In vitro synergy between cefepime and vancomycin against methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis

The in vitro activity of cefepime combined with vancomycin was assessed by the chequerboard method against 35 clinical isolates of methicillin-susceptible (MSSA, n = 8) or -resistant (MRSA, n = 10) Staphylococcus aureus and methicillin-susceptible (MSSE, n = 9) or -resistant (MRSE, n = 8) Staphylococcus epidermidis and S. aureus ATCC 25923 (MSSA). The combination was synergic against 16 isolates and additive/indifferent against 20. For 10 of the clinical isolates (two MSSA, three MRSA, two MSSE, three MRSE) and the reference strain, the interaction of cefepime and vancomycin was also determined by the time-kill method. Except for one MRSA isolate, synergic killing was demonstrated with clinically achievable concentrations of vancomycin (0.5-1 mg/L) and cefepime (methicillin-susceptible isolates: 0.5-1 mg/L; methicillin-resistant isolates: 2-64 mg/L).     

Mupirocin prophylaxis against methicillin-susceptible, methicillin-resistant, or vancomycin-intermediate Staphylococcus epidermidis vascular-graft infection

A rat model was used to investigate the efficacy of mupirocin in the prevention of vascular prosthetic graft infection due to Staphylococcus epidermidis strains with different susceptibility patterns (methicillin susceptible, methicillin resistant, and with intermediate resistance to vancomycin). The effect of mupirocin-soaked Dacron was compared to that of perioperative intraperitoneal prophylaxis with vancomycin. Graft infections were established in the back subcutaneous tissue of adult male Wistar rats by implantation of Dacron prostheses (1 cm(2)) followed by topical inoculation with 5 x 10(7) CFU of one staphylococcal strain. The study included a control group (no graft contamination), three contaminated groups that did not receive any antibiotic prophylaxis, three contaminated groups that received mupirocin-soaked grafts, three contaminated groups in which perioperative intraperitoneal vancomycin prophylaxis (10 mg/kg of body weight) was administered, and three contaminated groups that received mupirocin-soaked grafts and perioperative intraperitoneal vancomycin prophylaxis (10 mg/kg). The grafts were sterilely removed 7 days after implantation, and the infection was evaluated by using sonication and quantitative agar culture. Data analysis showed the efficacy of mupirocin against all three strains, with growth of the strains in treated rats significantly different than that in the untreated control. In addition, mupirocin was more effective than vancomycin against the strain with intermediate susceptibility to the glycopeptide. Finally, the combination of mupirocin and vancomycin produced complete suppression of the growth of all of the strains.     

Polycationic peptides as prophylactic agents against methicillin-susceptible or methicillin-resistant Staphylococcus epidermidis vascular graft infection

Several polycationic peptides isolated from animals, plants, and bacterial species possess a broad spectrum of antimicrobial activity. A rat model was used to investigate the efficacies of two peptides, ranalexin and buforin II, in the prevention of vascular prosthetic graft infections. The effect of peptide-soaked collagen-sealed Dacron was compared to that of rifampin-soaked collagen-sealed Dacron in the rat model of graft infection caused by methicillin-susceptible rifampin-susceptible Staphylococcus epidermidis and methicillin-resistant rifampin-susceptible S. epidermidis. Graft infections were established in the back subcutaneous tissue of 240 adult male Wistar rats by implantation of 1-cm(2) Dacron prostheses, followed by topical inoculation with 2 x 10(7) CFU of S. epidermidis. The study included a control group (no graft contamination), two contaminated groups that did not receive any antibiotic prophylaxis, two contaminated groups to which perioperative intraperitoneal cefazolin prophylaxis (30 mg/kg of body weight) was administered, six contaminated groups that received a peptide- or rifampin-soaked graft, and six contaminated groups that received a peptide- or rifampin-soaked graft and perioperative intraperitoneal cefazolin prophylaxis (30 mg/kg). The grafts were sterilely removed 7 days after implantation, and the infection was evaluated by using sonication and quantitative agar culture. Overall, the efficacies of the polycationic peptides against the methicillin-susceptible and methicillin-resistant strains were not significantly different from that of rifampin. Nevertheless, the combinations of ranalexin- and buforin II-coated grafts with cefazolin treatment demonstrated efficacies significantly higher than that of the combination of rifampin-coated grafts and cefazolin treatment against the methicillin-resistant strain.     

