Infection Flashcards
25595 – In relation to the toxins of Staphylococcus aureus
1: the enterotoxins are superantigens
2: most are cell wall associated
3: the systemic effects of toxic shock syndrome toxin are mediated by the release of cytokines
4: none have haemolytic activity
TFTF
Robbins 5th ed. Page: 335
13992 – Virulence factors found associated with Staphylococcus aureus include all of the following except
A. the enzyme coagulase
B. surface receptors that enable them to bind to host cells
C. enterotoxins
D. a variety of lytic enzymes (lysins)
E. lipid A endotoxin
E
Refer to Textbook of Surgery, Robbins, 6th Ed, Ch 9, page 365
22124 – Pneumonia caused by Streptococcus pneumonia
1: commonly causes residual fibrosis in the affected area of lung
2: is uniformly responsive to penicillin therapy
3: results in blood shunting through affected lung
4: is usually a community acquired infection
FFTT
Robbins 5th ed. Chapter: 15 Pages: 694-696
15949 – S: Pneumococcal pneumonia causes inflammation without significant lung necrosis because R: pneumococci induce chemotaxis, but elaborate no major toxins.
S is true, R is true and a valid explanation of S
There is some necrosis of pneumocytes - probably more from the attentions of leukocyte enzymes and oxidising free radicals than from the pneumococci. However, there is no tissue necrosis as we mean the term (eg staphylococcal abscess; infarct), with destruction of alveolar wall lattice-work. Therefore, regeneration of pneumocytes and resolution of inflammation leads to restoration of normality. Pneumococci produce a-haemolysis ie there is some tissue damage possible, but this is negligible - hence elaborate no major toxins.
8707 – The bacterium Enterococcus faecalis
1: is an increasingly important nosocomial pathogen
2: is susceptible to cephalosporins
3: reveals increasing resistance to vancomycin
4: should be considered in intra-abdominal sepsis originating from the upper gastrointestinal tract
TFTT
Smith & Payne, Aust NZJ, Surgery 1994; Smith & Payne, Integrated Basic Surgical Sciences, Ch
37.2
11672, 25984 – Cell walls of Gram-negative bacteria
1: have proteinaceous pores (porins) in the outer membrane
2: are a useful taxonomic aid
3: contain endotoxin in the form of lipopolysaccharide
4: may act as a barrier to the entry of antimicrobials
TTTT
J.M.B. Smith.
Although thinner than the cell wall of Gram-positive bacteria, the cell wall of Gram-negatives is more complex and is responsible for many of the intrinsic properties of Gram-negatives. This applies especially to the so-called outer membrane (OM) - a lipid bilayer external to the peptidoglycan structural backbone. Most antibiotics are not lipid soluble and have difficulty diffusing passively through this membrane; in order to penetrate they must disrupt the layer (eg cationic compounds such as gentamicin), be carried actively through the membrane, or pass through it via the water filled porin channels that bisect the membrane (eg water soluble antibiotics of sufficiently small molecular size). Extruding from the surface of the OM is the polysaccharide ‘tail’ of the lipopolysaccharide (LPS). The lipid A component of LPS is the classical endotoxin of Gram-negatives (although endotoxin and LPS are often used synonymously), while the polysaccharide portion is used in the taxonomy of many Gram-negatives (O or somatic antigen).
21788 – Gram negative bacterial lipopolysaccharide complexes, when injected intravenously
1: produce arteriolar dilatation
2: activate complement through the alternate pathway
3: injure endothelial cell membranes
4: inhibit intrinsic pathways of coagulation
TTTF
Robbins 6th ed. Page: 134-136
12991 – In patients with Gram-negative septicaemia, shock is commonly caused by
1: bacterial endotoxins
2: bacterial exotoxins
3: bacterial lipopolysaccharide
4: products of complement activation
TFTT
Endotoxins are a feature of Gram negative bacteria, and are associated with the lipopolysaccharide portion, in particular the lipid A (glycolipid), of the outer membrane of the cell wall. Liberation of these endotoxins from dying bacteria is responsible for the classical ‘shock’ seen in Gram negative septicaemia (A and C true); exotoxins are only rarely of significance in Gram negative bacteria (eg exotoxin A of Pseudomonas aeruginosa) and have more specific actions (B false). Pathophysiological features associated with the liberation of endotoxin include complement activation (D true), fever, and irreversible collapse of the microvascular circulation.
14813 – The bowel commensal Escherichia coli is a major causative agent of
1: haemorrhagic colitis
2: bacteraemic episodes in the early stages of peritonitis
3: vaginitis
4: osteomyelitis in IV drug abusers
TTFT
Refer to Robbins, 6th Ed, Ch 18, 24, page 807-809, 1039, 793, 1230.
