Pulsed-field Gel Electrophoresis Protocol Research Articles

Comparative Analysis Using Pulsed-Field Gel Electrophoresis Highlights a Potential Transmission of Salmonella Between Asymptomatic Buffaloes and Pigs in a Single Farm.

Buffaloes and pigs play an important epidemiological roll in the Salmonella infection cycle, and asymptomatic animals can act as key component in the dissemination of the disease by horizontal, vertical, and cross-species transmission. Our study aimed and was able to confirm evidences of a cross-species transmission of Salmonella Agona between asymptomatic buffaloes and pigs. Also, we described Salmonella infection within the pig production phases, involving serotypes Agona, Senftenberg and Schwarzengrund. Rectal samples were collected from Jafarabadi buffaloes (n = 25) and Piau pigs (n = 32), located on a single farm. Salmonella Agona was isolated from lactating buffaloes, gilts, pregnant sows, and weaned pigs, Salmonella Schwarzengrund from lactating sows and Salmonella Senftenberg from gilts, pregnant sows, lactating sows, and weaned pigs. Pulsed-field Gel Electrophoresis protocol (PFGE) was performed and revealed four different profiles. Profile 1 (Salmonella Agona), isolated from a pregnant sow, a gilt and two lactating buffaloes, revealed a indistinguishable PFGE pattern, confirming evidences of potential cross-species transmission. Profile 2 (Salmonella Agona), 3 (Salmonella Senftenberg), and 4 (Salmonella Schwarzengrund), isolated from pigs, revealed important indistinguishable PFGE patterns, evidencing Salmonella infection within the pig production phases. Considering the epidemiological relevance of buffaloes and pigs in the cycle of Salmonella infection, confirmation of a potential cross-species transmission of Salmonella Agona and potential Salmonella infection within the pig production phases highlights the importance of the correct establishment of preventive health strategies in farms, in special the importance of avoiding contact between buffaloes and pigs, since cross-species transmission can occur, increasing the risk of spreading the disease.

Molecular Typing of Salmonella by Pulsed-Field Gel Electrophoresis.

Salmonella is recognized as a major human foodborne pathogen and threat to public health world widely. It is important to carry out epidemiological investigations to determine the primary sources of bacterial contamination. Pulsed-field gel electrophoresis (PFGE) is an important method of the molecular typing, and play an important role in tracking the sources of infection and epidemic control. The PFGE is currently considered as "gold standard" of molecular typing methods for bacterial foodborne pathogen. Here, we describe the PFGE protocol to type the Salmonella from pork.

Prevalence of netB-positive Clostridium perfringens in Italian poultry flocks by environmental sampling.

Clostridium perfringens type G is one of the pathogens involved in enteric diseases in poultry. NetB, a pore-forming toxin, is considered the main virulence factor responsible for necrotic enteritis during C. perfringens infection. We carried out a field study involving 14 farms to evaluate the occurrence of netB-positive C. perfringens and the impact of infection in Italian poultry flocks. Environmental samples (n = 117) and 50 carcasses were screened by microbiologic and molecular methods. Microbiologic investigations yielded 82 C. perfringens isolates. DNA was extracted from all samples and screened for α-toxin and NetB encoding genes by real-time PCR. The C. perfringens α-toxin gene was detected in 151 of 167 extracts (90.4%), and 31 of 151 (20.5%) were netB gene positive also. Sixteen isolates from a turkey flock with mild enteric disorders were also netB positive, demonstrating their occurrence not only in broiler but also in turkey flocks. A pulsed-field gel electrophoresis protocol was optimized to evaluate the diversity among isolates and revealed high genetic heterogeneity. The complete NetB toxin-coding gene of 2 C. perfringens isolates from turkey and broiler flocks were analyzed and showed very high relatedness with analogous sequences worldwide.

Comparison of PFGE, IS6110-RFLP, and 24-Locus MIRU-VNTR for Molecular Epidemiologic Typing of Mycobacterium tuberculosis Isolates with Known Epidemic Connections.

