Predominant Phage Type Research Articles

Phenotypic Pattern of Vibrio choleraeIsolates from a Tertiary Care Hospital in Vadodara, Gujarat, India

Introduction: Cholera is an acute diarrhoeal disease caused by Vibrio cholerae (V.cholerae). Based on antigenic differences of O antigen, O1 serogroup can be divided into three serotypes. In addition, by performing various biochemical reactions, O1 Serogroup can be differentiated into two biotypes. Outbreaks of Cholera occur seasonally. It is associated with monsoon season, warm temperature, heavy rainfall and increased plankton population. Aim: The aim was to determine the trends in resistance pattern and phenotypic Pattern of Vibrio cholerae. Materials and Methods: A retrospective study was conducted during the period from June 2019-December 2019. Culture of Stool specimens were done on different agar media. Biotyping was done by conventional methods. Serotyping and phage typing was also done along with the Antibiotic susceptibility testing. Descriptive analysis was used and presented in terms of percentage. Results:V.cholerae was isolated in 72 patients and they belonged to serogroup O1 and biotype El Tor. The most common serotype was Ogawa. The predominant phage type were T2 by old scheme and T27 by new scheme of phage typing. The maximum number of V. cholerae isolates was seen in the month of November, 2019 followed by October, 2019. Conclusion: The phenotypic pattern and fluctuating seasonal trend of V. cholerae and antimicrobial resistance encourage the continued epidemiological and microbiological surveillance of the disease.

Analysis of Salmonella enterica Serovar Typhi by Outer Membrane Protein (OMP) Profiling, Random Amplification of Polymorphic DNA (RAPD) and Pulsed Field Gel Electrophoresis (PFGE)

A number of countries, including developed countries, still have typhoid fever as a major problem resulting in frequent outbreaks. The importance of controlling spread of typhoid fever is well known and necessitates periodic studies to delineate epidemiological relationships. Although phage typing remains to be the preferred conventional method for characterisation of typhoid bacilli, it is of limited use due to prevalence of few predominant phage types in the country like India. Therefore, an effort has been made to assess three molecular methods [Outer Membrane Protein (OMP) Profiling, Random Amplification of Polymorphic DNA (RAPD) and Pulsed Field Gel Electrophoresis (PFGE)] for typing of Salmonella enterica serovar Typhi. 128 Salmonella enterica serovar Typhi isolates were identified using biotyping and serotyping followed by antimicrobial susceptibility testing. These isolates were further subjected to OMP analysis, RAPD and PFGE. PFGE (114 unique clusters) was found to be the most discriminatory method followed by RAPD (94 unique clusters) and OMP profiling (50 unique clusters). Multidrug resistant strains were well discriminated by all three methods used in the study. PFGE still remains the most preferred method for detailed epidemiological investigations. However, random amplification of polymorphic DNA and outer membrane protein profiling can also be considered for molecular discrimination of the isolates in the laboratories lacking high-end facilities.

Genetic and functional diversity of double-stranded DNA viruses in a tropical monsoonal estuary, India

The present study illustrates the genetic diversity of four uncultured viral communities from the surface waters of Cochin Estuary (CE), India. Viral diversity inferred using Illumina HiSeq paired-end sequencing using a linker-amplified shotgun library (LASL) revealed different double-stranded DNA (dsDNA) viral communities. The water samples were collected from four stations PR1, PR2, PR3, and PR4, during the pre-monsoon (PRM) season. Analysis of virus families indicated that the Myoviridae was the most common viral community in the CE followed by Siphoviridae and Podoviridae. There were significant (p < 0.05) spatial variations in the relative abundance of dominant families in response to the salinity regimes. The relative abundance of Myoviridae and Podoviridae were high in the euryhaline region and Siphoviridae in the mesohaline region of the estuary. The predominant phage type in CE was phages that infected Synechococcus. The viral proteins were found to be involved in major functional activities such as ATP binding, DNA binding, and DNA replication. The study highlights the genetic diversity of dsDNA viral communities and their functional protein predictions from a highly productive estuarine system. Further, the metavirome data generated in this study will enhance the repertoire of publicly available dataset and advance our understanding of estuarine viral ecology.

