Typhoidal Salmonella: Distinctive virulence factors and pathogenesis.

Although nontyphoidal Salmonella (NTS; including Salmonella Typhimurium) mainly cause gastroenteritis, typhoidal serovars (Salmonella Typhi and Salmonella Paratyphi A) cause typhoid fever, the treatment of which is threatened by increasing drug resistance. Our understanding of S. Typhi infection in human remains poorly understood, likely due to the host restriction of typhoidal strains and the subsequent popularity of the S. Typhimurium mouse typhoid model. However, translating findings with S. Typhimurium across to S. Typhi has some limitations. Notably, S. Typhi has specific virulence factors, including typhoid toxin and Vi antigen, involved in symptom development and immune evasion, respectively. In addition to unique virulence factors, both typhoidal and NTS rely on two pathogenicity-island encoded type III secretion systems (T3SS), the SPI-1 and SPI-2 T3SS, for invasion and intracellular replication. Marked differences have been observed in terms of T3SS regulation in response to bile, oxygen, and fever-like temperatures. Moreover, approximately half of effectors found in S. Typhimurium are either absent or pseudogenes in S. Typhi, with most of the remaining exhibiting sequence variation. Typhoidal-specific T3SS effectors have also been described. This review discusses what is known about the pathogenesis of typhoidal Salmonella with emphasis on unique behaviours and key differences when compared with S. Typhimurium.

Pefloxacin as a surrogate marker for quinolone susceptibility in Salmonella enterica serovars Typhi & Paratyphi A in India.

BACKGROUND & OBJECTIVES: The emergence of resistance to fluoroquinolones in enteric fever despite the pathogen being susceptible by in vitro laboratory results, led to repeated changes in Clinical and Laboratory Standard Institute (CLSI) guidelines for this class of antibiotics to have specific and sensitive interpretative criteria. In 2015, CLSI added pefloxacin disk diffusion criteria as a surrogate marker for fluoroquinolone susceptibility. This study was carried out to evaluate the use of pefloxacin as a surrogate marker for ciprofloxacin, ofloxacin and levofloxacin susceptibility in clinical isolates of Salmonella Typhi and S. Paratyphi A. METHODS: A total of 412 strains of S. Typhi and S. Paratyphi A were studied for pefloxacin disk diffusion test as a surrogate marker for susceptibility to ciprofloxacin, ofloxacin and levofloxacin as per CLSI and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Molecular mechanisms of resistance to fluoroquinolones were also determined and correlated with pefloxacin susceptibility breakpoints. RESULTS: Of the total 412 strains, 34 were susceptible to ciprofloxacin and 33 each to levofloxacin and ofloxacin using CLSI minimum inhibitory concentration (MIC) breakpoints. There was a positive correlation between MICs with correlation coefficients 0.917, 0.896 and 0.958 for the association between ciprofloxacin and ofloxacin, ciprofloxacin and levofloxacin and ofloxacin and levofloxacin, respectively (P <0.001). The sensitivity, specificity and positive predictive value of pefloxacin as a surrogate marker using ciprofloxacin MIC as a gold standard were 100, 99.5 and 94.4 per cent, while 100, 99.2 and 91.7 per cent taking ofloxacin and levofloxacin MIC as gold standard. Mutations in target genes correlated with the pefloxacin susceptibility results. INTERPRETATION & CONCLUSIONS: Our results showed that pefloxacin served as a good surrogate marker for the detection of susceptibility to ciprofloxacin, ofloxacin and levofloxacin in S. Typhi and S. Paratyphi A. Further studies are required to confirm these findings.

The clinical and microbiological characteristics of enteric fever in Cambodia, 2008-2015.

