Providencia rettgeri, while not widely recognized, is a pathogenic bacterium capable of inducing diverse infections, notably affecting the urinary tract, digestive tract, and ocular tissues. Its distinct resistance to multiple antibiotics, encompassing carbapenems and extended-spectrum beta-lactamases (ESBLs), further complicates therapeutic strategies.  

Studies, including one by Penner and Hennessy (1979), have illuminated Providencia rettgeri‘s varied sources, revealing a distribution among humans (45%), animals (29%), and the environment (26%). Human isolates are often derived from blood (9%), feces (25%), urine (42%), and the eyes (7%). Animal sources predominantly include poultry (38%), pigs (14%), and cattle (18%), while environmental origins encompass water (49%), soil (19%), & food (10%).  

The global prevalence of Providencia rettgeri varies, with documented isolation from clinical specimens linked to urinary tract infections (UTIs), septicemia, and wound infections. This bacterium’s presence extends across both community-acquired and healthcare-associated infections. Its global footprint spans nations such as India, Brazil, Ecuador, Canada, and Nepal.  

Transmission predominantly occurs through person-to-person contact, often influenced by suboptimal hygiene practices and contaminated settings. In healthcare facilities, transmission might involve contaminated medical devices or procedures. Additionally, travel-associated cases underline potential exposure through water or food consumption, adding to the complexity of its spread.  

Distinct risk factors heighten susceptibility to Providencia rettgeri infections, including hospitalization, particularly for those undergoing invasive procedures or employing medical devices like urinary catheters. Antibiotic resistance, particularly among emerging multidrug-resistant strains, amplifies the challenge of effective treatment. Travelers to regions with compromised hygiene standards face an elevated risk, possibly encountering Providencia rettgeri-related conditions, such as traveler’s diarrhea.  

Notable studies, such as those by Hickman-Brenner et al. (1983), have contributed to the understanding of Providencia rettgeri‘s antigenic types and their potential genetic associations with related bacteria like Proteus, Morganella, and Providencia stuartii. Moreover, studies by Lee et al. (2018) & Al-Agamy et al. (2016) highlight instances of NDM-1-producing Providencia rettgeri, underlining the significance of monitoring and addressing emergent antibiotic resistance. 

Kingdom: Bacteria 

Phylum: Pseudomonadota 

Class: Gammaproteobacteria 

Order: Enterobacterales 

Family: Morganellaceae 

Genus: Providencia 

Species: Providencia rettgeri   

Providencia rettgeri is a rod-shaped bacterium with a Gram-negative cell wall. Exhibits motility, forming round, opaque, and convex colonies on nutrient agar.  

Cell size varies based on growth conditions, typically around 1-2 μm in length, 0.5-0.8 μm in width. The genetic material of P. rettgeri finds its abode within the cytoplasm, manifested as a singular, circular chromosome constructed from DNA strands.   

The outer membrane of P. rettgeri, a typical feature of Gram-negative bacteria, boasts a composition rich in lipopolysaccharides. Within the periplasmic space, nestled between the outer and inner membranes, lies a dynamic realm hosting enzymes, proteins, and a delicate peptidoglycan layer. 

The Type III Secretion System (T3SS) is an intricate mechanism certain bacteria use to inject their proteins directly into host cells. This molecular apparatus plays a strategic role in influencing the host’s immune responses, provoking inflammation, or even triggering cell death.

Encoded by an extensive cluster of genes, including spaP, spaQ, and spaR, the T3SS enables P. rettgeri to manipulate the host’s cellular environment for their benefit, underscoring its importance in the intricate host-pathogen dynamic.   

Hemolysins constitute a class of potent toxins that can rupture the host’s red blood cells, liberating essential iron required for bacterial growth. These virulence factors are governed by genes like hlyB, hlyA, and hlyC and grant P. rettgeri a distinct advantage in their survival strategy.   

NDM-1-Producing Strains and Sepsis-Causing Strain: Among bacterial strains, NDM-1 producers stand out due to their possession of the blaNDM-1 gene, encoding a carbapenemase enzyme capable of degrading a broad spectrum of beta-lactam antibiotics, including carbapenems. These strains, discovered in nations spanning Israel to Nepal, further complicate treatment by co-producing other beta-lactamases like PER-1, CTX-M-15, and SHV-12.

In a separate context, a strain isolated from a septic neonate following a challenging delivery in India spotlighted the real-world impact. This strain’s sensitivity to amikacin and gentamicin underlines the delicate balance between bacterial virulence and treatment modalities, offering insights into the intricacies of infections stemming from birth-associated complications. 

Providencia rettgeri‘s pathogenic journey commences with its adhesion to host tissues. Pili and fimbriae, protruding from the bacterial surface, play a pivotal role in this attachment process. These hair-like appendages facilitate binding to epithelial cells in diverse anatomical sites, such as the urinary and digestive tracts. This initial adhesion establishes a foundation for bacterial colonization and biofilm formation, creating a protected niche for P. rettgeri to flourish. 

P. rettgeri can utilize a type III secretion system (T3SS) to inject bacterial proteins into host cells, potentially influencing immune responses, inflammation, and cell survival. In certain infections, such as urinary tract infections (UTIs) or septicemia, the pathogen can traverse the bloodstream, disseminating from the initial infection site to other body parts. This dissemination can lead to secondary infections and perpetuate the cycle.

