Microbiology - Problem Drill 12: Principles of Disease and Epidemiology

Transcription

1 Microbiology - Problem Drill 12: Principles of Disease and Epidemiology No. 1 of Which term is NOT used to describe the occurrence of a disease in a human population? (A) Epidemic (B) Enzootic (C) Zoonoses (D) Outbreak When a disease occurs suddenly in a population with expected number of cases above that which is normally expected. Moderate prevalence of a disease in animals is termed enzootic. Animal diseases that can be transmitted to humans are termed zoonoses.e.g.recently all over the world, there was an outbreak of bird flu, which is transmitted from chicken to man. Sudden unexpected occurrence of a disease usually focally or in a limited segment of a population is called an outbreak. Epidemiology is a science which deals with occurrence of diseases, its distribution and control. An epidemiologist uses different terminologies to describe types of diseases, its determinants, factors responsible, etc.e.g; pandemic, epidemic, sporadic etc.pandemic is a disease which occurs over a large region in the world. AIDS is the first pandemic of the second half of the twentieth century. The terms used in animal epidemiology are slightly different from those used here. The words used in epizootiology (animal epidemiology) are enzootic,panzootic,etc.

2 No. 2 of Which definition best describes a commensal relationship? (A) Two species living together benefit from each other. (B) Two species live together but only one is benefited and the other is neither harmed nor helped. (C) Two species live together but none are benefited. (D) Two species start living together but one end up eating the other. This relationship is called mutualism. Commensalism is the relationship in which one member is benefited and the other is not affected. This relationship is called neutralism. This is called parasitism. Commensalism is a relationship in which one organism, the commensal, benefits while the host is neither harmed nor helped. Often both the host and the commensal eat at the same table. The spatial proximity of the two partners permits the commensal to feed on substances captured or ingested by the host. In many instances, the commensal is also provided with shelter by living either on or in the host. The commensal is not directly dependant on the host metabolically and causes it no particular harm. Example E.coli living in human colon benefits from the nutrients, warmth, and shelter found there but usually causes no disease or discomfort to the host.

3 No. 3 of The most significant reservoir of human infection is (A) Water (B) Human population (C) Soil (D) Animals Incorrect! Water is a major reservoir but not as significant as humans. It is a universal solvent used daily but only stagnant water or sewage water poses a threat and can be considered as a disease reservoir. Humans release billions of pathogenic bacteria through their faeces into water, which if ingested by a healthy individual can cause disease. Correct! Human beings are social animals and they live in a community in constant contact with each other. Because of their large numbers and bigger body size, they harbor organisms in a large numbers in and on their bodies, which can cause infections. This is also an important reservoir but not as significant as the human reservoir. Soil borne diseases are transmitted rarely to man. They are generally caused to people who work on fields or when a person has an open wound and then is exposed to soil. Though an important reservoir of pathogens but not as significant as the human body, because only a few diseases are transmitted from animals to man. Also, since pathogens are often species specific, they don t cause as much harm to humans with the exception of a few diseases. A reservoir is the location where a pathogen is normally found living and from which infection can occur. Reservoirs can be animate or inanimate. Examples of animate reservoirs are humans, animals, insects etc and inanimate sources of infection include: soil, water, animal or human excreta etc. Carriers are human reservoirs that though they carry a pathogen, they don t suffer from the disease. Carriers are of four types; active, convalescent, healthy, incubatory. Active carrier has an overt clinical case of the disease. Convalescent carrier is the one who has just recovered from a disease but still harbors a large number of the pathogen, which can cause the disease. An incubatory carrier is one who is incubating the organism in large numbers but has not yet developed the disease.

4 No. 4 of Lungs are generally free of microorganisms because of the followings EXCEPT. (A) Mucus (B) Oxygen (C) Lysozyme of nasal mucus (D) Coughing & sneezing Micro organisms are removed by the continuous stream of mucus produced by the ciliated epithelial cells. Oxygen should facilitate growth of aerobic bacteria it however has limited effect over all. Nasal mucus contains an anti bacterial substance called lysozyme which lyses bacteria by hydrolyzing the bond connecting N-acetyl muramic acid and N-acetyl glucosamine in the bacterial cell wall peptidoglycan. Coughing and sneezing reflexes clear the respiratory system of organisms by expelling air forcefully from the lungs through the mouth and nose respectively. The mammalian respiratory system has formidable defense mechanisms. Once inhaled, an organism must first survive and penetrate the air filtration system of upper respiratory and lower respiratory tracts. The micro organisms due to turbulence get deposited on the mucocilliary blanket of respiratory epithelium. Coughing & sneezing reflexes clear the respiratory system of organisms by expelling air forcefully from the lungs through the mouth and nose, respectively.

5 No. 5 of Which of the following makes the skin surface a hostile micro environment for colonization by pathogens? (A) Skin lotions (B) Abundance of moisture (C) Acidic ph and dryness of skin (D) Use of deodorants This in fact helps the wellness of skin. B. Incorrect! Water is needed for growth of organisms. In fact it will aid in the colonization by the pathogens. C. Correct! The acidic ph of the skin discourages colonization by many microorganisms. Deodorants have an antibacterial substance which kills gram positive bacteria but not gram negative bacteria. The skin of a person varies depending on the body location. Skin on the hands, feet, neck is dry skin on the palms, scalp, under arms, genitourinary and anal areas is moist. This leads to the colonization of totally different kinds of microbes in these places. Moisture abundant areas have more flora compared to dry areas. The flora on dry areas is typically dormant. Staphylococci present on the skin produce organic acids usually at low ph (4.6), which discourages certain groups of bacteria. This results in the productin of body odor. Deodorants preferentially kill gram positive bacteria but can lead to overgrowth of gram negative bacteria. The, skin is a dynamic organ having a great deal of bacterial activity.

