Pathogens, Infection Cycle and Disinfection Methods

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Pathogens, Infection Cycle and Disinfection Methods Essay

Conditions that favor the growth of pathogens
Several conditions can influence the growth of pathogens. First of all, warm temperatures help bacteria to grow faster and spread to other organisms easier. Thus, the temperature of a human body, for example, is a good condition for pathogens to grow. Next, moist environments also contribute to the speed of growth for bacteria. Moreover, these conditions also include the presence of oxygen, although some types of pathogens can grow without oxygen as well (Ling et al., 2015). Pathogens, Infection Cycle and Disinfection Methods Essay.

Infection cycle
The cycle of infection has six elements. The first one is the agent – the organism that causes an infection. Second is the reservoir – the individual that transfers the infection. The third is the mode of escape – the path for the agent to leave the body of the reservoir and transfer to another organism. It can be respiratory (escape through one’s nose and throat by coughing or sneezing), gastrointestinal (escape through one’s secretions), and dermal (escape through lesions and wounds). The next link is the vector, the way of connecting the reservoir and the future host of the disease. It can be established through the air, direct contact, water, or insects. The fifth is the mode of entry – how the infection enters one’s body. The final element is the host – an organism that gets the disease.

Concept of Medical asepsis
Medical asepsis is the process of preventing the spread of infections by destroying the pathogen that has left one’s system.Pathogens, Infection Cycle and Disinfection Methods Essay.

Concept of sanitation and differences with the disinfection
Disinfection may be more effective than sanitation because it is used to destroy the bacteria currently present on the surface of one’s organism. Sanitation is meant for reducing the number of bacteria and their growth. Sanitation does not destroy all present bacteria and only lowers the rate of their occurrence.

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Levels of disinfection
The low level of disinfection can kill some types of bacteria and viruses. The intermediate level also destroys mycobacteria, while the high level of disinfection is supposed to clean out almost all types of pathogenic organisms, except some complex bacteria (Jain, Clezy, & McLaws, 2017). Pathogens, Infection Cycle and Disinfection Methods Essay.

Methods of disinfection
Chemical disinfection is the use of alcohol, acids, hydrogen peroxide, and other substances. Pasteurization can also be used to kill bacteria and disinfect without any activating agents. Ultraviolet radiation is a way to destroy some viruses as well.

Concept of standard precautions
One should follow a set of standard precautions to prevent the spread of diseases and their transmission to uninfected organisms. It can include hygiene, protective equipment, the use of cleaning supplies, disinfection, and correct waste disposal. For example, hand hygiene is extremely important in preventing the spread of many diseases (Jain et al., 2017).

Regulations of OSHA related to disposing infectious waste
Infectious waste is divided into multiple categories, where each type should be treated with specific precautions. These categories include contaminated sharps, blood, bodily fluids, body parts, and other infectious waste. All waste should be disposed of in safe containers that prevent leakage or spillage of waste. They should be marked and sealed before being stored or transported (Reinhardt, 2018).Pathogens, Infection Cycle and Disinfection Methods Essay.

Characteristic’s of Biohazard waste disposal
Biohazardous waste should be disposed of with precautions. All types of this waste should be sealed and marked with a biohazard symbol before any other activities (Reinhardt, 2018). Some of them should be incinerated, while others may be placed in special waste containers. Persons disposing of these materials should use approved containers and follow the directions for this particular type of waste.

Recommendation of OSHA related to Blood-Borne pathogen training
Training for dealing with Blood-Borne pathogens usually includes information about the epidemiology of Blood-Borne diseases, their symptoms, the ways to reduce exposure, information about protective equipment, and vaccines (Reinhardt, 2018). Training also teaches individuals to contact in case of contamination or exposure, and possible work practices to avoid or reduce exposure.

References
Jain, S., Clezy, K., & McLaws, M. L. (2017). Glove: Use for safety or overuse? American Journal of Infection Control, 45(12), 1407-1410.

Ling, L. L., Schneider, T., Peoples, A. J., Spoering, A. L., Engels, I., Conlon, B. P.,… Jones, M. (2015). A new antibiotic kills pathogens without detectable resistance. Nature, 517(7535), 455-459.

Reinhardt, P. A. (2018). Infectious and medical waste management. Boca Raton, FL: CRC Press.

