Microbiology Flashcards

Question

Which of the following is true of Actinomyces israelii? (Please select 1 option) Colonies appear as sulphur granules Is a fast growing organism Is a frequent cause of urinary tract infection Is an aerobic organism Is Gram negative

Answer 1

Colonies appear as sulphur granules Actinomyces israelii species is a Gram positive, cast-forming, non-acid-fast, non-spore-forming anaerobic bacillus that is difficult to isolate and identify. Its filamentous growth and mycelia-like colonies have a striking resemblance to fungi. It is primarily a commensal microbe found in normal oral cavities, in tonsillar crypts, in dental plaques, and in carious teeth. Pathologically it can cause a keratitis, skin disease, tooth disease and wound infections. The organism is difficult to eradicate with surgery and extended penicillin-based therapy required.

Answer 2

Are neutralised by their homologous antitoxin Toxigenesis, or the ability to produce toxins, is an underlying mechanism by which many bacterial pathogens produce disease. At a chemical level, there are two types of bacterial toxins Lipopolysaccharides, which are associated with the cell walls of Gram negative bacteria, and Proteins, which are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth. The lipopolysaccharide toxins are referred to as endotoxins and the extracellular diffusible toxins are referred to as exotoxins. Exotoxins are soluble proteins produced by the living bacteria and are generally specific for the pathogenic bacteria involved (can be produced by both Gram positive and Gram negative bacteria, for example, enterotoxigenic Escherichia coli). Bacterial protein toxins are the most powerful human poisons known and retain high activity at very high dilutions. Their effect may be neutralised by the antitoxin and this is used as a treatment (toxoid).

Answer 3

May be transferred by conjugation between different strains Plasmids comprise a group of extra-chromosomal, usually circular, molecules of double-stranded DNA, and may contain genetic information for various bacterial characteristics, for example, toxin production, adhesins, etc. as well as enzymes. They can replicate autonomously (that is independently from the bacterial chromosome), and larger plasmids are transferred naturally by conjugation between bacterial strains. DNA transferred between bacteria can be integrated into the recipient host chromosome or maintained as a plasmid.

Answer 4

Enhance bacterial resistance to dehydration and phagocytosis Bacterial capsules are usually composed of polysaccharide and may be associated with mucoid colonial morphology. The slimy material functions as an anti-phagocytic agent and also protects the bacterial cell from the environment, for example, dehydration, and antibiotics which may be present. However, many important bacterial pathogens do not rely on capsules, for example, M. tuberculosis. Endotoxic shock is associated with the biological activity of Gram negative cell wall lipopolysaccharide (LPS), not capsules. Capsulated bacteria include Strep. pneumoniae and Pseudomonas. Although capsules may help to protect against antibiotics they do not transfer antibiotic resistance.

Answer 5

It is a severe infective process, but the skin initially appears normal In order to limit infection spread wide surgical excision is preferred to conservative excision. Benzylpenicillin is active against the main causative group of organisms, namely Streptococci. Antibiotics and supportive therapy are also administered. The skin initially appears normal as the pathology lies within the subcutaneous tissue and deep fascia. Necrotising fasciitis can arise without any history of injury, but can also follow operations or more localised infections.

Answer 6

Herpes simplex virus The Herpesviridae family of viruses are dsDNA viruses that include herpes simplex, Varicella zoster, cytomegalovirus (CMV) and Epstein-Barr virus (EBV). The influenza virus belongs to the Orthomyxoviridae family, and enteroviruses belong to the Picornaviridae family. Both are ssRNA viruses. Rotavirus and cystovirus are dsRNA viruses.

Answer 7

Epstein-Barr virus (EBV) The Herpesviridae family of viruses are dsDNA viruses that include herpes simplex, Varicella zoster, cytomegalovirus (CMV) and EBV. The papilloma virus, a small dsDNA virus, is a member of the Papovavirus family. Rabies, an ssRNA virus, is a member of the Rhabdovirus family.

Answer 8

Signifies previous hepatitis B infection This is the correct answerThis is the correct answer Elevated titres of anti-HBs are produced during recovery from hepatitis B (after about 3-6 months) and following immunisation. There is also usually a raised anti-HBc after previous infection but not after immunisation. These indicate immunity to this infection. During the incubation period HBsAg and HBeAg (an indicator of viral replication) are elevated. Anti-HBc is the first antibody to appear early in the illness. High titres of IgM anti-HBc suggest an acute and continuing viral replication in the period (variable: around 3-6 months) after HBsAg has disappeared and before anti-HBs is present.

