Bordetella holmesii: an under-recognised Bordetella species

Laure F Pittet, Stéphane Emonet, Jacques Schrenzel, Claire-Anne Siegrist, Klara M Posfay-Barbe

Bordetella holmesii, first described in 1995, is believed to cause both invasive infections (bacteraemia, meningitis, endocarditis, pericarditis, pneumonia, and arthritis) and pertussis-like symptoms. Infection with B holmesii is frequently misidentified as being with B pertussis, the cause of whooping cough, because routine diagnostic tests for pertussis are not species-specific. In this Review, we summarise knowledge about B holmesii diagnosis and treatment, and assess research needs. Although no fatal cases of B holmesii have been reported, associated invasive infections can cause substantial morbidities, even in previously healthy individuals. Antimicrobial treatment can be problematic because B holmesii’s susceptibility to macrolides (used empirically to treat B pertussis) and third-generation cephalosporins (often used to treat invasive infections) is lower than would be expected. B holmesii’s adaptation to human beings is continuing, and virulence might increase, causing the need for better diagnostic assays and epidemiological surveillance.

Introduction

Bordetella holmesii, a Gram-negative bacterium was first described as a cause of bacteraemia in patients with comorbidities such as asplenia.^1,2 The bacterium was also recovered in nasopharyngeal samples in otherwise healthy individuals with pertussis-like symptoms.³ However, debate exists as to whether B holmesii is a true respiratory pathogen or a colonising bacterium that has been identified instead of the correct disease-causing viruses or intracellular bacteria. B holmesii is possibly the leading cause of false-positive results when investigators screen symptomatic patients for whooping cough (caused by B pertussis) with use of PCR. Indeed, routine PCR does not discriminate between B holmesii and B pertussis because the target sequence typically used for clinical diagnosis (insertion sequence 481 [IS481]) is present in both genomes. The eﬀect of this misdiagnosis is not only important for individual patients because of its potential to lead to inappropriate antimicrobial treatment and risk of invasive disease, but also for public health because it can confound the assessment of eﬃcacy for the pertussis vaccine.^4–6 In this Review, we summarise knowledge about B holmesii and explore future research objectives.

History

In 1983, the US Centers for Disease Control and Prevention (CDC) recorded the first reported case of B holmesii infection, which was in a man aged 37 years with asplenia in Buffalo, NY, USA.¹ The CDC then isolated 14 additional strains in blood samples submitted from nine different states in the USA and from Saudi Arabia and Switzerland. Before identification, the bacterium was called CDC non-oxidiser group 2 (NO-2). Results of DNA-relatedness studies, 16S rDNA sequencing, guanine-plus-cytosine content analysis, and biochemical characterisation affiliated this strain to the Bordetella genus. Investigators gave the bacterium its present name in 1995 in honour of

Microbiology Bordetella species

The genus Bordetella belongs to the family of Alcaligenaceae and consists of nine species: B pertussis, B parapertussis, B bronchiseptica, B avium, B hinzii, B holmesii, B trematum, B petrii, and B ansorpii. The classic species are B pertussis, B parapertussis, and B bronchiseptica, occasionally referred to as the mammalian pathogens, by contrast with the avian species (B avium and B hinzii).

The classic species are known to cause mainly respiratory infections. The latter five, added in the past two decades, are considered to be new species.

B pertussis and a specific lineage of B parapertussis infect human beings exclusively, resulting in the classic symptoms of paroxysmal cough, whooping, and post-tussive vomiting. The other lineage of B parapertussis causes respiratory infection in sheep. B bronchiseptica, the ancestor of the mammalian pathogens,^7–9 is found mostly in dogs, pigs, rabbits, and cats, but has been occasionally reported in people in close contact with animals.^10–12 B avium, responsible for turkey coryza in wild or domesticated birds,¹³ can sometimes infect people with underlying pulmonary diseases.^14,15 Turkey coryza can also be caused by B hinzii,¹⁶ which has been recovered in a few patients with chronic diseases.^14,16–23B trematum has been isolated from human cutaneous lesions and in ear infections.^24,25 First described in the environment (river sediment),²⁶B petrii was anecdotally recovered in patients.^14,27–29 Finally, B ansorpii, the most recent addition to the Bordetella genus, was first described in 2005 after isolation from purulent exudate of an epidermal cyst³⁰ and blood samples.³¹ B holmesii is the most frequently reported bacterium of these new species in the published work and seems to be the only pathogen within this group that is capable of causing disease in otherwise healthy individuals.³²

