Enrico Tagliaferri

Synergistic activity of colistin plus rifampin against colistin-resistant KPC-producing Klebsiella pneumoniae.

ABSTRACT Infections caused by carbapenem-resistant KPC-producing Klebsiella pneumoniae are responsible for high rates of mortality and represent a major therapeutic challenge, especially when the isolates are also resistant to colistin. We used the checkerboard method to evaluate the synergistic activity of 10 antibiotic combinations against 13 colistin-resistant KPC-producing K. pneumoniae isolates (colistin MIC range of 8 to 128 mg/liter). Colistin plus rifampin was the only combination that demonstrated consistent synergistic bacteriostatic activity against 13/13 strains tested, reducing the colistin MIC below the susceptibility breakpoint (MIC ≤ 2 mg/liter) in 7/13 strains at rifampin concentrations ranging from 4 to 16 mg/liter. Bactericidal synergistic activity was also documented for 8/13 tested strains. Other antimicrobial combinations with carbapenems, gentamicin, and tigecycline showed variously synergistic results. Colistin plus rifampin also exhibited bacteriostatic synergistic activity against 4/4 colistin-susceptible KPC-producing K. pneumoniae isolates (colistin MIC range of 0.5 to 2 mg/liter) and 4/4 ertapenem-resistant extended-spectrum beta-lactamase (ESBL)-producing K. pneumoniae isolates (ertapenem MIC range of 16 to 32 mg/liter). Collectively, our data suggest that colistin plus rifampin is the most consistently synergistic combination against KPC-producing K. pneumoniae isolates, including colistin-resistant strains. Colistin-rifampin combinations may have a role in the treatment of multidrug-resistant K. pneumoniae and may possibly slow the selection of heteroresistant subpopulations during colistin therapy.

Microbiology of cardiac implantable electronic device infections

AIMS The aim of the study was to describe the microbiological findings of cardiac implantable electronic devices (CIEDs) infection in the 2000-2011 period at the Cardiology Unit of New Santa Chiara Hospital in Pisa (Italy). METHODS AND RESULTS Removed CIED leads and pocket material were seeded on solid media and isolates tested for antimicrobial susceptibility with the Kirby Bauer method. Electrodes from 1204 patients were analysed and 854 (70.9%) tested positive. In 663 (77.6%) cases only one species was isolated, in 175 (20.5%) two species, and in 14 (1.8%) >2 species. In 116 cases material from the pocket was also cultured. The result was consistent with that from the electrodes in 69 (59%) cases. In 359 cases a blood sample was also obtained for culture. The result was consistent with that from the leads in 124 (35%) cases. A total of 1068 strains were isolated from electrodes. Gram-positive organisms were most frequently isolated (92.5% of isolates); particularly, coagulase-negative staphylococci (CoNS), mainly Staphylococcus epidermidis, in 69% of cases and Staphylococcus aureus in 13.8%, Gram-negative rods in 6.1%, yeasts in 1% and molds in 0.4%. Overall, Oxacillin resistance was 30%, in particular 33% among CoNS and 13% among S. aureus. Oxacillin resistance and quinolones resistance have increased in the period 2006-2011 with respect to the 5 years before. Seventeen percent of Enterobacteriaceae strains had a phenotype compatible with extended spectrum beta-lactamase expression. CONCLUSIONS Culture of the leads offers the possibility of an aetiological diagnosis in the majority of cases. When material from the pocket can be obtained, the microbiological result is often consistent with that from the electrodes, while species isolated from blood cultures are often different and more likely to be the result of contamination. Cardiac implantable electronic device infection is more often monomicrobial, CoNS are most frequently isolated and S. epidermidis is largely the main single agent. Very early infections were associated with S. aureus infection. The pattern of susceptibility to antimicrobials is in general that of community-acquired infections, although oxacillin resistance and quinolones resistance has increased in the last 5 years.

Microbiological Activity and Clinical Efficacy of a Colistin and Rifampin Combination in Multidrug-Resistant Pseudomonas aeruginosa Infections

Abstract The aim of the study was to assess the microbiological activity and clinical efficacy of colistin and rifampin combination against multidrug-resistant (MDR) Pseudomonas aeruginosa infections. The antimicrobial activity of the colistin/rifampin combination was evaluated using the checkerboard and time-kill curve methods against different MDR P. aeruginosa strains. The combination of rifampin and colistin resulted fully (1 strain) or partially (5 strains) synergistic for 6/7 strains and minimum inhibitory concentrations (MICs) in combination were reduced to easily obtainable therapeutic levels. The time-kill curves showed that the combination was bactericidal against the strains tested. The clinical efficacy of the combination was tested in four patients with difficultto treat infections (sepsis or pneumonia) caused by MDR P. aeruginosa. All infections were successfully treated. Our microbiological and clinical observations suggest that the addition of rifampin to colistin may result in a synergistic bactericidal combination that may be useful in patients with infections caused by MDR P. aeruginosa which are difficult to cure.