Comparative activity of cloxacillin and vancomycin against methicillin-susceptible Staphylococcus aureus experimental endocarditis

OBJECTIVES: To compare the activity of cloxacillin and vancomycin against methicillin-susceptible Staphylococcus aureus and to determine how rapidly their bactericidal activity occurs in cardiac vegetations. METHODS: In vitro and in vivo studies using an experimental model of endocarditis in rabbits. Animals were treated for 1, 2 or 3 days with cloxacillin 200 mg/kg intramuscularly three times a day or vancomycin 25 mg/kg intravenously twice a day. RESULTS: Cloxacillin and vancomycin at concentrations 4- and 16-fold the MIC produced a modest decrease in the number of microorganisms at 4 h. After 24 h, cloxacillin produced a decrease in the counts of staphylococci from 2.19 to 4.84 log10 cfu/mL of inoculum. Only concentrations of vancomycin from 16- to 32-fold the MIC resulted in equivalent decreases. After 24 h of treatment, both antibiotics were equally effective in preventing mortality of rabbits. Cloxacillin produced a greater decrease in the number of staphylococci than vancomycin (3.50+/-2.18 log10 cfu/g vegetation and 6.25+/-1.28 log10 cfu/g vegetation, respectively; P<0.05) and 41% of rabbits had sterile vegetations in comparison with none with vancomycin (P=0.035). After 48 and 72 h of treatment, both antimicrobials exhibited equivalent activity. CONCLUSIONS: Vancomycin was less rapidly bactericidal than cloxacillin in vivo.     

Effect of azithromycin, roxithromycin and erythromycin on human polymorphonuclear leukocyte function against Staphylococcus aureus

The effect of three macrolides (azithromycin, roxithromycin and erythromycin) on the interaction in vitro of human polymorphonuclear leukocytes (PMNs) with Staphylococcus aureus was examined. The exposure of S. aureus to 0.25 MIC of roxithromycin and erythromycin but not of azithromycin significantly increased the uptake of opsonized bacteria by human PMNs. The preincubation of PMNs with 1, 10 and 25 mg/l of the three antimicrobial agents did not affect either the uptake of S. aureus or the superoxide radical production by human PMNs. At these same concentrations the three agents showed slight but not significant intracellular activity in PMNs against S. aureus. It is concluded that treatment of S. aureus with subinhibitory concentrations of roxithromycin and erythromycin enhanced phagocytosis by PMNs, but the three macrolides tested did not directly affect the functions of human PMNs against S. aureus.     

Comparative in vitro inhibitory and killing activity of cefpirome, ceftazidime, and cefotaxime against Pseudomonas aeruginosa, enterococci, Staphylococcus epidermidis, and methicillin-susceptible and -resistant and tolerant and nontolerant Staphylococcus aureus.

With a macrotube dilution method, MICs and MBCs were determined for three aminothiazolyl cephalosporins, cefpirome (HR 810), ceftazidime, and cefotaxime, against Pseudomonas aeruginosa, enterococci, Staphylococcus epidermidis, and methicillin-resistant, -susceptible, and -tolerant strains of Staphylococcus aureus. Comparatively, cefpirome was the most active agent against all gram-positive cocci, including enterococci and methicillin-resistant S. aureus, and was as active as ceftazidime against P. aeruginosa. MBCs of cefpirome were within two dilutions of the MICs for 91% of P. aeruginosa and 90% of gram-positive cocci strains tested, except methicillin-resistant S. aureus, for which the MBCs were within three dilutions for 90% of strains.     

