SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Chloramphenicol

202

Routine antimicrobial susceptibility testing (AST) can prevent deaths due to bacteria and reduce the spread of multi-drug-resistance, but cannot be regularly performed in resource-limited-settings due to technological challenges, high-costs, and lack of trained professionals. We demonstrate an automated and cost-effective cellphone-based 96-well microtiter-plate (MTP) reader, capable of performing AST without the need for trained diagnosticians. Our system includes a 3D-printed smartphone attachment that holds and illuminates the MTP using a light-emitting-diode array. An inexpensive optical fiber-array enables the capture of the transmitted light of each well through the smartphone camera. A custom-designed application sends the captured image to a server to automatically determine well-turbidity, with results returned to the smartphone in ~1 minute. We tested this mobile-reader using MTPs prepared with 17 antibiotics targeting Gram-negative bacteria on clinical isolates of Klebsiella pneumoniae, containing highly-resistant antimicrobial profiles. Using 78 patient isolate test-plates, we demonstrated that our mobile-reader meets the FDA-defined AST criteria, with a well-turbidity detection accuracy of 98.21%, minimum-inhibitory-concentration accuracy of 95.12%, and a drug-susceptibility interpretation accuracy of 99.23%, with no very major errors. This mobile-reader could eliminate the need for trained diagnosticians to perform AST, reduce the cost-barrier for routine testing, and assist in spatio-temporal tracking of bacterial resistance.

Concepts: Bacteria, Microbiology, Antibiotic resistance, Escherichia coli, Performance, Microorganism, Gram negative bacteria, Chloramphenicol

174

The first broad-spectrum antibiotic chloramphenicol and one of the newest clinically important antibacterials, linezolid, inhibit protein synthesis by targeting the peptidyl transferase center of the bacterial ribosome. Because antibiotic binding should prevent the placement of aminoacyl-tRNA in the catalytic site, it is commonly assumed that these drugs are universal inhibitors of peptidyl transfer and should readily block the formation of every peptide bond. However, our in vitro experiments showed that chloramphenicol and linezolid stall ribosomes at specific mRNA locations. Treatment of bacterial cells with high concentrations of these antibiotics leads to preferential arrest of translation at defined sites, resulting in redistribution of the ribosomes on mRNA. Antibiotic-mediated inhibition of protein synthesis is most efficient when the nascent peptide in the ribosome carries an alanine residue and, to a lesser extent, serine or threonine in its penultimate position. In contrast, the inhibitory action of the drugs is counteracted by glycine when it is either at the nascent-chain C terminus or at the incoming aminoacyl-tRNA. The context-specific action of chloramphenicol illuminates the operation of the mechanism of inducible resistance that relies on programmed drug-induced translation arrest. In addition, our findings expose the functional interplay between the nascent chain and the peptidyl transferase center.

Concepts: Protein, Bacteria, Amino acid, Ribosome, Messenger RNA, Protein biosynthesis, Chloramphenicol, Peptidyl transferase

168

The Gram-negative bacterium Burkholderia pseudomallei is a serious environmental pathogen and the causative agent of the often fatal melioidosis. Disease occurs following exposure to contaminated water or soil, usually through cuts in the skin or via inhalation. However, the underlying mechanisms of pathogenicity remain poorly understood. B. pseudomallei is endemic to South East Asia and Northern Australia where infections are associated with antibiotic resistance and high mortality rates. Categorization of the pathogen as a potential biowarfare agent has also made research into vaccine development a high priority. Recent genome-scale screening has produced a large number of putative gene candidates from B. pseudomallei with the potential for development into vaccines. This mini-review will discuss the advantages and limitations of this novel approach, how these new techniques can complement existing strategies, and outline aims for future research.

Concepts: Immune system, Bacteria, Microbiology, Burkholderia mallei, Burkholderia, Burkholderia pseudomallei, Chloramphenicol, Melioidosis

155

The incidence of neonatal late-onset sepsis (LOS) is inversely related to the degree of maturity and varies geographically from 0.61% to 14.2% among hospitalised newborns. Epidemiological data on very low birth weight infants shows that the predominant pathogens of neonatal LOS are coagulase-negative staphylococci, followed by Gram-negative bacilli and fungi. Due to the difficulties in a prompt diagnosis of LOS and LOS-associated high risk of mortality and long-term neurodevelopmental sequelae, empirical antibiotic treatment is initiated on suspicion of LOS. However, empirical therapy is often inappropriately used with unnecessary broad-spectrum antibiotics and a prolonged duration of treatment. The increasing number of multidrug-resistant Gram-negative micro-organisms in neonatal intensive care units (NICU) worldwide is a serious concern, which requires thorough and efficient surveillance strategies and appropriate treatment regimens. Immunological strategies for preventing neonatal LOS are not supported by current evidence, and approaches, such as a strict hygiene protocol and the minimisation of invasive procedures in NICUs represent the cornerstone to reduce the burden of neonatal LOS.