Molecular Characterization of Salmonella enterica Serovar Enteritidis, Genetic Basis of Antimicrobial Drug Resistance and Plasmid Diversity in Ampicillin-Resistant Isolates.

Salmonella enterica serovar Enteritidis is the most common cause of human salmonellosis worldwide. In this study, all clinical isolates of Salmonella Enteritidis recovered between January 2008 and June 2014 in a Spanish region (491) were screened for antimicrobial drug resistance and the phage type (PT) was determined for a significant number (265). PT1, PT14b, PT56, PT6, PT4, and PT8 were the predominant PTs, accounting together for 82% of the isolates. A total of 38.3% of the isolates were susceptible to all antimicrobials tested, 46.4% and 6.1% isolates were resistant to nalidixic acid and ampicillin, respectively, and single isolates were resistant to two (ampicillin and nalidixic acid) or six (ampicillin, chloramphenicol, streptomycin, sulfonamides, tetracycline, and trimethoprim) agents. Nalidixic acid resistance was statistically associated with PT1 and PT14b (p < 0.05, 95% CI), and ampicillin resistance with PT6/PT6a (p < 0.05, 95% CI). All ampicillin-resistant isolates (30) carried a plasmid-encoded blaTEM-1. All except one harbored the virulence plasmid specific of Salmonella Enteritidis (IncFIIA + IncFIB; 28 isolates) or a blaTEM-1-positive variant herein (IncFIIA + IncFIB; 1 isolate). Five additional blaTEM-1 plasmids, of the ColE1, IncX, IncF, and IncI incompatibility groups, were identified. The IncI plasmid, found in the single multidrug-resistant isolate, carried the strAB and sul2 genes together with genes of the virulence plasmid, including the spv operon. The obtained results highlight the high diversity of blaTEM-1 plasmids conferring ampicillin resistance in Salmonella Enteritidis, and support clonal expansion as the main cause of nalidixic acid resistance in this serovar.

Prevalence and characterization of Salmonella among humans in Ghana

BackgroundNon-typhoidal Salmonella (NTS) is a public health problem worldwide and particularly in Africa with high disease burden. This study characterized Salmonella isolates from humans in Ghana to determine serovar distribution, phage types, and antimicrobial resistance. Further, the clonal relatedness among isolates was determined.MethodsOne hundred and thirty-seven Salmonella isolates (111 clinical and 26 public toilet) were characterized using standard serotyping, phage typing, and antimicrobial susceptibility testing methods. The molecular epidemiology of common serovars (Salmonella Typhimurium and Salmonella Enteritidis) was established by pulsed field gel electrophoresis (PFGE).ResultsTwenty-two serovars were identified with S. Enteritidis, S. Typhimurium, and Salmonella Derby as the most dominant. One hundred and twelve isolates showed resistance to more than one antimicrobial. Fifty-eight (n = 58/112; 54.5%) strains were multi-resistant with low resistance to cephalosporins ceftazidime (8.0%), cefotaxime (4.5%), and cefoxitin (2.7%) with synergy to clavulanic acid indicating possible ESBLs. Isolates showed high resistance to trimethoprim (66.1%), tetracycline (61.6%), ampicillin (57.1%), sulfamethoxazole (46.4%), chloramphenicol (33.9%), and ciprofloxacin (25.0%). The most common resistance pattern of multi-resistant serovars was to ampicillin, chloramphenicol, sulphonamide, and trimethoprim. S. Enteritidis (18/43) strains reacted with typing phages but did not conform to any phage type with PT14B and PT4 as predominant definitive phage types. Six S. Typhimurium strains reacted but did not conform to any recognized phage type while seven were non-typable. The predominant definitive phage types were DT1 and DT22. PFGE patterns of human S. Enteritidis were closely related to patterns of poultry isolates obtained in a previous study in Ghana.ConclusionsCephalosporin resistance is uncommon among Salmonella from humans in Ghana. Poultry may be an important source of human salmonellosis. There is an urgent need for the implementation of routine surveillance of antimicrobial use and bacterial resistance among humans in Ghana.