Comparative efficacy and toxicity of roxithromycin and erythromycin ethylsuccinate in the treatment of streptococcal pharyngitis in adults

Roxithromycin is a novel oxime ether derivative of erythromycin. Previous studies have demonstrated similar in-vitro activity for roxithromycin and erythromycin. Roxithromycin has improved pharmacokinetic properties and may be a useful alternative agent for infections where erythromycin is indicated. We compared the efficacy and toxicity of roxithromycin and erythromycin ethylsuccinate in the treatment of streptococcal pharyngitis in adults. We also assessed compliance with treatment between the two agents. Roxithromycin and erythromycin ethylsuccinate were equally effective in resolving the symptoms and signs of pharyngitis. Erythromycin ethylsuccinate was superior to roxithromycin in achieving microbiological cure (90% vs. 33%, respectively). No differences were observed in toxicity or compliance with treatment between the two agents. Based on this prespective clinical trial, roxithromycin is not considered to be an acceptable alternative agent for acute streptococcal pharyngitis in adults.     

Comparative efficacy of clindamycin, erythromycin and spiramycin against Staphylococcus aureus in the rat croton oil pouch model

Spiramycin, a macrolide antibiotic, has inferior in-vitro activity to erythromycin, but superior tissue penetration. Recent publications have suggested that the in-vivo activity of spiramycin should be re-assessed. The efficacy of clindamycin, erythromycin and spiramycin was compared against Staphylococcus aureus infections in the rat croton oil pouch model. The concentration of spiramycin in the pouch fluid was lower than the concentration of clindamycin or erythromycin after single or multiple intraperitoneal injections. In contrast, the concentration of spiramycin in the pouch wall (73.3 +/- 14.5 micrograms/g) was markedly higher than that of erythromycin (less than 7.5 micrograms/g). Multiple doses of spiramycin had no significant effect upon bacterial growth in the pouch, whereas clindamycin and erythromycin had a significant bactericidal effect. The results suggest that spiramycin is bound to tissues, diffuses poorly into tissue fluid and may therefore be ineffective against infections in large collections of tissue fluid.     

米诺环素和多西环素对表皮葡萄球菌的体外抗菌活性比较

目的观察米诺环素和多西环素对表皮葡萄球菌的体外抗菌活性。方法采用二倍琼脂稀释法对124株表皮葡萄球菌进行米诺环素和多西环素体外抗菌实验,并进行两种抗生素的抗菌效果对比。结果米诺环素和多西环素均有很好的抗菌效果,米诺环素和多西环素对81株甲氧西林敏感的表皮葡萄球菌(MSSE)的最低抑菌浓度(MIC90)分别为1 mg/L和2 mg/L。对43株耐甲氧西林表皮葡萄球菌(MRSE)的MIC90均为2 mg/L。结论表皮葡萄球菌对米诺环素和多西环素的敏感率均为100%,表明米诺环素和多西环素均有较好的抗菌效果。     

Antagonism between penicillin and erythromycin against Streptococcus pneumoniae in vitro and in vivo

The combination of beta-lactam antibiotics and macrolides is often recommended for the initial empirical treatment of acute pneumonia in order to obtain activity against the most important pathogens. Theoretically, this combination may be inexpedient, as the bacteriostatic agent may antagonize the effect of the bactericidal agent. In this study, the possible interaction between penicillin and erythromycin was investigated in vitro and in vivo against four clinical isolates of Streptococcus pneumoniae with MICs of penicillin ranging from 0.016 to 0.5 mg/L and of erythromycin from 0. 25 to >128 mg/L. In vitro time-kill curves were generated with clinically relevant concentrations of penicillin (10 mg/L) and erythromycin (1 mg/L), either individually or in combination. Antagonism between penicillin and erythromycin was observed for the four isolates. In vivo interaction was investigated in the mouse peritonitis model. After intraperitoneal inoculation, penicillin and erythromycin were given either individually or in combination. For two of the four isolates, mortality was significantly higher in the groups treated with the combination of penicillin and erythromycin than in the groups treated with penicillin alone [32/36 (86%) vs. 3/12 (25%), P<0.05; and 24/36 (67%) vs. 3/12 (25%), P<0.05, respectively]. Using the mouse peritonitis model, in vivo time-kill curves showed that there was antagonism between erythromycin and penicillin for the examined isolate. The antagonism demonstrated in vitro and in vivo between penicillin and erythromycin suggests that ss-lactam antibiotics and macrolides should not be administered together unless pneumococcal infection is ruled out.     