Concepts: Epidemiology, Bacteria, Microbiology, Staphylococcus, Intensive care medicine, Pediatrics, Antibiotic, Chloramphenicol

37

OBJECTIVE:To quantify microbial contamination of human milk purchased via the Internet as an indicator of disease risk to recipient infants.METHODS:Cross-sectional sample of human milk purchased via a popular US milk-sharing Web site (2012). Individuals advertising milk were contacted to arrange purchase, and milk was shipped to a rented mailbox in Ohio. The Internet milk samples (n = 101) were compared with unpasteurized samples of milk donated to a milk bank (n = 20).RESULTS:Most (74%) Internet milk samples were colonized with Gram-negative bacteria or had >10(4) colony-forming units/mL total aerobic count. They exhibited higher mean total aerobic, total Gram-negative, coliform, and Staphylococcus sp counts than milk bank samples. Growth of most species was positively associated with days in transit (total aerobic count [log10 colony-forming units/mL] β = 0.71 [95% confidence interval: 0.38-1.05]), and negatively associated with number of months since the milk was expressed (β = -0.36 [95% confidence interval: -0.55 to -0.16]), per simple linear regression. No samples were HIV type 1 RNA-positive; 21% of Internet samples were cytomegalovirus DNA-positive.CONCLUSIONS:Human milk purchased via the Internet exhibited high overall bacterial growth and frequent contamination with pathogenic bacteria, reflecting poor collection, storage, or shipping practices. Infants consuming this milk are at risk for negative outcomes, particularly if born preterm or are medically compromised. Increased use of lactation support services may begin to address the milk supply gap for women who want to feed their child human milk but cannot meet his or her needs.

Concepts: Immune system, Bacteria, Microbiology, Escherichia coli, Milk, Breast milk, Chloramphenicol, Bacteriology

30

Multidrug-resistant gram-negative bacteria (MDR-GNB) are associated with an increasing proportion of infections among nursing home (NH) residents. The objective of this systematic review and meta-analysis was to critically review evidence of the prevalence of MDR-GNB among NH residents.

Concepts: Microbiology, Evidence-based medicine, Systematic review, Escherichia coli, Meta-analysis, Nursing home, Gram-negative bacteria, Chloramphenicol

27

Concerns about health issues and environmental pollution stimulate research to find new health and hygiene related products with healing properties and minimum negative effect on the environment. Development of new, natural antibacterial agents has become one of the most important research areas to combat some pathogens such as Gram- positive and Gram-negative bacteria, fungi, algae, yeast, and some microorganisms which cause serious human infections. Lawsonia Inermis (henna) leaf extracts for preparation of antibacterial poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) nanofibers via electrospinning technique were investigated. PEO and PVA based electrospun fibers containing henna extract were verified by the appearance of FTIR peaks corresponding to the pure extract. Our study demonstrates that 2.793 wt.% Li in PVA and PEO based solutions showed bactericidal effects against Staphylococcus aureus and bacteriostatic action to Escherichia coli. Concentrations of henna leaf extract strongly impacted antibacterial activities against both bacteria. Henna leaves have a great potential to be used as a source of a potent eco-friendly antimicrobial agent.

Concepts: Photosynthesis, Bacteria, Microbiology, Staphylococcus aureus, Escherichia coli, Tea tree oil, Henna, Chloramphenicol

27

ETHNOPHARMACOLOGICAL RELEVANCE: The leaves of Distephanus angulifolius and Ormocarpum trichocarpum are used for treating stomach-related ailments in traditional medicine. AIMS OF THE STUDY: The present study evaluated the antibacterial, antioxidant, mutagenic and antimutagenic properties of extracts obtained from the leaves of D. angulifolius and O. trichocarpum. MATERIALS AND METHODS: The microtitre bioassay was used to determine the antibacterial activity against three Gram-positive and three Gram-negative bacteria. Antioxidant activity was determined using the free-radical scavenging and β-carotene-linoleic acid model assays. The safety and possible protective properties of the extracts were investigated using Ames test. RESULTS: Dichloromethane fractions of both plants displayed a broad-spectrum antibacterial activity with minimum inhibitory concentrations ranging from 0.16 to 0.63mg/ml. A dose-dependent antioxidant activity was recorded in both plant species. All the evaluated samples showed no mutagenic as well as weak or no antimutagenic properties in the absence of exogenous metabolic activation. CONCLUSION: The results demonstrated the antibacterial and antioxidant activities of the leaves obtained from the two plant species. Furthermore, the data provides a rationale for the use of the plant species in treating stomach-related ailments in traditional medicine.

Concepts: DNA, Bacteria, Microbiology, Plant, Fern, Gram-negative bacteria, Chloramphenicol, Gram-positive bacteria

26

Published guidelines recommend amoxicillin for most children with community-acquired pneumonia (CAP), yet macrolides and broad-spectrum antibiotics are more commonly prescribed. We aimed to determine the patient and clinician characteristics associated with the prescription of amoxicillin versus macrolide or broad-spectrum antibiotics for CAP.

Concepts: Bacteria, Clarithromycin, Erythromycin, Chloramphenicol, Empiric therapy, Levofloxacin, Antibiotics

26

Gram-negative bacteria are an increasingly serious source of antibiotic-resistant infections, partly owing to their characteristic protective envelope. This complex, 20 nm thick barrier includes a highly impermeable, asymmetric bilayer outer membrane (OM), which plays a pivotal role in resisting antibacterial chemotherapy. Nevertheless, the OM molecular structure and its dynamics are poorly understood because the structure is difficult to recreate or study in vitro. The successful formation and characterization of a fully asymmetric model envelope using Langmuir-Blodgett and Langmuir-Schaefer methods is now reported. Neutron reflectivity and isotopic labeling confirmed the expected structure and asymmetry and showed that experiments with antibacterial proteins reproduced published in vivo behavior. By closely recreating natural OM behavior, this model provides a much needed robust system for antibiotic development.

Concepts: Bacteria, Virus, Antibiotic resistance, Escherichia coli, In vivo, In vitro, Gram-negative bacteria, Chloramphenicol