Phenotypic and antibiogram pattern of V. cholerae isolates from a tertiary care hospital in Mumbai during 2004–2013: a retrospective cross-sectional study

ObjectivesCholera is a major gastroenteric disease with reports on fluctuation and resistance. Hence, the objective is to determine the trend in seasonality, resistance pattern, prevalent biotypes, serotypes and phage types...

Prevalence and antimicrobial resistance of Salmonella serovars isolated from poultry in Ghana.

Poultry are possible sources of non-typhoidal Salmonella serovars which may cause foodborne human disease. We conducted a cross-sectional study to determine the prevalence of Salmonella serovars in egg-laying hens and broilers at the farm level and their susceptibility to antimicrobials commonly used in the poultry industry in Ghana. Sampling of faeces by a sock method (n = 75), dust (n = 75), feed (n = 10) and drinking water (n = 10) was performed at 75 commercial egg-laying and broiler farms in two regions of Ghana and skin neck (n = 30) at a local slaughterhouse from broilers representing different flocks. Salmonella was detected in 94/200 (47%) samples with an overall flock prevalence of 44·0%. Sixteen different serovars were identified with S. Kentucky (18·1%), S. Nima (12·8%), S. Muenster (10·6%), S. Enteritidis (10·6%) and S. Virchow (9·6 %) the most prevalent types. The predominant phage type of S. Enteritidis was PT1. All strains were susceptible to cefotaxime, ceftazidime and cefoxitin. Fifty-seven (60·6%) strains were resistant to one or more of the remaining nine antimicrobials tested by disk diffusion, of which 23 (40·4%) showed multi-resistance (resistance to ⩾3 classes of antimicrobials). Of the resistant strains (n = 57), the most significant were to nalidixic acid (89·5%), tetracycline (80·7%), ciprofloxacin (64·9%), sulfamethazole (42·1%), trimethoprim (29·8%) and ampicillin (26·3%). All S. Kentucky strains were resistant to more than two antimicrobials and shared common resistance to nalidixic acid or ciprofloxacin and tetracycline, often in combinations with other antimicrobials. PFGE analysis using XbaI of S. Kentucky demonstrated one dominant clone in the country. In conclusion, poultry produced in Ghana has a high prevalence of multi-resistant Salmonella and the common finding of clonal S. Kentucky in the Kumasi area warrants further investigations into the epidemiology of this serovar. There is an urgent need for surveillance and control programmes on Salmonella and use of antimicrobials in the Ghanaian poultry industry to protect the health of consumers.

Genetic diversity and evolution of Salmonella enterica serovar Enteritidis strains with different phage types.

Phage typing has been used for the epidemiological surveillance of Salmonella enterica serovar Enteritidis for over 2 decades. However, knowledge of the genetic and evolutionary relationships between phage types is very limited, making differences difficult to interpret. Here, single nucleotide polymorphisms (SNPs) identified from whole-genome comparisons were used to determine the relationships between some S. Enteritidis phage types (PTs) commonly associated with food-borne outbreaks in the United States. Emphasis was placed on the predominant phage types PT8, PT13a, and PT13 in North America. With >89,400 bp surveyed across 98 S. Enteritidis isolates representing 14 distinct phage types, 55 informative SNPs were discovered within 23 chromosomally anchored loci. To maximize the discriminatory and evolutionary partitioning of these highly homogeneous strains, sequences comprising informative SNPs were concatenated into a single combined data matrix and subjected to phylogenetic analysis. The resultant phylogeny allocated most S. Enteritidis isolates into two distinct clades (clades I and II) and four subclades. Synapomorphic (shared and derived) sets of SNPs capable of distinguishing individual clades/subclades were identified. However, individual phage types appeared to be evolutionarily disjunct when mapped to this phylogeny, suggesting that phage typing may not be valid for making phylogenetic inferences. Furthermore, the set of SNPs identified here represents useful genetic markers for strain differentiation of more clonal S. Enteritidis strains and provides core genotypic markers for future development of a SNP typing scheme with S. Enteritidis.

