The in-vitro bactericidal activities of combinations of antimicrobial agents against clinical isolates of Mycobacterium avium-intracellulare

The in-vitro activities of five antimicrobial agents (rifabutin, clarithromycin, ethambutol, ciprofloxacin and amikacin), alone and in combination, were evaluated against 21 strains of Mycobacterium avium-intracellulare isolated from patients with AIDS. The combined activities of these agents were studied on solid medium by a full chequerboard method. Synergy was demonstrated most frequently (28-71% of isolates) with those combinations that included ethambutol. In killing curve experiments where double and triple combinations of agents were tested against two of the strains, 99% kill was achieved in seven days at concentrations well below those that are attainable in serum. However, an additive rather than a synergic effect was seen in most instances. Although ciprofloxacin alone had the greatest bactericidal activity against these two strains, its activity was antagonized in the presence of rifabutin; this antagonism became inapparent when a third agent was added. Demonstration of bactericidal activity in broth culture may be more relevant than the results of susceptibility testing on solid medium when choosing antimicrobial therapy for patients with this infection.

Beta-lactamase stability and antibacterial activity of cefpirome alone and in combination with other antibiotics

The antibacterial activity of cefpirome (HR810), a new cephalosporin, was compared with that of other "third-generation" cephalosporins, as well as cefuroxime, piperacillin and gentamicin. Cefpirome was the most active beta-lactam antibiotic against Gram-negative bacteria. The MIC90 for Enterobacteriaceae was always less than 0.5 ml/l except for Enterobacter species. The MIC90 against Pseudomonas species was 2 mg/l, which was equal to that of ceftazidime and gentamicin. Cefpirome was also more active than the other beta-lactam antibiotics against Staphylococcus aureus. A relatively high frequency of synergy was observed when cefpirome was combined with aminoglycosides against both Gram-positive and Gram-negative bacteria. No antagonism was detected. This antibiotic was very stable to both plasmid- and chromosomally-mediated beta-lactamases. It was more resistant to Enterobacter cloacae P99 enzyme than ceftazidime, cefotaxime and cefotetan. Its stability to the Klebsiella K1 beta-lactamase was more than that of cefotaxime and ceftriaxone but slightly less than that of ceftazidime and latamoxef. MBC90 values for cefpirome were generally less than twice the corresponding MIC values.

Enoxacin as one day oral treatment of men with anal or pharyngeal gonorrhoea

The efficacy of two regimens of oral enoxacin (400 mg as a single dose or two 200 mg doses 12 hours apart) to treat anal and pharyngeal gonorrhoea was compared. Fifty men with confirmed gonorrhoea (40 with anal, six with pharyngeal, and four with both) were treated and assessed three to five and seven to 14 days after treatment. Of 44 evaluable patients who attended the first follow up, including those who were infected with penicillinase producing Neisseria gonorrhoeae (PPNG), all were cured. No haematological or biochemical abnormality associated with enoxacin was observed. Nine patients reported minor adverse effects during the trial period, only one of which was considered probably related to the treatment. Both regimens of 400 mg enoxacin were effective in treating anal and pharyngeal gonorrhoea.

Bactericidal activity of netilmicin compared with gentamicin and streptomycin, alone and in combination with penicillin, against penicillin tolerant viridans streptococci and enterococci

Netilmicin was compared with gentamicin and streptomycin for in-vitro activity against 30 strains of penicillin-tolerant streptococci including 16 strains of enterococci. Both netilmicin and gentamicin tested alone at 4 mg/l caused 99.9% kill of more than half of the 13 strains of viridans streptococci tested, whereas streptomycin, 4 mg/l, had no bactericidal effect against these strains. Netilmicin, gentamicin and streptomycin tested alone at 8.0 mg/l against 10 strains of Streptococcus faecalis resulted in 99.9% kill of six, one and zero strains respectively. Combinations of penicillin with 2 mg/l of either netilmicin or gentamicin resulted in bactericidal synergy against 12 of 13 strains of viridans streptococci and all 10 strains of S. faecalis after 18 to 24 h incubation. Parallel experiments showed that higher concentration of penicillin were required to obtain 99.9% kill of 10 streptococcal strains when 4 mg/l streptomycin was compared with 2 mg/l of the other aminoglycosides. Killing curves showed similar bactericidal synergy for netilmicin-penicillin and gentamicin-penicillin combinations against most streptococci tested after 24 h incubation but there was sometimes a greater bactericidal effect noted with netilmicin after only 6 h incubation of the broth or after 48 h incubation. The results of this in-vitro study suggest that netilmicin is at least as effective as gentamicin as a bactericidal synergic agent with penicillin against penicillin-tolerant viridans streptococci and S. faecalis strains isolated from patients with endocarditis. Neither gentamicin or netilmicin were effective as bactericidal synergic agents with penicillin against 4 of 6 strains of S. faecium tested.

In vitro effects of lymphoblastoid interferon on lymphocyte activation and cell-mediated cytolysis in patients with chronic hepatitis B virus infection

In addition to a direct anti-viral effect, interferons have important immunological properties including effects on cell-mediated immunity and antibody production as well as cell-mediated cytolysis. In chronic hepatitis B virus infection the host immune system is important for the elimination of replicating virus and in addition to directly inhibiting hepatitis B virus replication, interferons may affect host immune responses. We investigated the effect of lymphoblastoid interferon in vitro on lymphocyte activation and cell-mediated cytolysis in patients with chronic hepatitis B virus infection. The proliferative response to the mitogen PHA was significantly impaired in patients compared to controls. In addition supernatants of cultured mononuclear cells from patients stimulated with PHA contained less interleukin-2 activity than controls while the proportion of stimulated mononuclear cells expressing the interleukin-2 receptor was also reduced in patients. Prior incubation with 10(3) U ml-1 lymphoblastoid interferon increased both interleukin-2 activity and interleukin-2 receptor expression in patients and controls, although in patients the response was less marked. In contrast the proliferative response was unaffected. Natural killer cell activity against K562 cells was similar in patients and controls which in both groups was significantly augmented by prior incubation with 10(3) U ml-1 lymphoblastoid interferon; the increase was inversely proportional to baseline activity. In contrast incubation of target or effector cells with interferon did not augment T-cell cytotoxicity against autologous hepatocytes. The effects of lymphoblastoid interferon in vitro, were modest, but subtle changes in immunological status in addition to a direct effect on viral replication may be relevant to eventual clearance of the hepatitis B virus.

Screening for bacteriuria: Microstix and dipslides

The Microstix system has been tested, in parallel with dipslides, for suitability as a screening technique for the detection of bacteriuria. Results obtained using each method on 228 urine specimens were assessed by comparison with the results of quantitative counts. Dipslides had a higher sensitivity (86-7%) than Microstix. The best specificity (100%) was obtained from those results (77-6%) where both components of the Microstix system were in agreement. Advantages of Microstix are its greater shelf-life and its compactness.

New technique for investigating bacterial flora of female periurethral area

The bacterial flora of the female periurethral area was studied by impression cultures taken by polystyrene sponges, the results being recorded by photographic contact printing. With this technique it is possible to observe the preferential colonisation of different areas by different organisms and to detect persistent colonisation by pathogens. In assessing the possible aetiological importance of these results, and especially in comparing them with the findings of other workers, it is essential to use correct anatomical nomenclature.