Chapter 20: The Gram Negative Cocci and Bacilli

I. Pathogenic Gram Negative Cocci:Neisseria

Neisseria gonorrhoeae

A. Structure and Physiology of Neisseria
• Non-motile, gram negative diplococci coffee
bean shaped

What would be the outcome of prolonged infections that reach the epididymis in the male reproductive system for Neisseria gonorrhoeae?

It rarely causes infertility when the infection reaches the epididymis and causes scar tissue formation

II. Pathogenic Gram Negative Cocci:The Meningococcus

2. Neisseria meningitidis

• It causes most meningitis cases in children and adults under 20 years

Explain how the release of Lipid A by N. meningitides is different than the way Lipid A is released by other Gram-negative bacteria?

The LOS antigen (Lipid A): which is released
through a process called “blebbing”; lipid A causes
fever, inflammation, vasodilation, DIC and shock

Is it recommended to do a β-lactamase test on Neisserias?

No, a routine β-lactamase test is not recommended for managing Neisseria gonorrhoeae infections because penicillins are no longer part of standard first-line treatment.

Pathogenic, Gram-Negative, Facultative
Anaerobic Bacilli

What is an overview of the Enterobacteriaceae?

• These organisms are found in soil, water and decaying vegetation; but they can also be part of the normal flora of the GI tract of humans and animals

• They’re the most common Gram-negative pathogens of humans

• They are bacilli and coccobacilli 1 μm by 1-3 μm that
grow well on MAC and HE

What is the clinically significant groups of the
Enterobacteriaceae ?

1. The Coliforms: lactose fermenters that may be part of the normal flora of the GI tract: Escherichia, Klebsiella, Enterobacter, Serratia, Citrobacter***

2. The Non-coliforms: non-lactose fermenters that may also be part of the normal flora of the GI tract: Proteus, Providencia, and Morganella (PPM)

3. The Enteric Pathogens: non-lactose fermenters that are not part of the normal flora of the GI tract: Shigella and Salmonella (SS)

I. Pathogenic, Gram-Negative, Facultative Anaerobic Bacilli

C. Coliform Opportunistic Enterobacteriaceae

Escherichia coli
• The most common and important of the coliforms
consisting of numerous different strains
• It can cause many diseases from gastroenteritis and
pneumonia, to septicemia and meningitis

List the three main virulent factors of E. coli O157:H7. Which of these factors is the most dangerous?

a) Lipid “A”: endotoxin that causes fever, inflammation,
vasodilation, shock and DIC
b) Shiga-like toxin: a cytotoxin that inhibits protein
synthesis of cells; kills GI tract epithelium—>Once absorbed into the bloodstream, Shiga toxin can target endothelial cells in small blood vessels—particularly in the kidneys—leading to severe complications such as hemolytic uremic syndrome (HUS), acute kidney failure, destruction of red blood cells, and potential death. [1, 2]

Give the colonial characteristics of these organisms in MAC and HE. What is a key colonial characteristic that P. mirabilis exhibits in non-selective media?

—>Klebsiella pneumoniae (a coliform)=lactose fermenters that may be part of the normal flora

—>Proteus mirabilis (a non-coliform) =non-lactose fermenters that may also be part of the normal flora

P. mirabilis produces swarming in non-selective media

Other Enterobacteriaceae Organisms

Klebsiella pneumoniae (a coliform)

Proteus mirabilis (a non-coliform) cause 10% of UTI’s

II. Truly Pathogenic Enterobacteriaceae
(The Enteric pathogens)

This group consists mainly of the genera Salmonella,
and Shigella

What is the treatment protocol for Salmonella and Shigella?

—>Treatment of shigellosis involves replacement of fluids and electrolytes. The disease is usually self-limiting as the bacteria are voided in feces, but oral antimicrobial drugs, such as ciprofloxacin, sulfonamides, penicillin, or cephalosporin, can reduce the spread of Shigella to close contacts of the patient.

—→Treatment for salmonellosis involves fluid and electrolyte replacement. Typhoid fever is treated with antimicrobial drugs such as ampicillin or ciprofloxacin, though an extensively drug resistant strain (XDR Salmonella typhi) emerged in Pakistan in 2018. Physicians sometimes remove the gallbladder of a carrier to reduce the chance that others will become infected.

What organism is Non-Enteric Pathogen?

Yersinia pestis

The Pseudomonads

1. Pseudomonas aeruginosa

• Is found as free living bacteria in the soil and
aquatic environments; it colonizes plants and can
be part of the normal GI tract flora of many
animals
• It’s resistant to drying, soaps, and disinfectants;
and contaminates home and hospital settings
• It’s been isolated from ventilators, IV solutions
and anesthesia equipment