Tularemia treatment: experimental and clinical data

Tularemia is a zoonosis caused by the Gram negative, facultative intracellular bacterium Francisella tularensis. This disease has multiple clinical presentations according to the route of infection, the virulence of the infecting bacterial strain, and the underlying medical condition of infected persons. Systemic infections (e.g., pneumonic and typhoidal form) and complications are rare but may be life threatening. Most people suffer from local infection (e.g., skin ulcer, conjunctivitis, or pharyngitis) with regional lymphadenopathy, which evolve to suppuration in about 30% of patients and a chronic course of infection. Current treatment recommendations have been established to manage acute infections in the context of a biological threat and do not consider the great variability of clinical situations. This review summarizes literature data on antibiotic efficacy against F. tularensis in vitro, in animal models, and in humans. Empirical treatment with beta-lactams, most macrolides, or anti-tuberculosis agents is usually ineffective. The aminoglycosides gentamicin and streptomycin remain the gold standard for severe infections, and the fluoroquinolones and doxycycline for infections of mild severity, although current data indicate the former are usually more effective. However, the antibiotic treatments reported in the literature are highly variable in their composition and duration depending on the clinical manifestations, the age and health status of the patient, the presence of complications, and the evolution of the disease. Many patients received several antibiotics in combination or successively. Whatever the antibiotic treatment administered, variable but high rates of treatment failures and relapses are still observed, especially in patients treated more then 2-3 weeks after disease onset. In these patients, surgical treatment is often necessary for cure, including drainage or removal of suppurative lymph nodes or other infectious foci. It is currently difficult to establish therapeutic recommendations, particularly due to lack of comparative randomized studies. However, we have attempted to summarize current knowledge through proposals for improving tularemia treatment which will have to be discussed by a group of experts. A major factor in improving the prognosis of patients with tularemia is the early administration of appropriate treatment, which requires better medical knowledge and diagnostic strategy of this disease.

Case Studies and Literature Review of Francisella tularensis-Related Prosthetic Joint Infection

Tularemia is a zoonotic infection caused by Francisella tularensis. Its most typical manifestations in humans are ulceroglandular and glandular; infections in prosthetic joints are rare. We report 3 cases of F. tularensis subspecies holarctica-related prosthetic joint infection that occurred in France during 2016-2019. We also reviewed relevant literature and found only 5 other cases of Francisella-related prosthetic joint infections worldwide, which we summarized. Among those 8 patients, clinical symptoms appeared 7 days to 19 years after the joint placement and were nonspecific to tularemia. Although positive cultures are typically obtained in only 10% of tularemia cases, strains grew in all 8 of the patients. F. tularensis was initially identified in 2 patients by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry; molecular methods were used for 6 patients. Surgical treatment in conjunction with long-term antimicrobial treatment resulted in favorable outcomes; no relapses were seen after 6 months of follow-up.

Ulceroglandular Infection and Bacteremia Caused by Francisella salimarina in Immunocompromised Patient, France

Although Francisella tularensis is a well-known, highly virulent bacterium that causes tularemia in humans, other Francisella species have been associated with sporadic human infections. We describe a human cutaneous infection with bacteremia caused by F. salimarina, a Francisella species recently identified from seawater and fishes, in an immunocompromised patient in France.

Amoebae can promote the survival of Francisella species in the aquatic environment

Francisella tularensis, a tier 1 select agent, is the causative bacterium of tularemia, a zoonosis with a large animal reservoir. However, F. tularensis, like many other Francisella species, is assumed to have an aquatic reservoir. The mechanisms of Francisella species persistence in surface water remain poorly characterized. In this study, we deeply investigated the long-term interactions of the tularemia agent F. tularensis subsp. holarctica, F. novicida or F. philomiragia with amoebae of the Acanthamoeba species. In amoeba plate screening tests, all the Francisella species tested resisted the attack by amoebae. In in vitro infection models, intra-amoebic growth of Francisella varied according to the involved bacterial species and strains, but also the amoeba culture medium used. In co-culture models, the amoebae favoured Francisella survival over 16 days, which was likely dependent on direct contact between bacteria and amoebae for F. novicida and on amoeba-excreted compounds for F. novicida and for F. tularensis. In a spring water co-culture model, amoebae again enhanced F. novicida survival and preserved bacterial morphology. Overall, our results demonstrate that amoebae likely promote Francisella survival in aquatic environments, including the tularemia agent F. tularensis. However, bacteria-amoebae interactions are complex and depend on the Francisella species considered.

