Cell-wall-deficient bacteria and culture-negative febrile episodes in bone-marrow-transplant recipients

BACKGROUND

Although about 75-80% of neutropenic fevers are thought to be caused by infections, a causal organism can be confirmed microbiologically or suspected clinically in only 30-50%, and even fewer of these cases (16%) have a documented bacteraemia. The cause of neutropenic fever in the remaining cases remains elusive. We investigate the role of cell-wall-deficient bacteria in bone-marrow transplantation (BMT).

METHODS

Blood cultures were obtained from bone-marrow-transplant recipients and were inoculated into an aerobic bottle with resin, an anaerobic bottle, and a bottle to isolate cell-wall deficient bacteria. When growth was detected in the blood-culture bottle for cell-wall-deficient bacteria, 20 microL of the broth was subcultured and the isolate identified by standard biochemical methods. The microbiological findings were correlated with the clinical characteristics of the patients.

FINDINGS

From the 86 BMT recipients enrolled into the study, 798 sets of blood cultures were sent for laboratory analysis. 55 blood cultures were positive in the aerobic bottle, and the same isolates were also detected in 52 blood-culture bottles for cell-wall-deficient forms. For 20 sets of blood cultures, the isolates were detected only in the bottle for cell-wall-deficient forms. Blood for 13 (65%) of these 20 sets were sampled in the pre-engraftment neutropenic period, three (15%) during conditioning when the absolute neutrophil count was above 0.5 x 10(3)/L, and four (20%) in the post-engraftment period. 17 (85%) of the isolates were gram positive: four (20%) were Staphylococcus spp and ten (50%) were Bacillus spp. Antibiotic treatment was successful in 19 (95%) of 20 episodes.

INTERPRETATION

Bacteraemia due to cell-wall-deficient forms causes a significant proportion of so-called culture-negative febrile episodes in BMT recipients.

Identification of Mycobacterium neoaurum isolated from a neutropenic patient with catheter-related bacteremia by 16S rRNA sequencing

A rapidly growing pigmented mycobacterial strain with an ambiguous biochemical profile was isolated from the blood culture taken through the Hickman catheter of a 9-year-old girl with acute lymphoblastic leukemia. Whole-cell fatty acid analysis showed that the best match profile was that of Mycobacterium aurum, but the similarity index was only 0.217, meaning that there were no good matches between the isolate and the organisms in the database of the Microbial Identification System. The 16S rRNA gene of the mycobacterial strain was amplified, agarose gel purified, and sequenced. There were 44 base differences between the gene sequence of the isolate and that of M. aurum but only one base difference between the sequence of the isolate and that of Mycobacterium neoaurum, showing that the isolate was indeed a strain of M. neoaurum by using this "gold standard." This represents the first case of M. neoaurum infection documented by 16S rRNA sequencing.

Leukocytoclastic vasculitis complicating Klebsiella pneumoniae bacteremia

A 79-year old woman, with a history of hypertension, presented with clinical features of congestive heart failure, fever, a purpuric rash, and left lower quadrant abdominal tenderness. Contrast computed tomography scan of the abdomen showed features of acute diverticulitis, and blood culture was subsequently positive for Klebsiella pneumoniae. Histological examination of a biopsy of the rash confirmed a diagnosis of leukocytoclastic vasculitis (LCV). The bacteremia responded to intravenous amoxycillin/clavulanic acid and gentamicin and the rash subsided. This case represents the first case of LCV complicating K. pneumoniae bacteremia in the English literature. The English literature on bacteria-associated LCV is reviewed. Taking aside organisms such as Rickettsia that cause endothelial invasion, the associated bacterial species tends to be subacute or chronic pathogens e.g. Mycoplasma pneumoniae, Mycobacterium tuberculosis, and Yersinia enterocolitica; or the disease process is of a subacute or chronic nature e.g. endocarditis, bronchiectesis, and cystic fibrosis, leading to prolonged exposure to pathogens that apparently cause acute pyogenic infections, such as K. pneumoniae.

Cellulitis complicating lymphoedema

In ten hospitalised patients with cellulitis complicating lymphoedema encountered over a 3-year period (1996-1998), the underlying diseases were carcinoma of the cervix (n = 4), uterus (n = 1), vagina (n = 1), breast (n=2) and nasopharynx (n= 1), and retroperitoneal squamous cell carcinoma (n = 1). Three of the ten patients had positive blood cultures, compared to none of the 20 age-matched, sex-matched controls hospitalised for cellulitis without lymphoedema. The mean duration of fever, tachycardia and cellulitis was significantly longer in patients with lymphoedema than in those without (P<0.05, P<0.05, and P<0.005 respectively). Early treatment initiated by patients themselves may help stop bacterial replication in the initial stages and minimise further damage to the lymphatic system.