Atypical Bacteria

Atypical Bacteria

A brief summary about the typical characteristics of bacteria:

• cell wall (containing peptidoglycan)
• cell membrane
• no nuclear membrane
• reproduce by cell fission
• susceptible to antibiotics, but not to antifungal agents

Atypical bacteria

• In this section, we will discuss:
• fungus-like bacteria (streptomyces sp. and actinomyces sp.)
• acid-fast bacteria
• mycoplasmas
• chlamydias
• rickettsias

Fungus-like bacteria

• shape: filamentous
• gram posititve bacilli that form branching filaments
• prokaryotic

Fungus-like bacteria examples

• Streptomyces spp.:
• These are the most important source of antibiotics
• one of the most commonly isolated from soil
• the asexual spores-condiospores are capable of germinating into new colonies
• near 500 described species within this genus

• Actinomyces spp.:
• These can be found in the mouth and throat of humans and animals
• They have branching filaments and spore-case(sporangium)
• spores: sporangiospores

Why are fungus-like bacteria not classified as fungi?

• They have no membrane-bound organelles
• example: mitochondria, nucleus
• They reproduce by cell fission
• They are susceptible to penicillin, but not to antifungal agents

Acid-fast bacteria

• gram positive bacilli with waxy coat on cell wall
• cell wall structure is similar to gram negative cell wall,
• Mycolic acids replace the outermost lipopolysaccharide layer, forming a waxy, water-resistant coat
• wax helps improve the chance of survival in its environment

Acid-fast bacteria example

• mycobacterium spp.
• Have a slow growth rate
• sometimes takes weeks to form visible colonies
• common species
• M. tuberculosis (tuberculosis)
• M. leprae (leprosy)
• The organism is an obligate intra-cellular parasite that lacks many necessary genes for independt survival.
• The complex and unique cell wall that makes members of the mycobacterium genus difficult to destroy is apparently also
• M. ulcerans (buruli ulcer)
• M. ulcerans: the ulcerative condition on the skin and subcutaneous fat cells
• increasing in world; the actual transmission is unknown

Mycobacteria with acid fast stain

• Mycoplasmas
• They are the smallest known bacteria
• Because of their small size, they can easily pass through filters
• They are the only prokaryotes that lack a cell wall and contain sterols in their cytoplasmic membrane
• Therefore, they are highly pleomorphic
• They produce filaments that can resemble fungi
• myco = filamentous;
• plasma= fluid
• Mycoplasmas are the smallest microorganisms that can independently grow on a cell-free medium

• Example of Mycoplasmas
• M. pneumoniae
• The most significant human pathogen of this genus: M. pneumoniae
• Causes common mild form of pneumonia

Chlamydias

Rickettsias

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