BACKGROUND: Enteric fever remains a major public health problem in low resource settings and antibiotic resistance is increasing. In Asia, an increasing proportion of infections is caused by Salmonella enterica serovar Paratyphi A, which for a long time was assumed to cause a milder clinical syndrome compared to Salmonella enterica serovar Typhi. METHODOLOGY: A retrospective chart review study was conducted of 254 unique cases of blood culture confirmed enteric fever who presented at a referral adult hospital in Phnom Penh, Cambodia between 2008 and 2015. Demographic, clinical and laboratory data were collected from clinical charts and antibiotic susceptibility testing was performed. Whole genome sequence analysis was performed on a subset of 121 isolates. RESULTS: One-hundred-and-ninety unique patients were diagnosed with Salmonella Paratyphi A and 64 with Salmonella Typhi. In the period 2008-2012, Salmonella Paratyphi A comprised 25.5% of 47 enteric fever cases compared to 86.0% of 207 cases during 2013-2015. Presenting symptoms were identical for both serovars but higher median leukocyte counts (6.8 x 109/L vs. 6.3 x 109/L; p = 0.035) and C-reactive protein (CRP) values (47.0 mg/L vs. 36 mg/L; p = 0.034) were observed for Salmonella Typhi infections. All but one of the Salmonella Typhi isolates belonged to haplotype H58 associated with multidrug resistance (MDR) (i.e. resistance to ampicillin, chloramphenicol and co-trimoxazole).;42.9% actually displayed MDR compared to none of the Salmonella Paratyphi A isolates. Decreased ciprofloxacin susceptibility (DCS) was observed in 96.9% (62/64) of Salmonella Typhi isolates versus 11.5% (21/183) of Salmonella Paratyphi A isolates (all but one from 2015). All isolates were susceptible to azithromycin and ceftriaxone. CONCLUSIONS: In Phnom Penh, Cambodia, Salmonella Paratyphi A now causes the majority of enteric fever cases and decreased susceptibility against ciprofloxacin is increasing. Overall, Salmonella Typhi was significantly more associated with MDR and DCS compared to Salmonella Paratyphi A.

Evaluation of the Clinical and Microbiological Response to Salmonella Paratyphi A Infection in the First Paratyphoid Human Challenge Model.

Background: To expedite the evaluation of vaccines against paratyphoid fever, we aimed to develop the first human challenge model of Salmonella enterica serovar Paratyphi A infection. Methods: Two groups of 20 participants underwent oral challenge with S. Paratyphi A following sodium bicarbonate pretreatment at 1 of 2 dose levels (group 1: 1-5 × 103 colony-forming units [CFU] and group 2: 0.5-1 × 103 CFU). Participants were monitored in an outpatient setting with daily clinical review and collection of blood and stool cultures. Antibiotic treatment was started when prespecified diagnostic criteria were met (temperature ≥38°C for ≥12 hours and/or bacteremia) or at day 14 postchallenge. Results: The primary study objective was achieved following challenge with 1-5 × 103 CFU (group 1), which resulted in an attack rate of 12 of 20 (60%). Compared with typhoid challenge, paratyphoid was notable for high rates of subclinical bacteremia (at this dose, 11/20 [55%]). Despite limited symptoms, bacteremia persisted for up to 96 hours after antibiotic treatment (median duration of bacteremia, 53 hours [interquartile range, 24-85 hours]). Shedding of S. Paratyphi A in stool typically preceded onset of bacteremia. Conclusions: Challenge with S. Paratyphi A at a dose of 1-5 × 103 CFU was well tolerated and associated with an acceptable safety profile. The frequency and persistence of bacteremia in the absence of clinical symptoms was notable, and markedly different from that seen in previous typhoid challenge studies. We conclude that the paratyphoid challenge model is suitable for the assessment of vaccine efficacy using endpoints that include bacteremia and/or symptomatology. Clinical Trials Registration: NCT02100397.

Paratyphoid fever: splicing the global analyses.

The incidence of enteric fever caused by Salmonella enterica serovar Paratyphi A (S. Paratyphi A) is increasing in many parts of the world. Although there is no major outbreak of paratyphoid fever in recent years, S. Paratyphi A infection still remains a public health problem in many tropical countries. Therefore, surveillance studies play an important role in monitoring infections and the emergence of multidrug resistance, especially in endemic countries such as India, Nepal, Pakistan and China. In China, enteric fever was caused predominantly by S. Paratyphi A rather than by Salmonella enterica serovar Typhi (S. Typhi). Sometimes, S. Paratyphi A infection can evolve into a carrier state which increases the risk of transmission for travellers. Hence, paratyphoid fever is usually classified as a "travel-associated" disease. To date, diagnosis of paratyphoid fever based on the clinical presentation is not satisfactory as it resembles other febrile illnesses, and could not be distinguished from S. Typhi infection. With the availability of Whole Genome Sequencing technology, the genomes of S. Paratyphi A could be studied in-depth and more specific targets for detection will be revealed. Hence, detection of S. Paratyphi A with Polymerase Chain Reaction (PCR) method appears to be a more reliable approach compared to the Widal test. On the other hand, due to increasing incidence of S. Paratyphi A infections worldwide, the need to produce a paratyphoid vaccine is essential and urgent. Hence various vaccine projects that involve clinical trials have been carried out. Overall, this review provides the insights of S. Paratyphi A, including the bacteriology, epidemiology, management and antibiotic susceptibility, diagnoses and vaccine development.

