Prevalence of the virulence plasmids of nontyphoid Salmonella in the serovars isolated from humans and their association with bacteremia

Mobility of antimicrobial resistance across serovars and disease presentations in non-typhoidal Salmonella from animals and humans in Vietnam

Non-typhoidal Salmonella (NTS) is a major cause of bacterial enterocolitis globally but also causes invasive bloodstream infections. Antimicrobial resistance (AMR) hampers the treatment of these infections and understanding how AMR spreads between NTS may help in developing effective strategies. We investigated NTS isolates associated with invasive disease, diarrhoeal disease and asymptomatic carriage in animals and humans from Vietnam. Isolates included multiple serovars and both common and rare phenotypic AMR profiles; long- and short-read sequencing was used to investigate the genetic mechanisms and genomic backgrounds associated with phenotypic AMR profiles. We demonstrate concordance between most AMR genotypes and phenotypes but identified large genotypic diversity in clinically relevant phenotypes and the high mobility potential of AMR genes (ARGs) in this setting. We found that 84 % of ARGs identified were located on plasmids, most commonly those containing IncHI1A_1 and IncHI1B(R27)_1_R27 replicons (33%), and those containing IncHI2_1 and IncHI2A_1 replicons (31%). The vast majority (95%) of ARGS were found within 10 kbp of IS6/IS26 elements, which provide plasmids with a mechanism to exchange ARGs between plasmids and other parts of the genome. Whole genome sequencing with targeted long-read sequencing applied in a One Health context identified a comparatively limited number of insertion sequences and plasmid replicons associated with AMR. Therefore, in the context of NTS from Vietnam and likely for other settings as well, the mechanisms by which ARGs move contribute to a more successful AMR profile than the specific ARGs, facilitating the adaptation of bacteria to different environments or selection pressures.

Changes in epidemiology and antimicrobial susceptibility of nontyphoid Salmonella in children in southern Taiwan, 1997-2016

BACKGROUND

This study aimed to investigate the changing trends in serogroup distribution and antimicrobial susceptibility of nontyphoid Salmonella (NTS) isolated from children in the past two decades in Taiwan.

METHODS

This retrospective study enrolled patients aged younger than 18 years with culture-proven NTS infection in a tertiary medical center from 1997 to 2016. Data on age, Salmonella serogroup, culture sample, and antimicrobial susceptibility were obtained from medical records. The rates of Salmonella serogroups and antimicrobial resistance were compared between period 1 (1997-2006) and period 2 (2007-2016).

RESULTS

A total of 2075 NTS isolates were identified from 1997 to 2016 (1036 in period 1, 1039 in period 2). The major isolates were from feces (89.1%) and blood (10.4%). The most common serogroup was serogroup B (54.8%), followed by serogroup D (18.8%). There was a significant decline in the proportion of serogroup B with a concomitant rise in serogroup D in the past two decades. In period 2, resistance to cefotaxime and cefixime increased remarkably among serogroup B, whereas resistance to ampicillin increased notably among serogroup D. Furthermore, the incidence of multidrug-resistant (≥3 antibiotics) NTS significantly decreased in both serogroup B and serogroup D in period 2.

CONCLUSION

This study revealed a significant rise in serogroup D with a concomitant decline in serogroup B NTS infection in Taiwanese children. Moreover, antimicrobial resistance to third-generation cephalosporins increased in serogroup B. Continuous surveillance of NTS serogroup distribution and antimicrobial susceptibility is mandatory to formulate therapeutic strategies for NTS infections.

A Novel Hybrid Plasmid Carrying Multiple Antimicrobial Resistance and Virulence Genes in Salmonella enterica Serovar Dublin

Virulence plasmids and antibiotic resistance plasmids are usually maintained separately in Salmonella spp.; however, we report an instance of a hybrid plasmid (pN13-01125) in Salmonella enterica serovar Dublin. Review of the complete sequence of the 172,265-bp plasmid suggests that pN13-01125 is comprised of the previously described pSDVr and pSH696_135 plasmids and that the mechanism of hybridization likely involves IS6 (IS26) insertion sequence elements. The plasmid has a low conjugation frequency, confers resistance to six classes of antimicrobials, and contains a complete spv virulence operon.

