Emergence of multidrug-resistant mutants is increased under antibiotic selective pressure in Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most important opportunistic pathogens involved in nosocomial infections, cystic fibrosis patients included. Hospital isolates frequently present multidrug-resistance (MDR) phenotypes as the consequence of constant antibiotic selective pressure. The kinetics of emergence of P. aeruginosa MDR mutants under antibiotic selective pressure indicated that long-term incubation in the presence of the bacteriostatic antibiotic tetracycline increases the mutation rate per cell per day of P. aeruginosa PAO1 by several orders of magnitude. The tetracycline-resistant mutants obtained were stable, showed decreased susceptibility to antibiotics belonging to different structural families, and contained an outer-membrane protein not present in the wild-type P. aeruginosa strain PAO1. These data are consistent with the hypothesis that incubation in the presence of tetracycline favours the emergence of MDR mutants in P. aeruginosa. The results are relevant for understanding the rapid emergence of antibiotic-resistant mutants among bacterial populations during infections. Their relationship to other models of increased mutagenesis under stress is discussed with respect to the adaptive mutation phenomenon.

Environmental and clinical isolates of Pseudomonas aeruginosa show pathogenic and biodegradative properties irrespective of their origin

Virulence properties of pathogenic bacteria, as well as resistance to antibiotics, are thought to arise through a specialization process favoured by the strong selection pressure imposed in clinical treatments. Nevertheless, in the case of opportunistic pathogens, it is unclear whether strains can be classified into virulent and non-virulent isolates. Clones of the opportunistic pathogen Pseudomonas aeruginosa do not seem to be associated to a particular biovar or pathovar, which suggests that virulence characteristics in opportunistic pathogens may already be present in environmental (non-clinical) isolates. We have explored this possibility, studying environmental isolates (mainly from oil-contaminated soils) and clinical isolates (from bacteraemia and cystic fibrosis patients) of P. aeruginosa. All environmental strains were found to actively efflux quinolones, which are synthetic antibiotics not expected to be present in the environment. These strains contained multidrug resistance determinants, were capable of invading epithelial cells and presented genes from the quorum-sensing and type III secretion systems. Some of them expressed either haemolytic or proteolytic activities or both, characteristics considered to be typical of virulent strains. All the strains tested, of clinical or environmental origin, could use alkanes (oil hydrocarbons) as a carbon source. Our results suggest that clinical and non-clinical P. aeruginosa strains might be functionally equivalent in several traits relevant for their virulence or environmental properties. Selection of clinically relevant traits, such as antibiotic resistance or cellular invasiveness, in opportunistic pathogens present in soil ecosystems is discussed.

[Inhibition of pump and permeability mechanisms]

The presence of multidrug efflux-pump systems in bacteria showing resistance to various drugs is increasingly reported in the literature. These systems are inducible by compounds such as salicylate and can thus be involved in situations of phenotypic resistance at the point of the infection which would otherwise be barely detectable under standard laboratory testing conditions. On the other hand, mutants which overproduce efflux-pumps and show increased levels of antibiotic resistance are easily selectable. It has been shown that inactivation of efflux-pump determinants produces an increased susceptibility to different antibiotics as well as prevents the emergence of mutants with a high-level antibiotic resistance to drugs such as quinolones. The search for efflux-pump inhibitors to be used in combination with other currently used antibiotics is therefore an important task for the renewal of the antibacterial therapeutic armamentarium. No efflux-pump inhibitors are commercially available as yet. However, several companies are in the process of working on their development. In this review, we discuss four possible targets that could be useful in the screening of inhibitors of efflux-pump systems in bacteria.

