Synergistic effect of quinolones and oxacillin on methicillin-resistant Staphylococcus species

Therapeutic Options for Adult Patients With Persistent Methicillin-Susceptible Staphylococcus aureus Bacteremia: A Narrative Review

OBJECTIVE

To compare the efficacy of antimicrobial therapies used in the management of persistent methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia.

DATA SOURCES

A literature search using the PubMed database (inception to December 2022) was conducted using the search terms "Staphylococcus aureus bacteremia," "methicillin-susceptible Staphylococcus aureus bacteremia," "persistent methicillin-susceptible Staphylococcus aureus bacteremia," and "refractory methicillin-susceptible Staphylococcus aureus bacteremia ." In addition, therapeutic agents which could be used as treatment for MSSA including "nafcillin," "oxacillin," "cefazolin," "ceftaroline," "gentamicin," "rifampin," and "daptomycin" were also combined with the aforementioned search terms to capture data using these agents.

STUDY SELECTION/DATA EXTRACTION

Clinical data were limited to those published in the English language. Articles and abstracts were considered for inclusion in addition to ongoing trials identified through ClinicalTrials.gov.

DATA SYNTHESIS

A total of 78 articles were reviewed including 17 in vitro or animal model studies and 39 studies including patient data. The remaining 22 articles included guidelines, review articles, and editorials. Recent data evaluating use of dual β-lactam regimens for persistent MSSA bacteremia were limited to 8 case reports or case series.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

At present, there is little guidance on how to best manage patients with persistent MSSA bacteremia. This narrative review collates the available data to assist clinicians in selecting the best possible antimicrobial regimen when facing this clinical conundrum.

CONCLUSIONS

Modification of antimicrobial therapy, in conjunction with source control and infectious diseases consultation, may all be necessary to sterilize blood cultures in patients with persistent MSSA bacteremia.

Exploring the Relationships between Structure and Antimicrobial Potency of Quinolinequinones

Microorganisms are responsible for hospital infections, and methicillin-resistant Staphylococcus aureus is one of them. In looking for the most effective lead structures to cope with the rise of antimicrobial (antibiotic) resistance, we evaluated the antimicrobial profile of quinolinequinones for potential antimicrobial applications. 1,4-quinone molecules fused with heteroatom have been studied extensively for many years as a source of drugs and lead structures. The aims of this study were to evaluate the antimicrobial activity of quinolinequinones against bacterial and fungal strains, and to probe for potential lead structures. For this reason, the activity of these compounds against three different strains of Candida fungi (C. albicans, C. parapsilosis, and C. tropicalis) and Gram-positive and Gram-negative pathogenic bacteria were investigated, searching for potential lead compounds. Five of nine quinolinequinones showed activity mainly against the Gram-positive strains with a minimal inhibitory concentration within the Clinical and Laboratory Standards Institute (CLSI) levels. The results revealed that quinolinequinones have significant activity against bacteria including Staphylococcus aureus and Staphylococcus epidermidis, and fungi including Candida albicans and Candida parapsilosis. QQ1, QQ2, QQ3, QQ5, and QQ6 exhibited the highest growth inhibition against two essential species of the Gram-positive strains (Staphylococcus epidermidis and Staphylococcus aureus). Among these, four molecules (QQ2, QQ3, QQ5, and QQ6) were also active against Enterococcus faecalis, the other member of the Gram-positive strains. The antifungal profile of two quinolinequinones (QQ7 and QQ8) indicated that they were as effective as the reference drug Clotrimazole against Candida albicans. The same molecules also have potential inhibitory antifungal activity against Candida tropicalis. For better understanding, the most active two quinolinequinones (QQ2 and QQ6) were examined for biofilm inhibition and a time-kill kinetic study.

Potency of omadacycline against Mycobacteroides abscessus clinical isolates in vitro and in a mouse model of pulmonary infection

