It is important to know the spectrum of the microbial aetiology of prosthetic joint infections (PJIs) to guide empiric treatment and establish antimicrobial prophylaxis in joint replacements. There are no available data based on large contemporary patient cohorts. We sought to characterize the causative pathogens of PJIs and to evaluate trends in the microbial aetiology. We hypothesized that the frequency of antimicrobial-resistant organisms in PJIs has increased in the recent years. We performed a cohort study in 19 hospitals in Spain, from 2003 to 2012. For each 2-year period (2003-2004 to 2011-2012), the incidence of microorganisms causing PJIs and multidrug-resistant bacteria was assessed. Temporal trends over the study period were evaluated. We included 2524 consecutive adult patients with a diagnosis of PJI. A microbiological diagnosis was obtained for 2288 cases (90.6%). Staphylococci were the most common cause of infection (1492, 65.2%). However, a statistically significant rising linear trend was observed for the proportion of infections caused by Gram-negative bacilli, mainly due to the increase in the last 2-year period (25% in 2003-2004, 33.3% in 2011-2012; p 0.024 for trend). No particular species contributed disproportionally to this overall increase. The percentage of multidrug-resistant bacteria PJIs increased from 9.3% in 2003-2004 to 15.8% in 2011-2012 (p 0.008), mainly because of the significant rise in multidrug-resistant Gram-negative bacilli (from 5.3% in 2003-2004 to 8.2% in 2011-2012; p 0.032). The observed trends have important implications for the management of PJIs and prophylaxis in joint replacements.

Balancing access to antibiotics with control of antibiotic resistance is a global public health priority. Currently, antibiotic stewardship is informed by a 'use it and lose it' principle, in which population antibiotic use is linearly related to resistance rates. However, theoretical and mathematical models suggest use-resistance relationships are non-linear. One explanation is that resistance genes are commonly associated with 'fitness costs', impairing pathogen replication or transmissibility. Therefore, resistant genes and pathogens may only gain a survival advantage where antibiotic selection pressures exceed critical thresholds. These thresholds may provide quantitative targets for stewardship: optimising control of resistance while avoiding over-restriction of antibiotics. We evaluated the generalisability of a nonlinear time-series analysis approach for identifying thresholds using historical prescribing and microbiological data from five populations in Europe. We identified minimum thresholds in temporal relationships between use of selected antibiotics and rates of carbapenem-resistant Acinetobacter baumannii (in Hungary), extended spectrum β-lactamase producing Escherichia coli (Spain), cefepime-resistant Escherichia coli (Spain), gentamicin-resistant Pseudomonas aeruginosa (France), and methicillin-resistant Staphylococcus aureus (Northern Ireland) in different epidemiological phases. Using routinely generated data, our approach can identify context-specific quantitative targets for rationalising population antibiotic use and controlling resistance. Prospective intervention studies restricting antibiotic consumption are needed to validate Results Identifying non-linear temporal relationships: from experiment to applicationIn a Monte Carlo experiment we compared the ability of linear and non-linear time-series analysis (Multivariate Adaptive Regression Splines, MARS) to identify pre-defined relationships between simulated explanatory and outcome time-series (Supplementary Figure 1). Non-linear time-series analysis (NL-TSA) accurately identified both truly linear and nonlinear associations. However, linear time-series analysis provided biased estimations and overall poorer data-fit if relationships were non-linear. NL-TSA models applied to retrospective time-series data from five European study populations (examples 1-5), frequently identified minimum thresholds in antibiotic useresistance relationships, (figures 1-5 and Supplementary Table 1). 'Ceiling effects', in which further increases in explanatory variables did not affect resistance rates, were found at highlevels of use of some antibiotics and hand hygiene. Non-linearities in autoregression and population interaction terms further indicated the complexity of transmission dynamics within and between clinical populations. Example 1: Carbapenem-resistant Acinetobacter baumannii (Debrecen, Hungary) We examined ecological determinants of carbapenem-resistant A. baumannii (CRAb) in a tertiary hospital population in Debrecen, Hungary (figure 1). Betwee...

