Narrow-spectrum Antimicrobials Research Articles

Effect of broad- and narrow-spectrum antimicrobials on Clostridium difficile and microbial diversity in a model of the distal colon

Vancomycin, metronidazole, and the bacteriocin lacticin 3147 are active against a wide range of bacterial species, including Clostridium difficile. We demonstrate that, in a human distal colon model, the addition of each of the three antimicrobials resulted in a significant decrease in numbers of C. difficile. However, their therapeutic use in the gastrointestinal tract may be compromised by their broad spectrum of activity, which would be expected to significantly impact on other members of the human gut microbiota. We used high-throughput pyrosequencing to compare the effect of each antimicrobial on the composition of the microbiota. All three treatments resulted in a decrease in the proportion of sequences assigned to the phyla Firmicutes and Bacteroidetes, with a corresponding increase in those assigned to members of the Proteobacteria. One possible means of avoiding such "collateral damage" would involve the application of a narrow-spectrum antimicrobial with specific anti-C. difficile activity. We tested this hypothesis using thuricin CD, a narrow-spectrum bacteriocin produced by Bacillus thuringiensis, which is active against C. difficile. The results demonstrated that this bacteriocin was equally effective at killing C. difficile in the distal colon model but had no significant impact on the composition of the microbiota. This offers the possibility of developing a targeted approach to eliminating C. difficile in the colon, without collateral damage.

Characterization of the bacteriocin-producing strain Lactobacillus paracasei subsp. paracasei BGUB9

The strain Lactobacillus paracasei subsp. paracasei BGUB9 that was isolated from traditionally homemade hard cheese produces bacteriocin designated as BacUB9, with an approximate molecular mass of 4 kDa. Biochemical characterization and the antimicrobial activity test of BacUB9 were performed. The onset of BacUB9 biosynthesis was observed at the end of an exponential phase of growth. Bacteriocin UB9 retained the antimicrobial activity within the pH range from 1 to 10 and after treatment at 100oC for 30 min. The bacteriocin is susceptible to the activity of proteolytic enzymes. Bacteriocin BacUB9 has a very narrow antimicrobial spectrum, limited to several strains that belong to closely related species. The effect of BGUB9 on the growth of the strain Lactobacillus paracasei subsp. paracasei BGHN14 in a mixed culture was monitored. The mode of action of BacUB9 on the strain BGHN14 was identified as bacteriostatic. Plasmid curing results indicated that a plasmid, designated as pUB9, seemed to be responsible for both bacteriocin BacUB9 production and host immunity.

Drosomycin, an essential component of antifungal defence in Drosophila

Drosomycin is an inducible antifungal peptide of 44 residues initially isolated from bacteria-challenged Drosophila melanogaster. The systemic expression of drosomycin is regulated by the Toll pathway present in fat body, whereas inducible local expression in the respiratory tract is controlled by the Immune Deficiency (IMD) pathway. Drosomycin belongs to the cysteine-stabilized alpha-helical and beta-sheet (CSalphabeta) superfamily and is composed of an alpha-helix and a three-stranded beta-sheet stabilized by four disulphide bridges. Drosomycin exhibits a narrow antimicrobial spectrum and is only active against some filamentous fungi. However, recent work using recombinant drosomycin expressed in Escherichia coli revealed its antiparasitic and anti-yeast activities. Two evolutionary epitopes (alpha- and gamma-patch) and the m-loop have been proposed as putative functional regions of drosomycin for interaction with fungi and parasites, respectively. Similarity in sequence, structure and biological activity suggests that drosomycin and some defensin molecules from plants and fungi could originate from a common ancestor.

