Therapy of experimental meningitis due to Salmonella enteritidis

Bacteriological and molecular study of Salmonella species associated with central nervous system manifestation in chicken flocks

BACKGROUND AND AIM

Salmonella species often cause systemic health problems in poultry flocks, sometimes including nervous systems manifestations. This impact of Salmonella has rarely been studied. This study aimed to define an alternative pathogenic pathway for Salmonella spp. invasion of brain tissue in chicken flocks. Brain infection produces neurological manifestations; Salmonella strains isolated from brain tissue showed the presences of two virulence genes. Confirmation of the pathway of isolates from intestinal mucosa through the blood-brain barrier was attained using experimental infections in specific pathogen-free (SPF)-day-old chicks through two routes of inoculation.

MATERIALS AND METHODS

Isolation of Salmonella spp. from five chicken flocks that showed signs of the central nervous system (CNS) effects were isolated. Isolates were characterized by serotyping, and antimicrobial assays. In addition, virulence profiles were described using detection of virulence plasmid spvC, and Salmonella plasmid sopB. A pathogenicity study of isolates in specific pathogen-free (SPF)-day-old chicks through oral and intracerebral administration performed, and experimental infection in SPF embryonated chicken eggs through intra-yolk and intra-allantoic administration was investigated. Supporting histopathology and immunohistopathology against Salmonella antigen in brain tissue were performed for flock and experimental infections.

RESULTS

Three serotypes of Salmonella were isolated from the brains of five flocks (two Salmonella Virchow, two Salmonella Kentucky, and one Salmonella Enteritidis isolates). Phage related gene sopB and plasmid-mediated operon spvC were identified in all isolated strains. The Salmonella strains were re-isolated and identified from the brain and internal organs of post-experimental infected chicks. Infected chicks showed nervous manifestations associated with Salmonella infection. The presence of positively stained Salmonella antigen in brain tissues indicates penetration of the blood-brain barrier by the Salmonella species.

CONCLUSION

Our results indicate that some virulent systemic strains of Salmonella spp. can induce CNS manifestations in chicken hosts.

Interaction of Antibiotics with Innate Host Defense Factors against Salmonella enterica Serotype Newport

It is becoming increasingly understood that the current paradigms of in vitro antimicrobial susceptibility testing may have significant shortcomings in predicting activity in vivo. This study evaluated the activity of several antibiotics alone and in combination against clinical isolates of Salmonella enterica serotype Newport (meningitis case) utilizing both conventional and physiological media. In addition, the interactions of these antibiotics with components of the innate immune system were evaluated. Azithromycin, which has performed quite well clinically despite high MICs in conventional media, was shown to be more active in physiological media and to enhance innate immune system killing. Alternatively, chloramphenicol did not show enhanced immune system killing, paralleling its inferior clinical performance to other antibiotics that have been used to treat Salmonella meningitis. These findings are important additions to the building understanding of current in vitro antimicrobial assay limitations that hopefully will amount to future improvements in these assays to better predict clinical efficacy and activity in vivo.

This study examines the pharmacodynamics of antimicrobials that are used to treat Salmonella with each other and with key components of the innate immune system. Antimicrobial synergy was assessed using time-kill and checkerboard assays. Antimicrobial interactions with innate immunity were studied by employing cathelicidin LL-37, whole-blood, and neutrophil killing assays. Ceftriaxone and ciprofloxacin were found to be synergistic in vitro against Salmonella enterica serotype Newport. Ceftriaxone, ciprofloxacin, and azithromycin each demonstrated synergy with the human cathelicidin defense peptide LL-37 in killing Salmonella. Exposure of Salmonella to sub-MICs of ceftriaxone resulted in enhanced susceptibility to LL-37, whole blood, and neutrophil killing. The activity of antibiotics in vivo against Salmonella may be underestimated in bacteriologic media lacking components of innate immunity. The pharmacodynamic interactions of antibiotics used to treat Salmonella with each other and with components of innate immunity warrant further study in light of recent findings showing in vivo selection of antimicrobial resistance by single agents in this pathogen.

IMPORTANCE It is becoming increasingly understood that the current paradigms of in vitro antimicrobial susceptibility testing may have significant shortcomings in predicting activity in vivo. This study evaluated the activity of several antibiotics alone and in combination against clinical isolates of Salmonella enterica serotype Newport (meningitis case) utilizing both conventional and physiological media. In addition, the interactions of these antibiotics with components of the innate immune system were evaluated. Azithromycin, which has performed quite well clinically despite high MICs in conventional media, was shown to be more active in physiological media and to enhance innate immune system killing. Alternatively, chloramphenicol did not show enhanced immune system killing, paralleling its inferior clinical performance to other antibiotics that have been used to treat Salmonella meningitis. These findings are important additions to the building understanding of current in vitro antimicrobial assay limitations that hopefully will amount to future improvements in these assays to better predict clinical efficacy and activity in vivo.

