Genotypic and phenotypic characterization of a biofilm-forming Serratia plymuthica isolate from a raw vegetable processing line

Recently, we isolated from a raw vegetable processing line a Serratia strain with strong biofilm-forming capacity and which produced N-acyl-L-homoserine lactones (AHLs). Within the Enterobacteriaceae, strains of the genus Serratia are a frequent cause of human nosocomial infections; in addition, biofilm formation is often associated with persistent infections. In the current report, we describe the detailed characterization of the isolate using a variety of genotypic and phenotypic criteria. Although the strain was identified as Serratia plymuthica on the basis of its small subunit ribosomal RNA (16S rRNA) gene sequence, it differed from the S. plymuthica type strain in production of pigment and antibacterial compounds, and in AHL production profile. Nevertheless, the identification as S. plymuthica could be confirmed by gyrB phylogeny and DNA:DNA hybridization.     

青岛近海沉积物生物被膜中密度感应及密度感应淬灭细菌多样性

【背景】细菌密度感应(Quorum sensing,QS)是指细菌利用分泌的信号分子进行相互交流的现象,而密度感应淬灭(Quorumquenching,QQ)是指通过干扰信号分子的产生、释放、积累或应答从而阻抑密度感应通路。【目的】探究青岛近海沉积物生物被膜中密度感应和密度感应淬灭细菌的多样性。【方法】采用海水培养基2216E从青岛近海沉积物生物被膜中分离获取可培养细菌,采用平板交互划线和高通量筛选的方法分别筛选具有密度感应和密度感应淬灭的菌株。【结果】共分离获得83株共54种具有密度感应和密度感应淬灭的细菌,分属于四大细菌门类:变形菌门、拟杆菌门、厚壁菌门和放线菌门。其中,38株(45.8%)可以产生酰基高丝氨酸内酯(Acyl-homoserine lactone,AHL)类信号分子,它们分属于变形菌门(37株,15种)和拟杆菌门(1株,1种),优势属为弧菌属和鲁杰氏菌属;能够降解AHL类信号分子的有57株(68.7%),在变形菌门(41株,23种)、拟杆菌门(14株,10种)、厚壁菌门(5株,5种)以及放线菌门(1株,1种)中均有分布。【结论】在青岛近海沉积物生物被膜可培养细菌中,具有密度感应和密度感应淬灭现象的菌株具有很高的丰度和多样性,为后续生态学意义的研究与海洋微生物的开发提供了参考。     

Investigation of N-acyl homoserine lactone (AHL) molecule production in Gram-negative bacteria isolated from cooling tower water and biofilm samples

In this study, 99 Gram-negative rod bacteria were isolated from cooling tower water, and biofilm samples were examined for cell-to-cell signaling systems, N-acyl homoserine lactone (AHL) signal molecule types, and biofilm formation capacity. Four of 39 (10 %) strains isolated from water samples and 14 of 60 (23 %) strains isolated from biofilm samples were found to be producing a variety of AHL signal molecules. It was determined that the AHL signal molecule production ability and the biofilm formation capacity of sessile bacteria is higher than planktonic bacteria, and there was a statistically significant difference between the AHL signal molecule production of these two groups (p?<?0.05). In addition, it was found that bacteria belonging to the same species isolated from cooling tower water and biofilm samples produced different types of AHL signal molecules and that there were different types of AHL signal molecules in an AHL extract of bacteria. In the present study, it was observed that different isolates of the same strains did not produce the same AHLs or did not produce AHL molecules, and bacteria known as AHL producers did not produce AHL. These findings suggest that detection of signal molecules in bacteria isolated from cooling towers may contribute to prevention of biofilm formation, elimination of communication among bacteria in water systems, and blockage of quorum-sensing controlled virulence of these bacteria.     