Persistence of colicinogenic Escherichia coli in the mouse gastrointestinal tract

BackgroundThe ability of a bacterial strain to competitively exclude or displace other strains can be attributed to the production of narrow spectrum antimicrobials, the bacteriocins. In an attempt to evaluate the importance of bacteriocin production for Escherichia coli strain residence in the gastrointestinal tract, a murine model experimental evolution study was undertaken.ResultsSix colicin-producing, yet otherwise isogenic, E. coli strains were administered and established in the large intestine of streptomycin-treated mice. The strains' persistence, population density, and doubling time were monitored over a period of 112 days. Early in the experiment only minor differences in population density between the various colicin-producing and the non-producing control strains were detected. However, over time, the density of the control strains plummeted, while that of the colicin-producing strains remained significantly higher (F(7,66) = 2.317; P < 0.0008).ConclusionThe data presented here support prior claims that bacteriocin production may play a significant role in the colonization of E. coli in the gastrointestinal tract. Further, this study suggests that the ability to produce bacteriocins may prove to be a critical factor in determining the success of establishing probiotic E. coli in the gastrointestinal tract of humans and animals.

Why is community-associated MRSA spreading across the world and how will it change clinical practice?

Meticillin-resistant Staphylococcus aureus (MRSA) emerged in 1960 and over the following 40 years was a problem confined largely to the healthcare setting. In the late 1990s the first US reports of so-called community-associated MRSA (CA-MRSA) infections appeared. CA-MRSA infections were defined as MRSA infections occurring in patients who had no identifiable predisposing risk factors, such as healthy children and young adults. CA-MRSA is associated with a novel genetic profile and phenotype; it is remarkably fit and capable of spreading within communities, it is virulent and is often susceptible to multiple narrow-spectrum antimicrobials other than β-lactams. CA-MRSA infections involve predominantly skin and soft tissue; however, necrotizing pneumonia and necrotizing fasciitis have been described. At present, several reports suggest that CA-MRSA may be replacing the hospital-acquired MRSA strains (HA-MRSA), with potentially catastrophic consequences. Given the rapid spread and the high virulence of CA-MRSA, global strategies are needed. Prompt, appropriate treatment, guided by the site and type of infection and risk factors for HA-MRSA or CA-MRSA, increases the chances of a successful outcome and is urgently needed.

C. difficile Treatments in Pipeline Hold Promise

C. difficile Treatments in Pipeline Hold Promise

Characterization of bacteriocin produced byStreptococcus bovisJ2 40-2 isolated from traditional fermented milk ‘Dahi’

A bacteriocin-producing strain Streptococcus bovis J2 40-2 was isolated from traditional fermented milk 'Dahi' in Bangladesh. Despite its narrow antimicrobial spectrum, it showed strong antimicrobial activity against extremely challenging and problematic organisms in foods, such as Listeria monocytogenes. Bacteriocin was sensitive to several proteolytic enzymes and showed antimicrobial activity over a wide pH range of 2.0-10.0. It was stable when heated to 110 degrees C for 20 min, but lost 25% of its activity when heated to 121 degrees C for 15 or 20 min. Optimum bacteriocin production (5600 AU/mL) was achieved when the strain was cultured at 37 degrees C for 24 h in MRS medium rather than in TYLG, GM17, or skim milk medium. Bacteriocin was partially purified by ammonium sulfate precipitation (80% saturation), dialysis (cut-off MW: 3500) and gel filtration chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that bacteriocin had a molecular weight of approximately 4.5 kDa.

Production of Enterocins L50A, L50B, and IT, a New Enterocin, by Enterococcus faecium IT62, a Strain Isolated from Italian Ryegrass in Japan