Liver abscess caused by Salmonella choleraesuis

A 65-year-old man with long-term alcohol abuse presented with intermittent fever. Abdominal computed tomography revealed multiple masses. Abscess blood and pus cultures conducted after percutaneous catheter drainage with pigtail catheters yielded Salmonella choleraesuis. Antibiotic treatment with meropenem was started using multiple catheters in the liver. Drainage catheters in different locations were exchanged several times with larger-bored catheters. After septicemia was detected, abscesses spread to the peritoneal cavity. Pleural complications developed. Antibiotic treatment, with careful drainage guided by ultrasound or computed tomography, controlled the abscesses and complications. This report describes the difficult clinical course and treatment of a liver abscess from S. choleraesuis.

A real-time multiplex SYBR Green I polymerase chain reaction assay for rapid screening of salmonella serotypes prevalent in the European Union

A two-step real-time SYBR Green I multiplex polymerase chain reaction (PCR) assay with melting curve analysis was developed for rapid detection of 19 Salmonella serotypes frequently encountered in humans, animals, and animal-associated meat products within the European Union. The first-step single-tube reaction (Multiplex PCR I), consisting of five primer pairs, classified an initial test panel of eight Salmonella serotypes into five groups on the basis of characteristic amplicon melting temperatures produced by each strain. Following designation into groups, two subsequent triplex reactions (Multiplex PCR II-G1 and II-G3) allowed for further identification of five Salmonella serotypes by their melting peak temperatures. Primers for serotype differentiation were designed to target the genes encoding either phase 1 and 2 flagellar antigens fliC and fljB or unique serotype-specific loci. In addition, the assay simultaneously screened for the presence of the ampicilin-amoxicillin, chloramphenicol-florfenicol, streptomycin-spectinomycin, sulfanomides, and tetracycline (ACSSuT)-type multidrug resistance pattern, indicated by the floR gene, and for the Salmonella virulence plasmid encoded by the svp operon in Salmonella serotype Typhimurium. The established multiplex assays were successfully tested on 97 isolates, comprising 37 distinct Salmonella serotypes and 12 non-Salmonella strains. The two-step assay correctly detected 19 of 37 Salmonella serotypes and all non-Salmonella strains produced negative results. Of the 19 serotypes detected in the assays, 7 serotypes, including Salmonella serotypes Ohio, Goldcoast, Livingstone, Kedougou, Enteritidis, Kentucky, ACSSuT-type Salmonella serotype Typhimurium DT104 and DT104b, as well as non-ACSSuT-type Salmonella serotype Typhimurium strains, were definitively identified. The developed multiplex real-time SYBR Green I PCR assay represents a more rapid and reliable method for identification of large numbers of Salmonella serotypes prevalent throughout the European Union than assays using phenotypic serotyping methods.

Salmonella infection of a total knee replacement

Salmonella enterica serotype Choleraesuis is a rare infective pathogen in total knee arthroplasty and accounts for less than 1% of all cases. In the United Kingdom, the most prevalent organisms are Staphylococci, which account for over 50% of cases. We present an interesting case report of an infected revision total knee replacement following foreign travel to a region with an increased prevalence of Salmonella. The patient presented typically with an effused knee and raised inflammatory markers. Tissue samples demonstrated Salmonella choleraesuis as the infective organism. Though this serotype has previously been isolated from an infected total hip prosthesis, we believe this could be the first reported case involving a total knee replacement. Following involvement of our microbiology team and aggressive antibiotic therapy, the patient was successfully treated with two-stage revision surgery and at one-year post-op is making a satisfactory recovery.

Association of virulence plasmid and antibiotic resistance determinants with chromosomal multilocus genotypes in Mexican Salmonella enterica serovar Typhimurium strains

Background

Bacterial genomes are mosaic structures composed of genes present in every strain of the same species (core genome), and genes present in some but not all strains of a species (accessory genome). The aim of this study was to compare the genetic diversity of core and accessory genes of a Salmonella enterica subspecies enterica serovar Typhimurium (Typhimurium) population isolated from food-animal and human sources in four regions of Mexico. Multilocus sequence typing (MLST) and macrorestriction fingerprints by pulsed-field gel electrophoresis (PFGE) were used to address the core genetic variation, and genes involved in pathogenesis and antibiotic resistance were selected to evaluate the accessory genome.

