Osmotically stable L forms of Haemophilus influenzae and their significance in testing sensitivity to penicillins.

The sensitivity of Haemophilus influenzae to penicillins in vitro, determined either by serial antibiotic dilution in broth or by the disc method on agar, is apparently profoundly influenced by inoculum size if the results are read by macroscopic inspection. Microscopic inspection of the growth, however, reveals that the turbidity in heavily inoculated broth containing concentrations higher than the minimal inhibitory concentration is the product of L forms which have failed to succumb to osmotic lysis. Similarly, minute colonies appearing in the ;inhibition zone' of disc tests are composed of L forms. In both broth and agar tests reduction of the osmolality of the medium from 340 to 144 mOsm per kg failed to bring about lysis of organisms exposed either to ampicillin or amoxycillin. The significance of this remarkable osmotic stability of haemophilus L forms is discussed in relation both to testing of sensitivity of this organism to penicillins and to persistence of chronic haemophilus infections of the lower respiratory tract.

Characterisation of strains of Aeromonas spp. by phenotype and whole-cell protein fingerprint.

Sixty-eight isolates of Aeromonas spp. were examined biochemically and their cell proteins were analysed by silver-stained SDS-PAGE. Protein fingerprints did not correlate with phenotype. However, consideration of both phenotype and fingerprint showed clustering of epidemiologically related isolates. There was also evidence that similar strains could be found in infected people and water or other environmental samples.

Typing of Aeromonas species by protein fingerprinting: comparison of radiolabelling and silver staining for visualising proteins.

A method for typing Aeromonas species by silver staining of total soluble proteins separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis is described. There was good agreement with the results obtained by autoradiography of whole-cell proteins for isolates examined by both methods.

Induction of L-forms of Haemophilus influenzae in vitro.

The induction of L-forms of Haemophilus influenzae by penicillin, amoxycillin and glycine has been studies in vitro on a nutrient-agar medium. The minimal inducing concentrations of the antibiotics were generally the same as their minimal inhibitory concentrations, but the addition of a sub-inducing concentration of glycine lowered the minimal inducing concentration of penicillin. Preliminary observations have shown that L-forms are induced by penicillin or amoxycillin on a medium in which mucoid sputum forms the sole source of nutrients, and that they remain viable for at least 48 h in the absence of added osmotic stabiliser. The minimal inducing concentration on "sputum agar" is within the range of concentrations measured in sputum from patients receiving amoxycillin therapy. The implications of these observations in relation to bactericidal therapy of haemophilus infections of the respiratory tract are discussed.

Effects of incorporating ampicillin, bile salts and carbohydrates in media on the recognition and selection of Aeromonas spp. from faeces.

The effects of incorporating ampicillin, some bile salts and sugars into media on the primary recognition and selection of aeromonads from faeces were examined. Most (88%) of the 101 Aeromonas strains examined had an ampicillin MIC of greater than or equal to 40 mg/L, and would be isolated on blood agar containing ampicillin 30 mg/L. The strains with an ampicillin MIC of less than 40 mg/L were all of human origin and predominantly A. caviae. Although ampicillin at 10, 20 or 30 mg/L in blood agar inhibited faecal bacteria, the ability to detect Aeromonas strains with a high ampicillin MIC was less when the lower concentrations of ampicillin were used, without any improvement in the isolation of those strains with a low ampicillin MIC. Thirty-seven strains were tested for sensitivity to several different bile salts and found to be at least as resistant to them as Escherichia coli NCTC 10418. Bile salt sensitivity was not related to the species or source of a strain. There were minor differences in sensitivity to bile salts between some strains which related to whether strains had been isolated originally in the presence of bile salt or not. The effects of the presence of E. coli, Klebsiella spp. and Enterococcus faecalis on the growth of Aeromonas strains in mixed culture on media with and without carbohydrate were examined. The colony size of some Aeromonas strains was reduced in mixed culture but colony counts were not affected with any Aeromonas strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudomonas pickettii infections in a paediatric oncology unit.

Over a 3-month period, seven patients in a paediatric oncology unit developed Pseudomonas pickettii septicaemias. The outbreak was difficult to recognize since the cases occurred at widely spaced intervals and problems were experienced with the identification of the isolates. Many of the isolates were initially misidentified on the basis of a short sugar set used in the laboratory for identification of the non-fermenting Gram-negative bacilli. Moreover, the organisms had varying sensitivity patterns. The source of the organisms proved to be vials of 'sterile' distilled water which had been used for flushing the patients' indwelling Hickman lines. No further cases occurred once the use of this water was discontinued.

An epidemiological study of listeriosis complicating a bone marrow transplant.

