In this study, we systematically investigated the resistance mechanisms to ␤-lactams, aminoglycosides, and fluoroquinolones of 120 bacteremic strains of Pseudomonas aeruginosa. Pulsed-field gel electrophoresis genotyping showed that 97 of these strains were represented by a single isolate, 10 by 2 and 1 by 3 clonally related isolates, respectively. Seventy-five percent (90 out of 120) of the bacteremic P. aeruginosa strains displayed a significant resistance to one or more of the tested antimicrobials (up to 11 for 1 strain). These strains were found to harbor a great diversity of resistance mechanisms (up to 7 in 1 strain), leading to various levels of drug resistance. Interestingly, 11 and 36% of the isolates appeared to overproduce the MexAB-OprM and MexXY-OprM efflux systems, respectively. Altogether, our results show that P. aeruginosa may accumulate intrinsic (overproduction of cephalosporinase AmpC, increased drug efflux, fluoroquinolone target mutations, and deficient production of porin OprD) and exogenous (production of secondary ␤-lactamases and aminoglycoside-modifying enzymes) resistance mechanisms without losing its ability to generate severe bloodstream infections. Consequently, clinicians should be aware that multidrug-resistant P. aeruginosa may remain fully pathogenic.

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We report the emergence after 4 days of ciprofloxacin monotherapy of a double mutant of Pseudomonas aeruginosa overexpressing the multidrug efflux system MexAB-OprM and harbouring a mutation in the gyrB gene. Compared with its initial susceptible counterpart, this mutant exhibited a significant increase in resistance to most of the beta-lactam antibiotics tested (16 x MIC of ticarcillin) and to ciprofloxacin (128 x MIC). Combined ceftazidime and amikacin therapy finally eradicated the resistant isolate and cured the patient of his infection. This case illustrates how strains of P. aeruginosa may develop high levels of fluoroquinolone resistance by combining efflux mechanisms and target alterations.

The proportion of group D streptococcal infective endocarditis (IE) (predominantly due to Streptococcus gallolyticus) and the incidence of colorectal cancer are higher in France than in most European countries. We assumed that this could be explained by a high group D streptococci (GDS) fecal carriage rate. The aims of this study were to re-assess the GDS fecal carriage rate in France and its relationship with colorectal cancer. Consecutive adult subjects who were to undergo a complete colonoscopy were invited to participate. GDS were searched in subjects' stools before their colonoscopy using biomolecular techniques. Colonoscopic findings were sorted into four subgroups: normal colonoscopy, non-tumoral lesions, benign tumors, and premalignant/malignant tumors. GDS fecal carriages were calculated overall and in each subgroup and compared. The data from 259 subjects were analyzed. GDS were identified in the feces of 12 subjects, with the following distribution: S. lutetiensis (n = 9), S. pasteurianus (n = 2), and S. gallolyticus (n = 1). This accounted for an overall GDS fecal carriage rate of 4.6 %. The GDS fecal carriage rate was 6 % in case of normal colonoscopy, 1.3 % in case of non-tumoral lesions, 3.2 % in case of benign tumors, and 11 % in case of premalignant/malignant tumors. These four percentages were not statistically different. The GDS fecal carriage rate was lower than expected, which did not confirm our working hypothesis. Most strains belonged to S. bovis biotype II, while S. gallolyticus was found only once. These findings suggest that different GDS play different roles in the etiopathogenesis of IE and colorectal cancer.

Cysteine cathepsins have emerged as new players in inflammatory lung disorders. Their activities are dramatically increased in the sputum of cystic fibrosis (CF) patients, suggesting that they are involved in the pathophysiology of CF. We have characterized the cathepsins in CF expectorations and evaluated their use as markers of colonization by Pseudomonas aeruginosa. The concentrations of active cathepsins B, H, K, L and S were the same in P. aeruginosa-positive (19 Ps+) and P. aeruginosa-negative (6 Ps−) samples, unlike those of human neutrophil elastase. Also the cathepsin inhibitory potential and the cathepsins/cathepsin inhibitors imbalance remained unchanged and similar (∼2-fold) in the Ps+ and Ps− groups (p<0.001), which correlated with the breakdown of their circulating cystatin-like inhibitors (kininogens). Procathepsins, which may be activated autocatalytically, are a potential proteolytic reservoir. Immunoblotting and active-site labeling identified the double-chain cathepsin B, the major cathepsin in CF sputum, as the main molecular form in both Ps+ and Ps− samples, despite the possible release of the ∼31 kDa single-chain form from procathepsin B by sputum elastase. Thus, the hydrolytic activity of cysteine cathepsins was not correlated with bacterial colonization, indicating that cathepsins, unlike human neutrophil elastase, are not suitable markers of P. aeruginosa infection.