Lack of synergism of ampicillin and gentamicin in experimental listeriosis

Antibiotic treatment for invasive nonpregnancy-associated listeriosis and mortality: a retrospective cohort study

Little evidence exists addressing the clinical value of adding gentamicin to ampicillin for invasive listeriosis. A multicenter retrospective observational study of nonpregnant adult patients with invasive listeriosis (primary bacteremia, central nervous system (CNS) disease, and others) in 11 hospitals in Israel between the years 2008 and 2014 was conducted. We evaluated the effect of penicillin-based monotherapy compared with early combination therapy with gentamicin, defined as treatment started within 48 h of culture results and continued for a minimum of 7 days. Patients who died within 48 h of the index culture were excluded. The primary outcome was 30-day all-cause mortality. A total of 190 patients with invasive listeriosis were included. Fifty-nine (30.6%) patients were treated with early combination therapy, 90 (46.6%) received monotherapy, and 44 (22.8%) received other treatments. Overall 30-day mortality was 20.5% (39/190). Factors associated with mortality included lower baseline functional status, congestive heart failure, and higher sequential organ failure assessment score. Source of infection, treatment type, and time from culture taken date to initiation of effective therapy were not associated with mortality. In multivariable analysis, monotherapy was not significantly associated with increased 30-day mortality compared with early combination therapy (OR 1.947, 95% CI 0.691-5.487). Results were similar in patients with CNS disease (OR 3.037, 95% CI 0.574-16.057) and primary bacteremia (OR 2.983, 95% CI 0.575-15.492). In our retrospective cohort, there was no statistically significant association between early combination therapy and 30-day mortality. A randomized controlled trial may be necessary to assess optimal treatment.

Amoxicillin-bearing microparticles: potential in the treatment of Listeria monocytogenes infection in Swiss albino mice

The present study was aimed at evaluating the effectiveness of amoxicillin-bearing HSA (human serum albumin) and PLGA [poly(lactic-co-glycolic acid)] microparticles in combating Listeria monocytogenes infection in Swiss albino mice. Amoxicillin-bearing HSA microspheres were prepared by chemical cross-linking of a drug/albumin mixture with glutaraldehyde, and PLGA microspheres were prepared by the W/O/W (water-in-oil-in-water) emulsion technique. The microspheres were characterized for their size, ζ potential and entrapment efficiency using SEM (scanning electron microscopy) and a Zetasizer. Release kinetics was performed in a phosphate buffer (pH 7.4) at 37°C simulating physiological conditions. Bacterial burden in various vital organs and survival data established enhanced efficacy of PLGA and HSA microspheres as compared with free drug. Among the two delivery systems, PLGA microspheres, when compared with HSA microspheres, imparted better efficacy in terms of reduction in bacterial load as well as increase in survival. The results of the present study clearly demonstrate that microparticles successfully target the infected macrophages and the approach could be well exploited for targeting the intracellular pathogens as well.

Prosthetic valve endocarditis due to Listeria monocytogenes. Report of two cases and reviews

INTRODUCTION

Endocarditis due to Listeria monocytogenes is a rare but serious disease often leading to valve dysfunction and heart failure. Two cases of listerial prosthetic valve endocarditis are reviewed along with 66 cases previously reported.

RESULTS

The mean age of patients with listerial endocarditis increased from 47.1 years in the decades from 1955-1984 to 65.5 years from 1985-2000. Chronic debilitating diseases, solid tumours and immunosuppression associated with organ transplantation, hematologic neoplasia or AIDS were found in 41.1% of cases. Listerial endocarditis was a vegetative and destructive process, with dehiscense of the prosthesis and occasionally, abscess formation, fistulization and pericarditis. Treatment with penicillin or ampicillin alone or combined with gentamicin was adequate therapy in most cases. Vancomycin together with gentamicin may be a reasonable alternative therapy.

CONCLUSIONS

Despite problems associated with microbial persistence and relapses in other forms of human listeriosis, antimicrobial therapy alone may be a successful treatment for listerial endocarditis, including cases occurring on prosthetic valves. Valve replacement may be reserved for complicated cases with valve dehiscense, cardiac failure or myocardial abscess. Overall mortality was 35.3%, although most patients who died did so before 1985 and since then mortality has been significantly reduced to 12%.