Oral Gentamicin Gut Decontamination for Prevention of KPC-Producing Klebsiella pneumoniae Infections: Relevance of Concomitant Systemic Antibiotic Therapy

ABSTRACT Gut colonization represents the main source for KPC-producing Klebsiella pneumoniae (KPC-Kp) epidemic dissemination. Oral gentamicin, 80 mg four times daily, was administered to 50 consecutive patients with gut colonization by gentamicin-susceptible KPC-Kp in cases of planned surgery, major medical intervention, or need for patient transfer. The overall decontamination rate was 68% (34/50). The median duration of gentamicin treatment was 9 days (interquartile range, 7 to 15 days) in decontaminated patients compared to 24 days (interquartile range, 20 to 30 days) in those with persistent colonization (P < 0.001). In the six-month period of follow-up, KPC-Kp infections were documented in 5/34 (15%) successfully decontaminated patients compared to 12/16 (73%) persistent carriers (P < 0.001). The decontamination rate was 96% (22/23) in patients receiving oral gentamicin only, compared to 44% (12/27) of those treated with oral gentamicin and concomitant systemic antibiotic therapy (CSAT) (P < 0.001). The multivariate analysis confirmed CSAT and KPC-Kp infection as the variables associated with gut decontamination. In the follow-up period, KPC-Kp infections were documented in 2/23 (9%) of patients treated with oral gentamicin only and in 15/27 (56%) of those also receiving CSAT (P = 0.003). No difference in overall death rate between different groups was documented. Gentamicin-resistant KPC-Kp strains were isolated from stools of 4/16 persistent carriers. Peak gentamicin blood levels were below 1 mg/liter in 12/14 tested patients. Oral gentamicin was shown to be potentially useful for gut decontamination and prevention of infection due to KPC-Kp, especially in patients not receiving CSAT. The risk of emergence of gentamicin-resistant KPC-Kp should be considered.

Microbiology at first visit of moderate-to-severe diabetic foot infection with antimicrobial activity and a survey of quinolone monotherapy

Samples from 1295 patients with diabetic foot infection were evaluated; 4332 samples were collected with an average of 3.3 samples per patient. Fifty-seven percent of patients had a 2B ulcer and 23% had a 3B ulcer according to Texas University Classification. In 64.2% of samples collected at first visit an etiologic agent was identified. About 40% of the positive samples were polymicrobial. Gram positive bacteria were more frequently isolated (52.6%), Staphylococcus aureus was the most frequently isolated single agent (29.9%) and MRSA was 22% of S. aureus. Enterococcus spp., mainly Enterococcus faecalis, were 9.9%, all vancomycin susceptible except 2 isolates. Streptococci were 4.6%, more than 60% Streptococcus agalactiae. Gram negative rods were 40.6%, with enterobacteria 23.5% and Pseudomonas aeruginosa 10.3%. Anaerobes were only 0.3%, probably due to culture methods applied in our laboratory. Cotrimoxazole, rifampin and doxycycline were still active against S. aureus. ESBL producers, among enterobacteria, were 10%, mainly Escherichia coli and Proteus spp. Only colistin had a rate of susceptibility against P. aeruginosa above 90%. Levofloxacin had the best clinical activity with respect to the other quinolones, but when it failed, selected more resistant strains with respect to moxifloxacin among S. aureus and with respect to ciprofloxacin among P. aeruginosa.

Vancomycin-Resistant Enterococcus faecium (VRE) Bacteremia in Infective Endocarditis Successfully Treated with Combination Daptomycin and Tigecycline