Results

We found a low genetic diversity for both housekeeping and accessory genes. Sequence type 19 (ST19) was supported as the founder genotype of STs 213, 302 and 429. We found a temporal pattern in which the derived ST213 is replacing the founder ST19 in the four geographic regions analyzed and a geographic trend in the number of resistance determinants. The distribution of the accessory genes was not random among chromosomal genotypes. We detected strong associations among the different accessory genes and the multilocus chromosomal genotypes (STs). First, the Salmonella virulence plasmid (pSTV) was found mostly in ST19 isolates. Second, the plasmid-borne betalactamase cmy-2 was found only in ST213 isolates. Third, the most abundant integron, IP-1 (dfrA12, orfF and aadA2), was found only in ST213 isolates. Fourth, the Salmonella genomic island (SGI1) was found mainly in a subgroup of ST19 isolates carrying pSTV. The mapping of accessory genes and multilocus genotypes on the dendrogram derived from macrorestiction fingerprints allowed the establishment of genetic subgroups within the population.

Conclusion

Despite the low levels of genetic diversity of core and accessory genes, the non-random distribution of the accessory genes across chromosomal backgrounds allowed us to discover genetic subgroups within the population. This study provides information about the importance of the accessory genome in generating genetic variability within a bacterial population.

Extraintestinal focal infections in adults with nontyphoid Salmonella bacteraemia: predisposing factors and clinical outcome

BACKGROUND

Nontyphoid Salmonella (NTS) isolates lead to not only self-limited, acute gastrointestinal infections, but also bacteraemia with or without extraintestinal focal infections (EFIs). The risk factors associated with EFIs in adults with NTS bacteraemia were not clearly elucidated.

METHODS

In a medical center in southern Taiwan, patients aged > or = 18 years with NTS bacteraemia between January 1999 and June 2005 were included for analysis.

RESULTS

Of 129 patients, 51 (39.5%) were complicated with EFIs. The most common EFI was mycotic aneurysm, followed by pleuropulmonary infections and spinal osteomyelitis. Compared to patients with primary bacteraemia, those with EFIs had higher leucocyte counts (P = 0.004) and higher serum levels of C-reactive protein (P < 0.0001). The development of EFIs was associated with a higher mortality, more severe septic manifestations, longer hospital stays and duration of antimicrobial therapy. Univariate analysis revealed that diabetes mellitus (P = 0.02), hypertension (P = 0.02) and chronic lung disease (P = 0.006) were significantly associated with EFIs. However, patients with malignancy (P = 0.01) and immunosuppressive therapy (P = 0.03) were less likely to develop EFIs. On the basis of multivariate analysis, an independent factor for the occurrence of EFIs was age [adjusted odds ratio (aOR) 1.05; 95% confidence interval (CI) 1.02-1.07; P < 0.0001], whilst malignancy was negatively associated with EFIs (aOR 0.16; 95% CI 0.14-0.78; P = 0.01).

CONCLUSION

Amongst patients with NTS bacteraemia, EFIs often occurred in the aged, and were associated with a higher mortality and morbidity. Recognition of specific host factors is essential for identification of EFIs which often demand early surgical interventions and prolonged antimicrobial therapy.

Detection of multidrug-resistant Salmonella enterica serovar typhimurium phage types DT102, DT104, and U302 by multiplex PCR

Salmonella enterica serovar Typhimurium is a common cause of nontyphoidal salmonellosis in humans and animals. Multidrug-resistant serovar Typhimurium phage type DT104, which emerged in the 1990s, has become widely distributed in many countries. A total of 104 clinical isolates of Salmonella serogroup B were collected from three major hospitals in Taiwan during 1997 to 2003 and were examined by a multiplex PCR targeting the resistance genes and the spv gene of the virulence plasmid. A total of 51 isolates (49%) were resistant to all drugs (ACSSuT [resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline]), and all contained a 1.25-kb PCR fragment of integron that is part of the 43-kb Salmonella genomic island 1 (SGI1). The second group was resistant to SSu (28%), and the third was susceptible to all five drugs (13%). Fifty-nine isolates were serotyped to be serovar Typhimurium by the tube agglutination method using H antisera. The virulence plasmid was found in 54 (91.5%) of the 59 serovar Typhimurium isolates. A majority (94.1%) of the Salmonella serogroup B isolates with the ACSSuT resistance pattern harbored a virulence plasmid. Phage typing identified three major phage types: DT104, DT120, and U302. Analysis of the isolates by pulsed-field gel electrophoresis showed six genotypes. We found two genotypes in DT104 strains, two in DT120, and the other two in U302. The presence of a monophasic serovar (4,5,12:i:-) has added difficulty in the determination of the serovars of multidrug-resistant Salmonella serogroup B isolates. Nevertheless, the multiplex PCR devised in the present study appears to be efficient and useful in the rapid identification of ACSSuT-type serovar Typhimurium with SGI1, irrespective of their phage types.

