Minimal media is a defined medium with different compositions depending on microorganisms cultured. It contains a carbon source like sugar/succinate and inorganic salts like magnesium, nitrogen, sulfur, phosphorus. Carbon is a source of energy; magnesium and ammonium salts are the sources of ions for metabolism stimulation. Phosphate is a buffering agent.
Different Types Of Culture Media Used In Microbiology Pdf Download
CHROMagar is a microorganism-specific, chromogenic culture medium used for isolation and identification for a variety of organisms. CHROMagar was developed by Alain Rambach, who first formulated agars that were monochromogenic for the detection of E. coli and Salmonella spp. Second-generation agars are multicolor. Both types are differential and selective. The nutritive agar base includes peptone and glucose. Different additives, proprietary chromogenic mixtures, and antibiotics have resulted in a series of media-specific for such organisms as Listeria, S. aureus, methicillin-resistant S. aureus (MRSA), E. coli O157, yeasts, and other organisms.
MacConkey agar is a selective and differential medium used for the isolation of gram-negative organisms. The nutritive base includes a variety of peptones. The medium is made selective by the incorporation of bile (although at levels less than those used in other enteric media) and crystal violet, which inhibit gram-positive organisms, especially enterococci and staphylococci.
Neomycin egg yolk agar is a selective and differential medium used for the differentiation of anaerobic organisms that are lipase positive, including Clostridium spp., Prevotella intermedia, Fusobacterium necrophorum, and some strains of Prevotella loescheii.
The Septic-Chek system (Becton Dickinson Microbiology Systems) is a mycobacterial culture system that contains modified 7H9 broth and three types of solid media, modified Lowenstein-Jensen, Middlebrook 7H11, and chocolate agars, with various supplements.
Xylose-lysine-desoxycholate agar is a selective and differential medium used for the isolation and differentiation of enteric pathogens from clinical specimens. This medium is more supportive of fastidious enteric organisms such as Shigella. For Salmonella, which contains the lysine enzyme, this reaction reverts the pH to an alkaline state and the colony appears to be transparent or red with a black center. A number of other similar media for isolation of enteric pathogens exist, including xylose-galactosidase medium, which is more specific for Aeromonas spp.
Many types of culture media have been developed by scientists to grow selective or desired microorganisms. These are classified based on their nutrient composition, consistency, and application or use in life science laboratories.
All types of samples that may contain pathogens but could not be processed immediately require transport media. It may be a stool, urethral swabs, nasal and throat swabs and specimens for tissue culture, etc.Table of Contents
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Cell culture medium provides nutrients and growth factors necessary for cell proliferation. A typical basal cell culture medium is composed of amino acids, carbohydrates, vitamins, inorganic salts, glucose, trace elements, and a buffer system to maintain a stable pH. Traditionally, animal-derived serum is used to supplement basal media to provide a source of growth factors. Now, serum-free, chemically defined formulations are highly favored.
Most skin microbiome surveys have used amplicon sequencing. Over the past few years, however, major technical and analytical breakthroughs have enabled shotgun metagenomic sequencing studies. Figure 1 highlights the technical and procedural differences between amplicon and shotgun metagenomics and the different types of analyses that are possible with the data sets. As shotgun metagenomics does not sequence specific target regions, it simultaneously captures all genetic material in a sample, including human, bacterial, fungal, archaeal and viral, thus allowing relative kingdom abundances to be inferred, with the limitation that the DNA of different microorganisms may be differentially extracted depending on the sample preparation method14,15,16. Another advantage of shotgun metagenomic sequencing is that these data sets provide sufficient resolution to differentiate species and even strains within a species. This is crucial for identifying members of the Staphylococcus genus, which are difficult to classify to the species level with most amplicon sequencing approaches9. The ability to differentiate strains is important as more studies reveal the functional differences that exist between strains within a species17,18,19.
DNA sequencing is a useful and unbiased tool for revealing the microorganisms in a sample; however, it is unable to differentiate between live colonizing and dead transient organisms. Although traditional culture techniques can distinguish between live and dead microorganisms, results are skewed by the culture conditions used. RNA sequencing may address this issue by revealing the functional activity of the microbiota, but it is technically difficult given the low biomass of organisms on skin. To measure this activity indirectly, a new analysis technique was developed that compares read distributions at the origin of replication and with those elsewhere in the genome as evidence of active bacterial replication112.