Two molecular epidemiologic methods, IS6110 restriction fragment length polymorphism (IS6110-RFLP) and 24-locus mycobacterial interspersed repetitive unit-variable-number tandem repeat (MIRU-VNTR), are used worldwide in studies of Mycobacterium tuberculosis (MTB). Conversely, because of its poor resolution, pulsed-field gel electrophoresis (PFGE) is not widely used for MTB. In this study, we improved the 24-locus MIRU-VNTR and PFGE protocols and compared the effectiveness of these approaches for the molecular typing of MTB using 75 clinical isolates obtained from a cohort investigation of high-risk populations infected with MTB. The 24-locus MIRU-VNTR method demonstrated superior discriminatory ability, followed by PFGE and IS6110-RFLP. Next, we analyzed six isolates with clear epidemiologic connections; that is, isolates from patients who attended the same school. IS6110-RFLP and PFGE identified these samples as the same type. By contrast, according to MIRU-VNTR, two isolates differed from four other isolates at one locus each; one isolate was identified as Mtub29 and the other as QUB-26. In summary, the 24-locus MIRU-VNTR assay was the most useful molecular typing method among the three methods investigated due to its discriminatory power, short time required, and availability as an epidemiologic investigation tool. PFGE was the second-best method. Compared with the other loci assessed in the 24-locus MIRU-VNTR assay, the Mtub29 and QUB-26 loci appeared to exhibit greater variability during transmission.

Using Pulsed-Field Gel Electrophoresis to Analyze Schizosaccharomyces pombe Chromosomes and Chromosomal Elements.

Pulsed field gel electrophoresis (PFGE) uses alternatively oriented pulsed electrical fields to separate large DNA molecules. Here, we describe PFGE protocols and conditions for separating and visualizing chromosomes between 0.5 and 6 Mb (optimal for analyzing the endogenous fission yeast chromosomes of 5.7, 4.6, and 3.5 Mb), and for shorter chromosomal elements of between 50 and 600 kb, such as the 530 kb Ch16 minichromosome. In addition to determining chromosome size, this technique has a wide range of applications, including determining whether DNA replication or repair is complete, defining the molecular karyotype of cells, analyzing chromosomal rearrangements, assigning genes or constructs to particular chromosomes, and isolating DNA from specific chromosomes.

Bacterial flora and the epidemiology of staphylococcus aureus in the nose among patients with symptomatic nasal septal perforations

Conclusions Patients with symptomatic perforations of the nasal septum had a high prevalence of S. aureus in the nasal mucosa. Pulsed field gel electrophoresis (PFGE) analysis revealed a high genetic heterogeneity of S. aureus among both patients and controls. This indicates that presence of different strains of S. aureus can maintain a chronic inflammation in symptomatic nasal septal perforations. Objective The purpose of this study was to investigate the microbial flora around nasal septal perforations in patients having severe symptoms regarding bleeding, obstruction, and crustation associated with their perforation. Methods Twenty-five patients with untreated symptomatic nasal septal perforations were included. For culture, swabs around the perforations were collected. Bacteria were identified with standard laboratory techniques including a MALDI-TOF mass spectrometer. Epidemiological analysis was done using PFGE protocols. Bacteriological data were compared with data from a healthy control group. Results Staphylococcus aureus was present in the mucosa surrounding the nasal perforation significantly more often (p < 0.0001) in the patients (88%) compared to a control group (13%). Corynebacterium spp. and Propionibacterium spp. were significantly more frequently identified in the control group. The PFGE analysis of S. aureus strains revealed a high genetic heterogeneity and no specific S. aureus genotypes were associated with septal perforation.

Molecular typing of VTEC strains isolated from food, feed and animals

Molecular typing of VTEC strains isolated from food, feed and animals

Sub-Typing of Extended-Spectrum-β-Lactamase-Producing Isolates from a Nosocomial Outbreak: Application of a 10-Loci Generic Escherichia coli Multi-Locus Variable Number Tandem Repeat Analysis

