Mechanisms of failure to decontaminate the gut with polymixin E,gentamicin and amphotericin B in patients in intensive care

The objective of the present work was to assess the possible mechanisms of the poor efficiency of selective decontamination of the digestive tract (SDD) in medical and surgical intensive care unit (ICU) patients. Sixty-four consecutive mechanically ventilated patients received gut decontamination with polymixin E, gentamicin and amphotericin B via a nasogastric tube and were assessed for oropharyngeal, gastric and fecal colonization and for the presence of each antibiotic in the stomach and feces. A decrease in fecal colonization withEscherichia coli was observed over 20 days but not with other gram-negative bacteria or gram-positive cocci. Fifteen and 26 % of the fecal colonizing gram-negative bacteria were resistant to polymixin E and gentamicin, respectively, at admission. These proportions increased to up to 50 % after 16 days of treatment. Although 50 % of staphylococci were initially sensitive to gentamicin, all strains were resistant to this drug after four days of SDD. Both antibiotics were found in concentrations of less than 20 µg/g in 11 of 38 stools. Of these 38 stools, nine were not contaminated, 20 were colonized with resistant bacteria and 16 with strains sensitive to one antibiotic present in the stool. Therefore, the poor efficiency of gut decontamination observed was probably due to the great proportion of resistant strains on admission of the patients, to the selection of such resistant strains with SDD, to poor intestinal transit of the antibiotics, and to inactivation of the drugs by the feces. These results support stringent monitoring of fecal colonization in patients undergoing SDD in order to detect the fecal carriage of gram-positive and multiresistant gram-negative bacteria.     

Prevalence of Aminoglycoside Resistance in 20 European University Hospitals Participating in the European SENTRY Antimicrobial Surveillance Programme

The aim of this study was to analyse the current prevalence of aminoglycoside resistance in Europe and compare the in vitro activity of amikacin, gentamicin, and tobramycin against 7057 bacterial isolates from 20 university hospitals participating in the European SENTRY Antimicrobial Surveillance Programme. Amikacin exhibited better in vitro activity than tobramycin and gentamicin against most gram-negative bacilli in Europe. The resistance levels were 0.4–3% for amikacin, 2–13.1% for gentamicin, and 2.5–15.3% for tobramycin among different members of the family Enterobacteriaceae. Of the Staphylococcus aureus isolates tested, 75% were susceptible to gentamicin. Only 21% of all enterococcal strains tested were fully susceptible to gentamicin. Although intra-country variations in the prevalence of resistance phenotypes in Escherichia coli, Klebsiella spp., and Pseudomonas aeruginosa as well as in staphylococci and enterococci did occur, aminoglycoside resistance rates were generally higher in Italy, Portugal, Spain, Greece, France, the UK, and Poland than in Austria, Belgium, Germany, the Netherlands, and Switzerland. Compared with the 1987–88 data of the European Study Group on Antibiotic Resistance, gentamicin resistance has increased up to 5% in some gram-negative bacterial species. Furthermore, a greater than 10% increase in resistance to gentamicin has been seen in Staphylococcus aureus during the last decade. The reason for this observation is unclear, although changes in antibiotic prescribing patterns that result in increased selective pressure from gentamicin may have contributed to these increased rates of aminoglycoside resistance.     

Bacterial Resistance and Overgrowth due to Selective Decontamination of the Digestive Tract

 Infection of the lower airways is a major problem in ventilated patients and contributes substantially to morbidity and mortality in the intensive care unit. The selective decontamination of the digestive tract and its effect on the reduction of the gram-negative colonisation rate in patients has been studied widely. However, the findings are inconsistent. Most studies describe an increase in resistant gram-negative bacterial strains and/or an increase in the occurrence of gram-positive strains following selective decontamination of the digestive tract. In light of the unresolved questions concerning the efficacy of selective decontamination of the digestive tract, it would seem that the resultant effect of this treatment on the bacterial flora should be an important consideration when assessing the value of such treatment. To date, none of the studies available for examination have been designed to adequately assess the effect of selective decontamination of the digestive tract on the bacterial flora.     

