Preliminary clinical study using a multiplex real-time PCR test for the detection of bacterial and fungal DNA directly in blood

Early diagnosis of sepsis, rapid identification of the causative pathogen(s) and prompt initiation of appropriate antibiotic treatment have a combined impact on mortality due to sepsis. In this observational study, a new DNA-based system (LightCycler SeptiFast (LC-SF) test; Roche Diagnostics) allowing detection of 16 pathogens at the species level and four groups of pathogens at the genus level has been evaluated and compared with conventional blood cultures (BCs). One hundred BC and LC-SF results were obtained for 72 patients admitted to the intensive-care unit over a 6-month period for suspected sepsis. Microbiological data were compared with other biological parameters and with clinical data. The positivity rate of BCs for bacteraemia/fungaemia was 10%, whereas the LC-SF test allowed detection of DNA in 15% of cases. The LC-SF performance, based on its clinical relevance, was as follows: sensitivity, 78%; specificity, 99%; positive predictive value, 93%; and negative predictive value, 95%. Management was changed for four of eight (50%) of the patients because organisms were detected by the LC-SF test but not by BC. LC-SF results were obtained in 7-15 h, in contrast to the 24-72 h required for BC. According to the LC-SF results, initial therapy was inadequate in eight patients, and antibiotic treatment was changed. Our results suggest that the LC-SF test may be a valuable complementary tool in the management of patients with clinically suspected sepsis.

Effects of host iron transport compounds on growth kinetics and outer-membrane protein expression of Bilophila wadsworthia

Since the environmental iron concentration has emerged as an important attribute in the expression of bacterial virulence, the purpose of this study was to determine the effects of transferrin, lactoferrin, heme compounds, and inorganic iron sources (ferric and ferrous sulfate) on the growth of Bilophila wadsworthia and to study its outer membrane composition when grown under these different simulated in vivo conditions. Lactoferrin, transferrin, hemin and hemoglobin supported full growth of the bacteria in media lacking other iron sources. Bilophila wadsworthia was also capable of growing in the presence of ferrous and ferric sulfate. Profiles obtained by SDS-PAGE showed two iron-regulated outer membrane proteins (IROMPs) of 190 kDa and 88 kDa. The 190 kDa was susceptible to proteinase K cleavage in whole cells, indicating its exposure at the cell surface. These two major IROMPs were expressed in iron-restricted media supplemented with iron-bound organic sources and repressed by the addition of inorganic iron sources.

Bacterial flora of the low male genital tract in patients consulting for infertility

The physiological aerobic bacterial flora of the low male genital tract was determined. This prospective study was performed on 600 semen specimens collected from 543 asymptomatic males consulting for infertility. Semen cultures were sterile in 28.8%, with a polymicrobial flora and/or absence or low titres of Ureaplasma urealyticum in 49.3%, and with one or two aerobic and facultative bacteria > or =1 x 10(3) CFU ml(-1) and/or U. urealyticum with titres > or =10(4) CCU ml(-1) (colour changing units) in 21.8%. In standard aerobic cultures, Gardnerella vaginalis was the most commonly isolated species (26.1%), followed by coagulase-negative staphylococci (15.7%) and Streptococcus anginosus (14.2%). Ureaplasma urealyticum was absent in 84.5% of semen samples, but when recovered, high (> or =10(4) CCU ml(-1)) and low titres (< or =10(3) CCU ml(-1)) were counted in 7.2% and 8.3% respectively. Of 48 patients, the follow-up of semen cultures showed marked variations in time. This study shows that (i) there was no relationship between the bacterial flora and the leucocytospermia; (ii) low titres of U. urealyticum in semen were not associated with a disturbance of the ecosystem; (iii) the critical threshold for U. urealyticum should be raised to > or =10(4) CFU ml(-1) and (iv) a positive semen culture should be repeated before any treatment.

[Spondylodiscitis due to Salmonella enteritica serotype Typhi]

We reported a case of lombar spondylodiscitis caused by Salmonella enteritica serotype Typhi in an immunocompetent patient. Salmonella is a rare causative agent of spondylodiscitis. Early bacteriological diagnosis is essential to avoid longterm sequelae.

[Campylobacter fetus subsp fetus bacteremia in a female patient infected by the hepatitis C virus]

Campylobacter fetus subsp fetus was identified as an unusual etiologic agent of septicemia in an immuno-compromized patient VHC positive by utilizing a 16S rRNA molecular kit in our hospital's clinical laboratory. This method would appear as a performing approach to identify pathogens when discrepancies exist between phenotypical tests.

