chapter 21

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Miscellaneous Bacterial Agents of Disease

Chapter 21

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spirochetes

Gram negative human pathogens

• Treponema

• Leptospira

• Borrella

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Treponema

• thin, coiled cells

• live in the oral cavity, intestinal tract, & perigenital regions of humans & animals

• Pathogenic species are strict parasites

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Treponema pallidum• human is the natural host• extremely fastidious & sensitive, cannot survive long

outside of the host• causes syphilis• Primary syphilis • Secondary syphilis• Tertiary syphilis • Congenital syphilis – nasal discharge, skin eruptions,

bone deformation, nervous system abnormalities• treatment: penicillin G

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Chancre

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Darkfield Microscopy

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Leptospira• tight, regular individual coils with a bend or

hook at one or both ends• L. biflexa – harmless, free-living saprobe• L. interrogans – causes leptospirosis, a

zoonosis– bacteria shed in urine; infection occurs by contact;

targets kidneys, liver, brain, eyes– sudden high fever, chills, headache, muscle aches,

conjunctivitis, & vomiting– 50-60 cases a year in US

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Borrella

• large, 3-10 coils

• Borrelioses transmitted by arthropod vector

• B. hermsii - relapsing fever

• B. burgdorferi - Lyme disease

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B. hermsii - relapsing fever

• mammalian reservoirs –squirrels, chipmunks, wild rodents

• tick-borne• after 2-15-day incubation, patients have high fever,

shaking, chills, headache, & fatigue• nausea vomiting, muscle aches, abdominal pain;

extensive damage to liver, spleen, heart, kidneys, & cranial nerves

• parasite changes & immune system tries to control it- recurrent relapses

• tetracycline

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B. burgdorferi - Lyme disease• transmitted by ticks• complex 2-year cycle involving mice & deer• nonfatal, slowly progressive syndrome that mimics

neuromuscular & rheumatoid conditions• 70% get bull’s eye rash• fever, headache, stiff neck, & dizziness• if untreated can progress to cardiac & neurological

symptoms, polyarthritis• tetracycline, amoxicillin• vaccine for dogs, human vaccine discontinued• Prevention-insect repellant containing DEET

Life Cycle of Ixodes

Figure 21.18

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Lyme disease

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Vibrio cholera

• comma-shaped• One of top 7 causes of morbidity & mortality• ingested with food or water• infects surface of small intestine, noninvasive• cholera toxin causes electrolyte & water loss

through secretory diarrhea (“rice-water” stool), resulting dehydration leads to muscle, circulatory, & neurological symptoms

• treatment: oral rehydration, tetracycline• vaccine

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Vibrio cholera

Action of Cholera Toxin

Figure 21.25

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other Vibrio

• salt-tolerant inhabitants of coastal waters, associate with marine invertebrates

• Vibrio parahaemolyticus –gastroenteritis from raw seafood

• Vibrio vulnificus - gastroenteritis from raw oysters

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Campylobacter jejuni

• important cause of bacterial gastroenteritis• transmitted by beverages & food (poultry most common)

• reach mucosa at the last segment of small intestine near colon; adhere, burrow through mucus and multiply

• symptoms of headache, fever, abdominal pain, bloody or watery diarrhea that is self-limiting

• heat-labile enterotoxin

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Campylobacter jejuni

Helicobacter pylori• Curved cells discovered in 1979 in stomach biopsied specimens

• Slightly helical, highly motile bacterium that colonizes the stomach of its hosts

• Causes gastritis and most (if not all) peptic ulcers

• H. pylori produces numerous virulence factors that enable it to colonize the stomach