[Listeria monocytogenes infections in the adult. Clinical and microbiological issues of a changing disease]

Thirty-one cases of human listeriosis seen from 1971-1999 were reviewed. cases were grouped as follows: Group I composed of 14 patients were studied in the period 1971-1984; and group II composed of 17 cases studied in the period 1985-1999. We tried to assess changes in the incidence, clinical findings and outcome in both periods. The incidence of listeriosis remained constant along the years, 1.2 cases/20,000 discharges. The mean age of the patients significantly increased along the years (55 11 years versus 68 12 years; p 0.002). 77% of cases had one or more underlying diseases predisposing to listeriosis. We observed an increasing number of listeriosis in patients without chronic diseases in recent years. Listeriosis presented as meningitis or primary sepsis. Mortality was 61% and was strictly associated with the severity of the underlying disease. Patients with meningoencephalitis and seizures had a worse prognosis. We did not observe differences in mortality of patients who were treated with beta-lactam monotherapy in comparison with those who were treated with beta-lactam/aminoglucoside combination. Cotrimoxazole was uniformly successful treatment of human listeriosis in this series.

Listeria monocytogenes-infected phagocytes can initiate central nervous system infection in mice

Listeria monocytogenes-infected phagocytes are present in the bloodstream of experimentally infected mice, but whether they play a role in central nervous system (CNS) invasion is unclear. To test whether bacteria within infected leukocytes could establish CNS infection, experimentally infected mice were treated with gentamicin delivered by surgically implanted osmotic pumps. Bacterial inhibitory titers in serum and plasma ranged from 1:16 to 1:256, and essentially all viable bacteria in the bloodstream of treated mice were leukocyte associated. Nevertheless, CNS infection developed in gentamicin-treated animals infected intraperitoneally or by gastric lavage, suggesting that intracellular bacteria could be responsible for neuroinvasion. This was supported by data showing that 43.5% of bacteria found with blood leukocytes were intracellular and some colocalized with F-actin, indicating productive intracellular parasitism. Experiments using an L. monocytogenes strain containing a chromosomal actA-gfpuv-plcB transcriptional fusion showed that blood leukocytes were associated with intracellular and extracellularly bound green fluorescent protein-expressing (GFP+) bacteria. Treatment with gentamicin decreased the numbers of extracellularly bound GFP+ bacteria significantly but did not affect the numbers of intracellular GFP+ bacteria, suggesting that the latter were the result of intercellular spread of GFP+ bacteria to leukocytes. These data demonstrate that infected leukocytes and the intracellular L. monocytogenes harbored within them play key roles in neuroinvasion. Moreover, they suggest that phagocytes recruited to infected organs such as the liver or spleen are themselves parasitized by intercellular spread of L. monocytogenes and then reenter the bloodstream and contribute to the systemic dissemination of bacteria.

Intracerebral activity of antibiotics against Listeria monocytogenes during experimental rhombencephalitis

We used a model of rhombencephalitis in gerbils to test the efficacy of various antibiotics against Listeria monocytogenes. Gerbils were inoculated in the middle ear with strain EGD and treated subcutaneously with various antibiotics alone or in combination. We found that the most active antibiotics on intracerebral bacteria were amoxycillin, co-trimoxazole, rifampicin and imipenem. Vancomycin, gentamicin and ciprofloxacin were weakly or not active. The combinations amoxycillin-co-trimoxazole, amoxycillin-gentamicin and co-trimoxazole-rifampicin were highly active against intracerebral bacteria.

