Microbiology Nuts & Bolts Test Yourself – Skin & Bone Begin here

The patient in this test yourself case is entirely fictitious, however it is based on many clinical scenarios the author has come in to contact with during his medical career. Any similarity to a real case is entirely coincidental.

George 69 year old man Presents with a painful swollen left knee 1 year after a total knee replacement He has a normal temperature, heart rate and blood pressure On examination there is a large effusion in the knee joint

How should George be managed? Start antibiotics for presumed septic arthritis Aspirate the joint and withhold antibiotics Aspirate the joint and start antibiotics Replace the prosthesis A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Aspirate the joint and withhold antibiotics It is likely that George has a chronic infection in his knee prosthesis but it is not urgent to start treatment immediately Withholding the antibiotics at this stage allows the diagnosis of septic arthritis to be proven and antibiotic treatment to be tailored to treat whatever bacteria is causing the infection Different bacteria require different antibiotics and also often different surgical strategies, and this can only be decided once the bacterium is known If George were very unwell, and showing signs of sepsis, then empirical treatment should be started as soon as the joint had been aspirated

George The synovial fluid was sent to the laboratory and the Gram film was reported as showing Gram- positive cocci in clumps

What is the likely identification of the bacterium causing the septic arthritis? Staphylococcus aureus Streptococcus pyogenes Coagulase-negative Staphylococcus Escherichia coli A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Coagulase-negative Staphylococcus The presence of Gram-positive cocci in clumps suggests a Staphylococcus spp. in the synovial fluid, but the length of time the prosthesis has been in and the lack of systemic symptoms and signs of infection make Staphylococcus aureus less likely than a Coagulase-negative Staphylococcus S. aureus is an aggressive bacterium associated with severe infections, systemic symptoms and signs, and often sepsis Coagulase-negative Staphylococci cause more indolent and chronic infections and do not normally trigger a severe systemic response S. pyogenes is a Gram-positive coccus that forms chains and E. coli is a Gram-negative bacillus

Which of the following antibiotics could now be started empirically? Flucloxacillin Flucloxacillin PLUS Benzylpenicillin Meropenem Teicoplanin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Teicoplanin Vancomycin would be a suitable alternative as it is also a glycopeptide antibiotic The glycopeptides are the most commonly used antibiotics in the UK which are reliable first line empirical treatment of infections caused by Coagulase-negative Staphylococci It may not be necessary to start antibiotic treatment immediately the Gram film is known as ultimately the correct treatment of George involves removal of the infected prosthesis as well as antibiotics

George The orthopaedic surgeons plan on taking George to theatre the next day and ask what specimens the laboratory would like

How many specimens at least would you recommend the surgeons take? A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: 5 It is recommended that orthopaedic surgeons take at least 5 separate specimens when replacing a prosthetic joint that might be infected The result of the culture is considered positive if the same bacterium grows from at least 3 of the 5 samples If less than 3 samples are positive it might be due to contamination of the samples with skin flora, or the patient may have been inadvertently given a dose of antibiotics before the operation which stopped the bacteria from growing and has therefore made it difficult to diagnose the infection Remember: it is always best to wait for samples to be taken before giving antibiotics if at all possible

George George has his prosthesis removed and an antibiotic impregnated spacer put in to his knee All of his operative samples grow Staphylococcus epidermidis sensitive to Teicoplanin, Ciprofloxacin and Rifampicin

What initial treatment would you recommend for George? PO Ciprofloxacin PLUS PO Rifampicin IV Teicoplanin PLUS PO Ciprofloxacin IV Teicoplanin PLUS IV Rifampicin IV Teicoplanin PLUS PO Rifampicin A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: IV Teicoplanin PLUS PO Rifampicin The correct initial treatment phase for this type of infection is with 6 weeks of IV therapy (Teicoplanin) with PO Rifampicin in addition After the initial 6 week phase it is appropriate to change to a further 6 weeks of a highly bioavailable combination of oral antibiotics which in this case could be Ciprofloxacin PLUS Rifampicin The total duration of treatment would be 12 weeks before considering putting a prosthetic knee back in to George

George George was given 12 weeks in total of antibiotics before plans were made to reinsert a prosthetic knee

What blood tests should be monitored whilst George is on antibiotics? FBC, U&Es FBC, U&Es, LFTs FBC, U&Es, LFTs, Teicoplanin levels FBC, U&Es, LFTs, INR, Teicoplanin levels A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: FBC, U&Es, LFTs, Teicoplanin levels Long-term high dose Teicoplanin can suppress bone marrow function causing a fall in white blood cell counts, platelets and haemoglobin, therefore a weekly full blood count should be done Teicoplanin can also cause renal failure and so weekly Urea and Electrolytes should be checked Teicoplanin levels should be done every week to ensure the levels are adequate to treat a bone and joint infection as well as to make sure the levels are not toxic Rifampicin can cause hepatitis and so liver function tests should be monitored weekly It is important that someone takes responsibility for ensuring these tests are done as well as the results checked and any appropriate actions are taken

How long should George be off antibiotics before his 2 nd operation? 1 week 2 weeks 3 weeks 4 weeks A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: 2 weeks It is recommended that patients should be off antibiotics for at least 2 weeks between stopping treatment for an infected prosthetic joint and reinsertion of a new prosthesis This allows any residual bacteria to grow back by the time of surgery in sufficient numbers to be detectable by the microbiology laboratory in samples taken at the second operation If these samples are positive then antibiotics can be continued for a further 6-12 weeks depending on the bacterium grown

George The samples taken at the 2 nd stage operation are culture negative and George is eventually discharged from hospital Unfortunately his surgical wound continues to ooze post-operatively after he returns home A few weeks later the wound starts to breakdown from the outside inwards and he goes on to develop a sinus leading in to the joint space A further prosthetic joint infection is diagnosed

Which of the treatment options should NOT be used to treat this infection? Long-term antibiotic suppression Permanent resection arthroplasty Two-stage revision arthroplasty Debridement & retention of prosthesis (DAIR) A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Debridement & retention of prosthesis (DAIR) In DAIR the infected prosthesis is cleaned and as much infected material removed as possible All of the other treatment options could be considered but DAIR is contraindicated by the presence of a sinus because the infection will not be treated or suppressed by this method It is not unreasonable to give long-term antibiotic suppression to patients in this circumstance if surgery is not an option, as the antibiotics can prevent worsening of the infection or secondary complications such as sepsis even if they have no hope of curing the infection

George The fluid oozing from Georges wound was sent to the microbiology laboratory and an Enterobacter cloacae was cultured

What type of bacterium is Enterobacter cloacae? Gram-negative bacillus Gram-positive coccus Gram-negative coccus Gram-positive bacillus A B C D Choose A, B, C or D for the answer you feel best fits the question

Correct Answer: Gram-negative bacillus Enterobacter cloacae is a Gram-negative bacillus which likes to colonise moist sites, including inadequately healing post-operative wounds This bacterium does not normally cause skin and bone infections, but if allowed to colonise a prosthetic joint because there is a sinus that allows it to enter the joint then it can do so (as can any Gram-negative bacillus) E. cloacae is often resistant to many antibiotics due to the presence of a chromosomal AmpC enzyme causing resistance to many of the Beta-lactam antibiotics, although carbapenems such as Ertapenem, Imipenem and Meropenem usually remain active Prosthetic joint infections with Gram-negative bacilli are often very difficult to treat

George In the end George opted for permanent resection arthroplasty and the hip joint was removed George was left with reduced function in his knee and was unable to walk far without walking sticks The End

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