肺炎克雷伯菌生物被膜的体外模型建立

目的研究临床分离的肺炎克雷伯菌在体外形成生物被膜的情况,为进一步研究生物被膜肺炎克雷伯菌的耐药机制奠定基础。方法采用改良平板法建立肺炎克雷伯菌生物被膜模型,用喷金法和扫描电镜观察鉴定,并对生物被膜的形成进行定量分析。结果23株临床分离的肺炎克雷伯菌菌株生物被膜形成能力不同,以强阳性生物被膜形成能力者为最多数。结论绝大多数临床分离的肺炎克雷伯菌菌株具有较强的生物被膜形成能力。应用改良平板法能够较好的在体外建立其生物被膜模型。     

Evaluation of Adherence,Hydrophobicity, Aggregation,and Biofilm Development of <Emphasis Type="Italic">Flavobacterium johnsoniae</Emphasis>-Like Isolates

Flavobacterium spp. isolates have been identified in diverse biofilm structures, but the mechanism of adherence has not been elucidated. The absence of conventional biofilm-associated structures such as fimbriae, pili, and flagella suggest that surface hydrophobicity, and/or autoaggregation and coaggregation may play an important role in adherence and biofilm formation. The biofilm-forming capacity of 29 Flavobacterium johnsoniae-like isolates obtained from South African aquaculture systems was assessed using microtiter plate assays. The role of hydrophobicity [salting aggregation test (SAT) and bacterial adherence to hydrocarbons (BATH) assays], autoaggregation, and coaggregation on biofilm formation by Flavobacterium spp. was also investigated, while biofilm structure was examined using flow cells and microscopy. All isolates displayed a hydrophilic nature, but showed varying levels of adherence in microtiter assays. Significant negative correlations were observed between adherence and biofilm-forming capacity in nutrient-poor medium at 26°C and BATH hydrophobicity and motility, respectively. Isolates displayed strain-to-strain variation in their autoaggregation indices and their abilities to coaggregate with various Gram-negative and Gram-positive organisms. Microcolony and/or biofilm development were observed microscopically, and flavobacterial isolates displayed stronger biofilm structures and interaction with a Vibrio spp. isolate than with an Aeromonas hydrophila isolate. The role of extracellular polysaccharides and specific outer membrane proteins will have to be examined to reveal mechanisms of adherence and coaggregation employed by biofilm-forming F. johnsoniae-like strains.     

Effects of a topical essential oil-containing formulation on biofilm-forming coagulase-negative staphylococci

AIMS: To evaluate the antimicrobial effects of Polytoxinol (PT), a topical essential oil-based formulation, against biofilm positive strains of coagulase-negative staphylococci. METHODS AND RESULTS: Using a microtitre plate assay we measured inhibitory effects for PT against a selection of biofilm-forming clinical isolates of coagulase-negative staphylococci. Susceptibility varied considerably (MIC = 0.6-20 000 ppm). For the most tolerant clinical isolate (Staphylococcus warneri) biofilm growth was inhibited by a 32-fold lower PT concentration than planktonic growth. This inhibition of biofilm development, which was not observed with the other test isolates, was related to an inhibition of the initial phase of S. warneri cell adherence to the polystyrene surface. CONCLUSION: The antimicrobial efficacy of PT was verified against clinical isolates of coagulase-negative staphylococci in vitro. PT was able to inhibit biofilm formation in the most tolerant isolate at sub-inhibitory concentrations. SIGNIFICANCE AND IMPACT OF THE STUDY: These observations indicate that an ability to prevent biofilm formation, independently of effects on cell viability may contribute to the in vivo topical efficacy of essential oils.     

Molecular Identification and Biofilm-Forming Ability of Culturable Aquatic Bacteria In Microbial Biofilms Formed in Drinking Water Distribution Networks