Peritonitis due to Staphylococcus sciuri in a patient on continuous ambulatory peritoneal dialysis

Among the coagulase-negative staphylococci, Staphylococcus sciuri has rarely been described as the aetiology of continuous ambulatory peritoneal dialysis (CAPD) peritonitis. It has been reported in 1 case of endocarditis and has been isolated from peritoneal dialysis fluid in 2 patients. The case reported here describes CAPD peritonitis due to S. sciuri shortly after a previous episode due to S. aureus, showing the necessity to identify coagulase-negative staphylococci to find new species that cause CAPD peritonitis.

[Bacterial epidemiological study of acute otitis media in children observed at home in the Nord Pas-de-Calais region]

BACKGROUND

The aim of this work is the study of the bacteriologic epidemiology of acute otitis media in infants observed at home in Nord Pas-de-Calais area, and the analysis of bacteria associated to recurrent otitis and clinical failure.

OBSERVATIONS

A total of 295 specimens of ear pus specimens were collected from children (mean age: 18 months; average: one month-12 years). Pneumococcus strains were isolated from 52% of samples and 80% of these showed resistance to penicillin. H. influenzae was found in 35% of specimens and the half produced a beta lactamase. Pneumococcus is the predominant pathogen isolated in prolonged otitis media, while H. influenzae is preferentially found during recurrent otitis media. The main bacteriologic cause of failure traitement was penicillin-intermediate or -resistant pneumococci. The therapy administered 48 to 72 hours before collection of ear pus sample in therapeutic failure was ineffective (oral cephalosporins or macrolides), or administered to low dosage (50 mg/kg/j).

CONCLUSION

Our results demonstrate, in opposition to other studies, Streptococcus pneumoniae as the most frequent pathogen in acute otitis media. They also show the excellent correlation between antibiotic therapy and clinical failures.

Multicenter evaluation of an automated system using selected bacteria that harbor challenging and clinically relevant mechanisms of resistance to antibiotics

A multicenter study was carried out to evaluate the performance of a new commercial automated system in comparison with that of the reference agar dilution method. Ten clinical microbiology laboratories tested a collection of 61 strains of gram-negative bacilli (49 Enterobacteriaceae and 12 Pseudomonas aeruginosa), and 6 other laboratories tested a collection of 55 strains of gram-positive cocci (10 enterococci and 45 staphylococci) against 10-20 antimicrobial agents. The strains were selected on the basis that they harbored challenging and characterized mechanisms of resistance. In comparison with the agar reference method, the automated system gave an overall essential agreement (+/-1 dilution) of 94.5%, 93.5%, and 97% for the gram-negative bacilli, enterococci, and staphylococci, respectively. According to the interpretive standards of the National Committee for Clinical Laboratory Standards, the category agreement ranged from 96 to 96.4% for the three sets of organisms. The accuracy of the automated system, as determined by the kappa test, ranged from 0.80 to 0.88, reflecting an almost perfect agreement with the reference technique. Very major, major, and minor errors obtained with the automated system were 0.3%, 2.9%, and 6.6% for gram-negative bacilli, 3.4%, 0%, and 5% for enterococci, and 1%, 1.6%, and 2.7% for staphylococci, respectively. The high rate of very major errors in enterococci was mostly due to a single strain of multidrug-resistant Enterococcus faecium, which was found susceptible to several antibiotics in a majority of participant laboratories. The use of a heavy inoculum and of a broth test medium by the automated system might account for a better expression of certain resistance mechanisms, including beta-lactamases, as compared to the agar dilution reference method. The interlaboratory reproducibility was acceptable, as shown by the narrow dispersion of MICs and by the results of quality control.

Molecular identification of Pasteurella dagmatis peritonitis in a patient undergoing peritoneal dialysis

Pasteurella dagmatis was identified as the etiologic agent of peritonitis in a continuous ambulatory peritoneal dialysis patient by utilizing a molecular kit in our hospital's clinical laboratory. This method would appear a useful approach to identify a species of Pasteurella not included in the existing database of commercial identification kits when discrepancies exist between phenotypic tests.