Providencia rettgeri‘s pathogenic arsenal includes the production of toxins that enhance its virulence. Hemolysins, for instance, can rupture red blood cells, liberating iron essential for bacterial growth. This strategic breakdown of host cells aids nutrient acquisition, providing the bacterium with the resources necessary for its proliferation.   

Providencia rettgeri has been implicated in catheter-related infections, particularly among long-term catheterized patients. Its propensity to form biofilms on the surfaces of indwelling catheters amplifies its pathogenicity. Furthermore, its inherent ability to produce urease further complicates matters, potentially contributing to the development of infections. This biofilm formation and urease production combination underscore the bacterium’s adaptability and persistence in catheter-associated contexts. 

Through various practical methods, the human body’s innate defense serves as an initial level of protection against Providencia rettgeri. This intrinsic immunity promptly detects and combats the bacterium, utilizing strategies like opsonization, phagocytosis, oxidative burst, inflammation, and induction of fever.

The immune response triggered by P. rettgeri often results in tissue inflammation, marked by local manifestations such as redness, swelling, pain, and elevated temperature at the infection site. Phagocytosis, in which designated cells engulf and destroy the pathogen, is facilitated by opsonization, a process in which immune chemicals boost bacterium detection.

The resulting oxidative burst produces reactive oxygen species that neutralize the bacterium, assisting in its eradication. The immune system’s coordinated response causes inflammation, which not only aids in pathogen clearance but also attracts multiple immune cells to the infection site, increasing defensive efforts.  

Additionally, the induction of fever in response to Providencia rettgeri creates an unfavorable environment for the bacterium’s development and replication. This coordinated interplay of innate immunity components aids in infection containment and elimination.  

In addition to innate immunity, the adaptive immune system strengthens the protection against Providencia rettgeri. Adaptive immunity is characterized by a tailored response involving specialized immune cells such as T and B lymphocytes. These cells are critical in identifying and killing the bacterium via methods such as cell-mediated cytotoxicity.

Furthermore, adaptive immunity promotes the formation of memory cells, which provides long-term protection against future P. rettgeri infections. When exposed again, these memory cells retain the ability to recognize and kill the pathogen quickly, increasing the body’s resilience and ability to combat reinfection. 

Providencia rettgeri causes urinary tract infections, particularly affecting individuals with predisposing factors such as urinary catheters, kidney stones, or diabetes. The telltale signs of UTIs include: 

• Discomfort or stinging during urination. 
• An increased urge to urinate. 
• Blood or pus in the urine. 
• Elevated body temperature. 
• Aching lower back. 

This bacterium’s resistance to numerous antibiotics adds a layer of complexity to treatment, potentially making it challenging to manage the infection effectively. Providencia rettgeri can trigger traveler’s diarrhea, a type of acute gastroenteritis that commonly afflicts those visiting developing countries. Characterized by watery or bloody stools, abdominal cramps, nausea, vomiting, and dehydration, traveler’s diarrhea typically lasts for a short duration. 

Providencia rettgeri is also associated with eye infections, encompassing conditions like conjunctivitis, keratitis (cornea inflammation), and endophthalmitis (infection within the eye’s interior). Symptoms of eye infections consist of redness, swelling, discomfort, discharge, compromised vision, and heightened sensitivity to light. These infections can result from exposure to contaminated water or objects or spread from other infected sites.

Culture method: The cornerstone of Providencia rettgeri diagnosis, culture entails cultivating the bacterium on diverse media, such as nutrient agar, MacConkey agar, or blood agar. Incubating at 37°C for 24-48 hours unveils colony traits like size, shape, color, and hemolysis. P. rettgeri typically forms round, opaque, and convex colonies, distinguished by their lactose-negativity on MacConkey agar.   

Biochemical Tests: Delving into physiological properties, biochemical tests offer critical insights. The urease test identifies Providencia rettgeri‘s ability to hydrolyze urea, turning the indicator pink. The indole test detects indole production from tryptophan, inducing a red color change. P. rettgeri exhibits positive results in both these tests. Furthermore, the methyl red test highlights its capacity for mixed acid production, lowering medium pH and differentiating it from other Enterobacteriaceae. 

Molecular Tests: Unveiling genetic material, molecular tests provide a deeper understanding. Polymerase chain reaction (PCR) amplifies specific DNA segments, detecting Providencia rettgeri‘s genes like 16S rRNA or blaNDM-1. Combining PCR with gel electrophoresis or sequencing enhances DNA analysis. Matrix-assisted laser ionization/desorption time-of-flight mass spectrometry measures molecular masses, enabling rapid identification based on protein profiles. MALDI-TOF MS swiftly and accurately distinguishes P. rettgeri from cultures or direct specimens. 

• Adhering to safe food preparation and handling practices is essential. Cooking foods, especially meat and poultry, can help destroy P. rettgeri.  

• Access to safe & clean drinking water is critical for preventing diseases caused by waterborne pathogens such as Providencia rettgeri. Boiling or treating water before consumption in areas with questionable water quality can mitigate the risk of exposure. 

• For individuals with urinary catheters, proper care and maintenance of catheters are essential to minimize the risk of catheter-associated urinary tract infections (CAUTIs). 

Providencia Rettgeri: An Emerging Nosocomial Uropathogen in an Indwelling Urinary Catheterised Patient – PubMed (nih.gov)  

Providencia rettgeri – an overview | ScienceDirect Topics