Zoonotic Bacteria
Zoonosis ★★★
A disease that can be transmitted from animals to humans.
Bacteria causing zoonosis.
The deck's own first question is “What is zoonosis?” — so learn the one line exactly. Three genera follow: Brucella, Yersinia and Bacillus.
- Define zoonosis. → A disease that can be transmitted from animals to humans
- Define zoonotic bacteria. → Bacteria causing zoonosis
Brucella ★★★
| Species | Animal reservoir |
|---|---|
| B. abortus | Cattle |
| B. melitensis | Goat, sheep |
| B. suis | Swine |
| B. canis | Dog |
| Property | Detail |
|---|---|
| Morphology | Coccobacillus, 0.4–0.8 × 1.2 µm · Gram-negative · non-motile, non-spore-forming · microcapsule in some |
| Culture | Obligate aerobes · 5–10% CO₂ for B. abortus · fastidious · slow growth, 2–5 days |
| Intracellular | Facultative intracellular pathogens |
| Antigens | LPS, endotoxin. Two major serological determinants: A and M — A = abortus antigen, M = melitensis antigen |
| Virulence factors | Endotoxin (main) · invasiveness: capsule and hyaluronidase |
| Transmission | Intestinal tract — infected milk · respiratory tract — aerosols containing the bacteria · direct contact |
Disease — brucellosis
| Host | Disease |
|---|---|
| Animals | Infections of the genital system · abortion (erythritol) · inapparent infections — the source |
| Humans | Undulant fever |
The pathway of undulant fever: the organism, as a facultative intracellular parasite → the lymphatic system → the blood (bacteraemia) → liver, spleen, bone marrow and lymph nodes.
Immunity is cell-mediated (CMI). Prevention: pasteurisation of milk for drinking; slaughter and immunisation of animals; vaccination of high-risk persons. Treatment: tetracycline and ampicillin, prolonged.
Facultative intracellular pathogen. Cell-mediated immunity. Prolonged treatment. Those three lines are scattered across four slides and they are one idea.
An organism that lives inside host cells is out of reach of antibody, which cannot cross a cell membrane. So humoral immunity is useless and CMI is what controls it — the same reasoning that makes the tuberculin test meaningful in the next unit.
It is equally out of reach of most antibiotics, which is why treatment must use cell-penetrating drugs like tetracycline, and why it must be prolonged — and why the fever undulates, rising as organisms are released into the blood and falling as they retreat back into cells.
One property; the immunology, the therapy and the name of the disease.
The erythritol detail is worth a mark too: this sugar is abundant in the placenta of cattle, goats and swine but not of humans, which is why Brucella causes abortion in animals and not in people.
- Name the four Brucella species and their reservoirs. → B. abortus — cattle · B. melitensis — goat and sheep · B. suis — swine · B. canis — dog
- Describe the organism. → Gram-negative coccobacillus, non-motile, non-spore-forming, some with a microcapsule; obligate aerobe, fastidious, slow-growing (2–5 days); facultative intracellular
- Name its virulence factors. → Endotoxin (main); capsule and hyaluronidase for invasiveness
- How is it transmitted? → Infected milk (intestinal), aerosols (respiratory), direct contact
- What disease in humans, and what is its pathway? → Undulant fever — organism → lymphatics → blood (bacteraemia) → liver, spleen, bone marrow, lymph nodes
- What kind of immunity, and why? → Cell-mediated — the organism is a facultative intracellular parasite, out of antibody's reach
Yersinia pestis ★★★
| Species | Transmission | Disease |
|---|---|---|
| Y. pestis | Flea bite · respiratory tract | Plague |
| Y. enterocolitica | Digestive tract | Enterocolitis |
| Y. pseudotuberculosis | Digestive tract | Enterocolitis |
The historical scale is on the slides: during the 14th century, over a five-year period, 25 million deaths; the most recent pandemic, in Asia in 1904, a million deaths.
| Property | Detail |
|---|---|
| Morphology | Coccobacillus · Gram-negative with BIPOLAR STAINING · capsule · non-motile · non-spore-forming |
| Cultivation | Facultative anaerobe · slow growth · irregular, rough colony · optimum temperature 27–30 °C |
⭐ Antigenic structure and virulence factors — the same five
| Factor | Detail |
|---|---|
| F1 antigen (fraction I) | Capsular antigen |
| V-W antigen | Protein–lipoprotein |
| Yop | Yersinia outer membrane proteins |
| Murine toxin (MT) | An exotoxin, released only when cells are lysed; potent |
| Endotoxin | LPS |
Transmission
Rat ↔ rat by direct contact or the biting of rat fleas; then by rat fleas to a person; then person ↔ person by human fleas or the respiratory route.