The goal of disinfection of public water supplies is the elimination of the pathogens that are responsible for waterborne diseases. The transmission of diseases such as typhoid and paratyphoid fevers, cholera, salmonellosis, and shigellosis can be controlled with treatments that substantially reduce the total number of viable microorganisms in the water.

While the concentration of organisms in drinking water after effective disinfection may be exceedingly small, sterilization (i.e., killing all the microbes present) is not attempted. Sterilization is not only impractical, it cannot be maintained in the distribution system. Pathogens, Infection Cycle and Disinfection Methods Essay. Assessment of the reduction in microbes that is sufficient to protect against the transmission of pathogens in water is discussed below.

Chlorination is the most widely used method for disinfecting water supplies in the United States. The near universal adoption of this method can be attributed to its convenience and to its highly satisfactory performance as a disinfectant, which has been established by decades of use. It has been so successful that freedom from epidemics of waterborne diseases is now virtually taken for granted. As stated in Drinking Water and Health (National Academy of Sciences, 1977), “chlorination is the standard of disinfection against which others are compared.”

However, the discovery that chlorination can result in the formation of trihalomethanes (THM’s) and other halogenated hydrocarbons has prompted the reexamination of available disinfection methodology to determine alternative agents or procedures (Morris, 1975).

The method of choice for disinfecting water for human consumption depends on a variety of factors (Symons et al., 1977). These include:

its efficacy against waterborne pathogens (bacteria, viruses, protozoa, and helminths);
the accuracy with which the process can be monitored and controlled;
its ability to produce a residual that provides an added measure of protection against possible posttreatment contamination resulting from faults in the distribution system;
the aesthetic quality of the treated water; and
the availability of the technology for the adoption of the method on the scale that is required for public water supplies. Pathogens, Infection Cycle and Disinfection Methods Essay.
Economic factors will also play a part in the final decision; however, this study is confined to a discussion of the five factors listed above as they apply to various disinfectants.

The propensity of various disinfection methods to produce by-products having effects on health (other than those relating to the control of infectious diseases) and the possibility of eliminating or avoiding these undesirable by-products are also important factors to be weighed when making the final decisions about overall suitability of methods to disinfect drinking water. The subcommittee has not attempted to deal with these problems since the chemistry of disinfectants in water and the toxicology of expected by-products have been studied by other subcommittees of the Safe Drinking Water Committee, whose reports appear in Chapter III of this volume (Chemistry) and Chapter IV (Toxicity) of Drinking Water and Health, Vol. 3.

Organization of the Study
The general considerations noted in the immediately following material should be borne in mind when considering each method of disinfection. Available information on the obvious major candidates for drinking water disinfection—chlorine, ozone, chlorine dioxide, iodine, and bromine—is then evaluated for each method individually in the following sections. Other less obvious possibilities are also examined to see if they have been overlooked unjustly in previous studies or if it might be profitable to conduct further experimentation on them. Disinfection by chloramines is dealt with in parallel with that effected by chlorine because of the close relationship the former has to chlorine disinfection under conditions that might normally be encountered in drinking water treatment.

The evaluations in this report are not exhaustive literature reviews but, rather, are selections of the studies that, in the judgment of the committee, provide the most accurate and relevant information on the biocidal activities of each method of disinfection. The analytical methods that are described in this report are those that are most likely to be used by persons involved in disinfection research or water treatment. A review of all existing analytical methods, some of which may be more sophisticated than those described below, would be impractical within the constraints of time and space available and is not within the scope of this document.

After the methods of disinfection are examined individually, their major characteristics and biocidal efficacy are compared by means of summary tables and c · t (concentration, in milligrams per liter, times contact time, in minutes) values required for similar inactivations under identical conditions. The conclusions of the study are then recorded on the basis of this evidence.Pathogens, Infection Cycle and Disinfection Methods Essay.

General Aspects of Disinfection
In any comparison of disinfection methods, certain considerations should be discussed at the outset since they are relevant to most, if not all, methods. The quality of the raw water (i.e., its content of solids and material that will react with the disinfectant), treatment of the water prior to disinfection, and the manner in which the disinfectant is applied to the water will directly affect the efficacy of all disinfectants. Equally applicable to all methods are appropriate standards for verifying the adequacy of disinfection, differences in response to disinfectants between organisms that were obtained directly from the field and those that have been acclimated to laboratory culture, and the maintenance of potability from treatment plant to the consumer’s tap. The use of chlorination as presented in examples in the following pages does not imply that it is necessarily the method of choice. Rather, this method has been studied more thoroughly than other methods.