Eradication of biofilms on tympanostomy tubes with acetic acid treatment: an in vitro study

The purpose was to evaluate the eradicative effect of acetic acid on bacterial biofilm grown on tympanostomy tubes by an in vitro experiment. Biofilms of Pseudomonas aeruginosa and Staphylococcus aureus were grown on sterile tympanostomy tubes for 24 h. The tubes were treated with acetic acid solutions at various concentrations for 24 h. Main outcome was viability of bacteria after treatment. The presence of consistently attached biofilm was examined on selected tympanostomy tubes with confocal laser scanning microscopy. Both pH-adjusted and non-pH-adjusted media solutions were applied as control groups. Results showed complete eradication of P. aeruginosa biofilm with 0.50% v/v acetic acid. Biofilm of S. aureus was eradicated with 1.25% v/v acetic acid. Low pH value alone led to decreased growth of already established biofilm, but not eradication. In conlusion, acetic acid showed an eradicating effect on biofilm established on sterile tympanostomy tubes in vitro.     

3-0-demethyl fortimicin A: In vitro activity and interpretive zone standards for disk diffusion susceptibility tests

The in vitro activity of 3-0-demethyl fortimicin A was compared to that of amikacin and tobramycin against 5,230 clinical isolates in four institutions. Amikacin and tobramycin were more active than 3-0-demethyl fortimicin A againstPseudomonas aeruginosa andAcinetobacter spp., but all three drugs had similar activity against theEnterobacteriaceae andStaphylococcus aureus. Additional tests with 335 representative gram-negative bacilli compared five different aminoglycosides, demonstrating differences with some isolates. Standardized disk diffusion tests were also performed with 30μg 3-0-demethyl fortimicin A disks, according to the National Committee for Clinical Laboratory Standards. The following interpretive breakpoints are proposed: ? 11 mm for resistant (MIC ?32μg/ml) and ? 15 mm for susceptible (MIC ? 16μg/ml).     

Antibiotic Susceptibility of Bacterial Strains Isolated from Patients with Community-Acquired Urinary Tract Infections in France

 The aim of this study was to determine the distribution and antibiotic susceptibility patterns of bacterial strains isolated from adults with community-acquired urinary tract infections (UTI) in France. From December 1996 to March 1997, each of 15 private laboratories in France consecutively collected about 80 non-duplicate strains isolated from adult outpatients with UTI, including patients receiving care at home, and tested their susceptibility by the disk diffusion test. A total of 1160 strains were collected: 1031 gram-negative bacilli, including Escherichia coli (n=865), Proteus mirabilis (n=68) and Klebsiella spp. (n=40), and 129 gram-positive cocci, including Staphylococcus aureus (n=16), other staphylococci (n=25), group B streptococci (n=25) and enterococci (n=63). In the case of 430 bacterial isolates, the patients had either been hospitalised in the last 6 months or received antibiotic treatment in the last 3 months. The antibiotic susceptibility rates for Escherichia coli were: amoxicillin (58.7%), amoxicillin-clavulanic acid (63.3%), ticarcillin (61.4%), cephalothin (66.8%) cefuroxime (77.6%), cefixime (83.6%), cefotaxime (99.8%), ceftazidime (99%), nalidixic acid (91.9%), norfloxacin (96.6%), ofloxacin (96.3%), ciprofloxacin (98.3%), cotrimoxazole (78.2%), fosfomycin (99.1%) and gentamicin (98.4%). Of the Enterobacteriaceae, five strains produced an extended-spectrum beta-lactamase. Methicillin resistance was detected in nine Staphylococcus aureus isolates. The most important findings were two extended-spectrum, beta-lactamase-producing and three methicillin-resistant Staphylococcus aureus strains isolated from patients who had not been hospitalised in the last 6 months or taken antibiotics in the last 3 months. The findings indicate that these strains can spread within the community; therefore, monitoring antibiotic susceptibility of bacteria isolated in the community appears to be mandatory.     