Biochemical characteristics

Lancet Infect Dis 2014 Published Online April 8, 2014 http://dx.doi.org/10.1016/

S1473-3099(14)70021-0 Department of Paediatrics, Division of General Paediatrics, Children’s Hospital, University Hospitals of Geneva (L F Pittet MD, Prof C-A Siegrist MD, K M Posfay-Barbe MD), Department of Genetics and Laboratory Medicine, Department of Medical Specialties, University Hospitals of Geneva, (S Emonet MD, Prof J Schrenzel MD), and Neonatal Immunology, Departments of Pathology-Immunology and Paediatrics (C-A Siegrist), University of Geneva, Geneva, Switzerland Correspondence to:

Dr Klara M Posfay-Barbe, Children’s Hospital, University Hospitals of Geneva, 1211 Geneva 14, Switzerland klara.posfaybarbe@hcuge.ch

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culture, B holmesii produces brown soluble pigments that differentiate it from other Bordetella and Acinetobacter species. Moraxella canis is the only other organism known to produce such a pigment.³³ The lack of oxidase and haemolysing activity differentiates B holmesii from B pertussis, B bronchiseptica, and B avium. The absence of urease activity differentiates it from B parapertussis.¹ As with other Bordetella species, culture of B holmesii is time consuming and difficult, and needs a special medium for transportation and culture.

Similarity between B holmesii and other Bordetella species Origin and microarrays-genomic comparison

A 99·5% gene sequence identity was shown between B pertussis’ and B holmesii’s 16S rRNA gene.³² Several techniques have been used to establish B holmesii’s similarity with other Bordetella species. Use of comparative genomic hybridisation of B holmesii strains compared with those of B pertussis on microarray showed substantial divergence between the two.³⁴ Findings from multilocus sequence typing confirmed this divergence.

However, analysis of housekeeping genes showed that B holmesii possibly acquired both its 16S rRNA gene and iron-uptake island by lateral transfer from B pertussis.³⁴ IS481 (the sequence targeted by routine PCR for diagnosis of B pertussis) was present in high copy numbers (>50) in B pertussis, but there was only only eight to ten copies in B holmesii (figure 2).^35,36 The higher copy numbers suggest that IS481 has been present in B pertussis for a longer period than it has been in B holmesii.³⁵ Although IS481

was possibly inherited from a common ancestor of both B pertussis and B holmesii, evidence of a shared genomic site suggests horizontal transfer of this element.^3,36 The B holmesii genome also contains three to five copies of IS1001-like elements, named holmesii IS1001 (hIS1001).^35,37,38 Analyses of four other housekeeping genes show that B holmesii is more closely related to B hinzii and B avium (so-called avian species) than to mammalian (classic) Bordetella species.³⁴ Results of cellular fatty acid composition analyses and multilocus sequence typing also associated B holmesii with B avium.¹ Finally, draft genome sequences of B holmesii strains have enabled an updated phenogram, which shows the close relation between B holmesii and B avium.^39,40

Genetic analyses of the bvgAS two-component system (the master regulator of virulence gene expression) in B pertussis, B parapertussis, and B bronchiseptica revealed that the B holmesii bvgAS system is more closely related to that of B avium than to those of the mammalian species.⁴¹ Although some areas (such as the cytoplasmic signalling domains of the bvgS histidine kinase) might be functionally interchangeable between B holmesii and B pertussis, signal perception and respective levels of activity diﬀers between the two species.^41,42

Proteins produced by B holmesii seem to be more similar to those from B bronchiseptica than to those from B pertussis.⁴³ Link and colleagues⁴⁴ reported that B holmesii produces a factor highly related to filamentous haemaglutinin (FHA), a well known adhesin essential for colonisation in other pathogenic Bordetella spp. Similar to other Bordetella spp, its production is regulated by the bvgAS virulence regulatory system. However, this protein is more closely related to that found in B avium (55%

similarity) than to that in mammalian Bordetella spp.⁴⁴ B holmesii does not produce a pertussis toxin,^39,45,46 but this toxin is not necessary for the development of symptoms.