Answer 9

Influenza B infection Lymphocytosis may be found in infection with ``` EBV CMV Toxoplasmosis Rubella Acute HIV infection. Atypical lymphocytosis is not a feature of influenza B infection. ```

Answer 10

Bordetella pertussis, if present, is more likely to be recovered from a nasopharyngeal swab than a throat swab This scenario describes a baby with whooping cough. This illness tends to be more severe in younger infants, the organism responsible being Bordetella pertussis. This is more likely to be isolated from a nasopharyngeal swab than a throat swab. Clinical manifestations include: ``` A paroxysmal cough (100%) Whoops (60%) Dyspnoea Apnoea Emesis, and Leucocytosis with an absolute lymphocytosis (more than 10 ×109/L) is characteristic. Complications include: ``` ``` Pneumonia Bronchiectasis Emphysema, and Pneumothorax. The forcefulness of the paroxysms often results in subconjunctival haemorrhages. ```

Answer 11

Salmonella paratyphi There are numerous micro-organisms associated with osteomyelitis, with the commonest including ``` Staph. aureus Enterobacter Pseudomonas Streptococcus. Mycobacterium TB may be a rare cause of osteomyelitis, but Mycobacterium avium spp. would be particularly unusual. ``` Similarly S. paratyphi is associated with gastroenteritis, but other strains of Salmonella may cause osteomyelitis.

Answer 12

May cause autoimmune haemolytic anaemia Infectious mononucleosis, caused by Epstein-Barr virus, is spread through droplet infection or saliva. The incubation period is usually four to five weeks. Blood film shows lymphocytosis with many atypical lymphocytes. Heterophil antibodies develop (Paul-Bunnell test or monospot) early and disappear after about three months. Epstein-Barr virus specific IgM implies current infection, while IgG suggests that the patient has been previously infected. The complications of Epstein-Barr virus infection include ``` Encephalitis Autoimmune haemolytic anaemia Guillain-Barré syndrome Renal failure Pneumonitis Meningitis Hepatitis. Epstein-Barr virus infection is associated with the development of Burkitt's lymphoma and nasopharyngeal carcinoma. ```

Answer 13

Are lipopolysaccharides Endotoxins are lipopolysaccharides of the cell walls of Gram negative bacteria and released following cell death. Typically, larger amounts are required to produce effect compared with exotoxins. They are responsible for producing numerous effects of the infection (for example, Escherichia coli 0157) including Fever Disseminated intravascular coagulation (DIC) Myolysis. Endotoxins are often heat resistant.

Answer 14

Eye protection should always be worn during every procedure Surgeons should wear clean, comfortable antistatic shoes. If there is a risk of fluid spillage then boots should be worn. Paper masks should not be used as they become wet within a few minutes and lose their barrier qualities, masks should be made from disposable fibres. Double gloving is expensive, results in more discomfort, reduced sensitivity and dexterity and adds little additional protection. Eye protection should be worn in every case to protect the mucous membranes of the eyes. It is not necessary for surgeons to remove beards, however, a beard should be fully covered by a mask and hood of the balaclava type.

Answer 15

Is a recognised cause of the haemolytic uraemic syndrome This is the correct answerThis is the correct answer Escherichia coli 0157 / H7 characteristically cause a haemorrhagic colitis with abdominal pain but little or no fever. Pseudomembranous colitis is associated with Clostridium difficile. An outbreak of 500 cases in the USA was described in 1993. This outbreak was associated with the consumption of hamburgers. There were over 50 cases of haemolytic uraemic syndrome and 4 fatalities. The source of an outbreak in Wishaw, Scotland in 1996 was a butcher's. There were over 500 cases and 18 fatalities.

Answer 16

Measles vaccine Most live virus vaccines are contraindicated in patients who are HIV infected.

Answer 17

Are destroyed by povodine iodine Staph. epidermidis is part of the normal skin flora. As for Staph. aureus, Gram positive cocci in bunches are seen on microscopy. It is usually insensitive to penicillin. Although it is often a contaminant in blood cultures, it is associated with line infections. Central venous catheters are an especially likely site of infection even in the absence of overt exit site sepsis. They should not be ignored but interpreted in the clinical context, and usually the blood cultures should be repeated. In patients with central lines, blood cultures should be taken both peripherally and from the central line as semi-quantitative microbiological techniques are available that may point to the central line as the principal site of infection.