A UK clinical isolate of Bordetella hinzii from a patient with myelodysplastic syndrome

Introduction

Bordetella hinzii is a commensal of the respiratory tracts of fowl, and has been previously shown to have some pathogenic potential in immunocompromised humans (Cookson et al., 1994; Vandamme et al., 1995; Funke et al., 1996; Gadea et al., 2000). Isolation of B. hinzii from human sources remains extremely rare. Only seven instances of such isolation have been reported from six cases; two patients with AIDS (one with and one without respiratory infection) (Cookson et al., 1994; Gadea et al., 2000), one patient with cystic fibrosis (with sequential isolation) Funke et al. (1996), and one patient with fatal septicaemia (Kattar et al., 2000). There are little or no details from the remaining two cases; in one, isolation was from sputum, and in the other, from an endotracheal aspirate from a farmer with no apparent disease (Vandamme et al., 1995, 1996; Kattar et al., 2000). We report the case of a patient who presented with myelodysplastic syndrome.

Case report

A 79-year-old male with myelodysplastic syndrome was admitted to hospital for a blood transfusion. On admission blood tests revealed the following: 6.2 g haemoglobin dl⁻¹, 0.4×10⁹ white blood cells l⁻¹ (0.1×10⁹ neutrophils l⁻¹, 0.3×10⁹ lymphocytes l⁻¹, and monocytes, eosinophils and basophils all at 0.0×10⁹ l⁻¹). He had experienced malaise and flu-like symptoms for 1 week, and had been commenced on oral co-amoxiclav 500/125 (500 mg amoxicillin as trihydrate, 125 mg clavulanic acid as potassium salt) three times daily by his general practitioner 2 days earlier for a presumed chest infection. On admission his symptoms had improved and the clinical examination was unremarkable. The co-amoxiclav was discontinued. His previous medical history included diabetes mellitus, hypertension and Paget's disease. On the second day of admission he developed a fever of 38.4 °C prior to a blood transfusion. On examination he had a pulse rate of 71 beats min⁻¹, blood pressure of 141/55 mmHg, a respiratory rate of 18 breaths min⁻¹ and O₂ saturation of 95 % on air. Blood was taken for bacteriological culture before commencing therapy with intravenous vancomycin 1 g twice daily and intravenous ceftazidime 2 g twice daily. The following day his C-reactive protein had risen to 159 mg l⁻¹ from 70 mg l⁻¹ on admission. The patient was breathless but his chest X-ray was normal. The patient had no central venous catheters in situ and responded well to the empirical antibiotic therapy. Vancomycin was discontinued after 5 days and ceftazidime after 7 days. The patient recovered and was discharged home 13 days after admission. The patient had no known avian exposure.

Methods

Results

Preliminary test results at the RSIL on strain H062540035 were consistent with members of the genus Bordetella. The organism could be cultured on both MacConkey agar and charcoal blood agar, and colonies had the following phenotypic characteristics: positive reaction for oxidase and negative for slide agglutination with B. pertussis and B. parapertussis antiserum (Difco). Results of antimicrobial susceptibility testing by the hospital laboratory were: susceptible to amoxicillin, co-amoxiclav, co-trimoxazole, gentamicin, ceftazidime and meropenem, and resistant to cefuroxime, ceftriaxone and ciprofloxacin.

The ompA sequence from strain H062540035, showed maximum similarity, 100 % (600/600 nt), with the ompA gene from the type strain of B. hinzii NCTC13199^T (GenBank/EMBL/DDBJ accession no. AM748264) and 99.8 % (599/600 nt) with a non-type reference strain of the same species, NCTC13200 (accession number AM748265). The single nucleotide difference was a synonymous mutation (codon GAC to GAG, both coding for aspartic acid) in the predicted sequence of the OmpA protein. The species with the next highest similarity belonged to B. holmesii NCTC13202 (accession number AM748267), 92.9 % (455/490 nt). The SSU rRNA gene sequence from strain H062540035 (accession number AM748269), showed maximum similarity, 100 % (1411/1411 nt), with the same gene from the type strain of B. hinzii LMG 13501^T (accession number AF177667). The species with the next highest similarity, 99.4 % (1402/1410 nt), belonged to B. parapertussis DSM 4922 (accession number AJ278450). The phylogenetic relationships between strain H062540035 and the Bordetella species inferred from ompA and the SSU rRNA genes are shown in Fig. 1⇓.

Discussion

Currently, commercial systems, such as the biochemical identification API20NE strips, only include two Bordetella species, Bordetella bronchiseptica and B. avium, in their identification library. B. hinzii is rarely isolated from humans and this species is difficult to differentiate from B. avium by routine phenotypic methods. Confirmation can be reliably achieved using genotypic methods, and the greater nucleotide variation of the ompA gene compared to, for example, the 16S rRNA gene, allows unambiguous identification of this and other non-classical Bordetella species. Sequence similarity and phylogenetic analyses confirmed the identity of strain H062540035 as B. hinzii. The trees generated were similar to those already described for the genus (Ko et al., 2005; Gerlach et al., 2001).

The genus Bordetella comprises eight validly named species (von Wintzingerode et al., 2001), and one that awaits formal description, ‘Bordetella ansorpii’ sp. nov. (Ko et al., 2005; Fry et al., 2007). As in some of the previous cases, there was no known avian exposure in the case presented here, suggesting that the organism was obtained from other sources as yet unidentified. Similarly, it appears that this species is an opportunistic pathogen, and that underlying patient disease and/ or an impaired immune system makes patients susceptible to infection with these rarer non-classical Bordetella species. The authors would therefore recommend that the identity of all clinical isolates belonging to the non-classical Bordetella species, including those presumptively identified as B. avium, are confirmed by a reference laboratory.