A retrospective analysis of Salmonella serovars isolated from pigs in Great Britain between 1994 and 2010

A retrospective study analysing Salmonella serovars and antimicrobial resistance data from pigs in Great Britain between 1994 and 2010 was performed. Data were obtained through scanning surveillance and compared with prevalence data from other livestock species as well as human data. During the study period, two serovars, S. Typhimurium and S. Derby, predominated in British pigs. The total number of Salmonella incidents has decreased steadily over the study period, from 360 incidents per year in 1994 to 172 incidents in 2010. S. Typhimurium has been the most common serovar every year, but the relative percentage went down over the past few years. During the same time period, monophasic strains of S. Typhimurium have increased in numbers and were accounting for as much as 25% of incidents in 2010, representing the second most common serovar in British pigs in 2010. Antimicrobial resistance data from S. Typhimurium isolates show that the percentage of isolates which are resistant to six or more antimicrobials has increased from 27.2% in 1994 to 58.3% in 2010 and that the percentage of isolates fully sensitive to the panel of antimicrobials tested was only 3.3% in 2010. S. Typhimurium isolates belonged mainly to phagetypes DT193 and U288 in 2010, and an increase can be seen in the number of isolates belonging to phage type DT193. DT104, which was the predominant phagetype during the 1990s, has gone down considerably and represented less than 5% of all S. Typhimurium isolates in 2010. Monophasic strains of S. Typhimurium belonged mainly to phagetype 193 with less than 20% belonging to phagetype 120.The overall trend shows that the number of Salmonella incidents reported from British pigs has gone down considerably over the 17-year study period, but that the relative percentage of monophasic strains of S. Typhimurium has increased significantly. This trend seems to be in line with observations from other European countries, where an increase of this serovar can be seen both in livestock and in human patients. The increasing percentage of Salmonella-isolates which show multi-resistance is a matter of concern and has to be monitored carefully in order to assess any potential risks this may pose to human patients.

Genotyping, Phage Typing, and Antimicrobial Resistance of Salmonella Typhimurium Isolated from Pigs, Cattle, and Humans

Salmonella enterica serovar Typhimurium (ST) is one of the most common serovars isolated from humans and animals. It has been suggested that ST infections in Koreans are largely due to the consumption of contaminated pork and beef. To investigate the genotypes, phage types, and antimicrobial resistance patterns for ST isolates of different origins, a total of 70 ST strains, including 19 isolates from humans, 44 isolates from pigs, and 6 isolates from cattle, were analyzed using pulsedfield gel electrophoresis (PFGE), phage typing, and antimicrobial susceptibility tests. Forty-three distinct PFGE patterns were generated from 70 ST isolates, which were grouped into 14 PFGE groups (from A to N) at the level of 75% similarity. The most prevalent group was the A (A1-A17 subtypes) group, encompassing 54.5% (38/70) of ST isolates. ST isolates from pigs and cattle mostly belong to groups A and L, whereas ST isolates from humans mostly belong to groups F and C. Antimicrobial susceptibility tests using 11 antimicrobial agents showed that resistance to tetracycline (TE) (81.4%) was highly prevalent, followed by streptomycin (S) (64.3%) and nalidixic acid (NA) (31.4%) resistance. A total of seventeen antimicrobial resistance patterns were observed. Only 8.6% of isolates, including a reference strain, were susceptible to all antimicrobial agents tested. The most prevalent resistance pattern was TE-S (37.1%), which was seen in 66.6% of bovine, 40.8% of swine and 21.1% of human isolates. Three ST isolates from humans (15.9%) showed resistance to 7-8 antimicrobials. The most predominant phage type (PT) was U302 (64.3%), followed by DT170 (10.0%). PFGE types did not coincide with antimicrobial resistance patterns and phage types; therefore, the combination of those types allowed for further differentiation between tested ST isolates.

