Case study: A 35-year-old man had been feeling unwell for a few days with nonspecific aches and pains in his joints and a slight headache. The following day he felt considerably worse, with severe colicky abdominal pain and he developed bloody diarrhoea, going to the lavatory 10 times in the day and persisting overnight. He then went to the accident and emergency department at hospital where he was admitted. Because he was dehydrated he was given intravenous rehydration and blood and faeces samples were sent for culture. Infection with Campylobacter jejuni was suspected as his history revealed that he had consumed a chicken mayonnaise sandwich which he thought was "a bit odd". Some weeks later he began to develop weakness in his feet, which gradually spread to his legs and after more days the paralysis affected his leg muscles. With treatment, these symptoms gradually resolved.
Questions:
1. What was the likely source of infection in this case study? What are the common sources of Campylobacter jejuni infection that lead to human infection?
2. Is disease produced by Campylobacter classified as a "food infection" or "food intoxication"? Explain your reasoning, including definitions of these terms.
3. Campylobacter spp and Salmonella spp (including a variety of serotypes) are relatively common in the UK. Using Public Health England data (you must use these to plot your own single graph in EXCELTM), compare the number of cases of these pathogens over 10 YEARS UP TO 2012. Summarise and discuss your comparisons as a series of succinct bullet points.
4. Give an account of Campylobacter pathogenesis and virulence factors, and use this knowledge to explain the initial symptoms of gastroenteritis disease (as described in the case study).
5. Discuss long term consequences of Campylobacteriosis, particularly relating this to relevant symptoms described in the case study.
6. Briefly explain the routine laboratory techniques and tests (microscopy, bacterial culture - media and conditions and biochemical tests) used to isolate and identify Campylobacter. This section should contain descriptions and explanations of methods.
7. For each of the options below, state whether each statement is true or false and provide brief explanations/descriptions for every alternative to verify your true/false answers. (Marks will only be given if there are explanations).
C. jejuni can be typed:
(a) based on lipopolysaccharides
(b) using the Widal reaction.
(c) according to Lancefield's grouping
(d) using ‘phage typing.
8. Based on published literature, discuss two examples of types of ELISAs used in Campylobacter research/typing/identification, including whether they are direct or indirect ELISAs.
9. Several loci have been targeted for PCR-based identification of Campylobacter. Based on research literature, name these, describe what each encodes and discuss some applications of such molecular analysis in the identification of C.jejuni.
10. What antibiotic treatment may have been given to the patient in the case study? Briefly consider concerns about antibiotic resistance.
11. As part of the follow-up laboratory investigation it was decided to determine the heat sensitivity of Campylobacter by incubating bacteria at specific temperatures and performing viable counts by plating out suspensions onto blood agar. Viable count results are given in Table 1 below:
Table 1. The effect of temperature on Campylobacter jejuni
|
Time
(min)
|
Temperature (°C)
40 50 60
|
|
Number of colony forming units/ml
|
|
0
|
6.80 x 103
|
6.80 x 103
|
6.80 x 103
|
|
2
|
5.62 x 103
|
1.26 x 103
|
6.31 x 10'
|
|
4
|
3.16 x 103
|
3.98 x 10'
|
3.98 x 105
|
|
6
|
2.82 x 103
|
6.31 x 10°
|
56
|
|
8
|
1.58 x 103
|
1.58 x 106
|
Not determined
|
|
10
|
1.26 x 103
|
4.47 x 105
|
Not determined
|
|
20
|
1.78 x 107
|
63
|
Not determined
|
|
30
|
2.24 x 103
|
Not determined
|
Not determined
|
(a) Process these Campylobacter data, and plot an appropriate graph to calculate the Decimal Reduction Times (D-values) for the three concentrations of disinfectant against the Campylobacter. The graph MUST BE HANDDRAWN, plotted on standard graph paper, of sufficient size, with clear data points, AND lines showing how the D-values were determined must be clearly shown on the graph.
(b) Are these D-values consistent with published data? Comment and justify your answer.
(c) Using the counts in the table, what percentages of the original suspension had been killed after 4min at 40°C and 50°C? Show all your calculations.
12. The administration of prophylactic antibiotics or probiotics to animals (including poultry) is an approach designed to reduce problems with bacterial pathogens but also for other reasons. Discuss scientifically the rationale and effectiveness of both of these two and implications for human health.
13. According to WHO protocols, in the laboratory, how would a faecal specimen be processed and stored prior to the actual testing for rotaviruses?
14. Examination of poultry in the flock that supplied the factory showed that some birds harboured rotavirus. Discuss the significance of this for human infection.