Antimicrobial resistance of Salmonella enterica serovar Typhimurium isolated from cattle in Japan

The antimicrobial susceptibility of 144 Salmonella enterica serovar Typhimurium isolates collected from all over Japan between 1973 and 1998 were investigated. All the isolates exhibited resistance to four or more antimicrobials and 22 resistance patterns were observed. Isolates showing resistance patterns to ampicillin (A), chloramphenicol (C), streptomycin (S), sulfonamides (Su) and tetracycline (T), which are typical resistance patterns for S. Typhimurium DT104 (DT104), were predominant. Thirty-six of the 68 isolates that exhibited resistance to five or more antimicrobials (ACSSuT+) were identified as DT104 by phage typing. Another 103 S. Typhimurium strains gathered from cattle between 1977 and 1999 in a limited area of Japan were analyzed for molecular epidemiological studies. Results using fluorescent amplified-fragment length polymorphism and pulsed-field gel electrophoresis suggest that clonal exchange of S. Typhimurium among cattle in Japan has occurred since 1992, and that contemporary strains show a remarkable degree of homogeneity with DT104 at a molecular level. The clonal replacement by DT104 affected the antimicrobial resistance pattern of S. Typhimurium from cattle in Japan.     

Multidrug-resistant Salmonella Typhimurium DT104 in poultry

Salmonella Typhimurium isolates from feed ingredients or poultry sources isolated during 1995 to 1997 from different geographical locations within Minnesota were examined for the presence of Salmonella Typhimurium definitive type 104 (DT104). Antibiotic susceptibility studies indicated that 15 of 50 isolates of Salmonella Typhimurium had an antibiotic resistance pattern (ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline) that is usually observed with multidrug-resistant Salmonella Typhimurium DT104. Of the 15 isolates showing the antibiotic resistance pattern, 8 isolates were phage type 104, 3 isolates were typed as phage type 104 complex, and the remaining 4 isolates belonged to phage types 193, 81, and 126. DT104 was recovered from both feed ingredients and poultry samples. Of the seven feed ingredient-associated Salmonella Typhimurium isolates, four were DT104, whereas only 7 of 43 poultry-associated Salmonella Typhimurium isolates were DT104. A repetitive sequence-based polymerase chain reaction (rep-PCR) of 50 isolates of Salmonella Typhimurium representing 13 phage types identified seven distinct fingerprint profiles. No correlation between phage type and rep-PCR type was noticed. Eleven Salmonella Typhimurium isolates belonging to DT104 and its complex were grouped into two closely related rep-PCR types.     

Antimicrobial resistance and phage and molecular typing of Salmonella strains isolated from food for human consumption in Spain

The aims of this study were to ascertain the population structure and antimicrobial susceptibility of Salmonella enterica serovars isolated in 2002 from food in 16 Spanish regions. Serovars were characterized by serotyping, phage typing, antimicrobial susceptibility, and pulsed-field gel electrophoresis (PFGE) typing, and 264 nonrelated strains were selected for further analysis. The main sources were eggs and their derivatives (21.6% of strains), poultry and related products (16.6%), and seafood (16.3%). High serotype diversity was detected (51 serotypes); the most common were Enteritidis (n = 96, 36.3%) and Typhimurium (n = 53, 20.1%), followed by a miscellaneous group of 49 different serotypes (n = 115, 43.5%). A 15% increase in Salmonella Enteritidis isolation was observed. Common phage types for Salmonella Enteritidis were PT1 (41.6% of isolates), PT4 (9.4%), PT6 (9.4%), and PT6a (9.4%), and common types for Salmonella Typhimurium were DTU302 (18.8%), DT104 (15.1%), and DT104B (13.2%). Salmonella Enteritidis strains were categorized into eight PFGE types with a similarity of 81 to 96%, and 73.9% of the strains were grouped into just one cluster. Salmonella Typhimurium isolates were divided into 13 PFGE types with a similarity of 64 to 86%, and one predominant clone contained 41.5% of the strains. Resistance rates for Salmonella Enteritidis, Salmonella Typhimurium, and the miscellaneous group were, respectively, 8.3, 69.8, and 13.9% for ampicillin, 3.1, 52.8, and 59% for streptomycin, 40.6, 22.6, and 10.4% for nalidixic acid, 15.6, 71.7, and 31.1% for tetracycline, 7.3, 18.8, and 9.5% for trimethoprim-sulfamethoxazole, 0, 50.9, and 4.3% for chloramphenicol, and 6.2, 71.7, and 17.4% for multiple (at least four) antimicrobials. All the strains remained susceptible to other beta-lactams and fluoroquinolones. Surveillance of S. enterica isolated from food is strongly recommended to reduce community exposure to antimicrobial resistant strains.     

