Name: chlamydiae life cycle and host infection
Uploaded: 2025-08-01T06:53:04.000Z
Duration: 1 min 29 s
Channel: JoVE

Il phylum Chlamydiae è costituito da un unico ordine, Chlamydiales.Tipicamente, queste specie sono piccoli cocchi, di circa 0,5 μm di diametro, con un ciclo di sviluppo unico e genomi ridotti con dimensioni che vanno da 0,55 a 1 Mbp.Tutte le specie di Chlamydiae sono parassiti intracellulari obbligati di vari ospiti eucariotici come le amebe a vita libera e gli esseri umani.I patogeni umani meglio studiati sono nei generi Chlamydia e Chlamydophila.La Chlamydia trachomatis causa il tracoma, una delle principali cause di cecità e varie infezioni sessualmente trasmissibili.La Chlamydophila pneumoniae è legata alle condizioni respiratorie, mentre la Chlamydophila psittaci è l'agente eziologico della malattia psittacosi.Le specie di Chlamydiae hanno un ciclo di vita unico che coinvolge due tipi di cellule.I corpi elementari sono cellule piccole e dense che non si moltiplicano, specializzate per la trasmissione infettiva.Dopo la fagocitosi dei corpi elementari da parte delle cellule ospiti, questi si trasformano in corpi reticolati e si moltiplicano all'interno delle cellule ospiti.Successivamente, i corpi reticolari si trasformano in corpi elementari. Vengono rilasciati dopo la disintegrazione della cellula ospite, infettando le cellule vicine e perpetuando il ciclo vitale.

phylum batterico: chlamydia

Bacterial Phylum Chlamydiae

Il phylum Chlamydiae o Chlamydiota &#232; composto da un unico ordine, i Chlamydiales. Questo phylum comprende esclusivamente parassiti intracellulari obbligati che infettano ospiti eucarioti. Sebbene i patogeni umani appartenenti a questo gruppo siano stati ampiamente studiati, il phylum include numerose specie capaci di interagire con vari organismi eucarioti. I membri delle Chlamydiae sono tipicamente cocchi di piccole dimensioni, con un diametro di circa 0,5 &#956;m, e presentano un ciclo di sviluppo distintivo. Come accade per molti parassiti e simbionti obbligati, i loro genomi sono ridotti, con dimensioni comprese tra 0,55 e 1 Mbp.
Le specie di questo phylum sono altamente specializzate per invadere e colonizzare cellule eucariotiche, con specie differenti che infettano una vasta gamma di ospiti. Ad esempio, Parachlamydia acanthamoebae infetta amebe a vita libera, in particolare quelle del genere Acanthamoeba. Durante l&#8217;infezione delle amebe, Parachlamydia attraversa il tipico ciclo di sviluppo osservato anche in altre specie di Chlamydiae. Molti membri delle Chlamydiae possono moltiplicarsi o persistere all&#8217;interno di amebe a vita libera, suggerendo che tali ospiti svolgono un ruolo significativo nella sopravvivenza e distribuzione delle Chlamydiae in ambienti naturali. Analisi delle sequenze geniche dell&#8217;rRNA 16S rivelano un&#8217;elevata diversit&#224; ambientale delle Chlamydiae, indicando una loro ampia diffusione e la possibile esistenza di numerosi ospiti naturali ancora sconosciuti. Sebbene P. acanthamoebae infetti naturalmente le amebe, pu&#242; anche infettare l&#8217;uomo, bench&#233; in maniera meno efficiente rispetto alle specie adattate agli ospiti umani.
I patogeni umani pi&#249; studiati appartengono ai generi Chlamydia e Chlamydophila. Tra questi vi sono specie come Chlamydophila psittaci, responsabile della psittacosi; Chlamydia trachomatis, che causa il tracoma e altre patologie umane; e Chlamydophila pneumoniae, associata a determinate condizioni respiratorie. La psittacosi &#232; principalmente un&#8217;epidemia aviaria che pu&#242; occasionalmente trasmettersi all&#8217;uomo, provocando sintomi simili alla polmonite. Il tracoma, una malattia oculare debilitante caratterizzata da vascolarizzazione corneale e cicatrizzazione, rappresenta una delle principali cause di cecit&#224; a livello mondiale. Altri ceppi di C. trachomatis infettano l&#8217;apparato genito-urinario e sono tra le infezioni sessualmente trasmissibili pi&#249; comuni.
Le clamidie sono tra i batteri biochimicamente pi&#249; limitati noti, con genomi di circa 1 Mbp. Le loro capacit&#224; biosintetiche sono persino pi&#249; ridotte rispetto a quelle delle rickettsie, un altro gruppo di parassiti obbligati intracellulari. In particolare, il genoma di C. trachomatis &#232; privo del gene che codifica per FtsZ, una proteina considerata essenziale per la formazione del setto durante la divisione cellulare nella maggior parte dei procarioti. Inoltre, specifici geni di C. trachomatis sembrano essere stati acquisiti da ospiti eucariotici tramite trasferimento genico orizzontale, il che potrebbe aver migliorato la capacit&#224; del batterio di sopravvivere e proliferare all&#8217;interno delle cellule ospiti.
Il successo evolutivo delle Chlamydiae risiede nella loro strategia di sopravvivenza efficiente, che comporta lo sfruttamento delle risorse dell&#8217;ospite e la produzione di forme cellulari resistenti per la trasmissione. Il ciclo vitale delle clamidie include due forme cellulari distinte: (1) i corpi elementari, piccoli, densi e specializzati per la trasmissione infettiva, e (2) i corpi reticolati, pi&#249; grandi, meno densi e responsabili della duplicazione. I corpi elementari sono resistenti alla disidratazione e facilitano la trasmissione aerea, risultando particolarmente efficaci nell&#8217;invasione del sistema respiratorio. Al contrario, i corpi reticolati sono non infettivi e si moltiplicano all&#8217;interno delle cellule ospiti mediante scissione binaria, generando un ampio inoculo per infezioni successive.
I corpi reticolati si trasformano in corpi elementari dopo pi&#249; divisioni, e vengono rilasciati quando la cellula ospite si disintegra. Questi corpi elementari infettano quindi cellule adiacenti, perpetuando il ciclo. &#200; stato osservato che i corpi reticolati si dividono con tempi generazionali di 2&#8211;3 ore, un ritmo significativamente pi&#249; rapido rispetto alle rickettsie. A differenza delle rickettsie, tuttavia, le clamidie non sono trasmesse da artropodi, ma si affidano principalmente alla dispersione aerea.