The incidence of nontuberculous mycobacterial diseases in the United States is rising and has surpassed that of tuberculosis. Most notable among the nontuberculous mycobacteria is Mycobacteroides abscessus, an emerging environmental opportunistic pathogen capable of causing chronic infections. M. abscessus disease is difficult to treat, and the current treatment recommendations include repurposed antibiotics, several of which are associated with undesirable side effects. In this study, we have evaluated the activity of omadacycline, a new tetracycline derivative, against M. abscessus using in vitro and in vivo approaches. Omadacycline exhibited an MIC₉₀ of 0.5 µg/mL against a panel of 32 contemporary M. abscessus clinical isolates, several of which were resistant to antibiotics that are commonly used for treatment of M. abscessus disease. Omadacycline combined with clarithromycin, azithromycin, cefdinir, rifabutin, or linezolid also exhibited synergism against several M. abscessus strains and did not exhibit antagonism when combined with an additional nine antibiotics also commonly considered to treat M. abscessus disease. Concentration-dependent activity of omadacycline was observed in time-kill assessments. Efficacy of omadacycline was evaluated in a mouse model of lung infection against four M. abscessus strains. A dose equivalent to the 300-mg standard oral human dose was used. Compared to the untreated control group, within 4 weeks of treatment, 1 to 3 log₁₀ fewer M. abscessus CFU were observed in the lungs of mice treated with omadacycline. Treatment outcome was biphasic, with bactericidal activity observed after the first 2 weeks of treatment against all four M. abscessus strains.

β-Lactam Combinations That Exhibit Synergy against Mycobacteroides abscessus Clinical Isolates

Mycobacteroides abscessus (Mab) is an opportunistic environmental pathogen that can cause chronic pulmonary disease in the setting of structural lung conditions such as bronchiectasis, chronic obstructive pulmonary disease, and cystic fibrosis. These infections are often incurable and associated with rapid lung function decline. Mab is naturally resistant to most of the antibiotics available today, and current treatment guidelines require at least 1 year of daily multidrug therapy, which is often ineffective and is associated with significant toxicities. β-Lactams are the most widely used class of antibiotics and have a demonstrated record of safety and tolerability. Here, using a panel of recent clinical isolates of Mab, we evaluated the in vitro activities of dual-β-lactam combinations to identify new treatments with the potential to treat infections arising from a wide range of Mab strains. The Mab clinical isolates were heterogeneous, as reflected by the diversity of their genomes and differences in their susceptibilities to various drugs. Cefoxitin and imipenem are currently the only two β-lactams included in the guidelines for treating Mab disease, yet they are not used concurrently in clinical practice. However, this dual-β-lactam combination exhibited synergy against 100% of the isolates examined (n = 21). Equally surprising is the finding that the combination of two carbapenems, doripenem and imipenem, exhibited synergy against the majority of Mab isolates. In the setting of multidrug-resistant Mab disease with few therapeutic options, these combinations may offer viable immediate treatment options with efficacy against the broad spectrum of Mab strains infecting patients today.

Select β-Lactam Combinations Exhibit Synergy against Mycobacterium abscessus In Vitro

Mycobacterium abscessus is a nontuberculous mycobacterium that causes invasive pulmonary infections in patients with structural lung disease. M. abscessus is intrinsically resistant to several classes of antibiotics, and an increasing number of strains isolated from patients exhibit resistance to most antibiotics considered for treatment of infections by this mycobacterium. Therefore, there is an unmet need for new regimens with improved efficacy to treat this disease. Synthesis of the essential cell wall peptidoglycan in M. abscessus is achieved via two enzyme classes, l,d- and d,d-transpeptidases, with each class preferentially inhibited by different subclasses of β-lactam antibiotics. We hypothesized that a combination of two β-lactams that comprehensively inhibit the two enzyme classes will exhibit synergy in killing M. abscessus Paired combinations of antibiotics tested for in vitro synergy against M. abscessus included dual β-lactams, a β-lactam and a β-lactamase inhibitor, and a β-lactam and a rifamycin. Of the initial 206 combinations screened, 24 pairs exhibited synergy. A total of 13/24 pairs were combinations of two β-lactams, and 12/24 pairs brought the MICs of both drugs to within the therapeutic range. Additionally, synergistic drug pairs significantly reduced the frequency of selection of spontaneous resistant mutants. These novel combinations of currently available antibiotics may offer viable immediate treatment options against highly-resistant M. abscessus infections.

In vitro synergistic effects of various combinations of vancomycin and non-beta-lactams against Staphylococcus aureus with reduced susceptibility to vancomycin

The aim of our study was to determine the potential for synergistic effect of vancomycin combined with a non-beta-lactam agent and of combinations of orally available non-beta-lactam agents against vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA). Three VISA isolates, three hVISA isolates, and two vancomycin-susceptible S. aureus (VSSA) isolates were used. The combinations included vancomycin and one of clindamycin, ciprofloxacin, gentamicin, rifampicin, or trimethoprim/sulfamethoxazole. Pairwise combinations among five non-beta-lactam agents were also tested for synergy. Synergy was determined using time-kill curves at 24h. Vancomycin combined with either ciprofloxacin or gentamicin showed synergy against some isolates of VISA, hVISA and VSSA. Vancomycin combined with trimethoprim/sulfamethoxazole showed synergy against VISA and hVISA. Among orally available non-beta-lactam agents, only ciprofloxacin combined with either clindamycin or trimethoprim/sulfamethoxazole showed synergy against one isolate of VISA.

