Clinical Microbiology: Open Access

Table 1: CPBs and the number of positive isolates taken from a particular source/site/sample.

Figure 1: CPB proportion pie chart of each species and the sources in which they were isolated.

Sample Sourcing: Pseudomonas aeruginosa There are 466 samples of P. aeruginosa, the most common CPB isolated in this institution when compared to other CPBs such as K. pneumoniae (n = 52) and A. baumannii (n = 309). Majority of P. aeruginosa isolates are obtained and isolated from ETAs (n = 191, 41%), followed by wound sites (n = 160, 34%) and blood (n = 36, 7%). Isolates were also identified in samples such as CSF (n = 4, 0.8%), the cornea (n = 1, 0.2%) and abscesses (n = 1, 0.2%).

Organisms of interest are carbapenemase producers A. baumanii, K.pneumoniae and P.aeruginosa; all of which are taken from a tertiary-level private hospital in Davao City. A total of 827 CPB isolates were collected, comprising 22.5% of total overall bacterial isolates (n = 3671) in this five-year period.

ETA is the major site from which these CPBs were isolated, with A. baumanii having the highest number. Other significant sites include urine, wound, and blood. Less common are sources such as pleural fluids, sputum, CSFs and catheters.

Acinetobacter baumannii A. baumanii was found in 309 isolates, and are mostly taken from ETA samples (n = 227, 73%). Wound, blood, and urine are also significant sources for this organism. Notably, this microbe was also isolated from the lens (n = 1, 0.3%), gastric acid (n = 1, 0.3%), and CSF (n = 1, 0.3%).

Klebsiella pneumoniae

374 bacterial samples were positive for K. pneumonia, 13.9% (n = 52) of which were carbapenemase producers. Unlike P. aeruginosa and A. baumannii, sources for the organism are more widespread and are less localized to any single particular source. ETA (n = 135, 36%), urine (n = 85, 23%), wound (n = 86, 23%) and blood (n = 36, 13%) are the major sources of this organism with relatively greater distributions. An unusual isolate of K. pneumonia (n = 1, 0.3%) is taken from a gastric source. Other uncommon sites include aspirates (n = 1, 0.3%), catheters (n = 5, 1.6%) and pleural fluid (n = 1, 0.1%).

Drug Resistances

Figure 2: Comparison of the number of A. baumannii, K. pneumoniae and P. aeruginosa isolates that showed susceptibility and resistance against a set of carbapenem drugs.

About the species in question, resistance against ertapenem, imipenem and meropenem are present (n = 827, 71.9%). These drugs serve as indicators that these isolates, should they exhibit resistance, have mechanisms intrinsically present that grant them carbapenem resistance, and are effectively considered CPBs. A small set of isolates are noted to have intermediate resistance (n = 51), but for practical reasons these are to be treated as if they are completely resistant.

Pseudomonas aeruginosa: Resistance can be noted against imipenem (n = 152, 32.6%) and meropenem (n = 133, 28.5%). Fortunately, more isolates remained susceptible to imipenem (n = 297, 63.7%) and meropenem (n = 311, 66.7%). These species are intrinsically resistant to ertapenem.

Acinetobacter baumannii: A. baumannii has a resistance profile across imipenem (n = 237, 76.6%), and meropenem (n = 235, 76%). These species are intrinsically resistant to ertapenem.

Klebsiella pneumonia: Among the CPBs, K. pneumoniae has the most carbapenem susceptibility especially noting the relatively smaller amounts of resistant isolates to Ertapenem (n = 52, 13.9%), Imipenem (n = 52, 13.9%) and Meropenem (n =52, 13.9%) overall.

Table 3: Percentage of resistance to carbapenems 2012-2017.

(Table 3) shows yearly percentages of species-specific resistance. The highest percentage of carbapenemase-positive organisms was in year 2017, yielding a 5%-increase in carbapenem-resistant Acinetobacter baumannii.

Analysis and Discussion

This study focuses on 3 carbapenemase-producing gram negative bacteria namely, K. pneumonia, P. aeruguinosa and A. baumannii. The total number of isolates collected were 1,149. As shown in Table 1, the number of isolates per bacteria varies depending on what specimen it was collected from. For example, there were isolates of K. pneumonia and P. aeruguinosa collected from an abscess while there was none of the A. baumannii. Among bronchial wash specimens, the only isolate collected were that of A. baumannii and none of those from K. pneumonia and P. aeruguinosa. Hence, different bacteria can manifest variance in where these can be obtained. Some of which are present in a single specimen while others have their own unique specimen for which they can grow on. Of the three (3) bacteria mentioned, the highest number of isolate collected were that of

A. baumanii, and the specimen that yielded the highest isolate of A. baumanii is that of from ETAs. These isolates identified are commonly found in immunocompromised patients and those who are hooked on to ventilators, which might have contributed to a larger number of isolates found in ETA.

In (Figure 2), susceptibility testing showed Acinetobacter baumanii as the CPB that had the highest resistant profile to the carbapenems used, while Klebsiella pneumoniae had the highest susceptibility to the same drugs. Pseudomonas aeruguinosa, on the other hand, showed susceptibility to both imipenem and meropenem. This aspect is important in the treatment of common illnesses because carbepanem antibiotics is considered a last-line of defense against highly infectious resistant bacteria (14).

In relation to the specimen that was used to obtain these isolates and their resistance to the carbepenems mentioned above, it is important to understand the common scenario that are greatly affected in the data that was gathered. Endotracheal aspirate (ETA) are specimens collected from endotracheal tubes and these are most commonly used by ventilator-associated pneumonia. Ventilator associated pneumonia is the most common healthcare-associated infection in the intensive care unit particularly in adults (3). Aside from the ETA, wound specimen also contained a number of isolates. Wound infections are also common in surgical operations that is important when dealing with post-operative patients (8). A large number of isolates were also collected from both urine and blood specimens. Urine specimens are commonly used in urinalysis testing for urinary tract infections. Urinary tract infection is one of the most common cause of nosocomial infection in the hospital (18). Infection that are found in the blood is an alarming case because these are usually associated with sepsis which is considered a medical emergency and is one of the leading cause of death in hospitals (10).

In treating carbapenemase-resistant bacteria, it is important to take note of the site of infections because based on the data given, the site of infection of different CPB varies and the susceptibility of each CPB also depends on the type of carbapenem used and the organism isolated, A. baumanii, K. pneumoniae or P. aeruguinosa.

Conclusion

A significant number of CPBs are being collected in a particular institution in Davao City, indicating that resistant bacteria are already numerous, and that the presence of carbapenem resistance already poses a threat. In addition, there exists significant species-only variance in antibiotic resistances, warranting more nuanced approaches when handling patients that possess a particular CPB infection. Furthermore, this calls for heightened awareness amongst institutions in mounting greater infectious control efforts in response to this threat.

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