{"id":2794,"date":"2016-03-22T15:55:50","date_gmt":"2016-03-22T02:55:50","guid":{"rendered":"http:\/\/microbiologymatters.com\/?p=2794"},"modified":"2016-03-22T15:55:50","modified_gmt":"2016-03-22T02:55:50","slug":"on-second-thoughts","status":"publish","type":"post","link":"https:\/\/microbiologymatters.com\/?p=2794","title":{"rendered":"“On second thoughts…”"},"content":{"rendered":"

I love fallacies, old wives tales, and urban myths…<\/span><\/p>\n

You are probably familiar with the dogma that you should never use cotrimoxazole to treat infections due to Streptococcus pyogenes.<\/em><\/span><\/p>\n

In the laboratory setting we have traditionally never been much good at in-vitro susceptibility testing for cotrimoxazole against Streptococcus pyogenes…<\/em><\/span><\/p>\n

Why?<\/span><\/p>\n

In vitro susceptibility testing of Streptococcus pyogenes<\/em> against cotrimoxazole is dependent on\/vulnerable to the amount of thymidine in the susceptibility media. Thymidine allows Streptococcus pyogenes to bypass sulphonamide mediated inhibition of folate metabolism.<\/span><\/p>\n

In the past, media contained unregulated (and often high) levels of thymidine, particularly those media that contained blood. As a consequence Streptococcus pyogenes<\/em> survived quite happily on such media, even in the presence of sulphonamides and thus showed in-vitro resistance.<\/span><\/p>\n

However modern media such as Mueller-Hinton agar (MHA)\u00a0are now regulated as to their thymidine content. A study<\/span><\/a> in the Journal of Clinical Microbiology in 2012 using such agar showed at least 99% in-vitro\u00a0susceptibility of Streptococcus pyogenes<\/em> to cotrimoxazole.<\/span><\/span><\/p>\n

It is likely that our poor laboratory practice in the past has led to cotrimoxazole being labelled a ”No-No” for infections due to Streptococcus pyogenes. <\/em><\/span><\/p>\n

However this information above only refers to in-vitro susceptibility testing. Whether this translates into in-vivo susceptibility\/clinical response\u00a0is another question altogether, and in the modern day, will likely\u00a0 need clinical trials to answer. (See this article<\/span><\/a> for a bit about in-vitro and in-vivo susceptibility)<\/span><\/p>\n

All the textbooks<\/span><\/a> in my lab say that Streptococcus pyogenes is resistant to cotrimoxazole. That’s because they are all 10-20 years old!<\/span><\/p>\n

It is difficult to change people’s minds at the best of times. Old habits die hard…<\/span><\/p>\n

Michael<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

I love fallacies, old wives tales, and urban myths… You are probably familiar with the dogma that you should never use cotrimoxazole to treat infections due to Streptococcus pyogenes. In the laboratory setting we have traditionally never been much good at in-vitro susceptibility testing for cotrimoxazole against Streptococcus pyogenes… Why? In vitro susceptibility testing of … Continue reading “On second thoughts…”<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[4],"tags":[433,79,313,434],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p37jIp-J4","jetpack-related-posts":[{"id":2213,"url":"https:\/\/microbiologymatters.com\/?p=2213","url_meta":{"origin":2794,"position":0},"title":"“Impetigo: Where can the lab be of value?”","author":"michael","date":"February 27, 2015","format":false,"excerpt":"Impetigo is a common skin condition and we certainly still see plenty of it here in NZ. The word Impetigo comes from the Latin \"Impetere\" meaning \"to attack\". It can be classified clinically into the more common non-bullous (vesicles then crusts) and the less common bullous types. \u00a0 \u00a0 \u00a0\u2026","rel":"","context":"In "The Art of Microbiology"","block_context":{"text":"The Art of Microbiology","link":"https:\/\/microbiologymatters.com\/?cat=3"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":3270,"url":"https:\/\/microbiologymatters.com\/?p=3270","url_meta":{"origin":2794,"position":1},"title":"“Molecular diagnosis of wound infections: The Holy Grail.”","author":"michael","date":"January 23, 2017","format":false,"excerpt":"The slice of pie taken by the molecular department in the microbiology laboratory\u00a0is increasing, slowly but surely. On the contrary, the proportion of culture based microbiology is inexorably declining. 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Bacteria best avoid becoming resistant to a\u00a0particular\u00a0antimicrobial if they can avoid exposure ( i.e. hide)\u00a0to that anti-microbial (or a similar\u2026","rel":"","context":"In "Antimicrobial Resistance"","block_context":{"text":"Antimicrobial Resistance","link":"https:\/\/microbiologymatters.com\/?cat=14"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":2605,"url":"https:\/\/microbiologymatters.com\/?p=2605","url_meta":{"origin":2794,"position":3},"title":"“Hearing aids”","author":"michael","date":"November 29, 2015","format":false,"excerpt":"\u00a0 I have never found ear swabs a very satisfactory microbiological sample, the outer ear canal usually being filled with all manner of debris and micro-organisms regardless of whether an infection is present or not. (Try processing a swab from your own ear!) In addition it is often difficult to\u2026","rel":"","context":"In "The Science of Microbiology"","block_context":{"text":"The Science of Microbiology","link":"https:\/\/microbiologymatters.com\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":288,"url":"https:\/\/microbiologymatters.com\/?p=288","url_meta":{"origin":2794,"position":4},"title":"“Focused Anti-microbial Reporting.”","author":"michael","date":"January 10, 2013","format":false,"excerpt":"\"Note this post is really only useful for people who are working\/preparing to work\/might work in a clinical microbiology laboratory.\" The antimicrobials that are \u201creleased\u201d\u00a0 to clinicians vary enormously from lab to lab. When I say released I mean the antibiotic susceptibilities which are available for the clinicians to view.\u2026","rel":"","context":"In "The Science of Microbiology"","block_context":{"text":"The Science of Microbiology","link":"https:\/\/microbiologymatters.com\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":2792,"url":"https:\/\/microbiologymatters.com\/?p=2792","url_meta":{"origin":2794,"position":5},"title":"“Think twice”","author":"michael","date":"March 15, 2016","format":false,"excerpt":"What have the following got in common? E.coli resistant to nitrofurantoin E.coli resistant to fosfomycin Haemophilus influenzae resistant to ciprofloxacin Group B streptococcus resistant to penicillin. 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