Gram-Negative Cocci and Coccobacilli of Medical Significance

Last updated on May 28th, 2021

The most common gram-negative cocci of medical importance belong to the family Neisseriaceae which includes the genera Neisseria, Moraxella, Kingella, Acinetobacter etc. 

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.

Neisseria gonorrhoeae (Gram negative diplococci)
Neisseria gonorrhoeae (Gram negative diplococci)

N.meningitidis

N. meningitidis (Meningococci) is a gram-negative, nonsporeforming diplococcus. It is a leading cause of fatal bacterial meningitis. Meningitis may be accompanied by appearance of petechiae (rash) that is associated with meningococcal bacteremia (i.e.,meningococemia). Bacteremia leads to thrombocytopenia, disseminated intravascular coagulation, and shock. Less common infections include conjunctivitis, pneumonia, and sinusitis.

N. gonorrhoeae

It is a urogenital pathogen that is transmitted by sexual contact. Genital infections include purulent urethritis in males and cervicitis in females. Other localized infections include pharyngitis, anorectal infection, and conjunctivitis (ophthalmia neonatorum). Disseminated gonococcal diseases are pelvic inflammatory disease, bacteremia, arthritis, and metastatic infections at other body sites.

Moraxella (Branhamella) catarrhalis

Moraxella catarrhalis, a gram-negative diplococcus, is an exclusively human pathogen and is a common cause of otitis media in infants and children.  M.catarrhalis causes acute, localized infections such as sinusitis, and bronchopneumonia as well as life-threatening, systemic diseases including endocarditis and meningitis. M. catarrhalis can cause pneumonia, especially in patients with alcoholism or chronic obstructive lung disease. M. catarrhalis also causes exacerbations of chronic obstructive pulmonary disease (COPD) and chronic bronchitis in elderly patients.

Veillonella species

 They are rarely the sole or predominant organism in sputum smears of patients with pneumonia.

Gram Negative Coccobacilli

A coccobacillus is a type of bacterium with a shape intermediate between cocci and bacilli i.e., they are very short rods that may be mistaken for cocci. These small, pleomorphic gram-negative bacteria range in shape from round (cocci) to short, thin rods (bacilli); hence the bacteria are called “coccobacilli.”

Haemophilus species

Infections most commonly associated with encapsulated strains of Haemophilus influenzae include meningitis, epiglottitis, cellulitis with bacteremia, septic arthritis, ad pneumonia.  Non-capsulated strains usually cause localized infections such as otitis media, sinusitis, conjunctivitis.

Haemophilus ducreyi

It causes sexually transmitted infections chancroid, a major cause of genital ulceration in developing countries characterized by painful sores on the genitalia.

Acinetobacter species

Outbreaks of Acinetobacter infections typically occur in intensive care units (ICUs) and healthcare settings housing very ill patients. Acinetobacter baumannii accounts for about 80% of reported infections. Acinetobacter causes a variety of diseases, ranging from pneumonia to serious blood or wound infections, and the symptoms vary depending on the disease. Acinetobacter may also “colonize” or live in a patient without causing infection or symptoms, especially in tracheostomy sites or open wounds.

Kingella species

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

Francisella species

Francisella is an intracellular, facultative, gram-negative coccobacillus. Francisella tularensis is the agent of human and animal tularemia.

About Acharya Tankeshwar 474 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.