Medical Significance of Gram-Negative Cocci and Coccobacilli

The most commonly used gram-negative cocci of medical significance fall under the category of Neisseriaceae which comprises the genera Neisseria, Moraxella, Kingella, Acinetobacter etc.

Medical Significance of Gram Negative Cocci

Neisseria species 

The genus Neisseria contains 12 species, two of which, N.meningitidis and N. gonorrhoeae, are commonly pathogenic in humans. Both may cause infections in the CNS, primarily meningitis and meningoencephalitis, but also abscesses, empyemas, and thrombophlebitis.



N. meningitidis (Meningococci) is a gram-negative, nonsporeforming diplococcus. It is the leading cause of meningitis that is fatal. Meningitis may be accompanied by appearance of petechiae (rash) that is associated with meningococcal bacteremia (i.e.,meningococemia). Bacteremia causes thrombocytopenia, disseminated intravascular coagulation, and shock. Conjunctivitis is a less frequent infection as well as sinusitis, pneumonia, and conjunctivitis.

N. gonorrhoeae

This is an urogenital pathogen which can be transmitted through sexual contact. Genital infections are characterized by the urolithic urethritis of males as well as cervicalitis in females. Other localized infections are pharyngitis conjunctivitis and anorectal infection (ophthalmia neonatorum). Gonococcal disseminated diseases include an inflammatory condition of the pelvis as well as arthritis, bacteremia and metastatic infections in other body parts.


Moraxella (Branhamella) catarrhalis

Moraxella catarrhalis, which is a gram-negative diplococcus is an exclusively human pathogen that is a frequent cause of the condition known as otitis media, which is common in infants and kids. M.catarrhalis can cause acute, localized infections like the sinusitis and bronchopneumonia and life-threatening systemic illnesses like endocarditis and meningitis. M. catarrhalis may cause pneumonia, particularly in those who suffer from alcoholism and chronic OBL. M. catarrhalis can also cause the exacerbation of chronic obstructive pulmonary illness (COPD) as well as chronic bronchitis in patients who are elderly.

Veillonella species

They are seldom the sole or most prevalent organism found in sputum smears from patients suffering from pneumonia.


Medical Significance of Gram Negative Coccobacilli

A coccobacillus can be described as a kind of bacterium having a shape that is intermediate between cocci and bacilli i.e. they are rods with a short length that can be confused with cocci. These gram-negative, small, pleomorphic bacteria have shapes ranging that ranges from circular (cocci) to shorter small rods (bacilli) which is why they are referred to as “coccobacilli.”

Haemophilus species

The most frequent infections related to encapsulated strains Haemophilus influenzae include meningitis epiglottitis, bacteremia in cellulitis and septic arthritis. They also include pneumonia. Non-capsulated strains typically cause localized infections like sinusitis, otitis media, conjunctivitis.


Haemophilus ducreyi

It can cause sexually transmitted infections called chancroid, one of the main causes of genital ulceration, especially in developing countries , characterized by painful sores on the genital organs.

Acinetobacter species

Infections with Acinetobacter infections are typically seen within intensive care units (ICUs) as well as healthcare facilities that house patients with severe illness. Acinetobacter baumannii accounts for approximately 80percent of all reported infections. Acinetobacter can cause a range of ailments, ranging from pneumonia to severe wound infections or blood, and the signs vary based on the illness. Acinetobacter could be able to “colonize” or reside within a patient, without causing symptoms or infection particularly in tracheostomy sites or in open wounds.


Kingella species

Kingella kingae is a type of coccobacilli that are Gram-negative. Kingella kingae is recognized increasingly as a cause of skeletal infections (osteomyelitis/septic arthritis ) in children.

Francisella species

Francisella is an intracellular and facultative coccobacillus that is gram negative. Francisella tularensis is known as an cause of animal and human tularemia.


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