Susceptibility of anaerobic bacteria isolated from intra-abdominal infections to ofloxacin and interaction of ofloxacin with metronidazole

Comparative antimicrobial efficacy of Metapex, Metronidazole, BioPure MTAD, Aztreonam on Bacteroides fragilis and Propionibacterium acne

Aim:

The purpose of this study was to evaluate the comparative antibacterial efficacy of Biopure MTAD, Metapex, Metronidazole, and Aztreonam against two obligate anerobic bacteria.

Materials and Methods:

Antimicrobial efficacy of selected medicaments against two obligate anaerobic bacteria Bacteroides fragilis and Propionibacterium acnes was done by Agar disc-diffusion method. Pre-sterilized Whatman paper discs, 6 mm in diameter and soaked with the test solution, were prepared and placed onto the previously seeded agar Petri plates. Each plate was incubated in anaerobic jar for anerobic environment at 37°C for 48 hours. A zone of inhibition was recorded for each plate and the results were analysed statistically. Saline and ethanol used as control group in this study.

Results:

Biopure MTAD, Metapex and Metronidazole were effective against all the selected microorganisms. Aztreonam was effective against Bacteroides fragilis. Saline and ethanol used as control were ineffective.

Conclusions:

Metronidazole showed the superior antibacterial property amongst the tested medicaments.

Fluoroquinolones and Anaerobes

The usefulness of fluoroquinolones for the treatment of mixed aerobic and anaerobic infections has been investigated since these agents started being used in clinical practice. Newer compounds have increased in vitro activity against anaerobes, but clinically relevant susceptibility breakpoints for these bacteria have not been established. Pharmacodynamic analyses and corroboration by new data from clinical trials have enhanced our knowledge concerning the use of fluoroquinolones to treat selective anaerobic pathogens. These studies suggest that newer agents could be useful in the treatment of several types of mixed aerobic and anaerobic infections, including skin and soft-tissue, intra-abdominal, and respiratory infections. The major concerns with expanding the use of fluoroquinolones to treat anaerobic infections have been reports of increasing resistance in Bacteroides group isolates and the impact of these antibiotics on the incidence of Clostridium difficile-associated disease.

Review of the in vitro activity and potential clinical efficacy of levofloxacin in the treatment of anaerobic infections

The activity of levofloxacin against aerobic bacteria has been well documented both in vitro and clinically, but its anaerobic activity has been infrequently studied. This new fluoroquinolone exhibits good in vitro activity (MIC(S) < or =2.0 microg/mL) against many anaerobic pathogens associated with acute sinusitis, bite wounds, and other soft-tissue infections. It is less active against Bacteroides fragilis (MIC (90)=2-4 microg/mL ) and has poor inhibitory activity against non-fragilis B. fragilis group species that are associated with gastrointestinal and genitourinary tract infections. Levofloxacin does not antagonize the in vitro activity of clindamycin and metronidazole and often provides additive or synergistic activity against anaerobic bacteria with these agents. In pharmacodynamic models, levofloxacin exhibits rapid bactericidal activity at 2-4 times the MIC of anaerobic bacteria. Prolonged killing is observed when the area-under-the concentration-time-curve to MIC ratio is greater than 40. In clinical efficacy trials, levofloxacin has been effective in the treatment of patients with gynecologic, skin and skin-structure, and bone infections involving anaerobic pathogens. Both micro-biologic and pharmacodynamic studies support further evaluations of levofloxacin in the treatment of selective mixed aerobic/anaerobic infections.

Quinolone activity against anaerobes

The first generation of fluoroquinolones such as ciprofloxacin and ofloxacin are inactive against most anaerobic bacteria. However, some broad-spectrum quinolones, which have recently become clinically available or are under active development, have significant antianaerobic activity. This review summarises the in vitro activity of currently available, as well as experimental, quinolones against clinically significant anaerobic bacteria. Quinolones with low activity against anaerobes include ciprofloxacin, ofloxacin, levofloxacin, fleroxacin, pefloxacin, enoxacin and lomefloxacin. Compounds with intermediate antianaerobic activity include sparfloxacin and grepafloxacin. Trovafloxacin, gatifloxacin and moxifloxacin yield low MICs against most groups of anaerobes. Quinolones with the greatest in vitro activity against anaerobes include clinafloxacin and sitafloxacin (DU-6859a).

