According to the British Pest Control Association (BPCA, 2020) of 4600 cockroach species worldwide, two of the commonest types in the UK are the Oriental cockroach (Blatta orientalis) and the German cockroach (Blattella germanica), with a BPCA national survey noting that ‘[o]verall, there was a total of 5904 callouts for cockroaches made to the 292 local authorities operating a pest control service throughout the UK during 2015/16’ (BPCA, 2016).
So, it is significant that Molewa et al (2022) found ‘that cockroaches may be a potential vector for a diverse range of pathogenic bacterial agents. Most bacterial agents isolated are antidrugresistant and antibiotic-resistant …’ For example, Abdolmaleki et al (2019) evaluated antibiotic resistance in the MRSA strains isolated from US and German hospital cockroaches, concluding that ‘[h]ospital cockroaches are considered as a potential mechanical vector for MRSA strains.’ In an Indian study Fotedar et al (1991) reported that ‘hospital cockroaches may act as vectors of drug-resistant Klebsiella spp. and may contribute to the epidemiology of nosocomial infections.’
Shi et al (2022) indicate that the emergence of multidrug-resistant members of the order Enterobacterales threatens public health; that carbapenems have been a popular therapeutic choice due to their broad spectrum of activity, stability of extended-spectrum β-lactamase (ESBL) and proven safety; but with rising clinical use, carbapenem-resistant Enterobacterales have been increasingly reported worldwide. This is important for several reasons.
‘Given the relative rarity of cockroaches in Ireland …. at least one avenue of future research will involve tracing the evolutionary paths taken by Pseudocitrobacter and related micro-organisms’
First, Shi et al (2022) reported the isolation of a rare Enterobacterales member Pseudocitrobacter faecalis from a patient with a bloodstream infection in China, and the organism was resistant to carbapenems, quinolones and commonly used β-lactam/β-lactamase inhibitor combinations. Second, de Andrade et al (2022) reported the isolation of Pseudocitrobacter vendiensis at a haemodialysis unit in Brazil, ‘displaying a multidrug-resistant profile to broad-spectrum cephalosporins, carbapenems, chloramphenicol, and trimethoprim-sulfamethoxazole.’
However, when Guzman et al (2022) reported the isolation of Pseudocitrobacter corydidari from the gut of the Asian emerald cockroach Corydidarum magnifica, they noted that in contrast to Pseudocitrobacter faecalis and Pseudocitrobacter vendiensis, the genome of Pseudocitrobacter corydidari ‘did not encode for proteins conferring resistance to antibiotics.’
Against this background, it is significant that Kelly et al (2023) recently identified a novel species, Pseudocitrobacter limerickensis, ‘the first report of any Pseudocitrobacter species from Ireland, a genus first described in only 2013.’ University Hospital Limerick (UHL) has a documented history of antimicrobial-resistant organism detections, with researchers reporting outbreaks of linezolid-resistant and ESBL-producing organisms as well as carbapenemase-producing Enterobacteriaceae (CPE) which are endemic: ‘Indeed, UHL was the site of the first CPE detection in Ireland’ (Kelly et al, 2023).
The CPE-positive Pseudocitrobacter limerickensis was isolated from a rectal swab screening of an inpatient, who had no CPE detected when admitted to hospital. The patient, although colonised with the organism, was asymptomatic and did not require antimicrobial treatment. Pseudocitrobacter limerickensis appears to be closely related to, but distinct from, the Pseudocitrobacter corydidari, reported by Guzman et al (2022) which was isolated from the Asian emerald cockroach Corydidarum magnifica. However, as Kelly et al (2023) observe, ‘Isolation of P. limerickensis was from a clinical setting that is starkly different to the humid forests in which the emerald cockroach thrives’. And noting that although a recent Iranian study investigated US cockroaches from a hospital sewer system for evidence of healthcare-associated infection (HCAI), Kelly et al (2023) indicate that ‘cockroaches are very uncommon in Ireland; none have been detected at our hospital and there is no evidence supporting their role as HCAI vectors in this country.’
Although infection with Pseudocitrobacter limerickensis has not been reported to date, Kelly et al (2023) note that invasive infections caused by other species within the genus have been documented and observe that in the context of the global dissemination of CPE ‘and emerging reports of severe infections associated with Pseudocitrobacter isolates, we believe it credible to suggest that this and other novel Pseudocitrobacter species warrant further study and characterisation.’
It seems that, given the relative rarity of cockroaches in Ireland, allied to the role of these insects in HCAIs in other parts of the world, at least one avenue of future research will involve tracing the evolutionary paths taken by Pseudocitrobacter and related micro-organisms. This will further inform a growing evidence base and perhaps facilitate the development of appropriate mitigation measures.