Week 9: Final Blog of the Semester!

Hello everyone!  It is hard to believe that the semester is nearly over and we are halfway through the program!  Time has flown!  We certainly have covered quite a bit over the last couple of months in Infectious Diseases. We covered everything from infections of sterile body fluids such as CSF and blood to antibiotic susceptibility testing and virology.  In addition, we correlated what was learned in the classroom directly to testing performed in the student laboratory.  We’ve learned quite a bit and hopefully everyone is ready for the ASCP exam!  Good luck on finals!

The following is a link to a site that has a number of quizzes covering essentially all of the material we covered this semester in Infectious Diseases.  Hope you all find it useful in studying for the final!

http://microbiology.jbpub.com/8e/quizzes.cfm 

Week 8: Virology

Hello everyone, I’m sure everyone is happy to have completed the lab practical this afternoon!  This week we discussed viruses and basic methods for detecting viruses in patient specimens.  I will briefly discuss each method of viral detection below.

Cytological and Histological Exam

During a cytological exam, the tissue samples are stained with any of a variety of stains such as PAP, Giemsa, or H & E.  The tissue samples are then examined for synctia (multinucleated cells) and nuclear and cytoplasmic inclusions, which are clusters of viruses or viral materials.  This method is less sensitive than the culture method but safer and easier than culturing dangerous viruses.

Electron Microscopy

Electron microscopy allows for visualization of the actual viruses.  This technique is used more in research laboratories than clinical laboratories.  Electron microscopy can be useful in detecting viruses that can’t be grown using culture techniques.  This method however is labor intensive and relatively insensitive compared to other methods. 

Direct Detection of Viral Ag

Direct detection of viral antigen involves detection of antigens in specimens or after viruses has grown in cell culture.  Antigen detection can be accomplished by either direct fluorescence antibody detection methods which utilize fluorescently labeled antibodies that bind directly to viral antigens in the specimen or indirect fluorescence methods that involves direct labeled anti-human globulin against antibodies attached to corresponding viral antigens in a specimen.  Fluorescence is then measured and observed using a fluorescence microscope.

NA Probes

               

Nucleic acid probes can be useful in viral detection when the amount of virus is abundant.  This technique can be used when culture is not possible or slow. 

Conventional Cell Cultures and Shell Vial Method

The conventional cell culture method is the gold standard for viral detection.  Viruses require cells in order to survive and replicate, so culture by conventional methods is not possible.  A variety of cell lines including primary, low passage, and continuous cell lines are used to facilitate the growth of viruses.  Cultures are then examined for cytopathetic effect (morphological changes to the cells0 using a microscope or tested for hemadsorption/hemagglutination.  The Shell Vial technique is a combination of the conventional cell culture method and fluorescent antibody labeling technique.

Serological Testing

When viruses can not be grown using culture techniques and direct antigen detection is not possible, antibody detection can be performed.  Detection of IgM antibodies to viral antigens indicates an acute stage of infection while detection of IgG antibodies to viral antigens indicates immunity to the virus.

The following article discusses the discovery of a new Ebola virus species and discusses some of the viral detection techniques we discussed in class.  Enjoy!

 http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1000212

Week 7 Laboratory: Antibiotic Susceptibility Tests

Hello everyone! This week in the laboratory component of this course we completed antibiotic susceptibility testing on various organisms. I am going to review and summarize the principle of one of the tests performed in the laboratory in order to help everyone have a firmer grasp of the underlying concepts behind the test we performed. How you all find this helpful!

Microdilution Method

The basic principle behind the tube broth dilution method and the microdilution method are the same. In both, two fold dilutions of antimicrobics are tested against a standardized concentration of an organism being tested. The lowest concentration of a drug that will inhibit the growth of a organism is determined (this is the MIC, or minimal inhibitory concentration) by this method. The microdilution method utilizes bacterial broth volumes of 0.05-0.1 ml and microtiter trays with dilutions of antimicrobics dehydrated or frozen in the wells. A standardized suspension of a organism is prepared and poured into a seed tray. A special inoculator device (we used the Renok inoculator device) is used to draw up the broth and dispense a specific amount in each microtiter well. The trays are then incubated in a regular incubator. The results are read after 16-20 hours. Bacterial growth is determined by observing the bottom of the well with a mirror and looking for turbidity. Turbidity indicates growth and clear solution indicates no growth. The MIC can then be determined by observing the amount of drug in the last clear well, going from highest concentration of antimicrobial to the lowest concentration of antimicrobial.

