Microbiology II Flashcards
Which of the following is true of human immunodeficiency virus?
(Please select 1 option)
Decreases the risk of opportunistic infection
Induces an increase in CD4 lymphocytes, monocytes and antigen-presenting cells
Is a single stranded DNA retrovirus
Patients can be infective prior to seroconversion illness at about three months
The median survival with AIDS is greater than 10 years
Patients can be infective prior to seroconversion illness at about three months
HIV is a single stranded RNA retrovirus.
It induces immunodeficiency and increases the risk of opportunistic infection (for example, histoplasmosis, Pneumocystis jirovecii) and malignancy (for example, Kaposi’s sarcoma).
Patients may have asymptomatic or symptomatic disease for several years before developing AIDS.
The median survival with full AIDS is less than two years.
Proteolytic enzymes are released by which one of the following organisms? (Please select 1 option) Clostridium botulinum Mycobacterium tuberculosis Neisseria meningitides Salmonella typhi Streptococcus pyogenes
Streptococcus pyogenes This is the correct answerThis is the correct answer
Virulence factors are important in the bacterial survival in vivo.
In this sense bacterial extracellular proteolytic enzymes can be recognised as the legitimate target for this approach since they are involved either in direct or indirect destruction of an infected/colonised tissue and in dysregulation of many host defence pathways.
The best example of the last is an effect of bacterial proteinases on fibrinolytic, kallikrein-kinin and complement cascades, as well as degradation of immunoglobulins, inactivation of endogenous proteinase inhibitors, and dysregulation of cytokine network system.
Proteolytic enzymes are responsible for the virulence and activity of organisms such as Strep. pyogenes, Staph. aureus, Escherichia coli and Clostridium welchii enabling the necrolytic effects on the skin in cellulitis and gangrene.
Micro-organisms that can cause latent infection do not include which of the following? (Please select 1 option) Chlamydia trachoma Cytomegalovirus (CMV) Hepatitis A Mycobacterium tuberculosis Varicella zoster virus
Hep A
Most commonly clinical tuberculosis represents delayed reactivation.
Varicella zoster virus remains dormant in the dorsal root ganglia and can cause latent infections such as shingles.
Over 50% of the adult population have serological evidence of latent infection with CMV, although infection is generally symptomless.
Hepatitis A is self-limiting and usually over in 3-6 weeks.
Chlamydia trachomatis can remain latent for years but can later cause blindness, infertility, and ischaemic heart disease.
Recognised virulence factors in bacteria do not include which of the following?
(Please select 1 option)
Beta lactamases
Gonococcal pili
Ig A-proteases
Streptococcal M protein
The capsular polysaccharides in Haemophilus influenzae
Beta lactamases
Virulence factors can be exotoxins or endotoxins (such as the cell wall of Haemophilus influenzae).
M protein on some bacteria prevent phagocytosis pili on gonococcus, allow them to adhere to mucosal surface.
Beta lactamase or penicillaminase hydrolyses penicillin but has no direct effect on host tissue.
Which of the following cutaneous manifestations is not correctly paired with its underlying disease? (Please select 1 option) Erythema induratum - syphilis Erythema infectiosum - parvovirus B19 Erythema marginatum - Lyme disease Erythema multiforme - orf Erythema nodosum - tuberculosis
Erythema marginatum - Lyme disease
Erythema nodosum. This is characterised by tender red swellings usually over the shins. The most common cause is streptococcal infection. Tuberculosis, sarcoidosis, leprosy, sulphonamides and inflammatory bowel disease are other important causes.
Erythema marginatum. This is a non-itchy, pale red, macular eruption. It is a major criterion for the diagnosis of rheumatic fever but is also seen in acute glomerulonephritis and drug reactions.
Erythema multiforme. This is characterised by cutaneous “target” lesions and mucosal involvement. Children and young adults are more commonly affected. Orf, Mycoplasma and herpes simplex are among the known causes.
Erythema induratum. Cutaneous tuberculosis. Otherwise known as Bazin’s disease.
Erythema infectiosum. “Slapped cheeks”, caused by parvovirus B19.
Erythema chronicum migrans. An expanding annular lesion occurring in Lyme disease.
Erythema gyratum repens. Erythema forming repeated concentric rings. Often there is an underlying malignancy.
The germination of tetanus spores in a wound is inhibited by which of the following? (Please select 1 option) Antiseptic dressings Normal oxygen levels Injection of anti-toxin Intravenous metronidazole Therapeutic immunisation of toxoid
Normal oxygen levels
Germination occurs in damaged tissue where damage to the blood supply has reduced the supply of oxygen.
Early careful debridement of devitalised tissue and removal of foreign bodies is a useful preventative measure.
Antitoxin should be promptly administered in all cases of suspected tetanus. It is ineffective when the toxin is already fixed in the central nervous system.
Because spores of C. tetani are so widely distributed the only effective way to control tetanus is by prophylactic immunisation with tetanus toxoid.
Which of the following is true regarding subphrenic abscesses?
(Please select 1 option)
Are commonly associated with hiccups
Are commonly asymptomatic
Are associated with lung consolidations
Cause splenomegaly
Require laparotomy and thorough peritoneal lavage
Are commonly associated with hiccups
Subphrenic abscesses are associated with a swinging fever and marked toxaemia.
Hiccups are common and are usually distressing.
The liver is usually pushed down by the diaphragm and is therefore palpable. They are not associated with splenomegaly.
On chest x ray pleural effusions are commonly seen as well as air in the subphrenic space, and occasionally an air-fluid level.
Most subphrenic abscesses can be treated with ultrasound guided drainage and systemic antibiotics.
Which one of the following is true of radiological imaging in a septic patient?