Drinking water distribution networks are known to harbor microbial biofilms. The aim of the present work is to (i) identify the culturable bacteria presented in the drinking-water distribution network, (ii) investigate the ability of isolated bacteria to form biofilm under some environmental stress conditions and some eliminating or removing treatments. To achieve it, 57 strains were isolated from biofilm (43 isolates) and water samples (14 isolates) collected from five stations in drinking-water distribution network in Taif city, Kingdom of Saudi Arabia (KSA). Partial sequences of 16S rRNA gene in the 57 isolates ensured the presence of only 22 different strains in biofilm samples. Among these strains, only 14 strains were also detected in water samples. Gram-negative Aeromonas hydrophila was the most occurred bacterium in the microbial biofilm obtained from the purified-water storage tanks followed by Gram-negative Pseudomonas sp. Gram-positive Bacillus subtilis was the most occurred bacterium in the microbial biofilm collected from the ends of the distribution pipes. Among the 22 isolated strains, 13 strains were strong biofilm producers at 30 and 37°C. The effects of environmental stresses including nutrient starvation (diluted TSB, 20:1), heating (100°C for 10 min), UV-treatment (240 nm for 10 min) and dynamic incubation (150 rpm min^?1) on the formation of biofilm were also investigated. These conditions affected the biofilm formation ability of the isolated strains at different levels. Nutrient starvation enhanced biofilm formation by most of the isolates. Among some biofilm deforming treatments, SDS and trypsin had considerable effects on preventing biofilm formation by most of the isolated strains. In conclusion, the results of the present work indicated that not all biofilm strains released from biofilm to the drinking water. Also, not all biofilm strains were able to form biofilm. Most of isolated bacteria had ability to form biofilm at suboptimum temperature of growth. These results may provide basic information on formation of microbial biofilms and overcome the problem of deteriorating of water quality in the drinking-water distribution networks.     

食源假单胞菌群体感应信号分子的研究

从市售鲜鱼中分离的3株革兰氏阴性菌,经16S rDNA鉴定为假单胞菌属,该菌是一种导致食品腐败的重要腐败细菌。N-酰基-高丝氨酸内酯(AHLs)是革兰氏阴性菌群体感应(QS)系统中一类重要的信号分子,以密度依赖的方式调控某些生理性状的表达。利用AHLs检测菌株对3株假单胞菌进行检测发现,均产生AHLs类信号分子,且FML05-1和FML05-2至少产生两种AHLs,主要的信号分子是N-3-氧代-辛酰基-高丝氨酸内酯(N- 3-oxo-C_8-HSL)。同时对菌株FML05-2在生长过程中所产生的AHLs的活性变化进行研究,发现AHLs活性在菌体生长至12h时达到最大。首次对食源假单胞菌所产生的AHLs进行了研究,为以干扰腐败细菌群体感应为靶点的食品防腐保鲜策略提供研究基础。     

Enhanced biofilm-production in pathogens isolated from patients with rare metabolic disorders

Biofilm-producing bacteria were isolated from the urine of 19 patients with very rare metabolic disorders including: hyperlactacidaemia (8 cases), sugar intolerance and gammopathy (1 case), cystinuria (2 cases), Parkinson's disease (1 case), lipidaemia (2 cases), hyperaminoaciduria (1 case) and others (4 cases). A total of 34 strains were collected, Gram-negative and gram-positive microorganisms were equally distributed among the slime-producing bacteria, with a prevalence of Staphylococcus epidermidis (30%) the most frequent microorganism isolated together with Escherichia coli and Proteus mirabilis that accounted for 15% of this group of strains. A quantitative assay of the biofilm production revealed that in Gram-positive pathogens it was three times greater than that observed in bacteria collected from patients not affected by metabolic diseases (p = 0.0001). In Gram-negative strains the biofilm synthesis was 2.2 times higher than those detected in the same bacteria isolated in the absence of metabolic disorders (p = 0.0033). The results observed indicate that biofilm production is enhanced in bacteria isolated from the urine of patients with metabolic disorders. It is suggested that unusual metabolites might facilitate pathogen production of biofilm found in the urine of these patients.     

禽致病性大肠杆菌江苏、安徽分离株的生物学特性分析

[目的]研究禽致病性大肠杆菌(Avian Pathogenic Escherichia coli,APEC)江苏、安徽分离株的优势血清型,并分析其生物学特性.[方法]对分离自病禽的细菌进行鉴定,采用玻片凝集法测定禽致病性大肠杆菌的血清型,PCR方法检测14种毒力基因的分布,采用美国临床和实验室标准化研究所的方法进行药物敏感性检测,改良结晶紫半定量法检测分离细菌的生物被膜形成能力. [结果]共分离到禽致病性大肠杆菌56株,血清型检测结果表明,O78血清型占64.29％,为主要血清型.毒力基因检测显示,fimC、pfs、ompA和luxS的阳性率超过90％.药物敏感性检测显示,58.93％的菌株对8种以上的药物耐受.生物被膜检测显示,有16株细菌生物被膜形成能力为中等以上,其中68.75％的菌株耐8种以上的药物.[结论]O78为主要流行的血清型.fimC、pfs、ompA和luxS基因为APEC保守基因.多重耐药性仍很普遍,细菌生物被膜与耐药性具有相关性.     