Quinolone activity against anaerobes: microbiological aspects

Currently available quinolones are either inactive or marginally active against anaerobic bacteria. This review summarises the in vitro activity of currently available as well as experimental quinolones against clinically significant anaerobic bacteria. Quinolones with low activity against anaerobes include ciprofloxacin, ofloxacin, levofloxacin, fleroxacin, pefloxacin, enoxacin, lomefloxacin and probably E 4868 and NM 441. Compounds with intermediate anaerobe activity include sparfloxacin, grepafloxacin, PD 131628 and AM 1155. Quinolones that are very active against anaerobes include clinafloxacin and DU 6859a. CP 99,219, a naphthyridone, is also very active against anaerobes. Toxicity problems have necessitated the withdrawal of some quinolones shown to have intermediate activity (temafloxacin and tosufloxacin) and the discontinuation of the development of some investigational agents (Win 57273 and BAY Y 3118) with high activity. Conclusions regarding the therapeutic value of quinolones against human anaerobic infections await further clinical toxicological and pharmacokinetic studies.

In vivo efficacies of quinolones and clindamycin for treatment of infections with Bacteroides fragilis and/or Escherichia coli in mice: correlation with in vitro susceptibilities

Therapy with ofloxacin, ciprofloxacin, and lomefloxacin (alone or in combination with clindamycin) and therapy with sparfloxacin, clinafloxacin, and temafloxacin alone were given to mice with subcutaneous abscesses. The abscesses were caused by two Bacteroides fragilis isolates, one of which was susceptible and one of which was resistant to ofloxacin, ciprofloxacin, and lomefloxacin, alone or in combination with Escherichia coli. The abscesses were examined 5 days after inoculation. Numbers of B. fragilis organisms reached log10 10.2 to 11.8 per abscess, and numbers of E. coli organisms reached log10 10.6 to 11.8 per abscess. All of the quinolones reduced the number of susceptible B. fragilis isolates (log10 3.6 to 6.9) and E. coli isolates (log10 5.7 to 6.8). However, ciprofloxacin and lomefloxacin failed to reduce the number of resistant B. fragilis organisms in single-organism or mixed infections. The addition of clindamycin to either ofloxacin, ciprofloxacin, or lomefloxacin reduced the numbers of both susceptible and resistant B. fragilis organisms (log10 3.8 to 7.8). In contrast, sparfloxacin, clinafloxacin, and temafloxacin were effective as single therapy in eradicating B. fragilis resistant to ofloxacin, ciprofloxacin, and lomefloxacin. These in vivo data confirm the in vitro activity of these quinolones and suggest that although ofloxacin, ciprofloxacin, and lomefloxacin are occasionally effective as single agents in eradicating mixed infection by susceptible strains of B. fragilis and E. coli, addition of an agent with activity against anaerobic organisms will ensure their efficacy. Quinolones with good efficacy against B. fragilis may be effective as single-agent therapy of mixed infections.

Synergy and antagonism of fluoroquinolones with other classes of antimicrobial agents

In an attempt to overcome some of the gaps in their antibacterial spectrum, e.g. some Gram-positive bacteria (notably streptococci and Streptococcus pneumoniae) and anaerobes, the fluoroquinolones have been combined with other bactericidal and bacteriostatic agents. In general, the fluoroquinolones rarely show either synergy or antagonism when used in combination with other antimicrobial agents against most bacteria. Therefore, in infections where the fluoroquinolones do not provide cover against all potential organisms, combined treatment with an appropriate agent may be considered. Current data suggest that the fluoroquinolones are not antagonistic with beta-lactams, macrolides, clindamycin and the imidazoles. Aminoglycosides in combination with the fluoroquinolones do not show synergy. Antipseudomonal penicillins, ceftazidime or imipenem in combination with the fluoroquinolones are synergistic and may be useful for treating infections in immunocompromised patients. Rifampicin in combination with a fluoroquinolone for the treatment of staphylococcal endocarditis or osteomyelitis may be useful, although in vitro and in vivo results do not always coincide.