Temporal and spatial patterns of bovine Escherichia coli O157 prevalence and comparison of temporal changes in the patterns of phage types associated with bovine shedding and human E. coliO157 cases in Scotland between 1998-2000 and 2002-2004

BackgroundEscherichia coli O157 is an important cause of acute diarrhoea, haemorrhagic colitis and, especially in children, haemolytic uraemic syndrome (HUS). Incidence rates for human E. coli O157 infection in Scotland are higher than most other United Kingdom, European and North American countries. Cattle are considered the main reservoir for E. coli O157. Significant associations between livestock related exposures and human infection have been identified in a number of studies.ResultsAnimal Studies: There were no statistically significant differences (P = 0.831) in the mean farm-level prevalence between the two studies (SEERAD: 0.218 (95%CI: 0.141-0.32); IPRAVE: 0.205 (95%CI: 0.135-0.296)). However, the mean pat-level prevalence decreased from 0.089 (95%CI: 0.075-0.105) to 0.040 (95%CI: 0.028-0.053) between the SEERAD and IPRAVE studies respectively (P < 0.001). Highly significant (P < 0.001) reductions in mean pat-level prevalence were also observed in the spring, in the North East and Central Scotland, and in the shedding of phage type (PT) 21/28. Human Cases: Contrasting the same time periods, there was a decline in the overall comparative annual reported incidence of human cases as well as in all the major PT groups except 'Other' PTs. For both cattle and humans, the predominant phage type between 1998 and 2004 was PT21/28 comprising over 50% of the positive cattle isolates and reported human cases respectively. The proportion of PT32, however, was represented by few (<5%) of reported human cases despite comprising over 10% of cattle isolates. Across the two studies there were differences in the proportion of PTs 21/28, 32 and 'Other' PTs in both cattle isolates and reported human cases; however, only differences in the cattle isolates were statistically significant (P = 0.002).ConclusionThere was no significant decrease in the mean farm-level prevalence of E. coli O157 between 1998 and 2004 in Scotland, despite significant declines in mean pat-level prevalence. Although there were declines in the number of human cases between the two study periods, there is no statistically significant evidence that the overall rate (per 100,000 population) of human E. coli O157 infections in Scotland over the last 10 years has altered. Comparable patterns in the distribution of PTs 21/28 and 32 between cattle and humans support a hypothesized link between the bovine reservoir and human infections. This emphasizes the need to apply and improve methods to reduce bovine shedding of E. coli O157 in Scotland where rates appear higher in both cattle and human populations, than in other countries.

MOLECULAR TYPING OF METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS STRAINS BY PCR-RFLP OF SPA GENE: A REFERENCE LABORATORY PERSPECTIVE

Purpose: To characterize methicillin-resistant Staphylococcus aureus (MRSA) strains by molecular typing based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of spa gene and to assess the utility of spa genotyping over bacteriophage typing in the discrimination of the strains. Materials and Methods: Studies were undertaken on 125 MRSA strains representing the most predominant phage types and the non phage typeable strains. Strains were typed by bacteriophage typing and PCR-RFLP of spa gene. DNA sequence analysis of the amplified spa gene fragment of the representative RFLP patterns was performed using standard protocols. Results: All the strains resistant to oxacillin were found to contain mec A gene. Fifty-two per cent of these strains were typeable by the international basic set of 23 phages. Five different PCR-RFLP patterns were observed among 125 MRSA strains. Non phage typeable strains were differentiated into four PCR-RFLP patterns. Sequencing of the spa gene from the representative strains of each RFLP pattern confirmed the length of these restriction fragments due to variation in the 24 bp and the 174 bp tandem repeats. It also revealed the presence of three new spa repeat patterns. Conclusion: The study demonstrates the importance of spa genotyping in the discrimination of MRSA strains, which were otherwise indistinguishable by bacteriophage typing. spa genotyping allowed differentiation of strains within a particular phage type. Nucleotide sequencing of isolates of different PCR-RFLP patterns indicated a correlation between the RFLP patterns of a variable number of tandem repeats and the phage type. The study provides valuable information on the epidemiological characterization of MRSA strains.