25579 – Pseudomonas aeruginosa is
1: one of the few Gram negatives to elaborate a significant exotoxin
2: widely distributed in the hospital environment
3: readily contained by normal host defences
4: an important pathogen in burns units
TTTT
Robbins 5th ed. Pages: 352-353
25584 – Anaerobic Gram negative bacteria
1: are important pathogens following faecal leakage during colonic surgery
2: are important pathogens in lung abscesses following aspiration
3: are frequently associated with more oxygen tolerant microbes in lesions
4: include Clostridium perfringens
TTTF
Robbins 5th ed. Pages: 338-340
4: gram-positive anaerobes
25564 – The obligate anaerobe Bacteroides fragilis
1: is seldom resistant to clindamycin
2: has a capsule which is significant in abscess formation
3: is the most common anaerobe associated with intra-abdominal sepsis
4: is the only gut anaerobe associated with intra-abdominal abscesses
FTTF
Robbins 5th ed. Page: 339-340 Aust. NZ Journal Surgery
8717 – With intra-abdominal abscesses involving Bacteroides fragilis
1: surgical intervention is required wherever possible
2: the presence of the microbes polysaccharide capsule is an important virulence factor
3: metronidazole alone is satisfactory cover during any attempted needle aspiration process
4: other microbes are unlikely to be involved
TTFF
Smith & Payne, Aust, NZ Journal 1994; Smith & Payne, Integrated Basic Surgical Sciences, Ch 37.2
12986 – Bacterial exotoxins
1: sometimes produce severe local and distant effects
2: are generally more toxic than endotoxins
3: often stimulate the production of antibodies which provide a good measure of immunity
4: are characteristically complex lipopolysaccharide molecules
TTTF
Exotoxins may produce severe local effects, as in gas gangrene, and serious effects at sites distant from the portal of entry, as in tetanus (A true). Bacterial exotoxins are classically proteinaceous in nature (D false), as compared to endotoxins which are lipopolysaccharide. They are highly immunogenic (C true). They are secreted during the growth of many Gram positive bacteria (eg staphylococci, streptococci, corynebacteria, clostridia), unlike endotoxins which are liberated from the
cell wall of Gram negative bacteria following lysis. As a general rule, exotoxins are more potent than endotoxins (B true) and tend to have a more specific site of action.
25484 – Bacterial exotoxins differ from endotoxins in being
1: lipopolysaccharide in nature
2: convertible into toxoids
3: predominantly heat stable
4: cell wall associated
FTFT
Update Mp PAGE: 8 IBSS, Ch 37.2, p782-793.
11682, 25479 – Exotoxins are produced by
1: Corynebacterium diphtheria
2: Clostridium difficile
3: Staphylococcus aureus
4: Pseudomonas aeruginosa
TTTT
Robbins 5th ed. Pages: 318; 319; 335-340 Microbiology Update: PMP8.
Bacteria classically elaborate two types of toxins - exotoxins which are proteinaceous high molecular weight, antigenic compounds actively secreted by growing bacterial cells and which can have a variety of functions (eg tetanus toxin, staphylococcal enterotoxins), and endotoxins which are the lipid A portion of the outer membrane lipopolysaccharide component of the Gram-negative cell wall. Endotoxins are highly inflammatory compounds and initiate a series of events (starting with activation of excessive amounts
of cytokines such as tumour necrosis factor with subsequent vascular endothelial damage) leading to the classic endotoxic or septic shock syndrome (NB a similar series of events can be induced by some toxins from Gram-positive bacteria). As Gram-positives do not posses an outer membrane in the cell wall structure, endotoxins are limited to Gram-negative bacteria (eg E. coli, pseudomonads). In comparison, few Gram-negatives elaborate exotoxins which are a feature of Gram-positive bacteria (eg staphylococci, clostridia). Pseudomonas aeruginosa is one of the few Gram-negatives to excrete a significant exotoxin.
22063 – Lesions in which negligible polymorph infiltration accompanies extensive tissue injury include
1: streptococcal myositis
2: clostridial myositis
3: Cryptococcus neoformans meningitis
4: tuberculosis lymphadenitis
FTTT
Robbins 6th ed. CHAPTER: 9 Pages: 367; 369; 379
10383, 15177 – Necrotising fasciitis
1: commonly involves the deep underlying muscle
2: can be monomicrobial in aetiology
3: has diabetes mellitus as one of the common predisposing factors
4: always involves obligate anaerobes
FTTF
Refer to Smith & Payne, ANZ Journal of Surgery 1994.