Salmonella Meningitis Associated with Monocyte Infiltration in Mice

In the current study, we examined the ability of Salmonella enterica serovar Typhimurium to infect the central nervous system and cause meningitis following the natural route of infection in mice. C57BL/6J mice are extremely susceptible to systemic infection by Salmonella Typhimurium because of loss-of-function mutations in Nramp1 (SLC11A1), a phagosomal membrane protein that controls iron export from vacuoles and inhibits Salmonella growth in macrophages. Therefore, we assessed the ability of Salmonella to disseminate to the central nervous system (CNS) after oral infection in C57BL/6J mice expressing either wild-type (resistant) or mutant (susceptible) alleles of Nramp1. In both strains, oral infection resulted in focal meningitis and ventriculitis with recruitment of inflammatory monocytes to the CNS. In susceptible Nramp1^-/- mice, there was a direct correlation between bacteremia and the number of bacteria in the brain, which was not observed in resistant Nramp1^+/+ mice. A small percentage of Nramp1^+/+ mice developed severe ataxia, which was associated with high bacterial loads in the CNS as well as clear histopathology of necrotizing vasculitis and hemorrhage in the brain. Thus, Nramp1 is not essential for Salmonella entry into the CNS or neuroinflammation, but may influence the mechanisms of CNS entry as well as the severity of meningitis.

Reappraisal of parenteral antimicrobial therapy for nontyphoidal Salmonella enteric infection in children

Increasing antimicrobial resistance in nontyphoidal Salmonella (NTS) species complicates the use of antibiotics if indicated. We investigated the impact of antimicrobial resistance on clinical outcomes and discussed how to use antibiotics rationally. Hospitalized children in 2005-2006 with stool cultures positive for NTS were identified. The clinical and microbiological features were retrospectively reviewed. A total of 683 children were included [371 (54.3%) male; 89.5% <5 years of age]. Antibiotics were given to 56.5% of the patients; third-generation cephalosporin was the most commonly used drug class. Cases receiving antibiotics that were inactive in vitro did not have more complications than those receiving antibiotics active in vitro. Complications occurred in 7.9% of the patients, with bacteraemia being the most common (57.4%). Compared to the others, patients with longer febrile duration and higher C-reactive protein (CRP) levels (CRP ≥100 mg/L) were more frequently put on empirical antimicrobial therapy and had more complications. These patients usually had shorter hospitalization and duration of fever if antimicrobial agents that can reach high tissue concentrations in the intestinal mucosa were administered, such as fluoroquinolone or ceftriaxone. It is concluded that adequate antibiotics may be clinically beneficial to a subset of patients with high CRP and longer duration of fever among children with NTS enteritis. To prevent the induction of antibiotic resistance from this therapy, we suggested a short course (3-5 days) of intravenous ceftriaxone for such patients, which would lead to a faster clinical recovery.

Salmonella meningitis in an adult with type B viral hepatitis and an incidental schwannoma

Salmonella meningitis is an unusual complication of Salmonella sepsis that occurs almost exclusively in infants and young children. Cases that do occur in adults are associated with a high morbidity and mortality. The present study concerns a rare case of Salmonella meningitis, the first to be reported in Qatar, in a previously healthy young adult man who was admitted with fever, headache and nuchal rigidity. Cerebrospinal fluid (CSF) culture produced Salmonella paratyphi A, although cultures of blood were negative. The patient was admitted to the medical intensive care unit (MICU) and assisted with mechanical ventilation for 1 week, then transferred to the medical ward where he exhibited progressive improvement on treatment with meropenam for 3 weeks. The patient was found to have an incidental schwannoma causing right-sided hydronephrosis, and hydroureter, treated with double J stent insertion. He was discharged in good condition without any neurological sequelae.

The outcome of non-typhoidal salmonella meningitis in Malawian children, 1997-2006

INTRODUCTION

The clinical course and outcome of non-typhoidal salmonella (NTS) meningitis in Malawian children over a 10-year period (1997-2006) is described.

METHODS

Demographic, clinical and laboratory data were collected for all children over 2 months of age admitted with salmonella meningitis to Queen Elizabeth Central Hospital from 1997 to 2006. In the 1st year, salmonellae were susceptible to chloramphenicol, and children received 2 weeks of chloramphenicol treatment. When NTS resistance to chloramphenicol started to appear in 1998, treatment was changed to ceftriaxone. From 2002, the duration of antibiotic therapy was extended to 4-weeks which included 2 weeks of intravenous ceftriaxone and a further 2 weeks of oral ciprofloxacin.

RESULTS

The in-hospital case fatality rate (CFR) was 52.3% (48.2% until 2002 and 53.9% after prolonged antibiotic therapy was introduced). Of the survivors, one in 12 (8.3%) became completely well (sequelae-free) in the period 1997-2001 while 18 of 31 survivors (58.1%) made a complete recovery during 2002-2006 (p<0.01). After the 4-week course of antimicrobial therapy was introduced, the number of relapses or recurrences fell from nine in 15 (60%) survivors treated with chloramphenicol or ceftriaxone to three in 35 (8.7%) survivors who received 4 weeks of antibiotics (p<0.0001).

