- Volume 36, Issue 2, 1992

Induction by the 4-quinolone group of antibacterial drugs of the umuC gene, the SOS function most involved in error-prone DNA repair (together with umuD), was assessed in a strain of Escherichia coli harbouring a umuC::lacZ gene fusion. All 4-quinolones tested induced this umuC::lacZ fusion, with maximum induction at 4-quinolone concentrations close to their minimum inhibitory concentrations for this strain, and the SOS Inducing Potential (SOSIP) was closely related to antibacterial activity. Mitomycin C, a known mutagen, was a slightly better inducer (in terms of SOSIP) than any of the quinolones. In contrast, induction by 4-quinolones of the sfiA (sulA) gene, an SOS function involved in cell division inhibition, was better than induction by mitomycin C in an E. coli strain harbouring an sfiA::lacZ gene fusion. The umuC gene fusion was induced at lower concentrations of 4-quinolone than was the sfiA gene fusion.

Seventy amikacin-resistant clinical isolates of gram-negative bacteria belonging to nine genera were examined by immunoblotting and by DNA-DNA hybridisation for the presence of ACC(6′)1b enzyme, previously called AAC(6′)-4, or its encoding gene aacA1b. The organisms mostly had resistance profiles compatible with AAC(6′) production and were from South and North America, the Far East and Europe. Polyclonal (rabbit) anti-AAC(6′)-1b antisera and an intragenic aacA1b (aacA4) probe derived from the multiresistance plasmid pAZ007 were used. The aacA1b gene was found to be widespread. Positive hybridisation, and immunologically cross-reactive proteins, were observed in 44% of the isolates examined. They were present most frequently (£70%) in isolates of Klebsiella, Escherichia and Enterobacter spp., but less often (£25%) in Serratia, Citrobacter, Acinetobacter and Pseudomonas spp. The strains that reacted with the probe produced enzymes that varied in their apparent mol. wts between c. 24000 and 26000. The existence of multiple electrophoretic forms of amikacin-acetylating enzymes of the ACC(6′)-1b type may be useful in epidemiological surveys of AAC(6′)-mediated amikacin resistance.

Among a group of 116 clinically significant isolates of Bacteroides spp., 24 exhibited β-lactamase activity greater than the basal level characteristic of most Bacteroides strains. Investigation of specific enzyme activity, iso-electric point and enzyme inhibition profiles revealed that the β-lactamases involved could be divided into four groups, some showing similarity to those described in previous studies. Seven of the enzymes were able to hydrolyse cefoxitin, latamoxef or imipenem, and eight enzymes degraded penicillin in the presence of clavulanic acid. Five strains showed reduced susceptibility to cefoxitin, latamoxef or imipenem which was not associated with β-lactamase activity.

The rectal mucosa-associated flora (MAF) of patients with ulcerative colitis has been studied in 25 patients with newly diagnosed disease, 20 with relapse of existing disease, and 44 who were in remission. Patients with active disease were re-examined twice during treatment. The MAF was simpler and less dense than the microflora of faeces. Obligate anaerobes usually predominated in the MAF although the ratio of obligate anaerobes to facultative species was lower than that found in faeces. Viable counts of the total flora and of its constituent genera varied considerably between patients. Counts of the total flora, of obligate anaerobes (including bifidobacteria, eubacteria and clostridia), and facultative organisms and micro-aerobes (enterobacteria and lactobacilli) were reduced in patients with active disease compared with those with inactive disease; corresponding carriage rates were also lower. Counts and carriage rates increased during treatment and approached those found in quiescent disease. The alterations in the MAF were especially marked in patients experiencing their first attack of ulcerative colitis. The relationship between these alterations and the aetiology and pathogenesis of this disease remains unclear.

Nasal polyp cells in primary culture from cystic fibrosis (CF) and non-CF patients were compared for the ability to bind Pseudomonas aeruginosa cells and for the presence of sulphated glycoconjugates at the epithelial cell surface. Quantitation of bacterial adhesion, by scanning electronmicroscopy, showed no significant difference between the cells cultured from CF and non-CF patients. Micro-organisms associated with ciliated cells were mainly aggregated, in contrast with those from non-ciliated cells. Sulphated glycoconjugates were identified on cells cultured from both CF and non-CF patients, regardless of whether or not these cells had attached bacteria. A matrix-like material that surrounded the aggregated bacteria was more prominent on cells cultured from CF patients than on those from non-CF patients. The interaction of aggregated P. aeruginosa cells with polyp cells cultured from both CF and non-CF patients appeared to occur by means of this matrix material. Our findings suggest that chronic colonisation of the airways of CF patients cannot be explained by an increased affinity between the P. aeruginosa cells and the respiratory cell surface receptors in the CF patient. Nevertheless, the in-vitro observation that the matrix surrounding the bacteria reacted with a monoclonal antibody against respiratory mucins allows us to speculate that increased mucin secretion by cells from CF patients might, in vivo, play a decisive role in the interaction between P. aeruginosa and the respiratory epithelium.