Time course of the antibacterial activity of erythromycin stearate and erythromycin acistrate against two Staphylococcus aureus strains in vitro

The antibacterial efficacy of erythromycin stearate (ES) and a new erythromycin prodrug, erythromycin acistrate (EA, 2'-acetyl erythromycin stearate), was compared in two Staphylococcus aureus strains, one sensitive and the other resistant to erythromycin. The growth was continuously monitored turbidometrically for 24 h. With the sensitive S. aureus, the inhibitory effects of both ES and EA were visible within 1-2 h when the antibiotics were added at 0 or 1.5 h after the beginning of the incubation. When they were added at 3 h, their action was immediate at 0.5 and 1 mg/l, and 5 mg/l caused a complete inhibition of the growth. At 0.5 and 1 mg/l, however, ES was much more effective than EA. When EA and ES (1, 5 or 10 mg/l) were added at 0 or 1.5 h to the resistant staphylococcal culture, the lag phases (no detectable growth) were prolonged as a function of drug concentration but eventually the growth was restored. The action of EA was weaker and the lag phases were 2-5 h shorter than those after ES. When the compounds were added at 3 h, the antibacterial effect was visible immediately. The increase of absorbance was slowed down even by 1 mg/l of ES and almost prevented by 5 mg/l. At these concentrations EA was less effective than ES, but the two erythromycins were equally active at 10 mg/l. These results show that addition of EA acts on both staphylococci as rapidly as addition of ES but to a lesser extent. Evidently EA is antibacterially weaker than ES, or rapidly hydrolyzed to erythromycin after it has been added to the test system.     

Antibiotic activity in vitro against methicillin-resistant Staphylococcus epidermidis and therapy of an experimental infection.

Staphylococcus epidermidis is a major pathogen in early prosthetic valve endocarditis and cerebrospinal fluid shunt infections. Approximately 10 to 15% of hospital isolates are methicillin resistant. Ten clinically significant isolates of the latter were collected for antibiotic studies in vitro and in an experimental infection in animals. Time-kill studies of five strains showed gentamicin to be the single most effective antibiotic; however, dwarf colony variants emerged as survivors with two of these strains when challenged with gentamicin alone. The addition of a second antibiotic to gentamicin did not significantly improve the bactericidal rate but prevented the emergence of variant strains. A blood culture isolate of methicillin-resistant S. epidermidis combined with 5% hog gastric mucin was used to establish an experimental intraperitoneal infection in mice. Neither methicillin nor nafcillin treatment reduced mortality below that of untreated animals. Cephalothin treatment delayed early mortality but did not diminish overall mortality. Gentamicin was the most effective single antibiotic, and gentamicin in combination with vancomycin was the most effective regimen overall. The combination of rifampin plus vancomycin was as effective as gentamicin alone. The combinations of cephalothin or nafcillin with gentamicin and cephalothin with vancomycin demonstrated antagonism. The antagonism was not due to multiple injections or drug-drug inactivation.     

In vitro activity of tigecycline against Staphylococcus epidermidis growing in an adherent-cell biofilm model

The activity of tigecycline against Staphylococcus epidermidis growing in an in vitro adherent-cell biofilm model was determined. Tigecycline minimum bactericidal concentrations (MBCs) ranged from 1 to 8 microg/ml for S. epidermidis growing in a biofilm of adherent cells, compared to MBCs of 0.12 to >32 microg/ml for freely growing cells. The killing activity of tigecycline against the adherent bacteria was at least fourfold better than that of vancomycin and daptomycin.     

In vitro activities of oxazolidinone compounds U100592 and U100766 against Staphylococcus aureus and Staphylococcus epidermidis.

