medical microbiology

what are the different types of transmission

• respiratory or salivary spread

• decal-oral spread

• venereal spread

• vector (biting arthropod)

• vertebrate reservoir

• vector-vertebrate reservoir

how is respiratory or salivary spread controlled

not readily controllable

how is fecal-oral spread controlled

controllable by public health measures

how is venereal spread controlled 

• difficult to control as social factors are involved

• protected sex

what are some examples of vector transmission (biting arthropod)

• malaria

• sandfly fever

• typhus (louse-borne)

what are some examples of vertebrate reservoir transmission

• rabies 

• brucellosis 

what are some examples of vector-vertebrate reservoir transmission 

• plague

• yellow fever 

what is horizontal transmission

infection transmission via humans

examples of horizontal transmission

• polio

• influenza

• typhoid

what are some examples of vertical transmission

• HIV

• hepatitis B virus 

what type of bacteria is pseudomonas

opportunistic bacteria 

what does it mean if bacteria is termed ‘pseudomonades’

a term for bacteria which morphologically and physiologically resemble members of the genus pseudomonas 

what gram stain are pseudomonas bacteria and what is the diversity like in the group

• very diverse group

• gram-negative rods with strictly-respiratory mode of metabolism (require oxygen)

what is an important pseudomonades pathogen

• pseudomonas aeruginosa

• leading cause of hospital-acquired infections

• develops quite often resistance against antibiotics or detergents

what is borrelia burgdorferi also known as

Lyme disease

how is borrelia burgdorferi spread

by bites of ticks

what are the 3 stages of borrelia burgodorferi 

• distinctive expanding rash at the site of the bite

• dissemination stage with headache and fever

• persistent infection: nervous system is affected

how can borrelia burgdorferi be treated

with antibiotics

what is pneumonia caused by

can be caused by a wide variety of different pathogens and microorganisms

what is the most common cause of infection-related deaths int he US and Europe 

pneumonia 

what is the classic bacterial cause of acute community-acquired pneumonia 

streptococcus pneumonia 

causes of pneumonia in children 

• mainly viral 

• or bacterial secondary to viral respiratory infection- but only get the bacterial one because you had the viral 

what can neonates develop after pneumonia

may develop interstitial pneumonitis caused by chlamydia acquired from the mother at birth

what are the causes of pneumonia in adults

• bacterial

• causes more common than viral

what is the aetiology of pneumonia 

• varies with age

• occupation and geographical risk factors 

what are the 2 main types of pneumonia 

• community acquired

• hospital acquired

what are some examples of how you can get community acquired pneumonia

• alcoholics and vagrants

• HIV positive

• underlying respiratory tract disease

• occupational exposure

• exposure to animals 

• travel exposure 

what are some examples of how you can get hospital acquired pneumonia

• HIV positive

• immunocompromised.g. post organ transplant 

• underlying condition requiring assisted ventilation

what gram stain are endospore-forming bacteria 

• gram positive 

• usually rod shaped 

what are the 2 important endospore-forming bacteria

bacillus and clostridium

what type of extremophile is bacillus

aerobe

what is bacillus anthracis a cause of

anthrax

what is anthrax

a disease of cattle that can be transmitted to humans

what does bacillus cereus cause

food poisoning

what is vibrio cholerae usually associated with

natural disasters —> sanitation disturbed

what is vibrio cholerae

a disease of the intestinal tract

how are the vibrio cholerae bacteria typically ingested

by drinking water contaminated by improper sanitation or by eating improperly cooked fish, especially shellfish 

what do symptoms of vibrio cholerae include

• diarrhoea 

• abdominal cramps

• nausea

• vomiting 

• dehydration 

what is death from vibrio cholerae usually due to

due to the dehydration caused by the illness

how does vibrio cholerae mechanistically cause its watery diarrhoea symptom

• cholera toxin made up of 2 subunits A and B

• subunit binds to the GM1 receptor

• A subunit is taken into the cell and binds to G alpa S

• activates adenylate cyclate and activates cAMP

• cAMP activates CFTR

• CFTR leads to the efflux of Cl- out of the cell into the lumen of the GI tract

what is pyogenic cocci

spherical bacteria which cause various suppurative (pus-producing) infections in animals 

what are the leading pathogens of humans 

• gram positive cocci

• around 1/3 of all infections

where does staphylococcus aureus live

on skin and nasal membranes

what symptoms can staphylococcus aureus induce

• boils

• pimples

• wound infections

• pneumonia

• toxic shock syndrome

what is the leading cause of infections acquired in hospitals 

staphylococcus aureus 

what is staphylococcus aureus resistant to 

penicillin and many other antibiotics 

what is MSRA

methicillin resistant staphylococcus aureus

where is MRSA usually confined to

hospitals

how can MSRA be treated

by vancomycin

what is the peeling skin symptom called in staphylococcus aureus 

staphylococcus scaled skin syndrome (SSSS)

what are the different staphylococcal toxins

• alpha toxin

• beta toxin

• delta toxin

• exfoliate toxin

• enterotoxins

• toxic-shock syndrome toxin-1 (TSST-1)

what is the staphylococcal alpha toxin produced by 

produced by most staph aureus strains that case human disease 

what does the staphylococcal alpha toxin disrupt

disrupts the smooth muscle in blood vessels and is toxic to many cell types (damages tissues)

what toxin produces SSSS

exfoliate toxin

what are enterotoxins responsible for

staphylococcal food poisoning

what do delta toxins have a wide spectrum of

cytolytic activity

what is the percentage of staph aureus strains responsible for menstruation-associated TSS that produce TSST-1