CONCLUSION

In Malawi, salmonella meningitis has a CFR of approximately 50%, which has remained constant over many years. Residual morbidity, however, has decreased over 10 years, despite rising numbers of multi-drug-resistant cases of NTS. This improvement might be owing to better treatment and management and/or reduced pathogenicity of the multi-drug-resistant bacteria.

Oral infection of mice with Salmonella enterica serovar Typhimurium causes meningitis and infection of the brain

Background

Salmonella meningitis is a rare and serious infection of the central nervous system following acute Salmonella enterica sepsis. For this pathogen, no appropriate model has been reported in which to examine infection kinetics and natural dissemination to the brain.

Methods

Five mouse lines including C57BL/6, Balb/c, 129S6-Slc11a1tm1^Mcg, 129S1/SvImJ, B6.129-Inpp5dtm1^Rkh were used in the murine typhoid model to examine the dissemination of systemic Salmonella enterica serovar Typhimurium following oral infection.

Results

We report data on spontaneous meningitis and brain infection following oral infection of mice with Salmonella enterica serovar Typhimurium.

Conclusion

This model may provide a system in which dissemination of bacteria through the central nervous system and the influence of host and bacterial genetics can be queried.

Extended-spectrum-cephalosporin resistance in Salmonella enterica isolates of animal origin

A total of 112 out of 5,709 Salmonella enterica isolates from domestic animal species exhibited decreased susceptibilities to ceftiofur and ceftriaxone, and each possessed the blaCMY gene. Ten Salmonella serotypes were significantly more likely to include resistant isolates. Isolates from turkeys, horses, cats, and dogs were significantly more likely to include resistant isolates.

Treatment of Salmonella meningitis: two case reports and a review of the literature

BACKGROUND

Salmonella species now represent a leading cause of Gram-negative bacterial meningitis in the developing world. Various drugs have been used for the treatment of Salmonella meningitis over the past decades, but mortality, neurologic sequelae and relapse rates remain high. In this report we describe two children aged 8 and 9 months who presented within a week to our hospital with Salmonella meningitis. They were treated with penicillin and chloramphenicol but progressed rapidly to death within 48 h.

AIM

The aim of this article is to review all published English literature on the treatment of Salmonella meningitis and identify the best drug option for its treatment. This was done by comparing the outcomes such as cure, failure, relapse, and death rates.

METHOD

A Medline electronic search was carried out to find and retrieve articles that have been published since 1987, when the last review of Salmonella meningitis was done.

RESULTS

Salmonella typhimurium was the commonest organism reported, and 89.7% of infections occurred in children less than 1 year old. Fluoroquinolones had a cure rate of 88.9%, while the third-generation cephalosporins had a cure rate of 84.6%. Conventional antibiotics (chloramphenicol, ampicillin, and cotrimoxazole) had a cure rate of 41.2%, a relapse rate of 11.8%, and an associated mortality of 44.7%. Treatment with fluoroquinolone and imipenem resulted in no deaths. There were, however, only two cases that were treated with imipenem.

CONCLUSION

When Salmonella meningitis is suspected, third-generation cephalosporins, with or without a fluoroquinolone, may be the best option for treatment.

Salmonella meningitis in Thai infants: clinical case reports

Between June 1988 and September 1996 12 of 65 infants (18%) admitted to the Department of Pediatrics, Ramathibodi Hospital, Bangkok, Thailand with purulent meningitis were infected with Salmonella spp. Their ages ranged from 1.5 to 6 months. Six of the infants had diarrhoea, 9 had seizures, and 11 had subdural effusion or empyema. Six infants required surgical treatment; 2 had brain abscesses. Salmonella was recovered from the cerebrospinal fluid of 11 infants and from the subdural fluid of 10. Eight infants were successfully treated with cefotaxime alone or in combination with co-trimoxazole, one with co-trimoxazole, and one with the combination of co-trimoxazole and ampicillin. The duration of treatment was 6 weeks, except for one patient who had a large brain abscess and was treated for 8 weeks. The last 2 patients, despite the fact that the organisms were susceptible to cefotaxime, failed to respond clinically to appropriate doses of it. Both were cured after ciprofloxacin was added to the therapy. Ciprofloxacin is probably the drug of choice to be used in addition to the previously used antibiotics for severe cases of Salmonella meningitis in infants.

Salmonella meningitis in children in far north Queensland

Seven cases of Salmonella meningitis have occurred in infants in Far North Queensland since 1982. The mean age of onset was 2.8 months, and at least five of the cases were caused by Salmonella virchow. Five of the cases had significant complications during the acute illness: all required prolonged (median 34 days) inpatient management, and four developed permanent neurological sequelae. S. virchow is the serovar most frequently isolated from infants in Far North Queensland. The source of S. virchow infections in these infants remains uncertain, but transmission may occur through cross-infection and person-to-person transmission in the home.