W K Hadley

Therapeutic implications of inhibition versus killing of Mycobacterium avium complex by antimicrobial agents.

Patients with the acquired immune deficiency syndrome (AIDS) with disseminated Mycobacterium avium infection have responded poorly to treatment with rifabutine (Ansamycin) and clofazimine, in spite of the good in vitro response of M. avium to these antimicrobial agents. We compared the ability of these and other antimicrobial agents to kill versus the ability to inhibit the growth of strains of the M. avium complex isolated from patients with AIDS. Killing curve experiments showed that the concentrations of rifabutine and clofazimine needed to kill two log units of M. avium are at least 32 times greater than the concentrations needed to inhibit growth. Little or no killing occurred at concentrations of these antimicrobial agents that are achievable in serum. In contrast, five of seven strains tested were killed by ciprofloxacin at concentrations that can be achieved in serum. Ciprofloxacin should be studied further for possible use in the treatment of M. avium infections.

Antimicrobial synergism against Mycobacterium avium complex strains isolated from patients with acquired immune deficiency syndrome.

Pairs of 11 antimicrobial agents were tested in vitro for their ability to act synergistically against three strains of Mycobacterium avium complex isolated from patients with acquired immune deficiency syndrome. From the combinations tested, four drugs (ethambutol, rifampin, ciprofloxacin, and erythromycin) were selected for more extensive study against 20 strains of M. avium complex. The inhibitory and killing synergism obtained with combinations of two, three, or four drugs was assessed by determining the fractional inhibitory concentration index and fractional bactericidal concentration index. Inhibitory synergism occurred against 90 to 100% of the strains for all drug combinations in which ethambutol was included. Killing synergism occurred against 85 to 95% of the strains when ethambutol was used in combinations which included either rifampin or ciprofloxacin. However, killing synergism occurred against only 45% of the strains when drugs were tested at concentrations that can be obtained in patient serum. In other experiments, rifabutin (Ansamycin) gave results that were comparable to those obtained with rifampin. Clofazimine did not show synergistic killing activity at a concentration that is achievable in serum for any of the drugs tested. Our results indicate that there is considerable variability in the antimicrobial susceptibility of M. avium isolates obtained from patients with acquired immune deficiency syndrome. This variability could have significant impact on the clinical response to various therapies.

Broth microdilution testing of susceptibilities to 30 antimicrobial agents of Mycobacterium avium strains from patients with acquired immune deficiency syndrome.

A total of 31 strains of Mycobacterium avium complex isolated from patients with acquired immune deficiency syndrome were tested for susceptibility to 30 antimicrobial agents by using microdilution trays containing dried antimicrobial agents. MICs were determined over a period of 7 days of growth in a broth medium (7HSF) that is equivalent to 7H11 agar. MICs obtained by this method showed good agreement with MICs determined by the agar dilution method. Strains could be divided into two groups by their antimicrobial susceptibility patterns. All group 1 strains (8 of the 31 strains tested) were at least moderately susceptible to inhibition by a variety of beta-lactam antimicrobial agents, including amoxicillin-clavulanic acid and cefmenoxime. Group 2 strains (23 of 31) were susceptible only to amikacin (22 of 23 strains). All 31 strains were resistant to oxacillin, clindamycin, erythromycin, tetracycline, chloramphenicol, vancomycin, nitrofurantoin, and aztreonam at the highest concentration of antimicrobial agent present in the microdilution trays. The addition of Tween 80 to 7HSF broth increased the susceptibility of M. avium complex to many of the antimicrobial agents tested. Killing of M. avium complex (i.e., less than or equal to 1% survival after 7 days) was found to vary for different strains and antimicrobial agents. Killing of some strains by amoxicillin-clavulanic acid, carbenicillin, azlocillin, cefmenoxime, cefotaxime, amikacin, and ampicillin occurred at concentrations of antimicrobial agent that are achievable in serum. Further studies are needed to determine whether any of these antimicrobial agents has activity against M. avium complex cells that have been ingested by macrophages.

In vitro susceptibility of Mycobacterium avium complex to the new fluoroquinolone sparfloxacin (CI-978; AT-4140) and comparison with ciprofloxacin.

We tested the activity of the new fluoroquinolone sparfloxacin (CI-978; AT 4140) against 30 strains of Mycobacterium avium complex (MAC) isolated from patients with acquired immune deficiency syndrome. MICs of sparfloxacin (range, less than or equal to 0.06 to 4 micrograms/ml) were lower than MICs of ciprofloxacin for all 30 strains, and MBCs for acid-fast bacteria were lower for 28 of the 30 strains. In synergism experiments using 10 strains of MAC, fractional inhibitory concentration indices revealed that the combination of sparfloxacin plus ethambutol was synergistic against 9 strains, and the three-drug combination of sparfloxacin plus ethambutol plus rifampin was synergistic against all strains. In the absence of ethambutol, the combination of sparfloxacin plus rifampin appeared to be antagonistic against three of the MAC strains.