Raw Water Quality
In addition to potential pathogens, raw water may contain contaminants that may interfere with the disinfection process or may be undesirable in the finished product. Pathogens, Infection Cycle and Disinfection Methods Essay. These contaminants include inorganic and organic molecules, particulates, and other organisms, e.g., invertebrates. Variations among these contaminants arise from differences in regional geochemistry and between ground- and surface-water sources.

Disinfectant Demand
Many inorganic and organic molecules that occur in raw water exert a “demand,” i.e., a capacity to react with and consume the disinfectant. Therefore, higher “demand” waters require a greater dose to achieve a specific concentration of the active species of disinfectant. This demand must be satisfied to ensure adequate biocidal treatment.

Ferrous ions, nitrites, hydrogen sulfide, and various organic molecules exert a demand for oxidizing disinfectants such as chlorine. The bulk of the nonparticulate organic material in raw water occurs as naturally derived humic substances, i.e., humic, fulvic, and hymatomelanic acids, which contribute to color in water. The structure of these molecules is not yet fully understood. However, they are known to be polymeric and to contain aromatic rings and carboxyl, phenolic, alcoholic hydroxyl, and methoxyl functional groups. Humic substances, when reacting with and consuming applied chlorine, produce chloroform (CHCl3) and other THM’s. Water, particularly surface waters, may also contain synthetic organic molecules whose demand for disinfectant will be determined by their structure. Ammonia and amines in raw water will react with chlorine to yield chloramines that do have some biocidal activity, unlike most products of these side reactions. If chlorination progresses to the breakpoint, i.e., to a free-chlorine residual, these chloramines will be oxidized causing more added chlorine to be consumed before a specific free-chlorine level is achieved. This phenomenon is discussed more fully below.

The nature of the demand reactions varies with the composition of the water and the disinfectant. Removal of the demand substances leaves a water with a lower requirement for a disinfectant to achieve an equivalent degree of protection against transmission of a waterborne disease.

Physical and Chemical Treatments
Various treatments applied to raw water to remedy undesirable characteristics, e.g., color, taste, odor, or turbidity, may affect the ultimate microbiological quality of the finished water. Microorganisms may be physically removed or the disinfectant demand of the water altered. Pathogens, Infection Cycle and Disinfection Methods Essay.

Presedimentation to remove suspended matter, coagulation with alum or other agents, and filtration reduce the organic material in the raw water and, thus, the disinfectant demand. Removal of ferrous iron similarly reduces the demand for oxidizing disinfectants as will aeration, which eliminates hydrogen sulfide. Prechlorination to a free chlorine residual is practiced early in the treatment sequence as one method to alter taste- and odor-producing compounds, to suppress growth of organisms in the treatment plant, to remove iron and manganese, and to reduce the interference of organic compounds in the coagulation process.

The necessity for these treatments or others is determined by the characteristics of the raw water. The selection of one of the various methods to achieve a particular result will be based upon cost-effectiveness in the particular situation. When chlorination is used, the application or point of application in the treatment sequence of some of the above-mentioned procedures can affect the undesirable THM content of the finished water.

Reduction of precursors in raw water by coagulation and settling prior to chlorination reduces final THM production (Hoehn et al., 1977; Stevens et al., 1975). The Louisville Water Company reduced THM concentrations leaving the plant by 40%-50% by shifting the point of chlorination from the presedimentation basin to the coagulation basin (Hubbs et al., 1977). The available information on these variations is limited, and a universally applicable procedure cannot be recommended in view of the diverse treatments required for different raw waters.

