Filamentous gram-negative bacteria masquerading as actinomycetes in infectious endophthalmitis: a review of three cases

Pseudomonas species may appear strikingly filamentous in tissue sections: an important consideration for surgical pathologists and a reminder of the utility of modified silver impregnation methods

Although tissue culture is the gold standard for diagnosing infection, histologic examination of surgically resected tissue can be a critical component in the diagnosis of tissue infection. The goal of this brief report is to alert surgical pathologists that Pseudomonas species can appear strikingly filamentous histologically and may somewhat mimic the appearance of filamentous bacteria, such Actinomyces or Nocardia, or thin fungal hyphae. A secondary aim is to raise awareness that Pseudomonas can sometimes only be identified histologically through the use of a modified silver impregnation method (Steiner stain). Five cases of filamentous Pseudomonas were encountered in three different surgical pathology subspecialities (ophthalmic pathology, cardiovascular pathology, and dermatopathology) over a 1-year period. All cases were of formalin-fixed, paraffin-embedded tissue, stained using hematoxylin & eosin (H&E) and multiple histochemical stains. Four cases grew Pseudomonas aeruginosa in culture and, in the fifth case, a nonaeruginosa species was detected using polymerase chain reaction-based methods. The markedly filamentous-appearing Pseudomonas organisms were identified in five different tissue sites: vascular graft, enucleation (whole eye) specimen, scleral biopsy, soft-tissue excision, and skin punch biopsy. In one of the five cases the organisms were seen on H&E, and in only two of the five were the organisms seen on Brown-Hopps stain. In all five cases, the organisms were identified on Steiner stain. It is therefore important to recognize that Pseudomonas can appear markedly filamentous, Pseudomonas or other bacterial infection is suspected, the surgical pathologist would be advised to employ the Steiner stain to most consistently detect the organisms.

Klebsiella oxytoca Complex: Update on Taxonomy, Antimicrobial Resistance, and Virulence

Klebsiella oxytoca is actually a complex of nine species-Klebsiella grimontii, Klebsiella huaxiensis, Klebsiella michiganensis, K. oxytoca, Klebsiella pasteurii, Klebsiella spallanzanii, and three unnamed novel species. Phenotypic tests can assign isolates to the complex, but precise species identification requires genome-based analysis. The K. oxytoca complex is a human commensal but also an opportunistic pathogen causing various infections, such as antibiotic-associated hemorrhagic colitis (AAHC), urinary tract infection, and bacteremia, and has caused outbreaks. Production of the cytotoxins tilivalline and tilimycin lead to AAHC, while many virulence factors seen in Klebsiella pneumoniae, such as capsular polysaccharides and fimbriae, have been found in the complex; however, their association with pathogenicity remains unclear. Among the 5,724 K. oxytoca clinical isolates in the SENTRY surveillance system, the rates of nonsusceptibility to carbapenems, ceftriaxone, ciprofloxacin, colistin, and tigecycline were 1.8%, 12.5%, 7.1%, 0.8%, and 0.1%, respectively. Resistance to carbapenems is increasing alarmingly. In addition to the intrinsic bla_OXY, many genes encoding β-lactamases with varying spectra of hydrolysis, including extended-spectrum β-lactamases, such as a few CTX-M variants and several TEM and SHV variants, have been found. bla_KPC-2 is the most common carbapenemase gene found in the complex and is mainly seen on IncN or IncF plasmids. Due to the ability to acquire antimicrobial resistance and the carriage of multiple virulence genes, the K. oxytoca complex has the potential to become a major threat to human health.