The function of peritoneal macrophages induced by intraperitoneal (i.p.) injection of attenuated Streptococcus pyogenes (OK-432), Bacillus Calmette Guérin (BCG), protein-bound polysaccharide preparation isolated from Coriolus vesicolor (PSK) or Lactobacillus casei was examined. The PMA-triggered respiratory burst (production of O2 − and H2O2) of macrophages induced by OK-432, BCG or Lac. casei was greater than that of resident or thioglycollate-stimulated macrophages and was similar to that of BCG-activated macrophages. PSK failed to enhance the production of O2 − or H2O2 by macrophages. Alkaline phosphodiesterase (APD) activity was reduced in macrophages induced by OK-432, BCG or Lac. casei injection and in BCG-activated macrophages. The APD activity of macrophages obtained 7 and 13 days after i.p. injection of PSK was elevated, as with thioglycollate-stimulated macrophages. Listericidal activity in vitro was enhanced in macrophages obtained in 13 and 7 days, but suppressed in macrophages obtained 2 days after OK-432, BCG or Lac. casei injection. Lac. casei administered either 2 or 13 days before infection with Listeria monocytogenes was protective but OK-432, BCG (0.1 mg) and PSK were not, even though they were able to stimulate macrophage function.

The results of body fluid and surface cultures from 148 preterm infants 33 weeks gestational age obtained routinely on admission to a neonatal intensive care unit were reviewed. The aim was to determine the occurrence of congenital bacterial sepsis in this population and to examine whether surface cultures yielded information helpful in management. Gastric aspirate and umbilical, nasal and ear swabs were cultured and the results were compared to those of blood cultures. Nine infants (5.4%) had congenital bacterial sepsis diagnosed by positive blood cultures. Only the results of microscopy of gastric aspirate were available within hours of birth and before the results of blood culture. Microscopy of gastric aspirate, demonstrating pus cells, alone had a sensitivity of 0.86 in predicting congenital sepsis but a specificity of 0.49; the specificity, however, rose to 0.80 if both organisms and pus cells were observed on microscopy. Thus, only this combination was a useful pre-indicator of congenital sepsis. In infants who did not develop septicaemia, treatment was modified only if Streptococcus agalactiae was cultured from surface sites; in all such cases, the organism was grown from the ear swab. Our results demonstrate that congenital bacterial sepsis is common amongst very preterm infants admitted for neonatal intensive care but routine screening of surface cultures should be restricted to an ear swab only.

Although Neisseria gonorrhoeae can use haem as the sole exogenous iron source for growth in vitro, the mechanism of haem-iron uptake in the gonococcus is unknown. Two haemin-binding proteins (HmBPs) of 97 and 44 Kda were isolated by batch ligand affinitychromatography from whole cells or total membranes of gonococci grown under iron-limited conditions but not from those grown under iron-sufficient conditions. Competition binding experiments indicated that the haemin-protein interaction was specific; only haemin or haem-containing proteins, such as human haemoglobin or equine cytochrome c111, but not protoporphyrin IX, iron loaded human transferrin or lactoferrin, could abrogate binding. Identical HmBPs were isolated from three other clinical gonococcal strains, suggesting that these may be interstrain structural and functional homogeneity amongst these polypeptides.

A polyethylene glycol (PEG) precipitation method was used to examine sera of patients with active pulmonary tuberculosis (PT), leprosy and non-tuberculous pulmonary diseases and of healthy control subjects for immune complexes (ICs). Mycobacterium tuberculosis antigen 5 was detected in the ICs in 80% of patients with PT by the indirect (sandwich) enzyme-linked immunosorbent assay (ELISA). Detection of mycobacterial antigen in ICs has diagnostic potential as an adjunct in the laboratory diagnosis of PT, particularly when repeated bacteriological investigations for M. tuberculosis in clinical specimens are negative. Levels of ICs tend to decrease with the duration of anti-tuberculosis chemotherapy and their detection can also be used to assess the clinical response to therapy in patients with PT.

Factors influencing the production of streptococcin A-FF22 (SA-FF22) in liquid media were examined. Despite good growth of the producer strain, no SA-FF22 was detected during incubation at 40°, at pH 7, in Brain Heart Infusion Broth or in Mg2+-supplemented media. Optimal SA-FF22 production occurred at 32°, at pH 6.7, in cultures in Tryptic Soy Broth supplemented with glucose 2.25% and yeast extract 1%. Under these conditions SA-FF22 remained cell-associated but could be extracted with acid.