Nontyphoidal Salmonella causing focal infections in patients admitted at a Spanish general hospital during an 11-year period (1991–2001)

In focal infections (FI) caused by nontyphoidal Salmonella serotypes and recorded at a Spanish hospital 1991-2001, clinical and microbiological features were analyzed. Thirty-five revised episodes were related to infections of the digestive (10), urinary (10), pulmonar (4), vascular (4), osteoarticular (3) and central nervous (3) systems, and with a submaxillary lymph node. At least 16 episodes were associated with previous or concomitant gastroenteritis, 19 with primary or secondary bacteremia, and 18 with underlying diseases of different severity. Eighteen patients were male and 14 female (data were not available for three patients), while 1, 4, 12 and 15 patients were, respectively, categorized as children, young adults, senior adults and elderly. Sources of Salmonella strains were urine (13), blood (11), purulent abscess (8), cerebrospinal fluid (3), peritoneal fluid, pleural fluid, wound exudates, aneurism (2 of each), ascitic fluid, sputum, tracheal aspirate, needle aspirate, bone and lymph node (1 of each) samples. Only 28 Salmonella strains involved in FIs were available for further analysis. They were discriminated into 6 serotypes, and into 13 XbaI macrorestriction, 6 virulence, 11 antimicrobial resistance, 5 integron and 10 plasmid profiles. Broadly, the pattern of serotype distribution of salmonellas involved in FIs matched that of those causing gastroenteritis, with the pandemic Enteritidis and Typhimurium (18 and 6 strains, respectively) being clearly predominant. Within serotype, the same lineages (as revealed by XbaI-macrorestriction analysis as well as R- and V-profiles) were represented in both disease groups, with host-related factors apparently playing a more critical role than the individual strain in the outcome of the disease.

Protection of neonatal mice from lethal enterovirus 71 infection by maternal immunization with attenuated Salmonella enterica serovar Typhimurium expressing VP1 of enterovirus 71

This study describes the potential use of attenuated Salmonella enterica serovar Typhimurium strains to express and deliver VP1 of enterovirus 71 (EV71) as a vaccination strategy to prevent EV71 infection in mice. When orally administered to BALB/c mice, both attenuated carrier strains, CNP101 and SL7207, were able to efficiently invade livers and spleens, while only the virulence plasmid-carrying strain SL7207 persisted for more than 30 days in these organs. A recombinant in vivo-regulated promoter expression plasmid expressing VP1 antigen of EV71 was constructed. The expression of the VP1, directed by the pagC promoter, in attenuated Salmonella was confirmed by Western blot hybridization. Both humoral and cellular immune responses were elicited in mice by oral immunization with such Salmonella-based VP1 vaccines. We evaluated the protective efficacy of the vaccines in mice using a maternal immunization protocol. With a lethal challenge, ICR newborn mice born to dams immunized with Salmonella-based VP1 vaccine showed a 50-60% survival; in contrast, none of the mice in the control group survived the challenge. Our data indicated that Salmonella-based VP1 subunit vaccines are a promising vaccine strategy in the prevention of EV71 infection.

Prevalence of the virulence plasmid in Salmonella Typhimurium isolates from pigs

To determine the prevalence of the virulence plasmid in Salmonella Typhimurium isolates from pigs in Japan, a total of 106 porcine isolates were subjected to PCR amplification for the detection of the virulence plasmid. Out of the isolates of S. Typhimurium, 38 (35.8%) harbored the virulence plasmid. The presence of the virulence plasmid was widely observed in the isolates from systemically infected pigs (92.0%, 23/25), compared with diarrheic (18.8%, 12/64) and apparently healthy pigs (17.6%, 3/17) (P<0.01).

