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Chapter 5: Infectious Diseases

Eric D. Spitzer

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Learning Objectives

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  1. Determine if an organism of interest is a bacterium, fungus, parasite, or virus and learn how it is further classified among related organisms.

  2. Learn the organisms that produce the commonly encountered and better characterized infectious diseases.

  3. Distinguish pathogenic organisms from those found in normal flora.

  4. Learn the laboratory test results associated with the individual infectious diseases and how they are used in establishing the diagnosis.

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Introduction

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Humans live in a world of microbes. Many types of microbes are part of the normal human flora and rarely cause disease. Others have a greater potential for virulence and can cause disease depending on complex interactions between the host and the microbe. A small group of organisms are highly virulent and usually cause disease whenever they infect humans. This chapter on infectious diseases and clinical microbiology focuses on common pathogens and frequently encountered clinical syndromes. Infectious agents include a daunting array of viruses, bacteria, fungi, protozoans, and helminths. Table 5–1 provides information on the basic microbiology and clinical significance of common pathogens. The organisms are grouped based on shared properties because these are often relevant to the diagnostic process.

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Table Graphic Jump Location
Table 5–1Selected Clinically Significant Microorganisms
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Table 5–1 Selected Clinically Significant Microorganisms
Aerobic gram-positive cocci Aerobic gram-negative bacilli Mycoplasma and Ureaplasma

  • Occur singly or in pairs, tetrads, chains, or clusters

  • Catalase positive

    • Micrococcus

    • Staphylococcus aureus

    • Coagulase-negative staphylococci

  • Catalase negative

    • Aerococcus

    • Enterococcus faecalis

    • Enterococcus faecium

    • Gemella

    • Leuconostoc

    • Streptococcus agalactiae (group B streptococci)

    • Streptococcus gallolyticus (bovis) (group D nonenterococcus)

    • Streptococcus dysgalactiae (multiple species within group C or group G streptococci are classified as S. dysgalactiae)

    • Streptococcus anginosus/intermedius group (viridans streptococci)

    • Streptococcus mitis (viridans streptococci)

    • Streptococcus mutans group (viridans streptococci)

    • Streptococcus pneumoniae(pneumococcus)

    • Streptococcus pyogenes(group A streptococci)

    • Streptococcus salivarius group(viridans streptococci)

    • Streptococcus sanguis group (viridans streptococci)

  • Aerobic gram-negative cocci

  • Occur singly or in pairs or clumps; catalase positive, oxidase positive

  • Moraxella catarrhalis (Branhamella catarrhalis)

  • Neisseria gonorrhoeae

  • Neisseria meningiditis

  • Aerobic gram-positive bacilli

  • Rod-like organisms; only Bacillus species produce spores; some organisms in category are partially acid-fast

  • Bacillus

  • Corynebacterium

  • Erysipelothrix

  • Gardnerella vaginalis (Gram variable)

  • Lactobacillus

  • Listeria

  • Nocardia

  • Mycobacteria

  • Rod-like organisms; acid-fast stain positive; some stains are gram-positive; most are slow growing

  • Mycobacterium tuberculosis

  • Mycobacterium avium complex

  • Mycobacterium kansasii

  • Mycobacterium marinum

  • Mycobacterium fortuitum complex (rapid grower)

  • Mycobacterium abscessus(rapid grower)

  • Mycobacterium chelonae (rapid grower)

  • Enterobacteriaceae; rod-like organisms; oxidase-negative; ferment sugars

  • Citrobacter

  • Edwardsiella

  • Enterobacter

  • Escherichia

  • Ewingella

  • Hafnia

  • Klebsiella

  • Morganella morganii

  • Proteus

  • Providencia

  • Salmonella

  • Serratia

  • Shigella

  • Yersinia enterocolitica

  • Yersinia pestis

  • Yersinia pseudotuberculosis

  • Aerobic gram-negative bacilli

  • Nonenterobacteriaceae, fermentative; rod-like organisms; oxidase-positive; ferment sugars

  • Aeromonas

  • Chromobacterium

  • Pasteurella

  • Plesiomonas

  • Vibrio

  • Aerobic gram-negative bacilli

  • Nonenterobacteriaceae; rod-like organisms; catalase positive; do not ferment sugars; oxidase variable

  • Acinetobacter

  • Alcaligenes

  • Burkholderia

  • Chryseobacterium (Flavobacterium)

  • Empedobacter (Flavobacterium)

  • Flaviomonas

  • Flavobacterium

  • Pseudomonas

  • Stenotrophomonas

  • Aerobic fastidious gram-negative bacilli

  • Small, straight or curved gram-negative bacilli or coccobacilli; may require special conditions for adequate growth

  • Aggregatibacter

  • Afipia

  • Bartonella

  • Bordetella

  • Brucella

  • Campylobacter (microaerophilic)

  • Cardiobacterium...

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