L5 medically important gram negative bacteria

pathogen

any microorganism that has capacity to cause disease

virulence

is a measure of pathogenicity or the liklihood that a microorganism will cause disease after infecting someone

principal pathogens

may cause disease in the presence of an intact immune system- highly virulent

opportunist pathogens

only cause disease in those with underlying disease or compromised immune system- less virulent

classification of medically important gram negative bacteria

1. diplococci- eg neisseria meningitidis which produces endotoxins and N. gonorrhoeae which is an STI

2. coccoid rods- eg, haemophilus influenza- Upper RT and lower pnemonia in children. bordetella pertussis→ whooping cough

3. rods, eg klebsiella E coli, salmonella, pseudomonas

4. comma shaped, vibrio cholerae

vibrio cholerae

virulence factors: toxin genes, pilus

inoculum: size of the infecting dose 10^8-high dose for disease to develope

• Gram-negative, curved rod

• Motile (single polar flagellum)

• Oxidase-positive

• Facultative anaerobe

• Grows in alkaline environments (pH 8.5–9.5

causes cholera

features of cholera

• very severe watery diarrhoea; rice water stool

• death due to dehydration or electrolyte imbalance

• annual burden of disease: 3-5 million cases, 100000 deaths, most cases and deaths in africa

what causes disease

is a result of host- pathogen- environment interaction

host:

• genetic: ABO blood groups, groups A and B cause cholera to be less likely to develope as antigens stop it from binding

• immune status

• gastric acidity

environment

• climate

• santiation and water supply

infecting agent

• virulence factors: toxin genes, pillus

• inoculum: size of infecting dose

environmental factors and cholera

envionmental niche is saline coastal waters and estuaries

• lives in biofilm on zooplankton and shellfish

• during periods of nutrient deficiency→ viable non culturable forms in biofilms

• when conditions are favourable, zooplanktons bloom and proliferte→ humans ingest water and cholera in water increases

once in humans, outbreaks occur through faecal contamination

faecal-oral route

V.cholerae virulence factors

• colinises the gut mucosa, doesnt invade produces toxins

• flagellum moves the bacteria towards epitherlial surface

• cholera toxin coregulates pilus(TcpA) mediates attachment to mucosa, cholera toxin causes diarrhoea

• cholera used to be an environmental organism but has since become pathogenic to humans

how did cholera become pathogenic to humans?

non-pathogenic strains were infected by a bacteriophage: vibrio pathogenicity island phage VPIO

this VPIO encodes for TcpA

TcpA then acted as receptor for a second bacteriophage CTX O

CTX O has genes for cholera toxin CTX

describe the family of enterobacteriaceae

• faculative anaerobes

• have simple nutritional requirments- ferment glucose and other carbs

• often motile with multiple peritrichous flagella at multiple sites

• inhabit intestinal tracts of humans, animals

• includes some common and important pathogens

• eg: Ecoli and salmonella

salmonella enterica

salmonella infections are typically acquired by eating contaminated food of via person to person spread

there are two serotypes: typhoidal and non typhoidal

Typhoidal serotypes of salmonella enterica

• are human pathogens only

• humans may be asymptomatic carriers

• cause enteric fever(typhoid)- a serious illness with bacteraemia

  salmonella typhi

  salmonella paratyphi types A,B and C

non- typhoidal serotypes

• commensals of various animal species

• acquired by eating contaminated food

• usually self limiting diarrhoea in humans

• can cause disseminated disease in immunocompromised people

drug resistant salmonella infections

Multi-resistant Salmonella infections are a major public health threat.

Antimicrobial resistance in Salmonella spreads through humans, the food chain and the environment.

One Health is an integrated, unifying approach that aims to sustainably balance and optimize the health of people, animals and ecosystems

ecoli

One of most common inhabitants of the human GI tract • Commensal, not usually a pathogen • The best studied bacterium - genetics, physiology, molecular biology • Pathogenic strains are grouped according to their virulence factors/diseases

Enterohemorrhagic E. coli→ EHEC→effacement lesion is the virulence factor→Bloody diarrhoea, haemolytic uraemic syndrome – renal failure

how does livestock feeding affect ecoli in humans?

Approx. 30% of feedlot cattle are reservoirs of E. coli strain O157:H7.

Feedlot cattle are fed high grain rations to increase feed efficiency: ‘grain finished’ beef.

High grain rations -> some starch escapes ruminal microbial degradation and passes to the hindgut -> fermented by E. coli.

Total E. coli is higher in grain-fed than in grass-fed cattle: when cattle are switched from a high grain diet to an all hay diet, E. coli populations decline 1000-fold.

‘Grain finishing’ increases the risk of human infection with pathogenic E. coli strains, which can cause renal failure. ‘

Outbreaks associated with petting zoos, contaminated vegetables or meat

Pseudomonas aeruginosa

Widely distributed in soil, water, plants, gut of humans & animals

– Generally regarded as ubiquitous in soil and water environments, but is rarely found in pristine ecosystems

– Mostly detected in habitats contaminated by human activity, (human and animal faeces are important reservoirs)

• Reservoirs in urban communities – Include hot tubs, jacuzzis, and swimming pools

• Reservoirs in hospitals – Water distributions systems, sinks, plumbing, disinfectant solutions

• Importance as a human pathogen did not emerge until the second half of the twentieth century

• Often multi-drug resistant

P. aeruginosa infections in healthy patients

P. aeruginosa can cause infections in those with an intact immune system,eg hot tub foliculitis and swimmers ear but infections are more common in individuals with an immunocompromised state

P. aeruginosa infections in immune compromised patients

Cystic fibrosis - chronic lung infection occurs in >60% of adults with CF - linked to higher mortality

• Burn wound infections - a blue-green purulent discharge may be found

• Diabetes - malignant otitis externa

• Often healthcare associated:

• Organ transplant recipients or ICU patients

- pneumonia, urinary tract infections, bacteraemia

• Invasive devices, e.g., indwelling catheters or endotracheal tubes - at risk due to ability to form biofilms

stages of biofilm formation and dispersal

what are Healthcare-associated (nosocomial) infections

Acquired as a direct or indirect result of healthcare Bloodstream, pneumonia, urinary tract infections are most common.

Any healthcare setting: hospitals, general practice clinics, dental clinics, community health facilities, long-term care facilities

Many Gram-negative bacilli are common causes, particularly: Klebsiella spp Pseudomonas spp Acinetobacter spp

Methicillin-resistant S. aureus also Often multidrug-resistant