Evaluation of an automated system for identification of Enterobacteriaceae and nonfermenting bacilli

The performance of the Vitek 2 (bioMérieux, France), a new fully automated system allowing rapid identification of microorganisms and susceptibility testing, and the Vitek 2 ID-GNB card (bioMérieux) was evaluated using 502 clinical isolates and stock collection strains of gram-negative rods belonging to 70 taxa. The number of isolates correctly identified to species and genus levels was 430 (85.7%) and 485 (96.6%), respectively. Clinical isolates of both Enterobacteriaceae and non-Enterobacteriaceae were better identified at the species level (95.3% and 74%, respectively) than stock collection strains (86.4% and 52.2%, respectively). The Vitek 2 ID-GNB card provides after 3 h a highly acceptable level of accuracy for identification of Enterobacteriaceae and non-Enterobacteriaceae, including most atypical strains encountered in clinical situations.

[Contribution of direct bacteriologic examinations to the diagnosis of early materno-fetal bacterial infection: the Lille experience]

A prospective study was conducted in 3056 live-born infants delivered at the Jeanneade-Flandre maternity hospital of the Lille Teaching Hospital between January and August 1997. Clinical, laboratory test, and microbiological test findings were compared. A cohort of 1003 infants who remained in the maternity ward but were considered at increased risk of maternofetal infection (MFI) based on history and/or obstetrical criteria and/or neonatal criteria underwent routine collection of specimens including gastric fluid, auricular and anal swabs, amniotic fluid, and placental fragments. Microscopic examination of gastric fluid smears, the first result available to the clinician, was found to have 27.5% sensitivity (983 samples). Positive predictive value (PPV) was only 17.8% because of a high rate of colonization (16.8%), defined as absence of clinical symptoms and three peripheral specimens positive for the same organism. However, negative predictive value (NPV) was as high as 99.8% as a result of high sensitivity (97.8%) in the infected neonates. The gastric fluid smear was positive in 30% and 35% of neonates born to mothers with hyperpyrexia during early and late labor, respectively, and in 42% of neonates born to mothers with a history of group B streptococcus carriage during the pregnancy. Forty-two per cent of neonates with a history of fetal tachycardia had a positive gastric fluid smear. Diagnostic criteria for infection were three peripheral specimens positive for the same organism, C-reactive protein elevation, and/or one or more clinical signs suggestive of infection, and/or a positive central specimen (blood, CSF). The infection rate in infants who remained in the maternity ward was 1.6%. The most common causative organisms were group B streptococci. These findings illustrate the useful contribution of gastric fluid smears to the early diagnosis of MFI and confirm the predominant role of group B streptococci.

[Determination of the nosocomial origin of vancomycin-resistance strains of Enterococcus isolated from stool of patients in a hematology department]

Patients severely neutropenic, when hospitalized, occasionally receive selective digestive decontamination, and the risk of vancomycin-resistant strain selection is a drawback since glycopeptide resistance is often associated with betalactam and aminoglycosid resistance. Bacterial translocation can lead to multiresistant bacterial sepsis. Eighteen Enterococcus faecium strains were collected from patients hospitalized in the leukemia unit of the Universitary Hospital of Lille (CHRU, Pr Bauters) between October 1992 and July 1997 and were studied. Nosocomial acquisition or endogenous origin were investigated to choose well-adapted prevention. All the vancomycin-resistant strains were shown by Polymerase Chain Reaction having the van A gene. The clonality of these strains was investigated by Pulsed-Field-Gel-Electrophoresis after Sma I restriction. Pulsotype analysis showed variable homology (52%-100%). Our results do not show evidence of patient-to-patient E. faecium transmission and suggest vancomycin-resistant strains were independently selected by antibiotic therapy from individual fecal flora. Except when epidemic events or happen, this strain isolation is more related to antibiotic prescription than misuse of isolation techniques.

Characterization of the Acinetobacter baumannii Fur regulator: cloning and sequencing of the fur homolog gene

Growth kinetics, siderophore activity and iron-regulated bacterial proteins of Acinetobacter baumannii BM2580 were studied in iron-restricted and iron-supplemented chemically defined media. Iron-regulated outer membrane proteins of 75 kDa and 80 kDa were expressed under iron-restricted conditions. Cloning and sequencing of the complete iron-uptake regulatory (fur) gene from A. baumannii BM2580 is reported for the first time. This gene is preceded by a single autoregulated promoter whose -10 region overlaps the Fur binding site. The open reading frame identified encodes a polypeptide consisting of 145 amino acids. The fur gene is followed by a divergent open reading frame coding for the C-terminus of a putative PilU protein. Sequence analysis indicates that the Fur protein of A. baumannii was 63% identical to the Escherichia coli Fur protein.

