In vitro activity of various antimicrobial agents against Staphylococcus aureus isolates including fluoroquinolone- and oxacillin-resistant strains

Activity of moxifloxacin against pathogens with decreased susceptibility to ciprofloxacin

A panel of 279 clinical isolates of Gram-positive cocci and Gram-negative bacilli with varying levels of resistance to ciprofloxacin were analysed for susceptibility to moxifloxacin, ciprofloxacin, ofloxacin and nalidixic acid. Moxifloxacin was eight- to 32-fold more potent than ciprofloxacin and ofloxacin against staphylococci and Streptococcus pneumoniae, and equivalent to eight-fold more potent against enterococci. Although ciprofloxacin was intrinsically more potent than the other quinolones against highly susceptible Gram-negative isolates, the percentages of Gram-negative isolates susceptible to 1 mg/L of moxifloxacin or ciprofloxacin, or 2 mg/L of ofloxacin were 78%, 80% and 76%, indicating in-vitro equivalence of the agents against a collection that included isolates with diminished quinolone susceptibility. Staphylococci were analysed according to their ciprofloxacin susceptibility status. As ciprofloxacin resistance increased to high levels, all quinolone MICs increased, but moxifloxacin and ofloxacin MICs increased less than ciprofloxacin MICs. In mutational studies moxifloxacin inhibited more mutants (69%) at a concentration of 1 mg/L than did ciprofloxacin (63%) at 1 mg/L or ofloxacin at 2 mg/L (31%). The study indicated that moxifloxacin is more potent than ciprofloxacin and ofloxacin against Gram-positive pathogens, may be comparable in activity against less quinolone-susceptible Gram-negative isolates (other than Pseudomonas aeruginosa), and is less affected than ciprofloxacin by mechanisms responsible for increasing quinolone resistance in staphylococci.

Susceptibility of ciprofloxacin-resistant staphylococci and enterococci to trovafloxacin

The susceptibilities of clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and enterococci obtained over a 13-year period were tested for trovafloxacin, a new fluoroquinolone, and ciprofloxacin. For MRSA, MIC50 values for trovafloxacin increased from 0.03 microgram/ml to 1 microgram/ml from 1984-1985 to 1995-1996, but were lower than those noted for ciprofloxacin, which increased from 0.25 microgram/ml to > 8 micrograms/ml during the same period. Trovafloxacin also showed lower MIC50 values (0.12-0.25 microgram/ml) than ciprofloxacin (MIC50 of 0.5-1 microgram/ml) for E. faecalis isolates from 1985 through 1991, but against E. faecium and E. faecalis isolated in 1995-1996, the MIC50 values for both trovafloxacin and ciprofloxacin were 2 micrograms/ml and the MIC90 values were > or 8 micrograms/ml. Thus, cross-resistance between fluoroquinolones was shown for both enterococci and MRSA. Whether the greater intrinsic activity of trovafloxacin might allow its use in treating MRSA and enterococcal infections remains to be seen.

Imipenem/cilastatin: an update of its antibacterial activity, pharmacokinetics and therapeutic efficacy in the treatment of serious infections

The prototype carbapenem antibacterial agent imipenem has a very broad spectrum of antibacterial activity, encompassing most Gram-negative and Gram-positive aerobes and anaerobes, including most beta-lactamase-producing species. It is coadministered with a renal dehydropeptidase inhibitor, cilastatin, in order to prevent its renal metabolism in clinical use. Extensive clinical experience gained with imipenem/cilastatin has shown it to provide effective monotherapy for septicaemia, neutropenic fever, and intra-abdominal, lower respiratory tract, genitourinary, gynaecological, skin and soft tissues, and bone and joint infections. In these indications, imipenem/cilastatin generally exhibits similar efficacy to broad-spectrum cephalosporins and other carbapenems and is at least equivalent to standard aminoglycoside-based and other combination regimens. Imipenem/cilastatin is generally well tolerated by adults and children, with local injection site events, gastrointestinal disturbances and dermatological reactions being the most common adverse events. Seizures have also been reported, occurring mostly in patients with impaired renal function or CNS pathology, or with excessive dosage. Although it is no longer a unique compound, as newer carbapenems such as meropenem are becoming available, imipenem/cilastatin nevertheless remains an important agent with established efficacy as monotherapy for moderate to severe bacterial infections. Its particular niche is in treating infections known or suspected to be caused by multiresistant pathogens.