Occurrence of Salmonella enterica serotype typhimurium DT104A in retail ground beef

Surveillance data of cattle and human isolates of Salmonella enterica serovar Typhimurium DT104 indicate that this pathogen emerged worldwide in the 1980s, particularly in cattle. Studies were conducted to determine the prevalence of Salmonella Typhimurium DT104 in ground beef. Samples were also tested for the presence of generic Escherichia coli. A total of 404 fresh ground beef samples obtained at retail stores from New York, San Francisco, Philadelphia, Denver, Atlanta, Houston, and Chicago were shipped overnight to Georgia for processing. Salmonella spp. were isolated from 14 (3.5%) samples. Eight different serotypes were identified among the isolates, including Salmonella Typhimurium (5), Salmonella Lille (3), Salmonella Montevideo (1), Salmonella Hadar (1), Salmonella Meleagridis (1), Salmonella Cerro (1), Salmonella Kentucky (1), and Salmonella Muenster (1). Antibiotic resistance profiles indicated that all five Salmonella Typhimurium isolates were resistant to ampicillin, streptomycin, sulfamethoxazole, ticarcillin, and tetracycline but that they were sensitive to chloramphenicol. Phage typing revealed that all five Salmonella Typhimurium isolates were DT104A, a subtype of DT104. All five Salmonella Typhimurium DT104A isolates were obtained from ground beef sampled from retail outlets in San Francisco. Pulsed-field gel electrophoresis (PFGE) genomic DNA profiles of the five Salmonella Typhimurium DT104A isolates from ground beef were indistinguishable from those of four control Salmonella Typhimurium DT104 penta-resistant isolates from cattle that were used for comparison. A total of 102 generic E. coli isolates were obtained, only three of which were multiresistant to antibiotics. In addition, three E. coli isolates were recovered from samples that were positive for Salmonella Typhimurium DT104A. No correlation of antibiotic resistance profiles was observed between Salmonella Typhimurium DT104A and generic E. coli, as two of the three E. coli isolates were susceptible to all of the antibiotics tested, and the third isolate was resistant only to cephalothin. These data indicate that Salmonella Typhimurium DT104A can be isolated from retail ground beef, and because there was little overlap in antibiotic resistance patterns between Salmonella Typhimurium DT104A and E. coli isolates from the same ground beef samples, these limited data suggest that the transfer of antibiotic resistance genes among enteric bacteria in ground beef may not be common. This latter observation is further supported by the limited isolation of multiantibiotic-resistant E. coli from retail ground beef.     

Prevalence and number of Salmonella in irish retail pork sausages

A national Salmonella control program in the pork industry was enacted in Ireland in August 2002. This study was undertaken as part of a larger project investigating the role of pork as a source of human salmonellosis in Ireland. The objective of this survey was to assess the prevalence of Salmonella in Irish pork sausage at retail level. Samples, comprising branded prepacked sausages and loose sausages from supermarket meat counters and butcher shops, were collected from selected retail sites in four cities from October to December 2001 and from June to August 2002. A three-tube most-probable-number method was used to enumerate Salmonella in a selected number of samples that were positive by enrichment. Salmonella serotypes were detected in 4.4 and 1.7% of samples at each of the respective sampling periods, a level similar to those reported in other U.S. and U.K. studies. Isolates were characterized by serotype, phage type, and antimicrobial susceptibility. Eighteen (70%) were resistant to at least one antimicrobial, and 15 (58%) were resistant to four or more antimicrobials. Most of the isolates exhibited resistance to tetracycline. Five different phage types were detected. DT104 was the predominant phage type among Salmonella Typhimurium isolates. This study revealed that multidrug-resistant salmonellae are present in a proportion of Irish sausages and that further risk analysis work is necessary in order to quantify the risk posed to public health.     