Possible quorum sensing in marine snow bacteria: production of acylated homoserine lactones by Roseobacter strains isolated from marine snow

We report here, for the first time, that bacteria associated with marine snow produce communication signals involved in quorum sensing in gram-negative bacteria. Four of 43 marine microorganisms isolated from marine snow were found to produce acylated homoserine lactones (AHLs) in well diffusion and thin-layer chromatographic assays based on the Agrobacterium tumefaciens reporter system. Three of the AHL-producing strains were identified by 16S ribosomal DNA gene sequence analysis as Roseobacter spp., and this is the first report of AHL production by these alpha-PROTEOBACTERIA: It is likely that AHLs in Roseobacter species and other marine snow bacteria govern phenotypic traits (biofilm formation, exoenzyme production, and antibiotic production) which are required mainly when the population reaches high densities, e.g., in the marine snow community.     

Biofilm formation by strains of <Emphasis Type="Italic">Leuconostoc citreum</Emphasis> and <Emphasis Type="Italic">L. mesenteroides</Emphasis>

Although biofilms produced by various Leuconostoc sp. are economically important as contaminants of sugar processing plants, very few studies are available on these systems. Twelve strains of Leuconostoc citreum and L. mesenteroides that produce a variety of extracellular glucans were compared for their capacity to produce biofilms. 16s rRNA sequence analysis was used to confirm the species identity of these strains, which included four isolates of L. mesenteroides, five isolates of L. citreum, and three glucansucrase mutants of L. citreum strain NRRL B-1355. Strains identified as L. mesenteroides produce glucans that are generally similar to commercial dextran. Nevertheless, these strains differed widely in their capacity to form biofilms, with densities ranging from 2.7 to 6.1 log cfu/cm(2). L. citreum strains and their derivatives produce a variety of glucans. These strains exhibited biofilm densities ranging from 2.5 to 5.9 log cfu/cm(2). Thus, biofilm-forming capacity varied widely on a strain-specific basis in both species. The types of polysaccharides produced did not appear to affect the ability to form biofilms.     

Establishing bacterial communities by 'word of mouth': LuxS and autoinducer 2 in biofilm development

Multicellular bacterial communities (biofilms) abound in nature, and their successful formation and survival is likely to require cell-cell communication--including quorum sensing--to co-ordinate appropriate gene expression. The only mode of quorum sensing that is shared by both Gram-positive and Gram-negative bacteria involves the production of the signalling molecule autoinducer 2 by LuxS. A survey of the current literature reveals that luxS contributes to biofilm development in some bacteria. However, inconsistencies prevent biofilm development being attributed to the production of AI2 in all cases.     

Autoinducer-2 Could Affect Biofilm Formation by Food-Derived Bacillus cereus

Bacillus cereus is a foodborne pathogen and cause a frequent problem due to the biofilms forming in equipment of food production plants. Autoinducer-2 (AI-2) involved in interspecies communication, plays a role in the biofilm formation of B. cereus. In this study, biofilm formation by thirty-nine B. cereus strains isolated from foods produced in Korea was determined. To investigate the effect of AI-2 on biofilm formation by B. cereus SBC27, which had the highest biofilm-forming ability, biofilm densities formed after addition of the AI-2 from Staphylococcus aureus and Escherichia coli were analysed. As a result, it was found that the quorum sensing molecule AI-2 could induce biofilm formation by B. cereus within 24 h, but it may also inhibit biofilm formation when more AI-2 is added after 24 h. Thus, these results improve our understanding of biofilm formation by food-derived B. cereus and provide clues that could help to reduce the impact of biofilms, the biggest problem in food processing environments, which has an impact on public health as well as the economy.     