Assessing genetic diversity in plasmids from Escherichia coli and Salmonella enterica using a mixed-plasmid microarray

AIMS

To compare genetic composition of plasmids using microarrays composed of randomly selected fragments of plasmid DNA.

METHODS AND RESULTS

Separate shotgun libraries were constructed from plasmid DNA pooled from Escherichia coli and Salmonella enterica. Cloned fragments were used as probes for microarrays. Plasmid targets were labelled, hybridized overnight, and bound targets were imaged after enzymatic signal amplification. Control hybridizations demonstrated significantly higher signal when probes and targets shared >95% sequence identity. Diagnostic sensitivity and specificity of the assay was 95 and 99%, respectively. Cluster analysis showed close matches for replicate experiments with a high correlation between replicates (r = 0.91) compared with the correlation for nonreplicates (r = 0.09). Analysis of hybridization data from 43 plasmids generated five distinct clusters, two for known serovar-specific plasmids, one for enterohemorrhagic E. coli plasmids, and two for plasmids harboring a recently disseminated antibiotic resistance gene (bla(CMY-2)).

CONCLUSION

Mixed-plasmid microarrays are suitable for comparing genetic content of wild-type plasmids and hybridization results from this study suggest several novel hypotheses about plasmid gene exchange between E. coli and S. enterica.

SIGNIFICANCE AND IMPACT OF STUDY

Mixed-plasmid microarrays permit rapid, low cost analysis and comparison of many plasmids. This ability is critical to understanding the source, fate, and transport of plasmids amongst commensal and pathogenic bacteria.

Development of PCR primers for the detection of Salmonella enterica serovar Choleraesuis based on the fliC gene

Salmonella enterica serovar Choleraesuis may cause swine salmonellosis and human infection. Because the conventional method for detection of this Salmonella serovar may take 3 to 5 days, a PCR method for detection was evaluated. By comparing the sequence of the phase 1 flagellin (fliC) gene of Salmonella Choleraesuis with that of other Salmonella serovars and of other bacteria species available in GenBank, two PCR primers (flinC-F and flinC-R) were designed. Using these primers, all 97 Salmonella Choleraesuis strains assayed generated the expected PCR product, with a molecular mass of 963 bp. Except for S. enterica Paratyphi C, Salmonella isolates other than Salmonella Choleraesuis and non-Salmonella isolates, including strains of Enterobacteriaceae, all generated negative PCR results. Salmonella Paratyphi C could be differentiated from Salmonella Choleraesuis through the use of primers designed from the viaB gene. When Salmonella Choleraesuis isolates from swine stool, pork, liver, feed, and human whole blood samples were assayed with a preenrichment step, as low as 1 CFU/g or ml of the original sample could be detected.

Increasing ceftriaxone resistance in Salmonella isolates from a university hospital in Taiwan

OBJECTIVES

Salmonella infection is a distressing health problem worldwide. This study reports the changing epidemiology of Salmonella infections in Taiwan during 1999-2003, with emphasis on increasing ceftriaxone resistance.

METHODS

Records of Salmonella clinical isolates in Chang Gung Memorial Hospital during 1999-2003 were reviewed. All isolates were identified and antimicrobial susceptibility determined by standard methods. A total of 22 ceftriaxone-resistant isolates were investigated by PCR sequencing of the bla(TEM), bla(SHV), bla(CTX-M) and ampC genes. Southern-blot hybridization was used to localize the ampC gene. Infrequent-restriction-site PCR was used to genotype these isolates.

RESULTS

A total of 3635 Salmonella isolates, including 3592 (98.8%) non-typhoid Salmonella, were identified. Serogroup B (55.6%) remained the most predominant, but the prevalence has been decreasing. In contrast, serogroup D infections have increased significantly from 13.6 to 22.8%. Overall resistance to ampicillin and chloramphenicol remained high, with the highest rate (91% to both drugs) observed in Salmonella enterica serotype Choleraesuis in 2003. A sudden upsurge of ciprofloxacin resistance from zero to 69% was found in S. Choleraesuis. Ceftriaxone resistance increased in several serogroups (0.8-2.1%; average, 1.5%). The resistance was associated with plasmid-mediated bla(CMY-2) in 14 cases and extended-spectrum beta-lactamases (ESBLs), including CTX-M-3 (n=6), SHV-2a (n=1) and SHV-12 (n=1), in others. Diverse serotypes and genotypes were found among the ceftriaxone-resistant isolates.