Siderophore production by Staphylococcus aureus and identification of iron-regulated proteins

Siderophore activity of Staphylococcus aureus was detected in an iron-restricted chemically defined medium. The molecular mass of this siderophore, called aureochelin, was 577 Da. Surface-associated proteins of 120, 88, 57, 35, and 33 kDa were mainly expressed under iron restriction conditions. Results showed a relationship between siderophore production and the existence of the 120- and 88-kDa proteins. Western blotting of surface-associated proteins revealed that these proteins were recognized both by patients sera and polyclonal rabbit serum.

The binding of surface proteins from Staphylococcus aureus to human bronchial mucins

Colonization by Staphylococcus aureus is frequently observed in obstructive lung diseases, particularly in cystic fibrosis. It has been shown that the bacteria bind to mucins, the main constituent of bronchial secretions. The binding mechanism, however, remains unclear. We have investigated the interactions of two strains of S. aureus, one mucoid and one nonmucoid, with human bronchial mucins. Using a solution phase assay, the binding capacity of the two strains to radiolabelled bronchial mucins was assessed. The bacterial constituents were released by lysostaphin lysis and the surface components of the nonmucoid strain were extracted with the use of a detergent (3-([3-cholamidopropyl] dimethylammonio)-1-propane sulphonate (CHAPS)). All were analysed for mucin-binding using an overlay assay. The amount of mucins bound to the nonmucoid strain was threefold greater than that of the mucoid strain. In the lysostaphin extract from the mucoid strain, only a 57 kDa protein faintly bound 125I-labelled mucins, whereas three mucin-binding proteins (52, 57 and 71 kDa) were identified from the nonmucoid strain. Two surface proteins, one major at 60 kDa and one minor at 71 kDa, bound radiolabelled bronchial mucins and their binding was almost completely inhibited by ovine submaxillary mucin. These results indicate: 1) differences in the mucin-binding capacity from one strain of S. aureus to another; and 2) the presence of external and internal adhesins binding to human respiratory mucins in the nonmucoid strain.

The binding of surface proteins from Staphylococcus aureus to human bronchial mucins

Colonization by Staphylococcus aureus is frequently observed in obstructive lung diseases, particularly in cystic fibrosis. It has been shown that the bacteria bind to mucins, the main constituent of bronchial secretions. The binding mechanism, however, remains unclear. We have investigated the interactions of two strains of S. aureus, one mucoid and one nonmucoid, with human bronchial mucins. Using a solution phase assay, the binding capacity of the two strains to radiolabelled bronchial mucins was assessed. The bacterial constituents were released by lysostaphin lysis and the surface components of the nonmucoid strain were extracted with the use of a detergent (3-([3-cholamidopropyl] dimethylammonio)-1-propane sulphonate (CHAPS)). All were analysed for mucin-binding using an overlay assay. The amount of mucins bound to the nonmucoid strain was threefold greater than that of the mucoid strain. In the lysostaphin extract from the mucoid strain, only a 57 kDa protein faintly bound 125I-labelled mucins, whereas three mucin-binding proteins (52, 57 and 71 kDa) were identified from the nonmucoid strain. Two surface proteins, one major at 60 kDa and one minor at 71 kDa, bound radiolabelled bronchial mucins and their binding was almost completely inhibited by ovine submaxillary mucin. These results indicate: 1) differences in the mucin-binding capacity from one strain of S. aureus to another; and 2) the presence of external and internal adhesins binding to human respiratory mucins in the nonmucoid strain.

Pharmacokinetics and bronchial diffusion of single daily dose amikacin in cystic fibrosis patients

A single daily dose of amikacin 35 mg/kg by i.v. infusion over 30 min in 18 cystic fibrosis patients achieved mean serum peak and trough concentrations of 121.4 mg/L (+/- 37.3) and 0.88 mg/L (+/- 0.62), respectively. Pharmacokinetic parameters and bronchial diffusion of amikacin showed marked inter-patient variability. The highest concentrations in sputum were obtained at 2 h (10.95 +/- 7.55 mg/L) and decreased slowly to reach a mean concentration of 2.14 mg/L (range 0.2-3.8 mg/L) just before the following infusion. An increase in the body clearance of amikacin and a decrease in the volume of distribution according to age were observed.

