Antimicrobial agents sensitivity

Bacterial spores are the most resistant of all microbial forms to chemical treatment. The majority of antimicrobial agents have no useful sporicidal action, with the exception of the aldehydes, halogens and peroxygen compounds. Such chemicals are sometimes used as an alternative to physical methods for sterilization ofheat sensitive equipment. In these circumstances, correct usage of the agent is of paramount importance since safety margins are lower in comparison with physical methods of sterilization (Chapter 20). 

The vegetative fungal form is often as sensitive as vegetative bacteria to antimicrobial agents. Fungal spores (conidia and chlamydospores see Chapter 2) may be more... 

Susceptibility of viruses to antimicrobial agents can depend on whether the viruses possess a lipid envelope. Non-lipid viruses are frequently more resistant to disinfectants and it is also likely that such viruses cannot be readily categorized with respect to their sensitivities to antimicrobial agents. These viruses are responsible for many nosocomial infections, e.g. rotaviruses, picornaviruses and adenoviruses (see Chapter 3), and it may be necessary to select an antiseptic or disinfectant to suit specific circumstances. Certain viruses, such as Ebola and Marburg which cause haemorrhagic fevers, are highly infectious and their safe destruction by disinfectants is of paramount importance. 

Brown M.R.W. Gilbert P. (1993) Sensitivity ofbiofilms to antimicrobial agents. JAppl Bact Symp Suppl, 74, 87S-97S. 

At 24 to 48 hours, aerobic bacterial culture results should return. If a suspected pathogen is not sensitive to the antimicrobial agents being given, the regimen should be changed if the patient has not shown sufficient improvement. 

Definitive therapy should be based on results of appropriately collected cultures and sensitivities, as well as clinical response to empiric antimicrobial agents. 

The ability to eradicate bacteria from the urinary tract is directly related to the sensitivity of the organism and the achievable concentration of the antimicrobial agent in the urine. 

Mastitis is a complex of infections, caused by a variety of microorganisms with inherent differences in sensitivity to antimicrobial agents. Furthermore, sensitivity vitro does not assure efficacy vivo. Additionally, pathogens have the capacity to gain resistance to antibiotics, particularly under conditions of heavy and poorly controlled use. 

May be effective in the treatment of acute urinary tract infections caused by susceptible strains of gram-positive and gram-negative bacteria, especially Enterobacter sp. and Escherichia coii. It usually is less effective than other antimicrobial agents in the treatment of urinary tract infections caused by bacteria other than mycobacteria. Consider using only when the more conventional therapy has failed and when the organism has demonstrated sensitivity. 

Quinoxaline-1,4-dioxides are synthetic antimicrobial agents the best-known members are carbadox and olaquindox. Both compounds are rapidly metabolized to monoxy- and desoxy- compounds. The final product from carbadox and the one most often determined, mainly in liver (target tissue), is quinoxaline-2-carboxylic acid. Carbadox and olaquindox are light-sensitive compounds and sample manipulations should be performed only under the minimum of indirect incandescent illumination. Carbadox and desoxycarbadox are insoluble in water but are soluble in chloroform and methanol, while olaquindox is slightly soluble in water and some organic solvents. The solubility, however, of quinoxaline-2-carboxylic acid can be easily monitored by adjusting the pH because it is a strong carboxylic acid (pK 2.88). 

Microbiological inhibition tests are generally considered to be an unreliable method for detecting residues of antimicrobial agents in meat. The development of more specific, sensitive, reproducible, repeatable and robust chemical-based methods of analysis will offer methods capable of detecting residues previously undetectable by biological assays. 

Ideally, the antimicrobial agent used to treat an infection is selected after the organism has been identified and its drug sensitivity established. However, in the critically ill patient, such a delay could prove fatal and immediate empiric therapy is indicated. 

Disk diffusion method for determining the sensitivity of bacteria to antimicrobial agents. 

The organism is sensitive to physical agents such as heat sterilisation, radiation and cold shock [6,7], and it is therefore its resistance to antimicrobial agents which poses the major problem. The continued use of antibacterial agents will no doubt exacerbate the situation unless more effective agents are discovered. 

Naturally resistant strains. Some bacteria are innately resistant to certain classes of antimicrobial agent, e.g. coliforms and many other Gramnegative bacteria possess outer cell membranes which protect their cell walls from the action of certain penicillins and cephalosporins. Facultatively anaerobic bacteria (such as Escherichia colt) lack the ability to reduce the nitro group of metronidazole which therefore remains in an inactive form. In the course of therapy, naturally sensitive organisms are eliminated and those naturally resistant proliferate and occupy the biological space newly created by the drug. 

Krebs, F. Miller, S. Catalone, B. Welsh, P. Malamud, D. Howett, M. Wigdahl, B. Sodium dodecyl sulfate and C31G as microbicidal alternatives to N-9 comparative sensitivity of primary human vaginal keratocytes. Antimicrobial agents Chemotherapy 2000, 44, 1954-1960. 

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