INTRODUCTION:Preventing carriage of potentially pathogenic micro-organisms from the aerodigestive tract is an infection control strategy used to reduce the occurrence of ventilator-associated pneumonia in intensive care units. However, antibiotic use in selective decontamination protocols is controversial. The purpose of this study was to investigate the effect of oral administration of a probiotic, namely Lactobacillus, on gastric and respiratory tract colonization/infection with Pseudomonas aeruginosa strains. Our hypothesis was that an indigenous flora should exhibit a protective effect against secondary colonization.METHODS:We conducted a prospective, randomized, double-blind, placebo-controlled pilot study between March 2003 and October 2004 in a 17-bed intensive care unit of a teaching hospital in Clermont-Ferrand, France. Consecutive patients with a unit stay of longer than 48 hours were included, 106 in the placebo group and 102 in the probiotic group. Through a nasogastric feeding tube, patients received either 109 colony-forming units unity forming colony of Lactobacillus casei rhamnosus or placebo twice daily, from the third day after admission to discharge. Digestive tract carriage of P. aeruginosa was monitored by cultures of gastric aspirates at admission, once a week thereafter and on discharge. In addition, bacteriological analyses of respiratory tract specimens were conducted to determine patient infectious status.RESULTS:The occurrence of P. aeruginosa respiratory colonization and/or infection was significantly delayed in the probiotic group, with a difference in median delay to acquisition of 11 days versus 50 days (P = 0.01), and a nonacquisition expectancy mean of 69 days versus 77 days (P = 0.01). The occurrence of ventilator-associated pneumonia due to P. aeruginosa in the patients receiving the probiotic was less frequent, although not significantly reduced, in patients in the probiotic group (2.9%) compared with those in the placebo group (7.5%). After multivariate Cox proportional hazards modelling, the absence of probiotic treatment increased the risk for P. aeruginosa colonization in respiratory tract (adjusted hazard ratio = 3.2, 95% confidence interval - 1.1 to 9.1).CONCLUSION:In this pilot study, oral administration of a probiotic delayed respiratory tract colonization/infection by P. aeruginosa.TRIAL REGISTRATION:The trial registration number for this study is NCT00604110.

Extended spectrum beta-lactamases (ESBLs) confer bacterial resistance to third-generation cephalosporins, such as cefotaxime and ceftazidime, increasing hospital mortality rates. Whereas these antibiotics are almost impervious to classic beta-lactamases, such as TEM-1, ESBLs have one to four orders greater activity against them. The origins of this activity have been widely studied for the TEM and SHV-type ESBLs, but have received less attention for the CTX-M beta-lactamases, an emerging family that is now the dominant ESBL in several regions. To understand how CTX-M beta-lactamases achieve their remarkable activity, biophysical and structural studies were undertaken. Using reversible, two-state thermal denaturation, it was found that as these enzymes evolve a broader substrate range, they sacrifice stability. Thus, the mutant enzyme CTX-M-16 is eightfold more active against ceftazidime than the pseudo-wild-type CTX-M-14 but is 1.9 kcal/mol less stable. This is consistent with a "stability-activity tradeoff," similar to that observed in the evolution of other resistance enzymes. To investigate the structural basis of enzyme activity and stability, the structures of four CTX-M enzymes were determined by X-ray crystallography. The structures of CTX-M-14, CTX-M-27, CTX-M-9 and CTX-M-16 were determined to 1.10 Angstroms, 1.20 Angstroms, 0.98 Angstroms and 1.74 Angstroms resolution, respectively. The enzyme active sites resemble those of the narrow-spectrum TEM-1 and SHV-1, and not the enlarged sites typical of ESBL mutants such as TEM-52 and TEM-64. Instead, point substitutions leading to specific interactions may be responsible for the improved activity against ceftazidime and cefotaxime, consistent with observations first made for the related Toho-1 enzyme. The broadened substrate range of CTX-M-16 may result from coupled defects in the enzyme's B3 strand, which lines the active site. Substitutions Val231-->Ala and Asp240-->Gly, which convert CTX-M-14 into CTX-M-16, occur at either end of this strand. These defects appear to increase the mobility of B3 based on anisotropic B-factor analyses at ultrahigh resolution, consistent with stability loss and activity gain. The unusually high resolution of these structures that makes such analyses possible also makes them good templates for inhibitor discovery.