Diversity in the swimming motility and flagellar regulon structure of uropathogenic Morganella morganii strains

In current times, the opportunistic pathogen Morganella morganii is increasingly becoming a cause of urinary tract infections. The condition has been further complicated by the multiple drug resistance of most isolates. Swimming motility plays an important role in the development of urinary tract infections, allowing bacteria to colonize the upper urinary tract. We determined the differences between the growth, swimming motility, and biofilm formation of two M. morganii strains MM 1 and MM 190 isolated from the urine of patients who had community-acquired urinary tract infections. MM 190 showed a lower growth rate but better-formed biofilms in comparison to MM 1. In addition, MM 190 possessed autoaggregation abilities. It was found that a high temperature (37 °C) inhibits the flagellation of strains and makes MM 190 less motile. At the same time, the MM 1 strain maintained its rate of motility at this temperature. We demonstrated that urea at a concentration of 1.5% suppresses the growth and swimming motility of both strains. Genome analysis showed that MM 1 has a 17.7-kb-long insertion in flagellar regulon between fliE and glycosyltransferase genes, which was not identified in corresponding loci of MM 190 and 9 other M. morganii strains with whole genomes. Both strains carry two genes encoding flagellin, which may indicate flagellar antigen phase variation. However, the fliC2 genes have only 91% identity to each other and exhibit some variability in the regulatory region. We assume that all these differences influence the swimming motility of the strains.

Antimicrobial treatment of morganella morganii invasive infections: Systematic review

BACKGROUND

Morganella morganii is a Gram-negative, rod-shaped, facultative anaerobic bacillus divided into two subspecies, morganii and sibonii. Previously classified as Proteus morganii, it belongs to human gut commensal microbiota. Nevertheless, on rare occasions, especially in nosocomial and postoperative environment as well as in patients with the impaired immune system and young children, it may cause potentially fatal systemic infection.

OBJECTIVES

The aim of our systematic review was to determine whether and what invasive infections in humans were caused by Morganella morganii and to estimate outcomes of administered antibiotic management.

DATA SOURCES

This systematic review was registered at the PROSPERO database of systematic reviews and meta-analyses before initiation of the research (registration number CRD42020171919). Study eligibility criteria and participants. patients of any age and both sex harbouring Morganella morganii as the only microorganism in bodily fluids or tissues, from where it was isolated and identified by one or more of the following diagnostic methods: conventional techniques including colony morphology, Vitek 2, API or BD Phoenix biochemical systems, as well as more sophisticated methods, such as Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and species-specific PCR for M. morganii.

METHODS AND INTERVENTIONS

We have systematically searched MEDLINE, EBSCO, SCOPUS, SCINDEX and GOOGLE SCHOLAR for case reports and case series with M. morganii invasive infections.

RESULTS

M. morganii can cause serious infections of different tissue in patients of any age. The most isolates were susceptible to ceftazidime, imipenem and amikacin. Majority of the patients completely recovered after antibiotic treatment. About 15% of the patients died despite of the therapy. Gentamicin was the most frequently used antibiotic in the treatment of infection caused by M. morganii.

CONCLUSION

M. morganii invasive infections should be taken into consideration by the clinicians, especially in hospital conditions, due to its high degree of mortality and high potential of this bacterium to develop multidrug resistance. Treatment of M. morganii infections should include gentamycin in combination with third generation cephalosporin or another antibiotic to which M. morganii is susceptible (after testing isolates for third cephalosporin generation for the production of AmpC β -lactamases).

Enterococcus casseliflavus, Streptococcus equinus and Klebsiella oxytoca septicaemia associated with perinephric haematoma in a post-liver transplant patient with allograft cirrhosis

Liver transplant recipients are immunocompromised by the virtue of being on immunosuppressive agents which put them at risk of having infections from unusual and even multiple concomitant pathogens. We present a case of a 39-year-old man who developed septicaemia with Enterococcus casseliflavus, Streptococcus equinus and Klebsiella oxytoca in the setting of perinephric haematoma which resulted following a kidney biopsy performed to evaluate his nephrotic range proteinuria. E. casseliflavus has been known to cause infections in patients with liver disease/cirrhosis; however, simultaneous infection with S. equinus and K. oxytoca along with E. casseliflavus has never been reported earlier in post-transplant state.