Aerobic Gram-negative Bacteria Research Articles

Antimicrobial susceptibility of clinical isolates of aerobic Gram-negative bacteria in 2004

Antimicrobial susceptibility of clinical isolates of aerobic Gram-negative bacteria in 2004

Changing trends in bacteriology of peritonsillar abscess

To evaluate the type of aerobic bacteria commonly isolated from peritonsillar abscesses. A retrospective study involving 60 patients presenting with peritonsillar abscess treated between 2003 and 2006. The patients were treated in a tertiary care, teaching hospital. The records of the patients were reviewed and analysed. Gram-positive organisms were commonly isolated from the abscesses. However, an increasing trend towards Gram-negative bacterial isolates was noted. The antibiogram showed changing patterns of sensitivity, with a resistance to penicillin. There is an increasing incidence of Gram-negative aerobic bacteria causing peritonsillar abscess. Appropriate antibiotics for Gram-negative bacteria should be included in the regimen if such bacteria are isolated in culture and sensitivity studies. Empirical antibiotics with Gram-negative cover will be appropriate as adjunctive therapy.

Serum bactericidal activities of moxifloxacin and levofloxacin against aerobic and anaerobic intra-abdominal pathogens

We studied the serum bactericidal activity (SBA) of moxifloxacin and levofloxacin against common pathogens associated with complicated intra-abdominal infections. Ten healthy volunteers received a single dose of moxifloxacin (400 mg) and levofloxacin (750 mg) and serum samples were collected at 2, 4, 8, 12, and 24 h after the dose of each drug. Bactericidal titers in serum over time were determined for aerobic gram-negative bacilli ( Escherichia coli, Klebseilla pneumoniae, and Enterobacter cloacae) and anaerobic bacteria ( Bacteroides fragilis, Bacteroides thetaiotaomicron, Prevotella bivia, and Finegoldia magna). Both fluoroquinolones provided rapid (2 h) attainment and prolonged (24 h) SBA (titers ⩾1:8) against each of the aerobic bacilli studied. SBA was observed for at least 12 h against B. fragilis strains with MICs⩽2 μg/ml to moxifloxacin and ⩽4 μg/ml to levofloxacin. Prolonged (12 h) SBA (titers ⩾1:2) was also observed against isolates of B. thetaiotaomicron, P. bivia, and F. magna with moxifloxacin MICs⩽2 μg/ml.

Comparison of ticarcillin and piperacillin in Kenney's semen extender

Ticarcillin and piperacillin were compared to determine their effect on sperm motility and bacterial growth of equine semen samples diluted in Kenney's glucose skim milk semen extender. Each ejaculate ( n = 11) was divided into three portions and glucose skim milk semen extender solution was added. The control semen extender solution contained extended semen and no antibiotic, whereas ticarcillin and piperacillin solutions contained extended semen plus 1.0 mg/mL of ticarcillin or piperacillin, respectively. An aliquot was removed (1 h after collection) to evaluate sperm motility and microbial concentration. All three solutions were stored at 4 °C and aliquots were obtained at 24 and 48 h to determine sperm motility and microbial concentration. Mean percentages of motile and progressively motile sperm did not differ significantly among control and antibiotic-containing solutions after storage. Control-extended semen samples from ejaculates of stallions ( n = 11) were contaminated with aerobic gram-positive and gram-negative bacteria. In solutions that contained either antibiotic, growth of these microbes was inhibited after 1, 24, and 48 h at 4 °C. Semen samples from stallions ( n = 5) were extended with Kenney's glucose skim milk extender containing no antibiotic, ticarcillin or piperacillin and then inoculated with approximately 5 × 10 2 CFU/mL Klebsiella pneumoniae or Pseudomonas aeruginosa; there was no significant difference between antibiotics in the inhibition of microbial growth. In conclusion, piperacillin was an appropriate alternative to ticarcillin in extenders for equine semen.

