Week 4 Laboratory: Throat and Sputum Samples

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!

http://www.ncbi.nlm.nih.gov/pubmed/1465696 

Week 4: Lower Respiratory Infections

Hello everyone, this week in lecture we discussed lower respiratory infections.  I was particularly interested in the discussion of Legionella and Legionnaires’ disease.  Legionella pneumophila is responsible for roughly 90% of cases of Legionnaires’ disease.  Legionella is found primarily in water sources such as lakes, rivers, water distribution centers, cooling centers, fountains and potable water.  Legionella is contracted via inhalation of infectious aerosols.  There are 15 different serotypes of Legionella, serotype one being the most common serotype seen in infections.  Serotypes 4 and 6 are the next most common serotypes seen.  This bacterium is not spread by person to person contact.  The first symptoms of Legionnaires’ disease are non-specific.  Initial symptoms include fever, chills, cough, muscle pain, headache, chest pain, and diarrhea.  Pneumonia follows as well as possible renal failure, additional gastrointestinal problems, liver function abnormality, and central nervous system problems such as delirium, disorientation, confusion, and rare seizures. 

            Legionnaires’ disease occurs as sporadic cases, epidemic outbreaks, and as nosocomial infections.  Legionnaires’ disease has an incidence of roughly 8,000-18,000 cases per year in the United States.  The mortality rate is 10%-15% in healthy individuals and up to 75% in the immunocompromised.  Individuals predisposed to Legionnaires’ include cigarette smokers, the elderly, individuals with chronic lung disease, and people of immunosuppressive drugs.

            The following is a video from the BBC concerning windshield-wiper fluid contaminated with Legionella in the United Kingdom.  It was found that professional drivers in the UK are five times more likely to contract Legionnaires’ due to increased likelihood of contact with contaminated windshield wiper fluid.  

http://www.bbc.co.uk/news/10306411

Week 3: Upper Respiratory Infections

Hello everyone, this week we discussed upper respiratory infections.  One of the primary infections we discussed was pharyngitis, an infection characterized by pain, swelling, erythrema, gray-white exudate on the throat, fever and cervical lymphadenopathy.  The primary cause of bacterial pharyngitis is Streptococcus pyogenes.  I have decided to discuss Streptococcus pyogenes and its various clinical manifestations since the possible resulting conditions of an infection with Streptococcus pyogenes vary so greatly as far as clinical manifestations and severity of the conditions.  As previously mentioned, S. pyogenes can cause pharyngitis as a primary infection with such suppurative sequelae as sinusitis and otitis media.  Non-suppurative sequelae of S. pyogenes include Acute Rheumatic Fever and Acute Glomerular Nephritis.  Both of these conditions are immunological in nature.  ARF is believed to be autoimmune in nature and AGN is an immune complex issue.  Infections with Streptococcus pyogenes can also cause such cutaneous and soft tissue infections such as impetigo, erysipelas, and cellulitis.  Streptococcus pyogenes can also cause severe invasive syndromes such as severe scarlet fever, septicemia, severe pneumonia, streptococcal toxin shock-like syndrome and necrotizing fasciitis.  Necrotizing fasciitis is a deep seated infection of subcutaneous tissue involving progressive destruction of tissue, fascia, and fat.  This condition is associated with such streptococcal pyrogenic exotoxins as SPE A, B, and C.  Underlying conditions such as cancer, renal failure, diabetes, immunosuppression, peripheral vascular disease, skin trauma, burns, and skin infections can increase the risk of developing necrotizing fasciitis as a result of infection with Streptococcus pyogenes.  Treatment of necrotizing fasciitis includes antibiotic treatment, surgery, and amputation. 

            I have attached a video concerning necrotizing fasciitis that I found interesting.  Enjoy!

Week 3: Urine and CSF Cultures

Hello everyone, today I am going to discuss the process I went through to ID the bacteria present in my urine culture.  I received MAC, SBA and CHROMagar plates already plated with the urine specimen.  The specimen appeared as medium white-gray convex colonies on SBA, and nothing grew on MAC or CHROMagar.  No growth on MAC led me to deduce that the isolate was not a gram negative rod, but since my isolate failed to grow on the CHROMagar, I had no way of knowing what the possible microscopic morphology of the isolate was or the possible ID of the organism.  I was unable to proceed with any further biochemical testing since I didn’t know the microscopic morphology, so I decided to perform a gram stain.  The gram stain revealed gram positive cocci in clusters.  Knowing the microscopic morphology allowed me to proceed with testing.  I performed a catalase test which was positive, a coagulase test which was negative, and a Novobiocin susceptibility test which revealed resistance.  The results of these tests brought me to a final ID of Staphylococcus saprophyticus.  The next day, after reincubating my CHROMagar, colonies grew.  The colonies were pink and opaque.  Pink opaque colonies correspond with Staphylococcus saprophyticus.  Both pathways taken to identifying the organism brought me to the same conclusion.  The lesson to be learned here is that there are multiple ways to arrive at the same ID, and if one method of identifying an organism fails, another can be used.

