Clinical isolate Pseudomonas aeruginosa Mus showed resistance both to extended-spectrum cephalosporins and to aztreonam. We detected a typical double-disk synergy image when ceftazidime or aztreonam was placed next to a clavulanic acid disk on an agar plate. This resistance phenotype suggested the presence of an extended-spectrum beta-lactamase. Isoelectric focusing revealed that this strain produced three beta-lactamases, of pI 5.5, 7.4, and 8.2. A 2.6-kb Sau3A fragment encoding the extended-spectrum beta-lactamase of pI 5.5 was cloned from P. aeruginosa Mus genomic DNA. This enzyme, named OXA-18, had a relative molecular mass of 30.6 kDa. OXA-18 has a broad substrate profile, hydrolyzing amoxicillin, ticarcillin, cephalothin, ceftazidime, cefotaxime, and aztreonam, but not imipenem or cephamycins. Its activity was totally inhibited by clavulanic acid at 2 microg/ml. Hydrolysis constants of OXA-18 (Vmax, Km) confirmed the MIC results. Cloxacillin and oxacillin hydrolysis was noticeable with the partially purified OXA-18. The blaOXA-18 gene encodes a 275-amino-acid protein which has weak identity with all class D beta-lactamases except OXA-9 and OXA-12 (45 and 42% amino acid identity, respectively). OXA-18 is likely to be chromosomally encoded since no plasmid was found in the strain and because attempts to transfer the resistance marker failed. OXA-18 is peculiar since it is a class D beta-lactamase which confers high resistance to extended-spectrum cephalosporins and seems to have unique hydrolytic properties among non-class A enzymes.
Circulatory secretory non-pancreatic phospholipase A2 (snp-PLA2) was measured prospectively at the onset (day 0) of severe sepsis in 52 patients as well as on day 1 and 2 in 25 patients, in order to answer two questions: 1) does the snp-PLA2 plasma concentration differ according to the type and severity of infection? 2) what is the relation between snp-PLA2 and other mediators involved in severe sepsis, such as endotoxin, cytokines (TNF alpha, IL-1 beta, IL-6) and thromboxane B2 (the stable metabolite of thromboxane A2)? On day 0, the snp-PLA2 circulatory level was 78 +/- 17 nmol/min/ml in patients with severe sepsis as compared to 3.5 +/- 2 nmol/min/ml in 40 healthy volunteers. There was no statistical difference according to the outcome, the presence of shock, or the type of infection on day 0. However, snp-PLA2 remained elevated or even increased in patients who ultimately died, while it decreased in survivors (p = 0.01 by ANOVA). The cytokine profiles during the 2-day follow-up were similar to that of snp-PLA2, but the differences were not statistically significant between survivors and non-survivors. No correlation was found between snp-PLA2 and other mediators for either initial or peak values.
Central venous catheters (CVC) are an important source of nosocomial infection in intensive care units. The unnecessary removal of CVC suspected to be infected can probably be minimized. In order to test the accuracy of non-invasive methods for predicting catheter colonization, we prospectively compared the results of 50 consecutive CVC tip cultures, with cultures of the CVC hub and the skin at the insertion site. The CVC were separated into two groups based upon the underlying reason for CVC removal: group I (n = 20), suspicion of infection; group II (n = 30), no suspicion of infection. The skin culture (with a threshold of 15 CFU) was useful in both groups for assessing catheter colonization since it was always positive in cases of catheter colonization and always negative in the absence of catheter colonization. The contribution of the CVC hub cultures alone was minimal since there was no case of catheter colonization with negative skin cultures and positive hub cultures suggesting that the main route of catheter colonization was via the skin. Catheter-related bacteremia was identified in seven patients (six in group I and one in group II). In these patients, the ratio of bacterial colony counts (central/peripheral) was greater than 10:1 in only two cases.
The impact of antibiotics on total endotoxemia and circulating tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and IL-8 in 18 patients with severe bacteremic sepsis or septic shock due to gram-negative species was investigated. Endotoxemia, TNF-alpha, IL-6, and IL-8 were assayed before (H0) and 1 h (H1) and 4 h (H4) after the first antibiotic infusion. Endotoxemia decreased from H0 (median, 0.4 EU/mL; interquartile interval, 0.09-1.23) to H1 (median, 0.19 EU/mL; interquartile interval, 0.07-0.75; P = .03) and remained stable between H1 and H4 (median, 0.12 EU/mL; interquartile interval, 0.09-0.30; P = .4). IL-6 levels fell between H0 and H4 (P = .01) and between H1 and H4 (P = .03). IL-8 was higher at H0 than at H1 (P = .04) and at H4 (P = .01). These results suggest that endotoxemia is not increased by antibiotherapy of severe gram-negative bacteremia.
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