This week in lab we did throat swabs and cultures and sputum samples. An important part of our investigation into the pathogens of the upper and lower respiratory tract is the ability to differentiate between normal flora and potential pathogens. I have decided to discuss my sputum sample in order to illustrate this point. I received a plate with two isolates. Isolate #1 was large to medium in size on SBA, yellow, convex, and beta hemolytic. Isolate #2 was small, alpha hemolytic, gray and translucent. I immediately suspected S. aureus for isolate #1 considering the colony morphology. After performing a catalase test and coagulase test (both of which were positive) I confirmed that this isolate was indeed S. aureus. S. aureus is considered a pathogen in the lower respiratory tract and is associated with nosocomial pneumonia, aspiration pneumonia, and lung abscesses. I reported isolate #1 as a pathogen. Isolate #2 was catalase negative, alpha hemolytic, and bile insoluble, which lead me to an ID of viridans streptococcus. Viridans streptococcus is considered normal flora in the upper respiratory tract and is considered normal flora for sputum samples as well. Other normal flora found in throat and sputum samples include coagulase negative Staphylococcus, diptheroids, and Neisseria spp. I reported the viridans streptococcus as normal flora for this sample.
After this lab however, I was curious about my viridans streptococcus isolate. I knew I had been correct to report this isolate as normal flora for the area of the body in which it was isolated, but I wondered if viridans streptococcus was ever considered a pathogen in the lower respiratory tract. I did some investigation online and found this interesting article on Pubmed concerning viridans streptococcus and cases in which it was associated with a diagnosis of pneumonia. I suppose there is always an exception to every rule!
Very interesting link! I have never heard of cases like this. You are right- there are always exceptions with microorganisms. Any bacteria can cause infections and we should report even typical normal flora when isolated in a person who is sick and that is the only thing isolated.
ReplyDeleteI found the article about the patient with viridans streptococcus infections interesting. I think it shows as a medical technologist one still needs to be using their best judgment to determine what could be causing the patient problems. It would have been wonderful if the article could have provided information about the patient’s living and work situation. I would be curious to see if this could have put the patient at greater risk for this bacterium to cause an infection in theis particular patient.
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