Particulates and Aggregates
To inactivate organisms in water, the active chemical species must be able to reach the reactive site within the organism or on its surface. Inactivation will not result if this cannot occur. Microorganisms may acquire physical protection in water as a result of their being adsorbed to the enormous surfaces provided by clays, silt, and organic matter or to the surfaces of solids created during water treatment, e.g., aluminum or ferric hydrated oxides, calcium carbonate, and magnesium hydroxide. Viruses, bacteria, and protozoan cysts may be adsorbed to these surfaces. Such particles, with the adsorbed microorganisms, may aggregate to form clumps, affording additional protection. Organisms themselves may also aggregate or clump together so that organisms that are on the interior of the clump are shielded from the disinfectant and are not inactivated. Organisms may also be physically embedded within particles of fecal material, within larger organisms such as nematodes, or, in the case of viruses, within human body cells that have been discharged in fecal material.

To disinfect water adequately, the water must have been pretreated, when necessary, to reduce the concentration of solid materials to an acceptably low level. Pathogens, Infection Cycle and Disinfection Methods Essay.The primary drinking water turbidity standard of 1 nephelometric turbidity unit (NTU) is an attempt to assure that the concentration of particulates is compatible with current disinfection techniques. Where it is possible to obtain lower turbidities, this is desirable.

Disinfection studies in which the complications of adsorbed organisms, aggregation, or embedment were thought to occur were excluded from this study. The conclusions in this report should not be extrapolated to such situations as the disinfection of turbid or colored waters.

The Importance of Residuals
Water supplies are disinfected through the addition or dosage of a chemical or physical agent. With a chemical agent, such as a halogen, a given dosage should theoretically impart a predetermined concentration (residual) of the active agent in the water. From a practical point of view, most natural waters exert a “demand” for the disinfectant, as discussed above, so that the residual in the water is less than the calculated amount based on the dosage. The decrease in residual, which is caused by the demand, is rapid in most cases, but it may be prolonged until the residual eventually disappears. In addition, the chemical agent may decompose spontaneously, thereby yielding substances having little or no disinfection ability and exerting no measurable residual. For example, ozone not only reacts with substances in water that exert a demand, but it also decomposes rapidly. To achieve microbial inactivation with a chemical agent, a residual must be present for a specific time. Thus, the nature and level of the residual, together with time of exposure, are important in achieving disinfection or microbial inactivation. Because the nature of the dosage-residual relationship for natural waters has not been and possibly cannot be reliably defined, the efficacy of disinfection with a chemical agent must be based on a residual concentration/time of exposure relationship.Pathogens, Infection Cycle and Disinfection Methods Essay.

Residual measurements are important and useful in controlling the disinfection process. By knowing the residual-time relationship that is required to inactivate pathogenic or infectious agents, one can adjust the dosage of the disinfecting agent to achieve the residual that is required for effective disinfection with a given contact time. Thus, the effectiveness of the disinfection process can be controlled and/or judged by monitoring or measuring the residual.

Following disinfection of a water supply at a treatment plant, the water is distributed to the consumers. A persistent residual is important for continued protection of the water supply against subsequent contamination in the distribution system. Accidental or mechanical failures in the distribution system may result in the introduction of infectious agents into the water supply. In the presence of a residual, disinfection will continue and, as a result, offer continued protection to the users. Physical agents such as radiation may provide effective disinfection during application, but they do not impart any persistent residual to the water.

The dosage of a chemical agent that is used to effect microbial inactivation should not be so great that it imparts a health hazard to the water consumer. From another point of view, the aesthetic quality of the finished water should not be impaired by the dosage of the chemical agent or the residual that is required for effective disinfection. These qualities might include discoloration of water from potassium permanganate (KMnO4) or iodine or problems of taste and odor from excessive chlorine.

Application of the Disinfectant
Optimum inactivation occurs when the disinfectant is distributed uniformly throughout the water. To disperse the chemical disinfectant when it is added to the water, it must be mixed effectively to assure that all of the water, however small the volume, receives its proportionate share of the chemical. Additions of a disinfectant at points in a flowing water stream, e.g., from submerged pipes, is seldom adequate to assure uniform concentration. Pathogens, Infection Cycle and Disinfection Methods Essay. In such cases, mechanical mixing devices are needed to disperse the disinfectant throughout the water. Disinfection by radiation treatment also requires good mixing to bring all of the water within the effective radiation distance.