The effect of temperature on the growth and persistence of Salmonella in fermented liquid pig feed

Two studies were conducted to investigate the effect of temperature on the fate of Salmonella enterica subsp. enterica serovar typhimurium DT104:30 in fermented liquid pig feed. These were (1) by co-inoculation of feed with S. typhimurium DT104:30 and Pediococcus pentosaceus, as the fermenting organism, and (2) by fermenting feed for 48, 72 or 96 h prior to inoculation with S. typhimurium DT104:30. In co-inoculated feed incubated at 20 degrees C, S. typhimurium DT104:30 persisted for at least 72 h. In contrast, in feed incubated at 30 degrees C, no S. typhimurium DT104:30 were detectable 48 h after inoculation. In prefermented feed, S. typhimurium DT104:30 died four to five times faster in feed maintained at 30 degrees C (D(value) 34-45 min) compared with feed maintained at 20 degrees C (D(value) 137-250 min). This was not entirely due to differences in lactic acid concentration as feed fermented for 72 or 96 h at 20 degrees C and feed fermented for 48 h at 30 degrees C contained similar concentrations of lactic acid (160-170 mM). Low numbers of S. typhimurium DT104:30 were still detectable in fermented feed 24 h after inoculation at 20 degrees C. In contrast, none were detectable 6-7 h after inoculation at 30 degrees C. The results of these studies indicate that it would be advisable for pig producers to control the temperature of liquid feed tanks to reduce the risk of Salmonella contamination.     

Competitive inhibition bacteria of bovine origin against Salmonella serovars

Studies were conducted to isolate bacteria inhibitory to Salmonella enterica serovar Typhimurium definitive type (DT) 104 in vitro from cattle not carrying Salmonella and to determine the inhibitory activity of the isolated bacteria through competitive growth in cattle feces artificially contaminated with Salmonella Typhimurium DT104 and S. enterica serovar Newport. Fecal samples (108) were obtained from dairy and beef cows. S. enterica serovars were isolated from 9.25% of the samples and included Salmonella Newport (4), Salmonella Bareilly (1), Salmonella Mbandaka (1), Salmonella Montevideo (1), Salmonella Meleagridis (1), and monophasic Salmonella (2). All four Salmonella Newport isolates were resistant to at least nine antibiotics. Of 1,097 bacterial isolates from cattle feces screened, 30 were inhibitory to Salmonella Typhimurium DT104 in vitro. The inhibitory isolates included 22 Escherichia coli, 6 Bacillus circulans, 1 Serratia fonticola, and 1 Enterobacter cloacae. Typing by pulsed-field gel electrophoresis showed 17 distinguishable profiles among the 22 E. coli. Competitive inhibition isolates did not significantly reduce Salmonella Typhimurium DT104 during 21 days of storage at 37 degrees C in cattle feces. B. circulans (10(5) CFU/g of inoculum) significantly reduced Salmonella Newport on days 3 and 5 and on day 21 with 10(8) CFU/g of inoculum at 37 degrees C. At 21degrees C, significant reductions of Salmonella Typhimurium DT104 occurred with 10(8) CFU of gram-negative competitive inhibition bacteria per g and 10(5) CFU of B. circulans per g on day 5 only. No significant reductions were observed with Salmonella Newport at 21 degrees C. The 25 competitive inhibition bacteria identified in this study offer a first step in identifying competitive inhibition bacteria that may reduce the level of intestinal carriage and fecal shedding of Salmonella Typhimurium DT104 and Salmonella Newport in cattle.     

Comparison of antibiotic susceptibility profiles and molecular typing patterns of clinical and environmental Salmonella enterica serotype Newport

The genus Salmonella is composed of more than 2,400 serotypes, many of which cause enteric diseases in humans and animals. Several Salmonella serotypes are multidrug resistant, and there is evidence of the clonal spread of these strains from animals to humans. Salmonella enterica serotype Newport is one of the serotypes that increasingly present a multidrug-resistant phenotype. Source tracking and antibiotic resistance testing are important considerations for identifying the outbreak strain. The first goal of this study was to examine the antibiotic susceptibility patterns of clinical and environmental Salmonella Newport isolates from various geographic locations and to compare the discriminatory ability of two DNA fingerprinting techniques. The second goal was to determine whether the antibiotic resistance profiles and typing patterns correlated. Thirty Salmonella Newport isolates, including environmental and human clinical strains, were subjected to pulsed-field gel electrophoresis (PFGE), ribotyping, and antibiotic susceptibility testing. Eighty percent of the isolates showed total or intermediate resistance to one or more drugs; 75% of the isolates were multidrug resistant. Ribotyping with the EcoRI enzyme and PFGE with the XbaI enzyme each divided the isolates into 14 groups. Cluster analysis based on antibiotic susceptibility patterns generated 23 profiles. The susceptible and resistant isolates were not differentiated on the basis of either of the molecular typing techniques. Hence, no correlation was observed between the antibiotic resistance profiles and the DNA subtyping patterns. In conclusion, ribotyping is as discriminatory as PFGE and, when used in combination with antibiotic resistance profiles, provides a powerful tool for the source tracking of Salmonella Newport.     

