Note: Spin-exchange optical pumping in a van.

The advent of spin-hyperpolarization techniques designed to overcome the sensitivity issue of nuclear magnetic resonance owing to polarization transfer from more ordered systems has recently raised great enthusiasm. However, the out-of-equilibrium character of the polarization requires a close proximity between the area of production and the site of use. We present here a mobile spin-exchange optical pumping setup that enables production of laser-polarized noble gases in a standalone mode, in close proximity to hospitals or research laboratories. Only compressed air and mains power need to be supplied by the host laboratory.

3D-printed system optimizing dissolution of hyperpolarized gaseous species for micro-sized NMR.

Dissolution of hyperpolarized species in liquids of interest for NMR is often hampered by the presence of bubbles that degrade the field homogeneity. Here a device composed of a bubble pump and a miniaturized NMR cell both fitted inside the narrow bore of an NMR magnet is built by 3D printing. (129)Xe NMR experiments performed with hyperpolarized xenon reveal high and homogeneous dissolution of the gas in water.

[Chronic necrotizing pulmonary aspergillosis following an infection by Mycobacterium malmoense]. / Aspergillose pulmonaire chronique nécrosante compliquant une pneumopathie à Mycobacterium malmoense.

Pneumonia due to Mycobacterium malmoense is rare and usually occurs in damaged lung as is the case with Aspergillus infections. We report the case of a patient who developed chronic necrotizing pulmonary aspergillosis following an infection by atypical mycobacteria. A 53-year-old woman was hospitalized because of weight loss and fever. Direct examination of sputum smear was positive for acid fast bacilli and PCR and culture led to the diagnosis of infection with M. malmoense. Treatment was begun with clarithromycin, rifampicin and ethambutol. Despite initial improvement and excellent adherence to treatment, fever and weight loss recurred 6 months later. Relapse of the mycobacterial infection was excluded and the final diagnosis was necrotizing pulmonary aspergillosis. Infection with A. fumigatus complicating the treatment of M. malmoense is unusual. The management is challenging because of strong interactions between voriconazole and rifampicin, and thus requires a multidisciplinary and specialized approach.

Species-driven interpretation guidelines in case of a single-sampling strategy for blood culture.

The purpose of this paper is to define guidelines to interpret positive blood cultures (BCs) to distinguish bloodstream infection (BSI) from contamination in BCs drawn with a single venipuncture. During a 2-year period, each positive BC set (comprising six bottles from a single venipuncture) was prospectively categorised by clinicians, bacteriologists and hospital epidemiologists as BSI or contamination. For each case, the number of positive bottles per set, results from Gram staining and microorganism identification were analysed in order to define interpretation guidelines. We analysed 940 positive BC sets. The BSI rate in monomicrobial BC sets was positively correlated with the number of positive bottles. The positive predictive value was 88% with one and 100% with ≥2 positive bottles for Escherichia coli; 100% for Staphylococcus aureus, Pseudomonas and Candida spp., regardless of the number of positive bottles; 3.5%, 61.1%, 78.9% and 100% for coagulase-negative staphylococci (CoNS) with one, two, three and ≥4 positive bottles, respectively. Using a single-sampling strategy, interpretation guidelines for monomicrobial positive BCs are based on the number of positive bottles per set, results from Gram staining and microorganism identification: ≥4 positive bottles (≥2 with Gram-negative bacilli) always led to a diagnosis of BSI. The CoNS BSI rate positively correlates with the number of positive bottles.

Disseminated nontuberculous infections with Mycobacterium genavense during sarcoidosis.

Sarcoidosis is a chronic disease characterised by the development and accumulation of granulomas in multiple organs. We report two observations of disseminated Mycobacterium genavense infection in patients with proven sarcoidosis. High fever and abdominal pain appeared at 8 and 18 months following the initiation of immunosuppressive therapy. Abdominal computed tomography scans of the patients showed diffuse mesenteric lymphadenitis and splenomegaly. The diagnosis was obtained on bone marrow specimens for both patients with numerous acid-fast bacteria at direct examination and positive specific mycobacterial identification by nucleic acid amplification test. Despite prompt antimycobacterial therapy, occurrence of complications (peritonitis post-splenectomy surgery and lung carcinoma) resulted in a fatal outcome for both patients. These cases highlight that opportunistic infections like M. genavense or other nontuberculous mycobacterial infections should be considered for long-standing immunocompromised patients with sarcoidosis.

