Mircology Quiz

The tube test method detects both free coagulase and bound coagulase, making the correct answer 'Free coag (and also bound)'.

Some staph aureus strains produce fibrinolysins that can dissolve the formed clot during tube coag testing, resulting in a negative result. To avoid this, incubation should be done at a lower temperature to prevent the activity of fibrinolysins.

In the toluidine blue method, a positive DNAse result is indicated by the color pink. This is important information for interpreting the results of DNAse tests accurately.

In the HCl flood plate method for DNase testing, a positive result is indicated by the clearing of the agar around the bacterial growth, not by no change, precipitate, or color change.

Folliculitis is the inflammation of hair follicles, commonly caused by bacterial or fungal infection. Dermatitis, psoriasis, and eczema are skin conditions that are different from folliculitis.

A furuncle is a type of skin abscess that involves the hair follicle and surrounding tissue. An abscess, pustule, and cyst are different types of skin infections or growths that may resemble a boil but have distinct characteristics.

Carbuncles are a cluster of connected boils that form under the skin. Pustules are small bumps on the skin filled with pus, abscesses are pus-filled pockets in the skin, and fistulas are abnormal passageways that connect two body parts.

Impetigo is a highly contagious skin infection that commonly occurs on the face and is characterized by dry, crusty lesions. Incorrect answers: Eczema is a chronic skin condition that results in itchy, inflamed skin. Psoriasis is an autoimmune disease that causes red, scaly patches to appear on the skin. Rosacea is a common skin condition that causes redness and visible blood vessels on the face.

The correct answer highlights infections commonly associated with CNS involving staph epidermidis, while the incorrect answers do not typically relate to CNS infections caused by this bacterium.

Staph aureus is known to possess beta-lactamases, enzymes that can break down beta-lactam antibiotics like penicillin. The other options provided are not commonly associated with the majority of staph aureus bacteria.

Vancomycin is the drug of choice for treating MRSA infections due to its effectiveness against the bacteria. However, overusing vancomycin can lead to the development of VRSA, a vancomycin-resistant superbug that poses a serious threat to public health.

MRSA can be detected using various methods including cefoxitin screen, MH + 4% NaCl + oxacillin disk, chromagar, or molecular methods. It is not solely detected through blood cultures, visual inspection, or symptoms listening.

Micrococcus can be differentiated from staphs based on their pigmentation and cluster arrangement observed in the gram stain. Micrococcus are typically pigmented in yellow or red hues and tend to form distinct tetrad and octad clusters, whereas staphs may show different characteristics. These features help in distinguishing between the two bacterial types.

The D-test is specifically used to detect inducible clindamycin resistance in bacteria, as described in the correct answer.

MRSA differs from regular staph in preferring slower growth with longer incubation times, liking increased salt concentrations, and thriving in lower temperatures. The incorrect answers provided describe contrasting conditions that do not favor the growth of MRSA.

Group A strep, also known as Streptococcus pyogenes, is not considered part of one's normal flora even though individuals can carry it in their upper respiratory tract. It can cause various infections if it overgrows or spreads to other parts of the body.

Strep pneumo colonies appear concave as they age due to autolysis, which causes the center of the colony to break down and sink inwards.

Nutritionally variant streptococci (NVS) require vitamin B6 (pyridoxal) for growth, which can be provided by streaking a staphylococcus culture onto the agar plate for the NVS to utilize.

The correct answer highlights the key differences between acid extraction and enzyme extraction in typing Lancefield strep groups, along with the limitation of latex typing for alpha heme strep. The three incorrect answers provide misleading information for each option, emphasizing the importance of understanding the differences between the extraction methods and the limitations of latex typing in identifying specific strep groups.

Streptolysin S and Streptolysin O are the two streptolysins produced by strep. Streptolysin S is O2 stable and can be seen on the media as beta-hemolysis (BH), while Streptolysin O is O2 labile and can only be visualized as BH in stabs or if the plate has been incubated under anaerobic (ANO2) conditions.

When testing for bacitracin susceptibility in strep pyogenes, any zone size indicates susceptibility to the antibiotic. A zone size of no zone would mean the bacteria is resistant, a zone size of less than 10 mm would indicate intermediate susceptibility, and if the zone size varies it would suggest variable susceptibility.

The PYR test is used to detect the presence of the enzyme pyrrolidonyl aminopeptidase (PYR) in bacteria. Streptococcus pyogenes is PYR positive, meaning it gives a positive result on the test.

Strep pyogenes utilizes the m-protein to mimic heart tissue, leading the body to attack its own heart muscle and potentially causing rheumatic fever.

Streptococcus pyogenes' capsule is composed of hyaluronic acid, which helps the bacteria evade the host's immune system. The incorrect answers provided are common components found in other organisms but not in the capsule of this specific bacterium.

Erysipelas specifically refers to a bacterial infection that involves the upper dermis and superficial lymphatics. The other options are skin conditions but do not specifically refer to cellulitis of the face.

Erysipeloid is the term specifically used to describe cellulitis caused by Erysipelothrix rhusiopathiae, while the other options do not refer to this specific bacterial infection.

Bacitracin response refers to the susceptibility of the bacteria to bacitracin antibiotic. In the case of strep dysgalactiae (c,g,f), it shows resistance to bacitracin, resulting in no zone of inhibition when tested in the laboratory.

Group B streptococcus is commonly known as Strep agalactiae, distinct from other streptococcal species.