For example, B parapertussis can cause disease without any production of the pertussis toxin. Finally, other toxins and adhesins implicated in the Bordetella pathogenesis have not been detected in B holmesii isolates, including adenylate cyclase–hemolysin toxin, Bordetella type 2 and 3 secretion systems, pertactin, and fimbrial proteins.^39,40,46

Diavatopoulos and colleagues³⁴ postulated that the recent emergence of B holmesii as a human pathogen relates to the acquisition of a 66 kilo-base-pair-long genomic island by horizontal transfer with B pertussis. Among others, this island encodes for several virulence factors, such as a siderophore capable of scavenging free iron from the extracellular environment, and several antibiotic resistance eﬄux pumps. This addition might enhance colonisation of the host airway through an increase in resistance to host defensins and other endogenous antimicrobial peptides.³⁴ According to van den Akker,⁴⁷ diﬀerences in lipo-polysaccharide expression between B pertussis and B holmesii (important for pathogenesis) could explain the observed clinical dissimilarity of B pertussis, which mainly infects respiratory tract epithelium, and B holmesii, which

Figure 1: Bordetella holmesii growing on a sheep-blood agar plate Isolation of B holmesii on a sheep-blood agar plate shows small shiny grey non-haemolytic colonies 24 h after incubation in 5% CO2.

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can cause bacteraemia. Of note, no diﬀerence has been shown between the genomes of strains of B holmesii that cause respiratory or non-respiratory infections.^39,46

It is not known whether B holmesii has a capsule. Given the central role of the spleen in encapsulated bacteria clearance,⁴⁸ the presence of a capsule would explain why patients with hyposplenia or asplenia have an increased risk of B holmesii bacteraemia. Finally, it is not known whether B holmesii has the potential to increase its

Epidemiology

Prevalence and incidence

Little is known about the prevalence of B holmesii apart from in reported pertussis outbreaks or isolated studies (appendix pp 1–5). Several factors can explain this scarcity of information. First, chronic cough is often misdiagnosed and Bordetella is often overlooked. Second, the diagnostic used most frequently when Bordetella spp infection is suspected is a standard PCR, which does not always

Figure 2: Comparison of whole-genome maps of Bordetella pertussis and Bordetella holmesii

B holmesii strain F627 (GenBank: AOEW00000000·1) is shown on the left and B pertussis strain CS (GenBank: CP002695·1) on the right. The B holmesii genome is in the form of two individual contigs (shown in two different shades of green). The grey links indicate sequence similarities at the protein level between the two genomes. Only local gene synteny is observed between the two bacteria. Even if the two strains have only slight similarity, B holmesii contains several occurrences of IS481. Red dots show the positions of the IS481, which has 19 occurrences in the B holmesii strain F627, and 227 occurrences in the B pertussis strain CS.

See Online for appendix

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Africa (Tunisia), Asia (Japan), Canada (Alberta and Ontario), Europe (Belgium, Finland, France, Romania, Switzerland, and the Netherlands), South America (Argentina and Chile), and the USA (Massachusetts, California, Colorado, Ohio, and Washington), researchers identified B holmesii in 0–29·3% of nasopharyngeal isolates from patients with pertussis-like episodes (appendix pp 1–5).3,37,38,50–65 During the 2010 pertussis outbreak in Ohio, investigators identified B holmesii in 32% of patients with Bordetella-confirmed respiratory infection.⁵⁸ Almost half of the adolescents aged 11–18 years with pertussis-like illness (30 [45%] of 70 patients) had a final diagnosis of B holmesii and not B pertussis. However, since no other investigation of cause was reported in these studies, other pathogens such as viruses or intracellular bacteria could have been the true pathogenic agents in carriers of B holmesii. In Massachusetts, prevalence of B holmesii in nasopharyngeal specimens of people with whooping-cough-like episodes increased by six times over 3 years (from 0·1% in 1995, to 0·6% in 1998; p<0·001).³ Hypotheses to explain such an increase include a higher circulation rate of the bacterium, increased awareness of B pertussis by physicians, and improved laboratory detection.^3,66,67