Phylum Batterico: Chlamydia

Il phylum Chlamydiae o Chlamydiota &#232; composto da un unico ordine, i Chlamydiales. Questo phylum comprende esclusivamente parassiti intracellulari ...

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chlamydiae life cycle and host infection

Chlamydiae are bacteria that live inside eukaryotic host cells. The phylum Chlamydiae, also called Chlamydiota, contains a single order, Chlamydiales. These bacteria are obligate intracellular parasites, which means they must enter host cells to survive and grow.

Members of this group are usually very small cocci, about 0.5 μm across. They also have reduced genomes, usually between 0.55 and 1 Mbp. This limited genome fits their highly specialized way of life and their dependence on host resources. Many species infect a wide range of eukaryotic organisms, not just humans.

Some Chlamydiae infect free-living amoebae, especially Acanthamoeba. Parachlamydia acanthamoebae is one example, and it follows the same developmental cycle seen in other chlamydial species during amoeba infection. Amoebae may help Chlamydiae survive and spread in natural environments, because many species can multiply or persist inside these hosts. 16S rRNA gene studies also show that Chlamydiae are very diverse in the environment, which suggests that many natural hosts are still undiscovered.

Human pathogens in this phylum are best known from the genera Chlamydia and Chlamydophila. Chlamydophila psittaci causes psittacosis, which is mainly an avian disease that can spread to humans and cause pneumonia-like symptoms. Chlamydia trachomatis causes trachoma and other human diseases, and some strains infect the genitourinary tract and are among the most common sexually transmitted infections. Chlamydophila pneumoniae is linked to certain respiratory conditions.

Chlamydiae are also known for their highly limited biochemistry. Their genomes are around 1 Mbp, and their biosynthetic abilities are even more restricted than those of rickettsias. The genome of C. trachomatis also lacks the gene for FtsZ, a protein that most prokaryotes use for septum formation during cell division. Some genes in C. trachomatis appear to have come from eukaryotic hosts through horizontal gene transfer, which may help the bacteria survive and multiply inside cells.

Their life cycle has two main forms. Elementary bodies are small, dense, and built for infection and transmission. They are resistant to drying, which helps airborne spread and makes them effective invaders of the respiratory system. Reticulate bodies are larger, less dense, and non-infectious. They multiply inside host cells by binary fission, with generation times of about 2 to 3 hours, which is faster than in rickettsias.

After several rounds of division, reticulate bodies change into elementary bodies. The host cell then breaks apart and releases them, allowing nearby cells to be infected and the cycle to continue. Unlike rickettsias, chlamydias are not spread by arthropods. They rely mainly on airborne dispersal.

Chlamydiae Life Cycle and Host Infection

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key terms and concepts

Learn how Chlamydiae infect host cells, switch between elementary and reticulate bodies, and cause diseases like trachoma, psittacosis, and STIs.

Chlamydiae Life Cycle and Host Infection | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

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Chlamydiae Life Cycle and Host Infection

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