Community-acquired methicillin-resistant Staphylococcus aureus meningitis complicated by cerebral infarction. Role of antibiotic combination of linezolid plus levofloxacin

The therapeutic options available for central nervous system (CNS) infections due to resistant Gram-positive cocci remain limited. We report an unusual case of community-acquired methicillin-resistant Staphylococcus aureus meningitis complicated by cerebral infarction in the middle cerebral artery territory in a previously healthy young male. After an initial vancomycin-based regimen, treatment was completed with a seven-week course of linezolid and levofloxacin. The potential role of such a combination and, particularly, linezolid as a first-line therapy in serious CNS infections is also discussed.

Levofloxacin does not decrease mortality in Staphylococcus aureus bacteraemia when added to the standard treatment: a prospective and randomized clinical trial of 381 patients

OBJECTIVES

To study whether levofloxacin, added to standard treatment, could reduce the high mortality and complication rates in Staphylococcus aureus bacteraemia.

DESIGN

A prospective randomized multicentre trial from January 2000 to August 2002.

SETTING

Thirteen tertiary care or university hospitals in Finland.

SUBJECTS

Three hundred and eighty-one adult patients with S. aureus bacteraemia. Patients with meningitis, and those with fluoroquinolone- or methicillin-resistant S. aureus were excluded.

INTERVENTIONS

Standard treatment (mostly semisynthetic penicillin) (n = 190) or that combined with levofloxacin (n = 191). Supplementary rifampicin was recommended if deep infection was suspected.

MAIN OUTCOME MEASURES

Primary end-points were mortality at 28 days and at 3 months. Clinical and laboratory parameters were analysed as secondary end-points.

RESULTS

Adding levofloxacin to the standard treatment offered no survival benefit. Case fatality rates were 14% in both groups at 28 days, and 21% in the standard treatment and 18% in the levofloxacin group at 3 months. Levofloxacin combination did not differ from the standard treatment in the number of complications, time to defervescence, decrease in serum C-reactive protein concentration or length of antibiotic treatment. Deep infection was found in 84% of patients within 1 week following randomization with no difference between the treatment groups. At 3 months, the case fatality rate for patients with deep infection was 17% amongst those who received rifampicin versus 38% for those without rifampicin (P < 0.001, odds ratio = 3.06, 95% confidence intervals = 1.69-5.54).

CONCLUSIONS

Levofloxacin combined with standard treatment in S. aureus bacteraemia did not decrease mortality or the incidence of deep infections, nor did it speed up recovery. Interestingly, deep infections in S. aureus bacteraemia appeared to be more common than previously reported.

Mode of action of sulfanilyl fluoroquinolones

The mode of action of sulfanilyl fluoroquinolones (NSFQs) was investigated with NSFQ-104, NSFQ-105, and some structurally related compounds. Evidence arising from interactions with p-aminobenzoic acid and trimethoprim suggested that a sulfonamidelike mechanism of action makes little or no contribution to the in vitro activity of NSFQs. NSFQ-105 showed an activity that inhibits gyrase-catalyzed DNA supercoiling that is similar to the activity of other fluoroquinolones. Also, NSFQ-105 uptake was decreased by the presence of Mg2+ and increased by a lower pH. These results indicate that NSFQs having only one ionizable group could exhibit more favorable kinetics of access to the bacterial cell than zwitterionic fluoroquinolones.

Effect of different combinations of sparfloxacin, oxacillin, and fosfomycin against methicillin-resistant staphylococci

The in vitro activity of combinations of sparfloxacin/oxacillin, sparfloxacin/fosfomycin, and oxacillin/fosfomycin was investigated against 16 methicillin-resistant Staphylococcus aureus (MRSA) isolates and 12 methicillin-resistant Staphylococcus epidermidis (MRSE) isolates moderately resistant to sparfloxacin. Synergic interactions were observed more frequently against MRSE than against MRSA strains. The most effective combination on both species was fosfomycin plus oxacillin, synergistic against ten of 16 MRSA and eight of 12 MRSE strains.