Antibiotic resistance ofPseudomonas aeruginosa colonizing a urinary catheter in vitro

A modified Robbins Device was used to establish coherent biofilms ofPseudomonas aeruginosa on the surface of catheter material in an artificial urine milieu and the ability of an antibiotic to penetrate the biofilm and kill the enclosed bacteria was assessed. ThePseudomonas aeruginosa strain used had been isolated from a patient with urinary tract infection. Although planktonic (floating) cells of thePseudomonas aeruginosa strain were inhibited by less than 1 mg/l of tobramycin and killed by 50 mg/l, contact with 1,000 mg/l of tobramycin for 12 h failed to kill all the sessile (adherent) bacteria in the biofilms on the surface of the catheter material. Surviving sessile bacteria recovered directly from the exposure to 1,000 mg/l of tobramycin were inhibited by 0.4 mg/l of this agent when tested as dispersed planktonic cells by standard MIC methods. It is suggested that growth within thick adherent biofilms confers upon cells ofPseudomonas aeruginosa a large measure of resistance to aminoglycosides and other antibiotics that may help to explain the frequent failure of antibiotic chemotherapy in catheter-associated urinary tract infections.     

Effect of sub‐lethal doses of vancomycin and oxacillin on biofilm formation by vancomycin intermediate resistant Staphylococcus aureus

Biofilms are means of protection to bacteria against antibiotics and antibodies. Catheters and others tube devices used by patients are prone to accumulation of thick layers of biofilms as hiding place for etiologic agents, resulting in substantial morbidity and mortality. Methicillin‐resistant Staphylococcus aureus (MRSA) is a major cause of hospital‐acquired infections. Vancomycin remains the only treatment of choice for MRSA infections. In the present study a vancomycin resistant S. aureus (VRSA) (Labeled as CP2) was isolated from the blood of a post‐operative cardiac patient. It harbors a plasmid which carry vanA gene and exhibited low‐level vancomycin resistance (MIC 16μg/ml), high level of oxacillin/methicillin resistance (MIC 500 μg/ml) and was sensitive to teicoplanin. CP2 also found to carry icaA gene on its chromosome. This strain exhibited resistance to triton‐X100 induced autolysis under sub‐inhibitory concentration of vancomycin and produced some extracellular matrix material that surrounding the cells. These characteristic features have warranted us to study the biofilm formation by CP2 on biomedical indwellings in presence of vancomycin and oxacillin. Our findings suggest that sub‐lethal dose of vancomycin induced the biofilm formation by CP2 on nylon and silicon indwellings whereas oxacillin facilitated the biofilm formation on glass surfaces exclusively. This implicates that not only the antibiotics but also the indwelling material influences biofilm formation. Therefore, these implants serve as potential surfaces for bacterial adhesion that lead to biofilm formation, thus provide hiding places for pathogens from the actions of antimicrobials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of antibiotic susceptibility of <Emphasis Type="Italic">Burkholderia cepacia</Emphasis> complex organisms when grown planktonically or as biofilm in vitro

This study determined the antibiotic susceptibility of planktonic and biofilm cultures of Burkholderia cepacia complex organisms, a group of highly problematic pathogens associated with cystic fibrosis patients. The biofilm inhibitory concentrations were considerably higher than the corresponding minimum inhibitory concentrations for meropenem and piperacillin-tazobactam. However, tobramycin and amikacin were efficacious against both biofilm and planktonic cultures. Overall this study showed that biofilm susceptibility testing might be more clinically appropriate for determining antibiotic therapy for Burkholderia cepacia complex infections in cystic fibrosis patients.     

Effects of environmental factors on the in vitro potency of azithromycin

The effects of media, pH, cations, serum, CO₂ or anaerobic atmosphere, inoculum size and time of incubation on the in vitro potency of azithromycin were determined. The potency of azithromycin against all genera was particularly sensitive to changes in pH. The MIC forStaphylococcus aureus strains ranged from 50 µg/ml at pH 6 to 0.025 µg/ml at pH 8; for erythromycin the MIC change was less (1.6 to 0.05 µg/ml). Incubation for 18 h in 5 % CO₂ or an anaerobic atmosphere (10 % CO₂, 10 % H₂, 80 % N₂) lowered the pH by approximately 0.8 units with gram-negative organisms and 0.4 units with gram-positive organisms. This resulted in an MIC eight times greater than the aerobic MIC. In addition, the MIC100 for azithromycin and erythromycin againstBacteroides strains growing in Wilkins-Chalgren broth fell from 3.1 µg/ml in the anaerobic atmosphere to 0.2 and 0.4 µg/ml, respectively, when using the Oxyrase enzyme system to remove oxygen. With the Oxyrase system, the pH of the medium at the MIC remained at 7.2, while it fell to 6.7 in the anaerobic gas mixture. An increase in potency for both agents was also observed with other anaerobic species when using the Oxyrase system. The addition of serum produced an increase in potency of azithromycin and erythromycin that correlated with an increase in pH during incubation, despite the use of buffered media. Adding cations to Mueller-Hinton broth resulted in increased MICs for gram-negative organisms; the highest increases observed were four-fold forEscherichia coli. The activity of control antibiotics was not affected to the same degree as that of azithromycin. Increasing the incubation period from 24 to 48 h did not change the MIC values of azithromycin forStaphylococcus aureus orEscherichia coli; however, the MBC values were lower at 48 h and equalled the MIC values. Inoculum size or manner of preparation had no significant effect on the potency of azithromycin.     