Two clinical isolates of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae were noted to be less susceptible than expected to imipenem. Both were missing outer membrane proteins that serve as channels for antibiotic entry. The role of β-lactamase in resistance was investigated by eliminating the original ESBL and introducing plasmids encoding various ESBLs and AmpC β-lactamase types, by studying the effect of an increased inoculum, and by evaluating interactions with β-lactamase inhibitors. The contribution of porin deficiency was investigated by restoring a functional ompK36 gene on a plasmid. Plasmids encoding AmpC-type β-lactamases provided resistance to imipenem (up to 64 μg/ml) and meropenem (up to 16 μg/ml) in strains deficient in porins. Carbapenem resistance showed little inoculum effect, was not affected by clavulanate but was blocked by BRL 42715, and was diminished if OmpK36 porin was restored. Plasmids encoding TEM- and SHV-type ESBLs conferred resistance to cefepime and cefpirome, as well as to earlier oxyimino-β-lactams. This resistance was magnified with an increased inoculum, was blocked by clavulanate, and was also lowered by OmpK36 porin restoration. In addition, SHV-2 β-lactamase had a small effect on carbapenem resistance (imipenem MIC, 4 μg/ml, increasing to 16 μg/ml with a higher inoculum) when porins were absent. In K. pneumoniae porin loss can thus augment resistance provided either by TEM- or SHV-type ESBLs or by plasmid-mediated AmpC enzymes to include the latest oxyimino-β-lactams and carbapenems.

The effect of magnesium deficiency on glucose disposal, glucose-stimulated insulin secretion and insulin action on skeletal muscle was investigated in rats which were fed a low magnesium-containing diet for 4 days. Control rats were fed a standard diet. Compared to the control rats, the rats fed with low magnesium diet presented: 1) lower serum magnesium levels (0.45 +/- 0.02 vs 0.78 +/- 0.01 mmol/l, p < 0.001), 2) higher basal serum glucose (6.8 +/- 0.02 vs 5.5 +/- 0.2 mmol/l, p < 0.05) and similar basal serum insulin, 3) 40% reduction (p < 0.001) in the glucose disappearance rate after its i.v. administration, and 4) 45% reduction (p < 0.05) in the glucose-stimulated insulin secretion. The insulin action upon the glucose uptake by skeletal muscle was determined by means of hindquarter perfusions. Compared with control rats, magnesium-deficient rats presented: 1) normal basal glucose uptake, 2) lower stimulatory effect on the glucose uptake by insulin at the concentrations of 5 x 10(-10) mol/l (3.0 +/- 0.9 vs 5.4 +/- 0.6, p < 0.05) and 5 x 10(-9) mol/l (6.3 +/- 0.5 vs 8.0 +/- 0.5, p < 0.05), 3) normal glucose uptake at a maximal insulin concentration of 1 x 10(-7) mol/l, and 4) 50% reduction in the insulin sensitivity (ED50: 1.3 +/- 0.3 vs 0.55 +/- 0.1 mol/l, p < 0.05). In partially purified insulin receptors prepared from gastrocnemius muscle, 125I-insulin binding was similar in both groups of rats. However, the autophosphorylation of the beta-subunit of the insulin receptor was significantly reduced by 50% in magnesium-deficient rats and the tyrosine kinase activity of insulin receptors toward the exogenous substrate Poly Glu4; Tyr 1 was also reduced (p < 0.05) by hypomagnesaemia. The abundance of the insulin-sensitive glucose transporter protein (muscle/fat GLUT4), measured by Western blot analysis using polyclonal antisera, was similar in muscles of control and hypomagnesaemic rats. These findings indicate that hypomagnesaemia has a deleterious effect on glucose metabolism due to an impairment of both insulin secretion and action. The insulin resistance observed in skeletal muscle of magnesium-deficient rats may be attributed, at least in part, to a defective tyrosine kinase activity of insulin receptors.

OBJECTIVE: To evaluate the clinical significance of and describe factors associated with Corynebacterium striatum infection. METHODS: A retrospective chart review was performed of the C. striatum isolated in a university hospital from January 1991 to July 1995. C. striatum was identified using conventional methods, the API CORYNE system and cellular fatty acid profiles. RESULTS: In the study period, C. striatum was isolated from clinical samples in 127 patients. In 49 patients, data from clinical charts were considered insufficient for evaluation. In 26 cases, the microorganism was considered to be the etiologic agent of an infectious process. In the remaining 52 patients, the organism was considered to be a colonizer. Before the infection all the patients had been hospitalized for some underlying condition, and 22 (85%) of them had received antibiotics previously. Six patients died. In two of them, death was a consequence of their underlying disease and in the remaining four, death was related to the C. striatum infection. CONCLUSIONS: C. striatum, a microorganism traditionally considered to be an avirulent member of the normal human nasopharyngeal and skin flora, may opportunistically cause infections in hospitalized patients with underlying diseases and previous antibiotic treatments.