Attenuation of gentamicin-induced nephrotoxicity in rats by fleroxacin

The effect of fleroxacin on gentamicin-induced nephrotoxicity was evaluated with female Sprague-Dawley rats. Animals were injected during 4 or 10 days with saline (NaCl; 0.9%), gentamicin alone at doses of 10 and 40 mg/kg of body weight/12 h (subcutaneously), fleroxacin alone at a dose of 25 mg/kg/12 h (intraperitoneally), or the combination gentamicin-fleroxacin in the same regimen. Gentamicin induced a dose- and time-dependent renal toxicity as evaluated by gentamicin cortical levels, sphingomyelinase activity in the renal cortex, histopathologic and morphometric analysis, blood urea nitrogen and serum creatinine levels, and cellular regeneration ([3H]thymidine incorporation into DNA of cortical cells). The extent of these changes was significantly reduced when gentamicin was given in combination with fleroxacin. Although the mechanisms by which fleroxacin reduces the nephrotoxic potential of gentamicin are unknown, we propose that the fleroxacin-gentamicin combination enhances exocytosis activity in proximal tubular cells, as suggested by the higher excretion of urinary enzymes and lower cortical levels of gentamicin observed in animals treated with the combination fleroxacin-gentamicin compared with those treated with gentamicin alone. The protective effect of fleroxacin on gentamicin nephrotoxicity should be investigated further.

Fleroxacin. A review of its pharmacology and therapeutic efficacy in various infections

The fluoroquinolone antibacterial agent fleroxacin has a broad spectrum of in vitro activity which encompasses most Gram-negative species (particularly Enterobacteriaceae) and a number of Gram-positive organisms, including methicillin-sensitive staphylococci. It is available as oral and intravenous formulations. In clinical trials, fleroxacin has been evaluated in the treatment of uncomplicated urinary tract infections (single or multiple once-daily oral doses of 200 or 400mg), gonorrhoea and chancroid (single oral doses of 200 or 400mg), complicated urinary tract, nonpneumococcal lower respiratory tract and skin and soft tissue infections and typhoid fever (multiple once-daily oral or intravenous regimens, usually 400 mg/day), bacterial enteritis, and traveller's diarrhoea (single or multiple once-daily oral doses of 400mg). Bacteriological cure rates were generally around 90% or higher in complicated and uncomplicated urinary tract infections, uncomplicated gonorrhoea (approximately 100%), pyelonephritis, bacterial enteritis and typhoid fever, and exceeded 80% in lower respiratory tract, and skin and soft tissue infections and chancroid. These cure rates were similar to, or better than, those achieved with standard comparator antibacterial agents such as penicillins, cephalosporins, cotrimoxazole, or other quinolones. Fleroxacin 400mg once daily also achieved bacteriological cure in approximately 80% of patients with bone and joint infections in preliminary studies. In Japanese studies using a lower dosage of 200 or 300 mg/day, fleroxacin was reported to be bacteriologically effective in a range of infections, including urinary tract and upper and lower respiratory tract infections. Fleroxacin has a relatively long elimination half-life, which allows once-daily administration, and it appears to have less propensity for interactions with other medications in comparison to many other fluoroquinolones. Its tolerability profile is typical of this class of compound, with adverse events mostly relating to the gastrointestinal tract, CNS, and skin and appendages (including phototoxicity). Recent pooled tolerability data from worldwide clinical trials indicate that adverse events are reported by approximately 27% of patients receiving 200 mg/day orally or 400 mg/day orally or intravenously, and 17% of those receiving a single oral dose of 400mg. These exceed incidences reported for established fluoroquinolones, possibly indicating recent trends towards increased rates of reported adverse effects with these agents. However, in direct comparative studies with twice-daily fluoroquinolones, fleroxacin 400mg once daily produced a similar incidence of adverse effects to ofloxacin 800 mg/day and a slightly higher incidence than ciprofloxacin 1000 mg/day, while fleroxacin 200mg once daily produced a similar incidence to norfloxacin 800 mg/day.(ABSTRACT TRUNCATED AT 400 WORDS)

Synergy of levofloxacin (L-ofloxacin) and oxacillin against quinolone-resistant Staphylococcus aureus, measured by the time-kill method

The synergistic activity of levofloxacin and oxacillin against levofloxacin-resistant isolates of methicillin-resistant Staphylococcus aureus was tested by the time-kill method. The combination of levofloxacin at 1/4 the MIC for the isolate plus oxacillin at 8 micrograms/ml (< 1/4 the MIC) was synergistic against seven of nine isolates at 8 h, although no significant synergy was demonstrated at 24 h. This combination may prove to be effective against multidrug-resistant methicillin-resistant S. aureus, and further studies are warranted.