Comparison of the intracellular activities of clarithromycin and erythromycin against Mycobacterium avium complex strains in J774 cells and in alveolar macrophages from human immunodeficiency virus type 1-infected individuals.

The intracellular activities of clarithromycin and erythromycin, alone and in combination with other antimicrobial agents, were tested against Mycobacterium avium complex (MAC) strains inside mouse J774 cells and inside alveolar macrophages obtained from human immunodeficiency type 1-infected individuals. Clarithromycin alone had greater intracellular activity than erythromycin alone, and drug combinations that included clarithromycin were usually more active than combinations that included erythromycin.

Effects of antimicrobial agents on survival of Mycobacterium avium complex inside alveolar macrophages obtained from patients with human immunodeficiency virus infection.

Measurements of the activities of antimicrobial agents against the Mycobacterium avium complex (MAC) usually do not take into consideration the intracellular location of the organism. A recent study using mouse macrophage continuous cell line J774 (D. M. Yajko, P.S. Nassos, C. A. Sanders, and W. K. Hadley, Am. Rev. Respir. Dis. 140: 1198-1203, 1989) showed that certain combinations of antimicrobial agents are able to kill MAC inside macrophages and suggested that the J774 cell line could be used as a model for screening of drugs for intracellular activity against MAC. As a test of the validity of this model, alveolar macrophages were isolated from the bronchoalveolar lavages of 36 patients who had AIDS or an AIDS-related condition or were considered to be at risk for AIDS. The macrophages were infected with MAC and then treated with a drug or drug combination for 48 to 72 h. Survival of MAC was measured over time in drug-treated macrophages and untreated control macrophages. No single drug or two-drug combination that was tested was able to cause a decrease in the survival of every one of the MAC strains used in the study. However, several three-drug combinations that had been shown to cause a decrease in survival of all MAC strains inside J774 cells also caused a decrease in survival of all MAC strains inside alveolar macrophages from patients. The good agreement between these results and those obtained previously with J774 cells gives further evidence of the usefulness of the simpler J774 model for screening of drugs for intracellular activity against MAC.

In vitro activity of new beta-lactam antibiotics and other antimicrobial drugs against anaerobic isolates from obstetric and gynecological infections.

The in vitro activities of N-formimidoyl thienamycin, clindamycin, chloramphenicol, metronidazole, cefoperazone, cefotaxime, cefoxitin, moxalactam, penicillin G, and piperacillin were determined against 158 anaerobic bacteria isolated from endometrial wash cultures of women with pelvic infections. In general, N-formimidoyl thienamycin was the most active, with all organisms inhibited by less than or equal to 0.5 microgram/ml. Chloramphenicol, clindamycin, and metronidazole inhibited all organisms by less than or equal to 8 microgram/ml. The penicillins and cephalosporins exhibited variable activity of lesser degrees.

Occurrence of clindamycin-resistant anaerobic bacteria isolated from cultures taken following clindamycin therapy

MICs of clindamycin were determined by the agar dilution method against anaerobic organisms isolated from endometrial cultures in women with pelvic soft tissue infections. Cultures were obtained from 100 women both before and after clindamycin therapy, from 107 women before therapy with clindamycin or another antimicrobial agent or after treatment with an antimicrobial agent other than clindamycin, and from 9 women 1 to 9 weeks after they were discharged from the hospital following clindamycin therapy. Only 5 (0.7%) of 685 isolates tested from women who had not received clindamycin therapy were resistant to clindamycin. From the 100 cultures taken immediately after clindamycin therapy, 57 anaerobic bacteria were isolated from 28 cultures. Of the 40 anaerobic organisms for which MICs of clindamycin were determined, 25 (62.5%) were resistant to clindamycin (MIC greater than or equal to 8 micrograms/ml). The most common organisms isolated after therapy were the anaerobic gram-positive cocci (of which 32 isolates were discovered); of 28 coccal isolates tested, 64% were clindamycin resistant. Four of seven (57%) of the Bacteroides isolates tested, one unidentified gram-positive nonsporing rod, one unidentified gram-negative coccus, and one Mobiluncus sp. were also clindamycin resistant. Of 18 anaerobic isolates from the nine cultures taken 1 to 9 weeks after hospital discharge, 55% were resistant to clindamycin. The clinical significance of these findings is unknown since all patients recovered without incident and remained well. However, the data suggest that physicians need to be aware that patients with recent exposure to clindamycin may have clindamycin-resistant anaerobic organisms in a current infection. This may prevent the infection from responding to clindamycin treatment.

In vitro activity of cefbuperazone and other antimicrobial agents against isolates from the female genital tract.

Cefbuperazone (BMY 25182), a new cephamycin, showed activity similar to those of moxalactam and other cephalosporin-cephamycins against aerobic and anaerobic bacteria from female genital tract infections. MICs of the antimicrobial agents were less than or equal to 16 micrograms/ml for greater than 97% of organisms tested. All of the anaerobic bacteria tested were susceptible to clindamycin, metronidazole, and chloramphenicol.