Extended-spectrum β-lactamase producing Escherichia coli (ESBL-E. coli) were isolated from infants hospitalized in a neonatal, post-surgery ward during a four-month-long nosocomial outbreak and six-month follow-up period. A multi-locus variable number tandem repeat analysis (MLVA), using 10 loci (GECM-10), for ‘generic’ (i.e., non-STEC) E. coli was applied for sub-species-level (i.e., sub-typing) delineation and characterization of the bacterial isolates. Ten distinct GECM-10 types were detected among 50 isolates, correlating with the types defined by pulsed-field gel electrophoresis (PFGE), which is recognized to be the ‘gold-standard’ method for clinical epidemiological analyses. Multi-locus sequence typing (MLST), multiplex PCR genotyping of bla CTX-M, bla TEM, bla OXA and bla SHV genes and antibiotic resistance profiling, as well as a PCR assay specific for detecting isolates of the pandemic O25b-ST131 strain, further characterized the outbreak isolates. Two clusters of isolates with distinct GECM-10 types (G06-04 and G07-02), corresponding to two major PFGE types and the MLST-based sequence types (STs) 131 and 1444, respectively, were confirmed to be responsible for the outbreak. The application of GECM-10 sub-typing provided reliable, rapid and cost-effective epidemiological characterizations of the ESBL-producing isolates from a nosocomial outbreak that correlated with and may be used to replace the laborious PFGE protocol for analyzing generic E. coli.

Optimization of Pulse-Field Gel Electrophoresis for Subtyping of Klebsiella pneumoniae

A total of 110 strains of Klebsiella pneumoniae were used to optimize pulsed-field gel electrophoresis (PFGE) for subtyping of K. pneumoniae. For optimization of electrophoresis parameters (EPs) of XbaI-PFGE, 11 isolates were analyzed with XbaI digestion using three EPs. The EP of a switch time of 6 to 36 s for 18.5 h gave clearest patterns and was declared the optimal EP for XbaI PFGE of K. pneumoniae. By software analysis and pilot study, AvrII was chosen as another PFGE enzyme. Both XbaI- and AvrII-PFGE gave D-values higher than 0.99 for 69 K. pneumoniae isolated from different sources. Our results also showed good typeability, reproducibility of both XbaI- and AvrII-PFGE for K. pneumoniae subtyping. Furthermore, the established PFGE method also had good discriminatory power to distinguish outbreak K. pneumoniae strains and a high degree of consistency with multilocus sequence typing method. A rapid PFGE protocol was established here, which could be used for genotyping and other researches of K. pneumoniae.

Simple, time saving pulsed-field gel electrophoresis protocol for the typing of Stenotrophomonas maltophilia

We developed a time-saving and cost-efficient Pulsed Field Gel Electrophoresis (PFGE) method for the typing of Stenotrophomonas maltophilia by modifying the conventional procedures. Our modifications related to the cell suspension preparation, lysis of bacterial cells in plugs, washing steps, and consumption of restriction enzyme. Although few rapid PFGE protocols on Gram-negative bacteria are available, the use of comparatively large amounts of costly reagents prompted us to look for other alternative. Hence, by considering the speed, simplicity, and relatively low cost, the modified protocol may be of more practical value than other established protocols in investigating S. maltophilia nosocomial outbreaks.

Molecular Characterization of Pseudomonas fluorescens Isolates Involved in the Italian “Blue Mozzarella” Event

Between June and September 2010, widespread Italian consumer reports of unusual blue spoilage on fresh dairy products were publicized, resulting in the so-called blue mozzarella event. An inordinately high number of samples from mozzarella and whey cheese products of Italian and German production subsequently tested positive for Pseudomonas fluorescens. The aim of this study was to verify whether a selected P. fluorescens strain was responsible for this apparently unusual event. Molecular characterization of 181 isolated P. fluorescens strains was conducted using a newly optimized pulsed-field gel electrophoresis protocol. Although a high number of pulsotypes was found (132), only four pulsotypes were associated with more than one production plant, and only one German isolate had the same pulsotype as was detected in two Italian plants. This is the only evidence of possible cross-contamination among cheeses from the two countries. The overall results did not support the spread of contamination from German to Italian plants or the presence of one environmental strain that spread in both countries.