(Please select 1 option)
A chest radiograph is of little use in suspected intra-abdominal sepsis
A CT should be performed as soon as the diagnosis of severe acute pancreatitis is made
An indium-111 labelled white cell scan has a good sensitivity for identification of occult abscesses
Diagnostic ERCP is the investigation of choice in suspected obstructive biliary disease
Ultrasound is the investigation of choice to diagnose appendicitis
An indium-111 labelled white cell scan has a good sensitivity for identification of occult abscesses
An indium-111 labelled white cell scan has a good sensitivity for identification of occult abscesses
Which of the following is true regarding C-reactive protein (CRP)?
(Please select 1 option)
Is functionally analogous to immunoglobulin G (IgG)
Is increased when a patient is taking non-steroidal anti-inflammatory drugs (NSAIDs)
Is produced primarily in the affected tissue
Shows a less intense increase than the erythrocyte sedimentation rate (ESR) in acute inflammation
Synthesis is initiated by the release of adrenocorticotropic hormone (ACTH)
Is functionally analogous to immunoglobulin G (IgG
CRP is an abnormal protein produced by the liver during an acute inflammatory response.
Antigen-immune complexes to infecting agents and trauma initiate the synthesis of CRP.
Although functionally analogous to IgG it is not antigen specific.
CRP is more sensitive and responds more rapidly than ESR.
NSAIDs reduce the CRP response.
Which of the following is true regarding deep surgical site infections?
(Please select 1 option)
Are not related to rough handling of the tissues
Are usually asymptomatic
Can result in life threatening sequelae
Occur within sixty days of surgery if no implant is present
Rarely occur at the time of surgery
Can result in life threatening sequelae
They occur within 30 days of operation without an implant or up to one year with an implant.
The infecting organism usually originates from the patient’s own skin or from the theatre staff. They are usually associated with a fever (greater than 38°C) and pain.
Deep infections in a laparotomy wound can result in a spontaneous dehiscence.
Rough handling of the tissues results in tissue necrosis with subsequent infection.
In acute osteomyelitis, which of the following is correct?
(Please select 1 option)
Blood cultures are rarely positive
C-reactive protein changes slowly with the course of the disease
Joint aspiration should never be attempted
MR is the investigation of choice
Plain radiographs lag the clinical picture by 10 days
Plain radiographs lag the clinical picture by 10 days This is the correct answerThis is the correct answer
Blood cultures are positive in approximately 50% of patients.
CRP is the biochemical parameter of choice to monitor the condition.
Plain radiographs are usually normal in the early stages.
A three-phase bone scan is the investigation of choice.
The diagnosis is confirmed by culturing organisms from aspirated fluid or from operative samples.
In osteomyelitis which of the following statements is correct?
(Please select 1 option)
In the neonate it is commonly caused by anaerobes from the birth canal
Is frequently due to local blunt trauma
Is more common in the elderly
Is usually monofocal
Typically affects the epiphysis of the long bones
Is usually monofocal
In neonates the usual causative organisms are Streptococcus (group B), Staphylococcus aureus, and Gram positive bacteria.
Local blunt trauma causing subperiostal haematoma plays a small role, however, these haematomas then become infected by haematogenous spread (which is the commonest cause).
The most common age group affected is children aged 3 - 15 years.
It can also be multifocal, affecting multiple bones simultaneously.
The metaphyses of the long bones are most often affected due to the convoluted arrangement of end-arterioles trapping bacteria.
Which of the following is true regarding hepatitis C?
(Please select 1 option)
Can be prevented by vaccination
Carries a transmission risk of 30 - 40% following a needle stick injury
Has prevalence in the UK of
Has prevalence in the UK of
Which of the following is true regarding occupational infection with HIV?
(Please select 1 option)
Can occur rarely by percutaneous exposure
Is not related to the donor’s stage of disease
Is possible through aerosolisation of infected material
Is related to the population prevalence
Occurs more commonly in surgeons than other health care workers
Is related to the population prevalence
HIV is not contagious and therefore transmission does not occur by casual or social contact.
Percutaneous exposure to HIV-infected blood is the main route of occupational transmission.
Most reported cases of occupational acquisition of HIV have come from countries where there is a high prevalence of infected patients. Nurses and laboratory staff account for 71% of the reported cases.
The higher the viral load in the patient, the greater the risk of transmission.
Which one of the following is the normal flora found in the particular anatomical site? (Please select 1 option) Female genital tract: lactobacilli Nasopharynx: Propionibacteria Skin: Haemophilus spp Stomach: sterile Urinary tract: Escherichia coli
Female genital tract: lactobacilli
The normal flora found are:
Female genital tract: Flora of the large bowel plus Lactobacilli, Staphylococcus epidermidis, Streptococci, diphtheroids.
Nasopharynx: Staphylococci, Streptococci (including Pneumococci), Haemophilus spp., anaerobes.
Skin: Staphylococci, Streptococci, Propionibacteria.
Stomach: The acid content reduces the bacterial load, however, organisms can persist, for example, Helicobacter pylori.
Urinary tract: Normally sterile.
Which one of the following is untrue regarding hydradenitis suppurativa?
(Please select 1 option)
Can result in sterile abscesses
Complete excision of the affected tissue down to the deep fascia can be curative
Due to an antigen-antibody reaction
Occurs more often in overweight women
Represents an infection of the paracrine sweat glands
Represents an infection of the paracrine sweat glands This is the correct answerThis is the correct answer
This is a condition of the apocrine sweat glands. It is thought that it is an antigen-antibody complex clump that blocks excretion from the gland. The condition affects the axillae and perineum most often in overweight women.
Abscesses are commonly sterile and when pathogens are present they may represent commensal organisms.
The surgery can often be extensive and debilitating.