[Pet-rat bite fever and septic arthritis: molecular identification of Streptobacillus moniliformis]. / Arthrite septique après morsure de rat: identification de Streptobacillus moniliformis par biologie moléculaire.

Pet-rat bite fever is a relatively rare disease consecutive to a rat bite or scratch. The authors report a case of septic arthritis following a pet rat bite. Streptobacillus moniliformis was identified in the knee synovial fluid and identified by 16S rRNA sequencing. This is a rapid and efficient tool for identification of fastidious bacterium. The patient was cured by an amoxicillin treatment.

[From prevalence to predictive values: considerations on the antimicrobial susceptibility testing dealing with change of susceptibility rates]. / De la prévalence aux valeurs prédictives: l'antibiogramme face à l'évolution de la résistance aux antibiotiques.

The aim of the study was to quantify the influence of the variation of the susceptibility prevalence (frequencies of susceptible, intermediate and resistant isolates) on the predictive value of antimicrobial susceptibility testing reports performed with disk diffusion method, under several scenarios of distinct susceptibility prevalence. Prevalence variation effect was assessed through a modeling approach that enabled to take into account the technical variability and to control prevalence through scenarios. Results show how the prevalence impacts on the disk diffusion performance with level of discrepancies varying with prevalence. The phenomenon may be quantitatively noteworthy for some antimicrobial agents considering the prevalence recorded with time or location, leading to lowered performances. For instance, with amoxicillin+clavulanic acid, predictive values of susceptible and resistant reports varied respectively from 70 to 96 and from 33 to 97 %. For a 18-mm diameter, the probability the isolate is truly susceptible varied from 16 to 73 % according to the prevalence tested. Characteristic of the prevalence effect are described and consequences on zone diameter breakpoint policy raised. They include to (i) reevaluate disk diffusion breakpoint consistency when the prevalence impact is noteworthy and (ii) estimate the consequences of an international harmonized breakpoint policy on prediction quality and appropriate patient management.

In vitro activity of 10 antimicrobial agents against bacteria isolated from cows with clinical mastitis.

The susceptibility of 495 strains of bacteria, recently isolated in France from cows with clinical mastitis, to 10 antimicrobial agents--penicillin G, cloxacillin, oxacillin, cephalexin, cefazolin, cephapirin, cefquinome, neomycin, ampicillin and colistin--was determined by measuring their minimum inhibitory concentrations (MICS). Overall, the levels of resistance were very low except for staphylococci and penicillin G. The 167 streptococcal strains were susceptible to all of the beta-lactams tested, but six (3-6 per cent) were highly resistant to neomycin. Of the 171 staphylococcal isolates, 36.2 per cent were resistant to penicillin G, one strain of Staphylococcus sciuri was classified as methicillin-resistant, but they were all susceptible to neomycin. None of the 122 strains of Escherichia coli was resistant to colistin, but 12 had high MIC values for one or more of the cephalosporins.

Fitness and competitive growth advantage of new gentamicin-susceptible MRSA clones spreading in French hospitals.

Since 1991, new epidemic methicillin-resistant Staphylococcus aureus (MRSA) strains characterized by the unexpected reappearance of heterogeneous phenotypic expression of resistance to methicillin and by susceptibility to gentamicin and various other antibiotics (GS-MRSA) have been reported in France. GS-MRSA strains have progressively replaced MRSA clones expressing homogeneous resistance to methicillin and resistance to gentamicin (GR-MRSA). In this study, we investigated the physiological characteristics of these new clones. In particular, we evaluated and compared the maximal growth rate and the deduced generation times (related to fitness of strains) of the major French epidemic MRSA clones. The population studied consisted of 79 isolates including (i) GR-MRSA that comprised six different types on the basis of PFGE; (ii) GS-MRSA the majority of which clustered into two PFGE types, A1 (usually resistant to erythromycin) and B (usually susceptible to erythromycin); (iii) methicillin-susceptible S. aureus (MSSA). GS-MRSA-A1 and MSSA strains were shown to have a significant fitness benefit (about 20%) with shorter generation times (theta = 23.7 +/- 0.1 and 22.9 +/- 0.05 min, respectively) than GR-MRSA and GS-MRSA-B strains (theta = 30.3 +/- 0.2 and 32.5 +/- 0.5 min, respectively). These data suggest that a link exists between genetic patterns, resistance profiles and physiological properties. In vitro competitive experiments indicated that GS-MRSA- A1 strains were able to rapidly outgrow GR-MRSA strains. The growth advantage observed should be taken into account in understanding the spread of some new clones of MRSA.