Pulsed-Field Gel Electrophoresis (PFGE) standardization protocol for Proteus mirabilis

Objective: For the detection of outbreaks caused by Proteus mirabilis, strains clonal relations are determined methods as “pulsed-field gel electrophoresis (PFGE)”. The aim of this study was optimization of a pulsed-field gel electrophoresis for molecular typing of P. mirabilis. Methods: In this study, PFGE\' protocol is optimized for use in molecular typing of P. mirabilis. Phylogenetic analyzes of strains were evaluated with Bionumerics software system (version 6.01; Applied Maths, Sint-Martens-Latem, Belgium). Results: This protocol compared with Gram-negative bacteria PFGE protocols, NotI enzyme is suitable for this bacterium. Electrophoresis conditions should be revealed as; - block 1: initial pulse duration 1 sec, ending pulse duration 30 sec, striking angle 120d, the current 6 V/cm2, temperature 14dC, time 8 hours; - block 2: initial pulse duration 30 sec, ending pulse duration 70 sec, striking angle 120d, the current 6 V/cm2, temperature 14dC, time 16 hours; - TBE, pH=8.4. Conclusion: P. mirabilis strains were typed by PFGE and Bionumerics analysis program were determined clonal relationships. The procedure was simple, reproducible and suitable for these bacteria. Also it was evaluated, because of reducing time, the solution volumes and enzymes can be economically. Outbreaks of nosocomial infections due to bacteria studied assessment and the potential to provide useful information about the degree of prevalence. This optimized protocol is allowed different centers\' PFGE results to compare with other laboratories results. J Clin Exp Invest 2013; 4 (3): 306-312

Suitable restriction enzyme for standardization of pulsed-field gel electrophoresis protocol and interlaboratory comparison of Acinetobacter baumannii

Interlaboratory comparison of pulsed-field gel electrophoresis (PFGE) patterns is difficult. A key reference of standardized PFGE protocol for Acinetobacter baumannii may address this issue. This study aimed to determine restriction enzymes with rare cutting sites on A baumannii genomes and evaluate their cost-effectiveness, discriminatory power, and interlaboratory consistence of band assignments. There were 42 A baumannii isolates collected, including nine from three hospital outbreaks and 33 sporadic isolates. The numbers of cutting sites for the restriction enzymes were explored using the "Restriction Digest and PFGE" program. The cost-effectiveness for PFGE analysis was evaluated for the tested restriction enzymes, while its discriminatory ability was expressed through a discriminatory index and 95% confidence interval. The interlaboratory consistence of band assignments was evaluated for the 42 A baumannii isolates. ApaI was the most cost-effective restriction enzyme for a PFGE protocol for A baumannii. Both AscI and AsiSI were reasonable in terms of costs. ApaI, AscI, and AsiSI exhibited similar discriminatory indices. ApaI generated more than 40 fragments that were close and not easy to resolve, resulting in less consistence of band assignments. AscI and AsiSI generated 10-20 fragments that were clearly resolved, resulting in higher consistence of band assignments. AscI exhibited a close discriminatory power to that of AsiSI and at half of the cost of AsiSI for PFGE analysis. We recommend AscI as the primary enzyme and AsiSI as the secondary enzyme for standardizing the PFGE protocol and interlaboratory comparisons of A baumannii.

Enhanced PFGE protocol to study the genomic diversity of Clostridium spp. isolated from Manchego cheeses with late blowing defect

Late blowing defect (LBD) is caused by the outgrowth in cheese of strains of the genus Clostridium capable of fermenting lactic acid with production of butyric acid, acetic acid, carbon dioxide and hydrogen, resulting in the appearance of texture and flavour defects. In the present work, 223 Clostridium isolates (C. beijerinckii, C. butyricum, C. sporogenes and C. tyrobutyricum) from 45 Manchego cheeses with LBD were typed by a modified short pulsed field gel electrophoresis (PFGE) protocol that solved several problems of the original protocol such as DNA degradation, incomplete DNA digestion and reduced DNA release. Our modified protocol allowed the typification of all isolates and the study of their genetic diversity.Out of the 84 Clostridium pulsotypes found in Manchego cheeses with LBD, 54 pulsotypes were represented by more than one isolate. Isolates of the same pulsotype were found in the same cheese for 36 of those 54 pulsotypes, in different cheeses from the same factory for 5 pulsotypes, and in cheeses from different factories for 13 pulsotypes. Dates of manufacture of the cheeses from the same factory containing the same pulsotype differed by less than 40 days. Thirty-six out of the 45 cheeses with LBD contained more than one Clostridium pulsotype.Clostridium isolates from Manchego cheeses with LBD showed a high genetic diversity and could be grouped by their pulsotype according to the factory and the date of cheese manufacture.