Campylobacter and Salmonella in raw red meats in the United Kingdom: prevalence, characterization and antimicrobial resistance pattern, 2003-2005

The prevalence of Campylobacter and Salmonella was assessed in 3959 raw red meats in the UK during 2003-2005. Meats were more frequently contaminated with Campylobacter (7.2%) than with Salmonella (2.4%). Lamb and other meats (e.g. mutton, rabbit) exhibited the highest contamination from Campylobacter (12.6% and 19.8%, respectively), compared with pork (6.3%) and beef (4.9%). Pork however had the highest contamination from Salmonella (3.9%), followed by lamb (2.0%), other meats (2.0%) and beef (1.3%). Offal samples (36.6%) were more frequently contaminated with Campylobacter or Salmonella than muscle tissue (7.0%). C. jejuni predominated in all meat types. C. coli isolates were more likely to exhibit antimicrobial drug resistance, including quinolones, than C. jejuni. Salmonella typhimurium was the most frequent Salmonella serotype isolated from meats; S. typhimurium DT104/104b isolates exhibited higher rates of multiple drug resistance than other serotypes. The findings reinforce the importance of adequate cooking of meat and good hygiene to avoid cross-contamination.     

Comparison of antimicrobial resistance patterns and phage types of Salmonella Typhimurium isolated from pigs,pork and humans in Belgium between 2001 and 2006

Infections with non-typhoid Salmonella represent a major problem in industrialized countries.The emergence and spread of antimicrobial-resistant pathogens, among them Salmonella, has become a serious health hazard worldwide. One of the most commonly isolated non-typhoid Salmonella serovars in pigs, pork and humans is Salmonella Typhimurium. In this study the comparison of the incidences of resistance to nine antimicrobials, resistance patterns and phage types between S. Typhimurium isolated from pigs (n = 581), pork (n = 255) and humans (n = 1870) in Belgium in the period 2001 to 2006 was performed.Resistance to the antimicrobials ampicillin, chloramphenicol, streptomycin, sulfonamides and tetracycline was frequently observed and varied between 23.5% and 83.1%. Resistance ranged from 15.6% to 20.7% for the combination trimethoprim–sulfonamides and from 3.4% to 5.8% for nalidixic acid. Resistance to the critical important antimicrobials cephalosporins and fluoroquinolones was found sporadically (≤ 1.2%). Resistance to the different antimicrobials was observed to be similar in S. Typhimurium isolates from the various origins. Twenty-seven antimicrobial resistance patterns representing in total 75.2%, 89.0% and 89.6% of the isolates from pigs, pork and humans respectively were found to be common among the three groups and 73 combinations antimicrobial resistance pattern/phage type were found to be common among pork and human isolates, representing 70.1% of the pork isolates and 51.0% of the human isolates. The high percentage of isolates that have a common resistance pattern, and in a less pronounced way a common combination phage type/resistance pattern, are in agreement with the hypothesis of transfer of antimicrobial resistant Salmonella from pigs via the consumption of pork to humans as one of the possible pathways. The most prevalent combination in Belgium within both the pork isolates (7.4%) and the human isolates (13.2%) was S. Typhimurium DT104 resistant to ampicillin, chloramphenicol, streptomycine, sulfonamides and tetracycline.     

