Prognostic factors and clinical features of non-typhoid Salmonella bacteremia in adults

Comparison of global transcriptomes for nontyphoidal Salmonella clinical isolates from pediatric patients with and without bacteremia after their interaction with human intestinal epithelial cells in vitro

BACKGROUND

Nontyphoidal Salmonella (NTS) outbreaks of invasive diseases are increasing. Whether the genetic diversity of invasive NTS correlates with the clinical characteristics and bacteremia development in NTS infections remains unclear. In this study, we compared the global transcriptomes between bacteremic and nonbacteremic NTS strains after their interaction with human intestinal epithelial cells in vitro.

METHODS

We selected clinical isolates obtained from stool and blood samples of patients with or without bacteremia and patients with high and low C-reactive protein (CRP) levels. The bacterial RNA samples were isolated after coculturing with Caco-2 cells for RNA sequencing and subsequent analyses.

RESULTS

CRP is an unreliable predictive maker for NTS bacteremia with a median CRP level of 1.6 mg/dL. Certain Salmonella Pathogenicity Island (SPI)-1 genes (sipC, sipA, sicA, sipD, and sipB), SPI-2 genes (ssaP, ssrA, and ssaS), and six SPI-4 genes (siiA, siiB, siiC, siiD, siiE, and siiF) remained upregulated in the bacteremic blood-derived strains but significantly downregulated in the nonbacteremic strains after their interaction with Caco-2 cells. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis identified that arginine biosynthesis, ascorbate and aldarate metabolism, and phosphotransferase system pathways were activated in bacteremic NTS strains after Caco-2 cell priming.

CONCLUSION

CRP levels were not correlated with bacteremia development. Significant regulation of certain SPI genes in bacteremic NTS strains after Caco-2 cell priming; bacteremia development might be influenced by the host immune response and the extent to which specific metabolism pathways in NTS strains can be prevented from invading the bloodstream.

Toxin-Antitoxin Systems: A Key Role on Persister Formation in Salmonella enterica Serovar Typhimurium

The toxin and antitoxin modules in bacteria consist of a toxin molecule that has activity to inhibit various cellular processes and its cognate antitoxin that neutralizes the toxin. This system is considered taking part in the formation of persister cells, which are a subpopulation of recalcitrant cells able to survive antimicrobial treatment without any resistance mechanisms. Importantly, persisters have been associated with long-term infections and treatment failures in healthcare settings. It is a public health concern since persisters can be involved in the evolution and dissemination of antimicrobial resistance amidst the aggravating spread of multidrug-resistant bacteria and insufficient novel antimicrobial therapy to tackle this issue. Salmonella enterica serovar Typhimurium is one of the most prevalent Salmonella serotypes in the world and is a leading cause of food-borne salmonellosis. S. Typhimurium has been known to cause persistent infection and a wealth of investigations on Salmonella persisters indicates that toxin and antitoxin modules play a role in mediating the phenotypic switch of persisters, rendering its survival ability in the presence of antimicrobial agents. In this review, we discuss findings regarding mechanisms that underly persistence in S. Typhimurium, especially the involvement of toxin and antitoxin modules.

Complications and mortality of non-typhoidal salmonella invasive disease: a global systematic review and meta-analysis

BACKGROUND

Non-typhoidal salmonella can cause serious, life-threatening invasive infections involving the bloodstream and other normally sterile sites. We aimed to systematically review the prevalence of complications and case-fatality ratio (CFR) of non-typhoidal salmonella invasive disease to provide contemporary global estimates and inform the development of vaccine and non-vaccine interventions.

METHODS

We did a global systematic review and meta-analysis of studies investigating the complications and mortality associated with non-typhoidal salmonella invasive disease. We searched Embase, MEDLINE, Web of Science, and PubMed for peer-reviewed, primary research articles published from database inception up to June 4, 2021, with no restrictions on language, country, date, or participant demographics. Only studies reporting the proportion of complications or deaths associated with non-typhoidal salmonella invasive disease, confirmed by culture of samples taken from a normally sterile site (eg, blood or bone marrow) were included. We excluded case reports, case series, policy reports, commentaries, editorials, and conference abstracts. Data on the prevalence of complications and CFR were abstracted. The primary outcomes were to estimate the prevalence of complications and CFR of non-typhoidal salmonella invasive disease. We calculated an overall pooled CFR estimate and pooled CFR stratified by UN region, subregion, age group, and by serovar when available with a random-effects meta-analysis. A risk-of-bias assessment was done, and heterogeneity was assessed with Cochran's Q Test, I2, and τ2. This study was done in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, and is registered with PROSPERO, CRD42020202293.