Prevention of septicemia caused by gastrointestinal tract organisms in patients with granulopenia. Comparison of three gastrointestinal tract decontamination treatments

Three gastrointestinal tract decontamination regimens were tested in patients with granulopenia: vancomycin 250 mg, tobramycin 75 mg, and colistin 1 million international units (regimen A); vancomycin 125 mg, tobramycin 75 mg, and colistin 1 million IU (regimen B); and colistin 1 million IU (regimen C); nystatin was added to all three regimens. Effectiveness was evaluated by stool organism counts and blood cultures to detect bacterial translocation (passage of bacteria from the intestinal tract to the bloodstream). Regimen C proved insufficiently effective. Regimen A was found to be poorly tolerated by the digestive mucosa. Regimen B was the best treatment since the low dosage of vancomycin proved effective. Nystatin satisfactorily eliminated yeasts.     

Rapid method of MIC determinations utilizing tetrazolium reduction

A rapid preliminary method of determining antibiotic susceptibilities of clinically isolated gram-negative fermentative organisms has been evaluated. The method utilizes tetrazolium dye reduction as a colorimetric indicator of bacterial growth. Tetrazolium dye reduction is incorporated into the standard Micro-Media MIC microdilution testing system and shortens the required incubation period from 15 to 18 hours to 4 hours. Parallel MIC determinations were made by the standard MIC method and by the rapid tetrazolium method. The test organisms included 218 gram-negative fermentative clinical isolates. The overall correlation between the standard and the rapid MIC methods was 93%. Of the 7% discordant results, 6.3% represented minor discrepancies and 0.7% represented major discrepancies. There were no very major discrepancies. The study concluded that the rapid tetrazolium MIC method is an accurate, low-cost, easily implemented method of preliminary antibiotic susceptibility testing for gram-negative fermentative organisms.     

Ceftazidime- and Imipenem-Induced Endotoxin Release During Treatment of Gram-Negative Infections

To determine whether ceftazidime and imipenem, which target two different penicillin-binding proteins, result in different amounts of endotoxin and cytokine release in patients with gram-negative infection, plasma endotoxin, interleukin-6, and tumor necrosis factor alpha were measured during the first 24 h of antibiotic therapy in 27 patients with gram-negative infection who had been randomized to receive either ceftazidime 2 g t.i.d. (n=12) or imipenem/cilastatin 1 g t.i.d. (n=15). The source of infection was the digestive tract (n=13), the urinary tract (n=5), the respiratory tract (n=2), soft tissue (n=2), i.v. line (n=2), or other (n=3). After the first antibiotic injection, a significant increase in the median concentration of plasma interleukin-6 and plasma tumor necrosis factor alpha was noted, without significant differences related to the antibiotic administered. Antibiotic-induced endotoxemia was detectable in nine patients (including 7 with bacteremia). In conclusion, ceftazidime and imipenem had similar effects on endotoxin and cytokine release during the treatment of gram-negative infections. Electronic Publication     

The concomitant development of poly(vinyl chloride)-related biofilm and antimicrobial resistance in relation to ventilator-associated pneumonia.

