VL10 Control of Microbial Growth PDF

Control of microbial growth Mitja Remus-Emsermann KöLu 12-16 Raum 129 [email protected] Control of microbial growth What is death? Definition: The loss of membrane integrity and loss of electrical potential across the membrane How can we cont...

Control of microbial growth Mitja Remus-Emsermann KöLu 12-16 Raum 129 [email protected] Control of microbial growth What is death? Definition: The loss of membrane integrity and loss of electrical potential across the membrane How can we control bacterial growth? Life-Dead stain E.g. BacLight™ (Thermo) Consists of two dyes that interact with DNA Syto9 (green) crosses intact membranes Propidium iodide (red) cannot cross intact membranes Control of microorganisms Sterilization: The process by which all living cells, spores, and acellular entities (e.g., viruses) are either destroyed or removed from an object or habitat. Disinfection: The killing, inhibition, or removal of microorganisms that may cause disease; disinfection is the substantial reduction of the total microbial population and the destruction of potential pathogens Sanitization: Closely related to disinfection. In sanitization, the microbial population is reduced to levels that are considered safe by public health standards Antisepsis: The destruction or inhibition of microorganisms on living tissue; it is the prevention of infection or sepsis. Chemotherapy: The use of chemical agents to kill or inhibit the growth of microorganisms within host tissue Microbial control methods In the kitchen Are there any means to prevent microbial growth that you are using on a daily basis? Physical methods to control microbial growth Cardinal temperatures 160 T H E F O U N D AT I O N S O F M I C R O B I O L O G Y transport or can no long Enzymatic reactions occurring at maximal possible rate force, the organism cann maximum, the growth t Optimum which all or most cellul Enzymatic reactions occurring maximum rate and typic Growth rate at increasingly rapid rates the minimum (see Figure Temperature Classes Although there is a contin low temperature optima Minimum Maximum it is possible to distingui in relation to their grow with low temperature op Temperature perature optima; therm and hyperthermophile Membrane gelling; transport Protein denaturation; collapse processes so slow that growth of the cytoplasmic membrane; (Figure 5.20). cannot occur thermal lysis Mesophiles are widesp monly studied microorg Pushing temperature beyond maximum Leads to protein denaturation membrane collapse and cell lysis Dry heat not as effective as moist heat, but: “Cooking” in aqueous solution is limited to a max temperature 100 °C Pressure cooking pushes the boiling point of water beyond 100 °C Process of “autoclaving” 2 bar pressure, 121 °C for 15 minutes “Pasteurisation” short heating to below e.g. outer membranes Target molecule modification -> change of DNA sequence Acquisition of antibiotic resistance genes that modify the antibiotic compound -> plasmids, integrative conjugatable elements (ICE), phages Their population is following a “bet hedging” strategy i.e. one part of the population is growing, the other is not (e.g. spore formation or slowed growth)  anisms mples of bacterial resistance to antibiotics are R Antibiotic resistance. Sites of enzymatic modification of selected wn in Figure 27.33. Antibiotic resistance can be HO O O d by the microorganism on either the bacterial H3C n a plasmid called an R (for resistance) plas- HN Antibiotic 3) (Table 27.8). Because ofresistance genes may widespread existing RNH S CH3 CH3 codeemergence e and continual for of new resistance, OH O N COOH from clinical specimens must be tested for H Enzymes bility to ensure that appropriate inactivate treatment of an Phosphorylation β-Lactamase 7.5). antibiotics ant bacteria isolated from patients contain Adenylation Streptomycin Penicillin nes located Efflux pumps transmitted on horizontally that remove R an on the chromosome. The R plasmid genes antibiotics from the cell hat modify and inactivate the drug (Figure O H C CHCl2 an alternative t encode enzymes protein that prevent uptake that of the H N H mp it out. For example, Bacteria carrying R de resistancecannot be targeted by an 2ON C C C OH for the aminoglycoside strepto- nzymes thatantibiotic phosphorylate, acetylate, or ade- HO H H e modified drug then lacks antibiotic activity. Acetylation s, R plasmids encode b-lactamase, an enzyme actam ring, inactivating the antibiotic (Fig- Chloramphenicol mphenicol resistance is due to an R plasmid– Brock Figure 27.33 mical process, such as protein synthesis, and bind akly; if the agent is removed, the cells can resume ny antibiotics fall into this category. Bacteriocidal Antibiotics in diagnostics ontrast, bind tightly to their cellular targets and by l the cell. However, the dead cells are not lysed, and Nutrient agar plate Inoculate plate with a liquid culture of a test organism. Susceptibility tests Discs containing antimicrobial Minimum agents are placed inhibitory on surface. concentration T. D. Brock Incubate for 24–48 h. Test organism shows susceptibility to some agents, Zones of indicated by inhibition of growth inhibition bacterial growth around Antimicrobial agent susceptibility assay using dilution methods. s the minimum inhibitory concentration (MIC). A series of increasing discs (zones of inhibition). antimicrobial agent is prepared in the culture medium. Each http://www.bacteriainphotos.com/disc%20diffusion%20test.html d with a specific concentration of a test organism, followed by a Figure 5.41 Antimicrobial agent susceptibility assay using diffusion methods.  growing. Many antibiotics fall into this category. Bacteriocidal agents, by contrast, bind tightly to their cellular targets and by Determining the minimal inhibitory definition kill the cell. However, the dead cells are not lysed, and concentration (MIC) Discs contain antimicrobia Minimum agents are pl inhibitory on surface. concentration T. D. Brock Zones of low Antimicrobial concentration high growth inhibiti Review Key points Death is defined as a loss of membrane integrity and loss of electrical potential across the membrane Pushing growth conditions outside the “comfort zone” of bacteria leads to death Antimicrobials attack essential elements of bacterial life