Comparative antimicrobial susceptibility of aerobic and facultative bacteria from community-acquired bacteremia to ertapenem in Taiwan

BackgroundErtapenem is a once-a-day carbapenem and has excellent activity against many gram-positive and gram-negative aerobic, facultative, and anaerobic bacteria. The susceptibility of isolates of community-acquired bacteremia to ertapenem has not been reported yet. The present study assesses the in vitro activity of ertapenem against aerobic and facultative bacterial pathogens isolated from patients with community-acquired bacteremia by determining and comparing the MICs of cefepime, cefoxitin, ceftazidime, ceftriaxone, ertapenem, piperacillin, piperacillin-tazobactam, ciprofloxacin, amikacin and gentamicin. The prevalence of extended broad spectrum β-lactamases (ESBL) producing strains of community-acquired bacteremia and their susceptibility to these antibiotics are investigated.MethodsAerobic and facultative bacteria isolated from blood obtained from hospitalized patients with community-acquired bacteremia within 48 hours of admission between August 1, 2004 and September 30, 2004 in Chang Gung Memorial Hospital at Keelung, Taiwan, were identified using standard procedures. Antimicrobial susceptibility was evaluated by Etest according to the standard guidelines provided by the manufacturer and document M100-S16 Performance Standards of the Clinical Laboratory of Standard Institute. Antimicrobial agents including cefepime, cefoxitin, ceftazidime, ceftriaxone, ertapenem, piperacillin, piperacillin-tazobactam, ciprofloxacin, amikacin and gentamicin were used against the bacterial isolates to test their MICs as determined by Etest. For Staphylococcus aureus isolates, MICs of oxacillin were also tested by Etest to differentiate oxacillin-sensitive and oxacillin-resistant S. aureus.ResultsErtapenem was highly active in vitro against many aerobic and facultative bacterial pathogens commonly recovered from patients with community-acquired bacteremia (128/159, 80.5 %). Ertapenem had more potent activity than ceftriaxone, piperacillin-tazobactam, or ciprofloxacin against oxacillin-susceptible S. aureus (17/17, 100%)and was more active than any of these agents against enterobacteriaceae (82/82, 100%).ConclusionBased on the microbiology pattern of community-acquired bacteremia, initial empiric treatment that requires coverage of a broad spectrum of both gram-negative and gram-positive aerobic bacteria, such as ertapenem, may be justified in moderately severe cases of community-acquired bacteremia in non-immunocompromised hosts.

Diffusion of ertapenem into bone and synovial tissues

The degree of penetration of an antibiotic into the infected site is an important criterion for therapeutic success. Ertapenem is a new carbapenem, exhibiting activity against most Gram-positive and Gram-negative aerobic and anaerobic bacteria commonly recovered from community-acquired infections. However, no studies concerning its diffusion into bone and synovial tissue are available. Our objective was to quantify ertapenem bone and synovial tissue penetration and to compare our data with the MIC(90)s for causative pathogens. In an open-label study, 18 patients who were undergoing elective total hip replacement received a single, parenteral, 1 g dose of ertapenem. One serum, one cortical and cancellous bone and one synovial tissue sample was collected per patient a median [interquartile range (IQR)] of 1.6 (1.5-1.7), 12.4 (11.9-13.1) or 23.8 h (22.6-25.2) later and analysed by HPLC. The median (IQR) serum concentrations of ertapenem were 70.1 (56.1-75.9), 10.0 (9.1-11.2) and 2.6 mg/L (2.3-3.0), respectively, at the different time points. The median (IQR) cancellous bone tissue concentrations were 13.2 (10.2-14.8), 1.9 (1.7-2.1) and 0.6 microg/g (0.4-0.6) at the different time points, corresponding to a median (IQR) tissue/serum penetration ratio of 0.19 (0.18-0.23). The median (IQR) cortical bone tissue concentrations were 8.0 (6.5-9.5), 1.3 (1.2-1.3) and 0.3 microg/g (0.3-0.4) at the different time points, corresponding to a median (IQR) tissue/serum penetration ratio of 0.13 (0.12-0.14). The median (IQR) synovial tissue concentrations were 26.2 microg/g (22.7-28.4), 4.0 mg/L (3.7-4.4) and 1.0 mg/L (0.9-1.2) at the different time points, corresponding to a median (IQR) tissue/serum penetration ratio of 0.41 (0.39-0.42). The concentrations after an ertapenem 1 g dose achieved in cancellous and cortical bone tissue and in synovial tissue were greater than the MIC(90)s for most aerobic organisms for 24 h, and for 12 to 24 h for anaerobic bacteria in healthy volunteers undergoing total hip replacement.