CONCLUSIONS

Increasing ceftriaxone resistance in non-typhoid Salmonella appears to link to the spread of plasmid-mediated ampC or ESBL genes. Effective measures should be taken to prevent the problem worsening.

Influence of ciprofloxacin resistance on risk factors for endovascular infection in patients with infection due to group C nontyphoid salmonellae

From January 2000 through September 2004, a total of 54 patients with infection due to group C nontyphoid salmonellae were evaluated; 8 patients had gastroenteritis alone, and 46 patients had bacteremia. Of the 46 patients who had bacteremia, 12 had endovascular infection and 34 did not. The number of infections due to ciprofloxacin-resistant Salmonella organisms is increasing. Ciprofloxacin-resistant Salmonella organisms predisposed patients to acquire bacteremia, but they did not seem to predispose patients to acquire endovascular infection.

Risk Factors for Recurrent Bacteremia in Adult Patients with Nontyphoid Salmonellosis

BACKGROUND

This study sought to find the risk factors for recurrent bacteremia in adult patients with nontyphoid salmonellosis.

METHOD

Retrospective chart review.

RESULT

Between September 1984 and December 2003, 235 adult (age > or = 18 years old) patients with bacteremia with nontyphoid salmonellosis were admitted to our hospital. Among them, 130 patients (55%) had immunodeficiency, 31 patients (13%) had systemic lupus erythematosus, 26 patients (11%) had hematologic malignancies, 50 patients (21%) had solid organ cancers, and 39 patients (17%) had endovascular infections. Thirty-seven patients had recurrent bacteremia during the study period. Both univariate and multivariate analysis showed that immunodeficiency was the only predictor of recurrent bacteremia (odds ratio, 2.79; P = 0.013). The overall hospital mortality rate was 26%: 8% for patients with recurrent bacteremia and 29% for patients without recurrence. The independent risk factors of hospital death were old age, not recurrent infection, and solid organ cancers.

CONCLUSION

Old age, systemic lupus erythematosus, malignancies, and immunodeficiency were common in adult patients with nontyphoid Salmonella bacteremia. The incidence of recurrent bacteremia was 16%. Immunodeficiency predisposed patients to recurrent bacteremia. Recurrent bacteremia was associated with a lower hospital mortality rate, however.

Salmonella enterica serotype Choleraesuis: epidemiology, pathogenesis, clinical disease, and treatment

Nontyphoid Salmonella strains are important causes of reportable food-borne infection. Among more than 2,000 serotypes, Salmonella enterica serotype Choleraesuis shows the highest predilection to cause systemic infections in humans. The most feared complication of serotype Cholearesuis bacteremia in adults is the development of mycotic aneurysm, which previously was almost uniformally fatal. The advances in diagnostic techniques, surgical care, and antimicrobial therapy have greatly improved the survival of these patients. However, the recent emergence of serotype Choleraesuis that is resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and, notably, fluoroquinolone antibiotics has aroused concern about the use of these agents for the empirical treatment of systemic infection caused by this organism. In view of the serious implications of the situation, the chain of transmission and mechanism of resistance should be carefully studied to reduce the spread of infection and threat to human health. To date, there are no vaccines available to prevent serotype Choleraesuis infections in humans. The availability, in the near future, of the genome sequence of serotype Cholearesuis will facilitate the development of effective vaccines as well as the discovery of new targets for novel antimicrobial agents.

Nontyphoid salmonellosis in taiwan children: clinical manifestations, outcome and antibiotic resistance

OBJECTIVES

The purposes of this study were to investigate the epidemiologic, clinical, and microbiologic features of patients with nontyphoid salmonellosis and to elucidate the impact of resistance on the outcome of nontyphoid salmonellosis in Taiwan. The authors also sought to develop a severity score to derive an objective guideline for antibiotic use in nontyphoid salmonellosis in the era of increasing antibiotic resistance.