Ventilator-associated pneumonia is a major cause of death in intensive care patients and the endotracheal tube, commonly fabricated from poly(vinyl chloride) (PVC), is acknowledged as a significant factor in this. Bacteria colonise the biomaterial, thereby adopting a sessile mode of growth that progresses to the establishment of an antibiotic-resistant biofilm by the accretion of a protective glycocalyx. This study examined the sequential steps involved in the formation of biofilm on PVC by atomic force microscopy and the concomitant development of resistance to an antibiotic (ceftazidime) and to a non-antibiotic antimicrobial agent (hexetidine). Staphylococcus aureus and Pseudomonas aeruginosa isolated from ET tube biofilm were employed. The surface microrugosity of bacteria growing in sessile mode on PVC decreased significantly (p < 0.05) over the period 4, 24, 48 h and 5 d. The progressive accretion of bacterial glycocalyx was readily visualised in micrographs leading to a smoother surface topography with time. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) for ceftazidime and hexetidine against planktonic (suspension) S. aureus were lower than for Ps. aeruginosa. Furthermore, sessile populations of S. aureus and Ps. aeruginosa on PVC exhibited greater resistance to both ceftazidime and hexetidine when compared to planktonic bacterial growth. The efficacy of the agents, determined by kill kinetics, against sessile bacteria was dependent on age, with established biofilms (> or = 24 h) significantly more resistant (p < 0.05) than early sessile populations (< or = 4 h). Importantly, for practice, even newly colonised bacteria (1 h) were significantly more resistant to antibiotic than planktonic bacteria. Hexetidine was significantly more active (p < 0.05) than ceftazidime on biofilms of both isolates, irrespective of age, with total kill within 24 h treatment. Hexetidine may offer promise in the resolution of infection associated with PVC endotracheal tubes.     

Lack of emergence of significant resistance in vitro and in vivo to the new azalide antibiotic azithromycin

In vitro experiments were performed in which 6 to 12 strains ofStaphylococcus aureus, Streptococcus pyogenes, Haemophilus influenzae andEnterobacteriaceae were passaged nine times in sub-lethal concentrations of azithromycin or control antibiotics.Streptococcus pyogenes andStaphylococcus aureus quickly became resistant to rifampin as the MIC90 increased from 0.1 to > 50 µg/ml for both species. The MIC90 of azithromycin, erythromycin, amoxicillin and cefaclor increased by three dilutions forStaphylococcus aureus. The MIC values of azithromycin forStreptococcus pyogenes, Haemophilus influenzae andEnterobacteriaceae strains did not change significantly. However, forHaemophilus influenzae and theEnterobacteriaceae strains, the MIC values of erythromycin and oral cephalosporins increased four-fold. In the in vivo experiments, mice infected withStaphylococcus aureus orEscherichia coli contaminated sutures were administered azithromycin for three days, and on day 6 viable bacterial cells were recovered from the infection site. The sustained tissue concentrations of azithromycin indicated that the organisms would have been continuously exposed to azithromycin at the site of infection. Colonies isolated from azithromycin-treated and non-treated mice were cultured and their susceptibility to azithromycin compared. The azithromycin MIC values forStaphylococcus aureus cultures from treated and non-treated animals were identical. The azithromycin MICs forEscherichia coli recovered from treated animals were on average, less than one dilution higher than for control cultures. Emergence of significant resistance to azithromycin in the laboratory was not observed with the pathogens tested.     

Management of Catheter-Related<Emphasis Type="Italic"> Staphylococcus aureus</Emphasis> Bacteremia: When May Sonographic Study Be Unnecessary?

This study reviews the outcome of patients with uncomplicated catheter-related Staphylococcus aureus bacteremia diagnosed in our hospital from January 1997 to December 1999 and treated with short-course antibiotic therapy. Our aim was to assess the effectiveness of this regimen for minimizing complications (relapses, endocarditis and metastatic foci). A total of 213 episodes of bacteremia were registered and 167 (78.4%) were nosocomial. Among these, 87 (52.1%) were catheter-related Staphylococcus aureus bacteremia and 20 were primary nosocomial bacteremia. Endocarditis was diagnosed during the acute episode in 7/107 of these patients (2 by persistent fever after catheter removal and 5 by metastatic foci; 3 of them also had cardiac risk factors) and confirmed with transesophageal echocardiography. Among the 84/87 catheter-related Staphylococcus aureus bacteremia and 16/20 primary nosocomial bacteremia patients who did not develop endocarditis, 31 patients died during the acute episode (16 due to sepsis despite initiation of antibiotic treatment and 15 due to the underlying disease) and five had osteoarticular foci. The remaining 64 episodes were considered to be uncomplicated bacteremia (no cardiac risk factors, persistent fever, metastatic foci, or clinical signs of endocarditis) and were treated with 10–14 days of high-dose antistaphylococcal antibiotics. Echocardiography was not mandatory in these patients. Of the 64 uncomplicated episodes, 62 were followed for at least 3 months and none relapsed or developed endocarditis. Even though some of the patients might have had subclinical endocarditis, short-course therapy with high doses of antistaphylococcal antibiotics was effective for treating uncomplicated catheter-related Staphylococcus aureus bacteremia. Transesophageal echocardiography may not be necessary in these cases.     

