neisseria, rickettsia, chlamydias

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NEISSERIA, RICKETTSIA, CHLAMYDIAS & FACULTATIVE

ANAEROBIC GRAM NEGATIVE RODS.

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1).NEISSERIA

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What is Neisseria?

Neisseria is a large genus of commensal bacteria.

They colonize the mucosal surfaces of many animals.

Of the 11 species that colonize humans, only two are pathogens.

• N. meningitidis • N. gonorrhoeae

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Shape and Arrangement:-

All are diplococcal bacteria

N. elongata and N. weaveri,both occur as rods

Present in pairs or short chains.

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Characteristics:-

Gram-negative

aerobic

non-motile

non-spore-forming bacteria

All species are oxidase positive except N. elongata which are catalase positive.

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Culturing:-

Most species grow optimally at temperatures ranging between 35 to 37 °C

Growth is usually stimulated by carbon dioxide and humidity.

They grow on chocolate agar and Thayer-Martin agar.

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Importance:-

Pathogenic bacteria causes diseases,some which are followings:-

N. gonorrhoeae causes gonorrhea disease.

N. meningitidis one of the most common causes of bacterial meningitis.

N. meningitidis is causative agent of septicaemia.

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2).RICKETTSIA

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What is Rickettsia?

Rickettsia is a genus of gram-negative,

coccoid-shaped or rod shaped bacteria.

Classification

Rickettsia is divided into three catagories:-

Spotted fever group

Typhus group

Scrub typhus group

Classification:-

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History:-

Rickettsias are named after their discoverer, the American pathologist Harold Taylor Ricketts, who died of typhus in Mexico after confirming the infectious agent of that rickettsial disease.

coccoid-shaped or rod-shaped bacteriacocci (0.1 μm in diameter) thread like rods (1–4 μm long)

Shape and size:-

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Characteristics:-

non-motilenon-spore forming gram-negative bacteriahighly pleomorphicthey can produce ATP & LPSbeing obligate intracellular parasites, they require a living host cell to survive

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Culturing:-

Rickettsia cannot live in artificial nutrient environments and is grown either in tissue or embryo cultures (typically, chicken embryos are used).

Transmitted by arthropod vectors (lice, fleas, ticks, mites); thus, humans are accidental hosts

Transmission:-

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Mechanism of attack:-

invades the endothelial cells that line the blood vessels

pathogen causes changes in the host cell cytoskeleton that induces phagocytosis

they are able to avoid lysosomal fusion

oxidative burst by escaping from the phagosome into the cytoplasm where they multiply and spread

Causes many diseases

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Significance:-

R.prowazekii causes louse-borne typhus, carried by lice.

Flea, or murine typhus is caused by R. mooseri, is transmitted from rodents to people by fleas.

African tick typhus, are transmitted by ticks from animal hosts to people.

Mite-borne rickettsial infections include rickettsialpox, caused by Rickettsia akari

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3).CHLAMYDIAS

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What is Chlamydias?

Chlamydia is a genus of bacteria that are obligate intracellular parasites.

Chlamydia infections are the most common bacterial sexually transmitted diseases in humans and are the leading cause of infectious blindness worldwide.

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Chlamydia species:-

The four Chlamydia species includes:-1. Chlamydia trachomatis (a human pathogen)2. Chlamydia suis (affects only swine)3. Chlamydia pecorum (infects ruminants,koalas and

pigs)4. Chlamydia muridarum (affects only mice and

hamsters).

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Characteristics:-

characteristics intermediate between bacteria and virusesobligate intracellular parasites of people and animalsthey are capable of independent reproduction they do not synthesize ATPlife cycle lasts from 24 to 48 hoursaerobic

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Shape & size:-

coccoid or rod shapesize is about 0.3μm

Chlamydia infection is a common sexually transmitted infection (STI) in humans caused by the bacterium Chlamydia trachomatis.

Transmission:-

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Significance:-

Chlamydia trachomatis, and Chlamydophila, which includes Chlamydophila pneumoniae and Chlamydophila psittaci are susceptible to antibiotic therapy.

Chlamydia is a common infectious cause of genital and eye diseases in humans.

Study of chlamydia could open the way to new treatments and the development of a vaccine for this sexually transmitted disease.

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4).FACULTATIVE ANAEROBIC GRAM NEGATIVE RODS.

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What are Facultative anaerobes?

A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation or anaerobic respiration if oxygen is absent.

Enterobacteria.

Example:-

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Characters of Enterobacteriaceae:-

All Enterobacteriaceae Gram-negative rods Ferment glucose with acid production Reduce nitrates into nitrites Oxidase negative All enterobacteria have peritrichous flagella. Facultative anaerobes

Motile except Shigella and Klebsiella Non-capsulated except Klebsiella Non-fastidious

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Classification based on lactose fermentation:-

1. Lactose fermenters:-• Escherichia coli• Klebsiella sp.

2. Late lactose fermenters:-• Shigella sonnei• Para colons etc

3. Non lactose fermenters:-• Salmonella• Shigella etc.

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Culturing:-

There are several selective and differential media used to

isolate and distinguish between LF & LNFThe most important media are:

MacConkey agarEosin Methylene Blue (EMB) agarSalmonella Shigella (SS) agarTriple Sugar Iron (TSI) agar

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Growth of E.coli on nutrient agar,blood agar,macConkey agar

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VIRULENCE FACTORS:-

Surface antigens: O and K

O antigen – somatic lipopolysaccharide surface O antigen has endotoxic activity, protects the bacteria from phagocytosis and bactericidal effects of complement.

K antigen – affords protection against phagocytosis and antibacterial factors in normal serum.

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Importance:-

Salmonella species that cause intestinal disease known as salmonellosis

Klebsiella species, the causes of pneumonia,intestinal disease, and other infections

Yersinia pestis, the cause of plague

Escherichia coli is also a member of this group,which used for experimental work.

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Created by:Maria Mushtaq