Quorum Sensing in <Emphasis Type="Italic">Aeromonas</Emphasis> Species Isolated from Patients in Malaysia

Bacterial quorum sensing signal molecules called N-acylhomoserine lactone (AHL) controls the expression of virulence determinants in many Gram-negative bacteria. We determined AHL production in 22 Aeromonas strains isolated from various infected sites from patients (bile, blood, peritoneal fluid, pus, stool and urine). All isolates produced the two principal AHLs, N-butanoylhomoserine lactone (C4-HSL) and N-hexanoyl homoserine lactone (C6-HSL). Ten isolates also produced additional AHLs. This report is the first documentation of Aeromonas sobria producing C6-HSL and two additional AHLs with N-acyl side chain longer than C₆. Our data provides a better understanding of the mechanism(s) of this environmental bacterium emerging as a human pathogen.     

Quorum sensing: How bacteria can coordinate activity and synchronize their response to external signals?

Quorum sensing is used by a large variety of bacteria to regulate gene expression in a cell-density-dependent manner. Bacteria can synchronize population behavior using small molecules called autoinducers that are produced by cognate synthases and recognized by specific receptors. Quorum sensing plays critical roles in regulating diverse cellular functions in bacteria, including bioluminescence, virulence gene expression, biofilm formation, and antibiotic resistance. The best-studied autoinducers are acyl homoserine lactone (AHL) molecules, which are the primary quorum sensing signals used by Gram-negative bacteria. In this review we focus on the AHL-dependent quorum sensing system and highlight recent progress on structural and mechanistic studies of AHL synthases and the corresponding receptors. Crystal structures of LuxI-type AHL synthases provide insights into acyl-substrate specificity, but the current knowledge is still greatly limited. Structural studies of AHL receptors have facilitated a more thorough understanding of signal perception and established the molecular framework for the development of quorum sensing inhibitors.     

In vitro effect of subinhibitory concentrations of antibiotics on biofilm formation by clinical strains of Salmonella enterica serovar Typhimurium isolated in Slovakia

Aims: In this study, we examined the biofilm formation of 75 Salmonella enterica serovar Typhimurium (Salm. Typhimurium) human clinical isolates and the effect of subinhibitory concentrations (sub-MICs) of gentamicin, ciprofloxacin and cefotaxime on biofilm formation and exopolysaccharides (EPS) production. Methods and Results: Quantification of biofilm formation and EPS production were carried out using a modified microtitre plate assay and spectrophotometric method, respectively. The results indicate that 38 isolates (50·7%), which are predominantly of DT104 phage type, presented as the strong biofilm producers in vitro on plastic surface. When strains with the highest biofilm-forming capacity were grown in the presence of sub-MICs of gentamicin and ciprofloxacin, the inhibition of biofilm formation and EPS production was observed. In contrast, cefotaxime at 1/2 MIC (0·039 μg ml⁻¹) was able to significantly induce the production of biofilm as well as EPS in three isolates with nontypable and DT104 phage type, respectively. Conclusions: These results clearly indicate that all the three antibiotics tested are able to interfere with biofilm formation and EPS production by Salm. Typhimurium isolates. Significance and Impact of the Study: The current study demonstrated that cefotaxime at sub-MIC can be beneficial for the behaviour of pathogen Salm. Typhimurium in vitro.     

粘质沙雷氏菌AS-1中SpnR功能及卤化呋喃对其群体感应的抑制

通过分泌和感知一系列信号分子,细菌能够根据自身菌体密度的变化调控基因的表达,从而控制一系列重要的表现型,包括毒力因子的产生,生物膜的形成以及菌体发光等.这种广泛存在的信号机制被称为群体感应.在沙雷氏菌种中已经发现了多套群体感应机制.粘质沙雷氏菌AS-1从土壤中分离,其中含有LuxI/LuxR的同类蛋白,被称为SpnI/SpnR.粘质沙雷氏菌AS-1合成AHLs分子N-hexanoy1-L-homoserinelactone(C6-HSL)和N-(3.oxohexanoyl)-L-homoserine lactone(3-oxo-C6-HSL)作为其信号分子,通过群体感应感知菌体密度来控制基因的表达.通过基因替代的方法制得了spnR基因破坏的变异株,命名为粘质沙雷氏菌AS-1R.对粘质沙雷氏菌AS-1R的研究表明SpnR蛋白消极的调控沙雷氏菌红色色素的产生,运动性以及生物膜的形成等一系列由群体感应控制的性状:另一方面,作为一种天然的群体感应抑制剂,卤化呋喃能够有效的抑制粘质沙雷氏菌AS-1的群体感应,但并不干扰AHL-SpnR的相互作用.为运用粘质沙雷氏菌群体感应调节抑制其致病性提供了方法和依据,同时也为卤化呋喃对群体感应抑制机理的研究提供了新的思路.     

