Microbiology and Parasitology Reviewer for MTLE Philippines 2026

By LisensyaPrep Team | Last Updated: April 2026 | 11-minute read

Microbiology and Parasitology tests your knowledge of the microscopic organisms that cause disease in humans and the laboratory methods used to identify them. For many MTLE examinees, this is actually one of the more enjoyable subjects because the content is concrete and pattern-based. Each organism has specific characteristics, staining reactions, and media preferences that you can learn as a profile.

This reviewer covers the highest-yield organisms, staining techniques, culture media, and parasitology topics for the MTLE.

Bacterial Classification and Gram Staining

The Gram Stain

The Gram stain is the most fundamental technique in bacteriology and one of the most consistently tested topics in MTLE microbiology. Know every step, what each reagent does, and what the results mean.

Clinically Important Bacteria

Gram-Positive Cocci

Staphylococcus aureus: Gram-positive cocci in clusters. Coagulase positive (distinguishes it from other Staph). Causes skin infections, wound infections, food poisoning (via heat-stable enterotoxin), toxic shock syndrome, and pneumonia. MRSA (methicillin-resistant S. aureus) is a major concern in hospital settings.

Streptococcus pyogenes (Group A Strep): Gram-positive cocci in chains. Beta-hemolytic. Causes strep throat, scarlet fever, impetigo, and rheumatic fever. Bacitracin sensitive (used to differentiate from other beta-hemolytic Strep).

Streptococcus pneumoniae: Gram-positive lancet-shaped diplococci. Alpha-hemolytic. Optochin sensitive and bile soluble. Most common cause of community-acquired pneumonia, bacterial meningitis in adults, and otitis media in children.

Enterococcus: Gram-positive cocci in pairs or chains. Grows in 6.5% NaCl (salt tolerance test). Common cause of urinary tract infections and infective endocarditis.

Gram-Negative Rods

Escherichia coli: Gram-negative rod. Facultative anaerobe. IMViC pattern: indole positive, methyl red positive, Voges-Proskauer negative, citrate negative. Most common cause of urinary tract infections and the most common cause of gram-negative bacteremia.

Klebsiella pneumoniae: Gram-negative rod with thick capsule. IMViC: indole negative, MR negative, VP positive, citrate positive. Causes lobar pneumonia with currant jelly sputum (bloody, mucoid). Commonly associated with hospital-acquired infections.

Pseudomonas aeruginosa: Gram-negative rod. Non-fermenter. Produces a blue-green pigment (pyocyanin). Grape-like or fruity odor. Oxidase positive. Opportunistic pathogen in immunocompromised patients, burn victims, and cystic fibrosis patients.

Salmonella typhi: Gram-negative rod. Causes typhoid fever. Non-lactose fermenter on MacConkey agar. Produces H2S on triple sugar iron (TSI) agar. Found in blood (first week), urine (second week), and stool (third week) during infection.

Common Culture Media

Special Staining Techniques

Acid-Fast Stain (Ziehl-Neelsen Stain): Used to identify mycobacteria (M. tuberculosis, M. leprae) and some parasites (Cryptosporidium oocysts). Acid-fast organisms retain carbol fuchsin and appear RED against a blue background. The waxy cell wall resists decolorization with acid-alcohol.

India Ink Preparation: Used to identify Cryptococcus neoformans in cerebrospinal fluid. The thick polysaccharide capsule repels the ink, creating a clear halo around the organism against a dark background.

KOH (Potassium Hydroxide) Preparation: Used for fungal detection in clinical specimens. KOH dissolves keratin and host cells, leaving fungal elements (hyphae, pseudohyphae, yeast cells) visible.

Giemsa Stain: Used to identify blood parasites (Plasmodium species causing malaria, Trypanosoma, Babesia), Chlamydia inclusions, and Histoplasma within macrophages.

Parasitology: High-Yield Organisms for the MTLE

Blood Parasites

Plasmodium species (Malaria):

Diagnosis: Thick and thin blood smears stained with Giemsa. Thick smear for detection, thin smear for species identification.

Intestinal Parasites

Ascaris lumbricoides: Largest intestinal roundworm. Eggs are bile-stained, mammillated (bumpy) outer coat. Fertilized eggs are diagnostic. Heavy infections can cause intestinal obstruction.

Entamoeba histolytica: Causes amoebic dysentery. Trophozoites contain ingested RBCs (hematophagous trophozoites). This is the key diagnostic feature distinguishing E. histolytica from non-pathogenic amoebae.

Giardia lamblia (intestinalis): Most common intestinal protozoan worldwide. Trophozoite has a characteristic pear shape with two nuclei (owl-eye appearance) and four pairs of flagella. Causes giardiasis: foul-smelling, fatty (steatorrhea), non-bloody diarrhea.

Trichuris trichiura (Whipworm): Barrel-shaped eggs with polar plugs. Adults have a whip-like anterior end embedded in the colonic mucosa.

Taenia saginata (Beef tapeworm) and Taenia solium (Pork tapeworm): Adults attach to the small intestine via their scolex. T. saginata has an unarmed scolex (no hooks). T. solium has an armed scolex (with hooks). T. solium is uniquely dangerous because its eggs can cause cysticercosis.

Laboratory Safety in Microbiology

Biosafety Levels (BSL):

BSL-1: Standard microbiological practices. Non-pathogenic organisms.

BSL-2: Organisms of moderate hazard (E. coli, S. aureus, hepatitis B, HIV). Splash shields, face protection, limited access.

BSL-3: Serious or potentially lethal agents transmitted via the respiratory route (M. tuberculosis, SARS-CoV, C. burnetii). Negative pressure rooms, respiratory protection.

BSL-4: Dangerous and exotic agents with no available treatment (Ebola, Marburg, smallpox). Full-body pressure suits, maximum containment.

Microbiology and parasitology reward systematic study. Learn each organism as a profile: Gram stain result, morphology, key biochemical reactions, media preference, and disease caused.

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