Enterococcus faecium IT62, isolated from ryegrass in Japan, was shown to produce three different bacteriocins, two of which had molecular masses and amino acid sequences that corresponded to those of enterocin L50A and enterocin L50B. These peptides existed, however, as chemically modified forms that were either N formylated or N formylated and oxidized at Met(24). The third bacteriocin, named enterocin IT, had a molecular mass of 6,390 Da, was made up of 54 amino acids, and did not correspond to any known bacteriocin. However, enterocin IT was identical to the C-terminal part of the 16-amino-acid-longer bacteriocin 32 (T. Inoue, H. Tomita, and Y. Ike, Antimicrob. Agents Chemother., 50:1202-1212, 2006). For the first time, the antimicrobial activity spectra for enterocins L50A and L50B were determined separately and included a wide range of gram-positive bacteria but also a few gram-negative strains that were weakly sensitive. Slight differences in the activities of enterocins L50A and L50B were observed, as gram-positive bacteria showed an overall higher level of sensitivity to L50A than to L50B, as opposed to gram-negative ones. Conversely, enterocin IT showed a very narrow antimicrobial spectrum that was limited to E. faecium strains, one strain of Bacillus subtilis, and one strain of Lactococcus lactis. This study showed that E. faecium IT62, a grass-borne strain, produces bacteriocins with very different activity features and structures that may be found in strains associated with food or those of clinical origin, which demonstrates that a particular enterocin structure may be widespread and not related to the producer's origin.

Comparative analysis ofLactococcus lactis bacteriocins and preliminary characterisation of a new proteinase K resistant lactococcin member

Detection of lactic acid bacteria (LAB) bacteriocins producers is of great significance for food industry to establish starter bacterial association and to improve food safety. Eighty oneLactococcus lactis strains, isolated from traditional Tunisian dairy products, were screened for their antibacterial activity. Bacteriocin production in the supernatant was demonstrated for twelve strains by the well diffusion assay, protease susceptibility and by direct detection of the activity on SDS-PAGE. By using PCR with primers targeting structural genes of nisin and lactoccocin 481, we were able to predict their presence in 10 and one strain respectively. No amplifications were recorded with primers targeting lactococcin A, lactococcin 972 and bacteriocin J46 ofL. lactis. The remaining unidentified bacteriocin produced by strain BMG 6.25 and designed as lactococcin IAF 25, was further characterised. IAF 25 was shown to be a heat-stable proteinaceous inhibitory factor sensitive to papain and trypsin but resistant to proteinase K treatment. IAF 25 has an apparent molecular weight of 6 kDa and showed a narrow antimicrobial activity spectrum against closely related bacteria and genera. These original characteristics amongL. lactis bacteriocins coupled with cross inhibition tests with bacteriocin producers reference strains, led to the assumption of the novelty of lactococcin IAF 25.

Bacteriocins from plant pathogenic bacteria

Many bacteria produce antimicrobial substances such as nonribosomally synthesized antibiotics and ribosomally synthesized proteinaceous compounds referred to as bacteriocins. Secretion of antimicrobials is generally thought to contribute to the competitiveness of the producing organism, but there are indications that these compounds in some cases may have regulatory roles too. Bacteriocins most often act on closely related species only and are thus of interest for application as targeted narrow-spectrum antimicrobials with few side effects. Although the application of bacteriocins in plant disease control is an attractive option, very little is known about the occurrence and roles of these compounds in plant pathogenic bacteria and their natural competitors occurring in the same biotopes. This study presents an overview of current knowledge of bacteriocins from plant pathogenic bacteria.

Carbohydrazones of Substituted Salicylaldehydes as Potential Lead Compounds for the Development of Narrow-Spectrum Antimicrobials

Certain substituted salicylaldehydes are known to have highly potent antimicrobial activity against bacteria and fungi, but the mechanism underlying this remarkable activity is not known, and almost nothing has been reported on the effects of further modification of the structures, such as the formation of hydrazone-type derivatives. We report now a study on the antimicrobial properties of the carbohydrazone derivatives of several substituted salicylaldehydes. The compounds studied were synthesized from ring-substituted salicylaldehydes and carbohydrazide in the mole ratio 2:1. They were tested against Aspergillus niger, Bacillus cereus, Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Saccharomyces cerevisiae and Staphylococcus epidermidis using the agar diffusion method. The carbohydrazone derived from 2,3,4-trihydroxybenzaldehyde had distinctly higher activity than the parent aldehyde in the same molar concentration. This activity was limited to one test organism (S. epidermidis), while the free aldehyde had at least some (in some cases even high) activity against all of the microbes studied. All other ones of the effective carbohydrazone compounds were distinctly less active than the parent salicylaldehydes as such. The hydrazones studied had in general a narrower antimicrobial spectrum than the free aldehydes and are thus of interest as potential lead compounds for the development of narrow-spectrum anti-microbial drugs. The mechanism of action of the aldehydes as well as that of the carbohydrazones is discussed.