Effect of BMY-28100, a new cephalosporin,onStaphylococcus aureus nasal carriage

In order to examine the in vivo activity of BMY-28100, serial quantitative nasal cultures were taken from 52 nasal carriers of Staphylococcus aureus following administration of the antimicrobial. Nasal carriage rates and mean log titers decreased significantly during (days 2–4 and 5–8) and following (days 1–2 and 6–7) treatment. No change in antibiotic sensitivities was noted in follow-up isolates, and the MIC90 remained at 2mcg/ml. BMY-28100 demonstrated good in vivo activity against Staphylococcus aureus.     

Survey of blood culture isolates in an area of Sweden from 1980 to 1986

To demonstrate the local epidemiological situation with respect to septicemia in an area of Sweden, a survey was made of all blood cultures performed in the county of Örebro (270,000 inhabitants) from 1980 to 1986. From these blood cultures 4,057 organisms presumed clinically significant were isolated which gives an annual incidence of 215 isolates per 100,000 inhabitants. The two most frequently isolated species wereEscherichia coli (24.6%) andStaphylococcus aureus (16.9%). Only minor annual variations in the frequency of different species was observed. An increasing tendency in the isolation rate ofPseudomonas aeruginosa and enterococci since 1980 was noted. Comparison of the findings of the present study with those of other studies demonstrated differences between geographical areas and time-periods. Repeated monitoring of the local spectrum of organisms isolated from blood cultures and, if necessary, adjustment of the routine antibiotic regimen is thus recommended.     

Influence of gentamicin and tobramycin on binary biofilm formation by co-cultures of Burkholderia cepacia and Pseudomonas aeruginosa

The aim of this study was to investigate the stability and dynamics of binary culture biofilm formation following antibiotic treatment. Pseudo steady-state biofilm cultures of clinical strains of P. aeruginosa and B. cepacia concurrently isolated from a single CF patient were established in separate Constant Depth Film Fermenters (CDFFs). Pans, containing established biofilms, were swapped between CDFFs. Biofilms were treated either for 5 days with tobramycin (0.3 mg/ml) prior to pan-swapping, or with gentamicin (1 mg/ml) immediately following pan-swapping. In both instances stable binary biofilms were formed. In addition, fresh un-colonised surfaces added at the time of pan-swapping and exposed simultaneously to biofilm derived P. aeruginosa and B. cepacia and subjected to antibiotic challenge also established stable binary communities. Treatment of P. aeruginosa and B. cepacia with tobramycin or gentamicin, either prior to or immediately after surface colonisation had little effect on the establishment of stable binary biofilms. Such treatment also had little effect on the immigration of one organism into an established biofilm of a second organism.     

In vitro activity of MDL 62,879 against gram-positive bacteria andBacteroides species

The new thiazolyl peptide antibiotic MDL 62,879 (GE2270 A) showed excellent in vitro activity in testing against staphylococci and streptococci, with MIC90s ranging from 0.23 to 0.9 mg/l. It was very active againstClostridium difficile andPropionibacterium acnes (MIC90 0.06 mg/l in each case) and had variable activity againstBacteroides spp. MDL 62,879 had exceptionally good activity againstEnterococcus faecalis, including against a collection of high-level aminoglycoside-resistant isolates where it had an MIC90 of 0.047. The antibiotic was bacteriostatic for enterococcal isolates but bactericidal for a methicillin-resistant isolate ofStaphylococcus aureus.