METHODS

The authors prospectively monitored 311 children with nontyphoid salmonellosis in Kaohsiung, Taiwan. The demographic, clinical, and microbiologic features, underlying diseases, treatment regimen, complications, and outcome were analyzed. In vitro susceptibility testing of the isolates was performed.

RESULTS

The median age of affected patients was 15 months. Salmonella enteritidis B caused 68.5% of episodes, followed by S. enteritidis C1 (11.9%), D (7.7%), C2 (7.1%), E (2.6%), S. choleraesuis (1.6%), and S. paratyphi (0.6%). Sixty percent of isolates were resistant to ampicillin. Patients with bacteremia could not be differentiated from patients without bacteremia on clinical grounds. Patients receiving antibiotics that were inactive in vitro (discordant therapy) had more days of fever and longer hospital stay compared with patients receiving antibiotics that were active in vitro (concordant therapy). Patients receiving no antibiotic treatment had the fewest days of fever and shortest hospital stays, especially among patients with mild illness (severity score, 0-1).

CONCLUSION

Blood culture should be obtained in patients with nontyphoid salmonellosis to detect bacteremia. In treating antibiotic-resistant nontyphoid salmonellosis, antibiotics are still not mandatory for patients who present with primarily gastrointestinal symptoms and limited signs of systemic inflammation reflected by a low severity score (low C-reactive protein, fewer band cells in peripheral blood, and fewer days of fever before admission). Susceptibility data should be promptly obtained because use of discordant antibiotics appears to prolong illness.

Management of aortic aneurysm infected with Salmonella

BACKGROUND

This study reviewed the clinical outcomes of patients with an aortic aneurysm infected with Salmonella treated by a single centre over 6 years.

METHODS

Data were collected by a retrospective case-note review.

RESULTS

Between September 1995 and December 2001, 121 patients with non-typhoid Salmonella bacteraemia were treated, of whom 24 patients had an aortic aneurysm infected with Salmonella. Ten had a suprarenal and 14 an infrarenal aortic infection. The most common responsible pathogen was group C Salmonella (12 patients). All of the 20 patients who had combined medical and surgical therapy survived, whereas two of four who had medical therapy alone died. There were two late deaths during a mean follow-up of 23 (range 3-63) months.

CONCLUSION

The incidence of aortic infection in patients with non-typhoid Salmonella bacteraemia was high in Taiwan. Timely surgical intervention and prolonged intravenous antibiotic therapy resulted in excellent outcomes.

Risk factors for primary bacteremia and endovascular infection in patients without acquired immunodeficiency syndrome who have nontyphoid salmonellosis

This study sought to find the risk factors for primary bacteremia, endovascular infection, and in-hospital death for patients without acquired immunodeficiency syndrome who have nontyphoid salmonellosis. From September 1995 through September 2001, 301 patients with nontyphoid salmonellosis were admitted to our hospital; of these patients, 121 had primary bacteremia, and 28 had endovascular infection. Of the 121 patients with primary bacteremia, 64 were aged >50 years, and 26 had endovascular infection. Overall, 90 patients (29.9%) had immunodeficiency. Predictors of primary bacteremia were age; presence of systemic lupus erythematosus; group B, group C, or group D Salmonella infection; and immunodeficiency. The positive predictor of endovascular infection in adult patients with primary bacteremia was group C Salmonella infection, and negative predictors were immunodeficiency and solid-organ cancer. The overall in-hospital mortality rate was 12%; for primary bacteremia, it was 24.8%; for endovascular infection, it was 14.3%. Predictors of in-hospital death were age, extraintestinal infection, and solid-organ malignancy.

Redefining bacterial populations: a post-genomic reformation

Sexual reproduction and recombination are essential for the survival of most eukaryotic populations. Until recently, the impact of these processes on the structure of bacterial populations has been largely overlooked. The advent of large-scale whole-genome sequencing and the concomitant development of molecular tools, such as microarray technology, facilitate the sensitive detection of recombination events in bacteria. These techniques are revealing that bacterial populations are comprised of isolates that show a surprisingly wide spectrum of genetic diversity at the DNA level. Our new awareness of this genetic diversity is increasing our understanding of population structures and of how these affect host pathogen relationships.