Validation and Reproducibility Assessment of Tigecycline MIC Determinations by Etest

A multicenter study was conducted to validate Etest tigecycline compared to the Clinical Laboratory Standards Institute reference broth microdilution and agar dilution methodologies. A large collection of gram-negative (n = 266) and gram-positive (n = 162) aerobic bacteria, a collection of anaerobes (n = 385), and selected collections of nonpneumococcal streptococci (n = 369), Streptococcus pneumoniae (n = 372), and Haemophilus influenzae (n = 372) were tested. Strains with reduced susceptibility to tigecycline were used with all test methods. The Etest showed excellent inter- and intralaboratory reproducibility for all organism groups tested regardless of the test methodology. The essential agreement values with the reference method (+/-1 dilution) were >99% for the collection of gram-negative and gram-positive aerobes; >98% for the S. pneumoniae, H. influenzae, and anaerobe collections; and 100% for the group of nonpneumococcal streptococci. These results validate the performance accuracy and utility of Etest tigecycline and verify the reproducibility of this convenient predefined gradient methodology for tigecycline susceptibility determination.

An Urgent Problem of Aerobic Gram-Negative Pathogen Infection in Complicated Parapneumonic Effusions or Empyemas

Complicated parapneumonic effusion or empyema is a troublesome disease with a high mortality. The most common involved microorganisms seem to have changed over recent decades, influenced by the introduction of new antibiotics, and the increase of immunocompromised hosts, and the elderly population. More epidemiological studies on the current bacteriology are needed to help us to empirically select adequate antibiotics. A retrospective study via chart review in a university-affiliated tertiary medical center was conducted to assess the underlying bacterial pathogens and outcome of patients with complicated parapneumonic effusions or empyemas. During the 43-month study period (from December 2000 to June 2004), 304 patients were diagnosed with complicated parapneumonic effusions or empyemas and the mortality of these patients was 23% (69/304). Among these 304 patients, a total of 292 microorganisms were cultured from the pleural fluid samples of 207 patients (to yield a positive microbiological culture rate of 68% (207/304). Isolated bacteria included aerobic Gram-negative bacteria (n=129), aerobic Gram-positive bacteria (n=105), anaerobic bacteria (n=51), and M. tuberculosis (n=7). Of these aerobic bacterial infections, Gram-negative bacteria were isolated more frequently from the older population and involved a significantly higher mortality rate and longer stay, compared to those with other bacteria (p=0.001 and p<0.001 respectively). The increasing incidence of infection with aerobic Gram-negative pathogens may cause more critical conditions in complicated parapneumonic effusions or empyemas.

Bactericidal activity of ertapenem against major intra-abdominal pathogens

Treatment of intra-abdominal infections remains a challenge owing to their polymicrobial nature and associated mortality risk. Treatment regimens must provide broad-spectrum coverage, including Gram-positive and Gram-negative aerobic and anaerobic bacteria of gastrointestinal origin. Ertapenem is a long-acting 1-β-methyl parenteral group 1 carbapenem antibiotic that has a broad antibacterial spectrum and once-daily dosing supported by clinical studies. It is active against Gram-positive and Gram-negative bacteria, including Enterobacteriaceae, Streptococcus pneumoniae and most species of anaerobic bacteria. The aim of this study was to measure the killing effects of ertapenem against a selected group of strains responsible for intra-abdominal infections. Gram-negative isolates comprised the following species: Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Klebsiella ozaenae, Enterobacter cloacae and Proteus mirabilis (extended-spectrum β-lactamase (ESBL) producers and non-producers). Gram-positive isolates comprised methicillin-susceptible Staphylococcus aureus (MSSA), Enterococcus faecalis and anaerobic Bacteroides fragilis. Ertapenem activity was tested by determination of minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs). Killing curves were performed in monocultures and co-cultures at selected antibiotic concentrations. Ertapenem showed a rapid and potent bactericidal activity in the first few hours of the kinetic curves against E. coli (6 log 10 colony-forming unit (CFU) reduction in the first 2 h), B. fragilis (4 log 10 CFU reduction in 4 h), MSSA (3 log 10 CFU reduction in 4–6 h), K. ozaenae (ESBL+), K. pneumoniae (ESBL+ and −), E. cloacae (ESBL−) in 1 h and P. mirabilis (ESBL+) in the first 2 h. The potent bactericidal activity of ertapenem compared with ceftriaxone and piperacillin/tazobactam was well demonstrated in the co-cultures of E. coli–B. fragilis and E. coli–B. fragilis–E. faecalis, whilst ertapenem was shown to be bactericidal at 24 h in the mixed culture of S. aureus–P. mirabilis. These results support the potent in vitro bactericidal activity of ertapenem against all multiresistant strains selected in this study and the use of this drug in the treatment of intra-abdominal infections.

