The Microbiology Consultant was waiting for the new Microbiology Registrar to finish the authorisation before going through any problems or questions they had. They started with their first question, a urine isolate which was identified as Pseudomonas aeruginosa but the antibiotic sensitivities didn’t make sense. The bacterium was sensitive to Co-amoxiclav and Ceftriaxone but resistant to Gentamicin and Amikacin. Pseudomonas aeruginosa is normally resistant to Co-amoxiclav and Ceftriaxone and sensitive to Gentamicin and Amikacin. A “nonsensical” or “incorrect” result like this should normally prompt further investigation as to what might be wrong before it is authorised or released.
The patient’s mother was at her wits end. Her little boy’s head was covered in scaly skin. At first she thought his scaly hair was dandruff so she had washed his hair in medicated shampoo but this was met with screams and tears. She thought he was being a bit extreme “it’s only dandruff” but guessed kids can be funny about having soap in their eyes. He just kept saying “mummy my head is really sore”. Tonight he had refused to have his hair washed and while trying to get him into bed, she noticed he was going bald! She was so alarmed that she brought him in to the Emergency Department for help.
Gosh nearly 2,000 of you read last weeks’ blog on cholera (that’s a record) and it sparked a couple of really good questions to Nuts & Bolts.
One from Virginia related to the use of TCBS agar to grow Vibrio cholerae, so I thought that this week I would cover some “old fashioned” microbiology and talk about agar. Really! I hear you cry “that’s not very interesting”! Well, as “interesting” is banned when discussing microbiology, I’ll use “actually very clever” to describe the reasons why we use different types of agar in the laboratory… here goes…
Looking through the positive blood cultures in the morning, the Microbiology Registrar noticed a set positive for Staphylococcus lugdenensis. There were no clinical details on the request form but checking the patient’s blood tests showed a high white blood cell count and C-reactive protein. There was clearly something going on so the registrar gave the ward team a call. The team said the patient was being treated for pyelonephritis with Gentamicin but further questioning revealed that they also had a prosthetic aortic valve. The registrar wondered whether the patient might have infective endocarditis but the team weren’t convinced at first. The registrar explained the risks and suggested repeating the blood cultures as well as asking the Cardiologists for an opinion about the possible diagnosis.
An elderly patient was brought in to hospital having fallen in the garden where he had been for 3 days because he was unable to get himself back on his feet. He was unkempt and had a number of areas of broken skin on his head and neck as well as his arms. These wounds were infested with maggots which looked to have started to digest the healthy skin at the base of the wounds. The patient was very unwell with high blood inflammatory markers, renal failure and sepsis. He was started on IV Piptazobactam for sepsis of unknown origin.
The Microbiologist recently received a letter from a colleague asking for advice about how to manage a patient with Helicopter pylon. After a little pondering, it was decided that in fact advice was really required for a patient with Helicobacter pylori who had had failed two courses of treatment and was still symptomatic for peptic ulcer disease. It was clear that the automatic spell checker had made its own diagnosis! Spell checkers are a nightmare in medicine but often lead to some interesting questions. The colleague was asking whether the microbiology laboratory could perform culture and sensitivity on a biopsy sample and if so how the sample should be sent. There was also a question about what antibiotics to use next to treat the patient.
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An elderly diabetic man presents to hospital with a fever, tachycardia and hypotension. He is septic and so blood cultures are taken and he is started on IV Piptazobactam as per the hospitals empirical guidelines for sepsis. There is no obvious focus and therefore source control (e.g. draining of an abscess) at this time is not possible.
The next day his blood cultures signal positive and a beta-haemolytic streptococcus is isolated. What does this mean? What is the significance?
Does the terminology around beta-haemolytic streptococci confuse you? It did me when I was a student and junior doctor; I couldn’t understand why beta-haemolytic streptococcus wasn’t the Group B streptococcus! They both have a “B” in them just one is the Latin letter while the other is Greek; surely they are the same thing? Well no, they’re not so how did I eventually get to grips with them.
Previously I blogged about the use of antibiotics in pancreatitis and I mentioned procalcitonin as an exciting new marker of infection. I have little experience of this laboratory test but have heard many others talk about how useful it is. But what is it? What is it useful for? Can it help in the diagnosis and management of infection?
What is procalcitonin?
Procalcitonin (PCT) is a protein produced by the thyroid, lungs and intestine in response to inflammation, especially when the inflammation is caused by bacterial infection. In contrast, levels of PCT do not increase much when inflammation is caused by viruses or most non-infectious causes. Levels increase quickly (within 2-4 hours) and have a half-life of 24-36 hours. It is suggested (by the manufacturers of the PCT assay machines) that PCT can therefore be used to identify septic patients and predict who is at risk of developing severe sepsis. The amount of PCT is said to be related to the amount of inflammation therefore in theory the level of PCT can also be used to monitor response to treatment; a decrease in PCT corresponding to a favourable response to treatment.
An elderly man was brought in to see his GP by his son who was concerned about progressive memory loss in his father. The son reported that his father had been getting more forgetful over the past few weeks and he was concerned that this was more than a slow cognitive deterioration related to his age. The GP sent a number of basic tests to the laboratories including haematology and biochemistry tests and also decided to ensure there wasn’t an infective cause by sending urine for culture and a serum sample for syphilis serology.
The result of the syphilis serology came back showing:
EIA positive not confirmed in second assay
EIA and RPR likely to be false positives.
Treponemal infection unlikely but please repeat to confirm.
The GP stared at the result for a few minutes before rolling his eyes to the ceiling and saying “what does this all mean; why the heck did I do this test?” Good questions!