Microbiological Considerations1
Comparison of the biocidal efficacy of disinfectants is complicated by the need to control many variables, a need not realized in some early studies. Halogens in particular are significantly affected by the composition of the test menstruum and its pH, temperature, and halogen demand. For very low concentrations of halogen to be present over a testing period, halogen demand must be carefully eliminated. Different disinfectants may have different biocidal potential. In earlier work, analytical difficulties may have precluded defining exactly the species present, but new techniques allow the species to be defined for most disinfectants. Information on the species of disinfectant actually in the test system should be included in future reports on disinfection studies.

Investigators studying efficacy have usually adopted one of two extremes. Some have conducted carefully designed laboratory experiments with controls for as many variables as possible. Certain of these investigators have reduced the temperature to slow the inactivation reactions. Although these experiments yield good basic information and can be used to determine which variables are important, they often have little quantitative relationship to field situations. The other extreme, a field study or reconstruction of field conditions, is difficult to control. Moreover, their results are often not repeatable.

In addition to the variables noted above, prereaction of chemicals in the test system, the culture history of the organism being used, and the ”cleanup” procedures applied to it may also affect the observed results. Despite these problems, there have been some attempts to standardize efficacy testing.

Model Systems and Indicator Organisms
A major factor that influences the evaluation of the efficacy of a particular disinfectant is the test microorganism. There is a wide variation in susceptibility, not only among bacteria, viruses, and protozoa (cyst stage), but also among genera, species, and strains of the microorganism. It is impractical to obtain information on the inactivation by each disinfectant for each species and strain of pathogenic microorganism of importance in water.Pathogens, Infection Cycle and Disinfection Methods Essay. In addition, interpretation of the data would be confounded by the condition and source of the test microorganism (e.g., the degree of aggregation and whether the organisms were “naturally occurring” or laboratory preparations), the presence of solids and particulates, and the presence of materials that react with and consume the disinfectant.

The overwhelming majority of the literature on water disinfection concerns the inactivation of model microorganisms rather than the pathogens. These disinfectant model microorganisms have generally been nonpathogenic microorganisms that are as similar as possible to the pathogen and behave in a similar manner when exposed to the disinfectant. The disinfectant model systems are simpler, less fastidious, technically more workable systems that provide a way to obtain basic information concerning fundamental parameters and reactions. The information gained with the model systems can then be used to design key experiments in the more difficult systems. The disinfection model microorganism should be clearly distinguished from the indicator organism. The indicator microorganism, as defined in Drinking Water and Health (National Academy of Sciences, 1977), is a “microorganism whose presence is evidence that pollution (associated with fecal contamination from man or other warm-blooded animals) has occurred.” Following are criteria for the indicator microorganism (Fair and Geyer, 1954):

1.
The indicator should always be present when fecal material is present and absent in clean, uncontaminated water.

2.
The indicator should die away in the natural aquatic environment and respond to treatment processes in a manner that is similar to that of the pathogens of interest.

3.
The indicator should be more numerous than the pathogens.

4.
The indicator should be easy to isolate, identify, and enumerate.

Only a restrictive application of the second criterion is necessary for a disinfection model. The response of the test microorganism to the disinfectant must be similar to that of the pathogen that it is intended to simulate.Pathogens, Infection Cycle and Disinfection Methods Essay. The disinfection model is not meant to function as an indicator microorganism.

During the latter part of the nineteenth century, investigators recognized the presence of a group of bacteria that occured in large numbers in feces and wastewater. The most significant member of this group (currently called the coliform group) is Escherichia coli. Since the late nineteenth century, this coliform group has served as an indicator of the degree of fecal contamination of water, and E. coli has been used routinely as a disinfection model for enteric pathogens. Butterfield and co-workers (Butterfield and Wattie, 1946; Butterfield et al., 1943; Wattie and Butterfield, 1944) provided information on the inactivation of E. coli and other enteric bacterial pathogens with chlorine and chloramines. At pH values above 8.5, all strains of E. coli were more resistant to free chlorine than were Salmonella typhi strains. At pH values of 6.5 and 7.0, strains of S. typhi were more resistant. Only slight differences between the two genera were found when chloramines were used as the disinfectant. The bactericidal activity of chloramine was noticably less than that of free chlorine.

Bacteria of the coliform group, especially E. coli, have proved useful as an indicator and disinfection model for enteric bacterial pathogens but are poor indicators and disinfection models for nonbacterial pathogens. E. coli has been observed to be markedly more susceptible to chlorine than certain enteric viruses and cysts of pathogenic protozoa (Dahling et al., 1972; Krusé, 1969).

