Bacteriology lab assessment PDF

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lab report for Hubs 2601 bacteriology...

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HUBS 2601 Bacteriology assessment Case study 1 1. HBA is a non-selective growth media which contains horse blood which permits the distinction of the type of hemolysis. Most microorganisms release an enzyme which lyse red blood cells, some go partial lysis which is alpha hemolysis, complete lysis- beta hemolysis and no lysis. Is assists in making a distinction between species. A coagulase test is used to determine the presence of a exoenzyme coagulase a clotting enzyme through the conversion of fibrinogen to fibrin. The results indicate that the patient’s bacterium is staphylococcus aureus. Staphylococcus aureus show properties of positive to the coagulase enzyme, gram stain positive cocci, Beta hemolysis - HBA culture media which mirror the results of the patient’s sample. I would prescribe nafcillin or cefazolin.

streptococcus Patient sample

2.

Morphology Coccus, raised

Gram stain positive

coagulase Negative

HBA beta

Raised colonies

Positive

positive

alpha

MSA Pink- no growth yellow

visible

Nosocomial infections are infections contracted by patients receiving care in a healthcare facility. The infections occur when a immunodeficient host comes in contact with a microorganism or growth from an opportunistic bacteria. These infections affect the patient’s safety and wellbeing and the health care facility as they could lead to disease often due to decreased immune function or death. Another threat is the economic factor or prolonged time of stay. Furthermore, there is an increased risk of multi drug resistance during transmission and appropriate use of infection control procedures are essential.

Case study 2 3. Streptococci species are distinguished many ways such as morphology by observing the shape of the colonies. Another way to differentiate streptococci is by observing the way in which they lyse red blood cells. Some strep. Species exhibit partial/alpha hemolysis and species like Group A streptococci indicate total/beta hemolysis. A bacitracin test is used to differentiate non group A Beta-hemolytic streptococcus. Results showing no growth around the bacitracin indicate group A streptococcus as a small dose can inhibit the synthesis of peptidoglycan. Strep A agglutination test is a process used to differentiate strep. groups of mixing a sample in latex bead coated with antibodies, agglutination occurs when there is a antigen-antibody match. Further tests can be done to differentiate streptococci species such as the PYR test which isolates streptococcus pyogenes to other beta-hemolytic strep species. This test detects the presence of pyrrolidinyl aminopeptidase enzyme. Others also include nucleic acid testing and antibiotic resistance testing

4.

The culture results showed evidence of the group A streptococcus – streptococcus pyogenes. The results displayed beta hemolysis, gram stain positive, cocci colonies, bacitracin sensitivity and positive reaction to latex agglutination reagent. Streptococcus pyogenes colonises on the skin and in the throat, they become pathogenic by penetrating through to the tissue cells and producing inflammation and avoiding immune response leading to infection such as pharyngitis or streptococcal toxic shock syndrome.

Case study 3 5. MacConkey agar– the MAC agar is a selective and differential gram-negative agar designed to differentiate bacterium on their ability to ferment lactose. It prevents the growth of gram-positive bacteria and is originally red in nature. The MacConkey agar contains:

o o o

neutral red – is red at a ph. below 6.8 lactose and is colourless if ph is over 6.8 – the PH decreases when lactose is fermented, Crystal violet: inhibits growth of gram-positive bacteria Lactose - either fermented or respired.

Hekteon Enteric (HE) agar– differentiate shigella and salmonella. Salmonella appears to have black colonies or dark centres whereas shigella has clear transparent colonies. o o o o

Proteose, peptone and yeast extracts provide nutrients bile salts – inhibits growth of most gram positive sodium thiophosphate and ferric ammonium sulphate – detects the production of Hydrogen sulphide (H2S) gas from salmonella due to the release of enzymes bromothymol blue and acid fuchsin dyes – works as a pH indicator

Xylose-lysine-deoxycholate (XLD) agar – is a selective and differential medium for the identification of gram-negative pathogens in faecal matter mostly shigella and salmonella. The agar will show results of red colonies for shigella and red colonies with black centres for salmonella (1). o o o o 6.

Sodium deoxycholate – gives it its selective nature and inhibits the growth gram-positive microorganisms Fermentable sugars – xylose (smaller amount), lactose, sucrose sodium thiophosphate and ferric ammonium sulphate- indicate hydrogen sulphide production with black colonies. phenol red – pink colonies under basic state and yellow colonies under acidic state.

Based on the results the micro-organism causing the illness is salmonella. Salmonella is a gram negative. the MAC was colourless which rules out other bacterium and helps to confirm the suggestion of salmonella. The HE agar showed black colonies. The XLD agar displays red colonies with black centres. Salmonella is manifested when food from infected animal is poorly cooked. Salmonella passes through the gastric acid barrier; they then occupy the intestines and cause an inflammatory response which causes diarrhea becoming pathogenic.

Reference

1.

Aryal, S., chitenge, et al. (2018). Xylose Lysine Deoxycholate (XLD) Agar- Principle, Uses, Composition, Preparation and Colony Characteristics. Retrieved 18 March 2021, from https://microbiologyinfo.com/xyloselysine-deoxycholate-xld-agar-principle-uses-composition-preparation-and-colony-characteristics/

2.

Giannella RA. Salmonella. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 21. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8435/

3.

Golińska, E., van der Linden, M., Więcek, G., Mikołajczyk, D., Machul, A., Samet, A., Piórkowska, A., Dorycka, M., Heczko, P. B., & Strus, M. (2016). Virulence factors of Streptococcus pyogenes strains from women in perilabor with invasive infections. European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology, 35(5), 747–754. https://doi.org/10.1007/s10096016-2593-0

4.

Jia, et al (2019). Impact of Healthcare-Associated Infections on Length of Stay: A Study in 68 Hospitals in China. BioMed Research International, 2019, pp.1-7.

5.

Patterson MJ. Streptococcus. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Chapter 13. Available from: https://www.ncbi.nlm.nih.gov/books/NBK7611/

6.

Sikora A, Zahra F. Nosocomial Infections. [Updated 2021 Feb 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK559312/

7.

Spellerberg B, Brandt C. Laboratory Diagnosis of Streptococcus pyogenes (group A streptococci) 2016 Feb 10. In: Ferretti JJ, Stevens DL, Fischetti VA, editors. Streptococcus pyogenes : Basic Biology to Clinical Manifestations [Internet]. Oklahoma City (OK): University of Oklahoma Health Sciences Center; 2016-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK343617/

8.

Tankeshwar, A. (2013). MacConkey Agar (MAC): Composition, preparation, uses and colony characteristics. Retrieved 20 March 2020, from https://microbeonline.com/macconkey-agar-mac-composition-preparation-usesand-colony-characteristics/

9.

Tankeshwar, A. (2013). Staphylococcus aureus: Disease, Properties, Pathogenesis, and Laboratory diagnosis Learn Microbiology Online. [online] Available at:

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