Multicenter in vitro comparative study of fluoroquinolones against 25,129 gram-positive and gram-negative clinical isolates

In vitro activities of fleroxacin, ciprofloxacin, ofloxacin, and lomefloxacin were evaluated against 25,129 fresh bacterial isolates from 51 US hospital or medical center laboratories, beginning in October of 1990. Susceptibility rates were > or = 85% against most species of Gram-negative bacteria. Notable exceptions were Pseudomonas, Acinetobacter, Xanthomonas, and Providencia. The study drugs displayed similar activity against most Gram-negative species. At least 90% of oxacillin-susceptible staphylococci were susceptible but, of oxacillin-resistant strains, only approximately 60% of Staphylococcus epidermidis and 25% of Staphylococcus aureus were susceptible to the quinolones tested. Staphylococcus saprophyticus strains were less susceptible to fleroxacin (42%) than to the other compounds (79%-97%). Ofloxacin and ciprofloxacin were more active against streptococci, and none of the compounds demonstrated appreciable activity against enterococci. Thus, the spectra of activity of fluoroquinolones illustrate that they remain effective agents for the treatment of many types of infections caused by Gram-negative pathogens.

Flavanones with potent antibacterial activity against methicillin-resistant Staphylococcus aureus

With the therapeutic concept of using the defensive ability of plants against microbial infections, phytoalexin, an antimicrobial phytochemical was studied for its ability to inhibit the growth of methicillin-resistant Staphylococcus aureus (MRSA). Extracts from Sophora exigua (Leguminosae) were fractionated by serial chromatography and the anti-MRSA activity of each fraction was determined by the agar-plate method. Among the active isolates, 5,7,2',6'-tetrahydroxy-6-isoprenyl-8-lavandulyl-4'-methox yflavanone (exiguaflavanone D) completely inhibited the growth of all the MRSA strains examined at the concentration of 1.56-6.25 micrograms mL-1, and 5, 2',6'-trihydroxy-8-lavandulyl-7-methoxy-flavanone (exiguaflavanone B) inhibited at a concentration of 50 micrograms mL-1. This former compound is expected to be a phytotherapeutic agent for MRSA infections as an alternative to conventional antibiotics with unwanted side-effects or the appearance of antibiotic-resistant bacteria.

Multicenter in vitro comparative study of fluoroquinolones after four years of widespread clinical use

In vitro activities of ciprofloxacin, fleroxacin, lomefloxacin, ofloxacin, and seven other oral antimicrobials including amoxicillin-clavulanic acid (A/C), oxacillin, cefaclor, cefixime, cefuroxime, erythromycin, and trimethoprim-sulfamethoxazole (T/S) were evaluated against 1708 fresh bacterial isolates from four hospital laboratories approximately 4 years after the introduction of ciprofloxacin. T/S and ofloxacin had the lowest MIC90s and greatest percentage of susceptible strains overall, followed by the other three quinolones. Quinolones were the most active drugs tested against Gram-negative bacteria, with little variation in the activity among the four compounds against most species. Quinolone resistance was detected to some degree in the majority of Gram-negative species tested, with Pseudomonas, Acinetobacter, Xanthomonas, and Providencia demonstrating the highest percentage of resistant strains. Ofloxacin and ciprofloxacin were relatively more active against Gram-positive bacteria than were fleroxacin and lomefloxacin, but T/S and A/C had more susceptible strains than any of the quinolones. Oxacillin-resistant staphylococci, enterococci, and streptococci exhibited the least quinolone susceptibility. This study showed that while resistance is developing among several previously susceptible bacterial species, quinolones remain important alternatives for the oral treatment of many types of infections. Actions to prevent or limit resistance will be important to maintain the viability of the quinolones as therapeutic agents in both hospital and community environments.