Enterococci are a leading cause of nosocomial bacteremia and endocarditis 1, and vancomycin-resistant enterococci (VRE), mostly Enterococcus faecium, are increasingly involved, especially in critical patients with co-morbid conditions. Optimal antimicrobial therapy is still undefined, but there is evidence that antibiotics with in vitro bactericidal activity should be sought 2. novel antimicrobial compounds such as quinupristin/dalfopristin, linezolid, and daptomycin have shown in vitro bactericidal activity against VRE 3, and also tigecycline, although bacteriostatic, has shown potential for treating infections caused by VRE and other multidrug resistant (MDR) strains 4,5. Daptomycin is a cyclic lipopeptide with documented bactericidal activity against VRE, and has been shown to be safe and effective in the treatment of drug-resistant Gram-positive bloodstream infections and endocarditis 6,7. However, the emergence of daptomycin resistance 8 and cases of daptomycin treatment failure in VRE endocarditis have been reported 9,10. in such difficult-to-treat infections, the accurate evaluation of minimum inhibitory concentrations (MiC), minimal bactericidal concentrations (MBC) and serum antibacterial activity of combinations of antibiotics may be useful to guide therapy. We hereby report a case of MDR E. faecium endocarditis treated successfully with a combination of daptomycin and tigecycline, following failure of daptomycin monotherapy. An 86-year-old man was admitted to the infectious Diseases Unit of Pisa Hospital in italy, in December 2007 for persistent fever, despite home treatment with different antibiotic regimens (levofloxacin followed by ceftriaxone plus clarithromycin). His medical history included cerebrovascular disease and heart failure due to ischemic cardiomiopathy with atrial fibrillation. in June 2006 he had been admitted to hospital because of a liver abscess and duodeno-cholecystic fistula treated with percutaneous aspiration under ultrasonographic guide and antibiotic therapy. no culture of the abscess was performed. since september 2007 he had had recurrent episodes of fever responding to different antibiotic regimens. On admission he was febrile; examination revealed a 3/6 holosystolic murmur. A vancomycin-resistant E. faecium (vancomycin MiC >256 mg/L) grew from 5 blood cultures in 3 days. The strain was also resistant to penicillin, ampicillin, rifampin and showed high-level resistance to gentamicin and streptomycin. it was susceptible to daptomycin (MiC of 4 mg/L), tigecycline (MiC 0.094 mg/L), linezolid (MiC 4 mg/L) and quinupristin/dalfopristin (MiC 0.5 mg/L). A trans-thoracic echocardiogram did not reveal clear valve vegetation but showed an increased shape of the aortic valve leaflets. Rheumatoid factor was positive. According to The Duke University criteria, endocarditis was diagnosed based on the presence of one major criterion (blood cultures constantly positive for a typical pathogen) and three minor criteria (fever, echocardiographic minor signs and positive rheumatoid factor). A trans-esophageal echocardiogram was not performed. An ultrasonography of the abdomen ruled out abscess of the spleen or any other organ. Daptomycin (6 mg/kg/die) was chosen as initial therapy due to the bacteriostatic activity of linezolid and tigecycline and the lack of central venous catheter for quinupristin/dalfopristin. During daptomycin treatment blood cultures remained persistently positive for 13 days, but no increase in the MiC was observed. We tested the MBC of daptomycin and we found that the E. faecium strain showed tolerance (MBC 64 mg/L). We decided to add another agent and considered tigecycline since the MiC of linezolid was the same as the breakpoint according to EUCAsT guidelines 11 and we were reluctant to insert a central venous catheter for quinupristin/dalfopristin in a patient with persistent bacteremia. We used the checkerboard method to test in vitro the synergism between daptomycin and tigecycline: twofold dilutions of each drug were combined in the wells of a microdilution plate, one diluted along the ordinate and the other along the abscissa, and then a 0.5 McFarland turbidity standard inoculum was added. The Fractional inhibition index (SFiC) was defined as FiC A + FiC B, where FiC A is the MiC of drug A in combination/MiC of drug A alone and FiC B is the MiC of drug B in combination/MiC of drug B alone. The combination is considered fully synergistic when the SFiC is ≤0.5, partially synergistic when the SFiC is >0.5 to <1, additive when SFiC=1, indifferent when SFiC >1 to <4 and antagonistic when SFiC ≥4 12. in our case an additive activity was found (SFiC:1). After 14 days of daptomycin monotherapy, tigecycline was added. in two days blood cultures became negative and the patient was discharged 10 days later without fever and with persistently negative blood cultures. At a 3-month follow-up visit, the patient was afebrile, C reactive protein was normal and blood cultures were negative. Daptomycin is a cyclic lipopeptide with bactericidal activity against Gram-positive microorganisms including MRsA, penicillin-resistant streptococci and VRE 13. However, evidence of its clinical efficacy in the treatment of serious VRE infections is still limited and controversial. segreti et al. reported the death of 6 out of 10 patients treated with daptomycin for VRE bacteremia, including patients with endocarditis 9. Resistance to daptomycin leading to therapeutic failure has been documented in E. faecium isolated after 17 days of therapy from a patient with pyelonephritis and bacteremia 8. in our case, despite the clinical failure of daptomycin treatment, all the clinical isolates showed daptomycin MiCs within the range of susceptibility (4 mg/mL). Failure of daptomycin monotherapy without evidence of daptomycin resistance has been previously reported in a case of endocarditis due to a vancomycin “hetero-resistant” strain of E. faecium 14. in an attempt to enhance efficacy, an antimicrobial combination is frequently administered empirically. Many antimicrobial combinations have been studied for their synergism in vitro and in vivo against Enterococci. The above menAzienda Ospedaliera Universitaria Pisana, U.O. Malattie infettive, Pisa, italy.