Aminoglycoside resistance mediated by the bifunctional enzyme 6'-N-aminoglycoside acetyltransferase-2"-O-aminoglycoside phosphotransferase

The expression of the bifunctional aminoglycoside inactivating enzyme 6'-N-aminoglycoside acetyltransferase-2"-O-aminoglycoside phosphotransferase is the most important mechanism of high-level aminoglycoside resistance in Staphylococcus and Enterococcus. The enzyme is unique because it presents two different aminoglycoside-modifying activities located in different regions of the molecule. The gene aac(6')-aph(2") which encodes the synthesis of the enzyme is present in Tn4100-like transposons which are inserted both in R plasmids and the chromosomes of aminoglycoside-resistant isolates. The genetic structure of aac(6')-aph(2")-containing isolates indicates that their origin is not clonal, but plasmid conjugation together with multiple insertion events are in the basis of the rapid spread of aminoglycoside resistance among Gram-positive bacteria. There is not any prevalent genetic linkage of aac(6')-aph(2") with other antibiotic-resistance determinant. However, most methicillin resistant Staphylococcus strains present also high-level aminoglycoside resistance as the consequence of constant antibiotic pressure. This situation could change in the next future with the reported reemergence of gentamicin-susceptible MRSA isolates. Recent data show that inhibitors of eukaryotic protein kinases inhibit as well the aminoglycoside phosphotransferase activity. This effect indicates a common structure for these two families of proteins and opens the possibility for a meaningful survey of inhibitors of 6'-N-aminoglycoside acetyltransferase-2"-O-aminoglycoside phosphotransferase useful in clinical practice.

Metal accumulation and vanadium-induced multidrug resistance by environmental isolates of Escherichia hermannii and Enterobacter cloacae

Contaminated soils from an oil refinery were screened for the presence of microorganisms capable of accumulating either nickel, vanadium, or both metals. Three strains of bacteria that belonged to the family Enterobacteriaceae were selected. Two of them were Escherichia hermannii strains, and outer membrane profile (OMP) analysis showed that they were similar to a strain of clinical origin; the other one was an Enterobacter cloacae strain that differed from clinical isolates. The selected bacteria accumulated both nickel and vanadium. Growth in the presence of vanadium induced multidrug resistance phenotypes in E. hermannii and E. cloacae. Incubation with this metal changed the OMP profile of E. hermannii but did not produce variations in the expression of the major OMPs of E. cloacae.

[Angina caused by subclavian-coronary steal in patients revascularized with internal mammary artery]

After coronary bypass surgery in the left internal mammary artery, occlusive atherosclerosis in the proximal subclavian artery can produce reverse flow in the mammary artery and myocardial ischemia (coronary-subclavian steal syndrome). This is a rare cause of recurrent myocardial ischemia. We present two patients with postoperative complete obstruction in the proximal subclavian artery and inverse flow in the mammary artery producing severe ischemia in the left anterior descending artery territory. Both patients were treated with subclavian-subclavian bypass, which in one patient was ineffective in producing an adequate anterograde flow in the left internal mammary artery. We review clinical management, diagnostic methods and therapeutic options used in the coronary-subclavian steal syndrome.

Ultrastructure of fish cells involved in cellular defences against Saprolegnia infections: evidence of non-leucocytic nature

Fish cells attached to hyphae were observed in brown trout Salmo trutta L. infected with Saprolegnia parasitica. Earlier studies with light microscopy indicated that these cells were lymphocytes and neutrophils and that they were involved in the defence mechanisms against Saprolegnia infections. However, using electron microscopy, we found these attached cells did not show leucocytic characteristics, but instead shared some ultrastructural features with filament-containing cells. The pressure of a dense mass of cytoplasmic filaments precludes the leucocytic nature of these cells. How these cells could be involved in cellular defences against fungi is discussed.

In vitro plasmid-encoded resistance to quinolones

The possibility of plasmid-encoded quinolone resistance is explored in two model systems. In the first, increasing amounts of wild-type gyrA allele moderately increased minimum inhibitory concentrations to quinolone antibiotics. In the second model, a mutant gyrA allele encoded by a multicopy plasmid produced a quinolone resistance phenotype upon its expression in a quinolone-susceptible Escherichia coli strain.

