The genus Neisseria consists of commensal species that colonize the mucosal surfaces of many animals. Of the eleven species that colonize humans, only two are pathogens. Neisseria meningitidis and Neisseria gonorrhoeae often cause asymptomatic infections, a commensal-like behavior. Most gonoccocal infections are asymptomatic and self-resolving, and epidemic strains of the meningococcus may be carried in more than 95% of a population where systemic disease occurs at less than 1% prevalence. Bacteria of the Neisseria genus are Gram-negative and are included among the proteobacteria, a large group of Gram-negative organisms. The microorganisms exist as diplococci.

Neisseria gonorrhoeae and Neisseria meningitidis are Gram-negative diplococci. N. gonorrhoeae is the causative agent of gonorrhoea and is transmitted via sexual contact. N. meningitidis is transmitted via respiratory droplets leading to colonization of the nasopharynx and can cause meningitis and septicemia.

1. Neisseria: Molecular Mechanisms of Pathogenesis
2. Microbiology books

Labels: brief notes, diplococci, gonococcus, gonorrhoea, gonorrhoeae, meningitidis, meningococcal, meningococcus, Neisseria, Neisseria gonorrhoeae

The genus Acinetobacter is a group of Gram-negative, non-motile and non-fermentative bacteria belonging to the family Moraxellaceae. They are important soil organisms where they contribute to the mineralisation of, for example, aromatic compounds. Acinetobacter are able to survive on various surfaces (both moist and dry) in the hospital environment, thereby being an important source of infection in debilitated patients. These bacteria are innately resistant to many classes of antibiotics. In addition, Acinetobacter is uniquely suited to exploitation for biotechnological purposes.

The genus Acinetobacter has emerged to be in the focus of scientists, both in light of fundamental biological questions and in light of its pathogenic potential. Several species persist in hospital environments and cause severe, life-threatening infections in compromised patients, sadly underlined by severe cases of Acinetobacter infections in soldiers returning from Iraq. The spectrum of antibiotic resistances of these organisms together with their survival capabilities make them a threat to hospitals as documented by recurring outbreaks both in highly developed countries and elsewhere.

An important factor for their pathogenic potential is probably an efficient means of horizontal gene transfer, even though such a mechanism has so far only been observed and analyzed in Acinetobacter baylyi, a species that lives in the soil and has never been associated with infections. The capability of this organism to incorporate linear DNA into its own chromosome is among the most efficient transformation processes known and makes it an ideal model organism highly amenable for genetic manipulation. Being true soil bacteria, members of the genus thrive on substrates typically found in soil, such as organic acids or aromatic compounds.

1. Acinetobacter Molecular Biology
2. Microbiology books

Labels: acinetobacter, brief notes, soil microbiology

A conventional view delineates cellular life into only two basic types called prokaryotes and eukaryotes. The prokaryotes are further subdivided into the Bacteria and the Archaea based on small subunit ribosomal RNA comparisons and conserved mechanisms for information processing. The study of Archaeal prokaryotes has matured rapidly in part initiated by genomic science as well as a continuing interest in the biochemistry and metabolism of extremophiles.

The "concept" of Archaea arose over 30 years ago when Woese and Fox (1977) proposed that prokaryotes were not a monophyletic group (single root) because of differences between their small subunit ribosomal RNA sequences. Instead, they defined two distinct evolutionary lineages represented by the Bacteria and the Archaea (formerly called archaebacteria). This distinction has since received considerable support from diverse sources. A compelling example comes from whole genome sequencing studies that reveal extensive examples of genetic conservation common to the Archaea but absent from the Bacteria and the Eukarya (eukaryotes). Archaea are subdivided into four phyla of which two, the Crenarchaeota and the Euryarchaeota, are most intensively studied. The identity and function of the conserved features of the Archaea remain enigmatic and are worthy of research endeavour.

1. Archaea: New Models for Prokaryotic Biology
2. Microbiology books

Labels: archaea, brief notes

Species of the Bordetella genus are the causative agents of pertussis or whooping cough. World-wide, pertussis still kills between 200,000 and 400,000 children each year, and the disease still ranks highly among the causes of death due to infection. World-wide, pertussis still kills between 200,000 and 400,000 children each year, and the disease still ranks highly among the causes of death due to infection. Some members of the genus cause diseases in other mammals and in birds.

Bordetella bacteria are small (0.2 - 0.7 μm), Gram-negative coccobacilli. They are obligate aerobes and are highly fastidious and difficult to culture.

1. Microbial Toxins
2. Microbiology books

Labels: brief notes, pertussis, whooping cough

Acanthamoeba is an opportunistic protozoan that is widely distributed in the environment. The organism has two stages in its life cycle, an active trophozoite stage during which Acanthamoeba reproduces, and a dormant cyst stage during which it remains inactive with little metabolic activity, but viable, for years.

During the last few decades, Acanthamoeba has become increasingly appreciated as an important microbe and now is well-recognized to produce serious human infections, including a vision-threatening keratitis (called Acanthamoeba keratitis) and a rare but fatal encephalitis, known as granulomatous amoebic encephalitis. Initially the term "granulomatous amoebic encephalitis" was coined specifically to describe brain infection due to Acanthamoeba. However, with the discovery of a number of amoebae that can produce granulomatous encephalitis, including Acanthamoeba, Balamuthia mandrillaris, Sappinia diploidea, and perhaps other unidentified amoebae, it is necessary to differentiate the disease according to its causative agent.

1. Acanthamoeba: Biology and Pathogenesis
2. Microbiology books

Labels: brief notes

Aspergillus is the name used for a genus of molds that reproduce only by asexual means. Mainly because of its economic importance, the genus Aspergillus has one of the better described taxonomies among filamentous fungi. The aspergilli exhibit immense ecological and metabolic diversity. These include notorious pathogens such as Aspergillus flavus, which produces aflatoxin, one of the most potent, naturally occurring, compounds known to man. Conversely, also included are other fungi, such as A. oryzae, involved in the industrial production of soy sauce and sake or A. niger used for the production of citric acid and enzymes such as glucose oxidase and lysozyme.

Such is the interest in Aspergillus that, to date, the sequences of fifteen different Aspergillus genomes have been determined providing scientists with an exciting resource to improve the understanding of Aspergillus molecular genomics and act as a spring board for mining for new metabolites and novel genes of industrial or medical importance.

1. Aspergillus: Molecular Biology and Genomics
2. Microbial Toxins

Labels: brief notes