Structural Development, Haematological Immunological and Pharmacological Effects of Quinolones

The interest of the medical community in quinolones has not decreased despite more than ten years of continuous and growing use of these agents. The constant need for new anti microbials has produced a variety of newer quinolones termed as I, II, III, and IV generation. Nalidixic acid and other early quinolones had limited use due to poor pharmacokinetics, relatively narrow antimicrobial spectrum of activity, and frequent adverse effects. Extensive pharmacologic and clinical development of quinolone antimicrobial agents has resulted in improved antimicrobial activity, pharmacokinetic features, toxicity, and drug-drug interaction profiles. These attributes, coupled with their expanded spectrum and the immune enhancing phenomena of quinolones with a cyclopropyl moiety at position 1 of the quinolone ring suggest that the newer fluoroquinolones are so far the most ideal agents for the empirical treatment of many common infections. The above has made it desirable to review the status of these agents as revealed in published literature. The thrust of this review is on the structural development, pharmacological, haematological and immunological effects of quinolones. Recent patents filed are also discussed.

Experience with a clinical decision support system in community pharmacies to recommend narrow-spectrum antimicrobials, nonantimicrobial prescriptions, and OTC products to decrease broad-spectrum antimicrobial use.

Overuse of antibiotics increases the incidence of bacterial resistance and contributes avoidable costs to the health care system. To determine the feasibility of a protocol-driven community pharmacy intervention that was designed to decrease broad-spectrum antimicrobial (BSA) use in patients with upper respiratory tract infections. The intervention involved pharmacists who conducted guided interviews regarding patient symptoms in a cohort of patients with BSA prescription visiting 2 rural community pharmacies during peak respiratory illness season. A clinical decision support system was provided to aid in pharmacist diagnosis and assist in determining if the BSA therapy was appropriate. Upon patient consent, pharmacists attempted to contact primary care providers (PCPs) to confirm the diagnosis and recommend appropriate alternative therapy. There were 192 subjects with prescriptions for BSAs and symptoms of respiratory tract infection. Only 3% of the patients who were approached declined to discuss their symptoms and treatment with the pharmacist. A mean of 3 minutes was required to collect symptom and treatment information from the patients. However, when patients were asked if the pharmacist could contact their PCP to recommend alternative therapy, only 7% (n=4) of patients agreed to the intervention. The PCPs who were contacted by pharmacists were receptive to altering the BSA to first-line antimicrobial therapy such as amoxicillin or doxycycline. Despite a description of the importance of the intervention, more than 90% of patients prescribed a BSA declined to permit the community pharmacist to contact the prescriber to discuss first-line therapeutic alternatives. This experience in a pilot study to explore the feasibility of pharmacist intervention at the point of dispensing of a BSA made clear that a successful community pharmacy intervention to reduce BSA use would require an alternative method, perhaps via a collaborative practice protocol that does not require patient consent to make the drug substitution to first-line antibiotic therapy.

Otitis media, tympanostomy tube placement, and use of antibiotics

Objective. To investigate potential links between antimicrobial drug use for acute otitis media (AOM) and tympanostomy tube placements, and the relationship between parental views and physician antimicrobial prescribing habits. Design. Cross-sectional community study repeated after five years. Subjects. Representative samples of children aged 1–6 years in four well-defined communities in Iceland, examined in 2003 (n = 889) and 1998 (n = 804). Main outcome measures. Prevalence of antimicrobial treatments for AOM, tympanostomy tube placements, and parental expectations of antimicrobial treatment. Results. Tympanostomy tubes had been placed at some time in 34% of children in 2003, as compared with 30% in 1998. A statistically significant association was found between tympanostomy tube placement rate and antimicrobial use for AOM in 2003. In the area where antimicrobial use for AOM was lowest in 1998, drug use had further diminished significantly. At the same time, the prevalence of tympanostomy tube placements had diminished from 26% to 17%. Tube placements had increased significantly, from 35% to 44%, in the area where antimicrobial use for AOM was highest. Parents in the area where antimicrobial consumption was lowest and narrow spectrum antimicrobials were most often used were less likely to be in favour of antimicrobial treatment. Conclusions. Comparison between communities showed a positive correlation between antimicrobial use for AOM and tympanostomy tube placements. The study supports a restrictive policy in relation to prescriptions of antibiotics for AOM. It also indicates that well-informed parents predict a restrictive prescription policy.