The bacterial viruses of E. coli have received increased attention as possible disinfection models and indicators of enteric viruses in water and wastewater. At present, the data to justify the bacterial viruses as indicators for enteric viruses are limited and inconsistent. Pathogens, Infection Cycle and Disinfection Methods Essay. However, there is a growing body of knowledge on the utilization of bacterial viruses as disinfection models.

Hsu (1964) and Hsu et al. (1966) first reported the use of the f2 virus as a model for disinfection studies with iodine. They showed that inactivation of both the f2 virus and poliovirus 1 were inhibited by increasing concentrations of iodide ion and that both f2 RNA and poliovirus 1 RNA were resistant to iodination.

Dahling et al. (1972) compared the inactivation of two enteric viruses (poliovirus 1 and coxsackievirus A9), two DNA phages (T2 and T5), two RNA phages (f2 and MS2), and E. coliATCC 11229 under demand-free conditions with free chlorine at pH 6.0. They found enteric viruses to be most resistant to free chlorine followed by RNA phages, E. coli, and the T phages.

Shah and McCamish (1972) compared the resistance of poliovirus 1 and the coliphages f2 and T2 to 4 mg/liter combined residual chlorine. The f2 virus was shown to be more resistant to this form of chlorine than poliovirus 1 and T2 coliphage.

Cramer et al. (1976) compared the inactivation of poliovirus 3 (Leon) and f2 with chlorine and iodine in buffered wastewater. Both viruses were treated together in the same reaction flask, thereby eliminating any inherent differences due to virus preparations and replicate systems. In wastewater effluent at pH 6.0 and 10.0 with a 30 mg/liter dosage of halogen under prereacted (halogen added to wastewater, allowed to react, viruses added at zero time) and dynamic (viruses added to wastewater, halogen added at zero time) conditions, f2 was, in each case, at least as or more resistant to chlorine and iodine than poliovirus 1. The f2 virus appears to be more sensitive to free chlorine but more resistant to combined chlorine than poliovirus 1 is. Pathogens, Infection Cycle and Disinfection Methods Essay.

Neefe et al. (1945) observed that the agent of infectious hepatitis was inactivated by breakpoint chlorination (free chlorine) but not completely inactivated by combined chlorine.

Engelbrecht et al. (1975) reported that the use of a yeast (Candida parapsilosis) and two acid-fast bacteria (Mycobacterium fortuitum and Mycobacterium phlei) may provide suitable disinfection models. They observed that the yeast was more resistant to free chlorine than were poliovirus 1 and the enteric bacteria under all conditions tested. The acid-fast bacilli were most resistant.

There is no generally accepted disinfection model for protozoan cysts. In disinfection studies for protozoan diseases, investigators have used the pathogen or its cysts. Work with such systems is, however, generally difficult.

The use of disinfection models provides useful information that is helpful to the comparison of the relative efficiencies of various disinfectants in the laboratory and in controlled field investigations. Strains of E. coli have been used extensively as models for enteric pathogenic bacteria. While not as widely accepted, the bacterial viruses of E. coli are used as disinfection models for enteric viruses. The difficulty of available methods has limited the number of disinfection studies with protozoan cysts.

Laboratory Cultures versus “Naturally Occurring” Organisms
The resistance or sensitivity to disinfectants of some bacteria (e.g., E. coli) in the laboratory may bear very little resemblance to their responses in nature. This is true in spite of the fact that standardized procedures govern the conditions under which cells are grown, harvested, washed, etc., when they are used as inocula. Examples of such differences range from Gram-negative bacteria and their comparative resistance to disinfectants in general (Carson et al., 1972; Favero et al., 1971, 1975) to Gram-positive bacterial spores and heat resistance (Bond et al., 1973) and to halogen resistance of Entamoeba histolytica cysts from simian hosts as opposed to those grown in in-vitro systems (Stringer et al., 1975). Presumably, the mechanisms creating this phenomenon among these three groups vary widely.