Genotypic and Phenotypic Diversity of Salmonella Enteritidis Isolated from Chickens and Humans in Korea

Salmonella Enteritidis is the most common cause of salmonellosis in humans in South Korea. It has been recognized that the principal source of human infection with S. Enteritidis is chickens and their products such as meat and eggs. A total of 173 S. Enteritidis isolates from humans (65 isolates) and chickens or their products (108 isolates) were analyzed by antibiotic susceptibility assay, phage typing, and pulsed-field gel electrophoresis (PFGE). Drug resistance was found to streptomycin (32.3%), ampicillin (30.6%), nalidixic acid (30.1%), ticarcillin (30.1%), and tetracycline (28.3%). More than 70% of the isolates were found to be resistant to one or more antibiotics tested. The most frequent patterns of resistant isolates were resistance to nalidixic acid only (28.3%) and resistance to two antibiotics (four combinations; 20.2%). The most predominant phage type (PT) was PT1 (27.2%) followed by PT21 (20.8%) and PT4 (8.7%) in chicken and human isolates. Nineteen different PFGE patterns were found among the 173 isolates, and A1 was the most common PFGE pattern, followed by A6 (17.3%). Most S. Enteritis isolates (except two isolates with patterns B and C) showed similar PFGE patterns that differed by only a few bands. These results show that 2 or 3 subtypes of S. Enteritidis are shared to a large extent by humans and chickens. This implies the possibility of the spread of chicken S. Enteritidis to humans.

Phage types and pulsed-field gel electrophoresis patterns of Salmonella enterica serovar Enteritidis isolated from humans and chickens

We analyzed 66 Salmonella Enteritidis isolates in 2002. Thirty isolates were obtained from human patients with diarrhea, and 36 were obtained from chickens. A total of ten phage types (PT) were identified in the human and chicken isolates. PT1 and PT21 were the predominant PTs in both the human (20% and 13%) and chicken (17% and 47%) isolates. Twelve pulsotypes were generated by PFGE and divided into two major groups. Most of the PFGE types were categorized into cluster group 1. Eighteen chicken isolates in cluster group 1 showed high-level genetic association (>95%) with 22 other human isolates. Additionally, six chicken isolates from cluster group 2 showed fairly high-level genetic association (>95%) with the other seven human isolates. The highest levels of genetic association in humans and chickens were seen with A5-PT21 (11 isolates), A2-PT1 (7 isolates), and B1-PT4 (6 isolates). The Pulsed-Field Gel Electrophoresis (PFGE) and phage typing provided conclusive evidence that human Salmonella infections are attributable to the consumption of contaminated chicken.

CHANGING PATTERNS OF VIBRIO CHOLERAE IN SEVAGRAM BETWEEN 1990 AND 2005

Purpose: A retrospective analysis was done to note changes in prevalence, distribution of biotypes, serotypes, antibiotic susceptibility patterns and phage types of Vibrio cholerae isolated in Mahatma Gandhi Institute of Medical Sciences, Sevagram over a period of 16 years. Methods: A total of 535 strains of V. cholerae were isolated from 10,406 stool samples and rectal swabs from January 1990 to December 2005. These comprised of serogroups O1 - 427 (79.89%), O139 - 86 (16.07%) and non O1, non O139 - 22 (4.11%). No classical V. cholerae was isolated. Results:Vibrio cholerae serogroup O1 serotype Ogawa was the predominant isolate till 1992. During 1993, serogroup O139 became the main isolate; however, it completely disappeared during 1995-1996 only to reappear in 1997. Serotype Inaba in our area was conspicuous by its absence with only two strains being isolated till June 1999, but during July-December 1999, 11 out of 15 V. cholerae O1 isolates were El Tor Inaba. T4 was the predominant phage type till 1990, T2 during 1991-1994 and T27 (as per the new scheme) thereafter. Resistance to tetracycline varied between 2 and 17% for V. cholerae O1. Conclusions: The paper reports on the changing epidemiological markers of V. cholerae isolated from a rural hospital over a period of 16 years.

