Hello everyone, I'm having some problems with the antibiogram of some Haemophilus influenzae detected from sputum samples in children with Cystic Fibrosis. I know that Eritromicin resistence is quite common, but I'm finding a lot of undefined halo around amoxicili/clavulanate and cefotaxime antibiotic disk. I've tryed to perform it on MH-F as Eucast guide line says and also on PVX (cooked blood agar) but the results remains the same: it looks like the Haemophilus is resistant, or not completely sensible to these drugs. Sometimes I can see a sort of dopple halo, like if the strain had double phenotype. And I'm sure it is pure culture (it has been isolated carefully).
Do you have any informations about Haemophilus influenzae (not b type, so not invasive) resistance pattern? Is it common/possible to find amoxicillin/clavulanate resistance?
What kind of test do you use to perform antibiogram on this bacteria?
Thank you in advance for any useful answers.
Ramona.
You may check this paper for resistance types in H. influenzae (http://aac.asm.org/content/54/1/65.full).
In general, bacterial isolates from CF patients are difficult. Since in CF lungs bacteria often grow within biofilms, antibiotic susceptibility is reduced. You may than find metapopulations of different variants (both, in terms of phenotype and antimicrobial susceptibility), originating from a common ancestor, but having been adapted in various ways to the specific environmental conditions found in the lungs of CF patients. This has been demonstrated impressively by Workentin et al for P. aeruginosa (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0060225). They have shown, that even colonies of the same phenotype can have different MIC's for a given antimicrobial. I guess that the phenotype(s) you see are a result of adaptation in due of the environment. What, if you retest the isolate from the inside the double halo? Best regards, Oliver
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0060225
http://aac.asm.org/content/54/1/65.full
Thank you so much, very precise and kind answer.
I'm going to retest that sample again as you said, but then I figure we will have to tell the clinical doctor that his patients cannot recive amoxicillin/clavulanate as therapy anyway... Which can be a problem I don't know how to solve. But this is a very interesting thing anyway, and I will certanly focus on the next sample to verify it.
Thank you again.
Greetings,
Ramona.
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