven MDR and twenty-eight MDS isolates were positive for both mod A and pslA genes. Among the strong biofilm-forming pus isolates, a greater number of MDR isolates (n = 13 each) had modA and pslA genes compared to MDS isolates (modA p = 0.017; pslA p = 0.014).

Conclusions

Our findings clearly showed a statistically significant association among strong biofilm formation, modA, pslA genes, and drug resistance in P. aeruginosa isolated from clinical samples. Additional studies are needed to explore other genes and factors responsible for weak and moderate biofilm formation and drug resistance.

Combination of Meropenem and Zinc Oxide Nanoparticles; Antimicrobial Synergism, Exaggerated Antibiofilm Activity, and Efficient Therapeutic Strategy against Bacterial Keratitis

Pseudomonas aeruginosa is an opportunistic gram-negative human pathogen that causes a wide range of infections, including nosocomial infections. Aside from the intrinsic and acquired antimicrobial resistance against many classes of antibiotics, P. aeruginosa can produce an extracellular polymeric matrix called "biofilm" that protects bacteria from antibiotics and harmful factors. Biofilm enables P. aeruginosa to develop chronic infections. This study assessed the inhibitory action of ZnO-nanoparticles against biofilms formed by multidrug-resistant P. aeruginosa strains. A collection of 24 clinical strains of P. aeruginosa were tested for their antimicrobial resistance against different antibiotics using the disk diffusion method. The antibiofilm activity of ZnO-NPs was assessed using the microtiter plate biofilm assay. The application of ZnO-NPs dramatically modulated the resistance profile and biofilm activity of P. aeruginosa. The combination of ZnO-NPs and meropenem showed synergistic antipseudomonal activity with lower MICs. The scanning electron microscope (SEM) micrographs revealed complete inhibition of biofilms treated with the meropenem-ZnO-NPs combination. Reduced expression of biofilm regulating genes lasR, pslA, and fliC was detected, reflecting the enhanced antibiofilm effect of ZnO-NPs. In vivo application of this antimicrobial mixture completely cured P. aeruginosa-induced keratitis in rats. Our findings represent a dual enhancement of antibacterial and antibiofilm activity via the use of meropenem-ZnO-NPs combination against carbapenem-resistant P. aeruginosa infections.

Biofilm-Associated Multi-Drug Resistance in Hospital-Acquired Infections: A Review

Biofilm-related multi-drug resistance (MDR) is a major problem in hospital-acquired infections (HAIs) that increase patient morbidity and mortality rates and economic burdens such as high healthcare costs and prolonged hospital stay. This review focuses on the burden of bacterial biofilm in the hospital settings, their impact on the emergence of MDR in the HAIs, biofilm detection methods, recent approaches against biofilms, and future perspectives. The prevalence of biofilm-associated MDR among HAIs ranges from 17.9% to 100.0% worldwide. The predominant bacterial isolates causing HAIs in recently published studies were S. aureus, A. baumannii, K. pneumoniae, and P. aeruginosa. In addition to the use of qualitative and quantitative methods to detect biofilm formation, advanced PCR-based techniques have been performed for detecting biofilm-associated genes. Although there are suggested therapeutic strategies against biofilms, further confirmation of their efficacy for in vivo application and antibiotics targeting biofilm-associated genes/proteins to minimize treatment failure is required for the future.

Characterization of antibiotic resistance genes and bacteria in a municipal water resource recovery facility