Changing patterns of &lt;i&gt; Vibrio cholerae&lt;/i&gt; in Sevagram between 1990 and 2005

A retrospective analysis was done to note changes in prevalence, distribution of biotypes, serotypes, antibiotic susceptibility patterns and phage types of Vibrio cholerae isolated in Mahatma Gandhi Institute of Medical Sciences, Sevagram over a period of 16 years. A total of 535 strains of V. cholerae were isolated from 10,406 stool samples and rectal swabs from January 1990 to December 2005. These comprised of serogroups O1 - 427 (79.89%), O139 - 86 (16.07%) and non O1, non O139 - 22 (4.11%). No classical V. cholerae was isolated. Vibrio cholerae serogroup O1 serotype Ogawa was the predominant isolate till 1992. During 1993, serogroup O139 became the main isolate; however, it completely disappeared during 1995-1996 only to reappear in 1997. Serotype Inaba in our area was conspicuous by its absence with only two strains being isolated till June 1999, but during July-December 1999, 11 out of 15 V. cholerae O1 isolates were El Tor Inaba. T4 was the predominant phage type till 1990, T2 during 1991-1994 and T27 (as per the new scheme) thereafter. Resistance to tetracycline varied between 2 and 17% for V. cholerae O1. The paper reports on the changing epidemiological markers of V. cholerae isolated from a rural hospital over a period of 16 years.

Multi-locus variable-number tandem repeat analysis for outbreak studies of Salmonella enterica serotype Enteritidis

BackgroundSalmonella enterica subsp. enterica serotype Enteritidis is known as an important and pathogenic clonal group which continues to cause worldwide sporadic cases and outbreaks in humans. Here a new multiple-locus variable-number tandem repeat analysis (MLVA) method is reported for highly-discriminative subtyping of Salmonella Enteritidis. Emphasis was given on the most predominant phage types PT4 and PT8. The method comprises multiplex PCR specifically amplifying repeated sequences from nine different loci followed by an automatic fragment size analysis using a multicolor capillary electrophoresis instrument. A total of 240 human, animal, food and environmental isolates of S. Enteritidis including 23 definite phage types were used for development and validation. Furthermore, the MLVA types were compared to the phage types of several isolates from two recent outbreaks to determine the concordance between both methods and to estimate their in vivo stability. The in vitro stability of the two MLVA types specifically for PT4 and PT8 strains were determined by multiple freeze-thaw cycles.ResultsSeventy-nine different MLVA types were identified in 240 S. Enteritidis strains. The Simpson's diversity index for the MLVA method was 0.919 and Nei diversity values for the nine VNTR loci ranged from 0.07 to 0.65. Twenty-four MLVA types could be assigned to 62 PT4 strains and 21 types to 81 PT8 strains. All outbreak isolates had an indistinguishable outbreak specific MLVA type. The in vitro stability experiments showed no changes of the MLVA type compared to the original isolate.ConclusionThis MLVA method is useful to discriminate S. Enteritidis strains even within a single phage type. It is easy in use, fast, and cheap compared to other high-resolution molecular methods and therefore an important tool for surveillance and outbreak studies for S. Enteritidis.

Survey of Salmonella Contamination of Non–United Kingdom-Produced Raw Shell Eggs on Retail Sale in the Northwest of England and London, 2005 to 2006

