Exploring new strategies to fight drug-resistant microbes

Rhamnusalaternus Plant: Extraction of Bioactive Fractions and Evaluation of Their Pharmacological and Phytochemical Properties

Rhamnus alaternus, is a wild-growing shrub, belonging to the Rhamnaceae family. Widely distributed in the Mediterranean basin, R. alaternus is used in the usual medicine in numerous countries, mostly Tunisia, Algeria, Morocco, Spain, France, Italy, and Croatia. A large number of disorders-including dermatological complications, diabetes, hepatitis, and goiter problems-can be treated by the various parts of R. alaternus (i.e., roots, bark, berries, and leaves). Several bioactive compounds were isolated from R. alaternus, including flavonoids, anthocyanins, and anthraquinones, and showed several effects such as antioxidant, antihyperlipidemic, antigenotoxic, antimutagenic, antimicrobial, and antiproliferative. This review summarizes the updated information concerning the botanical description, distribution, extraction processes applied on R. alaternus, and its ethnopharmacology, toxicity, phytochemistry, and pharmacological effects.

Antimicrobial treatment of upper respiratory tract infections from the Dutch perspective

The worldwide problem of multiple resistant strains should be attacked by a more adequate, rational prescription behaviour of antibiotics. As most upper respiratory tract infections (URTIs) have a viral cause and are selflimiting, antibiotics should be used for certain indications only. The development of evidence based guidelines, based on outcome studies in the field of URTIs carried out in general practice populations is recommended. The general practitioners (GPs) with defined practice populations are in a key position for research and a restrictive antibiotic policy. Several RCTs are carried out in general practice indicating that antibiotic prescriptions can be reduced. This will contribute to the decrease of resistant strains.

Retrospective study of bacterial isolates and their antimicrobial susceptibilities in equine uteri during fertility problems

Bacterial pathogens are a potential cause when a mare fails to conceive to a fertile stallion on a well-managed breeding farm on one or more cycles in the same season. Furthermore, emerging bacterial resistance to commonly used (topical) antibiotics has been demonstrated. In this study, a total of 586 uterine swabs from mares with fertility problems were evaluated and the bacterial isolates were identified and measured for resistance to 10 antibiotics most commonly used during bacterial equine infection. Forty-nine percent of the examined mares were positive at bacteriological investigations. Amongst 347 successful isolations, 31.7% were Streptococcus group C and 18.4% Escherichia (E.) coli, both considered frequently associated with fertility problems. Determination of the antibiotic susceptibility pattern of Streptococcus group C (110 organisms) revealed that only the amoxicillin/clavulanic acid was highly active with 82.7% of the isolates being inhibited. For E. coli, a major number of drugs displayed a high potency.

Competitive release and facilitation of drug-resistant parasites after therapeutic chemotherapy in a rodent malaria model

Malaria infections frequently consist of mixtures of drug-resistant and drug-sensitive parasites. If crowding occurs, where clonal population densities are suppressed by the presence of coinfecting clones, removal of susceptible clones by drug treatment could allow resistant clones to expand into the newly vacated niche space within a host. Theoretical models show that, if such competitive release occurs, it can be a potent contributor to the strength of selection, greatly accelerating the rate at which resistance spreads in a population. A variety of correlational field data suggest that competitive release could occur in human malaria populations, but direct evidence cannot be ethically obtained from human infections. Here we show competitive release after pyrimethamine curative chemotherapy of acute infections of the rodent malaria Plasmodium chabaudi in laboratory mice. The expansion of resistant parasite numbers after treatment resulted in enhanced transmission-stage densities. After the elimination or near-elimination of sensitive parasites, the number of resistant parasites increased beyond that achieved when a competitor had never been present. Thus, a substantial competitive release occurred, markedly elevating the fitness advantages of drug resistance above those arising from survival alone. This finding may explain the rapid spread of drug resistance and the subsequently brief useful lifespans of some antimalarial drugs. In a second experiment, where subcurative chemotherapy was administered, the resistant clone was only partly released from competitive suppression and experienced a restriction in the size of its expansion after treatment. This finding raises the prospect of harnessing in-host ecology to slow the spread of drug resistance.