Effect of Tigecycline on Normal Oropharyngeal and Intestinal Microflora

Antibacterial agents disrupt the ecological balance of the normal human microflora. Tigecycline, a member of a new class of antibiotics (glycylcyclines), has been shown to have a potent broad-spectrum activity against most gram-positive and gram-negative aerobic and anaerobic bacteria. The aim of the study was to investigate the ecological effects of tigecycline on the normal oropharyngeal and intestinal microflora of healthy subjects. Thirteen healthy white subjects (six females and seven males) between 20 and 31 years of age received 100 mg of tigecycline in the morning on day 1 as a 30-min intravenous infusion followed by a 50-mg dose of tigecycline every 12 h as a 30-minute infusion for 10 days. One subject was withdrawn on day 2 because of an adverse event (urticaria). Serum, saliva, and fecal samples were collected before, during, and after administration for microbiological cultivation and for assays of tigecycline. All new colonizing bacteria were tested for susceptibility (resistance of > or =8 mg/liter) during the investigation period. The fecal concentrations on day 8 were from 3.0 to 14.1 mg/kg, with a mean value of 6.0 mg/kg and a median value of 5.6 mg/kg. The saliva concentrations were generally low (0 to 0.12 mg/liter). A minor effect on the oropharyngeal microflora was observed. The numbers of enterococci and Escherichia coli cells in the intestinal microflora were reduced at day 8 (P < 0.05), while those of other enterobacteria and yeasts increased. There was a marked reduction of lactobacilli and bifidobacteria (P < 0.05) but no impact on bacteroides. No Clostridium difficile strains were isolated. Two Klebsiella pneumoniae strains and five Enterobacter cloacae strains resistant to tigecycline were found on day 8.

Mode of delivery and cord blood cytokines: a birth cohort study

BackgroundThe mechanisms for the association between birth by cesarean section and atopy and asthma are largely unknown.ObjectiveTo examine whether cesarean section results in neonatal secretion of cytokines that are associated with increased risk of atopy and/or asthma in childhood. To examine whether the association between mode of delivery and neonatal immune responses is explained by exposure to the maternal gut flora (a marker of the vaginal flora).MethodsCBMCs were isolated from 37 neonates at delivery, and secretion of IL-13, IFN-γ, and IL-10 (at baseline and after stimulation with antigens [dust mite and cat dander allergens, phytohemagglutinin, and lipopolysaccharide]) was quantified by ELISA. Total and specific microbes were quantified in maternal stool. The relation between mode of delivery and cord blood cytokines was examined by linear regression. The relation between maternal stool microbes and cord blood cytokines was examined by Spearman's correlation coefficients.ResultsCesarean section was associated with increased levels of IL-13 and IFN-γ. In multivariate analyses, cesarean section was associated with an increment of 79.4 pg/ml in secretion of IL-13 by CBMCs after stimulation with dust mite allergen (P < 0.001). Among children born by vaginal delivery, gram-positive anaerobes and total anaerobes in maternal stool were positively correlated with levels of IL-10, and gram-negative aerobic bacteria in maternal stool were negatively correlated with levels of IL-13 and IFN-γ.ConclusionCesarean section is associated with increased levels of IL-13 and IFN-γ, perhaps because of lack of labor and/or reduced exposure to specific microbes (e.g., gram-positive anaerobes) at birth.