Bacterial infection is among the top ten most common causes of death worldwide [2]. Microbial flora in clinical specimens obtained from different parts of the human body includes a variety of different organisms both pathogenic and non-pathogenic. Traditionally, diagnosis of bacterial or fungal infections relied solely on culture based techniques and culture has been considered the gold standard of pathogen detection. However, some organisms may not be easily detectable by conventional culture methods used in most laboratories due to many factors. In a conventional clinical microbiology laboratory setting, microbial culture of most specimens will be carried out under aerobic conditions. Clinical specimens are not routinely investigated for a variety of pathogens e.g. fungi, anaerobes or rickettsial pathogens unless specifically requested or indicated by the clinical history. Standard culture techniques rely largely on morphological and biochemical characterisation for identification, which can lead to decreased specificity. Also, only a fraction of organisms can be successfully cultured in a multipathogen sample due mostly to various factors such as fastidious growth requirements, non-viable organisms or inhibition of pathogenic organisms due to bacteriocin production by other microbes present in clinical specimens [3, 4]. These factors make accurate diagnosis and treatment of infections a challenge.
Out of 17 PPCN (PCR positive, culture negative) specimens (see Table 4), 2 (P1, P5) failed to meet the quality parameters for successful bioinformatics analysis (i.e. less than 2000 reads of >300 bp at Phred quality score 16) and were designated as conflicts. Though these specimens showed successful amplification of expected bacterial fragment at the library preparation step, the concentration of the purified library was too low for successful sequencing and subsequent bioinformatics analysis. Metagenomic results for 8 specimens (P14, P24, P30, P34, P40, P51, P57 and P81) can be readily explained as to why these specimens were reported as culture negative. These specimens predominantly contain anaerobic bacteria which would not grow in standard aerobic culture media as was used in this case. Additionally, M. hominis detected in another specimen (P54), is a fastidious organism, which would typically take up to 4 days to grow and lacks a cell wall which makes Gram staining and morphological identification difficult [18, 19]. Therefore, these 9 metagenomic workflow results in context can be attributed as false negatives in culture. Furthermore, fungal metagenomics showed that 2 specimens (P37 and P81) had fungal species (Saccharomyces cerevisiae and Candida albicans respectively). Inhibition of bacterial culture growth due to the presence of fungal species is a distinct possibility, and can be considered as an example of the limitation of bacterial culture. Therefore, out of a total of 17 PPCN, the discrepancies of 10 specimens (P14, P24, P30, P34, P37, P40, P51, P54, P57 and P81) can be attributed to the limitations of standard culture methods.
Although many bacterial culture media are available commercially, there is a continuous effort to develop better selective media for bacteria, which cannot be grown on existing media. While exploring antibacterial properties of clove, we observed that it has the potential to selectively inhibit growth of certain types of bacteria. This led us to do the experiments, which resulted in developing a new media which selectively allowed the growth of only Gram-negative bacteria, while inhibiting the Gram-positive bacteria.
Mueller Hinton Agar (MHA) was used as the base media and was modified to develop MHA-C15 (MHA containing 15% volume/volume water extract of clove). Gram-negative bacterial pathogens Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium and Pseudomonas aeruginosa grew on MHA-C15. However, none of the major Gram-positive bacterial pathogens such as Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus mutans, Bacillus spp. and Enterococcus spp. grew on it. Taken together, these findings show that MHA-C15 is a newly developed selective media for culture of Gram-negative bacteria.
Plants are rich in a wide variety of chemical compounds such as tannins, terpenoids, alkaloids, and flavonoids which have been found to possess antimicrobial properties against wide variety of bacterial pathogens. Since prehistoric times, traditional healers have used plants to prevent or cure infectious conditions [11]. Cloves are aromatic flower buds of the tree, Syzygium aromaticum. They have been widely known for their antibacterial, antiviral and antifungal properties and also for their use in herbal medicine for centuries. Cloves are used as a spice in cooking different types of food items and also used in food preservations for its antimicrobial effect with no known side effects. Clove essential oil (CEO) is traditionally used in the treatment of burns and wounds, and as a pain reliever in dental care as well as treating tooth infections and toothache [12]. The extracts of clove exhibit antimicrobial effect on multidrug resistant microorganisms as well as methicillin-resistant Staphylococcus aureus, Bacillus subtilis, Salmonella typhi and Serratia marcescens. Various phytochemicals such as sesquiterpenes, monoterpenes, hydrocarbon, and phenolic compounds are present in cloves. In clove oil, eugenyl acetate, eugenol, and β-caryophyllene are the most important phytochemicals exhibiting antibacterial activity [13]. 2ff7e9595c
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