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Genera of Medically Important Microbial Families

Enterobacteriaceae

• Gram-negative rods whose natural habitat is the intestinal tract of humans and animals.
• Currently has 53 genera (and over 170 named species).
• Facultative anaerobe (bacteria that can grow in the presence or absence of oxygen).
• Gram-negative, non-sporing, rod-shaped bacteria
• Motility is by peritrichous flagella except Shigella and Klebsiella that are not motile.
• Grow on bile-containing media like MacConkey agar
• Many are normal inhabitants of the intestinal tract, while some are enteric pathogens or urinary and or respiratory tract pathogens.
• Differentiation is based on biochemical reactions and differences in antigenic structure.
• Causes 3 million deaths/year, and 4 billion infections worldwide.
• Family genera include Escherichia, Shigella, Citrobacter, Klebsiella, Hafnia, Enterobacteriaceae, Providencia, Edwardsiella, Pectinobacterium, Salmonella, Morganella, Enterobacter, Serratia, Proteus, Yersinia, Erwinia.

Mycobacteriaceae

• Has Mycobacterium as its single genus.
• Organisms belonging to this genus are quite diverse in their ability to cause disease in humans.
• Some are strict pathogens, while others are opportunistic or nonpathogenic.
• Obligate aerobic organisms, considered Gram-positive.
• Non-motile rod-shaped bacteria with fastidious growth requirements.
• Characterized by their ability to form unique cell walls rich in mycolic acids, contributing to their resistance to many antibiotics and disinfectants.
• These long-chain (C-60 to C-90) fatty acids in the cell wall make all mycobacterial species “acid-fast” as they resist acid-alcohol decolorization
• Diseases caused include Tuberculosis group (typical) 1-Mycobacterium tuberculosis (MTB), 2-M.bovis, 3-M.avium, Jhons disease, Leprosy disease , Oppurtunistic diseases.

Pseudomonadaceae

• The genera include Frateuria, Pseudomonas (the type genus), Xanthomonas, Zoogloea.
• Gram-negative, rod-shaped, and polar-flagellated bacteria, aerobic and non-fermentative.
• They are chemoorganotrophic with some species being chemolithotrophic using hydrogen or carbon dioxide for energy sources. Species of these genera are common saprophytes in both fresh and marine waters and soil and are pathogenic to plants, animals, and humans.
• Many members produce derivatives of the fluorescent pigment pyoverdine
• The presence of oxidase and polar flagella and the inability to carry out fermentation differentiate pseudomonads from Enterobacteriaceae.
• Pseudomonas aeruginosa is the most common human pathogen

Debaryomycetaceae

• Pathogen is candida albicans.
• Candida albicans is a common commensal fungus that colonizes the oropharyngeal cavity, gastrointestinal and vaginal tract, and healthy individuals' skin.
• Causes opportunistic infection in immunocompromised people.
• Small, oval, measuring 2-4 µm in diameter.
• Yeast form, unicellular, reproduces by budding asexually and doesn't perform meiosis.
• Encapsulated and diploid, also form true hyphae.
• Polymorphic fungus (yeast and pseudohyphal form)
• 80-90% of the cell wall is carbohydrate

Tremellaceae

• Pathogen is cryptococcus neoformans.
• Found in the environment growing as unicellular yeast and they reproduce by budding.
• Exists as a saprophytic and encapsulated yeast-like.
• The yeast cells are dry, and light, making them easy to aerosolize.
• Undergoes sexual reproduction forming dikaryotic hyphae and basidiospores supported by a club-shaped basidium with hyphae that have a complex septate. Characterized by the presence of a polysaccharide capsule, the formation of melanin, and urease activity, which all function as virulence determinants.
• Affect immunocompetent persons but more often in patients with HIV/AIDS, tuberculosis, hematogenous malignancies, and hospitalized patients majorly those with invasive devices causing meningitis.

Coronaviridae

• Coronavirus [Severe acute respiratory syndrome coronavirus-2 (SARS- CoV-2)] , is the pathogen.
• Enveloped, positive single-stranded RNAs.
• They are spherical virions with a core-shell and a surface that resembles a solar corona based on its surface protein projections, hence their name (Latin: corona = crown).
• There are four main genera; alpha-, beta-, gamma-, and delta- coronaviruses.
• Alpha- and beta-coronaviruses originate from mammals, mainly bats, and are thought to cause more severe and fatal diseases in humans.
• Gamma- and delta-viruses mainly originate from birds and pigs and are thought to cause asymptomatic or mild disease in humans.
• Beta-coronaviruses have three important envelope proteins: Spike (S) protein, Membrane (M) protein, and Envelope (E) protein.
• S protein mediates viral attachment to the cell membrane receptor, membrane fusion, and ultimately viral entry into the host cell.
• M protein, the most abundant membrane protein, together with E protein are responsible for the coronavirus membrane structure.
• Another component of the beta-coronavirus is the N protein, which is the protein component of the helical nucleocapsid that includes the genome RNA.

Hepatitis Viruses

• Cause Hepatitis, an inflammation of the liver.
• There are 5 main hepatitis viruses, referred to as types A, B, C, D and E.
• These 5 types are of greatest concern because of the burden of illness and death they cause and the potential for outbreaks and epidemic spread.
• Types B and C lead to chronic disease in hundreds of millions, and are the most common cause of liver cirrhosis and cancer.
• Hepatitis A and E are typically caused by ingestion of contaminated food or water.
• Hepatitis B, C and D usually occur as a result of parenteral contact with infected body fluids.
• Morphology is icosahedral either naked or enveloped, except HBV has three types of particles that include: 1, the 42 nm Dane particles (infectious virus); 2, the 22 nm HBsAg particles; 3, the 22 nm (diameter) HBsAg filaments.