Municipal water resource recovery facilities (WRRFs) are important sources of antibiotic-resistant bacteria and genes (ARB and ARGs). In this study, antibiotic-resistant total heterotrophic bacteria (THB_R ) counts (CFU/ml) cultivated from influent, effluent of activated sludge process, and outflow of disinfection unit of an urban WRRF were investigated for the presence of 16, 32, 64, and 128 μg/ml of nine antibiotics. The isolates of Pseudomonas spp., Acinetobacter spp., and Escherichia coli obtained from effluent of activated sludge process were subjected for molecular identification by detecting the 16S rRNA gene sequences. Additionally, using the polymerase chain reaction method (PCR), the isolates were investigated for the presence of bla_SHV , bla_TEM , bla_CTX-M , bla_VIM , sul1, and qnrS genes. According to the results, the abundance of THB_R counts was not significantly reduced by the biological treatment except for cefixime and sulfamethoxazole; it also increased for some antibiotics after disinfection unit. The average removal efficiency of THB_R resistant to ciprofloxacin, sulfamethoxazole, and ceftazidime were 7.9 ± 1.7%, 41.8 ± 2.1%, and 14.4 ± 6.2%, respectively. Also, all the tested isolates were resistant to at least four antibiotics. For all antibiotics, the resistance ratio (THB_R /THB) significantly increased in the effluent and after chlorination unit. Among 12 resistant isolates, bla_TEM and sul1 genes were the most frequently detected ones involved in 92% and 83% of the isolates, respectively. Both bla_TEM and sul1 genes were found in 100% of E. coli, and 83% and 67% of Pseudomonas spp. isolates, respectively. Further efforts are necessary to limit the transmission of ARB and ARGs from WRRFs into the environment and prevent human health threats. PRACTITIONER POINTS: The ratio of resistance significantly increased after biological treatment. Up to 40% of heterotrophic bacteria in the effluent was antibiotic resistant. bla_TEM and sul1 genes were more prevalent (92%) in all isolates of bacteria. Both bla_TEM and sul1 genes were found in 100% of E. coli isolates. Pseudomonas spp. holds bla_TEM and sul1 genes in 83% and 67% of isolates, respectively.

A phenotypic and molecular investigation of biofilm formation in clinical samples of Pseudomonas aeruginosa

Pseudomonas aeruginosa is identified as a versatile opportunistic microorganism with metabolic diversity contributing to a wide range of health burdens, especially in immunocompromised patients. This bacterium is the cause of 10 to 20% of nosocomial infections. In this study, we evaluated the phenotypic characterizations of biofilm formation in P. aeruginosa clinical isolates using micro-titer plate assay. Indeed, we estimated the prevalence of QS (rhlI, rhlR, rhlAB, lasB, lasI, lasR, aprA) and virulence genes (pslA and cupA) by PCR. The results showed that among 69% of the isolates forming biofilm, 9% were strong biofilm producers, whereas 13% and 47% of isolates produced moderate and low amounts of biofilm, respectively. All isolates possessed cupA and seven QS genes (rhlI, rhlR, rhlAB, lasB,  lasI, lasR, aprA), while 92% of the isolates possessed the pslA gene. Identification of these genes and their association with biofilm formation can be advantageous in adopting therapeutic methods.

Bacterial exo-polysaccharides in biofilms: role in antimicrobial resistance and treatments

Background

Bacterial biofilms are aggregation or collection of different bacterial cells which are covered by self-produced extracellular matrix and are attached to a substratum. Generally, under stress or in unfavorable conditions, free planktonic bacteria transform themselves into bacterial biofilms and become sessile.

Main body

Various mechanisms involving interaction between antimicrobial and biofilm matrix components, reduced growth rates, and genes conferring antibiotic resistance have been described to contribute to enhanced resistance. Quorum sensing and multi-drug resistance efflux pumps are known to regulate the internal environment within the biofilm as well as biofilm formation; they also protect cells from antibiotic attack or immune attacks. This review summarizes data supporting the importance of exopolysaccharides during biofilm formation and its role in antibiotic resistance.

Conclusions

Involvement of quorum sensing and efflux pumps in antibiotic resistance in association with exopolysaccharides. Also, strategies to overcome or attack biofilms are provided.

Occurrence, virulence, carbapenem resistance, susceptibility to disinfectants and public health hazard of Pseudomonas aeruginosa isolated from animals, humans and environment in intensive farms

AIMS

This work aimed to determine the occurrence, virulence, antibiogram, carbapenem resistance genes and susceptibility to disinfectants of Pseudomonas aeruginosa isolated from animals, environment and workers in intensive farms.