Biochemical detection of N-Acyl homoserine lactone from biofilm-forming uropathogenic Escherichia coli isolated from urinary tract infection samples

Background:

N-Acyl homoserine lactone (AHL) is found to be the main component of quorum sensing (QS) in Gram-negative bacteria and plays an important role in biofilm formation. Little information is available regarding the role of AHL in biofilm formation in Escherichia coli (E. coli). The purpose of this investigation was to biochemically detect and characterize AHL activity in biofilm-forming uropathogenic E. coli (UPEC) isolated from urine samples of the patients with urinary tract infections (UTIs) in Kerman, Iran.

Methods:

Thirty-five UPEC isolates were obtained from urine samples of the patients with UTIs referred to the Afzalipoor hospital. The isolates were identified by biochemical tests. Biofilm analyses of all the isolates were performed using the microtiter plate method at OD 490nm. N-Acyl homoserine lactone was separated from cell mass supernatants by liquid-liquid extraction (LLE) and analyzed by a colorimetric method. N-Acyl homoserine lactone functional groups were identified by Fourier Transform-Infrared Spectroscopy (FT-IR).

Results:

The biofilm formation assay identified 10 (28.57%) isolates with strong, 16 (45.71%) with moderate, and 9 (25.71%) with weak biofilm activities. The UPEC isolates with strong and weak biofilm activities were subjected to AHL analyses. It was found that isolates with the highest AHL activities also exhibited strong adherence to microplate wells (P≤0.05). Two E. coli isolates with the highest AHL activities were selected for FT-IR spectroscopy. Peaks at 1764.33, 1377.99, and 1242.90 cm^-1 correspond to the C=O bond of the lactone ring, and the N=H and C-O bonds of the acyl chain, respectively.

Conclusion:

We found that many UPEC isolates exhibited strong biofilm formation. The control of this property by AHL may contribute to the pathogenesis of the organism in UTI’s.Key Words: Biofilm, FT-IR, N-acylhomoserine lactone, Uropathogenic Escherichia coli     

Detection of quorum sensing signal molecules and identification of an autoinducer synthase gene among biofilm forming clinical isolates of Acinetobacter spp

Background

Quorum sensing is a term that describes an environmental sensing system that allows bacteria to monitor their own population density which contributes significantly to the size and development of the biofilm. Many gram negative bacteria use N-acyl-homoserine lactones as quorum sensing signal molecules. In this study, we sought to find out if the biofilm formation among clinical isolates of Acinetobacter spp. is under the control of autoinducing quorum sensing molecules.

Methodology/Principal Findings

Biofilm formation among clinical isolates of Acinetobacter spp. was assessed and the production of signal molecules were detected with Chromobacterium violaceum CV026 biosensor system. Characterisation of autoinducers was carried out by mass spectrometric analysis. We have also reported the identification of an autoinducer synthase gene, abaΙ among the isolates that produce quorum sensing signal molecules and have reported that the mutation in the abaI gene influences their biofilm forming capabilities. Using a microtitre-plate assay it was shown that 60% of the 50 Acinetobacter spp. isolates significantly formed biofilms. Further detection with the biosensor strain showed that some of these isolates produced long chain signal molecules. Mass spectrometric analysis revealed that five of these isolates produced N-decanoyl homoserine lactone and two isolates produced acyl-homoserine lactone with a chain length equal to C₁₂. The abaΙ gene was identified and a tetracycline mutant of the abaΙ gene was created and the inhibition in biofilm formation in the mutant was shown.

Conclusions/Significance

These data are of great significance as the signal molecules aid in biofilm formation which in turn confer various properties of pathogenicity to the clinical isolates including drug resistance. The use of quorum sensing signal blockers to attenuate bacterial pathogenicity is therefore highly attractive, particularly with respect to the emergence of multi antibiotic resistant bacteria.