Characterization of a laboratory-derived, high-level ampicillin-resistant Salmonella enterica serovar Typhimurium strain that caused meningitis in an infant

A Salmonella enterica serovar Typhimurium strain that harbored a plasmid carrying a TEM-1-type beta-lactamase gene was isolated from the blood and cerebrospinal fluid of an infant with meningitis. This 3.2-kb plasmid was further characterized to be a nonconjugative pGEM series cloning vector containing a foreign insert. The strain was likely laboratory derived and contaminated the environment before it caused the infection.

The emergence in Taiwan of fluoroquinolone resistance in Salmonella enterica serotype choleraesuis

BACKGROUND

Salmonella enterica serotype choleraesuis is a cause of serious systemic infections. Because fluoroquinolones are the drug of choice for the treatment of severe salmonella infections, the emergence and dissemination of fluoroquinolone-resistant S. enterica serotype choleraesuis have clinical consequences.

METHODS

In Taiwan, a hospital-based surveillance system has been in place since 1987 to monitor the incidence of S. enterica serotype choleraesuis infections and the antimicrobial susceptibility of the isolates. We investigated the rapid emergence of fluoroquinolone resistance in this serotype in 2000 and 2001. Pigs in Taiwan were evaluated as a potential source of the resistant salmonella.

RESULTS

A total of 501 clinical isolates of S. enterica serotype choleraesuis were recovered in our hospital from 1987 through 2000. The proportion of total salmonella isolates made up by S. enterica serotype choleraesuis decreased from an average of 8.4 percent before 1995 to 2.7 percent in 1996 through 1998. During 1999 and 2000, this proportion increased significantly, to an average of 5.0 percent. Ciprofloxacin resistance in S. enterica serotype choleraesuis has been observed since 2000. In the third quarter of 2001, 60 percent of isolates were resistant to ciprofloxacin. Molecular typing indicated that the primary source of S. enterica serotype choleraesuis isolates was herds of swine. All the resistant isolates from humans and swine had mutations that led to the substitution of phenylalanine for serine at position 83 and asparagine for aspartic acid at position 87 in the gene for DNA gyrase A.

CONCLUSIONS

This investigation in Taiwan indicates that fluoroquinolone-resistant S. enterica serotype choleraesuis can spread from swine to humans. The use of fluoroquinolones in food animals should be prohibited.

Large drug resistance virulence plasmids of clinical isolates of Salmonella enterica serovar Choleraesuis

Salmonella enterica serovar Choleraesuis generally causes systemic human salmonellosis without diarrhea, and therefore, antimicrobial treatment is essential for such patients. The drug resistance information on this organism is thus of high value. Serovar Choleraesuis usually harbors a virulence plasmid (pSCV) of 50 kb in size. Of the 16 clinical isolates identified to be serovar Choleraesuis, all except one harbored a pSCV and seven of them carried a pSCV of more than 125 kb in size. A pSCV was defined as a plasmid carrying spvC and characteristic deletions detected by PCR and by DNA-DNA hybridization (for the former criterion). The results of PCR, restriction fragment profiles, and Southern DNA-DNA hybridizations of the profiles all indicated that such larger pSCVs were derived from the 50-kb plasmid recombined with non-pSCVs found in some clinical isolates. Fifteen of the 17 strains, including a laboratory strain, were then tested for drug resistance against 16 antibiotics with E-test and the dilution method. The laboratory strain, which harbored a 50-kb pSCV and a 6-kb non-pSCV, was resistant only to sulfonamides (SUL), and its resistance gene, sulII, checked with PCR and DNA-DNA hybridization, was located on the 6-kb non-pSCV. All 14 clinical strains were resistant to multiple drugs. Of the 14, 7 were resistant to SUL, and the resistance gene was located on a plasmid. The sulII gene, but not bla(TEM-1), was carried only on the 6-kb non-pSCV. Of the remaining six large plasmids, three of 90 kb, two of 136 kb, and one of 140 kb, the last three were pSCVs and carried the other SUL gene (sulI) and the bla(TEM-1) gene. The six strains were also resistant to trimethoprim-sulfamethoxazole. None of the 50-kb pSCVs carried resistance genes. These drug resistance genes on the large pSCVs were apparently also acquired through recombination.