A rapid PFGE protocol for typing Legionella isolates from fresh or frozen samples

Within the realm of studies on nosocomial infections and epidemiology, pulsed field gel electrophoresis (PFGE) is often considered as the "gold standard" for typing of Legionella or other bacteria. Performing this protocol usually requires 2-5 days; this excessive time requirement, lack of a standardized procedure, and high cost have limited its use. However, recently the typing of Legionella with PFGE has been reduced to about 2 days, and we further shortened the procedure by reducing the time for the plug preparation and electrophoresis steps. To shorten plug preparation, we used a strong thermal shock and high-temperature washes to reduce cell lysis and DNA isolation time, and we stressed the electrophoresis to obtain comparable macrorestriction patterns among strains in 16 h. The DNA digestion phase was not altered. We also applied this protocol directly to frozen bacteria from strain collections with the aim of shortening the entire procedure. We developed a protocol that can be completed in 24 h, or less if necessary, while avoiding some typical artifacts of traditional procedures. This new protocol also provides good results when directly applied to frozen material from strain collections, thus saving bacteria growth time. Our observations indicate that PFGE tolerates a wide range of adjustments, allowing its application to fresh or frozen samples in a short amount of time.

Anatomical distribution and genetic relatedness of antimicrobial-resistant Escherichia coli from healthy companion animals

Escherichia coli have been targeted for studying antimicrobial resistance in companion animals because of opportunistic infections and as a surrogate for resistance patterns in zoonotic organisms. The aim of our study is to examine antimicrobial resistance in E. coli isolated from various anatomical sites on healthy dogs and cats and identify genetic relatedness. From May to August, 2007, healthy companion animals (155 dogs and 121 cats) from three veterinary clinics in the Athens, GA, USA, were sampled. Escherichia coli was isolated from swabs of nasal, oral, rectal, abdomen and hindquarter areas. Antimicrobial susceptibility testing against 16 antimicrobials was performed using broth microdilution with the Sensititre™ system. Clonal types were determined by a standardized pulsed-field gel electrophoresis protocol. Although rectal swabs yielded the most E. coli (165/317; 52%) from dogs and cats, the organism was distributed evenly among the other body sites sampled. Escherichia coli isolates from both dogs and cats exhibited resistance to all antimicrobials tested with the exception of amikacin, cephalothin and kanamycin. Resistance to ampicillin was the most prevalent resistance phenotype detected (dogs, 33/199; 17%; and cats, 27/118; 23%). Among the resistant isolates, 21 resistance patterns were observed, where 18 patterns represented multidrug resistance (MDR; resistance ≥ 2 antimicrobial classes). Also among the resistant isolates, 33 unique clonal types were detected, where each clonal type contained isolates from various sampling sites. Similar resistance phenotypes were exhibited among clonal types, and three clonal types were from both dogs and cats. Healthy companion animals can harbour antimicrobial-resistant E. coli on body sites that routinely come in contact with human handlers. This study is the first report that demonstrates a diverse antimicrobial-resistant E. coli population distributed over various sites of a companion animal's body, thereby suggesting potential transfer of resistant microflora to human hosts during contact.

Evolution of tigecycline resistance inKlebsiella pneumoniaein a single patient

Carbapenemase-producing Klebsiella pneumoniae infections carry serious clinical and infection-control implications. Isolates possessing such hydrolyzing enzymes have been described in the United States and around the world. Besides being resistant to carbapenems, they usually confer resistance to fluoroquinolones, piperacillin-tazobactam, and extended-spectrum cephalosporins. Tigecycline demonstrates in vitro activity against these organisms, but reported resistance raises concern about tigecycline use for these infections. We describe a carbapenemase-producing K pneumoniae evolving resistance to tigecycline in a 75-year-old male after a prolonged stay in a critical care unit.