Management of listeriosis

Determination of the MIC in vitro is often used as the basis for predicting the clinical efficacy of antibiotics. Listeriae are uniformly susceptible in vitro to most common antibiotics except cephalosporins and fosfomycin. However, the clinical outcome is poor. This is partially because listeriae are refractory to the bactericidal mechanisms of many antibiotics, especially to ampicillin-amoxicillin, which still is regarded as the drug of choice. A true synergism can be achieved by adding gentamicin. Another point is that listeriae are able to reside and multiply within host cells, e.g., macrophages, hepatocytes, and neurons, where they are protected from antibiotics in the extracellular fluid. Only a few agents penetrate, accumulate, and reach the cytosol of host cells, where the listeriae are found. Furthermore, certain host cells may exclude antibiotics from any intracellular compartment. Thus, determination of the antibacterial efficacy of a drug against listeriae in cell cultures may be a better approximation of potential therapeutic value. Certain host cells may have acquired the property of excluding certain antibiotics, for example macrolides, from intracellular spaces, which might explain therapeutic failures of antibiotic therapy in spite of low MICs. Animal models do not completely imitate human listeriosis, which is characterized by meningitis, encephalitis, soft tissue and parenchymal infections, and bacteremia. Meningitis produced in rabbits is a hyperacute disease, whereby most listeriae lie extracellularly, fairly accessible to antibiotics that can cross the blood-cerebrospinal fluid barrier. In the murine model of systemic infection, Listeria monocytogenes is located mainly within macrophages and parenchymal cells of the spleen and liver, hardly accessible to certain drugs, such as ampicillin and gentimicin. The therapeutic efficacy of drugs clearly depends on the model used. Thus, for example, the combination of ampicillin with gentamicin acts synergistically in the rabbit meningitis model but not in the mouse model. Since conventional antimicrobial therapy with antibiotics is not satisfactory, particularly in the immunocompromised host (about 30% of patients with listeriosis die in spite of a rational choice of antibiotics), other possibilities must be considered for therapy as well as prevention. Indeed, listeriae are highly susceptible to several endogenous antibiotics, such as defensins. Bacteriocins produced by related bacterial species, e.g., lactobacilli and enterococci, are rapidly bactericidal. However, unfortunately, the use of such alternative measures along with immunization and immunmodulation is not yet feasible.

Is amoxicillin-cotrimoxazole the most appropriate antibiotic regimen for listeria meningoencephalitis? Review of 22 cases and the literature

From June 1983 to January 1994, 22 adult patients with severe Listeria monocytogenes meningoencephalitis were observed in our Intensive Care Unit. Listeria monocytogenes was obtained in culture in cerebrospinal fluid or blood for every patient. Seven patients were treated with the combination ampicillin-aminoglycoside (group A) and 15 patients with the combination ampicillin (or amoxicillin)-cotrimoxazole (group A + C). Risk factors and gravity scores were similar in both groups. Failure of the 'gold standard' regimen (group A) was significantly higher (57%) compared to group A + C (6.7%) (P < 0.05). Mortality related to L. monocytogenes was 23.5% in group A compared to 6.7% in group A + C. Morbidity was reduced in group A + C (13.3%) compared to group A (60%) (P = 0.15). This unique study seems to demonstrate that amoxicillin-cotrimoxazole should be the most appropriate therapeutic regimen for Listeria meningoencephalitis.

Antimicrobial chemotherapy of human infection due to Listeria monocytogenes

Listeriosis is an uncommon infection, but when it occurs it carries a high mortality rate. Early diagnosis is essential and thereafter appropriate antimicrobial chemotherapy. Ampicillin or penicillin plus gentamicin remains the treatment of choice for most manifestations of listeriosis, and adequate doses must be given, i.e. greater than 6g/day of ampicillin or penicillin. Co-trimoxazole appears to be an excellent alternative agent with good penetration into the cerebrospinal fluid. Vancomycin is an appropriate agent for the treatment of primary bacteraemia but does not cross the blood-brain barrier sufficiently well to be useful in meningitis, while erythromycin may be used to treat listeriosis in cases of pregnancy. Treatment of bacteraemia requires one to two weeks' therapy, while meningitis cases may need to be treated for longer; for example, it has been found that most patients with acute meningitis in the UK were treated for 20 days. Infective endocarditis needs treatment for six to eight weeks. Doses should be varied with patients' altered organ function and antimicrobial serum monitoring performed when appropriate.

Inhibition of intracellular growth of Listeria monocytogenes by antibiotics

We studied the activities of 15 antibiotics on the intracellular growth of Listeria monocytogenes in a HeLa cell line. After 24 h of contact with the infected cells, the antibiotics most effective against the intracellular growth of the 10 strains tested were amoxicillin, temafloxacin, and sparfloxacin, which nevertheless failed to totally eliminate the intracellular bacteria. Rifampin and co-trimoxazole had variable effects, depending on the isolates studied. The most active combinations were amoxicillin-sparfloxacin, co-trimoxazole-gentamicin, and sparfloxacin-co-trimoxazole. The results suggest the value of using a cell culture technique to study the activities of antibiotics against certain bacteria with intracellular sites of multiplication.

Therapeutic activities of antibiotics in listeriosis

In vitro practically all common antibiotics except cephalosporins are active against nearly all natural isolates of Listeria monocytogenes; the therapeutic efficacy of antibiotic treatment is, however, rather limited, since up to 30% listeriosis patients will succumb to this infection. At least one reason for this low in vivo efficiency is the intracellular habitat of L. monocytogenes. In animal experiments ampicillin or amoxicillin, respectively, are still the most active drugs. In addition, rifampicin also has pronounced protective activity. Coumermycin, which unfortunately cannot be given to humans, is the most reliable drug in animals.