Acidic pH induced STM1485 gene is essential for intracellular replication of Salmonella.

During the course of infection, Salmonella has to face several potentially lethal environmental conditions, one such being acidic pH. The ability to sense and respond to the acidic pH is crucial for the survival and replication of Salmonella. The physiological role of one gene (STM1485) involved in this response, which is upregulated inside the host cells (by 90- to 113-fold) is functionally characterized in Salmonella pathogenesis. In vitro, the ΔSTM1485 neither exhibited any growth defect at pH 4.5 nor any difference in the acid tolerance response. The ΔSTM1485 was compromised in its capacity to proliferate inside the host cells and complementation with STM1485 gene restored its virulence. We further demonstrate that the surface translocation of Salmonella pathogenicity island-2 (SPI-2) encoded translocon proteins, SseB and SseD were reduced in the ΔSTM1485. The increase in co-localization of this mutant with lysosomes was also observed. In addition, the ΔSTM1485 displayed significantly reduced competitive indices (CI) in spleen, liver and mesenteric lymph nodes in murine typhoid model when infected by intra-gastric route. Based on these results, we conclude that the acidic pH induced STM1485 gene is essential for intracellular replication of Salmonella.

Bickerstaff's brainstem encephalitis complicating Salmonella Paratyphi A infection.

Patients with enteric fever frequently develop neurological complications during their illness. Among them, majority has encephalopathy, but focal deficits or peripheral nervous involvements are occasionally encountered. We describe a young woman who developed a neurological syndrome consistent with Bickerstaff's brainstem encephalitis, with symptoms and signs including convulsion, impaired consciousness, external ophthalmoplegia, ataxia, bulbar palsy and pyramidal signs, following Salmonella Paratyphi A infection. This is the first case report of this syndrome after S. Paratyphi A infection, and it is the second case of Bickerstaff's brainstem encephalitis complicating enteric fever reported in the literature. This case also demonstrated, for the first time, a positive anti-GQ1b IgG response in a patient with Bickerstaff's brainstem encephalitis and related disorders that appear as complications during enteric fever.

Analysis of characteristics of paratyphoid A in 157 Chinese inpatients between 1998 and 2009.

The objectives of this study were to understand the epidemic rules, clinical characteristics, and drug resistance of paratyphoid A by analyzing 157 cases in the Wenzhou area of China during a 12-year period. The subjects included in the present study were patients with paratyphoid A who were admitted to the First Affiliated Hospital of Wenzhou Medical College (Wenzhou, ZJ, China) between 1998 and 2009. The disease mainly occurred in persons aged 20 to 50 years. The peak incidence was between 2001 and 2003 (n = 85). Paratyphoid A was more likely to occur in winter and spring in this area. In many cases (33.8%), the condition was complicated by underlying diseases. The length of hospital stay was relatively long, averaging 17.68 days. The white blood cell (WBC) count was 2-8 × 10(9)/L in 88.5% of cases. Eosinophils disappeared in 51.7% of cases. The erythrocyte sedimentation rate (ESR) was not significant and lower than 60 mm/h in 88.5% of cases. Alanine aminotransferase (ALT) was ≤3-fold greater than the normal value in 84.3% of cases. The Widal test was positive in only 7.7% of our cases. The sensitivity of many antibiotics was over 90%. Paratyphoid A in the Wenzhou area has unique epidemic rules, clinical characteristics, and drug resistance. The results of our retrospective analysis are instructive for the early diagnosis and rational treatment of paratyphoid A.

SPC-P1: a pathogenicity-associated prophage of Salmonella paratyphi C.