Presence of Francisella tularensis subsp. holarctica DNA in the Aquatic Environment in France

In 2018, the incidence of tularemia increased twofold in the west of France, with many pneumonic forms, suggesting environmental sources of infection. We investigated the presence of Francisellatularensis subsp. holarctica and other Francisella species DNA in the natural aquatic environment of this geographic area. Two sampling campaigns, in July 2019 and January 2020, allowed the collection of 87 water samples. Using a combination of real-time PCR assays, we tested the presence of either Francisella sp., F. tularensis/F. novicida, and F. tularensis subsp. holarctica, the latter being the only tularemia agent in Europe. Among 57 water samples of the first campaign, 15 (26.3%) were positive for Francisella sp., nine (15.8%) for F. tularensis and/or F. novicida, and four (7.0%) for F. tularensis subsp. holarctica. Ratios were 25/30 (83.3%), 24/30 (80.0%), and 4/30 (13.3%) for the second campaign. Among the thirty sites sampled during the two campaigns, nine were positive both times for Francisella sp., seven for F. tularensis and/or F. novicida, and one for F. tularensis subsp. holarctica. Altogether, our study reveals a high prevalence of Francisella sp. DNA (including the tularemia agent) in the studied aquatic environment. This aquatic environment could therefore participate in the endemicity of tularemia in the west of France.

Tularemia: A Case Series of Patients Diagnosed at the National Reference Center for Rickettsioses From 2008 to 2017

BACKGROUND

We describe the epidemiological, clinical, and prognostic aspects of 177 tularemia cases diagnosed at the National Reference Center for rickettsioses, coxiellosis, and bartonelloses between 2008 and 2017.

METHODS

All patients with a microbiological diagnosis of tularemia made in the laboratory were included. Clinical and epidemiological data were collected retrospectively from clinicians in charge of patients using a standardized questionnaire. Diagnostic methods used were indirect immunofluorescence serology, real-time polymerase chain reaction (PCR), and universal PCR targeting the 16S ribosomal ribonucleic acid gene.

RESULTS

The series included 54 females and 123 males (sex ratio, 2.28; mean age, 47.38 years). Eighty-nine (50.2%) were confirmed as having tularemia on the basis of a positive Francisella tularensis PCR or seroconversion, and 88 (49.8%) were considered as probable due to a single positive serum. The regions of France that were most affected included Pays de la Loire (22% of cases), Nouvelle Aquitaine (18.6% of cases), and Grand Est (12.4% of cases). Patients became infected mainly through contact with rodents or game (38 cases, 21.4%), through tick-bites (23 cases, 12.9%), or during outdoor leisure activities (37 cases, 20.9%). Glandular and ulceroglandular forms were the most frequent (109 cases, 61.5%). Two aortitis, an infectious endocarditis, a myocarditis, an osteoarticular infection, and a splenic hematoma were also diagnosed. Tularemia was discovered incidentally in 54.8% of cases. Seventy-eight patients were hospitalized, and no deaths were reported.

CONCLUSIONS

Our data suggest that in an endemic area and/or in certain epidemiological contexts, tularemia should be sought to allow an optimized antibiotic therapy and a faster recovery.

Genomic trajectories to fluoroquinolone resistance in Francisella tularensis subsp. holarctica live vaccine strain

OBJECTIVES

Fluoroquinolone (FQ)-resistant mutants were previously selected from the live vaccine strain (LVS) of Francisella tularensis (F. tularensis) subsp. holarctica. This study further characterised all genetic changes that occurred in these mutants during the evolutionary trajectory toward high-level FQ resistance, and their potential impact on F. tularensis antibiotic resistance and intracellular fitness.

METHODS

The whole genomes of FQ-resistant mutants were determined and compared with those of their parental strain. All detected mutations were evaluated for their potential impact on FQ resistance and intracellular multiplication of F. tularensis.

RESULTS

As compared with the parental LVS genome, 28 mutations were found in the derived FQ-resistant mutants. These mutations involved all genes encoding type II topoisomerases (i.e. gyrA, gyrB, parC, and parE). Interestingly, some of them were not previously associated with FQ resistance, warranting further characterisation. Mutations associated with FQ resistance were also found in other genes, including three encoding proteins involved in transport processes. Most of the detected mutations did not alter multiplication of the corresponding mutants in J774 cells. In contrast, all mutations at locus FTL_0439 encoding FupA/B, a membrane protein involved in iron transport, were associated with FQ resistance and fitness loss.

CONCLUSION

FQ resistance in F. tularensis is complex and may involve single or combined mutations in genes encoding type II topoisomerases, transport systems and FupA/B. In vivo studies are now required to assess the potential role of these mutations in FQ treatment failures.

Optimized MALDI TOF Mass Spectrometry Identification of Francisella tularensis Subsp. holarctica

Francisella tularensis is a tier 1 agent causing the zoonosis tularemia. This highly infectious Gram-negative bacterium is occasionally isolated from human samples (especially blood samples) in routine clinical microbiology laboratories. A rapid and accurate method for identifying this pathogen is needed in order to optimize the infected patient’s healthcare management and prevent contamination of the laboratory personnel. MALDI TOF mass spectrometry has become the gold standard for the rapid identification of most human pathogens. However, F. tularensis identification using such technology and commercially available databases is currently considered unreliable. Real-time PCR-based methods for rapid detection and accurate identification of F. tularensis are not available in many laboratories. As a national reference center for tularemia, we developed a MALDI TOF database allowing accurate identification of the species F. tularensis and its differentiation from the closely related neighbor species F. tularensis subsp. novicida and F. philomiragia. The sensitivity and specificity of this database were validated by testing 71 F. tularensis strains and 165 strains from 63 species not belonging to the Francisella genus. We obtained accurate identification at the species level and differentiation of all the tested bacterial strains. In particular, F. tularensis could be accurately differentiated from other small Gram-negative bacilli occasionally isolated from human samples, including species of the HACEK group and Brucella melitensis.