This survey was prompted by a change in the epidemiology of Salmonella Enteritidis infections in England and Wales and elsewhere in Europe and, to our knowledge, is the first survey to provide information on Salmonella contamination of non–United Kingdom eggs on retail sale. Based on 10,464 non–United Kingdom eggs (1,744 pooled samples of six eggs) purchased between March 2005 and July 2006, the total weighted prevalence estimate for all Salmonella detected in non–United Kingdom eggs was 3.3%. Of the eggs sampled, most were produced in Spain (66.3%), France (20.0%), or The Netherlands (7.4%). Salmonella was detected from 4.4 and 0.3% of eggs produced in Spain and France, respectively, with weighted prevalence estimates. Eight different Salmonella serotypes were recovered from non–United Kingdom eggs, of which Salmonella Enteritidis predominated, with an estimated prevalence of 2.6%. Salmonella Enteritidis was obtained only from Spanish eggs. Nine different phage types of Salmonella Enteritidis were identified, with phage type 1 found to be the predominant phage type. Most of the Salmonella Enteritidis isolates obtained from Spanish eggs in the survey were resistant to nalidixic acid with concomitant decreased susceptibility to ciprofloxacin (0.125 to 1.0 mg/liter) or ampicillin (8.0 mg/liter). Salmonella Enteritidis phage type 1 until now had not been detected in eggs examined as part of previous United Kingdom egg surveys but has been detected in eggs of Spanish origin examined during recent national outbreaks of Salmonella Enteritidis non–phage type 4 infections in England and Wales. Eggs are a commonly consumed food that may occasionally be contaminated with Salmonella. The rates of contamination may be linked to the origin of the eggs. Consumers and caterers need to be aware of this continuing hazard, adopt appropriate control measures, and follow advice provided by national food agencies in order to reduce the risk of infection.

Drastic decrease of Salmonella Enteritidis isolated from humans in Belgium in 2005, shift in phage types and influence on foodborne outbreaks.

In Belgium, non-typhoidal salmonellosis and campylobacteriosis are the two most frequently reported foodborne illnesses. During 2005, a 71% decrease of Salmonella Enteritidis infections compared with the average annual number cases in the period 2000-2004 was recorded by the Belgian National Reference Centre for Salmonella and Shigella. After the peak of 1999, the total number of salmonellosis cases decreased gradually, with the exception of 2003 when an increase was again recorded due to the rise of isolates belonging to the serotype Enteritidis. PT4, the predominant phage type of serotype Enteriditis over recent years (except in 2003), became the second most prevalent phage type in 2005 after PT21. We present in this paper the epidemiology (incidence and trends) of human salmonellosis in Belgium and assess the role of the vaccination programme in layer flocks on the decline of the incidence of human salmonellosis and foodborne outbreaks due to S. Enteritidis.

Relationship of pulsed-field profiles with key phage types of Salmonella enterica serotype Enteritidis in Europe: results of an international multi-centre study

Salmonella is one of the most common causes of foodborne infection in Europe with Salmonella enterica serovar Enteritidis (S. Enteritidis) being the most commonly identified serovar. The predominant phage type for S. Enteritidis is phage type (PT) 4, although PT 8 has increased in incidence. Within these phage types, pulsed-field gel electrophoresis (PFGE) provides a method of further subdivision. The international project, Salm-gene, was established in 2001 to develop a database of PFGE profiles within nine European countries and to establish criteria for real-time pattern recognition. It uses DNA fingerprints of salmonellas to investigate outbreaks and to evaluate trends and emerging issues of foodborne infection within Europe. The Salm-gene database contains details of about 11 700 S. Enteritidis isolates, demonstrating more than 65 unique PFGE profiles. The clonal nature of S. Enteritidis is evidenced by the high similarity and distribution of PFGE profiles. Over 56% (6603/11 716) of the submitted isolates of several different phage types were profile SENTXB.0001, although this profile is most closely associated with PT 4. The next most common profiles, SENTXB.0002 and SENTXB.0005, were closely associated with PT 8 and PT 21 respectively. Studies to investigate the relationship of profile types with outbreaks and possible vehicles of infection suggest that the incidence of PFGE profile SENTXB.0002, and thus PT 8, in some countries may be due to importation of foods or food production animals from Eastern Europe, where PT 8 is amongst the most frequently identified phage types. Collation of subtyping data, especially in the commonly recognized phage types, is necessary in order to evaluate trends and emerging issues in salmonella infection.