METHODS AND RESULTS

A total of 610 samples from intensive beef cattle and sheep farms in Kafr El Sheikh Governorate, Egypt were screened for the presence of P. aeruginosa using bacteriological assays. The isolates were characterized by PCR and tested for susceptibility to antibiotics using disk diffusion method and disinfectants by quantitative suspension test. In all, 60 P. aeruginosa isolates were recovered in this study and all isolates harboured at least one of the virulence genes tested. Human P. aeruginosa isolates were highly resistant to cephalosporins, fluroquinolones, aminoglycosides, carbapenems and penicillins+β-lactamase inhibitors than non-human isolates. Colistin resistance was higher in non-human than human P. aeruginosa isolates, whereas low resistance to aztreonam was observed in non-human and human isolates. Carbapenem-resistant P. aeruginosa (CRPA) strains were recovered from workers (56.5%), sheep (8.3%) and cattle (8.3%). All CRPA harboured at least one of the carbapenem resistance genes tested and most of them showed multidrug resistance (MDR) or extensive drug resistance (XDR) phenotypes. Glutaraldehyde 1% and hydrogen peroxide 3% eliminated P. aeruginosa completely in the absence and presence of organic matter within short contact time compared with other disinfectants.

CONCLUSIONS

This study reported the occurrence of CRPA in animals and workers in intensive farms. Glutaraldehyde and hydrogen peroxide were the most effective disinfectants against P. aeruginosa.

SIGNIFICANCE AND IMPACT OF THE STUDY

The occurrence of CRPA in intensive livestock farms is a serious challenge that threatens animal and human health and increases the risk of P. aeruginosa infection in the community. Therefore, it is vital to control the spread of CRPA by banning or restricting the use of antibiotics and applying proper cleaning and disinfection protocols in livestock farms.

Patterns of antimicrobial resistance observed in the Middle East: Environmental and health care retrospectives

Antimicrobial resistance is one of the biggest worldwide challenging problems that associates with high morbidity and mortality rates. The resistance of bacteria to various antibiotic classes results in difficulties in the treatment of infectious diseases caused by those bacteria. This paper highlights and provides a critical overview of observational and experimental studies investigating the presence of antibiotic resistant bacteria in different environments in Middle East countries and the mechanisms by which bacteria acquire and spread resistance. The data of this research considered the published papers within the last ten years (2010-2020) and was carried out using PubMed. A total of 66 articles were selected in this review. This review covered studies done on antibiotic resistant bacteria found in a wide range of environments including foods, animals, groundwater, aquatic environments as well as industrial and hospital wastewater. They acquire and achieve their resistance through several mechanisms such as antibiotic resistant genes, efflux pumps and enzymatic reactions. However, the dissemination and spread of antibiotic resistant bacteria is affected by several factors like anthropogenic, domestic, inappropriate use of antibiotics and the expulsion of wastewater containing antibiotic residues to the environments. Therefore, it is important to increase the awareness regarding these activities and their effect on the environment and eventually on health.

Tetracycline Induces the Formation of Biofilm of Bacteria from Different Phases of Wastewater Treatment

The study monitored the effect of tetracycline on bacterial biofilm formation and compared biofilm formation by resistant bacterial strains in different phases of the wastewater treatment process in wastewater treatment plant (WWTP). The crystal violet staining method was used to evaluate the biofilm formation. Biofilm-related bacterial properties were characterized by hydrophobicity, autoaggregation and motility tests. The relative abundance of tetracycline resistance genes (tetW, tetM, tetO, tetA and tetB) in wastewaters were subsequently quantified using qPCR. The results show that the isolates from the nitrification tank produce biofilm with up to 10 times greater intensity relative to the isolates from the sedimentation tank. In isolates of Aeromonas sp. from the nitrification tank, increased biofilm production in the occurrence of tetracycline from a concentration of 0.03125 µg/mL was observed. The tetW gene showed the highest relative abundance out of all the tested genes. From the sampling points, its abundance was the highest in the sedimentation tank of the WWTP. Based on these results, it can be assumed that resistant bacteria are able to form a biofilm and sub-inhibitory tetracycline concentrations induce biofilm formation. WWTPs thus represent a reservoir of antibiotic resistance genes and contribute to the spread of resistance in the natural environment.