90%

what is death in patients with TSS caused by

hypolovemic shock leading to multiorgan failure

what type of extremophile is clostridium

anaerobe

what can clostridium bacteria produce

endospores

what does clostridium tetani cause

tetanus

what does clostridium perfringens cause

• food poisoning

• anaerobe wound infection

• gangrene

what does clostridium difficile cause

severe form of colitis

what is the first sign of tetanus

• lockjaw (trismus)

• followed by stiffness of the neck and back

• stiffness and spasming of muscles expands throughout the body inferiorly

what is the percentage of patients of tetanus victims that die

30%

what blocks inhibitory transmitter release in nerve-muscle transmission in patients who have tetanus

tetanospasmin

what does the blocking of inhibitory transmitter release mean for nerve-muscle transmission in patients with tetanus

• continuous stimulation by excitatory transmitter

• therefore muscles cant relax

where are enteric bacteria found

• in the intestinal tract of animals

what gram stain are enteric bacteria and what type of metabolism do they have

• gram-negative rods

• with facultative anaerobic metabolism

what is the second most important bacteria in the gut

E. coli

are there a lot of strains of E. coli that are pathogenic

• no

• only few strains

how much E. coli should be in 1L of drinking water

less than 5 E. coli bacteria

what does shigella dysenteriae cause

bacillary dysentery

what is the most common cause of food-associated diarrhoea

salmonella

where is salmonella widely distributed in

in animals

how do you get salmonella associated diarrhoea

• salmonella enteriditis ingestion

• absorbed to epithelial cells in terminal portion of small intestine

• bacteria penetrate cells and migrate to lamina propria layer of illeocecal region

• multiply in lymphoid follicles causing reticuloendothelial hyperplasia and hypertrophy

• polymorphonuclear leukocytes confine infection to GI tract

• inflammatory response also mediates release of prostaglandins

• stimulates cAMP and activate fluid secretion

• diarrhoea

incubation period, duration, and symptoms of salmonella

• 6hrs-2 dyas

• 48hrs-7days

• watery diarrhoea, vomiting, abdominal cramps, and fever

incubation period, duration, and symptoms of shigella

• 1-4 days

• 2-3 days

• bloody diarrhoea, abdominal cramps, fever

incubation period, duration, and symptoms of vibrio cholerae

• 2-3 days

• up to 7 days

• water diarrhoea, vomiting, abdominal cramps, and fever

incubation period, duration, and symptoms of clostridium perfringens

• 8hrs-1 days

• 12hrs- 1 day

• watery diarrhoea, abdominal cramps

incubation period, duration, and symptoms of EHEC

• 3-4 days

• 5-10 days

• bloody diarrhoea, committing, abdominal cramps

what are the top10 sexually transmitted diseases

• papillomavirus

• Chlamydia trachomatis (D-K serotypes)

• chlamydia trachomatis (L1, L2, L3 serotypes)

• candida albicans

• trichomonas vaginalis

• HSV 1 and 2

• Neisseria gonorrhoeae

• HIV

• temponema pallidum

• Hepatitis B virus

• Haemophilus ducreyi

what are the different viral infections

• acute infection-common cold

• acute infection- rare late complication measles, SSPE

• latent infection- VZV

• chronic infection- hepatitis B

• chronic infection- late disease HIV

• slow infection- prion

why are wild-type polio infections becoming rarer

because of the success of the polio vaccine

what can polio cause

• asymptomatic illness

• abortive poliomyelitis

• non paralytic poliomyelitis or aseptic meningitis

• paralytic polio

what is the percentage that makes up asymptomatic illness

90% of infections

abortive poliomyelitis

• non-specific febrile illness

• occurring in 5% of infected people

• fever, headache, sore throat, vomiting

non paralytic poliomyelitis or aseptic meningitis

• in 1-2% of patients

• progression of virus into CNS causes back pain and muscle spasms in addition to abortive poliomyelitis symptoms

paralytic polio

• occurs in 0.1-2% of patients

• appears 3-4 days after the first symptoms have subsided

• produces a biphasic illness

• virus spreads form the blood to anterior horns cells of spinal cord and motor cortex of the brain

• severity of paralysis is determined by the extent of the neuronal infection and which neurons are affected

what are the largest viruses

• poxviruses

• 230-300 nm

when was small pox eradicated

1980

what does the viral genome of smallpox consist of

double stranded linear DNA

where does the replication of small pox take place

within the host cell cytoplasm

what happens when someone has the measles virus

• inoculation of respiratory tract

• local replication in respiratory tract

• lymphatic spread

• viremia

• wide dissemination

• CNS, lymphatic system, small blood vessels, urinary tract affected

• virus infected endothelial cells plus immune T cells

• rash

• recovery

what are the 3 other outcomes of measles that are really rare

• post infectious encephalitis

• subacute sclerosing panencephalitis (virus infection of CNS)

• no resolution of acute infection caused by defective CMI

if the site of measles growth is in the lungs what would clinical outcomes look like for a well nourished child with good medical care compared to a malnourished child with poor medical care

• temporary respiratory failure

• life-threatening pneumonia

if the site of measles growth is in the ear what would clinical outcomes look like for a well nourished child with good medical care compared to a malnourished child with poor medical care

• otitis media quite common

• otitis media more common, more severe

if the site of measles growth is in the oral mucosa what would clinical outcomes look like for a well nourished child with good medical care compared to a malnourished child with poor medical care

• koplik’s spots

• severe ulcerating lesions

if the site of measles growth is in the conjunctiva what would clinical outcomes look like for a well nourished child with good medical care compared to a malnourished child with poor medical care

• conjunctivitis

• severe corneal lesions, secondary bacterial infections, blindness may result

if the site of measles growth is in the skin what would clinical outcomes look like for a well nourished child with good medical care compared to a malnourished child with poor medical care

• maculopoular rash

• hemorrhagic rashes may occur