The middle colony growth is Staphylococcus saprophyticus .   The picture at the very top is a gram stain of  Staphylococcus.

Week 2 Laboratory: Blood Cultures

Hello everyone, it is me again.  Today in the laboratory we read the plates prepared yesterday and completed additional testing in order to come up with a final ID for our blood culture sample.  I am going to discuss the process I went through to identify the pathogen in my blood culture specimen.  The purpose of this discussion is to show how easily one pathogen can be mistaken for another and the importance of complete and thorough testing on a specimen.

I began by making a gram stain of my specimen using the blood from the blood culture bottle.  After allowing the stained slide to dry, I examined the slide under oil immersion.  I quickly identified the morphology of the bacteria as gram positive cocci in chains.  Having determined the morphology and gram stain, I then plated the specimen on the appropriate media, in this case SBA with a “P” disk.  I then incubated the plate overnight in CO2.  

The next day I retrieved my specimen and examined the macroscopic morphology of the bacterial colonies.  The colonies were small, white to gray in color, convex and semi-opaque.  The specimen also displayed beta-hemolysis.  The gram stain and colony morphology lead me to declare the preliminary ID to be beta-hemolytic Streptococcus.  I believed my specimen specifically to be S. pyogenes; the macroscopic and microscopic morphology fit that of S. pyogenes perfectly.  I performed two additional tests in order to come up with a final ID: a catalase test and a PathoDX Strep grouping testing.  As expected the catalase was negative and I believed I saw agglutination for Group A strep on the PathoDX card.  This supported my ID of S. pyogenes.  However, Mrs. Jeff told me this was incorrect.  I performed the PathoDX test again, this time inoculating the reagent broth with more colonies from my plate.  This time there was clear visual agglutination for Group G Strep, making my final ID Streptococcus dysgalactiae subsp. equisimilis, a Group C or G strep species.  The colony morphology for Group C and G strep is almost identical to that of Group A strep, making it fairly easy to confuse the two as I originally did.  So the lesson here is to always complete all necessary testing, never make a final ID on the colony morphology alone!

Which is which???  Pretty similar huh?  The specimen below is  Group G  Strep and the specimen above is Group A Strep.

Week 2: Bloodstream Infections

Hello everyone, hope you are all having a nice week.  In Tuesday’s Infectious Diseases lecture we discussed bloodstream infections.  Endocarditis is an important topic when discussing bloodstream infections, so I have decided to devote more attention to the subject.  Endocarditis is defined as the inflammation of the heart’s inner lining which can lead to damage of the heart valves.  The duration of this condition is less than six weeks.  Endocarditis is the classic example of intravascular bacteremia and can involve normal or prosthetic valves.  If endocarditis is suspected, two to three cultures should be collected over one to two hours.  Endocarditis is treated with Penicillin, aminoglycoside, antifungal agents (should a fungal species such as Candida or Aspergillus be the root cause of the endocarditis), and surgery. 

Many different bacterial agents may involved in endocarditis, including the HACEK organisms, opportunistic organisms found as normal flora in the oral cavity but may become involved in periodontal disease, endocarditis and other diseases.  Haemophilus, the “H” in HACEK, is the most prevalent HACEK agent involved in endocarditis.  Other HACEK organisms involved in endocarditis include Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella.  Capnocytophaga, Bartonella, S. aureus, S. epidermidis, S. pneumoniae, S. pyogenes, N. gonorrhoeae, and P. aeruginosa are additional bacteria that may be involved in endocarditis.  Viridans streptococci, Enterococcus (other group D strep), anaerobic and microaerophilic strep, as well as the HACEK organisms may be involved in subacute bacterial endocarditis, a condition that lasts six weeks or longer.  Like endocarditis, subacute endocarditis is treated with Penicillin and aminoglycoside.

           The following is an entertaining yet informational video concerning endocarditis.  Enjoy! http://www.youtube.com/watch?v=Udgbbz1_qe0&feature=related

Welcome!

Welcome to my blog about big bad bugs and infectious diseases!  I am writing this blog as part of my graduate infectious disease course at the University of Alabama at Birmingham.  I'll be posting once a week about topics discussed in class and the laboratory.  I am hoping to find interesting articles and links concerning microbiology and infectious diseases to post here, articles that will move a bit beyond what is discussed in class.  I am also going to try to find some relevant biology fun facts, ones that can be dropped causally in conversations at parties and what not.  Facts to impress your friends with!  Anyway, thats all for now!