Plasmid donor affects host range of promiscuous IncP-1beta plasmid pB10 in an activated-sludge microbial community

Horizontal transfer of multiresistance plasmids in the environment contributes to the growing problem of drug-resistant pathogens. Even though the plasmid host cell is the primary environment in which the plasmid functions, possible effects of the plasmid donor on the range of bacteria to which plasmids spread in microbial communities have not been investigated. In this study we show that the host range of a broad-host-range plasmid within an activated-sludge microbial community was influenced by the donor strain and that various mating conditions and isolation strategies increased the diversity of transconjugants detected. To detect transconjugants, the plasmid pB10 was marked with lacp-rfp, while rfp expression was repressed in the donors by chromosomal lacI(q). The phylogeny of 306 transconjugants obtained was determined by analysis of partial 16S rRNA gene sequences. The transconjugants belonged to 15 genera of the alpha- and gamma-Proteobacteria. The phylogenetic diversity of transconjugants obtained in separate matings with donors Pseudomonas putida SM1443, Ralstonia eutropha JMP228, and Sinorhizobium meliloti RM1021 was significantly different. For example, the transconjugants obtained after matings in sludge with S. meliloti RM1021 included eight genera that were not represented among the transconjugants obtained with the other two donors. Our results indicate that the spectrum of hosts to which a promiscuous plasmid transfers in a microbial community can be strongly influenced by the donor from which it transfers.

Drug resistance and Giardia

Giardiasis is a worldwide disease that can cause serious morbidity. Metronidozole is the current recommended drug for treatment, and is mostly still effective. However, Giardia duodenalis, the causative agent, is capable of developing resistance to high levels of metronidozole and other drugs, in vitro, via a number of mechanisms. Resistance, in vivo, has been reported and many cases of treatment failure have been variously attributed to a number of causes, including resistance. Here, Jacqueline and Peter Upcroft ask: is this the beginning of another chapter of drug resistance? or is the situation likely to remain as a 'few refractory cases'? Should we wait to find out or can we act positively to avert the possibility of yet another valuable drug in our limited pharmacopoeia becoming obsolete?

Combining mathematical models and statistical methods to understand and predict the dynamics of antibiotic-sensitive mutants in a population of resistant bacteria during experimental evolution

Temporarily discontinuing the use of antibiotics has been proposed as a means to eliminate resistant bacteria by allowing sensitive clones to sweep through the population. In this study, we monitored a tetracycline-sensitive subpopulation that emerged during experimental evolution of E. coli K12 MG1655 carrying the multiresistance plasmid pB10 in the absence of antibiotics. The fraction of tetracycline-sensitive mutants increased slowly over 500 generations from 0.1 to 7%, and loss of resistance could be attributed to a recombination event that caused deletion of the tet operon. To help understand the population dynamics of these mutants, three mathematical models were developed that took into consideration recurrent mutations, increased host fitness (selection), or a combination of both mechanisms (full model). The data were best explained by the full model, which estimated a high mutation frequency (lambda = 3.11 x 10(-5)) and a significant but small selection coefficient (sigma = 0.007). This study emphasized the combined use of experimental data, mathematical models, and statistical methods to better understand and predict the dynamics of evolving bacterial populations, more specifically the possible consequences of discontinuing the use of antibiotics.

Synthetic peptide vaccine and antibody therapeutic development: prevention and treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa and Pseudomonas maltophilia account for 80% of opportunistic infections by pseudomonads. Pseudomonas aeruginosa is an opportunistic pathogen that causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, and a variety of systemic infections, particularly in patients with severe burns, and in cancer and AIDS patients who are immunosuppressed. Pseudomonas aeruginosa is notable for its resistance to antibiotics, and is therefore a particularly dangerous pathogen. Only a few antibiotics are effective against Pseudomonas, including fluoroquinolones, gentamicin, and imipenem, and even these antibiotics are not effective against all strains. The difficulty treating Pseudomonas infections with antibiotics is most dramatically illustrated in cystic fibrosis patients, virtually all of whom eventually become infected with a strain that is so resistant that it cannot be treated. Since antibiotic therapy has proved so ineffective as a treatment, we embarked on a research program to investigate the development of a synthetic peptide consensus sequence vaccine for this pathogen. In this review article we will describe our work over the last 15 years to develop a synthetic peptide consensus sequence anti-adhesin vaccine and a related therapeutic monoclonal antibody (cross-reactive to multiple strains) to be used in the prevention and treatment of P. aeruginosa infections. Further, we describe the identification and isolation of a small peptide structural element found in P. aeruginosa strain K (PAK) bacterial pili, which has been proven to function as a host epithelial cell-surface receptor binding domain. Heterologous peptides are found in the pili of all strains of P. aeruginosa that have been sequenced to date. Several of these peptide sequences have been used in the development of an consensus sequence anti-adhesin vaccine targeted at the prevention of host cell attachment and further for the generation of a monoclonal antibody capable of prevention and treatment of existing infections.