Development of a multilocus variable-number of tandem repeat typing method for Listeria monocytogenes serotype 4b strains

Listeria monocytogenes serotype 4b strains have been identified as the causative agent in many human listeriosis epidemics as well as in a considerable number of sporadic cases. Due to the genetic homogeneity of serotype 4b isolates, development of rapid subtyping methods with high discriminatory power for serotype 4b isolates is required to allow for improved outbreak detection and source tracking. In this study, multilocus variable-number tandem repeat analysis (MLVA) was developed and used to characterize 60 serotype 4b isolates from various sources. All isolates were also characterized by automated EcoRI ribotyping, single enzyme pulsed-field gel electrophoresis (PFGE) with ApaI, and a multilocus sequence typing (MLST) scheme targeting six virulence and virulence-associated genes. Discriminatory power of MLVA (as determined by Simpson Index of Discrimination) was higher than the discriminatory power of any of the other three methods. MLVA markers targeted were found to be stable and did not change when three isolates were passaged daily for 70 days. Cluster analyses of MLVA, PFGE and MLST consistently grouped the same isolates into three major clusters, each of which includes one of the three major L. monocytogenes epidemic clones (i.e., ECI, ECIa and ECII). We conclude that the MLVA method described here (i) provides for more discriminatory subtyping of L. monocytogenes serotype 4b strains than the other three methods, (ii) identifies three major groups within the serotype 4b, which are consistent with the groups identified by other subtyping methods, and (iii) is easy to interpret. Use of MLVA may thus be recommended for subtyping of serotype 4b isolates, including as a secondary more discriminatory subtyping method that could be used after initial isolate characterization by PFGE or ribotyping.     

Characterisation of Danish isolates of Listeria monocytogenes by multilocus enzyme electrophoresis.

A total of 84 strains of Listeria monocytogenes were analysed by multilocus enzyme electrophoresis at twelve enzyme loci. Eight enzyme loci were polymorphic with between 2 and 4 alleles per locus. Fourteen electrophoretic types (ETs) were identified. Among 62 human clinical isolates from Denmark, 8 different ETs were defined. Two ETs, designated ET 1 and ET 6, accounted for 77% of the human clinical isolates investigated. These ETs are identical with those responsible for several epidemics in Switzerland and in the United States. Comparison of 58 isolates of L. monocytogenes, typed by MEE, in relation to phage typing showed that phage typing was more discriminatory than MEE. The ability of MEE to distinguish between phage types of Epi-type and other phage types, however, was almost optimal. MEE typed 23 of 24 strains of Epi-type as belonging to ET 1. In contrast ET 1 was not found in 26 strains with phage types other than the Epi-type.     

Multiple-locus variable number of tandem repeat analysis (MLVA) of Listeria monocytogenes directly in food samples

Listeria monocytogenes is the etiologic agent of listeriosis responsible for severe and fatal infections in humans. Listeria contamination occurs quite often in a wide range of foods due to its ubiquitous nature. Isolates need to be characterized to a strain level for accurate diagnosis of Listeria infection, epidemiological studies, investigation of outbreaks and effective prevention and control of food-borne listeriosis. The purpose of this research was to evaluate the multiple-locus variable number of tandem repeat analysis (MLVA) for sub-typing L. monocytogenes isolates in pure cultures and in food matrices. Two multiplex PCR assays were formulated to amplify six specific loci using fluorescently-labeled primers; and the amplicons were analyzed by capillary electrophoresis. The MLVA method resulted in 34 unique DNA fingerprint patterns from 46 L. monocytogenes isolates of 10 serotypes which had 29 or 30 PFGE patterns with a single restriction enzyme and 34 AFLP patterns. The MLVA patterns of the 46 isolates remained unchanged in the presence of pre-enriched food matrices including sausage, ham, chicken, milk and lettuce. The MLVA method successfully typed L. monocytogenes strains spiked in cheese, roast beef, egg salad and vegetable samples after 48 h enrichment at the initial inoculation levels of 1-5 CFU per 25 g of food or higher. The limits of detection (typing) of the MLVA method were 10³-10⁴ CFU/mL of pre-enriched food broth when evaluated using post-spiked sausage, ham, chicken, milk and lettuce samples. The MLVA method was simple, highly discriminatory, and easy to perform with portable (numerical) results. To our knowledge, this is the first report that describes the application of the MLVA method directly to food samples and demonstrates the possibility to obtain rapid and accurate subtyping results before an isolate is obtained.     