The new oxazolidinone antimicrobial agents U100592 and U100766 demonstrated good in vitro inhibitory activity against clinical strains of Staphylococcus aureus and Staphylococcus epidermidis regardless of methicillin susceptibility. Both agents appeared bacteriostatic by time-kill analysis. Stable resistance to low multiples of the MIC of either drug could be produced only in methicillin-resistant S. aureus.     

Human immunoglobulin G recognizing fibrinogen-binding surface proteins is protective against both Staphylococcus aureus and Staphylococcus epidermidis infections in vivo

A human donor-selected immunoglobulin G for intravenous injection (IGIV) product with elevated titers against the staphylococcal fibrinogen-binding MSCRAMM proteins ClfA and SdrG (INH-A21) was tested in vitro and in vivo. INH-A21 contained a significantly increased ability to inhibit the fibrinogen-binding activity of recombinant forms of both ClfA and SdrG. Evaluation of the opsonizing potential of INH-A21 was evaluated using fluorescently labeled bacteria; this assay indicated an increase in phagocytic activity compared to normal IGIV. The prophylactic efficacy of INH-A21 against an intraperitoneal challenge of methicillin-resistant Staphylococcus epidermidis (MRSE) was evaluated in a neonatal rat model. INH-A21 was also evaluated for prophylactic and therapeutic efficacy in a rabbit model of catheter-induced aortic valve infective endocarditis caused by either MRSE or methicillin-resistant Staphylococcus aureus (MRSA). Results from the in vivo models demonstrated potent prophylactic and therapeutic efficacy against both MRSE and MRSA. These data suggest that INH-A21 may be an important tool for the prevention and treatment of staphylococcal infections, especially in high-risk populations.     

In vitro activities of arylomycin natural-product antibiotics against Staphylococcus epidermidis and other coagulase-negative staphylococci