Antimicrobial resistance pattern, genetic distribution of ESBL genes, biofilm-forming potential, and virulence potential of Pseudomonas aeruginosa isolated from the burn patients in Tehran Hospitals, Iran

Introduction

according to the studies performed, researchers considered Pseudomonas aeruginosa (P. aeruginosa) as the major cause of infectious diseases like burn and wound infection that makes it one of the most threatening opportunistic pathogens. The present research aimed at investigating antimicrobial resistance, biofilm-forming abilities, and frequency of the genes contributed to bla_VEB-1, bla_PER-1, and bla_PSE-1 genes and virulence of P. aeruginosa separated from the burn infections in Tehran, Iran.

Methods

we evaluated the resistance of 156 P. aeruginosa isolates to fifteen antimicrobial agents and generation of the ESBL and MBL enzymes phenotypically based on the CLSI instructions. Moreover, the biofilm forming potential has been assayed in a microtitre plate. In addition, PCR has been used to examine the frequency of virulence-and biofilm-related genes. Furthermore, the PCR of bla_VEB-1, bla_PSE-1, and bla_PER-1 genes has been amplified.

Results

according to the results, 72.2% of P. aeruginosa isolates have been MDR and 35.6% and 55.5% have been positive for producing MBL and ESBL, respectively. Moreover, 67.8% have been positive for forming biofilms. It has been found that 15.3% isolates are ESBL-positive; from among them 60% belong to the females and 40% belong to the males. In addition, one and two isolates respectively harbored the bla_VEB-1and bla_PER-1genes.

Conclusion

the present research outputs indicated the higher frequency of the multi drug resistance and higher percent of the virulence-related genes in the clinical P. aeruginosa isolates in Iran.

Isolation and Molecular Identification of Aeromonas Wound Infection in Iranian Burn Patients

INTRODUCTION

Aeromonas have recently emerged as opportunistic pathogens and only a few studies are available regarding the isolation of these bacteria from burn wound infections. This study aimed at isolating Aeromonas as an infrequent cause of infection in this group of immunocompromised patients.

METHODS

A total of 300 samples were collected from the wounds of burn patients hospitalized in Gotbodin Shirazi Burn Center in 2013. The samples were cultured on Aeromonas specific media and then confirmed using standard biochemical tests and 16S rRNA gene amplification and sequencing. The antibiotic susceptibility of the isolates was determined using the disk diffusion and broth microdilution methods.

RESULTS

Biochemical tests demonstrated five presumptive samples of Aeromonas, while, molecular testing confirmed only three. All isolates were resistant to ampicillin-sulbactam, erythromycin, oxacillin, and vancomycin. However, they were susceptible to gentamicin, meropenem, nitrofurantoin, chloramphenicol, cephalexin, and cefotaxime. Two Aeromonas veronii isolates were resistant to sulfamethoxazole-trimethoprim and sensitive to nalidixic acid, while Aeromonas bestiarum was sensitive to the former and resistant to the latter antibiotics. Lastly, only one of the A. veronii isolates was found to be resistant to tetracycline.

CONCLUSION

This study is the first to report on the isolation of Aeromonas spp. from burn patients in Iran. Moreover, this is the first report of isolating A. bestiarum from burn wounds. The results of this study confirm earlier findings that the use of molecular methods is essential to accurately identify these bacteria.

High incidence of type III secretion system associated virulence factors (exoenzymes) in Pseudomonas aeruginosa isolated from Iranian burn patients

Objective

The present study aimed to determine the prevalence of virulence factors and antimicrobial resistance profile of Pseudomonas aeruginosa strains isolated from Iranian burn patients.