Effect of vancomycin and teicoplanin alone or in combination with fusidic acid or amikacin against methicillin-resistant staphylococci

The action of two glycopeptides (vancomycin and teicoplanin) alone or in combination with amikacin or fusidic acid has been studied against 10 non-repetitive strains of methicillin-resistant Staphylococcus. The plotted killing curves show that the combination of vancomycin or teicoplanin plus fusidic acid always exhibited an antagonist effect at 24 h for the 10 strains. The combination vancomycin or teicoplanin plus amikacin shows the same effect at 24 h as vancomycin or teicoplanin alone. Thus, the combination glycopeptide plus amikacin does not alter the activity of the glycopeptide but does increase the spectrum of activity of the combination versus Gram-negative nosocomial bacteria (Pseudomonas aeruginosa, Acinetobacter sp). The vancomycin or teicoplanin plus fusidic acid combination may be responsible for bacteriological failure against methicillin-resistant Staphylococcus.

In vitro bactericidal effect of a beta-lactam+aminoglycoside combination against multiresistant Pseudomonas aeruginosa and Acinetobacter baumannii

Pseudomonas aeruginosa and Acinetobacter baumannii are frequently isolated in hospital outbreaks of nosocomial infections. In our hospital, among 1018 strains isolated one year in an intensive care unit, 84 strains (8.3%) of P. aeruginosa and 155 strains (15.2%) of A. baumannii were considered responsible for infections. The major problem related to these bacteria is their multiresistant characteristic which confers great difficulty in treating infections. We carried out a 24 h time-kill study to assess the bactericidal effect of three beta-lactams [imipenem (IPM), ticarcillin+clavulanic acid (TCC), piperacillin+tazobactam (PTB)] in combination with each other and with sulbactam (SUL) and amikacin (AKN) against 8 P. aeruginosa strains and 8 A. baumannii strains. The initial inoculum was 10(6) cfu/ml. Antibiotics were tested at clinically achievable concentrations: TCC (112 mg/l), PTB (100 mg/l), IPM (25 mg/l) and AKN (15 mg/l). The results showed: IMP + TCC + AKN = PTB + SUL + AKN = PTB + TCC + AKN > > IMP + SUL + AKN against P. aeruginosa; and PTB + SUL + AKN = PTB + TCC + AKN > IMP + SUL + AKN or IMP + TCC + AKN against A. baumannii. When infection due to these multiresistant strains was suspected, PTB + AKN combined with either TCC or SUL was bactericidal against both strains. These combinations appeared to be an alternative therapy in the treatment of undocumented nosocomial infections in intensive care units. These in vitro results are being evaluated in patients and seem to give good results for the moment.

Iron depletion and virulence in Staphylococcus aureus

Staphylococcus aureus is able to grow in the presence of extremely low iron concentrations (0.04 microM). In iron-limiting conditions, this species develops alternative metabolic strategies such as highly efficient iron-uptake mechanisms which are only partially shared with S. epidermidis. Here we summarize the mechanisms induced by iron starvation in S. aureus in order to elucidate the virulence characteristics of this bacterium.

Choice of a routine method for detecting methicillin-resistance in staphylococci

Four methods were compared for their abilities to detect methicillin-resistance of Staphylococcus strains using mecA gene PCR analysis in 6 h as the gold standard. 57 Staphylococcus aureus and 100 coagulase negative staphylococci (CNS) were evaluated by the oxacillin disc diffusion method (Kirby-Bauer), the automated API (ATB-plus) system (bioMérieux, La Balme les Grottes, France) in 24 h, the rapid BBL Crystal MRSA ID system (Becton Dickinson, Cockeysville, Md.), the oxillin MICs using the NCCLS agar dilution method in 24 h, and the mecA gene PCR analysis. For S. aureus, the correlation was excellent between the BBL Crystal MRSA ID system and mecA gene PCR analysis (positive predictive value = 100%; negative predictive value = 97%) and oxacillin MIC (positive predictive value = 96%; negative predictive value = 96%). The correlation between BBL Crystal MRSA ID and mecA gene PCR was not reliable for CNS (negative predictive value = 68%). For CNS, the slower routine susceptibility methods to identify intrinsic methicillin-resistance were better: API ATB Staph has a positive predictive value = 94% and a negative predictive value = 82%, and the disc diffusion test has a positive predictive value = 95% and a negative predictive value = 74%. However, BBL Crystal MRSA ID was as reliable as some of the other methods tested for CNS after 6 h incubation when the inoculum was increased: positive predictive value = 94% and a negative predictive value = 77%. These results emphasize that genotypic detection of methicillin-resistance will undoubtedly become important to detect rapidly methicillin-resistance, especially for CNS.