Ascites in childhood liver disease

Ascites is a common clinical problem in children with liver disease. The peripheral arterial vasodilation hypothesis is mostly accepted as the pathophysiological basis of ascites. The most important complication is spontaneous ascitic fluid infection in the form of spontaneous bacterial peritonitis (SBP) and its variants. Aerobic gram-negative bacteria, primarily Escherichia coli, are the most common isolates. Diagnostic paracentesis is done in patients with ascites when diagnosed first time and at the beginning of each admission to hospital. Ascitic fluid is evaluated for cell count with differential, albumin level, total protein and culture. Serum-ascites albumin gradient (SAAG) is the best single test for classifying ascites into portal hypertensive (SAAG> 1.1 g/dL) and non-portal hypertensive (SAAG < 1.1 g/dL) causes. In patients with tense ascites LVP should be performed. A neutrophil count of > 250 cells/mm3 is highly suggestive of bacterial peritonitis. Intravenous cefotaxime is the empiric antibiotic of choice. Long-term administration of oral norfloxacin 5-7.5 mg/Kg once a day in cirrhotic patients with ascitic fluid protein content of < 1g/dL or prior episode of SBP is recommended for prevention of SBP. Oral dual diuretic therapy of single morning dose of spironolactone along with furosemide in the ratio of 5:2 is recommended. While obtaining satisfactory diuretic response dual diuretic therapy can be changed over to monotherapy with spironolactone. Patients should be on sodium restricted diet. Management of ascites might ultimately require liver transplantation.

Chromatographic analysis of penicillins in pharmaceutical formulations and biological fluids

Natural penicillin (benzylpenicillin) is the oldest antibiotic observed by Alexander Fleming in 1928. To broaden its spectrum of activity, natural penicillin was modified, giving rise to a group of antibiotics under the name 'penicillins'. Although an increasing number of bacteria appear to be resistant to them, penicillins are used to treat a variety of bacterial infections including Gram-positive, Gram-negative aerobic and anaerobic bacteria. Consequently, they are widely used in human and veterinary medicine to prevent and treat diseases. This review covers the analytical methodologies, mainly chromatographic, employed to the penicillins determination in pharmaceutical formulations, biological fluids and in production-scale fermentations reported in the literature. Results of published assays are comparatively presented focusing on sample preparation regarding isolation and purification, chromatographic conditions and method validation. Information on chemical structure, spectrum of activity and action mechanism of common penicillins has also been given.

The role of selective decontamination of the digestive tract in acute stroke

following a stroke, morbidity and mortality is high, with aspiration pneumonia being a common complication. to determine the levels of colonisation by and isolation of aerobic Gram-negative bacteria (AGNB) in acute stroke patients and determine the effect of selective decontamination of the digestive tract (SDD) on oral flora and whether it reduces both morbidity and mortality after an acute stroke. a prospective, randomised, placebo-controlled double blind trial. acute stroke assessment units of three hospitals in the northwest of England. 203 patients admitted to hospital following a first acute stroke. participants were randomised to SDD oral gel or placebo. Swallow was assessed on admission to hospital, and oral swabs were obtained thrice weekly. Demographic and clinical data were recorded. 203 patients (106 males and 97 females) participated, of whom 20 died during their hospitalisation, 19 withdrew and full follow-up was obtained for the remaining 164. A total of 122 AGNB were isolated in 105 samples from 48 patients. Abnormal swallow on admission was found in 58 patients (29%). A total of 34 patients carried a single gram-negative micro-organism that was present on one or more occasions. More than one AGNB was carried in 14 patients, and organisms were significantly more likely to be isolated from the placebo group than the active group during weeks 2 and 3 of treatment (P = 0.034, chi-squared). Seven patients in the placebo group and one in the treatment group developed pneumonia (P = 0.029, Fisher's exact test). high carriage of and colonisation by AGNB was found within this study, which was reduced by the addition of SDD. Although SDD reduced the presence of both organisms and documented episodes of pneumonia, mortality remained unchanged.