Empiric antimicrobial therapy for severe sepsis in the intensive care unit: In early, hit hard, out early

Summary Sepsis is becoming more common in hospital patients and, despite developments in management, the morbidity and mortality of severe sepsis is still significant. Early, appropriate antimicrobial therapy has a significant positive effect on outcome and should be a priority in the management of these patients. This means treating empirically with broad-spectrum antimicrobials until the pathogen is identified. Balancing this is the need to avoid increasing antimicrobial resistance which has been shown to be proportional to antimicrobial use. While every effort should be made not to fail individual patients by inadequately treating their sepsis, it is important to minimize resistance by avoiding unnecessary and excessive antimicrobial use. Traditionally, empiric treatment has involved starting with a narrow antimicrobial spectrum and escalating it as culture results become known. Current opinion, however, is veering towards initiating empiric therapy as soon as possible with broad-spectrum antimicrobials, narrowing the spectrum once the organism is identified (de-escalation), and limiting duration of therapy to the minimum effective period. This approach improves outcome and controls antimicrobial resistance. Many of the recommendations on this subject are not supported by high level evidence. Much of the research has been done on hospital and ventilator acquired pneumonia. For the purposes of this paper we are assuming that these findings have relevance to other forms of sepsis. This review of some of the current literature attempts to clarify antimicrobial issues for the Intensive Care SHO or registrar dealing with the onset of severe sepsis in critically ill adults.

Antibiotic susceptibility of bacteria most commonly isolated from bone related infections: the role of cephalosporins in antimicrobial therapy

Bone infections, which can be acute or chronic, often require aggressive antibiotic therapy, whether treated at home or in the community. Surveillance programmes are essential tools in the monitoring of antimicrobial resistance and can act as a resource to maintain effective prescribing. The Surveillance Network ® (TSN ®), which collects organism and patient-specific data from a network of laboratories across the United States, was used to analyse susceptibility of common bacterial species isolated from bone infections during 2000–2002. Narrow-spectrum antimicrobials such as vancomycin, quinupristin-dalfopristin and linezolid demonstrated good activity against Staphylococcus aureus and streptococci, and were active against 100% of isolates. However, Gram-negative species were also commonly isolated from these sites of infection. Later-generation cephalosporins, represented by ceftriaxone, cefotaxime and cefepime, exhibited a broad spectrum of activity including Enterobacteriaceae, streptococci and methicillin-susceptible S. aureus, but they were not active against methicillin-resistant S. aureus (MRSA) and showed variable activity against Pseudomonas aeruginosa. Using ceftazidime as a marker for extended spectrum β-lactamase (ESBL) expression, less than 3% of Escherichia coli or Klebsiella pneumoniae expressed this phenotype. Based on current in vitro activity, the third-generation cephalosporins provide broad-spectrum coverage useful for the empirical therapy of suspected bone infections, especially for patients treated in the community or hospitalised with community-acquired infections.

Modifications of therapy

Rates of response to empirical therapy in the neutropenic patient with fever, range between 40 and 90%. Modifications of therapy are needed in patients who do not respond but may also be considered in patients who respond. In patients with unexplained fever and rapid defervescence, switch to oral therapy is an acceptable option and there is no need to continue the regimen until neutrophil recovery. Neutropenic patients with persistent undefined fever and those with progressive pneumonia benefit from the addition of antifungals while the empiric addition of a glycopeptide is unlikely to be effective. In patients with gram-negative bacterial infection initially treated with monotherapy, response may be increased after the addition of an aminoglycoside. In cases of a defined etiology, the institution of narrow-spectrum antimicrobials in a persistent neutropenic patient carries a substantial risk for superinfection and is not generally recommended. Improved diagnostic tools and sensitive clinical risk-assessment methods will allow selecting and targeting therapy modifications better.