Bactericidal effect of beta-lactams and amikacin alone or in association against Klebsiella pneumoniae producing extended spectrum beta-lactamase

Ten extended spectrum beta-lactamases producing strains of Klebsiella pneumoniae characterized by analytical isoelectric focusing and studied for their susceptibility to beta-lactam antibiotics, either alone or in combination with a beta-lactamase inhibitor (clavulanic acid and sulbactam) and in association with amikacin. The extended spectrum beta-lactamases were derived from either TEM (CTX-1 = TEM-3) or SHV (CAZ-4 = SHV-5). Killing curves were studied with antibiotics at clinical by achievable concentrations, at MIC and MIC x 4. At MIC, cefotetan, cefotaxime and ceftazidime lacked bactericidal activity. Imipenem was more rapidly bactericidal than meropenem or co-amoxiclav. At MIC x 4, cefotetan and cefotaxime exhibited bactericidal effect but this was less than for imipenem which gave a reduction of 4 log10 of the inoculum. Cefotaxime plus sulbactam gave no bactericidal effect compared with cefotaxime plus co-amoxiclav. A bactericidal effect with cefotaxime plus sulbactam was seen with the addition of amikacin. At clinical concentrations cefotaxime plus co-amoxiclav +/- amikacin was as efficient as imipenem +/- amikacin with a rapid bactericidal effect (5-6 log10 in 30-60 min). We proposed that cefotaxime+co-amoxiclav might be considered as an alternative to imipenem for the treatment of extended spectrum beta-lactamase associated K. pneumoniae injections.

Influence of iron depletion on growth kinetics, siderophore production, and protein expression of Staphylococcus aureus

Growth rates, siderophore secretion, and bacterial proteins of two clinical isolates of Staphylococcus aureus were studied over 72 h of growth in iron-supplemented and iron-restricted chemically defined media. Under iron restriction the growth rates were decreased to different extents depending on the strain. Production of siderophore was detected in the mid-exponential and stationary phases of growth. The expression of iron-regulated proteins of 81, 23, and 17 kDa was time-dependent, associated with the same stage of growth, and might be involved in siderophore efficiency.

Bactericidal activity of selected antimicrobial agents against Bilophila wadsworthia and Bacteroides gracilis

Bactericidal assays of Bacteroides gracilis (six strains) and Bilophila wadsworthia (12 strains) in brucella broth with appropriate supplements were performed by the time-kill kinetic method. Antimicrobial agents tested were ampicillin/sulbactam (final concentrations, 16/8 micrograms/mL), ticarcillin/clavulanate (128/2 micrograms/mL), imipenem (8 micrograms/mL), cefoxitin (32 micrograms/mL), chloramphenicol (16 micrograms/mL), clindamycin (4 micrograms/mL), and metronidazole (16 micrograms/mL). Although all antimicrobial agents tested inhibited growth of all Bilophila strains during the first 24 hours, bactericidal activity was variable; only metronidazole was uniformly bactericidal. Most strains of Bilophila showed 1-2 log increases in growth at 6 hours with clindamycin and chloramphenicol. With chloramphenicol, some Bilophila strains tested showed regrowth starting at 30 hours. B. gracilis strains were generally more susceptible to all agents tested. Metronidazole, ticarcillin/clavulanate, chloramphenicol, and imipenem were most active. Several strains of B. gracilis were not killed by ampicillin/sulbactam, clindamycin, or cefoxitin. Activity was variable among strains and antimicrobial agents.

Effectiveness of resins in removing antibiotics from blood cultures

The present study evaluates the effectiveness of BACTEC NR-26A resin-containing medium in removing eight antibiotics from blood cultures. Peak concentrations achievable clinically were chosen. All antibiotics were prepared in fresh human blood samples. Blood samples were obtained prior to and at 15 min and 2, 24, 48, and 72 h after inoculation. Aztreonam, ceftriaxone, imipenem, teicoplanin, and ticarcillin were partially removed from blood cultures.