Selective Decontamination of the Digestive Tract: Cumulating Evidence, at Last?

Selective decontamination of the digestive tract (SDD), an infection-control strategy designed to prevent nosocomial pneumonia in mechanically ventilated patients, has been implemented in numerous studies for more than 2 decades, but its role remains controversial. Sentinel studies in the 1960s and 1970s identified a link between colonization of the upper respiratory tract and subsequent increased risk of developing nosocomial pneumonia in critically ill patients. Studies in the 1980s found that prophylaxis with topical and systemic antibiotics to decontamination of the upper respiratory tract and gastrointestinal tract (particularly depleting gram-negative aerobic bacteria) was associated with lower rates of infections. However, impact on survival was not substantiated. However, several recent studies (including randomized trials and meta-analyses) suggest that SDD may improve survival in selected cohorts of critically ill patients in intensive care units (ICUs). Because liberal use of SDD (or any antimicrobial prophylactic strategy) may lead to escalating antimicrobial resistance, the risk of resistance varies according to local pathogens and resistance patterns. This review describes the development of the SDD concept, discusses recently published trials, and develops points for discussion and research. Additional studies are required to further define appropriate indications and limitations of this preventative strategy.

Evaluation of Antimicrobial Resistance Among Gram-Negative Isolates Collected from Intensive Care Units and Reliability of Routine Disc Susceptibility Tests at a Teaching Hospital in Tehran

Antibiotic resistance of Intensive Care Unit (ICU) born aerobic gram-negative bacteria was evaluated during a six months period at a teaching hospital in Tehran, and determination of the validity of the results obtained from disc diffusion tests, using discs manufactured in Iran. Disc susceptibility tests using Iranian and standard discs (diffusion discs available in international markets) were performed on 108 aerobic gram-negative isolates obtained from the clinical samples of patients with at least 72 hours of stay in the ICU. The Minimum Inhibitory Concentrations (MIC) was subsequently determined by collaborators not involved with the disc testing evaluation. Acinetobacter was the most frequently isolated gram negative species (26%). High resistance rates were obtained for all antibiotics studied except for imipenem (98% sensitive). Results of disc diffusion tests performed by the Iranian discs were in moderate to strong agreement with those obtained from the standard discs. When comparing disc results with the MIC results, it was noted that the total number of very major, and minor discrepancies were approximately the same with both sets of discs. The total number of major discrepancies was higher for the Iranian discs (more false positive results). The total number of very major discrepancy rates was more than the acceptable 1.5% limits for each antibiotic tested, using both Iranian and standard discs. High rates of resistance in aerobic gram-negative isolates studied, leaves imipenem as the only reliable agent for the empirical treatment of ICU infections. The high rates of very major discrepancies with both sets of discs show that physicians cannot rely on disc diffusion tests only, in order to guide therapy for the treatment of very serious infections in the ICUs, even if standard discs are used instead of the Iranian discs, and there is great need to establish a fast and easy way to determine the MIC values. Although it is better to repeat the study with a much larger sample size in order to make good judgment.

Antimicrobial susceptibility of clinical isolates of aerobic gram-negative bacteria in 2002

Antimicrobial susceptibility of clinical isolates of aerobic gram-negative bacteria in 2002

A Randomized Double-Blind Trial of Iseganan in Prevention of Ventilator-associated Pneumonia

Iseganan, an antimicrobial peptide, is active against aerobic and anaerobic gram-positive and gram-negative bacteria as well as fungi and yeasts. The drug has shown little resistance in vitro and to be safe and well tolerated in 800 patients with cancer treated for up to 6 wk. To determine the efficacy of iseganan for the prevention of ventilator-associated pneumonia (VAP). Mechanically ventilated patients in the United States and Europe were randomized to oral topical iseganan or placebo (1:1) and treated six times per day while intubated for up to 14 d. Patients were eligible if randomized within 24 h of intubation and estimated to survive and remain mechanically ventilated for 48 h or more. The primary efficacy endpoint of the study was VAP measured among survivors at Day 14. A total of 709 patients were randomized and received at least one dose of study drug. The two groups were comparable at baseline except iseganan-treated patients were, on average, 3 yr older. The rate of VAP among survivors at Day 14 was 16% (45/282) in patients treated with iseganan and 20% (57/284) in those treated with placebo (p = 0.145). Mortality at Day 14 was 22.1% (80/362) in the iseganan group compared with 18.2% (63/347) in the placebo group (p = 0.206). No pattern of excess adverse events in the iseganan group compared with placebo was observed. Iseganan is not effective in improving outcome in patients on prolonged mechanical ventilation.

