Piromidic acid, a new antibacterial agent: absorption, distribution, excretion, and metabolism

Single-channel characterization of the chitooligosaccharide transporter chitoporin (SmChiP) from the opportunistic pathogen Serratia marcescens

Serratia marcescens is an opportunistic pathogen that can utilize chitin as a carbon source, through its ability to produce chitin-degrading enzymes to digest chitin and membrane transporters to transport the degradation products (chitooligosaccharides) into the cells. Further characterization of these proteins is important to understand details of chitin metabolism. Here, we investigate the properties and function of the S. marcescens chitoporin, namely SmChiP, a chitooligosaccharide transporter. We show that SmChiP is a monomeric porin that forms a stable channel in artificial phospholipid membranes, with an average single-channel conductance of 0.5 ± 0.02 nS in 1 M KCl electrolyte. Additionally, we demonstrated that SmChiP allowed the passage of small molecules with a size exclusion limit of <300 Da and exhibited substrate specificity toward chitooligosaccharides, both in membrane and detergent-solubilized forms. We found that SmChiP interacted strongly with chitopentaose (K_d = 23 ± 2.0 μM) and chitohexaose (K_d = 17 ± 0.6 μM) but did not recognize nonchitose oligosaccharides (maltohexaose and cellohexaose). Given that S. marcescens can use chitin as a primary energy source, SmChiP may serve as a target for further development of nutrient-based antimicrobial therapies directed against multidrug antibiotic-resistant S. marcescens infections.

The Serratia gene cluster encoding biosynthesis of the red antibiotic, prodigiosin, shows species- and strain-dependent genome context variation

The prodigiosin biosynthesis gene cluster (pig cluster) from two strains of Serratia (S. marcescens ATCC 274 and Serratia sp. ATCC 39006) has been cloned, sequenced and expressed in heterologous hosts. Sequence analysis of the respective pig clusters revealed 14 ORFs in S. marcescens ATCC 274 and 15 ORFs in Serratia sp. ATCC 39006. In each Serratia species, predicted gene products showed similarity to polyketide synthases (PKSs), non-ribosomal peptide synthases (NRPSs) and the Red proteins of Streptomyces coelicolor A3(2). Comparisons between the two Serratia pig clusters and the red cluster from Str. coelicolor A3(2) revealed some important differences. A modified scheme for the biosynthesis of prodigiosin, based on the pathway recently suggested for the synthesis of undecylprodigiosin, is proposed. The distribution of the pig cluster within several Serratia sp. isolates is demonstrated and the presence of cryptic clusters in some strains shown. The pig cluster of Serratia marcescens ATCC 274 is flanked by cueR and copA homologues and this configuration is demonstrated in several S. marcescens strains, whilst these genes are contiguous in strains lacking the pig cluster.

Control of a Serratia marcescens outbreak in a maternity hospital

During the period between October 1984 and January 1985, an outbreak of Serratia marcescens took place in the Serlin Maternity Hospital in Tel-Aviv. Four major and six minor infections were noted in newborn and preterm infants. An additional group of 24 neonates were asymptomatic carriers of S. marcescens. Extensive control measures were undertaken, including closing the SCBU to further admissions and the opening of a new SCBU. Other measures included maintaining babies in cohort groups, strict handwashing, and use of gloves and gowns. There was also intensified encouragement of breast feeding and thorough cleansing and disinfection of the SCBU and nurseries. After 3 months, the outbreak was controlled. No identified source for the outbreak was detected. We feel that the extensive measures employed were responsible for controlling the outbreak within a relatively short time.

Serratia bacteremia

During a 6-yr period, 146 patients at our institution had Serratia bacteremia (3.8% of the total number of episodes of bacteremia), with an incidence of 1.24/1000 admitted patients. We chose a random group of 50 cases for clinical analysis in the present study. The disease was community-acquired in 8% of the cases and nosocomially-acquired in the remaining 92%. The bacteremia was unimicrobial in 84% and part of a polymicrobial bacteremia in 16% of the episodes. The most frequently isolated species of the Serratia genus was S. marcescens. Portals of entry, in decreasing order of frequency, were: urinary, unknown, respiratory, and surgical wound infections. Clinically, the most frequent finding was fever (100%). Shock occurred in 28% of the patients, and none of our cases showed evidence of disseminated intravascular coagulation. We found 62% of Serratia isolates resistant to gentamicin. Overall mortality was 38% and factors associated with a poor prognosis were: severity of the underlying disease, critical clinical situation at onset of bacteremia, presence in the intensive care unit (I.C.U.), occurrence of shock or polymicrobial bacteremia, portal of entry in the respiratory tract, and inadequate treatment.