I was interested in finding an article concerning drug-resistant bacteria, so I found this interesting article and video concerning MRSA found on bedbugs!  Hope you enjoy it!http://abcnews.go.com/Health/Wellness/bedbugs-carry-drug-resistant-bacteria-study/story?id=13571434

　

Week 7: Antimicrobial Action and Antimicrobial Susceptibility Tests

Hello everyone! I’m sure everyone is happy about completing our second Infectious Diseases exam and is ready for the weekend! However, if you want to get a jump start on studying for our next exam, you have come to the right spot! This week we discussed antimicrobial action and susceptibility tests in lecture. Since this unit involved quite a few new terms and concepts, I decided to create a matching quiz in order to help everyone obtain a firmer grasp on the concepts presented in Tuesday’s lecture. Hope this helps! Match the terms on the left with the definitions on the right.

1. Bactericidal	A. Chemical produced by organism that inhibits growth of other microorganisms
2. Broad-spectrum antibiotics	B. Agents that inhibit the growth of microorganisms
3. Antibiotic	C. Antibiotics that are effective against specific families or even species of microorganisms
4. Bacteriostatic	D. Agents that kill microorganisms
5. Narrow-spectrum antibiotics	E. Plastic strip containing exponential gradient of antibiotic on one side and calibrated MIC reading scale on the other placed on inoculated plate
6. Beta Lactams	F. Antibiotics that act against a wide range of bacteria, both gram positive and gram negative bacteria
7. Transpeptidase enzyme	G. antibiotic agents that act on cell walls, include Penicillin, penicillinase-stable penicillins, broad-spectrum antibiotics, etc
8. Tetracyclines	H. Least amount of that will kill 99.9% of a standardized suspension of organisms
9. Aminoglycosides	I. Antibiotic which blocks formation initiation complex by preventing tRNA binding at acceptor (A) site, preventing addition of new amino acids to peptide
10. Macrolides	J. Antibiotic that binds the 50 S ribosome unit and inhibits translocation of peptidyl tRNA from acceptor site to exit site leading to interruption of transpeptidation or translation
11. MIC	K. Antibiotic which prevents transfer tRNA from A to P site, prevent elongation
12. Turbidity	L. Also called penicillin binding protein, reforms the peptide crosslinks between rows and layers of peptidoglycan
13. Kirby Bauer disk	M. Disk used for agar disk diffusion
14. E-test	N. Lowest concentration of drug that will inhibit growth of organism
15. MBC	O. indicates growth in the microdilution tube method of antibiotic susceptibility testing

　

1 D; 2 F; 3 A; 4 B; 5 C;6 G; 7 L; 8 I; 9 K; 10 J;11 N;12 O;13 M;14 E; 15 H

Week 6: Wounds, Ears, Eyes, and Sinuses

Hello everyone, in honor of our upcoming test, I decided to put together a little quiz of questions concerning wounds, eyes, ears, and sinuses to help everyone study.  Hope you find it helpful! Answer are written below (don’t peek!).

1.)  What is another name for a painful boil filled with pus?

2.) What are three common agents involved with infections of hair follicles?

3.) What type of antibiotics is MRSA resistant to?

4.) Ringworms are due to what organism?

5.) Nonbullous impetigo is caused by what bacteria?

6.) Erysipeloid is due to what organism?

7.) What is the most common organism found in abscesses (think lungs)?

8.) What is myositis?

9.) What is another name for gas gangrene?

10.) A double zone of beta hemolysis is seen with what organism?

11.) Necrotizing fasciitis is associated with what organisms?

12.) What are agents commonly associated with bedsores?

13.) Infections due to trauma and contact with infected saltwater are commonly associated with what group of organisms?

14.) Infections due to contaminated prosthetic devices are associated with what organisms?

15.) What is the preferred specimen for a closed abscess?

16.) What is the preferred specimen for an open or superficial wound?

17.) What media should be used for superficial wounds, burns and bites?