BACKGROUND: Salmonella paratyphi C is one of the few human-adapted pathogens along with S. typhi, S. paratyphi A and S. paratyphi B that cause typhoid, but it is not clear whether these bacteria cause the disease by the same or different pathogenic mechanisms. Notably, these typhoid agents have distinct sets of large genomic insertions, which may encode different pathogenicity factors. Previously we identified a novel prophage, SPC-P1, in S. paratyphi C RKS4594 and wondered whether it might be involved in pathogenicity of the bacteria. RESULTS: We analyzed the sequence of SPC-P1 and found that it is an inducible phage with an overall G+C content of 47.24%, similar to that of most Salmonella phages such as P22 and ST64T but significantly lower than the 52.16% average of the RKS4594 chromosome. Electron microscopy showed short-tailed phage particles very similar to the lambdoid phage CUS-3. To evaluate its roles in pathogenicity, we lysogenized S. paratyphi C strain CN13/87, which did not have this prophage, and infected mice with the lysogenized CN13/87. Compared to the phage-free wild type CN13/87, the lysogenized CN13/87 exhibited significantly increased virulence and caused multi-organ damages in mice at considerably lower infection doses. CONCLUSIONS: SPC-P1 contributes pathogenicity to S. paratyphi C in animal infection models, so it is possible that this prophage is involved in typhoid pathogenesis in humans. Genetic and functional analyses of SPC-P1 may facilitate the study of pathogenic evolution of the extant typhoid agents, providing particular help in elucidating the pathogenic determinants of the typhoid agents.

Salmonella paratyphi spondylitis: a case report.

This is a case report of acute L3/4 vertebral osteomyelitis due to Salmonella paratyphi A confirmed by culture from vertebral needle biopsy. From a review of the literature this is the first reported case with bacteriological confirmation. The rarity of Salmonella paratyphi spondylitis and the options for treatment are discussed.

Fulminant hepatic failure caused by Salmonella paratyphi A infection.

We report a case of fulminant hepatic failure associated with Salmonella paratyphi A infection, in a 29-year-old patient who was admitted to the intensive care unit (ICU) with fever of two days, headache and vomiting followed by behavioural changes and disorientation. On examination, the patient appeared acutely ill, agitated, confused, and deeply jaundiced. Temperature 38.5 degrees of C, pulse 92/min, blood pressure 130/89 mmHg. Both samples of blood grew S. paratyphi A, which was sensitive to ceftriaxone and ciprofloxacin. Ceftriaxon was administered with high-dose dexamethasone. Two weeks after treatment with ceftriaxon, the patient was discharged in satisfactory condition.

Lipschütz genital ulceration: a rare manifestation of paratyphoid fever.

In 1913, a distinctive clinical entity of acute genital ulcer occurring in an adolescent girl with a non-venereal infectious aetiology was described by Lipschütz. Since the initial description, several aetiologies have been discussed, and among them, paratyphoid fever is very uncommon. After her return from a trip, a 25-year-old girl developed high fever and diarrhoea. Examination of the vulva revealed a genital ulcer. The rest of the general examination was normal. Blood cultures identified Salmonella paratyphi A, and a diagnosis of Lipschütz's ulcer associated with paratyphoid fever was made. Bacteriaemia was then treated with antibiotics and the vulvar ulceration rapidly disappeared. Lipschütz described a distinctive clinical entity of acute genital ulcers occurring in adolescents. To our knowledge, we report herein the second case associated with proved paratyphoid fever. The authors thus recommend that typhoid or paratyphoid fever should be included in the differential diagnosis of genital ulcerations.

[Typhoid and paratyphoid fevers in childhood. Apropos of 210 cases]. / Fiebres tifoparatíficas en la infancia. A propósito de 210 observaciones.

The authors reviewed 210 children with typhoid and paratyphoid fevers; 191 were infected with S. typhi, 13 with S. paratyphi A and 6 with S. paratyphi B. The proportion was higher in school children. Fever, headache, tongue furred, stupor, and hepatomegaly were the most important clinical findings. Salmonella was cultured from the blood of 42% patients, the Widal reaction was negative only in one case, and faeces culture was positive in 25%. All patients received chloramphenicol.