Antimicrobial resistance and the ecology of Escherichia coli plasmids

Four hundred and seven clinical isolates of Escherichia coli were examined for the presence of plasmids. These isolates comprised 189 which were collected irrespective of antimicrobial resistance (VP) and 218 which were collected on the basis of high-level trimethoprim resistance (TPR). The VP isolates were divided into drug sensitive (VPS) and drug-resistant (VPR) subpopulations. Plasmids were detected in 88% of VP isolates (81% of VPS and 94% of VPR) and 98% of TPR isolates. The distribution of plasmids in both groups and subpopulations was very similar. However, there were small but statistically significant differences between the plasmid distributions. These showed that more isolates in the resistant groups harboured plasmids than in the sensitive subpopulation (VPS) and that the number of plasmids carried by resistant isolates was greater. Multiple drug resistance was significantly more common among TPR isolates than the VPR subpopulation and this was paralleled by increased numbers of plasmids. Fifty-eight per cent of VPR and 57% of TPR isolates transferred antimicrobial resistance and plasmids to E. coli K12. Of the R+ isolates, 60% carried small plasmids (MW less than 20Md) and 52% of these co-transferred with R-plasmids. These results are discussed.

Transfer of drug-resistance plasmids by conjugation from nosocomial strains of Serratia marcescens to Escherichia coli in biological fluids of human origin

Six independent isolates of multi-resistant Serratia marcescens associated with nosocomial infections were examined for their ability to transfer drug-resistance plasmids by conjugation to Escherichia coli in biological fluids of human origin, such as normal and pathological urine, faeces, blood plasma and ascitic fluid. Luria broth was used as a control. Positive transfer was found in all media assayed. The different patterns of linked transferable resistance found in the transconjugants corresponded to the phenotypic expression of five plasmids. The frequencies of transfer varied with plasmid types and media employed. The culture media did not affect the phenotypic expression of the plasmids.

beta-Lactam resistance in Serratia marcescens: comparison of action of benzylpenicillin, Apalcillin, Cefazolin, and ceftizoxime

The intrinsic mechanisms of resistance to beta-lactam antibiotics in Serratia marcescens IFO 12648 were investigated, comparing the action of benzylpenicillin, apalcillin, cefazolin, and ceftizoxime. The minimal inhibitory concentrations for this strain were 1,600, 3.13, 6,400, and 0.05 microgram/ml, respectively. The addition of ethylenediaminetetraacetic acid markedly reduced the minimal inhibitory concentrations of benzylpenicillin and cefazolin, whereas those of apalcillin and ceftizoxime were not influenced. S. marcescens IFO 12648 produced only a low level of beta-lactamase activity constitutively, and the production was considerably increased by the addition of benzylpenicillin. Cefazolin was hydrolyzed rapidly by beta-lactamase activity, whereas benzylpenicillin, apalcillin, and ceftizoxime were poorly hydrolyzed. Peptidoglycan synthesis in ether-treated strain IFO 12646 cells was inhibited by a concentration of ceftizoxime markedly lower than that of cefazolin and by a concentration of apalcillin moderately lower than that of benzylpenicillin.

A nosocomial epidemic of antibiotic-resistant Serratia marcescens urinary tract infections

Serratia marcescens is an important pathogen in hospitalized urologic patients. We herein describe an epidemic of 134 urinary tract infections caused by a multipe antibiotic-resistant Serratia marcescens. A common source in the cystoscopy area was responsible for 105 infections Cross-contamination on patient floors amplified the magnitude of the epidemic. There was significant patient morbidity, although no deaths could be attributed directly to the outbreak. Particular attention is directed to patient risk factors and the clinical significance of nosocomial Serratia marcescens infections. The clinical approach to epidemic antibiotic-resistant Serratia urinary tract infection should not rely primarily on antibiotic therapy. Stress is placed on the importance of an interdisciplinary approach to hospital-acquired infections in general and Serratia marcescens urinary tract infections in particular.