Surveillance and antimicrobial resistance of Salmonella strains isolated from slaughtered pigs in Spain

The prevalence of and the antibiotic resistance shown by Salmonella isolated from pigs in Andalusia (southern Spain) is reported. Salmonella enterica was recovered from 40 (33%) of 121 sampled herds, and a total of 65 isolates were serotyped. The most common Salmonella serotypes were Typhimurium and Rissen (30.7% each); others included Derby (9.2%), Brandenburg (9.2%), Newport (7.7%), Bredeney (4.6%), Anatum (3.0%), Hadar (1.5%), and Goldcoast (1.5%). One strain (1.5%) belonging to the monophasic variant of the Typhimurium serotype (Salmonella 4,5,12:i: -) was also detected. Definitive phage type (DT) 104b was the most common Typhimurium phage type isolated. These Salmonella strains were resistant to various antimicrobial agents, including tetracycline (84.6%), streptomycin (69.2%), neomycin (63.0%), sulfonamides (61.5%), ampicillin (53.8%), and amoxicillin (53.8%). All isolates were fully susceptible to ceftriaxone, ciprofloxacin, and colistin. Thirty-nine strains (64%) resistant to four or more antimicrobial agents were defined as multidrug resistant. Multidrug resistance profiles were observed in Salmonella serotypes Typhimurium, Rissen, Brandenburg, Bredeney, a monophasic variant, Gold-coast, Hadar, and Anatum, with serotypes Typhimurium and Brandenburg showing the most complicated resistance patterns (resistant to > or = 11 drugs).     

Application of Random Amplified Polymorphic DNA (RAPD) and Pulsed-Field Gel Electrophoresis (PFGE) Analysis to Listeria monocytogenes: A Review of Methodology and Results

Random amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) analyses have been found to be powerful molecular methods for differentiating isolates of a given bacterial species. When applied to Listeria monocytogenes, both methods have been found highly effective in tracking isolates involved in food borne outbreaks of listeriosis and in identifying routes of contamination in food processing plants. Among the two methods, PFGE is considered somewhat superior in discriminatory power. However, the use of two or more independent random primers with RAPD is considered to result in a level of discrimination equal to that of PFGE. When results from both methods are combined, a maximum level of discrimination that exceeds that obtained with both methods independently can be achieved. Individually, both methods far exceed the discriminatory power of serotyping and phage typing of L. monocytogenes strains in that serotypes 1/2a, 1/2b, and 4b, represent over 90% of all human isolates, and phage typing at times has allowed typing of no more than about 50% of isolates. In addition, both RAPD and PFGE on occasion have been found to be superior to ribotyping, multilocus enzyme electrophoresis, and restriction enzyme analysis of L. monocytogenes isolates.     

Development and application of Multiple-Locus Variable number of tandem repeat Analysis (MLVA) to subtype a collection of Listeria monocytogenes

In this study we report the development and application of a Multiple-Locus Variable number of tandem repeat Analysis (MLVA) strategy for subtyping Listeria monocytogenes. Genome profiles of a collection of forty-five food-borne L. monocytogenes isolates were compared using MLVA. These isolates were obtained as part of an active surveillance programme of foods in the south-east region of Ireland. MLVA successfully discriminated amongst the isolates. The method was easy to perform, relatively fast and could be deployed in any molecular laboratory with basic laboratory equipment. This approach is a valuable tool, which has the capability to provide comparable results when compared with other more established typing methods, including pulsed-field gel electrophoresis (PFGE).     

Antibiotic Resistance and Molecular Characterization of Seafood Isolates of Nontyphoidal Salmonella by PFGE

Emergence of multidrug resistant nontyphoidal Salmonella is a major health concern worldwide due to the predominant occurrence of Salmonella enterica sub-species enterica serovar Typhimurium phage type 104 (DT104) conferring resistance to ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline. Apart from antibiotic resistance, the identification and genotypic characterization of pathogens is essential for epidemiological surveillance and outbreak investigations. In this study 39 isolates of Salmonella obtained from seafood samples were examined for their susceptibility to various antibiotics and subjected to PFGE analysis using the restriction enzyme Xba1. The highest percentage resistance was for erythromycin (100%) followed by nalidixic acid (15.38%), co-trimoxazole (15.38%), chloramphenicol (12.82%), ampicillin (12.82%) and tetracycline (10.25%). Six (15.38%) of the 39 isolates were multidrug resistant. The XbaI digested chromosomal DNA generated 7 clusters suggesting the presence of diverse Salmonella strains in seafood. The Discriminatory Index for PFGE obtained by XbaI restriction enzyme was 0.91. The PFGE has been found highly discriminatory for subtyping S. Weltevreden and S. Newport. The XbaI PFGE was not only discriminatory but could also distinguish multidrug-resistant strains from the sensitive ones as the two groups they belonged to different pulsotypes. The study also demonstrated multiple clones of S. Weltevreden, S. Newport and S. Oslo present in seafood from the south west coast of India. Genetic diversity among the similar seafood sources suggests the presence of different clones of Salmonella which further increases the risk of seafood being a potential source of highly pathogenic bacteria like Salmonella.     