Results

This cross-sectional study performed on 100 P. aeruginosa isolates which were recovered from burn wound specimens in 2014–2015. All presumptive isolates were identified by standard microbiologic tests. Antimicrobial susceptibility test was carried out by disk diffusion method. The presence of virulence genes was determined by PCR method. Antibiotic susceptibility results revealed that the isolates were mostly susceptible to amikacin (61%), ceftazidime (60%), and imipenem (55%). Moreover, 59% of the isolates were multi-drug resistance (MDR). The most prevalent MDR pattern was aminoglycosides–penicillins–fluoroquinolones–carbapenems (15%). The presence of exoT, exoY, exoS and exoU genes was detected in 100%, 100%, 59%, and 41% of the tested isolates, respectively. Results points out the pattern of MDR and genetic diversity of type III secretion system among P. aeruginosa strains isolated from the burn population. Overall, the association of MDR and the presence of the specific virulence genes can be a predictive marker for the persistence of these isolates in the hospitals and subsequently a worse clinical condition for the affected patients.

Persistence of antibiotic resistance genes and bacterial community changes in drinking water treatment system: From drinking water source to tap water

As emerging contaminants, antibiotic resistance genes (ARGs) have become a public concern. This study aimed to investigate the occurrence and diversity of ARGs, and variation in the composition of bacterial communities in source water, drinking water treatment plants, and tap water in the Pearl River Delta region, South China. Various ARGs were present in the different types of water. Among the 27 target ARGs, floR and sul1 dominated in source water from three large rivers in the region. Pearson correlation analysis suggested that sul1, sul2, floR, and cmlA could be potential indicators for ARGs in water samples. The total abundance of the detected ARGs in tap water was much lower than that in source water. Sand filtration and sedimentation in drinking water treatment plants could effectively remove ARGs; in contrast, granular activated carbon filtration increased the abundance of ARGs. It was found that Pseudomonas may be involved in the proliferation and dissemination of ARGs in the studied drinking water treatment system. Bacteria and ARGs were still present in tap water after treatment, though they were significantly reduced. More research is needed to optimize the water treatment process for ARG removal.

Antimicrobial resistance, biofilm-forming ability and virulence potential of Pseudomonas aeruginosa isolated from burn patients in northern Iran

OBJECTIVES

Pseudomonas aeruginosa is a frequent cause of infectious diseases, such as burn and wound infections, making it one of the most menacing opportunistic pathogens. The aim of this study was to investigate the antimicrobial resistance, biofilm-forming ability, and frequency of genes involved in biofilm formation and virulence of P. aeruginosa isolated from burn infections in Iran.

METHODS

Resistance of 90 P. aeruginosa isolates to 12 antimicrobial agents as well as production of extended-spectrum β-lactamase (ESBL) and metallo-β-lactamase (MBL) enzymes were assessed phenotypically according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Biofilm-forming capacity was assayed in a microtitre plate. The frequency of biofilm- and virulence-associated genes was investigated by PCR. Mutations in gyrA and parC in ciprofloxacin-resistant isolates were also determined by PCR.

RESULTS

In phenotypic assays, 72.2% (65/90) of P. aeruginosa isolates were multidrug-resistant (MDR), 55.5% (50/90) and 35.6% (32/90) were positive for ESBL and MBL production, respectively, and 67.8% (61/90) were positive for biofilm formation. Biofilm- and virulence-associated genes were identified in >50% of the P. aeruginosa isolates, with toxA and lasB being the most frequent. All of the virulence genes were more common in biofilm-forming and MDR phenotypes. Two point mutations in gyrA and one in parC in high-level ciprofloxacin-resistant isolates were identified.

CONCLUSIONS

The results of this study indicate that there is a high frequency of multidrug resistance and a high percentage of virulence-associated genes present in clinical P. aeruginosa isolates in Iran.