BioArgos: a fully automated blood culture system

BioArgos (Sanofi Diagnostics Pasteur, Marnes-la-Coquette, France) is a fully automated blood culture system that detects carbon dioxide production by infrared spectroscopy through a glass bottle. This hands-off system was compared with the BACTEC NR-660 system (Becton Dickinson Diagnostic Instrument Systems, Towson, Md.). A total of 336 microorganisms belonging to 74 taxa were tested in simulated blood cultures by both systems. Experimental data showed no significant differences between the two systems. The inclusive detection times (+/- the standard deviations) were 33.2 +/- 28.7 and 35.0 +/- 30.6 h with BioArgos and BACTEC, respectively. Anaerobes were detected earlier with BioArgos, whereas detection of some organisms that need oxygen to grow was slightly delayed. In conclusion, BioArgos is as reliable and accurate as BACTEC NR-660 and shows better practicability owing to noninvasive detection, reduction of vial manipulation, and absence of daily maintenance.

Effects of iron depletion and sub-inhibitory concentrations of antibodies on siderophore production by Staphylococcus aureus

The effect of various sub-MICs of oxacillin and amikacin, alone or in combination, on siderophore production by Staphylococcus aureus growing under iron-depleted conditions was evaluated. Siderophore production varied greatly from strain to strain, ranging from 3.0 to 383.4 microM of Desferal equivalents. Siderophore production by some S. aureus strains was reduced significantly (P less than 0.001) under some sets of conditions. However, siderophore excretion in cultures with amikacin was sometimes equal to or greater than control cultures. Thus, at some sub-MICs, the bacteria tested were able to increase siderophore production under metabolic stress. This phenomenon may be a secondary effect of the antibiotics upon intermediary metabolism as a consequence of inhibition of peptidoglycan or protein synthesis. Alternatively the antibiotics may decrease the cellular association of siderophore molecules.

Influence of blood carbon dioxide pressure on growth index values in non-radiometric Bactec vials

The influence of blood carbon dioxide pressure on growth index values yielded by the Bactec NR 660 system was evaluated. Growth index values of 1,175 Bactec blood culture vials collected from 293 patients were related to blood pCO2 and leukocyte concentrations. Thirty-three blood cultures were considered false-positive. These were significantly more frequently encountered in hypercapnia patients (5.4%) than in hypocapnia patients (1.7%) or normal patients (2.5%). There was no relationship between the growth index values and leukocyte concentrations.

A seven year survey of antibiotic susceptibility and its relationship with usage

Bacterial susceptibilities to 14 antibiotics of 7385 clinical isolates, belonging to six species of Gram-negative bacilli, were analysed during seven years (1980-86). The recovery of Serratia marcescens, Acinetobacter calcoaceticus and Pseudomonas aeruginosa increased while their sensitivity to antibiotics decreased significantly, especially to aminoglycosides and tetracycline. There were significant correlations between increase in antibiotic use and decrease in susceptibility. There was a striking relationship between third-generation cephalosporin use and increasing number of isolates of the species mentioned above.

Routine evaluation of BACTEC NR-16A and NR-17A media

The purpose of this study was to determine whether the BACTEC NR-16A and NR-17A media were more effective than the BACTEC NR-6A and NR-7A media in recovering organisms from the blood of patients undergoing antimicrobial therapy. A total of 986 sets of four blood culture bottles were compared, giving 141, 174, 93, and 104 isolates with BACTEC NR-6A, NR-16A, NR-7A, and NR-17A, respectively. BACTEC NR-6A and NR-7A media recovered 234 isolates, whereas BACTEC NR-16A and NR-17A media recovered 278 isolates. The recovery rate of bacteria when aerobic resin media were used was better than that with conventional aerobic media (P less than 0.001). The mean detection times were 51.5 and 69.7 h with NR-16A and NR-6A, respectively (P less than 0.01), whereas they were 68.2 and 71.3 h with NR-17A and NR-7A, respectively (P greater than 0.05). The small number of anaerobes recovered precluded a statistical comparison of relative recovery for that group of organisms.

Computerized colonization-surveillance based on antimicrobial susceptibility patterns

In order to estimate the occurrence of hospital-acquired colonizations, a specific program based on antimicrobial susceptibility tests was developed for the early recognition of clusters of colonized patients. This program allowed: (a) estimation of the endemic level of nosocomial colonization every three days within an intensive care unit; (b) detection of outbreak of hospital-acquired infections; (c) distinction between primary and secondary infections according to the dates of admission and collection; (d) provision of the latest profiles of susceptibility to antimicrobials for the 5 pathogens studied (Staphylococcus aureus, S. epidermidis, Serratia spp., Pseudomonas spp., Acinetobacter spp.). This study reported the experience of a two-year trial in colonization surveillance.