南京地区猪肉源中沙门氏菌分子分型及耐药性分析

沙门氏菌是造成我国食源性疾病的常见细菌之一,也是肉类消费过程中密切监测的重点对象。在2018年~2021年期间,共计采集了南京市545份猪肉源食品样本,利用选择性培养法分离得到44株沙门氏菌,采用血清学方法和分子生物学方法（MLST）对其进行分型鉴定,并分析其耐药性。结果表明,市售样本中共计检出44株沙门氏菌,平均检出率为8.07%,其中内脏样本检出率相对最高（检出率为30.49%）;血清型分析表明,检出的菌株中以鼠伤寒沙门氏菌（Salmonella typhimurium）、罗森氏沙门氏菌（Salmonella rissen）、德尔卑沙门氏菌（Salmonella derby）和伦敦沙门氏菌（Salmonella london）4种血清型沙门氏菌最为常见;基因分型表明,ST19型为猪肉源中优势沙门氏菌株,占比为20.45%;检出的沙门氏菌中,38株菌株对四环素具有明显耐药性,占全部检出菌株的86.36%,而对头孢他啶、头孢噻肟和头孢西丁的耐药不超过10%。此外,对检出的1株多重耐药性沙门氏菌耐药基因分析发现,共筛查出了包括7大类抗生素及与耐药相关的基因。该实验详细分析了南京市场猪肉源食品中沙门氏菌污染状况,也为后期沙门氏菌的综合防治提供了理论依据。     

Evaluation of <Emphasis Type="Italic">flaA</Emphasis> Short Variable Region Sequencing,Multilocus Sequence Typing,and Fourier Transform Infrared Spectroscopy for Discrimination between <Emphasis Type="Italic">Campylobacter jejuni</Emphasis> Strains

Discriminatory and robust typing methods are needed to improve the understanding of the dynamics of food-borne Campylobacter infections and epidemiology in primary animal production. To evaluate the strain discriminatory potential of typing methods, flaA short variable region (SVR) sequencing and Fourier transform infrared (FTIR) spectroscopy were applied on a collection of 102 epidemiologically related and unrelated Campylobacter jejuni strains. Previous application of FTIR spectroscopy for subtyping of Campylobacter has been limited. A subset of isolates, initially discriminated by flaA SVR sequencing, were further subjected to multilocus sequence typing (MLST). It was found that flaA SVR sequencing had a slightly higher discriminatory power than FTIR spectroscopy, based on the Simpson diversity index. The clustering of strains indicated that FTIR spectroscopy is indeed a suitable method for discrimination of Campylobacter. The isolates were assigned to six clusters based on flaA SVR sequences and nine clusters based on the FTIR spectroscopy profiles. Furthermore, the cluster analysis of flaA SVR sequences, MLST, and FTIR spectroscopy profiles showed a high degree of congruence, assigning the isolates to similar cluster structures. In conclusion, FTIR spectroscopy can be applied for subtyping of Campylobacter, and the high discriminatory potential of both flaA SVR sequencing and FTIR spectroscopy render them suitable screening methods for large numbers of strains.     

CALCOFLUOR AS A FLUORESCENT PROBE TO DETECT BIOFILMS OF FOODBORNE PATHOGENS

Biofilms enable foodborne pathogens to resist removal from surfaces, survive disinfection and elude detection. This study evaluated the use of Calcofluor, which binds to polysaccharides containing β-D-glucans, to detect biofilms produced by Salmonella enterica serovar Berta and Salmonella enterica serovar Typhimurium DT104 (St DT104), Escherichia coli, Aeromonas hydrophila, Vibrio cholerae O139 and Hyphomonas adhaerens. Biofilms produced by St DT104, S. berta and V. cholerae on five types of surfaces (glass, polypropylene, Teflon™, stainless steel and aluminum) were detected by Calcofluor. Results suggest the potential use of Calcofluor as probes of foodborne pathogens in biofilms.