Following an unrelated-donor bone marrow transplant a six-year-old child with severe aplastic anaemia developed Listeria monocytogenes septicaemia and meningitis. Cook-chill foods consumed during his stay in hospital were found to contain strains of L. monocytogenes and other Listeria species. Whole cell protein SDS-PAGE was performed on all isolates. No food isolates were found that were identical to the patient's strain by this technique or by serotyping. The usefulness of whole cell protein SDS electrophoresis for listeria strain differentiation is discussed.

An outbreak of Enterobacter cloacae associated with contamination of a blood gas machine.

Over a 3-month period, five cases of Enterobacter cloacae bacteraemia occurred on our neonatal unit. In at least three of these, isolation of the organism coincided with clinical deterioration and evidence of sepsis. In one case, the same strain was isolated from an abscess on the neonate's forearm. The isolates had identical sensitivity patterns being resistant to all beta-lactams tested except imipenem. The extended time course of the infections made cross-infection an unlikely explanation. Moreover, close questioning of the staff and observation of their practices with regard to blood culture collection, failed to reveal any likely mechanism for pseudobacteraemia. On extensive investigation of the environment to try to identify a potential source of the organism, a strain of Enterobacter cloacae, was isolated from the probe of the blood gas machine and the probe cover. No other environmental samples were found to harbour the organism. Subsequent typing procedures showed the blood gas isolate to be indistinguishable from the clinical isolates. Five neonates were successfully treated with imipenem and gentamicin. The exact mechanism whereby these bacteraemias occurred remains obscure. In one case, the baby had positive blood cultures within 2 h of being on the unit and contamination of the blood culture bottle by the doctor taking the culture was suspected. Most of the episodes, however, appeared clinically to be genuine septicaemias. When vigorous infection control procedures were instituted to prevent staff acquisition of the organism from the machine, cases on the unit ceased.

Ceftazidime as first-line therapy for fever in acute leukaemia.

Fifty patients with acute non-lymphocytic leukaemia were treated by random allocation with either ceftazidime alone or a combination of piperacillin, netilmicin and cefotaxime for 65 febrile neutropenic episodes. Nineteen of 33 patient episodes (58%) responded to ceftazidime alone compared with 21 of 32 episodes (66%) treated with the combination. There was one infective death in a patient given the combination; rates of documented superinfection were low. The treatment groups appeared identical in terms of patient demography, underlying disease and other risk factors, though patients with a clinical site of infection responded more slowly than those without. Bacteraemia per se did not appear to influence outcome. Bactericidal serum concentrations greater than or equal to 8 X the minimum bactericidal concentration were predictive of a rapid response (within 4 days) to antibiotics. Furthermore, serum from patients treated with ceftazidime maintained adequate cidal activity against Pseudomonas aeruginosa for longer than that obtained from patients treated with the three-drug combination. Ceftazidime was shown to be a safe and effective alternative to the three-drug combination for the initial management of febrile neutropenic episodes in leukaemic patients.

Whole-cell protein electrophoresis for typing Mycobacterium tuberculosis.

A method of discriminating between strains of Mycobacterium tuberculosis by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins combined with a sensitive silver stain is described. Thirty-five isolates of M. tuberculosis and five isolates from other species of Mycobacterium were examined, including serial isolates from the same patients and isolates from a small cluster of hospital cases. Different species of Mycobacterium were clearly distinguished, and within the species M. tuberculosis, different fingerprints were obtained, allowing discrimination of some strains from different patients. The reproducibility and discrimination of the technique are discussed.

Assay of vancomycin by fluorescence polarisation immunoassay and EMIT in patients with renal failure.

Serum with vancomycin concentrations between 5 and 15 mg/L from patients on dialysis were assayed by fluorescence polarization immunoassay (FPIA) and enzyme multiplied immunoassay technique (EMIT). The concentrations as determined by FPIA were higher than those using EMIT (mean difference 2.1 mg/L, S.D. 1.5; range -0.8-6.3) with substantial interpatient variability in the difference between the two assays. This suggests that concentrations of active vancomycin are lower than indicated by FPIA and thresholds for redosing may need to be adjusted.

Amikacin dosage in the preterm newborn.

Twenty-two preterm infants of gestational age 26 to 34 weeks were treated with amikacin for suspected bacterial infection, using a dose of 7.5 mg/kg, 12-hourly, intra muscularly. Blood levels were measured using a radio-immunoassay kit capable of giving results within 4 h. One-hour peak levels showed wide variation and the mean level one hour after the first dose was 18.2 mg/1; in severe infections an initial loading dose of 10 mg/kg is therefore recommended. Trough levels in individual infants also varied considerably from day to day, but showed no overall accumulation. There was no obvious adverse effect on hepatic or renal function.