FINDINGS

The systematic review returned a total of 8770 records. After duplicates were removed, 5837 titles and abstracts were screened, yielding 84 studies from 35 countries after exclusions. Of these included studies, 77 (91·7%) were hospital-based and 66 (78·6%) were located in Africa or Asia. Among 55 studies reporting non-typhoidal salmonella disease-associated complications, a total of 45 different complications were reported and 1824 complication events were identified among 6974 study participants. The most prevalent complication was septicaemia, occurring in 171 (57·2%) of 299 participants, followed by anaemia in 580 (47·3%) of 1225 participants. From 81 studies reporting the CFR of non-typhoidal salmonella invasive disease, the overall pooled CFR estimate was 14·7% (95% CI 12·2-17·3). When stratified by UN region, the pooled CFR was 17·1% (13·6-21·0) in Africa, 14·0% (9·4-19·4) in Asia, 9·9% (6·4-14·0) in Europe, and 9·6% (0·0-25·1) in the Americas. Of all 84 studies, 66 (78·6%) had an overall high risk of bias, 18 (21·4%) had a moderate risk, and none had a low risk. Substantial heterogeneity (I2>80%) was observed in most (15 [65·2%] of 23) CFR estimates.

INTERPRETATION

Complications were frequent among individuals with non-typhoidal salmonella invasive disease and approximately 15% of patients died. Clinicians, especially in African countries, should be aware of non-typhoidal salmonella invasive disease as a cause of severe febrile illness. Prompt diagnoses and management decisions, including empiric antimicrobial therapy, would improve patient outcomes. Additionally, investments in improving clinical microbiology facilities to identify non-typhoidal salmonella and research efforts towards vaccine development and non-vaccine prevention measures would prevent non-typhoidal salmonella invasive disease-associated illness and death.

FUNDING

EU Horizon 2020 research and innovation programme.

Clinical presentation and outcomes of non-typhoidal Salmonella infections in patients with cancer

Background

Non-typhoidal Salmonella (NTS) infection is thought to be more severe in cancer patients, but this has not been studied since the development of new cancer therapies, increasing antibiotic resistance and the introduction of new antibiotics. We sought to describe the demographic characteristics, microbiological findings, clinical manifestations, and outcomes of NTS infections in cancer patients at our institution.

Methods

We reviewed microbiology laboratory records and identified patients who had cancer and from whom NTS organisms were recovered between January 1, 2000 and December 31, 2013, at a comprehensive cancer center in Houston, Texas. Descriptive statistics were used to summarize patient characteristics, clinical presentation and outcomes.

Results

We identified 110 isolates from 82 patients with 88 episodes of NTS infection (including five relapses [6%] in four patients, and two consecutive episodes in one patient). Fifty-five patients (67%) had hematologic malignancies. Most NTS isolates were susceptible to the commonly prescribed antimicrobials. Sixty-nine percent of patients had sepsis and one-third had severe sepsis or septic shock. Gastroenteritis, bacteremia, or both were present in 69% of patients, and the rest had focal infection. Mortality at 30 days was low (8%). Relapses occurred only in patients receiving ≤ 10 days of antibiotic therapy.

Conclusions

NTS affects predominantly patients with hematologic malignancies, followed by gastrointestinal and genitourinary cancers. Invasive disease, sepsis, and septic shock are common presentations among admitted patients. Antimicrobial prophylaxis may not prevent NTS infection. Thirty-day mortality and attributable mortality rates were low in our series compared to older case series. Early appropriate antibiotic therapy may have had a role in decreasing mortality. Relapses occurred in patients receiving ≤ 10 days of therapy, suggesting the need for longer duration of antibiotic therapy in cancer patients with uncomplicated NTS infections.

Clinical characteristics in adult patients with Salmonella bacteremia and analysis of ciprofloxacin-nonsusceptible isolates

BACKGROUND/PURPOSE

The purpose of this study is to describe clinical characteristics of Salmonella bacteremia in adult patients and analyze ciprofloxacin-nonsusceptible isolates.

METHODS

A total of 101 Salmonella blood isolates from adult patients were collected from January 2011 to December 2013 in MacKay Memorial Hospital. Eight ciprofloxacin-nonsusceptible Salmonella blood isolates were screened for carbapenemase and other β lactamase genes. Isolates were examined by PCR for the quinolone resistance-determining region (QRDR) of all subunits for DNA gyrase (gyrA and gyrB) genes and topoisomerase IV (parC and parE) genes.