Influences of changes in calcium concentrations, cocaine and clonidine on the cardiac effect of acetaldehyde in rat isolated atria

1. Cardiovascular responses to acetaldehyde (AChO) were investigated in rat isolated atria. 2. Results show that two different doses of AChO (0.29 and 0.88 mM) induce positive inotropic effects on rat atria, and express Ca2+ dependence when analyzed at three external Ca2+ concentrations (0.6, 1.1, 2.2 mM). 3. Cocaine (3.5 and 35 microM) produced significant potentiation of the AChO-positive (0.29 and 0.88 mM) inotropic effect in 1.1 mM Ca2+ medium. 4. Clonidine (40 microM) increased the peak tension developed (PTD) induced by AChO (both 0.29 and 0.88 mM) only 1.1 mM Ca2+ medium. 5. It is suggested that the positive inotropic effect produced by AChO involves a Ca2(+)-dependent mechanism, which can be potentiated by the additional stimulation of alpha-adrenergic receptors.

H-NS and RpoS regulate emergence of Lac Ara+ mutants of Escherichia coli MCS2

Two master growth-phase regulatory proteins, H-NS and sigmaS, are involved in the formation of araB-lacZ fusion clones of Escherichia coli MCS2. The stationary-phase sigma factor RpoS is strictly required for the appearance of such mutants, whereas the histone-like protein H-NS represses their emergence. Our results support the idea that genetic changes leading to adaptive mutation in this model system are regulated by physiological signal transduction networks.

Multiple antibiotic resistance in Stenotrophomonas maltophilia

A cryptic multidrug resistance (MDR) system in Stenotrophomonas maltophilia, the expression of which is selectable by tetracycline, is described. Tetracycline resistance was the consequence of active efflux of the antibiotic, and it was associated with resistance to quinolones and chloramphenicol, but not to aminoglycosides or beta-lactam antibiotics. MDR is linked to the expression of an outer membrane protein (OMP54) both in a model system and in multidrug-resistant clinical isolates.

Growth of Escherichia coli in acetate as a sole carbon source is inhibited by ankyrin-like repeats present in the 2',5'-linked oligoadenylate-dependent human RNase L enzyme

Expression of low levels of the 2',5'-linked oligoadenylate-dependent human RNase L, an enzyme induced by interferons, is highly toxic in Escherichia coli. This protein contains an ankyrin domain responsible for RNase L toxicity. The only known ORF in E. coli containing ankyrin repeats is yjaC in the acetate metabolic cluster. We have investigated if expression of mutant forms of RNase L interfere with metabolism of acetate in E. coli. Our findings demonstrate that E. coli expressing RNase L ankyrin repeats is unable to grow in medium containing acetate as the sole carbon source, while it can grow when expressing other domains of the protein. This defect correlates with a severe decrease in the levels of induction of enzymes in the glyoxylate bypass.

Multiple mechanisms of N-phosphonacetyl-L-aspartate resistance in human cell lines: carbamyl-P synthetase/aspartate transcarbamylase/dihydro-orotase gene amplification is frequent only when chromosome 2 is rearranged

Rodent cells resistant to N-phosphonacetyl-L-aspartate (PALA) invariably contain amplified carbamyl-P synthetase/aspartate transcarbamylase/dihydro-orotase (CAD) genes, usually in widely spaced tandem arrays present as extensions of the same chromosome arm that carries a single copy of CAD in normal cells. In contrast, amplification of CAD is very infrequent in several human tumor cell lines. Cell lines with minimal chromosomal rearrangement and with unrearranged copies of chromosome 2 rarely develop intrachromosomal amplifications of CAD. These cells frequently become resistant to PALA through a mechanism that increases the aspartate transcarbamylase activity with no increase in CAD copy number, or they obtain one extra copy of CAD by forming an isochromosome 2p or by retaining an extra copy of chromosome 2. In cells with multiple chromosomal aberrations and rearranged copies of chromosome 2, amplification of CAD as tandem arrays from rearranged chromosomes is the most frequent mechanism of PALA resistance. All of these different mechanisms of PALA resistance are blocked in normal human fibroblasts.

[Scheduled biliary surgery and antibiotic prophylaxis. Is its use always justified?]

AIM

Evaluate the need to give prophylactic antibiotic therapy in patients that undergo elective surgery for cholelithiasis.