The comparative resistance to disinfectants among Gram-negative bacteria varies greatly. A good example of this is the study of Favero and Drake (1966). They first applied the term “naturally occurring” to certain Gram-negative bacteria with the potential for rapid growth in water. Pathogens, Infection Cycle and Disinfection Methods Essay. They observed that Pseudomonas alcaligenes, a common bacterial contaminant in iodinated swimming pools, could grow well in swimming pool waters that had been sterilized by membrane filters and rendered free of iodine or chlorine. Starting with contaminated swimming pool water that contained a variety of bacteria, they isolated a pure culture of P. alcaligenes by an extinction-dilution technique in which filter-sterilized swimming pool water was used as the diluent and growth medium. Since these cells had been isolated in pure culture without exposure to conventional laboratory culture media, they were referred to as “naturally occurring” P. alcaligenes. Subsequent tests showed that these naturally occurring cells were significantly more resistant to free iodine than were cells of the same organism that had been subcultured one time on trypticase soy agar. In fact, standard disinfectant tests using the cells that had been subcultured on an enriched laboratory medium suggested that P. alcaligenes should never be found in pools that had been disinfected even minimally with iodine. This was obviously an erroneous assumption. The discovery that naturally occurring cells were extremely resistant to iodine explained the relatively high concentrations of P. alcaligenes that accumulated in pool water that had been iodinated for several weeks.

Subsequently, Favero et al. (1971, 1975) and Carson et al. (1972) published a series of papers showing that Pseudomonas aeruginosa could grow rapidly in distilled water, which they obtained from hospitals, and could reach high concentrations of cells that remained stable for a long time. Naturally occurring cells that were grown in distilled water reacted quite differently to chemical and physical stresses than did cells grown on standard laboratory culture media. For example, naturally occurring cells of P. aeruginosa were significantly more resistant to chlorine, quaternary ammonium compounds, and alkaline glutaraldehyde than were subcultured cells. Pathogens, Infection Cycle and Disinfection Methods Essay.

In halogen-disinfected waters, naturally occurring bacteria can be from one to two orders of magnitude more resistant to the disinfectant than cells of the same organism that had been subcultured on conventional laboratory culture media. Since standard disinfectant testing necessarily employs subcultured and washed bacterial cells, a false sense of confidence may be created if these data are used as an absolute criterion for the dilution of a disinfectant. These results could explain the frequent discrepancies between tests that are performed under laboratory conditions and those that are performed under field conditions.

If bacteria could be used in their naturally occurring state, one might explore the possibility of bridging the gaps between laboratory and field conditions by using this experimental system. The ability of some Gram-negative bacteria to grow in water makes it possible to produce and control large numbers of cells for such studies.

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More difficult to answer is the more basic question of why naturally occurring cells of Gram-negative water bacteria become more sensitive to disinfectants when grown in a rich medium than the same strain when grown in water. One would expect the reverse to occur. Pathogens, Infection Cycle and Disinfection Methods Essay. Milbauer and Grossowicz (1959) showed that cells of E. coli were much more sensitive to chlorine when grown on a medium of glucose mineral salts than when grown on nutrient agar. Since Favero and Drake (1966) reported that filter-sterilized dehalogenated swimming pool water could be considered a minimal medium, one would expect that P. alcaligenes cells that were grown in this environment would be less resistant to iodine than those grown in trypticase soy broth. This phenomenon has not been explained. Evidently it is not primarily a genetic response since the extreme difference in iodine resistance occurs with one subpassage on trypticase soy agar.

Over the years various investigators have tried without success to “train” bacteria to become more resistant to chlorine and/or iodine (Favero, 1961; Favero et al., 1964; Krusé, 1969). This failure is not surprising, because, if halogens are truly a general cytoplasmic poison that affects primarily the sulfhydryl groups of enzymes (see pp. 36-39), it would be very difficult for an organism to modify its physiology to the extent that it becomes resistant, very unlike the situation with antibiotics and bacteria. Consequently, the extreme resistance or differing resistances of naturally occurring bacteria can be attributed only to “environmental” factors and, perhaps, to the different compositions of cell walls and membranes. However, there have been no data to substantiate this hypothesis.

Despite the questions that have been raised by differences in the behavior of organisms under both laboratory and field conditions, valuable comparative information can be obtained from studies of disinfectants that are conducted in similar laboratory systems. Pathogens, Infection Cycle and Disinfection Methods Essay.