RESULTS

There were 22 (21.78%) S. enterica serovar B, 5 (4.95%) S. enterica serovar C1, 7 (6.93%) S. enterica serovar C2, 65 (64.36%) S. enterica serovar D, and 2 (1.98%) S. enterica serovar Typhi (S. typhi) isolates. β-lactamase gene screening and sequencing yielded only one blaCMY-2-positive isolate. In multivariate risk factor analysis, renal insufficiency [odds ratio (OR) 3.774; p = 0.020] and heart disease (OR 2.922; p = 0.027) were more common among elderly patients (≥65 years). Independent risk factors for ciprofloxacin-nonsusceptible strains included S. enterica serovar C2 (OR 28.430; p = 0.032), renal insufficiency (OR 13.927; p = 0.032), and immunosuppression agent usage (OR 60.082; p = 0.006). 87.50% (7/8) of isolates had gyrA mutation, 62.50% (5/8) had parC mutation, and none had gyrB and parE mutations. Isolates with both Ser83Phe/Asp87Asn gyrA and Thr57Ser/Ser80Ile parC mutation genes were highly ciprofloxacin-resistant (minimum inhibitory concentration ≥4 mg/L).

CONCLUSIONS

Elderly patients with renal insufficiency and heart disease were at risk for Salmonella bacteremia. Those for ciprofloxacin-nonsusceptible strains included S. enterica serovar C2, renal insufficiency, and immunosuppression agent usage. The 8 ciprofloxacin-nonsusceptible isolates carried gyrA and parC mutations, which cause resistance that poses a major concern.

Helicobacter and salmonella persistent infection strategies

Some host-adapted bacterial pathogens are capable of causing persistent infections in humans. For example, Helicobacter pylori inhabits the human gastric mucosa and persistence can be lifelong. Salmonella enterica serovar Typhi causes systemic infections that involve colonization of the reticuloendothelial system and some individuals become lifelong carriers. In this review, I compare and contrast the different lifestyles of Helicobacter and Salmonella within the host and the strategies they have evolved to persist in mammalian hosts. Persistently infected carriers serve as the reservoirs for these pathogens, and the carrier state is an essential feature that is required for survival of the bacteria within a restricted host population. Therefore, investigating the chronic carrier state should provide insight into bacterial survival strategies, as well as new therapeutic approaches for treatments.

The Salmonella SPI2 effector SseI mediates long-term systemic infection by modulating host cell migration

Host-adapted strains of Salmonella enterica cause systemic infections and have the ability to persist systemically for long periods of time despite the presence of a robust immune response. Chronically infected hosts are asymptomatic and transmit disease to naïve hosts via fecal shedding of bacteria, thereby serving as a critical reservoir for disease. We show that the bacterial effector protein SseI (also called SrfH), which is translocated into host cells by the Salmonella Pathogenicity Island 2 (SPI2) type III secretion system (T3SS), is required for Salmonella typhimurium to maintain a long-term chronic systemic infection in mice. SseI inhibits normal cell migration of primary macrophages and dendritic cells (DC) in vitro, and such inhibition requires the host factor IQ motif containing GTPase activating protein 1 (IQGAP1), an important regulator of cell migration. SseI binds directly to IQGAP1 and co-localizes with this factor at the cell periphery. The C-terminal domain of SseI is similar to PMT/ToxA, a bacterial toxin that contains a cysteine residue (C1165) that is critical for activity. Mutation of the corresponding residue in SseI (C178A) eliminates SseI function in vitro and in vivo, but not binding to IQGAP1. In addition, infection with wild-type (WT) S. typhimurium suppressed DC migration to the spleen in vivo in an SseI-dependent manner. Correspondingly, examination of spleens from mice infected with WT S. typhimurium revealed fewer DC and CD4⁺ T lymphocytes compared to mice infected with ΔsseI S. typhimurium. Taken together, our results demonstrate that SseI inhibits normal host cell migration, which ultimately counteracts the ability of the host to clear systemic bacteria.

Bacteria belonging to the genus Salmonella are capable of causing long-term chronic systemic infections, and bacteria primarily reside within macrophages in lymphoid tissues and sporadically are shed in the feces. These persistently infected individuals serve as a significant reservoir for disease transmission. Despite the importance of Salmonella as a human pathogen, relatively little is known about the host immune response or virulence mechanisms of long-term systemic infections. Host-adapted Salmonella strains invade and manipulate host cells by releasing specialized bacterial effector proteins into the host cell. We show that one of these bacterial effector proteins, SseI (SrfH), is required for Salmonella to maintain a long-term chronic systemic infection in mice. SseI is able to block the migration of host immune cells and consequentially attenuate the host's ability to clear systemic bacteria. SseI accomplishes this inhibitory activity in part by associating with the host protein IQGAP1, an important regulator of cell migration. The amino acid sequence of SseI is similar to several other protein sequences of known bacterial pathogens, including PMT/ToxA, a toxin, indicating that these factors may function similarly to one another and may comprise a new family of bacterial effector proteins.