METHODS

Prospective study in 35 patients the underwent surgery for cholelithiasis, without infectious risk factors. All of them, the hemocultives, endotoxin and Tumor Necrosis Factor has been evaluated along the surgical process.

RESULTS

The hemocultives were in all the patients negatives. The levels of Tumor Necrosis Factor decreased along the surgical process, without modifications of endotoxin levels. There were no significant differences in either of the points of the analysis.

CONCLUSIONS

Biliary surgery in patients that undergo elective surgery for cholelithiasis, without infectious risk factors, is a clean surgery, and so, in this patients is not indicated systematically an antibiotic prophylaxis.

Oleoylanilide, a possible causative agent of toxic oil syndrome, interferes with the cytoskeleton in a neuronal cell line

We have examined the effects of oleoylanilide, one of the main candidates in the etiology of the toxic oil syndrome, in the neuroblastoma cell line N2A. Oleoylanilide treatment causes two kinds of phenomena: alteration of the actin cytoskeleton, creating a brush-like protrusion of actin at the periphery of the cells, and reduction of the adhesiveness of these cells to laminin and fibronectin, two of the main components of the extracellular matrix in the central nervous system. These effects could be correlated with symptoms shown in the acute and chronic phases of the disease.

[Quality of drug prescriptions by the Spanish internal medicine services]

Many registered drugs in different countries not always have been tested by clinical assays and their efficacy has no definitively proved. Good clinical practice must assume the prescription of the more efficacy drugs. The aim of this study is to evaluate the quality of the drugs prescribed by spanish general internists. We analyze the treatments prescribed by general internists using their hospital medical records. The records were offered by the Heads of the Internal Medecine Departments of Spanish hospitals with 250 beds or more when required by the Spanish Society of Internal Medecine. A random sample, stratified by the hospital size, was obtained from the whole of the Spanish hospitals. Quality of the drugs was determined using two criteria: A. Their intrinsic value; it was decided it was high if clinical assays showed their efficacy and security, and low of it was not B. The number of different chemical substances in the drug; we considered a high quality criteria if only one chemical substance, or two with proved synergistic efficacy were present, and low if it was more than two, or without proved synergistic efficacy. The sample was 250 clinical records, with 1022 different prescriptions; the records were collected between February and July 1994. We found that 94.06 +/- 1.45 of evaluated treatments have a high intrinsic value, and 96.93 +/- 1.06 have only one chemical component. The drugs without a high intrinsic value were: oral hypoglycaemics, some including several combinations of vit B, drugs acting on the cerebral blood flow and some mucolitics. Spanish general Internists usually prescribed monocomponent drugs with proved efficacy and safety.

pH modulation of aminoglycoside resistance in Staphylococcus epidermidis harbouring 6'-N-aminoglycoside acetyltransferase

The kinetic constants of the aminoglycoside-modifying enzyme 6'-N-aminoglycoside acetyltransferase (AAC(6')IV) from the clinical strain Staphylococcus epidermidis RYC 13036 differed depending on whether tobramycin and amikacin (glycosamine group) or gentamicin and netilmicin (garosamine group) were used as substrates. Acetylation of the glucosamine antibiotics was highly susceptible to substrate inhibition which increased with pH whereas the garosamine group compounds showed limited substrate inhibition over a wide pH range. These differences in activity correlated with MIC values of S. epidermidis RYC 13036 for different aminoglycosides. Aminosugars moiety and pH markedly influenced the AAC(6')IV-aminoglycoside interactions.

Chromosomal localization of the major and 5S rRNA genes in the European eel (Anguilla anguilla)

The major (18S, 5.8S, and 28S) and 5S rRNA genes have been mapped by double fluorescent in situ hybridization to European eel metaphase chromosomes. The major rRNA genes were localized to a submetacentric pair of chromosomes that showed a consistent size polymorphism among the individuals studied. The 5S rRNA genes were clustered in a single locus that mapped to the centromeric region of an acrocentric pair. In contrast to the major rRNA genes, no detectable polymorphism, in either size or intensity of the fluorescent signal, was observed. The chromosomal organization of both families of rRNA genes are discussed in terms of genomic organization and chromosomal evolution.