Photocatalytic Inactivation of Legionella Pneumophila and an Aerobic Bacteria Consortium in Water over TiO2/SiO2 Fibres in a Continuous Reactor

A continuous photoreactor, working in a total recycle mode and irradiated by a low-pressure Hg lamp, has been used to study the bactericidal effect of a photocatalyst, formed by TiO2 embedded in SiO2 fibres, on Legionella pneumophila and a consortium of common gram-negative aerobic bacteria (Escherichia coli, Klebsiella sp., Pseudomona sp. and Proteus sp.) in water. The kinetic modeling of the inactivation process, carried out with the measured values of viable bacteria concentration at the outlet of photoreactor, evidenced that for each pass inside the photoreactor the ratio between the outlet and inlet cell concentrations was of order of 0.01 for the inactivation of L. pneumophila. For the other aerobic bacteria, which are usually taken as reference in photocatalytic bacteria inactivation studies, this ratio was of order of 0.3 for the first hour of illumination, while upon prolonged irradiation (up to 9 h) this ratio increased to 0.7. Several factors inducing this latter decrease of efficiency are possible, as e.g. competition for photocatalytic attack between microorganisms and organic compounds released by damaged bacteria or photoinduced alteration of a small fraction of still viable bacteria making them less interactive with the photocatalyst. The inactivation mechanism normally proposed for common bacteria involves an initial attack of the photogenerated radicals to the outer membrane; the consequent membrane dispersion allows the radicals to damage the cytoplasmic membrane. The higher lethality of the photocatalytic method observed towards Legionella (in comparison to the other aerobic bacteria) is explained considering that the radicals attack the Legionella secretion system, which is adapted for high virulence and would become activated for and through adhesion to the TiO2 surface. This attack would then be able to inactivate L. pneumophila without dispersing the outer membrane. Apart from this, the water flow through the catalyst fibres can facilitate the bacteria transport towards the anatase surface, and additionally the generated shear stress may help adhesion, at least for some bacteria as E. coli, contributing further to improve the photokilling efficiency; both factors may contribute to the efficiency of this photoreactor configuration.

Colonization and Resistance Dynamics of Gram-Negative Bacteria in Patients during and after Hospitalization

The colonization and resistance dynamics of aerobic gram-negative bacteria in the intestinal and oropharyngeal microfloras of patients admitted to intensive care units (ICU) and general wards were investigated during and after hospitalization. A total of 3,316 specimens were obtained from patients upon admission, once weekly during hospitalization, at discharge from the ICU, at discharge from the hospital, and 1 and 3 months after discharge from the hospital. Five colonies per specimen were selected for identification and susceptibility testing. In both patient populations, the gram-negative colonization rates in oropharyngeal specimens increased during hospitalization and did not decrease in the 3 months after discharge. In rectal specimens, colonization rates decreased during hospitalization and increased after discharge. There was a change in species distribution among the dominant microfloras during hospitalization. Klebsiella spp., Enterobacter spp., Serratia marcescens, and Pseudomonas aeruginosa were isolated more often, whereas the frequency of Escherichia coli declined. The percentage of ICU patients colonized with ampicillin- and/or cephalothin-resistant fecal E. coli was significantly increased at discharge from the hospital and did not change in the 3 months after discharge. The emergence of multidrug resistance was observed for E. coli during patient stays in the ICU. Resistance frequencies in E. coli significantly increased with the length of stay in the ICU. For the general ward population, no significant changes in resistance frequencies were found during hospitalization. From a population perspective, the risk of dissemination of resistant gram-negative bacteria into the community through hospitalized patients appears to be low for general ward patients but is noticeably higher among ICU patients.