The ability of certain antimutagenic agents to prevent development of antibiotic resistance

Resistance to multiple antimicrobial agents has now become a prominent fact of contemporary life. It is believed that poor patient compliance, e.g. interrupted or premature cessation of therapy; and misuse or abuse of antibiotics, e.g. wrong antibiotic or insufficient dose, play important roles in resistance development. We present evidence that, this form of resistance often stems from spontaneous mutations accompanied by the positive selecting pressure of the doses of antibiotics being between the MIC and MBC levels. A number of antimutagenic agents, e.g. green tea catechins, and other antioxidants, etc. are able to suppress the emergence of resistance. In many cases, these agents are capable of exerting these effects at doses which by themselves produce no visible effect on growth. In a number of cases antimutagenic substances capable of preventing resistance emergence are present in normal food stuffs. These effects are exerted against resistance to tetracyclines, fluoroquinolones, macrolides, beta-lactams, aminoglycosides and the like. The implications of these laboratory findings for practical chemotherapy are discussed.

Novel macrolides through genetic engineering

Erythromycin, a complex polyketide antibiotic belonging to the macrolide class, is produced as a natural product by the bacterium Saccharopolyspora erythraea. The genes encoding the enzymes responsible for the synthesis of the antibiotic have been cloned and sequenced, revealing that the polyketide backbone of the molecule in produced by a polyketide synthase (PKS) composed of multifunctional proteins that contain discrete functional domains for each step of synthesis. Genetic manipulation of the PKS-encoding genes can result in predictable changes in the structure of the polyketide component of erythromycin, many of which are not easily achievable through standard chemical derivatization or synthesis. Many of the changes can be combined to lead to the further generation of navel structures. Whereas genetic engineering of the erythromycin structure has been practiced for a number of years, the re cent and continuing discoveries of modular PKSs for the synthesis of many other important complex polyketides has raised the possibility of generating novel structures in these molecules by genetic manipulation, as well.

Recent progress in novel macrolides, quinolones, and 2-pyridones to overcome bacterial resistance

Macrolides, such as clarithromycin and azithromycin, having good activity against pathogens such as Legionella, Chlamydia, Campylobacter spp, Branhamella spp, Pasteurella multocida and streptococci, have gained wide acceptance for the treatment of both upper and lower respiratory tracts, as well as cutaneous infections. Emergence of bacterial resistance, particularly in gram-positive bacteria, has been observed. Macrolide-resistant Streptococcus pneumoniae and S. pyogenes are found in France and many other countries, resulting in failure of therapy for pneumonia, pharyngitis, and skin infection. RU 004, HMR 3647, and TE 802 were reported to be active against these resistant strains. Research at Abbott produced several macrolide derivatives in the anhydrolide, tricyclic and tetracyclic ketolides as well as 6-O-alkyl ketolides series having potent activity against macrolide resistant S. pyogenes and S. pneumoniae. Research on streptogramins to overcome bacterial resistance in gram-positive bacteria has produced interesting compounds. Another class of antibacterial agent called quinolones is useful for the treatment of bacterial infections of respiratory tract, urinary tract, skin and soft tissues, as well as sexually transmitted diseases. Ciprofloxacin, the market leader, however, has low potency against anaerobes. Bacterial resistance ( such as Pseudomonas aeruginosa and methicillin- resistant Staphylococcus aureus ) to ciprofloxacin is increasing rapidly. Many quinolone compounds are being synthesized to address these drawbacks. The new quinolones currently under development are characterized by enhanced activities against streptococci, staphylococci, enterococci, and anaerobes. This presentation reviews the current research in the identification of agents to overcome the macrolide and quinolone resistance.

Antimicrobial activity of spices

Spices have been shown to possess medicinal value, in particular, antimicrobial activity. This study compares the sensitivity of some human pathogenic bacteria and yeasts to various spice extracts and commonly employed chemotherapeutic substances. Of the different spices tested only garlic and clove were found to possess antimicrobial activity. The bactericidal effect of garlic extract was apparent within 1 h of incubation and 93% killing of Staphylococcus epidermidis and Salmonella typhi was achieved within 3 h. Yeasts were totally killed in 1 h by garlic extract but in 5 h with clove. Some bacteria showing resistance to certain antibiotics were sensitive to extracts of both garlic and clove. Greater anti-candidal activity was shown by garlic than by nystatin. Spices might have a great potential to be used as antimicrobial agents.

Indication-based use of antimicrobials in Finnish primary health care. Description of a method for data collection and results of its application

OBJECTIVE

To collect population-based information on treatment of infections with antibiotics in PHC.

DESIGN

A questionnaire study for general practitioners (GPs).

SETTING

All health centres of Pirkanmaa Hospital District in Finland.

PATIENTS

Patients with any infection attending health centre during 1 week in November 1994.

MAIN OUTCOME MEASURES

An infection diagnosis by the GP.