Molecular typing of Salmonella enterica serovar Sofia in Australia by pulsed‐field gel electrophoresis and repetitive element PCR typing

In this study, we used two molecular fingerprinting methods to investigate the genetic and clonal relationship shared by Australian Salmonella Sofia isolates. A total of 84 Australian Salm. Sofia isolates from various states in Australia were typed using pulsed-field gel electrophoresis (PFGE) (XbaI and SpeI) and repetitive element PCR (REP1R-I primer). The previous problem of DNA degradation of Salm. Sofia strains was solved by modifying the lysis solution used to treat the bacterial plugs, allowing Salm. Sofia to be subtyped using PFGE. Molecular typing of isolates resulted in the generation of eight XbaI, six SpeI and five REP1 pattern profiles. Individual typing methods showed low discrimination index values (<0·5), indicating the poor discriminatory ability of the methods. However, the combination of the typing methods was able to improve the discrimination of isolates, further dividing them into 16 subtypes and raising the index value to 0·721. The combination of typing methods was shown to be the best approach to fingerprint Salm. Sofia. The Australian Salm. Sofia isolates only showed limited genetic diversity and probably share a clonal relationship. A majority of the Salm. Sofia isolates were not geographically restricted with the predominant pattern subtype observed amongst the isolates from various states. We have successfully devised a PFGE protocol that counteracts DNase activity of Salm. Sofia, enabling typing of this serovar.

Re-evaluation, Optimization, and Multilaboratory Validation of the PulseNet-Standardized Pulsed-Field Gel Electrophoresis Protocol for Listeria monocytogenes

The PulseNet Methods Development and Validation Laboratory began a re-evaluation of the standardized pulsed-field gel electrophoresis (PFGE) protocols with the goal of optimizing their overall performance and robustness. Herein, we describe a stepwise evaluation of the PulseNet-standardized PFGE protocol for Listeria monocytogenes that led to the modification of several steps which significantly improved the overall appearance and reproducibility of the resulting PFGE data. These improvements included the following: (1) reducing the cell suspension concentration, (2) increasing lysozyme incubation temperature from 37 degrees C to 56 degrees C, and (3) decreasing the number of units of restriction enzymes AscI and ApaI. These changes were incorporated into a proposed protocol that was evaluated by 16 PulseNet participating laboratories, including 2 international participants. Results from the validation study indicated that the updated L. monocytogenes protocol is more robust than the original PulseNet-standardized protocol established in 1998 and this resulted in the official adoption of the new protocol into the PulseNet system in the spring of 2008. The modifications not only represent an improvement to the protocol but also describe procedural improvements that could be potentially applied to the PFGE analysis of other Gram-positive organisms.

Molecular Typing of Japanese Field Isolates and Live Commercial Vaccine Strain of Mycoplasma synoviae Using Improved Pulsed-Field Gel Electrophoresis andvlhAGene Sequencing

In the present study, pulsed-field gel electrophoresis (PFGE) and vlhA gene sequence analysis were applied and verified for typing the Mycoplasma synoviae live vaccine MS-H strain and field isolates from diseased chickens in Japan. The previously published PFGE protocol using SmaI digestion could not allow the discrimination of two of the 11 M. synoviae field isolates from the vaccine strain and had relatively low discrimination power (D = 0.885). On the other hand, our new PFGE protocols using BlnI and BamHI digestions as well as the vlhA sequence analysis allowed the discrimination of all 11 M. synoviae field isolates from the vaccine strain. In addition, these PFGE protocols using BlnI and BamHI digestions generated unique fragment patterns in epidemiologically unrelated isolates, including those with identical SmaI-digested patterns or vlhA gene sequences (D = 0.987 and 1.000, respectively), and generated indistinguishable or closely related patterns in epidemiologically related isolates. Therefore, we believe that they would be useful tools to determine whether M. synoviae clinical isolates from diseased chickens are derived from the vaccine strain or wild-type strain and to further elucidate the epidemiology of M. synoviae infection.