Necrotising fasciitis involves the areolar
tissue layers under the skin [really the fibrous tissue overlying muscles (superficial) and structures such as nerves and blood vessels (deep fascia)]. Where muscle is involved, the term myositis is applicable; in contrast to fasciitis, the primary location of infection is skeletal muscle. Although group A streptococcal (Streptococcus pyogenes) necrotising fasciitis has received recent publicity world wide (‘the flesh eating bug’), this bacterium is not the dominant cause of necrotising fasciitis. The microbial aetiology is usually polymicrobial, involving at least one obligate anaerobe (eg peptostreptococci) in combination with one or more facultative anaerobes (eg Gram-negative enteric bacilli, Staphylococcus aureus, St. pyogenes) or aerobic (eg Pseudomonas aeruginosa) species. S. aureus and St. pyogenes appear more commonly when infections involve the extremities or head and neck region. Monomicrobial infections (eg with S. aureus) occurs in only about 10% of cases. Predisposing associations include diabetes and peripheral vascular disease, trauma, alcoholism, surgery and the use of anti-inflammatory agents (eg NSAIDs). Treatment strategies include excision (with a margin) of involved tissues, and appropriate antimicrobial therapy. In light of the known causal agents, empiric therapy with the likes of cefuroxime (anti-staphylococcal and streptococcal) plus
ciprofloxacin (anti-Gram negative bacilli) plus clindamycin or metronidazole (for anaerobes) makes sense. On a pharmacokinetic bases, penicillin and flucloxacillin would appear inferior to the likes of cefuroxime for staphylococci and streptococci. Following microbiological investigations, more specific
therapy can be initiated.
25589 – Which one of the following statements does NOT apply to gas gangrene (clostridial myonecrosis)
A. disease is exacerbated by the presence of foreign bodies
B. is associated with marked oedema and necrosis of involved muscle
C. lesions reveal marked infiltration by neutrophils
D. blood may appear completely haemolysed in the terminal stages
E. gas bubbles appear early in the gangrenous tissues
C
Robbins 5th ed. Page: 339
25605 – Clostridial myonecrosis
1: is most commonly caused by Clostridium septicum
2: commonly involves tissues with an impaired blood supply
3: has a mortality rate less than 5%
4: apart from debridement, requires the use of high dose gentamicin therapy
FTFF
Aust. N.Z.J. Surgery Paper Textbook Surgery - Clunie 97
1: c. perfringens
4: gent not effective in anaeorobes
25509 – Clostridium perfringens
1: is an obligate aerobe
2: relies on the presence of a capsule for its virulence
3: is susceptible to metronidazole
4: is an important microbe to be considered when formulating antibiotic prophylaxis for lower limb amputation
FFTT
Robbins 5th ed. Antibiotic Supplement
1/2: gram +ve anaerobes
18304 – Which one of the following statements applies most correctly to synergistic gangrene (chronic progressive bacterial gangrene)?
A. Crepitus is an early physical sign
B. The presence of crepitus confirms clostridial infection
C. The overall mortality rate is about 10%
D. Hyperbaric oxygen is the treatment of choice
E. Clostridium perfringens is usually involved in the process
C
Synergistic gangrene occurs in debilitated patients and has a significant mortality of around 10% (C). Crepitus is not usually an early sign and if present, does not confirm clostridial infection. Hyperbaric oxygen therapy is adjunctive to surgery, and Clostridium perfringens is not the common organism.
12674 – S: Synergistic gangrene responds dramatically to high doses of penicillin because R: Synergistic gangrene is typically due to clostridial infection
both S and R are false
Synergistic bacterial gangrene is caused by anaerobic streptococci in association with other bacteria, eg Proteus, pseudomonas, Staphylococcus aureus, beta-haemolytic streptococci, anaerobes (R false). The condition presents with swelling and pain followed by necrosis of local skin and subcutaneous tissues. Wide excision and drainage are mandatory; antibiotic therapy is only complementary (S false).
12969 – Principles to be followed in the treatment of tetanus include
1: surgical excision of the wound which is left open
2: administration of penicillin intravenously
3: administration of human hyperimmune globulin intramuscularly
4: sedation of the patient and respiratory support
TTTT
Tetanus is attributed to the anaerobic spore former, Clostridium tetani. Spores in the environment enter cutaneous wounds, and if conditions for germination and growth of the microbe occur - eg necrotic devitalised tissue, anaerobic conditions - the tetanus exotoxin is produced and liberated. This is a neurotoxin which has been referred to as tetanospasmin. Prevention of such infections, which may follow apparently minor skin trauma, therefore, relies on preventing conditions suitable for the growth of the anaerobe. Dead tissue should be excised from wounds which should be left open, ie aerobic (A true). Treatment consists of high doses of penicillin (B true) and the use of hyperimmune globulin (C true) in an attempt to convey some degree of passive immunity to the toxin. The main effect of the toxin is muscle hyperirritability. The toxin blocks inhibitory neurones in the CNS so that stimulatory signals remain unopposed and muscles, including those in the jaw and respiratory system, are constantly stimulated (D true). NB. IV for clinical (active) desease, but in prophylaxis/prevention give IM (C true).