Routine evaluation of the nonradiometric BACTEC NR 660 system

The present study compares the sensitivity, accuracy, and practicability of a nonradiometric blood culture system with those of the standard blood culture system in use in our laboratory. A total of 1,080 sets of four blood cultures bottles were compared, giving 143 positive aerobic-medium associations and 139 positive anaerobic-medium associations. The conventional system recovered 171 isolates, whereas the BACTEC NR 660 system (Johnston Laboratories, Towson, Md.) recovered 155 isolated. There were no significant differences in total isolates with either system (P more than 0.05). The BACTEC NR 660 system recovered a slightly lower number of Serratia marcescens and Streptococcus faecalis but a higher number of Pneumococcus spp. The mean detection times were 55.9 h with the conventional system and 31.6 h with the BACTEC NR 660 system (P less than 0.001). Our results demonstrate that the BACTEC NR 660 system is suitable for routine use.

Presence of alveolar macrophages as a criterion for determining the suitability of sputum specimens for bacterial culture

The microscopic and bacteriological findings in paired saliva and sputum specimens from 66 patients with chronic bronchitis were compared in order to determine whether the presence of alveolar macrophages is a valid criterion for determining the suitability of a sputum specimen for bacterial culture. Alveolar macrophages were mainly present in sputum specimens, the culture results of which differed from the culture results of the matching saliva specimen (p less than 0.001). Sputum specimens containing alveolar macrophages appeared to be contaminated less with oropharyngeal flora than specimens which did not contain alveolar macrophages. Potential pathogens such as Streptococcus pneumoniae and Haemophilus influenzae were isolated only from sputum specimens containing alveolar macrophages. It is concluded that the presence of alveolar macrophages indicates that sputum originates from the lower respiratory tract. The results also showed that the presence of leukocytes in sputum may be considered significant if alveolar macrophages are also present.

Automated reading of a microtitre plate: preliminary evaluation in antimicrobial susceptibility tests and Enterobacteriaceae identification

An automated microELISA Reader was evaluated for its ability to read and interpret microtitre plates. A total of 309 microtitre plates were investigated by automated and visual methods. There was disagreement between the methods in one hundred and twelve (0.6%) wells. However agreements between the two methods for susceptibility tests and Enterobacteriaceae identification were respectively 98.8% and 89.3%.

Comparison of the MIC 2000 enteric media with API 20 E and conventional methods for identification of Enterobacteriaceae

By using MIC 2000 Enteric Identification Media the identification of Enterobacteriaceae was evaluated. 421 strains of Enterobacteriaceae belonging to 23 taxa were identified by MIC 2000, and the conventional method API 20 E, respectively. The results obtained are almost identical, i.e. 96.2% and 96.7%. Besides, the results showed no statistical difference between the two miniaturized systems (p greater than 0.1). The MIC 2000 Enteric Media are capable of identifying the majority of Enterobacteriaceae with a reasonable degree of reliability. This system appears to be efficient and flexible. It is convenient to determine the minimal inhibitory concentration of the tested strain on the same microplate.

A microcomputer system for clinical bacteriology: experience of 12 months' trial

A data processing system using microcomputers was developed in a hospital bacteriology laboratory processing more than 60 000 specimens yearly. The purchase price of the hardware was frs 200 000 (17 500 pounds) and the software was written by the authors. The system has been running since May 1980 without general breakdown. The present configuration allows the processing of specimens, enquiries, scientific and administrative tasks but multiprogramming and cumulative reports are not possible.

Quantitative bacteriological analysis of amniotic fluid

Quantitative bacteriological analysis of amniotic fluid (AF) was performed on 60 fluid samples collected by catheter from 50 selected labor patients regarded as liable to infection. AF cultures were positive in 52 cases. The bacterial colony counts ranged from less than 10(2) colony-forming units (CFU) per milliliter to 10(9) CFU/ml. Pathogenic bacteria in neonates such as group B Streptococcus, Escherichia coli, and Listeria monocytogenes were encountered with numerations equal to or greater than 10(7) CFU/ml in groups with clinical findings. An excellent correlation was noted between bacterial counts in AF and clinical data (p less than 0.00006). The results confirm that the quantitative bacteria analysis of the AF is a useful tool for evaluation of an infection risk for neonates.