18.) What is keratitis?

19.) What organisms are associated with “swimmer’s ear”?

20.) What media should be used to investigate bacteria collected from an internal ear swab?

1-furnucle; 2-S. aureus, Enterobacteriaceae, Pseudomonas; 3- beta-lactam antibiotics; 4 – dermatophytes; 5- S. pyogenes; 6- Erysipelothrix rhusiophathiae; 7- S aureus; 8- inflammation of the muscle tissue; 9- clostridial myonecrosis; 10- C. perfringens; 11- S. pyogenes, S. aureus, anaerobes; 12- B. fragilis, E. coli, S. aureus, P. aeruginosa; 13- Vibrio spp; 14- S. epidermidis, other CNS, diptheroids, and P. acnes; 15- aspirate fluid; 16- deep swab; 17- SBA, MAC, Thio broth, gram stain; 18- inflammation of the cornea

19- P. aeruginosa; 20- SBA, CHOC, MAC, Thio broth, and anaerobic 

Week 6: Mycobacteria

Hello everyone, this week in our Infectious Disease lecture we discussed Mycobacteria.  We spent a great deal of time discussing Mycobacterium tuberculosis, the etiological agent responsible for most case of tuberculosis in humans.  In the United States 4,495 cases of tuberculosis were documented in 2009, 126 of which were in Alabama.  According to the World Health Organization, there are 8.4 million new cases of tuberculosis each year worldwide.  Tuberculosis tends to be most prevalent among immigrants, drug or alcohol abusers, the homeless, and the immunocompromised, particularly those infected with HIV.  Risk factors associated with tuberculosis infection include crowded living conditions, health status of the individual, behavioral risks, environmental and social factors, poverty level, and the fact that the organism is found everywhere.  M. tuberculosis is transmitted primarily through inhalation of droplet nuclei expelled through talking, sneezing, and singing, although it may also be contracted via aerosols due to contact with wounds and tissue of an infected individual.  The spectrum of the diseases associated with M. tuberculosis range from asymptomatic to the typical pulmonary condition, to military tuberculosis in which the disease presents in areas other than the lungs including the spleen, liver, bone marrow and kidneys, to name a few.  Symptoms of typical pulmonary tuberculosis include a productive, prolonged cough, chest pain, and hemoptysis.  Systemic symptoms include fever, chill, night sweats, appetite loss, weight loss, and easy fatigability.

The following is an interesting article I found regarding tuberculosis in ancient Egypt.  Scientists have been able to utilize molecular techniques in order to identify M. tuberculosis in mummies.  Hope you enjoy it!

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(05)65185-9/fulltext

Week 5 Laboratory: Gastrointestinal Infections

Hello everyone, today I am going to discuss the experiments performed in the laboratory on Thursday and Wednesday.  Specifically, I am going to discuss my rectal sample, since most people in the class did not receive this particular bacterial species on their pre-prepared plates.  For the rectal samples, we received four prepared plates, an SBA, a MAC, an XLD, and a CVA.  My pathogenic isolate appeared as a clear colony on MAC, a gray colony on SBA, yellow colonies on XLD, and showed no growth on CVA.  No growth on CVA revealed that my isolate was not Campylobacter since this plate is specific for Campylobacter.  Clear growth on MAC revealed that my isolate was a non-lactose fermenting gram negative rod.  The yellow colonies on the XLD confused me slightly at, since normal GI flora typically appear yellow on XLD.  However, I remembered that Yersinia may appear clear to slightly yellow on XLD, so I began to suspect a possible Yersinia infection.  I performed an API 20 E to confirm this.  My API results yielded a perfect match for Yersinia enterocolitica, which can cause such diseases as mesenteric lymphadenitis, hemorrhagic enterocolitis, and terminal ileitis.  Although I chose to perform an API 20 E to confirm my identification of Yersinia enterocolitica, I could have performed an entirely different set of tests and come to the same conclusion.  If KIA, LIA, and Urea tests had yielded Alk/A, P/Y, and +/- and motility tests had been negative at 35° and positive at room temperature, I would have also come up with an ID of Yersinia. 

Below is a transmission electron microscopic view of Yersinia enterocolitica.  I had never seen an image quite like this, so I thought I would included it!