Antibiotic susceptibility of Francisella tularensis subsp. holarctica strains isolated from tularaemia patients in France between 2006 and 2016

Objectives

To determine the in vitro susceptibility to 18 antibiotics of human strains of Francisella tularensis isolated in France between 2006 and 2016, to check the absence of acquired resistance and to evaluate potential therapeutic alternatives.

Methods

Fifty-nine clinically unrelated F. tularensis subsp. holarctica strains identified at the French National Reference Centre for Francisella as belonging to the phylogenetic subclade B.FTNF002-00 were used. MICs were determined in CAMHB medium supplemented with 2% PolyViteX®, using the CLSI broth microdilution method.

Results

All strains were susceptible to fluoroquinolones (ofloxacin, ciprofloxacin, levofloxacin and moxifloxacin; MIC range: 0.016-0.25 mg/L), aminoglycosides (gentamicin and tobramycin; MIC range: ≤0.03-0.25 mg/L), doxycycline (MIC range: 0.125-0.25 mg/L) and chloramphenicol (MIC range: 0.5-2 mg/L). The erythromycin MIC range (0.5-2 mg/L) confirmed that all isolates belonged to biovar I of F. tularensis subsp. holarctica. Azithromycin and telithromycin displayed lower MIC ranges (0.25-1 and 0.03-0.5 mg/L, respectively). The tigecycline MIC range (0.25-1 mg/L) was slightly higher than that of doxycycline. All strains were resistant to ampicillin, meropenem, daptomycin, clindamycin and linezolid.

Conclusions

F. tularensis strains isolated in France remain susceptible to antibiotic classes recommended for tularaemia treatment. Because fluoroquinolones display the lowest MIC90, have bactericidal activity and have lower therapeutic failure rates compared with doxycycline, they may be advocated as first-line treatment of mild cases of tularaemia, predominant in Europe. MIC data also indicate that azithromycin or telithromycin may be possible therapeutic options against biovar I strains from Western Europe in case of contraindication to first-line antibiotics.

Tularemia as a waterborne disease: a review

Francisella tularensis is a Gram-negative, intracellular bacterium causing the zoonosis tularemia. This highly infectious microorganism is considered a potential biological threat agent. Humans are usually infected through direct contact with the animal reservoir and tick bites. However, tularemia cases also occur after contact with a contaminated hydro-telluric environment. Water-borne tularemia outbreaks and sporadic cases have occurred worldwide in the last decades, with specific clinical and epidemiological traits. These infections represent a major public health and military challenge. Human contaminations have occurred through consumption or use of F. tularensis-contaminated water, and various aquatic activities such as swimming, canyoning and fishing. In addition, in Sweden and Finland, mosquitoes are primary vectors of tularemia due to infection of mosquito larvae in contaminated aquatic environments. The mechanisms of F. tularensis survival in water may include the formation of biofilms, interactions with free-living amoebae, and the transition to a 'viable but nonculturable' state, but the relative contribution of these possible mechanisms remains unknown. Many new aquatic species of Francisella have been characterized in recent years. F. tularensis likely shares with these species an ability of long-term survival in the aquatic environment, which has to be considered in terms of tularemia surveillance and control.

Bacteremia caused by multidrug-resistant bacteria in a French university hospital center: 3 years of collection

BACKGROUND

The aim of the study was to describe the profile of patients and the characteristics of all bacteremias caused by multidrug-resistant (MDR) bacterial strains in a teaching hospital and to assess the mortality related to these events.

METHODS

A monocentric retrospective observational cohort study was conducted. All patients with bacteremia caused by MDR bacteria between 2011 and 2013 were included. The characteristics of patients and bacteremias, antibiotic therapy within the first day, and 30-day mortality were collected from the electronic medical records database.

RESULTS

A total of 228 patients were included with bacteremias caused by Enterobacteriaceae-producing extended-spectrum β-lactamase (n = 102), Enterobacteriaceae overproducing AmpC β-lactamase (n = 59), carbapenem-resistant Enterobacteriaceae (n = 3), ceftazidime- or carbapenem-resistant Acinetobacter baumannii (n = 2), ceftazidime- or carbapenem-resistant Pseudomonas aeruginosa (n = 23), methicillin-resistant Staphylococcus aureus (n = 40), and vancomycin-resistant Enterococcus (n = 2). The median Charlson comorbidity score was 6. Inappropriate antibiotic therapy was prescribed in 41.7% of bacteremias, and 30-day mortality was 23%. For 20.9% of the patients who had had a positive bacteriologic sample in the preceding 2 months, the initial antibiotic therapy was inappropriate.

CONCLUSION

In this cohort of bacteremia patients, a high rate of mortality and numerous patient comorbidities were observed. Taking greater account of antecedents of MDR bacterial infections could improve the rate of appropriate initial antibiotic therapy.