Biofilm Formation, Antimicrobial Resistance, and Sanitizer Tolerance of Salmonella enterica Strains Isolated from Beef Trim

In the beef industry, product contamination by Salmonella enterica is a serious public health concern, which may result in human infection and cause significant financial loss due to product recalls. Currently, the precise mechanism and pathogen source responsible for Salmonella contamination in commercial establishments are not well understood. We characterized 89 S. enterica strains isolated from beef trim with respect to their biofilm-forming ability, antimicrobial resistance, and biofilm cell survival/recovery growth after sanitizer exposure. A total of 28 Salmonella serovars was identified within these strains. The most common serovars identified were Anatum, Dublin, Montevideo, and Typhimurium, with these accounting for nearly half of the total strains. The vast majority (86%) of the strains was able to develop strong biofilms, and the biofilm-forming ability was highly strain dependent and related to cell surface expression of extracellular polymeric structures. These strains also demonstrated strong tolerance to quaternary ammonium chloride (QAC) and chlorine dioxide (ClO₂), but were more sensitive to chlorine treatment. Sanitizer tolerance and bacterial postsanitization recovery growth were closely associated with strains' biofilm-forming ability. Thirty percent of the examined strains were found resistant to multiple antimicrobial agents and the resistance phenotypes were serovar associated, but not related to strains' biofilm-forming ability. Pulsed-field gel electrophoresis analysis tended to group strains by serovar rather than by biofilm-forming ability. Collectively, these data indicate that the strong biofilm formers of certain S. enterica strains/serovars possess significant potential for causing meat product contamination in meat processing environment.

Dexamethasone abrogates the antimicrobial and antibiofilm activities of different drugs against clinical isolates of Staphylococcus aureus and Pseudomonas aeruginosa

Staphylococcus aureus and Pseudomonas aeruginosa are part of the human microbiota and are also important bacterial pathogens, for which therapeutic options are lacking nowadays. The combined administration of corticosteroids and antimicrobials is commonly used in the treatment of infectious diseases to control inflammatory processes and to minimize potential toxicity of antimicrobials, avoiding sequelae. Although different pharmaceutical dosage forms of antimicrobials combined to corticosteroids are available, studies on the interference of corticosteroids on the pharmacological activity of antimicrobials are scarce and controversial. Here, we provide evidence of the interference of dexamethasone on the pharmacological activity of clinically important antimicrobial drugs against biofilms and planktonic cells of S. aureus and P. aeruginosa. Broth microdilution assays of minimal inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum biofilm eradication concentration (MBEC) of gentamicin, chloramphenicol, oxacillin, ceftriaxone and meropenem were conducted with and without the addition of dexamethasone. The effect of all drugs was abrogated by dexamethasone in their MIC, MBC, and MBEC, except gentamicin and meropenem, for which the MBC was not affected in some strains. The present study opens doors for more investigations on in vitro and in vivo effects and safety of the combination of antimicrobials and glucocorticoids.

Phage therapy against Enterococcus faecalis in dental root canals

Antibiotic resistance is an ever-growing problem faced by all major sectors of health care, including dentistry. Recurrent infections related to multidrug-resistant bacteria such as methicillin-resistant Staphylococcus aureus, carbapenem-resistant Enterobacteriaceae, and vancomycin-resistant enterococci (VRE) in hospitals are untreatable and question the effectiveness of notable drugs. Two major reasons for these recurrent infections are acquired antibiotic resistance genes and biofilm formation. None of the traditionally known effective techniques have been able to efficiently resolve these issues. Hence, development of a highly effective antibacterial practice has become inevitable. One example of a hard-to-eradicate pathogen in dentistry is Enterococcus faecalis, which is one of the most common threats observed in recurrent root canal treatment failures, of which the most problematic to treat are its biofilm-forming VRE strains. An effective response against such infections could be the use of bacteriophages (phages). Phage therapy was found to be highly effective against biofilm and multidrug-resistant bacteria and has other advantages like ease of isolation and possibilities for genetic manipulations. The potential of phage therapy in dentistry, in particular against E. faecalis biofilms in root canals, is almost unexplored. Here we review the efforts to develop phage therapy against biofilms. We also focus on the phages isolated against E. faecalis and discuss the possibility of using phages against E. faecalis biofilm in root canals.