Linezolid for endocarditis: a case series of 14 patients

Response of MRSA and MSSA endocarditis was 2/3 (67%) and 4/5 (80%), respectively. All other cases were cured: one VRE; three MRSE; and two cases of polymicrobial endocarditis. Response of native valve endocarditis was 7/8 (87.5%) and that of prosthetic valve endocarditis was 2/2 (100%). In three out of four patients with PM endocarditis (75%), the removal of the PM combined with antibiotic therapy, linezolid monotherapy in one case, was able to heal the infection. In these three patients, PM culture was still positive for the same S. epidermidis strain as isolated from the blood, probably due to the inactivity of linezolid against slime-producing bacteria. 4 Therefore, for PM endocarditis, linezolid may be an option only if the entire device is removed. Patients were followed up for at least 6 months, and no relapses were recorded.

Daptomycin concentrations in valve tissue and vegetation in patients with bacterial endocarditis

ABSTRACT In a patient with mitral-aortic native-valve Streptococcus oralis endocarditis, daptomycin concentrations in aortic and mitral valves were 8.6 and 30.8 μg/g, respectively, and 26 μg/g in the mitral vegetation. In the case of porcine-aortic-valve Staphylococcus epidermidis endocarditis, the daptomycin concentrations were 53.1 μg/g in the valve and 18.1 μg/g in perivalvular tissues. Daptomycin achieved apparently adequate tissue concentrations. S. epidermidis was eradicated, whereas Streptococcus oralis persisted, and its daptomycin MIC displayed a 4-fold increase.

Three-Times Weekly Teicoplanin as Outpatient Treatment of Chronic Osteoarticular Infections

Abstract Treatment of difficult-to-treat infections such as osteomyelitis or infections related to indwelling medical devices requires lengthy antibiotic therapy and adequate surgical debridement. teicoplanin, a glycopeptide antibiotic with a long half-life, was used three-times weekly in the treatment of these infections. After a period of daily dosing with teicoplanin, patients were treated with an intravenous dose of 12 mg on mondays, Wednesdays and Fridays. A control group of patients were treated with teicoplanin daily. Teicoplanin levels were measured during the study. Thirty-six patients were enrolled in the study: 14 with vertebral osteomyelitis, 12 with infected orthopedic implants, 7 with osteomyelitis and 3 with arterial prosthetic infections. The duration of treatment ranged from 60 to 360 days. Cure was obtained in 21 (58%) patients and improvement in 15 (42%) patients. trough and peak serum concentrations in three-time weekly patients were 16.2±7.2 mg/L and 58.7±14.4 mg/L. in the control group trough and peak serum concentrations were 18.9±13.6 mg/L and 52.2±27 mg/L. Adverse events occurred in 6 patients: mainly mild liver toxicity. three times weekly teicoplanin seems to be a valuable option in the treatment of chronic infections.

Cardiovascular implantable electronic device endocarditis treated with daptomycin with or without transvenous removal

BACKGROUND AND METHODS Nine patients with cardiovascular implantable electronic device (CIED) endocarditis were treated with daptomycin after the failure of previous treatment. The blood and CIED lead cultures of 1 patient were negative. In the other 8 patients, we observed 6 monomicrobic infections and 2 polymicrobic infections. Overall, 10 strains were isolated in these patients: 4 methicillin-sensitive Staphylococcus aureus, 2 methicillin-sensitive Staphylococcus epidermidis, 1 methicillin-resistant Staphylococcus aureus, 1 methicillin-resistant Staphylococcus epidermidis, 1 methicillin-sensitive Staphylococcus hominis, and 1 Propionibacterium acnes. The CIED was removed transvenously in 7 patients. Two patients were too sick for the removal of their CIED, and were cured with 6 mg/kg of daptomycin for 60 and 110 days, respectively, without adverse events. RESULTS One patient died 4 days after the removal of his CIED because of a complicated abdominal aortic aneurysm. The other 8 patients were cured, with a mean follow-up of 17 ± 8 months. The removed leads were negative, after daptomycin therapy, in 4 cases out of 7. The mean ratio between peak daptomycin concentration and minimal inhibitory concentration (MIC) of the causative strains was 38.3 ± 18.5. For patients whose data were available, the ratio between peak daptomycin concentration and minimal bactericidal concentration (MBC) was 13.2 ± 3.2. CONCLUSION Daptomycin monotherapy may be a useful therapeutic tool in difficult-to-treat CIED endocarditis, resulting in a high rate of cures and sterilized leads removed. The ratio between peak daptomycin concentration and MIC or MBC may be useful as predictive tool for treatment success.