The present study sought to determine whether the pigment produced by Proteus mirabilis from the L-forms of various aromatic amino acids under aerobic conditions is melanic in nature. It is a black-brown pigment which behaves like a melanin in many respects, namely solubility features, bleaching by oxidizing agents and positive response to the Fontana-Masson assay. In the present study, for the first time, it was shown by electron spin resonance analysis that a bacterial melanin is able to act as a free radical trap, as was previously demonstrated for other melanins. Scanning electron microscopy studies showed a specific organized structure of the pigment as rounded aggregates of spherical bodies. DNA hybridization data did not reveal, in the P. mirabilis genome, any nucleotide sequence related to Shewanella colwelliana mel A, one of the two melanogenesis systems already defined at the molecular level in bacteria. Results obtained from experiments on pigment production inhibition suggest a possible role of tyrosinase in P. mirabilis melanogenesis. In conclusion, from the bulk of our results, it appears that the pigment produced by P. mirabilis is melanic in nature.

DNA, Bacterial↗

PubMedDate not supplied

In vitro activity of piperacillin/tazobactam against 615 Pseudomonas aeruginosa strains isolated in intensive care units.

From May 1996 to September 1997, 615 Pseudomonas aeruginosa strains isolated from patients in intensive care units collected from different Italian laboratories were studied. The susceptibility of piperacillin/tazobactam, in comparison with other antipseudomonal antibiotics, to their NCCLS breakpoints was evaluated: amikacin 79. 6%, carbenicillin 67.0%, ceftazidime 73.4%, ciprofloxacin 55.8%, imipenem 64.1%, piperacillin 88.1%, piperacillin/tazobactam 92.4% and ticarcillin/clavulanic acid 69.0%. Seventy-three strains were selected because of their resistance to piperacillin and the mechanisms underlying such a resistance were investigated. Isoelectric focusing and hydrolysis assays revealed the presence of 15 plasmid-mediated beta-lactamases. Chromosomal beta-lactamase derepression was demonstrated in 34 isolates. The remaining 24 piperacillin-resistant strains did not produce beta-lactamases and an 'intrinsic mechanism' of resistance was inferred. The piperacillin/tazobactam combination restored resistance in 25 piperacillin strains. Nine of these were derepressed for chromosomal beta-lactamase, 8 showed impermeability and 8 showed plasmid enzymes.

Drug Therapy, Combination↗

PubMedDate not supplied

In vitro activity of cefpirome against beta-lactamase-inducible and stably derepressed Enterobacteriaceae.

Most members of the Enterobacteriaceae and Pseudomonas aeruginosa possess an inducible chromosomal class I beta-lactamase. Bacterial strains which produce high levels of beta-lactamase constitutively can be isolated from infections; these derepressed mutants are responsible for resistance to third-generation cephalosporins and ureidopenicillins. Minimum inhibitory concentrations of cefpirome, a fourth-generation cephalosporin, and other beta-lactam antibiotics were determined for a series of mutants of Citrobacter freundii, Enterobacter cloacae, Morganella morganii, Proteus vulgaris and Serratia marcescens with inducible stably derepressed or basal expression of chromosomal class I beta-lactamases. All the antibiotics tested were almost equally active against beta-lactamase-inducible organisms and their basal mutants. Imipenem and cefpirome showed better activity against derepressed mutants than third-generation cephalosporins and ureidopenicillins.

Anti-Bacterial Agents↗

PubMedDate not supplied

Clinical isolate of a Xanthomonas maltophilia strain producing L-1-deficient and L-2-inducible beta-lactamases.

Xanthomonas maltophilia produces two inducible beta-lactamases, L-1 and L-2, and resists the antimicrobial activity of beta-lactam antibiotics including carbapenems. L-1 has carbapenemase activity and L-2 is a cephalosporinase. It has been suggested that these beta-lactamases share regulatory components. We isolated a recent clinical X. maltophilia strain susceptible to carbapenems and resistant to almost all the other beta-lactam antibiotics tested. beta-Lactamase induction with cefotaxime showed that the clinical isolate had low-level expression of L-1 beta-lactamase but remained inducible for L-2 enzyme. The possible relationship of this enzyme to carbapenem sensitivity is considered.

Anti-Bacterial Agents↗

PubMedDate not supplied

In vitro activity of biapenem against recent gram-negative and gram-positive clinical isolates.

The in vitro activity of biapenem, a new carbapenem, against 535 clinical recent isolates was compared with those of other antibiotics. Biapenem showed broad-spectrum activity against gram-negative and gram-positive clinical isolates. The new carbapenem was more active than imipenem against members of the family Enterobacteriaceae with MIC90S ranging from 0.12 to 2 mg/l and from 0.25 to 4 mg/l, respectively. Moreover it was 2-fold more active than imipenem against Pseudomonas aeruginosa (MIC90, 8 and 16 mg/l, respectively). Taken together, these results indicate that biapenem shares the favorable in vitro activity properties of imipenem and merits further study in the treatment of infections caused by a wide range of pathogens.

Gram-Negative Bacteria↗

PubMedDate not supplied

Clonal spread of Acinetobacter baumannii in a general intensive care unit.

The epidemiological characterization of multiply resistant Acinetobacter baumannii isolates from a six-bed Intensive Care Unit (ICU) is described. Investigations for A. baumannii were performed in three subsequent surveillance studies. In the first study, surveillance cultures were taken from patients, health care personnel and the environment; in the second study surveillance cultures were taken at 0, 4, and 7 days from all patients admitted consecutively to the ward; and in the third study surveillance cultures were taken from patients, health care personnel and the environment. During the first study all four hospitalized patients were found to harbour A. baumannii. Hand cultures did not grow any A. baumannii when staff entered the ward from home, but 7 positive health care workers were identified out of 25 samples taken during work, and two cultures of environmental specimens grew A. baumannii. During the second study, 4 of 86 (4.6%) patients resulted colonized with A. baumannii. In the third epidemiological study, no A. baumannii was cultured from either patients, health care personnel or the environment. All isolates recovered from various patients or sources produced conserved macrorestriction Pulsed-Field Gel Electrophoresis (PFGE) patterns and showed the same antibiotic resistance; therefore, they can be considered indistinguishable. The same antibiotic resistance and macrorestriction patterns were observed in previously isolated A. baumannii strains in the ward during May 1997, suggesting the persistence of a single A. baumannii in the ICU. The present study confirms that molecular typing is an essential tool in the epidemiology and control of nosocomial infections, showing here the persistence of a single A. baumannii clone in the ICU. The origin of this strain remains unknown but, when basic infection control measures were reinforced, emphasizing the importance of hand antisepsis and judicious use of gloves, control of A. baumannii spread in the ward was achieved.

Acinetobacter baumannii↗