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To provide a comprehensive description of the histologic and bacteriologic characteristics of human nosocomial bronchopneumonia (BPN), the lungs of 83 critically ill patients decreased after a period of mechanical ventilation were examined in the immediate postmortem period. In addition, the accuracy of the protected minibronchoalveolar lavage (BAL) technique in the diagnosis of nosocomial BPN was evaluated. In each patient, a surgical pneumonectomy was performed at the bedside within 30 min following death. Each pulmonary lobe was sampled and bacteriologically analyzed using semiquantitative cultures in 50 patients and quantitative cultures in 33 patients. The entire lung was histologically analyzed using 5 to 10 slices per lung segment. In 69 patients, the bacteriologic result of a protected mini-BAL performed within 48 h preceding death was compared with histologic and bacteriologic results of study of the lung tissue itself. Histologic lesions of BPN were found in 43 of the 83 lungs examined. These lesions were (1) severe in the majority of patients (confluent BPN, n = 23; lung abscess, n = 6), (2) preferentially found in dependent lung segments, (3) often associated with nonspecific alveolar damage, (4) associated with positive lung cultures in 65% of patients (53% with gram-negative bacteria), (5) polymicrobial in 28% of patients, (6) characterized by a lobar bacterial burden greater than 10(3) cfu/g in 32% of cases. Using semiquantitative bacteriologic analysis, the sensitivity and the specificity of the protected mini-BAL in the diagnosis of nosocomial BPN were found to be 70 and 69%, respectively. Protected mini-BAL identified 77% of causative microorganisms of BPN.(ABSTRACT TRUNCATED AT 250 WORDS)

Cephalosporin hyper‐resistant Enterobacter cloacae strains are isolated with increasing frequency from hospital infections. Resistance is principally due to the chromosomal ampC gene encoding a cephalosporinase. In contrast to Escherichia coli which expresses ampC constitutively from a promoter located in the upstream frdD gene, E. cloacae displays inducible ampC expression. By cloning the ampC gene it was shown that a linked genetic locus, ampR, mediated the induction by beta‐lactams. In the absence of the antibiotic the 30,500 dalton AmpR protein represses ampC expression. The ampR gene shows a highly compact arrangement and is situated between the divergently expressed ampC gene and the frd operon from which it is separated by a bifunctional transcription terminator. The promoters for ampR and ampC substantially overlap and mRNA analyses showed that on induction transcription from the ampC promoter increased greatly whereas that from ampR did not. Two regions of sequence homology flank the ampR gene and it is proposed that a homologous recombination event between these in an ancestral enteric bacterium may have led to the deletion of ampR from the E. coli genome.

A clinical isolate of Enterobacter cloacae, strain NOR-1, exhibited resistance to imipenem and remained susceptible to extended-spectrum cephalosporins. Clavulanic acid partially restored the susceptibility of the strain to imipenem. Two 13-lactamases with isoelectric points (pI) of 6.9 and >9.2 were detected in strain E.cloacae NOR-1; the higher pl corresponded to AmpC cephalosporinase. Plasmid DNA was not detected in E. cloacae NOR-1 and imipenem resistance could not be transferred into Escherichia coli JM109. The carbapenem-hydrolyzing 13-lactamase gene was cloned into plasmid pACYC184. One recombinant plasmid, pPTN1, harbored a 5.3-kb Sau3A fragment from E. cloacae NOR-1 expressing the carbapenem-hydrolyzing 13-lactamase. This enzyme (pl 6.9) hydrolyzed ampicillin, cephalothin, and imipenem more rapidly than it did meropenem and aztreonam, but it hydrolyzed extended-spectrum cephalosporins only weakly and did not hydrolyze cefoxitin. Hydrolytic activity was partially inhibited by clavulanic acid, sulbactam, and tazobactam, was nonsusceptible to chelating agents such as EDTA and 1,10-o-phenanthroline, and was independent of the presence of ZnCl2. Its relative molecular mass was 30,000 Da. Induction experiments concluded that the carbapenem-hydrolyzing ,3-lactamase biosynthesis was inducible by cefoxitin and imipenem. Subcloning experiments with HindIII partial digests of pPTN1 resulted in a recombinant plasmid, designated pPTN2, which contained a 1.3-kb insert from pPTN1 and which conferred resistance to 13-lactam antibiotics.Hybridization studies performed with a 1.2-kb Hindlll fragment from pPTN2 failed to determine any homology with ampC of E. cloacae, with other known 13-lactamase genes commonly found in members of the family Enterobacteriaceae (blaTEM-l and blasHv.3 derivatives), and with previously described carbapenemase genes such as those from Xanthomonas maltophilia, Bacilus cereus, Bacteroidesfragilis (cfA), and Aeromonas hydrophila (cphA). This work describing the biochemical properties of a novel chromosome-encoded 13-lactamase from E. cloacae indicates that this enzyme differs from all the previously described carbapenemases. This is the first reported cloning of a Enterobacteriaceae.