Identification and Characterization of Two Bacteriocin-Producing Bacteria Isolated from Garlic and Ginger Root

Two bacteriocin-producing bacterial strains were isolated from garlic and ginger root by the agar overlay method. The bacteria were identified by 16S rRNA sequence analyses and fermentation patterns as Leuconostoc mesenteroides (garlic isolate) and Lactococcus lactis (ginger isolate). The bacteriocins were assigned the names leucocin BC2 and lactocin GI3, respectively. Physiochemical properties and antimicrobial spectra of the bacteriocins were determined by the spot-on-lawn method. Both bacteriocins were inhibited by proteolytic enzymes. Leucocin BC2 exhibited a narrow antimicrobial spectrum, inhibiting only Bacillus, Enterococcus, and Listeria species. Lactocin GI3 had a broader spectrum, inhibiting Bacillus, Clostridium, Listeria, Enterococcus, Leuconostoc, Pediococcus, and Staphylococcus species. Both bacteriocins remained active when heated at 90°C for 15 min or 120°C for 20 min. Leucocin BC2 assayed at 37°C showed an inhibitory activity of 1,600 AU/ml, whereas at 8°C the activity was 12,800 AU/ml. Conversely, lactocin GI3 activity was the same at both assay temperatures. Both bacteriocins remained active over a pH range of 2.0 to 9.0 and in various organic solvents. The activity of leucocin BC2 was increased when treated with 0.5% acetic acid and 0.5% lactic acid, whereas lactocin GI3 activity was decreased with either acid. The molecular mass values were 3.7 kDa for leucocin BC2 and 3.9 kDa for lactocin GI3. These results show that the inhibitory substances produced by the bacteria isolated from garlic and ginger are bacteriocins that appear to be different in some characteristics from previously reported bacteriocins.

Individual and group antimicrobial usage rates on 34 farrow-to-finish swine farms in Ontario, Canada

Antimicrobial drug-use was assessed on 34 farrow-to-finish operations that marketed at least 500 hogs/yr. These operations either did not use any antimicrobials or used narrow-spectrum or broad-spectrum antimicrobials in rations of post-weaning pigs. Total antimicrobial use was measured for two months after obtaining inventories and records of all antimicrobials used. The collection of empty medication bottles and inventories of drugs on hand was convenient for producers and useful for estimating or validating recorded treatment rates, particularly for antimicrobials that were used only in one class of pig. Treatment records, however, underestimated by approximately 35% the amounts used for 27/29 farm–antimicrobial combinations. Rates of individual-pig treatment varied from 0–24.1 pigs treated/1000 pig-days, with a median of 5.29. Most individual animal treatments were given to piglets and sows at parturition and penicillin was the most commonly used antimicrobial. Gentamicin was administered to suckling piglets on 19 of the farms.

Antibacterial polypeptides of Lactobacillus species

Twelve of 79 strains of the genus Lactobacillus, mainly isolated from plants or fermenting material, were found to inhibit at least one of the nine indicator strains of the species Lact. brevis, Pediococcus damnosus and Leucanostoc oenos. The antimicrobial activities from Lact. brevis B 37 and Lact. casei B 80 were caused by polypeptides detectable in the culture liquids. They are bacteriocins with a narrow antimicrobial spectrum. Brevicin 37 from Lact. brevis B 37 was active against many lactic acid bacteria and Nocardia corallina, whereas caseicin 80 from Lact. casei B 80 inhibits only one other strain of Lact. casei. Brevicin 37 is stable at 121d̀C, caseicin 80 is inactivated above 60d̀C, and both are inactivated under alkaline conditions.