RESULTS

A total of 4150 questionnaires were received from 223 doctors. Respiratory tract infections comprised 80% of all infections. Of all patients 64% received antimicrobial treatment. Unspecified upper respiratory tract infections and pharyngitis were rarely treated with antimicrobials (10 and 21%, respectively), whereas patients with acute bronchitis received antibiotics as often (83%) as patients with otitis media (93%) or tonsillitis (86%). The most commonly prescribed substances were cephalosporins (19% of all antimicrobials), penicillin V (17%), and amoxycillin (17%). Half of the cephalosporin use could be regarded as overuse. Half of the sulphatrimethoprims were used for otitis media. A quarter of the patients expressed a desire to receive antibiotic treatment.

CONCLUSION

The method was practical, inexpensive, and successful in giving such information, which is needed for supervising the rational use of antibiotics in primary health care.

Porin alteration and active efflux: two in vivo drug resistance strategies used by Enterobacter aerogenes

Enterobacter aerogenes is among the five most frequently isolated nosocomial pathogens in France, and this bacterium also shows increasing multidrug resistance. In this study, various E. aerogenes strains isolated from hospital units were characterized for their outer-membrane proteins, antibiotic susceptibilities (inhibition diameters and MICs) and resistance mechanisms associated with modification of envelope permeability (porin alteration and active efflux). Diminished outer-membrane permeability due to porin alterations was found in conjunction with the expression of an enzymic barrier in resistant isolates. Interestingly, changes in the functional expression of porins appeared to play a special role in susceptibility to cefepime. An active efflux to quinolones was also identified. Simultaneous changes in envelope permeability, i.e. a porin deficiency (in) and an efflux mechanism (out), were clearly evident in two clinical strains.

Are we facing a 'post-antibiotic era'?--a review of the literature regarding antimicrobial drug resistance

Since the introduction of antibiotics in the 1940s, antibiotic resistance has become an increasing problem. Today, multiple-antibiotic resistance is commonly associated with a number of clinically important pathogens and is therefore an important issue in clinical nursing practice. Epidemiological studies identify a number of important factors associated with increases in antimicrobial resistance. These include patterns of antimicrobial use, changes in medical and veterinary care and social practices affecting the transmission of microbes. Bacterial mechanisms of antibiotic resistance and the genetics of resistance-gene transfer are explored, with the intention of developing nurses' knowledge and understanding of control measures.

The global problem of antimicrobial resistance

Along with other multidrug-resistant pathogens previously identified, Streptococcus pneumoniae is becoming a serious concern in hospital and ambulatory care settings. The AIDS pandemic has increased the threat of resistance in Mycobacterium tuberculosis. Antimicrobial drug resistance involves three molecular mechanisms drug inactivation, altered cell permeability, and alteration of target sites. Surveillance and multidisciplinary approaches will be key to containing the threat of global antimicrobial resistance.

Prevalence of outer membrane porin alteration in beta-lactam-antibiotic-resistant Enterobacter aerogenes

We evaluated the prevalence of impermeability as a mechanism associated with resistance against beta-lactam antibiotics in members of the family Enterobacteriaceae. During a 1-year period, 80 strains were selected from 3,110 routinely isolated strains according to their noticeable cross-resistance pattern to cephalosporins. They were tested for (i) outer membrane nonspecific porins involved in the entry of small hydrophilic molecules; (ii) the MICs of cefepime, cefotaxime, imipenem, and moxalactam; and (iii) beta-lactamase production. Immunological investigations using specific probes showed that 23 of 80 strains presented an alteration of the porin content, most of them expressing an additional resistance mechanism. The prevalence of this porin-deficient phenotype is especially high in Enterobacter aerogenes and concerns 6.4% of the clinical isolates.

In vitro stepwise selection of resistance to quinolones, beta-lactams and amikacin in nosocomial gram-negative bacilli

The ability of six antibiotics to produce resistance by stepwise selection on agar medium was assessed in 24 gram-negative rods. Escherichia coli was the strain least prone to selection of resistance, whereas Pseudomonas aeruginosa frequently developed resistance to all antibiotics. When used alone, ciprofloxacin, pefloxacin, amikacin, ceftazidime and cefpirome were associated with a comparable risk of acquired resistance (in 14 to 17 out of 24 strains); imipenem selected resistant strains in 10/24 isolates (5/18 in non-pseudomonas strains). The number of strains exhibiting cross resistance with structurally unrelated antibiotics was 11 after pefloxacin treatment, eight after exposure to ciprofloxacin, six after ceftazidime, and one after imipenem or cefpirome. The combination of ciprofloxacin with amikacin was less efficient in reducing acquisition of resistance than the combination of ciprofloxacin with a beta-lactam: ciprofloxacin plus cefpirome was especially potent in this respect.