⭐ The three forms of plague
| Form | Frequency | Features | Mortality |
|---|---|---|---|
| Bubonic plague | The most common | Enlarged and inflamed lymph nodes — around the armpits, neck and groin | 30–75% |
| Pneumonic plague | The second most common | 90–95% | |
| Septicaemic plague | The most rare | Close to 100% |
The deck's sequence for the Black Death: infected fleas bite → bubonic plague → spreads → pneumonic plague → disseminated intravascular coagulation → intravascular thrombi and purpuric lesions → gangrene and blackening all over the body — the black death.
Prevention: elimination of rats and fleas; an effective formalin-killed vaccine. Treatment: streptomycin and tetracycline, rapidly. The deck's own emphasis: “Control of plague is based upon flea and rodent control!”
The deck's own multiple-choice asks exactly this: the primary epidemiologic difference between the two clinical forms is… — the route of infection.
Bubonic arrives through the skin, from a flea bite. The organism travels to the draining lymph node, which swells into the bubo that names the disease. It is a disease of rats and fleas, and it does not spread from person to person.
Pneumonic arrives through the lungs — either by spread from a bubonic case or, critically, by the respiratory route from another patient. That single fact turns a rodent disease into a human epidemic, which is why it kills 90–95% rather than 30–75%: there is no lymph node to contain it and no time to treat.
And it is why the control measure is flea and rodent control. Break the first route and the second never starts.
- Name the three Yersinia species with transmission and disease. → Y. pestis (flea bite, respiratory) → plague; Y. enterocolitica and Y. pseudotuberculosis (digestive) → enterocolitis
- Describe Y. pestis. → Gram-negative coccobacillus with BIPOLAR staining, capsulate, non-motile, non-spore-forming; facultative anaerobe, slow growth, rough irregular colony, optimum 27–30 °C
- Name its five virulence factors. → F1 (capsular) antigen · V-W antigen · Yop · murine toxin (exotoxin, released on lysis) · endotoxin
- Name the three forms of plague with mortality. → Bubonic (most common, swollen lymph nodes, 30–75%) · pneumonic (second, 90–95%) · septicaemic (rarest, near 100%)
- What is the primary epidemiological difference between bubonic and pneumonic? → The route of infection
- On what is plague control based? → Flea and rodent control
Bacillus anthracis ★★★
| Species | Disease |
|---|---|
| B. anthracis | Anthrax |
| B. cereus | Food poisoning |
| Property | Detail |
|---|---|
| Morphology | Gram-positive rod with SQUARE ENDS in long chains — the “bamboo” appearance · central spore · capsule of D-glutamate |
| Culture | Aerobic or facultatively anaerobic · colony with irregular margins · non-haemolytic |
| Resistance | Strong resistance to dry heat, desiccation and disinfectant; sensitive to oxidants and autoclaving |
⭐ The two virulence factors — the deck asks this directly
| Factor | Detail |
|---|---|
| 1 · Capsule | Poly-D-glutamate polypeptide |
| 2 · Anthrax toxin | Protective antigen (PA) — proteolytic activation · lethal factor (LF) · oedema factor (EF). PA + EF = oedema toxin · PA + LF = lethal toxin — responsible for shock and death |
Disease — anthrax
| Detail | |
|---|---|
| Source | Herbivorous animals |
| Transmission | Direct contact · digestive tract · respiratory tract |
| Clinical types | Cutaneous anthrax (90%) — papule → vesicle → ulcer → eschar Intestinal anthrax (5%) Pulmonary anthrax (5%) — woolsorter's disease |
Prevention: contaminated animals, carcasses or hides should be burned or deeply buried; vaccination of animals and of humans at risk. Treatment: penicillin, tetracycline, erythromycin.