The arylomycins are a class of natural-product antibiotics that act via the inhibition of type I signal peptidase (SPase), and we have found in diverse bacteria that their activity is limited by the presence of a resistance-conferring Pro residue in SPase that reduces inhibitor binding. We have also demonstrated that Staphylococcus epidermidis, which lacks this Pro residue, is extremely susceptible to the arylomycins. Here, to further explore the potential utility of the arylomycins, we report an analysis of the activity of a synthetic arylomycin derivative, arylomycin C₁₆, against clinical isolates of S. epidermidis and other coagulase-negative staphylococci (CoNS) from distinct geographical locations. Against many important species of CoNS, including S. epidermidis, S. haemolyticus, S. lugdunensis, and S. hominis, we find that arylomycin C₁₆ exhibits activity equal to or greater than that of vancomycin, the antibiotic most commonly used to treat CoNS infections. While the susceptibility was generally correlated with the absence of the previously identified Pro residue, several cases were identified where additional factors also appear to contribute.The coagulase-negative staphylococci (CoNS) are a heterogeneous group of at least 15 different species of Gram-positive bacteria that have emerged in recent decades as important nosocomial pathogens (10, 31). A particularly problematic species is Staphylococcus epidermidis, which is responsible for a growing number of infections among hospital patients with compromised immune systems and is especially notorious for forming biofilms that adhere to surgical equipment and other hospital surfaces and indwelling devices (3, 18). Methicillin was traditionally the first-line antibiotic against CoNS, but its widespread use has resulted in resistance in 50% to 80% of CoNS infections and 75 to 90% of nosocomial S. epidermidis infections (18). As a result, vancomycin is now the first line agent for treating CoNS infections; however, isolates with reduced susceptibility to vancomycin have also been observed (11, 26), and the emergence of enterococci harboring mobile elements that confer vancomycin resistance has raised concerns that resistance might be transferred to S. epidermidis and/or other CoNS (17, 28). These concerns continue to motivate the search for new antibiotics that are active against CoNS, especially S. epidermidis.The arylomycins (Fig. ​(Fig.1)1) are a novel class of natural-product antibiotics that act by inhibiting bacterial type I signal peptidase (SPase) (19, 25). SPase is a Ser-Lys dyad protease that removes N-terminal signal sequences from preproteins following their translocation across the cytoplasmic membrane (5, 20). SPase is an attractive target for antibiotic therapy because it is conserved, essential, and located in the relatively accessible outer leaflet of the cytoplasmic membrane. Furthermore, because bacterial SPase acts via a catalytic mechanism that is distinct from that of its eukaryotic homologues, the arylomycins are unlikely to exhibit mechanistic toxicity in humans (5, 20).Open in a separate windowFIG. 1.Structures of arylomycin A₂ (R = iso-C₁₂) and arylomycin C₁₆ (R = iso-C₁₆) [iso-C₁₂ = CH₂(CH₂)₇CH(CH₃)₂ and iso-C₁₆ = CH₂(CH₂)₁₁CH(CH₃)₂].Despite the apparent accessibility, essentiality, and conservation of SPase, initial reports suggested that the arylomycins were active against only a few Gram-positive bacteria, including Streptococcus pneumoniae, Rhodococcus opacus, and Brevibacillus brevis (15, 25), and not against other important Gram-positive pathogens or against any Gram-negative bacteria. However, after reporting the first synthesis of an arylomycin, arylomycin A₂, as well as the synthetic derivative arylomycin C₁₆ (Fig. ​(Fig.1),1), we found that each potently inhibits the growth of S. epidermidis (24) and that S. epidermidis evolves resistance to the arylomycins by mutating residue 29 of one of its two SPases, SpsIB, from Ser (Ser²⁹) to Pro (Pro²⁹) (29). Moreover, a Pro residue is naturally present at the analogous position in the homologous SPases of the pathogens Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and we showed that it imparts resistance by reducing the affinity with which the arylomycins bind. Furthermore, we found that a remarkably diverse range of both Gram-positive and Gram-negative bacteria whose SPases lack a Pro at the analogous position are susceptible to the arylomycins, including Staphylococcus epidermidis, Streptococcus pyogenes, Helicobacter pylori, Chlamydia trachomatis, and some strains of Francisella tularensis (29). In total, the results suggest that the identified SPase polymorphism is a major contributor to naturally occurring arylomycin resistance. However, we also showed that Yersinia pestis and some strains of S. aureus are susceptible to the arylomycins despite the presence of an analogous Pro, while others, such as many of the Lactobacillales, Clostridia, and Bacteriodetes, are resistant despite its absence, implying that in some cases, susceptibility must depend on additional factors, such as variable levels of toxicity associated with the inhibition of protein secretion.The potent activity of the arylomycins against a strain of S. epidermidis (RP62A) suggests that they might be useful in the treatment of this and perhaps other CoNS. Here, to examine the spectrum of activity of the arylomycins against clinical isolates of S. epidermidis and other CoNS, we report the activity of arylomycin C₁₆ against two panels of isolates from hospitals in geographically diverse locations and compare the activity to that of vancomycin. The results reveal that the arylomycins have potent antibacterial activity against a range of important CoNS species whose SpsIB orthologs lack the previously identified resistance-conferring Pro, while less activity is observed against species where Pro is present. While we generally observed similar susceptibilities for different isolates within a species, significant differences were observed in several cases, with one atypical instance of susceptibility resulting from the presence of a Ser in place of the resistance-conferring Pro. Significant differences in susceptibility between isolates of the same species are usually observed with clinically deployed antibiotics where selection for resistance has occurred during therapy (2, 9, 14, 21), and therefore, these results may be relevant to understanding the natural evolution of arylomycin resistance in nature.     

In vitro and in vivo efficacy of the combination trimethoprim-sulfamethoxazole against clinical isolates of methicillin-resistant Staphylococcus aureus.

The in vitro susceptibilities of 16 independent, geographically distinct clinical isolates of methicillin-resistant Staphylococcus aureus to trimethoprim (TMP) in combination with sulfamethoxazole (SMX) were evaluated. Although methicillin-resistant S. aureus strains appear to be universally resistant to SMX, the combination TMP-SMX was found to be synergistic in vitro (in combination, the MICs of both drugs decreased 6- to 25-fold) as well as in vivo (5- to 6-fold reduction in TMP at 50% effective doses).