Bacterial Classification and Disease

Bacterial Classification and Disease Paul A. Gulig, Ph.D.

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Purpose To provide an overview of how physicians think when confronted with a bacterial infection To alert you to the importance of bacterial classification in treatment The importance of knowing the etiology of organ system based infection and the Gram stain

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Purpose Some microbiology courses teach infectious diseases in a “bug parade” – Here are all of the gram-positive cocci, and here’s what they do. Here are their random virulence factors, … That is not our philosophy (see Schaechter). This lecture provides that framework for students who want the bug parade organization.

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Purpose The detail in this lecture is NOT to be memorized for exams. The principles ARE testable.

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Bacterial Classification Based on several major properties Gram stain (and other stains) Morphology Metabolic behavior (e.g., oxygen) Infection patterns (e.g., zoonoses) Obligate intracellular Antigenic composition DNA sequence

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Metabolic properties May influence the type of disease caused, but not necessarily Anaerobes have a greater propensity to cause abscesses Mycobacterium tuberculosis is an obligate aerobe affects tissue tropism Acid fast organisms grow slowly – chronic infections Vibrio vulnificus grows fast – rapid progression

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Bacterial classification Cell morphology Bacteria Shapes Rod Cocci G+ G- Acid Wall Intra Spiral fast less cellular Filamentous Associations Rod Cocci Rod Cocci Spiral Individual Diplo- Staphylo- Strepto- Filaments

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Bacteria Gram + Gram – Acid Fast Intra Wall Cellular Less Cocci Rod Spiral Rod Cocci M.t.M.l. Rickettsia Mycoplasma N.c. Coxiella Ureaplasma ErlichiaChlamydia Staph.Strep. Entero Non-spore Spore Treponema Neisseria coccus Borrelia Moraxella Leptospira Fil Rod +O -O 2 2 S. a. A A.i. C.d. B.a. C.b. Curve Straight S. e. B L. m. B.c. C.t. S. s. Pn C.p. Vibrio Vir C.d. Campylobacter Other Helicobacter +O +/-O -O 2 2 2 P.a. Enteric BacteroidesMany! Resp. Zoonoses GU Bordetella Yersinia H. ducreyi Haemophilus Pasteurella Gardnerella Legionella BrucellaFrancisellaStreptobacillus

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Classification and Disease Gram-positive cocci – pyogenic Streptococcus pyogenes Staphylococcus aureus Gram-negative cocci – pyogenic Neisseria gonorrhoeae Neisseria meningitidis Spirals – chronic infections Treponema pallidum Borrelia burdorferi Leptospira

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How a physician approaches bacterial diseases Organ system approach Which bacteria cause disease in a certain location The “usual suspects” Gram stain approach The Gram stain is used to treat empirically before cultures are completed Requires that one is able to get a Gram stain directly from a patient sample, which is not always the case (e.g., stool, sinus, endocarditis) The combination of these is ideal1

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Upper Respiratory Tract Pharyngitis mostly viral lots of normal flora (Gram stain little value) rapid test (e.g., Phadebact), culture If Streptococcus pyogenes (Group A strep) must treat – why? Other causes – young adult Mononucleosis Gonorrhea Diphtheria (not likely – why?)

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Pneumonia Sputum Gram stain (and other stains) very helpful (why?) Coupled with chest X-ray Other signs, symptoms, history

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Gram stain What is this? 2

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Gram stain What is this?

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Acid fast stain What is this?

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Silver stain What is this?

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Otitis media and Sinusitis Gram stain and culture not practical Otitis media – tympanostomy Sinusitis – must access sinus os Usual suspect list (same) Streptococcus pneumoniae Haemophilus influenzae Moraxella catarrhalis Empiric therapy

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Meningitis Gram stain practical and extremely important CSF sterile, few host cells Note bacteria and host cells Couple with age Neonate Child Adult

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Meningitis Neonate E. coli K1 Group B streptococcus (S. agalactiae) Listeria monocytogenes Children and adults Streptococcus pneumoniae Neisseria meninigitidis

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Meningitis

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Meningitis 3

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Meningitis

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Endocarditis Gram stain not practical Can’t access infection site! Bacteremia too low Usual suspects Oral streptococci Enterococci Staphylococci

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Enteric infections Gram stain not practical Can’t access infection site Too much stuff in stool Mostly viral Blood and pus indicators of disease

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Abdomen Organisms come from the GI tract Gram-negative rods Facultative anaerobes (Enterobacteriaceae) Obligate anaerobes (Bacteroides, Fusobacterium) Sometimes gram positive cocci Aerobic (Enterococcus and Streptococcus) Anaerobic (Peptostreptococcus) Obligate anaerobic gram positive rods (Clostridium)

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Skin Infections Skin flora – gram-positive cocci Staphylococcus aureus Streptococcus pyogenes Complex skin infections Skin flora plus enteric flora and environmental flora

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Urinary tract infection Because of proximity to GI tract enteric flora are the prime suspects Facultative aerobic enteric gram- negative rods predominate (E. coli) Unusual to find staphylococci and streptococci or anaerobes

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Sexually Transmitted Only a few bacteria Neisseria gonorrhoeae Chlamydia trachomatis Treponema pallidum

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Sexually Transmitted 4

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Sexually Transmitted

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Sexually Transmitted Dark field 5

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Take home messages Classification is boring but important for initial therapy. Know what organisms are common at the various sites of infection as you go through the course. Know the Gram stain and metabolic properties of the common bacteria found at each organ system infection. Don t memorize it for this lecture. It will be taught in the lectures that follow.

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