[Renal differential aging processes and ofloxacin pharmacokinetics in the elderly]. / Vieillissement différentiel rénal et pharmacocinétique de population de l'ofloxacine chez le sujet agé.

Ageing generates an important inter- and intra-individual variability in drug pharmacokinetics. The increasing frequency of ofloxacin adverse effects in elderly patients results from increased ofloxacin plasma levels about two or threefold over normal concentrations. A retrospective study of ofloxacin population pharmacokinetics in 17 elderly patients (83.6 +/- 6.8 years) shows the existence of three subgroups according to ofloxacin total clearance [group 1: 1.44 l/h, group 2: 4.37 l/h and group 3: 15.08 l/h] reflecting the important inter-individual variability. No correlation between this clearance and creatinine clearance, nor between this clearance and age, could be established, showing the limits of traditional drug monitoring in the elderly. Ofloxacin pharmacokinetic parameters estimated by the non-parametric software NPEM2 in the 17 elderly patients (absorption rate constant, Ka: 2.668 +/- 1.256 h-1; apparent volume of distribution related to weight, Vs: 1.272 +/- 0.778 l/kg; elimination rate constant, Ks: 0.265 +/- 0.247 10(-3) min/ml/h) are clearly different from those estimated in young adults. These results show the limits of classic drug monitoring in the elderly, and also the interest of adaptive control of a drug regimen.

A statistical evaluation of the bactericidal effects of ceftibuten in combination with aminoglycosides and ciprofloxacin.

The bactericidal effects of ceftibuten in combination with netilmicin, isepamicin or ciprofloxacin against two strains of Escherichia coli and three of Klebsiella pneumoniae were studied by the killing curve method. Interpretation of the results was made on a statistical basis by comparing the bactericidal effects observed when the antibiotics were tested alone with those when they were tested in combination. The results were also assessed by survival probabilities according to the ratio of the number of viable bacteria at time t(N(t)) to the initial number of viable bacteria (N(0)). The effects of the combinations were defined in terms of antagonism, indifference, single agonism, addition and synergy by taking account of the confidence intervals of the survival probabilities. All of the combinations exhibited bactericidal activities which were time-dependent. Synergy was demonstrated when ceftibuten was combined with the aminoglycosides, except against the two extended-spectrum beta-lactamase-producing strains of K. pneumoniae, but not when ceftibuten and ciprofloxacin were combined. Antagonism was not demonstrated with any of the combinations.

Mathematical model for comparison of time-killing curves.

The relevance of mathematical modeling to investigations of the bactericidal effects of antimicrobial agents has been emphasized in many studies of killing kinetics. We propose here a descriptive model of general use, with four parameters which account for the lag phase, the initial number of bacteria, and the limit of effectiveness and bactericidal rate of antimicrobial agents. The model has been applied to several kinetic datum sets with amoxicillin, cephalothin, nalidixic acid, pefloxacin, and ofloxacin against two Escherichia coli strains. It is a useful tool to compare killing curves by taking into account model parameter confidence limits. This can be illustrated by studying drug effects, strain effects, and concentration effects. For the antibiotics used here, concentration effects had an influence mainly on the length of the lag phase and the minimum number of living cells observed. It is therefore clear that differences in the killing curves with changes in one or more parameters could occur.

Maintenance requirements of Escherichia coli ATCC 25922 in the presence of sub-inhibitory concentrations of various antibiotics.

Escherichia coli ATCC 25922 was grown in minimal medium M63, with glucose 0.1 gL as limiting energy substrate, in the presence of sub-inhibitory concentrations of netilmicin, habekacin, tobramycin, dibekacin, amikacin, kanamycin, amoxycillin, ampicillin, cephalothin, cefoxitin and nalidixic acid. Maintenance requirements were determined with a simple relationship derived from batch growth curves. The apparent relationship between maintenance requirements and antibiotic concentration is an exponential increase, log m(c) = log mo + k.c, where m is maintenance, c antibiotics concentration, mo maintenance without antibiotics, and k a constant. Values for k were found to be in the range 0.5-2.0 mg-1.L.