OBJECTIVE To assess trends in the susceptibility to beta-lactam agents and to fluoroquinolones of clinically relevant Enterobacteriaceae isolated over a 3-year period in 14 French hospital laboratories. METHODS During the second quarter of 1996, 1997 and 1998, 180 consecutive non-duplicate isolates of Enterobacteriaceae were collected in each center. Sixteen beta-lactams and four quinolones were tested by the disk diffusion method. In addition, the double-disk synergy test was used to screen for the production of extended-spectrum beta-lactamase (ESBL). RESULTS Totals of 2507, 2312 and 2506 clinical isolates were obtained in each period, respectively. The distribution of Enterobacteriaceae species according to clinical specimens and wards was similar in each study period. No significant variation in the susceptibility rates to beta-lactams and fluoroquinolones was observed, except in Klebsiella pneumoniae and Enterobacter aerogenes. The prevalence of ESBL-producing isolates decreased from 18% to 9% in the former, while it increased from 32% to 54% in the latter. At the same time, the susceptibility to ofloxacin and pefloxacin increased for K. pneumoniae (P < 0.003) and cephalosporinase-producing species (P < 0.05), except Enterobacter spp. CONCLUSION Over the 3-year study period beta-lactams and fluoroquinolones remained highly active against Enterobacteriaceae clinical isolates, with the exception of E. aerogenes, probably as a result of the dissemination of multiresistant clones in French hospitals.

BACKGROUND:The efficacy of systemic antibiotics on the treatment of ventilator-associated infectious maxillary sinusitis (VAIMS) is debated. The objective of this study was to determine the etiologic diagnosis of VAIMS in patients receiving antibiotics.METHODS:Patients mechanically ventilated for more than or equal to 72 h, who had persistent fever while on antibiotics for more than or equal to 48 h, underwent computed tomography scan followed by transnasal puncture of involved maxillary sinuses. VAIMS was defined as follows: fever greater than or equal to 38 degrees C, radiographic signs (air fluid level or opacification of maxillary sinuses on computed tomography scan), and a quantitative culture of sinus aspirate yielding more than or equal to 103 colony-forming units/ml.RESULTS:Twenty-four patients had radiographic signs of sinusitis. The mean +/- SD prior durations of mechanical ventilation and antibiotic exposure were 9.5 +/- 4.7 days and 6 +/- 4 days, respectively. Six unilateral and nine bilateral VAIMS were diagnosed in 15 patients. The median number of etiologic organisms per patient was two (range, one to four). The bacteriologic cultures yielded gram-positive bacteria (n = 21), gram-negative bacteria (n = 22), and yeasts (n = 5). Forty percent of causative agents were susceptible to the antibiotics prescribed. Seven patients with VAIMS developed 10 concomitant infections: ventilator-associated pneumonia (n = 5), urinary tract infection (n = 3), catheter infections (n = 2). In all cases of ventilator-associated pneumonia, the implicated agents were the causative agents of VAIMS.CONCLUSION:In VAIMS patients on antibiotics, quantitative cultures of sinus aspirates may contribute to establish the diagnosis. The frequent recovery of microorganisms susceptible to the antimicrobial treatment administered suggests that therapy of VAIMS with systemic antibiotics may not be sufficient.

The most common plasmid-mediated β-lactamases in the Enterobacteriaceae are TEM-1, TEM-2 and SHV-1, which have a weak activity against first-generation cephalosporins. Neither oximino β-lactams, in particular cefotaxime and ceftazidime, nor monobactams and carbapenems were hydrolyzed by TEM-1 or −2 or SHV β-lactamases until enzyme mutants emerged in the mid-1980s.

A case of nosocomial meningitis due to aKlebsiella pneumoniae producing a CAZ-5 extendedspectrum β-lactamase and anEnterobacter aerogenes producing a derepressed cephalosporinase is reported. The intrathecal catheter incriminated was removed and a treatment with ceftazidime (4 g/24 h) and amikacin (1.5 g/24 h) was started. After 24 h ceftazidime was replaced by imipenem (2 then 4 g/24 h). This treatment failed to obtain cerebrospinal fluid sterilization; therefore the imipenem dosage was increased to 8 g/24 h and two intrathecal infusions of amikacin (50 mg) were carried out. Thereafter the patient recovered.