A modification of the competitive balance between B pertussis and other species secondary to the introduction of the acellular pertussis vaccine in 1996 cannot be excluded.⁶⁷ Indeed, compared with the pertussis whole-cell vaccine, awhole-cellular vaccines have a lower eﬃcacy against B parapertussis in animals.⁶⁸ The introduction of acellular vaccine could have changed the competitive balance to favour non-pertussis Bordetella species, such as B holmesii, B parapertussis, or B bronchiseptica.⁶⁷

Transmission and reservoir

No data are available for mode of transmission for B holmesii. Transmission is probably mostly through respiratory droplets,⁵⁷ but other modes of transmission could exist, such as through the environment or blood products. B holmesii is presumed to be strictly a human pathogen because no animal reservoir has been reported as yet. However, this exclusivity has not been investigated thoroughly and might be challenged since B holmesii is closely related to the avian species of Bordetella.32,34,39,40,67

Furthermore, findings of two case reports suggested animals as potential sources of infection.^69,70B holmesii has been isolated in human sputum^71,72 and could therefore be a transient pathogen of the upper respiratory tract.⁶⁹ This localisation is further suggested by a case of B holmesii endocarditis that occurred 2 months after dental manipulation.⁷³ Investigators have also detected B holmesii in two platelet concentrates. The bacterium presumably survived during platelet concentrate storage, but at too low a count for detection by routine bacterial screening.⁷⁴ The duration of incubation and degree of infectivity or attack rate is not known. Finally, investigators have reported a seasonal variability.^3,54,57,65

Some evidence suggests that B pertussis and B holmesii co-circulate.^3,65,75 B holmesii has been isolated during several B pertussis outbreaks,57,58,65,76 and five cases of B holmesii and B pertussis coinfection were reported during the 2010 Ohio pertussis outbreak.^58,65

Susceptibility factors for respiratory infection

Healthy adults and adolescents seem to be at greater risk for respiratory infection with B holmesii than are younger individuals, and this age group are the most represented in published reports about B holmesii (appendix pp 1–5).

In Massachusetts, 19 (83%) of 23 B holmesii respiratory infections reported were in adolescents (aged 11–19 years).³ In the Ohio pertussis outbreak, adolescents aged 11–18 years constituted about two-thirds of patients with B holmesii and only a third of patients with B pertussis (p=0·001).⁵⁸ The reason why adults and adolescents seemed to be at higher risk is not clear, but it might be linked to waning immunity against B pertussis (although there is no evidence of cross-protection between the two species) or to the fact that this population is the reservoir of B pertussis in many countries. Because B holmesii possibly co-circulates with B pertussis, the increased prevalence of B pertussis infection in this age group could explain the increased risk of detection of B holmesii. B holmesii respiratory infections occurred in children, seven in infants younger than 6 months.⁵⁹

Underlying conditions for invasive B holmesii infection Some categories of patients seem to be at increased risk for B holmesii infection. Asplenia (functional or anatomical) is the most frequently identified risk factor,^2,75 but B holmesii infection has also been reported in patients with chronic obstructive pulmonary disease,⁷¹ ulcerative colitis,⁷⁷ diabetes mellitus,^1,75,77 lymphoma,^1,71,78,79 common variable immunodeficiency,⁷⁷ HIV infection,² nephrotic syndrome,^80,81 high-dose corticosteroid drugs,⁸⁰ systemic lupus erythematosus,^82,83 anorexia nervosa,⁸⁴ after solid-organ transplantation,⁸¹ and in infants.^2,69 The common feature between these disorders seems to be that of immune modulation, including in infants, secondary to disease or immunosuppressive therapy.⁸⁵

Clinical features

Pertussis-like respiratory infection

When B holmesii is isolated from respiratory samples, the corresponding presentation is similar to that of whooping cough, including low-grade fever, cough, and post-tussive vomiting. Yih and colleagues³reported that patients infected with B holmesii presented with milder symptoms than did those with B pertussis—ie, two or fewer of the

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three classic pertussis symptoms: paroxysmal cough, whoop, and post-tussive vomiting (p<0·01). Rodgers and colleagues⁵⁸reported similar frequencies of classic features among patients infected with B pertussis or B holmesii colleagues⁵⁹ reported milder respiratory symptoms in nine children (including seven infants younger than 6 months) infected with B holmesii—none had cyanosis or apnoea, whereas in children with B pertussis infection, 34% had cyanosis and 14% had apnoea.

