![]() However, at least two phyla comprise diderms that do not have LPS. The remaining phyla contain bacteria with two cell membranes, and most of these “diderms” have large molecules called lipopolysaccharides (LPS) in their outer membranes. The tree of life contains about 30 bacterial phyla, but only three of them contain bacteria that are surrounded by a single cell membrane, which are also known as “monoderms”. These different reactions to the stain reflect fundamental differences in the cell envelopes of these bacteria: Gram-positive bacteria usually have a single cell membrane that is encased by a thick wall made of a polymer called peptidoglycan, whereas Gram-negative bacteria tend to have two membranes with a thin wall of peptidoglycan sandwiched between them. The Gram stain is a violet-colored dye that is retained by Gram-positive bacteria but not by Gram-negative bacteria. They are usually sensitive to carbapenems such as meropenem or imipenem.For more than a century bacteriologists have used the Gram stain reaction to classify bacteria. coli or klebsiella and typically cause urinary tract infections but can also cause other infections such as pneumonia. They can be resistant to a very broad range of antibiotics.ĮSBLs tend to be e. They produce beta lactamase enzymes that destroy the beta-lactam ring on the antibiotic. Eradication usually involves a combination of chlorhexidine body washes and antibacterial nasal creams.Īntibiotic treatment options for MRSA are:Įxtended Spectrum Beta Lactamase bacteria (ESBLs)ĮSBLs are bacteria that have developed resistance to beta-lactam antibiotics. Patients being admitted for surgery or treatment are screened for MRSA infection by taking nasal and groin swabs so that extra measures can be taken to try to eradicate them and stop their spread. If these bacteria become part of an infection they can be difficult to treat. People are often colonised with MRSA bacteria and have them living harmlessly on their skin and respiratory tract. Think about MRSA in patients that have had hospital admissions or come from a nursing home or other healthcare institution. They are a problem in healthcare settings where antibiotics are commonly used. ![]() MRSA refers to staphylococcus aureus bacteria that have become resistant to beta-lactam antibiotics such as penicillins, cephalosporins and carbapenems. ![]() Methicillin-Resistant Staphylococcus Aureus (MRSA) The atypical bacteria that cause atypical pneumonia can be remembered using the mnemonic “ legions of psittaci MCQs”: Atypical bacteria are most often implicated in pneumonia. The definition of atypical bacteria is that they cannot be cultured in the normal way or detected using a gram stain. If the bacteria is not listed above then it is probably gram negative. Use the mnemonic “ corney Mike’s list of basic cars”: Then add a counterstain (such as safranin) which binds to the cell membrane in bacteria that don’t have a cell wall ( gram negative bacteria) turning them red/ pink. It involves two main steps:Īdd a crystal violet stain which binds to molecules in the thick peptidoglycan cell wall in gram positive bacteria turning them violet. PABA is then converted to DHFA which is converted inside the cell to THFA then folic acid.Ī gram stain is used as a quick way to check a sample under the microscope to look for bacteria. ![]() This chain starts with PABA, which is directly absorbed in to the cell across the cell membrane. Folic acid cannot be created or directly imported into the cell and requires a chain of intermediates to get in to the cell. Ribosomes are where bacteria proteins are synthesised within the bacterial cell.įolic acid is essential for synthesis and regulation of DNA within the bacteria. Nucleic acid is essential component of bacterial DNA. The cell wall is a structure that surrounds the outer cell membrane and is found on gram positive bacteria. There are some key components to learn about as they are the target of antibiotic treatment: Rod shaped bacteria are called bacilli and circular shaped bacteria are called cocci. Atypical bacteria cannot be stained or cultured in the normal way.īacteria can also be classified based on their shapes. Gram negative bacteria don’t have this thick peptidoglycan cell wall and don’t stain with crystal violet stain but will stain with other stains. Gram positive bacteria have a thick peptidoglycan cell wall that stains with crystal violet stain. Learning where bacteria fall within these categories helps you work out which antibiotics will be effective against them.Īerobic bacteria require oxygen whereas anaerobic bacteria do not. They can be categorised into aerobic and anaerobic, gram positive and gram negative and atypical bacteria. These pathogenic bacteria are the most relevant to learning medicine. Most bacteria are not harmful however some are pathogenic and cause infectious diseases.
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