Recurrent Listeria monocytogenes bacteraemia in a liver transplant patient

We report a case of a recurrent Listeria monocytogenes bacteraemia in a 46 year-old liver transplant patient. Serotyping revealed that the two episodes of bacteraemia were caused by different strains. The possibility of a recrudescence of a persisting infection was rejected. We concluded that the recurrent bacteraemia in this predisposed patient was due to re-infection, and that antibiotic treatment (amoxicillin plus an aminoglycoside) resulted in a complete eradication of the infective microorganism. Therefore long-term suppressive antibiotic treatment was not indicated. The source of these L. monocytogenes infections was not found.

Perinatal listeriosis in Dresden 1981-1986: clinical and microbiological findings in 18 cases

Between 1981 and 1986 Listeria monocytogenes was isolated from blood cultures, CSF, meconium/stools or external swabs from 18 newborn infants of two neonatal intensive care units (ICU) in adjacent pediatric clinics of Dresden. The epidemiological and clinical data of infants and their mothers, as well as microbiological and laboratory, x-ray, EEG and ultrasonic findings, are presented. All infants had an early onset of their disease. Cases were classified as granulomatosis infantiseptica (three cases), sepsis (three cases), meningitis (eight cases) and listerial infection without distinct organ manifestations (four cases), respectively. As far as the predominant symptoms at admission were concerned, no typical clinical signs of neonatal listeriosis could be evaluated. Cases with manifest clinical infections had an overall mortality rate of 21% (3/14) despite the immediate initiation of antibiotic therapy; at discharge, a further five patients showed neurological residuals. Serotyping and phagetyping have proved to be methods for recognition or exclusion of epidemiological relationships.

Therapeutic activity of teicoplanin on experimental listeriosis compared with that of vancomycin and ampicillin

Several strains of Listeria monocytogenes and other Listeria spp. are without exception susceptible to teicoplanin (MIC 0.25 mg/l). Vancomycin as well as ampicillin are likewise active. A bactericidal effect of teicoplanin was only achieved at rather high concentrations and after incubation of several hours. There is no synergistic effect between teicoplanin and gentamicin. The therapeutic activity of teicoplanin as well as vancomycin in mice infected with L. monocytogenes is low. The efficacy of ampicillin could not be achieved. Treatment of chronically infected athymic, nude mice with teicoplanin is ineffective. Consequently, teicoplanin is not able to replace ampicillin in the therapy of listeriosis.

Listeria monocytogenes infections--therapeutic possibilities and problems

Listeriosis in humans is a rare disease, which, however, is known to be epidemic and endemic. The prognosis has remained unsatisfactory up to today, the fatality being at least 10% and often considerably higher depending on the clinical features of the disease and the patient's age. Three population groups are at risk: pregnant women, fetuses and newborn infants. Furthermore, immunosuppression in older patients due to disease, therapy, or age also plays a role. The incidence of Listeria infections in patients over 45 is clearly increasing. Due to the nature of the pathogen (in vivo bactericidal concentrations of antibiotics are often not attainable; intracellular growth) a high dosage of ampicillin is recommended. Although the present therapeutic possibilities are not satisfactory, a combination of ampicillin and an aminoglycoside appears to be the best therapy at present. Other combinations such as rifampicin and beta-lactam antibiotics have exhibited in vitro antagonism. The preferred therapy, ampicillin, can only be recommended with reservations because it is not optimally effective.

Therapy of experimental listeriosis--an evaluation of different antibiotics

The therapeutic activities of various antibiotics were evaluated in two murine models, i.e. the infection of normal mice as well as of nude mice. Coumermycin and rifampicin were the most active drugs, since not only inhibition of multiplication but also rapid elimination of Listeria monocytogenes could be achieved in normal and immunocompromised animals. Ampicillin was the most active beta-lactam antibiotic followed by azlocillin. The other beta-lactam antibiotics were definitely less active. The combination of ampicillin with gentamicin expressed no synergistic effect in vivo. Co-trimoxazole as well as ciprofloxacin were of moderate therapeutic value. The bacteriostatic drugs such as tetracycline and erythromycin were able to inhibit the bacterial multiplication in the normal mouse but not in the immunocompromised host. Thus an optimal drug for therapy of listeriosis does not yet exist.