Lipolytic activity copurified with the outer membrane of Serratia marcescens

Lipase, nuclease, and protease activities could be shown primarily with the purified outer membrane fraction from Serratia marcescens. These activities increased and decreased in the different compartments dependent on the growth phase of the cell culture. Penicillin-hydrolyzing activity was exclusively demonstrated with the outer membrane fraction.

Outer membrane of Serratia marcescens: apparent molecular weights of heat-modifiable proteins in gels with different acrylamide concentrations

The major proteins from the outer membrane of Serratia marcescens SM-6 are heat modifiable. The analysis of their apparent molecular weights in gels with different concentrations of acrylamide and the results obtained by radioactive labeling indicate that the major proteins are covalently linked to carbohydrate moieties.

Pleiotropic consequences of mutations towards antibiotic-hypersensitivity in Serratia marcescens

Various mutants (oxas) were isolated from Serratia marcescens SM-6 by selecting for hypersensitivity towards oxacillin. All mutants found are highly pleiotropic and able to yield spontaneous revertants which behave like the wild-type. Mutant W 1421 mostly studied shows the following phenotypic properties not found in the wild-type: (1) The growth is hypersensitive to various antibiotics, detergents and dyes which differ remarkably in their chemical structure and antibacterial action-mechanism, (2) the cells can be easily solubilized by 0;05% Sodium-dodecyl-sulfate, (3) the cells allow the adsorption of the rough-mutant specific Salmonella phage 6SR; (4) strong cellular binding of crystal violet, (5) agglutination of the cells in 0.3% auramin solution and (6) reduced formation of red pigment. Strain W 1421 is assumed to be a lipopolysaccharide-defective mutant. The outer membrane of mutant W 1421 analyzed by Sodium-dodecylsulfate-polyacrylamide gel electrophoresis possesses a single protein less than that of the wild-type. Mutant W 1421 is further characterized by its low exolipase activity; exoprotease and exonuclease activities are as in the wild-type. This specific exoenzyme deficiency can be overcome either by backmutation to oxacillin-resistance or by growing mutant W 1421 in a medium supplemented with certain non-metabolizable polysaccharides, e.g. glycogen or pectin B. Both polysaccharides increase the exolipase activity of the wild-type too.

Gentamicin use and Pseudomonas and Serratia resistance: effect of a surgical prophylaxis regimen

An outbreak of prosthetic valve endocarditis due to methicillin-resistant Staphylococcus epidermidis prompted a change in antimicrobial prophylaxis for open heart surgery in a general hospital from a regimen of aqueous penicillin G, methicillin, and kanamycin to a 5-day regimen of cefazolin and gentamicin. As a result, total gentamicin use in the hospital more than doubled. Increased resistance of pseudomonas and serratia isolates paralleled the increased total use of gentamicin. For pseudomonas species, the incidence of gentamicin resistance increased from 3 to 15%; for serratia species, from 8 to 88%; and for the total of both organisms, from 4 to 28%. Resistance decreased rapidly after removal of gentamicin from the prophylaxis regimen. Review of serratia isolates from the urinary tract showed that gentamicin resistance was associated with prior antibiotic therapy, especially with gentamicin, care on the surgical services, especially the surgical intensive care unit, and presence of indwelling bladder catheters. Gentamicin use in a 5-day antimicrobial prophylaxis regimen for open heart surgery can represent a large proportion of the total hospital use of that antibiotic, with potential adverse effects on hospital flora.

Piromidic acid and its ethylic ester: absorption, distribution, excretion

The absorption, distribution and excretion of piromidic acid and its ethyl ester were investigated in the rat. When administered orally the ethyl ester was well absorbed and subsequently hydrolysed, giving much higher blood and tissue concentration than a corresponding dose of the parent compound. The antimicrobial activity of urine and bile samples was also investigated.