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.

Relative beta-lactamase- and transpeptidase-inhibitory activities of the new quinolone WIN-57273 in Staphylococcus aureus

The new quinolone WIN-57273 was shown to inhibit Staphylococcus aureus beta-lactamase activity noncompetitively in vitro with an apparent Ki value of 0.5 mM. MICs of penicillin G for a highly quinolone-resistant, beta-lactamase-negative strain in the presence of exogenous beta-lactamase decreased considerably when subinhibitory concentrations of WIN-57273 were added. Furthermore, the attachment transpeptidase reaction, investigated on whole cells of S. aureus, was impeded by WIN-57273 concentrations of greater than or equal to 30 microM. While these interactions suggest a novel mechanism of action for this compound, they are probably not relevant to the overall antibacterial potency of WIN-57273.

Synergy and antagonism of combinations with quinolones

Combinations of fluoroquinolones with other antimicrobial agents have been extensively investigated. Combinations of fluoroquinolones with aminoglycosides, beta-lactams, imidazoles, macrolides and clindamycin infrequently show synergy against Enterobacteriaceae and gram-positive bacteria. These combinations rarely show antagonism. Combinations of rifampin with fluoroquinolones tested against Staphylococcus aureus have been reported to show synergy and antagonism, and in vitro results have not correlated with results of animal infection experiments. Against Pseudomonas aeruginosa combinations of antipseudomonas penicillins or imipenem with fluoroquinolones are synergistic for 20% to 50% of isolates in vitro and also are synergistic in animal models of infection, whereas combinations of aminoglycosides with fluoroquinolones rarely show synergy against Pseudomonas aeruginosa. Against anaerobic species such as Bacteroides fragilis combinations of fluoroquinolones with clindamycin, anti-anaerobic penicillins, cephalosporins or imidazoles are occasionally synergistic but usually indifferent. Ciprofloxacin and ofloxacin combined with antituberculosis agents have activity against Mycobacterium tuberculosis and atypical mycobacteria. In general, fluoroquinolones should be combined with other agents not to achieve synergy, which is extremely variable, but to provide activity against bacteria inadequately inhibited by the fluoroquinolones.

Newly documented antimicrobial activity of quinolones

The improved antimicrobial activity of newer fluoroquinolones and novel applications recently found for the drugs already marketed are reviewed. Several new compounds are more active against gram-positive bacteria than the presently marketed fluoroquinolones. WIN 57273, the most potent compound in vitro on a weight basis, is 16 to 128 times more active than ciprofloxacin against various staphylococci, streptococci, Enterococcus spp., Corynebacterium spp., Listeria monocytogenes and Bacillus spp. BMY 40062, PD 117558, PD 127391, sparfloxacin, temafloxacin and tosufloxacin also show enhanced in vitro efficacy against these species. These drugs also possess increased activity against various anaerobes, notably Clostridium perfringens, Clostridium difficile and the Bacteroides fragilis group. Mycobacterium tuberculosis, rapidly growing mycobacteria other than Mycobacterium chelonae, and Mycobacterium leprae are often susceptible to quinolones displaying bactericidal activity which is potentially useful for curing difficult-to-treat mycobacteriosis. In addition, a number of new products, notably those containing a cyclopropyl group, are more active than reference fluoroquinolones against Mycobacterium leprae. Sparfloxacin, BMY 40062 and WIN 57273 compare favorably with older fluoroquinolones in the killing of intracellular Legionella spp., and several of the newer compounds have greater antichlamydial potency. Improved antibacterial activity has also been found against Mycoplasma hominis, Ureaplasma urealyticum, Acinetobacter spp. and Pseudomonas maltophilia. By contrast, the newer quinolones have similar or less activity against Pseudomonas aeruginosa and Enterobacteriaceae. Recently, pefloxacin, ofloxacin and ciprofloxacin were found to be active against protozoa, including Plasmodium spp., Trypanosoma cruzi and Leishmania donovani, but not against Toxoplasma gondii. In the near future, more specific research testing unusual pathogens may lead to the identification of quinolones with more selective activity.