H. pylori and

Peptic Ulcers

Figure 21.27.1

H. pylori and Peptic Ulcers

Figure 21.27.2

H. pylori and Peptic Ulcers

Figure 21.27.3

Diagnosis, Treatment, and Prevention• Diagnosis

– Presence of H. pylori can be demonstrated by a positive urease test

– Biochemical tests provide a definitive identification

• Treatment– Antimicrobial drugs are used in combination with drugs

that inhibit acid production

• Prevention– Prevention involves good hygiene, adequate sewage

treatment, water purification, and proper food handling

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Rickettsia

• obligate intracellular parasites• gram-negative cell wall• among the smallest bacteria• nonmotile pleomorphic rods or coccobacilli• ticks, fleas & louse are involved in their life cycle • bacteria enter endothelial cells & cause necrosis of

the vascular lining – vasculitis, vascular leakage & thrombosis

• treat with tetracycline & chloramphenicol

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4 types of rickettsioses1. epidemic typhus – R. prowazekii carried by lice; starts

with a high fever, chills, headache, rash; May have a chronic, recurrent form

2. endemic typhus – R. typhi, harbored by mice & rats; occurs sporadically in areas of high flea infestation; milder symptoms

3. Rocky Mountain spotted fever – R. rickettsii zoonosis carried by dog & wood ticks; most cases on eastern seaboard; distinct spotted rash; may damage heart & CNS

4. Ehrlichia genus contains 2 species of rickettsias; tickborne bacteria cause human monocytic & granulocytic ehrlichiosis

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Rocky Mountain Spotted Fever

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Rocky Mountain Spotted Fever Rickettsia rickettsii

Distribution of cases over a 4-year period

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Coxiella burnetti• causes Q fever• intracellular parasite • produces an unusual resistant spore• harbored by a wide assortment of vertebrates &

arthropods• transmitted by air, dust, unpasteurized milk, ticks• usually inhaled causing pneumonitis, fever, hepatitis• tetracycline treatment• vaccine available

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Coxiella burnetti

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Bartonella

• small gram-negative, fastidious, cultured on blood agar

• Bartonella-caused diseases– trench fever, spread by lice– cat-scratch disease, a lymphatic infection associated

with a clawing injury by cats. • Organism carried by 40% of cats• Most infections localized and resolve a a couple weeks

– bacillary angiomatosus in AIDS patients

• tetracycline, erythromycin & rifampin

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Cat-scratch diseaseBartonella henselae

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Chlamydia• obligate intracellular parasites• small gram-negative cell wall• C. pneumoniae – causes an atypical pneumonia

that is serious in asthma patients• C. psittaci – causes ornithosis, a zoonosis

transmitted to humans from bird vectors; highly communicable among all birds; pneumonia or flulike infection with fever, lung congestion

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Chlamydia trachomatis• human reservoir• 2 strains• trachoma strain– attacks the mucous membranes of the eyes,

genitourinary tract & lungs– ocular trachoma – uncommon in U.S. but common in Africa

and Asia. Severe infection, deforms eyelid & cornea, may cause blindness

– inclusion conjunctivitis – occurs as babies pass through birth canal; prevented by prophylaxis

– STD – urethritis, cervicitis, salpingitis (PID),infertility, scarring

• lymphogranuloma venereum strain– disfiguring disease of the external genitalia & pelvic lymphatics

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Chlamydia trachomatis

Lymphogranuloma venereum lesion

Trachoma

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Mycoplasma

• naturally lack cell walls, highly pleomorphic• treated with tetracycline, erthyromycin• M. pneumoniae – primary atypical pneumonia;

pathogen slowly spreads over interior respiratory surfaces, causing fever, chest pain & sore throat.

• M. hominis & Ureplasma urealyticum – weak sexually transmitted pathogens

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Bacteria in dental disease• oral cavity is a complex, dynamic ecosystem,

containing 400 species • dental caries – slow progressive infection of

irregular areas of enamel surface1. begins with colonization by slime-forming species of Streptococcus &

cross adherence with Actinomyces

2. process forms layer of thick, adherent material (plaque) that harbors masses of bacteria which produce acid that dissolves enamel

3. If plaque is allowed to stay, secondary invaders appear – Lactobacillus, Bacteroides, Fusobacterium, Porphyromonas, Treponema.

4. Acid dissolves tooth enamel

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Thin mucous coating of salivary proteins

Streptococcus mutans

Secondary invaders

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Peridontal disease

• soft tissue disease• when plaque becomes calcified into calculus

above and below the gingiva• this irritates tender gingiva causing inflammation

– gingivitis • pockets between tooth & gingiva are invaded by

bacteria (spirochetes & gram-negative bacilli)• tooth socket may be involved (peridontitis)• tooth may be lost