Bacteraemia

Unlike B pertussis, which is a pathogen of the respiratory tract, B holmesii has been described as a cause of bacteraemia.² Over 18 years between 1983 and 2000, the CDC identified 30 patients with B holmesii bacteraemia in 16 states in the USA.² In 25 of 26 patients, B holmesii was the only microorganism isolated from blood samples, and researchers recovered B holmesii in more than half (54%) of patients in at least a second blood sample. In Northern Alberta, Kanji and colleagues⁷⁷identified eight cases of B holmesii bacteraemia over 5 years. In New York, Layton and colleagues⁸⁶reported on a cluster of five cases of B holmesii bacteraemia. Tartof and colleagues⁷⁵later reported an investigation of 22 cases of B holmesii bacteraemia in less than 10 months in the USA: 91% of patients had at least one underlying medical condition.

Bacteraemia remains a rare presentation, but it can be severe and can even cause admission to critical care.^2,75 As yet, no fatalities have been reported secondary to B holmesii bacteraemia. The clinical course is usually characterised by a non-specific febrile illness and is not typically associated with other signs, such as rash. White-blood-cell count and other routine laboratory investigation are not characteristic.

B holmesii bacteraemia is generally reported in patients with risk factors such as asplenia or immunosuppression.

All age groups can get B holmesii bacteraemia, but in a retrospective study by Shepard and colleagues,² 85% of patients were younger than 40 years (median age 20·5 years), and mean age was 43 years in another Canadian study.⁷⁷ In a US study, the median age was 17·1 years, but the age distribution was wide (2–77 years).⁷⁵

Other infection types

Pneumonia with B holmesii has been described in a previously healthy 14-year-old girl and a 15-year-old boy with chronic nephrotic syndrome.^80,87 Outcomes for both

productive and not whooping. In a woman aged 41 years, B holmesii triggered exacerbation of chronic obstructive pulmonary disease, and she needed intubation and admission to critical care.⁷¹

Non-respiratory sites of B holmesii infection have been reported (appendix pp 6–11). There have been nine reports of patients with B holmesii endocarditis on native and prosthetic valves.1,33,71,73,82,88–90 Symptoms ranged from subacute endocarditis to septic shock with acute renal failure, usually needing valve replacement. Investigators reported on two patients with B holmesii pericarditis; one patient stayed in hospital for longer than 2 months.^78,87 Researchers have also reported meningitis in two patients:

a girl aged 14 years with anorexia nervosa and a woman aged 37 years with end-stage renal disease secondary to systemic lupus erythematosus.^83,84In the woman, the outcome was severe, with persistent convulsions needing continuous intravenous diazepam and mechanical ventilation.⁸³ Septic arthritis with B holmesii, both in patients with normal and in those with prosthetic knees, has been reported;^1,91,92 one immunocompetent woman aged 54 years had to get her prosthesis removed.⁹² Finally, B holmesii was isolated four times in the blood culture of a 67-year-old patient receiving rituximab who presented with three episodes of cellulitis and one episode of pneumonia. Later, asymptomatic nasal carriage of B holmesii was reported in the same patient.⁷⁹ This severe invasive disease range has never been described for B pertussis and shows the particularity of B holmesii infections, which are ubiquitous and can go from barely symptomatic to life-threatening invasive disease. Although most patients with invasive B holmesii infection had an underlying disease, severe infections have been reported in previously healthy individuals.^33,69,87

Diagnosis

The identification of B holmesii by culture from biological fluids (blood, pleural or articular fluid, or nasopharyngeal samples) is cumbersome because the mean incubation time of blood cultures to be positive is 40 h⁴⁹ and the bacteria do not grow well on MacConkey agar.⁹³ As with B pertussis, rapid specimen transfer in an appropriate transport medium is crucial to ensure optimum sensitivity.^94,95 Cefalexin, an antimicrobial drug

Dans le document Bordetella holmesii, une bactérie méconnue, potentiellement invasive et préjudiciable à l'évaluation de l'efficacité du vaccin contre la coqueluche (Page 44-54)