Monod's bacterial growth model revisited.

An attempt to justify Monod's bacterial growth model is presented. The justification is based on a mechanistic approach to growth which leads to a differential equation with delay and then to Monod's model. An unexpected increase of parameter K(s) with µm is predicted by the theory. A survey of literature shows that this effect is present in a large majority of published data.

[In vitro antibacterial activity of piperacillin-tazobactam combination on hospital isolates and regression curve]. / Activité antibactérienne de l'association pipéracilline + tazobactam sur les bactéries hospitalières et courbe de concordance.

Minimal inhibitory concentrations (MICs) of piperacillin (P) in combination with 4 micrograms/ml of tazobactam (T) were evaluated by agar dilution for 1,245 strains isolated in 4 hospitals. In addition antibiograms by agar diffusion were performed with disks loaded of 75 micrograms of P + 10 micrograms of T. For naturally non beta-lactamase producing Enterobacteriaceae (E), MIC 50 and 90% of P + T were (microgram/ml): E. coli 1-2; P. mirabilis: 0.5-1; activity was practically identical on plasmid mediated penicillinase (Pase) producing strains. Strains of K. pneumoniae only resistant (R) to amino- and carboxypenicillins (C) had MICs less than or equal to 4 (mode MIC 2); MICs of strains R to cephalothin and/or cefotaxime were 2 to 16 (mode MIC 4). For chromosomal cephalosporinase (Case) producing species, MICs of P + T were less than or equal to 8, including for acquired Pase producing strains, but were greater than or equal to 16 for Case hyperproducing strains. Strains of P. aeruginosa susceptible (S) to C were inhibited by 1 to 16 (with MIC 4) and strains R to C by 8 to greater than 128. MICs were generally 2 to 32 for A. baumannii S to C at 0.12 to greater than 128 for strains R to C. Haemophilus, S or R to ampicillin, were inhibited by 0.008 to 2 (MIC 50 and 90: 0.016-0.12). S. aureus S to methicillin (M), Pase producing on not, were inhibited by 0.5 to 2 (mode MIC 1) and strains R to M by 8 to greater than 128. Activity of P + T for coagulase-Staphylococci was similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Biphasic kinetics of bacterial killing by quinolones.

The early phases of the bactericidal dynamics of three quinolones against two Escherichia coli strains were studied. Four concentrations of nalidixic acid, pefloxacin and ofloxacin were tested against each strain. In each case biphasic killing of bacteria was observed after a lag phase, and a biexponential model of microbial death could be fitted to the data. A direct relationship existed between the length of the lag phase and the drug concentration. The other parameters of the model appeared to be either strain-dependent, drug-dependent or both, and were characterised by narrow fluctuations. The degree of killing was always higher for ofloxacin. A paradoxical effect seemed to exist for nalidixic acid and pefloxacin in that survival was greater in the presence of 5 x MIC than in the presence of 3 x MIC. It was clear that ofloxacin did not act in the same way as nalidixic acid and pefloxacin. The study illustrated the relevance of mathematical modelling to investigations of the bactericidal effects of antibiotics.

[Expert systems and antibiotic sensitivity test]. / Les systèmes experts et l'antibiogramme.

Artificial intelligence is a part of computer science that deals with programs mimicking intelligence of man. Artificial intelligence is now used to check the quality of the determination of antibiotics susceptibility of bacteria. This application is useful because antibiotic susceptibility is subject to biological and technical variation that have to be detected. Three types of reasoning are used either by the biologist or by expert systems: low level quality checking dealing with individual results, microbiological interpretation of the whole set of results and medical interpretation of the results. The use of artificial intelligence in these fields is sustained by the structured nature of the knowledge. Two type of expert systems are already of routine use, either based on production rules (ATB plus EXPERT, bioMerieux, La Balme-les-Grottes, France and SIR, 12A, Montpellier, France), or on object-oriented representation of the knowledge (EXPRIM from our laboratory). The main problem is, as usually in artificial intelligence applications, to transfer human expertise into an adapted knowledge base. The advantage of experts systems over man are their reproducibility of answer and their availability.