6 No. 6 of Which of the following is a major microorganisms of adult female genital tract? (A) Streptococcus faecalis (B) Lactobacilli (C) Cornybacterium sps (D) None of the above It is occasionally found in the distal portion of the urethra. It is an acid tolerant bacterium which breaks down the glycogen produced by the vaginal epithelium forming lactic acid. It is rarely found in the urethra. D. Incorrect There is one correct answer above. The genitourinary tract consists of kidneys, ureters and urinary bladder. These three parts are generally free of microorganisms. In females, microbiota is complex within the tract due to mucus secretion and flora changes as a consequence of the menstrual cycle. Lactobacilli are present in large numbers in the vagina. Lactobacilli break down the glycogen produced by the vaginal epithelium and forms lactic acid. So the ph of vagina is 4.4 to 4.6. The most commonly observed organisms of the vigina in descending order of abundance are Lactobacilli, bacteroids, cornybacteria and staph.epidermis.

7 No. 7 of Which is a sterile organ in our body? (A) Skin (B) Lungs (C) Colon (D) None of the above The skin is home to billions of bacteria. Since it has a large surface area, it provides a favorable environment for bacteria to grow. Lungs are sterile because microorganisms are constantly removed by mucus and alveolar macrophages. The colon has the largest microbial population in the body. There is one organ mentioned above that is sterile. Skin is directly exposed to the atmosphere which is rich in all kinds of microorganisms. Excretion in the case of colon whish has ~300 different types of microbes.

8 No. 8 of Gnotobiotic animals tend to get infected if exposed to the environment by the following organisms EXCEPT (A) Staphylococci (B) E.histolytica (C) E.coli (D) Streptococcus mutans Staphylococci are micro floras which will colonize any susceptable host. E.histolytica feeds on E.coli and since these germ free animals do not have E.coli in their colon, E.histolytica does not colonize these animals. E. coli are normal biota and will attempt to colonize a susceptable animal.. Pathogenic and would attempt to infect a susceptible animal. Germ free animals are generally kept in separate aseptic enclosures and handled aseptically. Since they are born in sterile environment and fed sterile food, their colon lacks the usual flora of a normal animal. Amoebic dysentery is the consequence of infection by the protozoan Entamoeba hystolytica which feed on the microbiota of the gut. Organisms like Staphylococci, E.coli and S.mutan will infect a susceptible target animal.. Once the gut flora is established in the colon of gnotobiotic animals the Entamoeba hystolytica can attack and cause disease.

9 No. 9 of When a breast fed baby is weaned to a bottle, its gut flora changes as follows: (A) Lactobacilli to Bifidobacterium (B) Bifidobacterium to lactobacilli (C) Lactobacilli to E.coli. (D) Bifidobacterium to staphylococci When the baby is on mothers milk, this milk is rich in a disaccharide sugar, which is an important growth factor of Bifidobacterium and not lactobacilli.hence,bifidobacterium colonizes and not lactobacilli. Human milk contains a disaccharide amino sugar that Bifidobacterium requires as a growth factor. Once it is shifted to another milk soucrce the,bifidobacterium growth factor is depleted. Lactobacilli flourish in milk. Therefore it will not be replaced by E.coli. There is a replacement of Bifidobacterium but not by staphylococci because staphylococci do not thrive in the gut. The gut flora is an ever changing dynamic population depending on what is eaten. Example a cow eats plants, the plant material consists chiefly of cellulose, pectin and starch. Hence the chief organism present in rumen (the stomach of herbivore) are cellulolytic bacteria, example Bacteroids succinogenes and Ruminococcus flavofaciens. Similarly a new born human baby it is initially breast fed. Human milk has a sugar, which only bifoidobacterium can metabolize hence we see a flourishing of bifidobacterium. But as the baby is shifted to other milk other organisms like lactobacilli which can degrade milk start colonizing.

10 No. 10 of After heavy antibiotic treatment in a female, the predominant microorganism in the vagina is. (A) Lactobacilli (B) Candida albicans (C) E.coli (D) None of the above Lactobacilli are the normal flora of the vagina, but after antibiotic treatment, it is eliminated as antibiotics kill them. Candida albicans are present in small numbers in the vagina. They are unable to colonize due to the presence of lactobacilli but the absence of lactobacilli they multiply and cause vaginal infections. E.coli is very rarely found in the vagina. They are predominantly found in gut. There is one correct answer above. In females, due to the hormone estrogen, the vaginal epithelium produces increased amounts of glycogen. Lactobacillus species called Doderleins bacilli degrade this to form lactic acid. This also keeps the other pathogens in check. Cervical mucus also has some antibacterial activity. But soon after any antibiotic treatment in a woman, the lactobacilli are killed along with the infectious agent being treated. The lack of lactobacilli allows organisms like Candida albicans to multiply and cause vaginal infections. That is the reason why doctors recommend a diet rich in curd or yogurt or vitamin B supplements soon after antibiotic treatment.