The deck's speaker notes carry a detail that explains a rule of veterinary law: sporulation of B. anthracis requires oxygen, and therefore does not occur inside a closed carcass. The vegetative cells in the carcass are killed within a few days by putrefaction.
So a sealed dead animal is, left alone, self-sterilising. Cut it open and you give the organism the oxygen it needs to form spores — which, per the resistance row above, survive dry heat, desiccation and disinfectant, and will contaminate that ground for decades.
That is why regulations in most countries forbid post-mortem examination of animals when anthrax is suspected, and why carcasses are burned or buried deeply rather than dissected.
The PA/LF/EF scheme is worth understanding rather than memorising, too. Neither LF nor EF can enter a cell alone; PA is the delivery system — Unit 6's B subunit, mediating adherence and entry — and LF and EF are two different A subunits it can carry. One binding component, two payloads, two toxins.
- Describe B. anthracis. → Gram-positive rod with square ends in long 'bamboo' chains, central spore, D-glutamate capsule; aerobic or facultatively anaerobic, irregular non-haemolytic colonies
- Name its two virulence factors. → The poly-D-glutamate capsule and anthrax toxin
- What are the three components of anthrax toxin, and the two toxins? → PA, LF, EF; PA + EF = oedema toxin, PA + LF = lethal toxin (responsible for shock and death)
- Name the three clinical types with their frequencies. → Cutaneous 90% · intestinal 5% · pulmonary 5% (woolsorter's disease)
- What is the cutaneous sequence? → Papule → vesicle → ulcer → eschar
- Why must a suspected anthrax carcass not be opened? → Sporulation needs oxygen; opening the carcass lets highly resistant spores form and contaminate the ground
⭐ The deck's own questions
Intestinal anthrax (5%) — the digestive tract.
Pulmonary anthrax (5%) — the respiratory tract, also called woolsorter's disease.
The source in every case is herbivorous animals.
Plague is caused by… — a. Y. pestis.
Which bacteria can cause food poisoning? — a. B. cereus.
The primary epidemiologic difference between bubonic and pneumonic plague is… — b. route of infection. Bubonic arrives through the skin from a flea bite; pneumonic through the lungs, and can pass from person to person.
The correct pairing, from slide 5 of the same deck:
B. abortus — cattle (abortus = the A antigen, abortion in cattle)
B. melitensis — goat and sheep (the M antigen; melitensis from Malta, and Malta fever)
B. suis — swine (sus = pig)
B. canis — dog (canis = dog)
Three of the four species names are the answer. Learn them that way and the question cannot catch you.
Revision
The three genera on one screen
| Brucella | Yersinia pestis | Bacillus anthracis | |
|---|---|---|---|
| Gram | G− coccobacillus | G− coccobacillus, bipolar | G+ rod, square ends, bamboo chains |
| Spore | None | None | Central |
| Capsule | Microcapsule (some) | F1 antigen | Poly-D-glutamate |
| Main virulence | Endotoxin | F1 · V-W · Yop · MT · endotoxin | Capsule + anthrax toxin (PA, LF, EF) |
| Transmission | Milk · aerosol · contact | Flea bite · respiratory | Contact · digestive · respiratory |
| Disease | Undulant fever | Plague — bubonic, pneumonic, septicaemic | Anthrax — cutaneous 90%, intestinal 5%, pulmonary 5% |
| Treatment | Tetracycline, ampicillin — prolonged | Streptomycin, tetracycline — rapid | Penicillin, tetracycline, erythromycin |
- Define zoonosis. → A disease that can be transmitted from animals to humans
- Match the Brucella species to their reservoirs. → abortus–cattle · melitensis–goat and sheep · suis–swine · canis–dog
- Name the three forms of plague with mortality. → Bubonic 30–75% · pneumonic 90–95% · septicaemic near 100%
- Give the anthrax toxin equations. → PA + EF = oedema toxin; PA + LF = lethal toxin
- Name the three clinical forms of anthrax and their routes. → Cutaneous 90% (contact) · intestinal 5% (digestive) · pulmonary 5% (respiratory, woolsorter's disease)
- Why is brucellosis treated for a long time? → It is a facultative intracellular pathogen, controlled by cell-mediated immunity and hard for antibiotics to reach