![]() Loss of pain sensation and the presence of skin lesions increase susceptibility to secondary injuries and infections with other pathogens.īacteria in the genus Corynebacterium contain diaminopimelic acid in their cell walls, and microscopically often form palisades, or pairs of rod-shaped cells resembling the letter V. leprae, is the cause of Hansen’s disease ( leprosy), a chronic disease that impacts peripheral nerves and the integrity of the skin and mucosal surface of the respiratory tract. Complicating treatment even further is the development and spread of multidrug-resistant strains of this pathogen.Īnother pathogenic species, M. tuberculosis is challenging and requires patients to take a combination of drugs for an extended time. tuberculosis and millions of new infections occur each year. It has been estimated that one-third of the world’s population has been infected with M. tuberculosis is the causative agent of tuberculosis, a disease that primarily impacts the lungs but can infect other parts of the body as well. The genus Mycobacterium is an important cause of a diverse group of infectious diseases. ![]() Because of this, a special acid-fast staining procedure is used to visualize these bacteria. This waxy coat protects the bacteria from some antibiotics, prevents them from drying out, and blocks penetration by Gram stain reagents (see Staining Microscopic Specimens). The genus Mycobacterium is represented by bacilli covered with a mycolic acid coat. (credit a: modification of work by “GrahamColm”/Wikimedia Commons credit b: modification of work by Centers for Disease Control and Prevention credit c: modification of work by Mwakigonja AR, Torres LM, Mwakyoma HA, Kaaya EE) This micrograph shows a Pap smear from a woman with vaginosis. ![]() (c) The gram-variable bacterium Gardnerella vaginalis causes bacterial vaginosis in women. (b) Corynebacterium diphtheria causes the deadly disease diphtheria. israelii is an anaerobe notorious for causing endocarditis (inflammation of the inner lining of the heart) ( Figure 4.18).įigure 4.18 (a) Actinomyces israelii (false-color scanning electron micrograph ) has a branched structure. inhabit the human mouth and are opportunistic pathogens, causing infectious diseases like periodontitis (inflammation of the gums) and oral abscesses. play an important role in soil ecology, and some species are human pathogens. The genus Actinomyces is a much studied representative of Actinobacteria. One distinctive feature of this group is the presence of several different peptidoglycans in the cell wall. Most Actinobacteria live in the soil, but some are aquatic. Some Actinobacteria are very large and complex, whereas others are among the smallest independently living organisms. Their microscopic appearance can range from thin filamentous branching rods to coccobacilli. The name Actinobacteria comes from the Greek words for rays and small rod, but Actinobacteria are very diverse. Actinobacteria: High G+C Gram-Positive Bacteria The class Bacilli comprises low G+C gram-positive bacteria, which have less than 50% of guanine and cytosine nucleotides in their DNA. The class Actinobacteria comprises the high G+C gram-positive bacteria, which have more than 50% guanine and cytosine nucleotides in their DNA. Microbiologists currently recognize two distinct groups of gram-positive, or weakly staining gram-positive, prokaryotes. For many years, the retention of Gram stain was one of the main criteria used to classify prokaryotes, even though some prokaryotes did not readily stain with either the primary or secondary stains used in the Gram stain procedure.Īdvances in nucleic acid biochemistry have revealed additional characteristics that can be used to classify gram-positive prokaryotes, namely the guanine to cytosine ratios (G+C) in DNA and the composition of 16S rRNA subunits. Crystal violet, the primary stain of the Gram stain procedure, is readily retained and stabilized within this matrix, causing gram-positive prokaryotes to appear purple under a brightfield microscope after Gram staining. Prokaryotes are identified as gram-positive if they have a multiple layer matrix of peptidoglycan forming the cell wall.
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